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Control Network
Distributed Control System and Programmable Logic Control



        Course Aim


               The aim of this training course is to build up the procedural and
        declarative knowledge required to be recognized by projects engineer that
        don not have past background of DCS or PLC. This will help them to
        supervise projects dealing with control systems with a strong background.
        In this course, the training cycle is divided in five steps that necessitate
        the cooperation between the instructor and the trainees. These steps are
        shown in figure below, they are summarized as follows:
            1. Define the knowledge and skills required to be developed.
            2. Define the elements of each knowledge or skill.
            3. Formulate a verbal phrase for the learning objective of each
               element.
            4. Choose an adequate instructional activity to present each element.
            5. Set up an indicator to measure the outcomes of the course and
               modify the training skills to adapt the vocational needs.



                                  Define
                                Knowledge                Determine
                                 & Skills                Elements




                           Measure                            Learning
                          & Correction                        Objectives

                                           Instruction
                                             Activity

                                            Training Cycle.




                                                                                    1
Knowledge and Elements


   Illustrate DCS & PLC Benefits, Usage and History.
        Overview of control system history.
        Control system benefits and usage.
        Types of control


   Develop Knowledge of DCS Components (Hardware & Software).
        Infrastructure [Communication Bus, Interfaces, Controllers,
          Gateways, RTU, Others].
        Hardware and technologies.
        Software [Configuration, Graphics, Alarming, Trending, System
          Management, Others].


   Extend Knowledge of DCS installation and Maintenance.
        Site Installation, Commissioning and Startup.
        Diagnostics, Spares, Tools and Power Distribution.
        Maintenance [Backup, Replacements and System Installation].


   Develop Knowledge of PLC Components.
        PLC fundamentals.
        PLC Logic.
Table of Contents


                              Section I
Chapter 1    Introduction
Chapter 2    Regulatory Control
                              Section II
Chapter 3    DCS Infrastructure
Chapter 4    DCS Hardware
Chapter 5    DCS Software
                             Section III
Chapter 6    Installation
Chapter 7    Maintenance
Chapter 8    Power Distribution
                             Section IV
Chapter 9    PLC Fundamentals.
Chapter 10   Ladder Logic And SFC


                             Appendices
    A        Electrical Relay Diagram And P&ID Symbols
    B        Serial Communication
    C        Networking
    D        Software Engineering
Distributed Control System and Programmable Logic Control




                                                            4
Distributed Control System and Programmable Logic Control




                                                 Chapter 1
                                           Control Systems

        1.1 Automation System Structure


                 Although applications differ widely, there is little difference in the
        overall architecture of their control systems. Why the control system of a
        power plant is not sold also for automating a brewery depends largely on
        small differences (e.g. explosion-proof), on regulations (e.g. Food and
        Drug Administration) and also tradition, customer relationship.
        The ANSI/ISA standard 95 defines terminology and good practices
         Level
         4          Business Planning & Logistics             Enterprise Resource
                      Plant Production Scheduling
                     Operational Management, etc.


         Level              Manufacturing
         3                Operations & Control
                   Dispatching Production, Detailed Product   Manufacturing Execution
                     Scheduling, Reliability Assurance,...



         Level
         2,1,0
                  Batch          Continuous       Discrete    Control & Command
                  Control         Control         Control




        1.1.1 Large Control System Hierarchy


            • Administration: Production goals, planning
            • Enterprise: Manages resources, workflow, coordinates activities of
                 different sites, quality supervision, maintenance, distribution and
                 planning.



                                                                                        5
• Supervision: Supervision of the site, optimization, on-line
    operations. Control room, Process Data Base, logging (open loop)
• Group (Area): Control of a well-defined part of the plant. closed
    loop, except for intervention of an operator)
       o Coordinates individual subgroups
       o Adjusting set-points and parameters
       o Commands several units as a whole
• Unit (Cell): Control (regulation, monitoring and protection) of a
    small part of a group (closed loop except for maintenance).
       o Measure: Sampling, scaling, processing, calibration.
       o Control: regulation, set-points and parameters
       o Command: sequencing, protection and interlocking
• Field: Sensors & Actors, data acquisition, digitalization, data
    transmission, no processing except measurement correction and
    built-in protection.


4     Planning, Statistics, Finances                               administration

3     Workflow, Resources, Interactions                                enterprise


                                  SCADA                            supervisi on
      Supervisory                Supervisory
2
                                 And Data




      Group Control


      Unit Control
1
      Field

      Sensors                                                                       T
      & Actors                                              A      V

0     Primary



                       Figure 1.1 Large control system hierarchy
1.1.2 Response Time and Hierarchical Level


   Planning                                                        ERP (Enterprise
   Level                                                          Resource Planning)



                                                   MES
   Execution                                  (Manufacturing
   Level                                     Execution System)

                                          SCADA
                                 (Supervisory Control
   Supervisory                   and Data Acquisition)
   Level
                                DCS
                            (Distributed
                          Control System)
   Control
   Level                   PLC
                      (Programmable
                      Logic Controller)

                 ms      seconds     hours     days       weeks         month   years
                      Figure 1.2 Response Time And Hierarchical Level



1.2 What is DCS?


   A DCS is an integrated set of modules with distributed functions.
         – Multi-loop controllers (10’s-100’s) that connect to field
               devices
         – Supervisory coordinating controllers
         – Multi-loop operator stations and engineering stations
         – Servers for system data management
         – Control network for intercommunication
         – External connections
Supervisory     Operator
                                     System                   Stations
  Remote Users                                 Controller
                         www         Server
                                                                         Engineering
                                                                           Station

                     Remote
                     Server

           Control Network


             Multi-loop
             Controller

     Direct I/O Module




                                                                                Other Industrial Devices




                                        Figure 1.3 DCS Hierarchy



    A DCS, throughout the whole system, must provide:
              –          Performance: control must be faster than the process.
              –          Determinism: control must always take the same time.
              –          Fault tolerance: redundancy; must fail to a known state.
              –          Security: must have access restrictions/controls.


        Even though performance, ease of use, and interoperability are key
evaluation criteria for any control system software package, the following
is intended to provide the manufacturing engineer with a concise list of
control system software evaluation criteria.
        1. INTEROPERABILITY.
        This refers to the interaction of all control system hardware and
        software components at all levels.
        2. INTERCONNECTIVITY.
        This criterion is concerned with the transmission medium, which is
        constrained by the network topology and how efficiently the
        system’s components communicate with each other.
3. DISASTER PROCESSING.
This component is defined by the efficiency with which the
software provides the operator with system failure information and
the ease at which the operator is permitted to bring the system back
to maximum operation after system failure.
4. DATABASE.
This refers to the software’s ability to maintain the system’s
database.
5. PROCESSES/DATA.
This criterion is concerned with the variety of processes and data
that can be controlled by the SCADA package.
6. DIAGNOSTICS.
The SCADA package’s ability to assist in the resolution of system
failures is evaluated by this diagnostic utility.
7. SECURITY.
This component is concerned with the levels of security provided
by the software.
8. MONITORING/CONTROL
Monitoring of a given process in real-time and control of that
process, within preset parameters, is evaluated by this criteria.
9. ALARM MANAGEMENT/LOGGING.
This is the category for detecting, annunciating, managing, and
storing alarm conditions.
10. STATISTICAL PROCESS CONTROL.
This is the portion of the SCADA package that evaluates the
process data. Production and quality is greatly effected by this data.
12. OPERATOR INTERFACE.
The graphical user interface (GUI) is evaluated using this criterion.
13. TRENDING.
      The software’s ability to display trending plots using historical and
      current data is considered in this category.
      14. REPORT GENERATION.
      The production of logs and reports using current real-time data and
      data retrieved from historical files is evaluated under this category.


      Due to the advancements in computer technology and low cost, a
personal computer-based distributed control system can be installed for a
fraction of the cost required just a few years ago. However, prior to
selecting any piece of DCS equipment, first examine the existing
equipment, in particular the smart controllers, for network compatibility.
Then, examine and select the software to be employed.


1.3 What is PLC?


      A programmable logic controller, also called a PLC or
programmable controller, is a computer-type device used to control
equipment in an industrial facility. The kinds of equipment that PLCs can
control are as varied as industrial facilities themselves. Conveyor
systems, food processing machinery, auto assembly lines…you name it
and there’s probably a PLC out there controlling it.
      In a traditional industrial control system, all control devices are
wired directly to each other according to how the system is supposed to
operate. In a PLC system, however, the PLC replaces the wiring between
the devices. Thus, instead of being wired directly to each other, all
equipment is wired to the PLC. Then, the control program inside the PLC
provides the “wiring” connection between the devices.
The control program is the computer program stored in the PLC’s
memory that tells the PLC what’s supposed to be going on in the system.
The use of a PLC to provide the wiring connections between system
devices is called soft-wiring.
      Let's say that a push button is supposed to control the operation of
a motor. In a traditional control system, the push button would be wired
directly to the motor. In a PLC system, however, both the push button and
the motor would be wired to the PLC instead. Then, the PLC's control
program would complete the electrical circuit between the two, allowing
the button to control the motor.




                           Figure 1.4 PLC development



A PLC basically consists of two elements:
   • The central processing unit
   • The input/output system


1.3.1 The Central Processing Unit


      The central processing unit (CPU) is the part of a programmable
controller that retrieves, decodes, stores, and processes information. It
also executes the control program stored in the PLC’s memory. In
essence, the CPU is the “brains” of a programmable controller. It
functions much the same way the CPU of a regular computer does, except
that it uses special instructions and coding to perform its functions. The
CPU has three parts:
   • The processor
   • The memory system
   • The power supply
The processor is the section of the CPU that codes, decodes, and
computes data. The memory system is the section of the CPU that stores
both the control program and data from the equipment connected to the
PLC. The power supply is the section that provides the PLC with the
voltage and current it needs to operate.




                        Figure 1.5 Microprocessor Hardware



1.3.2 The input/output (I/O) system


      It is the section of a PLC to which all of the field devices are
connected. If the CPU can be thought of as the brains of a PLC, then the
I/O system can be thought of as the arms and legs. The I/O system is what
actually physically carries out the control commands from the program
stored in the PLC’s memory.
The I/O system consists of two main parts:
   • The rack
      The rack is an enclosure with slots in it that is connected to the CPU.
   • I/O modules
      I/O modules are devices with connection terminals to which the field
      devices are wired.


Together, the rack and the I/O modules form the interface between the
field devices and the PLC. When set up properly, each I/O module is both
securely wired to its corresponding field devices and securely installed in
a slot in the rack. This creates the physical connection between the field
equipment and the PLC. In some small PLCs, the rack and the I/O
modules come prepackaged as one unit.




                               Figure 1.6 I/O Racks
1.4 How is a DCS different from a PLC system?


                  DCS                                          PLC
Mfr sells a complete system of integrated   Mfr sells some components; an SI
components.                                 acquires others and engineers the system.
Mfr supports the system.                    Mfr supports the components.
On-line repair/ maintenance are the norm. Off-line repair/ maintenance are the norm.
System management built-in.                 System management designed per project.
Users expect to evolve/upgrade/expand a     System is a one-off project (like a house).
system over 10/20/30 years.                 Upgrades / expansions are new projects.



1.5 Redundancy and Fault Tolerance


1.5.1 Redundancy
    • Hardware redundancy
        – add extra hardware for detection or tolerating faults
    • Software redundancy
        – add extra software for detection and possibly tolerating faults


1.5.2 Fault Tolerance
    • Error Detection
    • Damage Confinement
    • Error Recovery
    • Fault Treatment


1.5.2.1 Error Detection
    • Ideal check
        – Check should be independent from system
        – Check fails if system crashes
• Acceptable check
      – Cost
      – Reasonable check, e.g. monitor rate of change
   • diagnostics
      – Performed “by system on system components”
      – E.g. power-up diagnostics


1.5.2.2 Damage Confinement
   • Error might propagate and spread
   • Identify boundaries to state beyond which no information exchange
      has occurred


1.5.2.3 Error Recovery
   • Backward recovery
      – State is restored to an earlier state
      – Requires checkpoints
      – Most frequently used
      – Recovery overhead
   • Forward recovery
      – Try to make state error-free
      – Need accurate assessment of damage
      – Highly application-dependent


1.5.2.4 Fault Treatment
   • If transient fault: restart system, goto error-free state
   • System repair
      – On-line, no manual intervention, (automatic)
      – Dynamic system reconfiguration
      – Spare (hot or cold)
1.5.2.5 Fault Coverage
  • Measure of system’s ability to perform:
     – Fault detection
     – Fault location
     – Fault containment
     – (and/or fault recovery)
  • Note:
     – Recovery implies that the system as a whole is operational
     – This does not imply that a “repair” occurred
     – E.g. duplex system with benign fault can recover to continue
     operation on one non-faulty processor


1.5.2.6 Hardware Redundancy
  • Passive (static)
     – Uses fault masking to hide occurrence of fault
     – No action from the system is required
     – E.g. voting
  • Active (dynamic)
     – Uses comparison for detection and/or diagnoses
     – Remove faulty hardware from system => reconfiguration
  • Hybrid
     – Combine both approaches
     – Masking until diagnostic complete
     – Expensive, but better to achieve higher reliability


1.5.2.7 Passive Hardware Redundancy
  • N-Modular Redundancy (NMR)
     – N independent modules replicate the same function
• Parallelism
      – Results are voted on requirements: N >= 3
   • TMR (Triple Modular Redundancy)


1.5.2.8 Fault tolerant structures
      Fault tolerance allows continuing operation in spite of a limited
number of independent failures. Fault tolerance relies on work
redundancy.


1.5.2.9 Static redundancy: 2 out of 3
   • Workby of 3 synchronised and identical units.
      – All 3 units OK:                            Correct output.
      – 2 units OK:                                Majority output correct.
      – 2 or 3 units failure:             Incorrect output.
      – Otherwise:                                 Error detection output.


                                               Process input


                           sync                 sync




                                      Voter

                                                Process output

                        Figure 1.7 (2 out of 3) Redundancy

1.5.2.10 Dynamic Redundancy
   • Redundancy only activated after an error is detected.
   – Primary components (non-redundant)
   – Reserve components (redundancy), standby (cold/hot standby)
Input



                         Primary unit                                     Standby unit



                                        Switch
                                                           Output

                                     Figure 1.8 Dynamic Redundancy

1.5.2.11 Workby and Standby
                 Workby                      Hot standby                      Cold standby




                  sync                                 sync
       on-line             workby            on-line           standby


                   =?



    Both computers are doing                                               Standby is no operational
                               Standby is not computing
        the same calculations                                               Error detection needed.
                                Error detection needed.
        at the same time                                                    Long switchover period
                               Easy switchover in case
      Comparison for easy                                                    with loss of state info.
                                       of failure.
         error detection.     Easy repair of reserve unit.                 No aging of reserve unit.
    Comparator needed. Non-
     redundant continuation
          in case of failure?

                                     Figure 1.9 Workby and Standby

1.5.2.12 Workby Fault-Tolerance for Integrity and Persistency
                          input                                               input

                  synchronization                                        synchronization

         Worker                         Co                    E Worker                     Co      E
                                     W-orker                  D                          W-orker   D
                    Matching                                               Matching

                         Output                                               Output


                                    comparator                            commutator

    disjunctor


                          output                                              output

                        INTEGER                                            PERSISTENT

                 Figure 1.10 Workby Fault-Tolerance for Integrity and Persistency
1.5.2.13 Hybrid Redundancy
Mixture of workby (static redundancy) and standby (dynamic redundancy).


     work-     work-    work-    stand-   stand-
      by        by       by        by       by


               voter


                       Reconfiguration     work-                work-   work-   stand-
                                                     failed
                       (self-purging        by                   by      by       by
                       redundancy)

                                                     voter



                                Figure 1.11 Hybrid Redundancy



1.6 Microprocessor Control


      For simple programming the relay model of the PLC is sufficient.
As more complex functions are used the more complex VonNeuman
model of the PLC must be used. A computer processes one instruction at
a time. Most computers operate this way, although they appear to be
doing many things at once. Consider the computer components shown in
Figure 1.12.




                   Figure 1.12 Simplified Personal Computer Architecture
Input is obtained from the keyboard and mouse, output is sent to the
screen, and the disk and memory are used for both input and output for
storage. (Note: the directions of these arrows are very important to
engineers, always pay attention to indicate where information is flowing.)
This figure can be redrawn as in Figure 1.13 to clarify the role of inputs
and outputs.




                   Figure 1.13 An Input-Output Oriented Architecture



      In this figure the data enters the left side through the inputs. (Note:
most engineering diagrams have inputs on the left and outputs on the
right.) It travels through buffering circuits before it enters the CPU. The
CPU outputs data through other circuits. Memory and disks are used for
storage of data that is not destined for output. If we look at a personal
computer as a controller, it is controlling the user by outputting stimuli on
the screen, and inputting responses from the mouse and the keyboard.
      A PLC is also a computer controlling a process. When fully
integrated into an application the analogies become;
   • Inputs - the keyboard is analogous to a proximity switch input
      circuits - the serial input chip is like a 24Vdc input card
• Computer - the 686 CPU is like a PLC CPU unit
   • Output circuits - a graphics card is like a triac output card
   • Outputs - a monitor is like a light
   • Storage - memory in PLCs is similar to memories in personal
      computers


It is also possible to implement a PLC using a normal Personal Computer,
although this is not advisable. In the case of a PLC the inputs and outputs
are designed to be more reliable and rugged for harsh production
environments.


1.7 Role Play


Each trainee should act a role play on the following:
   1. Automation system structure.
   2. What DCS and PLC and their differences?
   3. Redundancy and fault tolerance.
Chapter 2
                        Regulatory Control

2.1 Learning Objectives


• Introduce Regulatory Control.
• Understanding PID control.
• Differentiate between various control loops.


2.2 Introduction


      Most of the applications of industrial control process used simple
loops which regulated flows, temperatures, pressures and levels.
Occasionally ratio and cascade control loops could be found. There are
many benefits for using regulatory control. One of the most important is
simply closer control of the process. Process control is one part of an
overall control hierarchy that extends downwards to safety controls and
other directly connected process devices, and upward to encompass
process optimization and even higher business levels of control such as
scheduling, inventory management.


      Most control engineers would recognize the form of response
shown in figure 2.1. Actually the response could be determined by
solving a differential equation. It is more important to have a good
understanding of the physical response than to be able to predict the
solution by solving the differential equation.
Figure 2.1 Response of simple dynamic process to step input change

      Instrumentation, control and process engineers abstract the pictorial
form of the process into an iconographic diagram called "Piping and
Instrumentation Diagram", i.e. P&ID. Figure 2.2 is an example of the
P&ID.




                    Figure 2.2 Control loop representation used on P&IDs.

      For description and analysis of a control loop, without referring to
whether it is implemented with analog or digital hardware, a block
diagram as shown in figure 2.3 is beneficial.




          Figure 2.3 Simplified block diagram representation of process control loop.
2.3 PID Control


2.3.1 Feedback Control


      The principle of feedback is one of the most intuitive concepts
known. An action is taken to correct a less satisfactory situation then the
results of the action are evaluated. If the situation is not corrected then
further action takes place. Feedback control can be classified by the form
of the controller output. One of the simplest forms of output is discrete
form, also called on-off or two position control. An example of this is the
household thermostat, which activates heating unit if the temperature is
below the setting, or deactivates the unit if the temperature is above the
setting.




                           Figure 2.4 On-Off Control.

      The idea of two position control can be extended to multi-position
control; an example is commercial air-conditioning refrigeration
equipment which is operated by loading and unloading compressor
cylinders. The ultimate extension is infinite number of positions which is
called modulating control; an example is the process controller output
that can drive a valve to any position between 0 and 100 percent, as
shown in figure 2.5.
Figure 2.5 Flow versus position, infinite position Control.



2.3.2 Modes of Control


      Feedback controllers use one, two, or three methods to determine
the controller output. These methods, called the modes of control,
including the following:
• Proportional (P)
• Integral (I)
• Derivative (D)
In general these modes can be used singly or in combination.


2.3.2.1 Proportional Mode


      With a controller containing only the proportional mode, the
controller output is proportional to the measurement value only. Neither
history of the measurement value nor consideration to the rate of change
is utilized. Adjustment, i.e. tuning, of the controller is simple because
there is only one adjustment as shown in figure 2.6.
Figure 2.6 Relationship between input and output for proportional control.

      Figure 2.7 illustrates a proportional control system. The rate of
fluid flow into the tank represents the load. To be in equilibrium, the
outflow must be the same as the inflow. The outflow is achieved by a
particular valve position where the fixed mechanism between the float,
pivot and link attain.




                                Figure 2.7 Proportional control.



2.3.2.2 Integral Mode
      An integrator is the ideal device for automating the procedure for
adjusting the controller output bias. It is called the automatic reset.


2.3.2.3 Derivative Mode
      The derivative is used to anticipate the effect of load changes by
adding a component to the controller output that is proportional to the rate
of change of the measurement. See figure 2.8.
Figure 2.8 PID control.



2.3.3 Control Loop Structure


      For microprocessor control system, control strategy is configured
by a series of software function blocks. Just like a set of hardware
modules require interconnections to form a complete control system, a set
of software function blocks also acquire interconnections, i.e. soft-wiring.


Figure 2.9 shows a simple feedback loop with the software portion
consists of three function blocks:
• An analog input block that causes the analog to digital converter to
   convert the incoming 4-20mA signal to an analogous value. The value
   is deposited in a memory register.
• A PID control block which obtains the measurement value from the
   analog input block and compares it with the setpoint then it executes a
   PID algorithm to calculate the output.
• An analog output block that obtains from the PID block the required
   valve position value. The value is converted by a digital to analog
   converter to 4-20mA signal.
Figure 2.9 Control loop hardware/software structure.



2.3.4 Control Loop Tuning


      The power of PID control is that by good choice of control
parameters the controller can be adjusted to provide the desired behavior
on a wide variety of process applications. Determining acceptable values
of these parameters is called tuning the controller. A good criterion for
acceptable performance is the "quarter cycle decay" shown in figure 2.10.




                      Figure 2.10 quarter cycle decay criterion



Most loops are tuned by experimental techniques, i.e. trial and error.
Figures 2.11 and 2.12 give a tuning map for adjusting control parameters.
Figure 2.11 Gain and Reset effects.




                           Figure 2.12 Derivative effects.

2.4 Control Loop Types
2.4.1 Ratio Control


      Figure 2.13 shows the P&ID of a process heater in which the fuel
flow is measured and multiplied by the required air-to-fuel ratio; this
results in the required air flow rate, which is introduced as a setpoint of
the feedback controller. The required air-to-fuel ratio is automatically
adjusted as the output of the stack O2 controller.
Figure 2.13 ratio Control..

2.4.2 Cascade Control


      In figure 2.14 the temperature controller cascades a steam flow
controller. The temperature controller would react to outlet temperature
drop by increasing the setpoint of the steam flow controller, which in turn
would increase the signal to the valve. The flow will quickly respond to
increased demand from the temperature controller and thus reaching the
desired setpoint of the outlet temperature stream.




                           Figure 2.13 Cascade Control.

2.4.3 Feedforward Control


      With feedforward control, the objective is to drive the controlling
device from a measurement of the disturbance that is affecting the
process, rather than from the process variable itself. In figure 2.14, the
application was analyzed the variation in process inlet temperature was
the principle of disturbance. Hence, a feedforward controller is used to
drive the fuel flow controller by sensing the inlet temperature.




                         Figure 2.14 Feedforward Control.

2.4.4 Selector (Override) Control


        There are several ways of using selector switches in control
strategies. One way is to select the higher (or lower) of several
measurement signals to pass the process variable to a feedback controller.
For example, the highest of several process temperatures may be selected
automatically to become the controlling temperature as shown in figure
2.15.




                           Figure 2.15 Override Control.
2.4.5 Split Range Control


      Split range control when one process variable such as plant inlet
pressure is used to manage two different output devices such as plant
bypass control valve and flow control loop for fractionation area. The 4-
12 mA signal is used to control the flow control loop. If the plant cannot
handle all incoming feed, the 12-20 mA signal control the plant bypass
valve to direct extra feed to the outside of the plant.


2.5 Role Play


The trainees are required to play roles about:
   1. Introducing regulatory control.
   2. Introducing modes of control.
   3. Intruding control loop types.
Distributed Control System and Programmable Logic Control




                                                            33
Distributed Control System and Programmable Logic Control




                                         Chapter 3
                                  DCS Infrastructure

        3.1 Learning Objectives


        • Introduce system infrastructure interoperability and interconnectivity.
        • Illustrate system components of level 2 control.


        3.2 Communication Bus




                                    Figure 3.1: Communication Bus

               The communication bus, i.e. the Nodebus, interconnects stations
        (Control Processors, Application Processors, Application Workstations,
        and so forth) in the system to form a process management and control
        node. Depending on application requirements, the node can serve as a
        single, stand-alone entity, or it can be configured to be part of a more
        extensive communications network.
               Operating in conjunction with the Nodebus interface electronics in
        each station, the Nodebus provides high-speed, redundant, peer-to-peer
        communications between the stations.
               The high speed, coupled with the redundancy and peer-to-peer
        characteristics, provide performance and security superior to that


                                                                               34
Distributed Control System and Programmable Logic Control



        provided by communication media used in conventional computer-based
        systems. Station interfaces to the Nodebus are also redundant, further
        ensuring secure communications between the stations. The Nodebus can
        be implemented in a basic, non-extended configuration or it can be
        extended through the use of Nodebus Extenders and Dual Nodebus
        Interface Extenders.


        3.2.1 Nodebus Interface


               The Nodebus Interface is a module which allows direct connection
        of a personal workstation (PW), with appropriate Nodebus connector card
        and software, to the Nodebus figure 3.2. In this configuration, the PW
        functions as a station on the node. The Nodebus Interface allows
        connection of a station application workstation hosting an Ethernet
        configuration to Nodebus. See figure 3.2.




                           Figure 3.2 Nodebus Interface Implementation (Typical)




                                                                                   35
Distributed Control System and Programmable Logic Control



               An Attachment Unit Interface (AUI) cable, connects the PW or an
        Ethernet hub configuration to the Nodebus via a Nodebus Interface. A
        coaxial cable (ThinNet) connects an Ethernet daisy chain configuration to
        the Nodebus via a Nodebus Extender. The Nodebus Interface is non-
        redundant, and can be used in any of the Nodebus configurations
        described.


        3.2.2 Dual Nodebus Interface


               The Dual Nodebus Interface (DNBI) is a module which allows
        direct connection of stations to the appropriate Nodebus. Connection
        between the DNBI and station is made via an AUI cable.


               For data transmission security, a separate (RS-423) control cable
        connects between the station and the DNBI to allow switching between
        the two redundant Nodebus cables. Switching of the Nodebus cables is
        controlled by the station, which transmits commands to the DNBI via the
        control cable. Figure 3.3 shows connection of a station to the Nodebus
        using a DNBI.




                                 Figure 3.3 Local Connection of Station



        3.2.3 Dual Nodebus Interface Extender


               The Dual Nodebus Interface Extender (DNBX) is functionally
        similar to the DNBI, but provides a greater cabling distance. The

                                                                              36
Distributed Control System and Programmable Logic Control



        principal transmission medium used is a coaxial Ethernet cable directly
        connected to the station end by a standard Ethernet transceiver. Figure 3.4
        remote connection of a station to the Nodebus using a DNBX.




                                Figure 3.4 Remote Connection of Station



        3.3 Control Processor


            The Control Processor performs regulatory, logic, timing, and
        sequential control together with connected:
            •   Fieldbus Modules (FBMs)
            •   Fieldbus Cluster I/O Cards (FBCs)
        It also performs data acquisition (via the Fieldbus Modules), alarm
        detection and notification, and may optionally serve as an interface for
        one or more Panel Display Stations.
        The non-fault-tolerant version of the Control Processor is a single-width
        processor module. The fault-tolerant version consists of two single-width
        processor modules.


        3.3.1 Enhanced Reliability


                The Control Processor offers optional fault- tolerance for enhanced
        reliability. The fault-tolerant control processor configuration consists of
        two parallel-operating modules with two separate connections to the
        Nodebus and to the Fieldbus.

                                                                                37
                                                                                37
Distributed Control System and Programmable Logic Control



                  The two control processor modules, married together as a fault-
        tolerant pair, are designed to provide continued operation of the unit in
        the event of virtually any hardware failure occurring within one module
        of       the   pair.   Both   modules   receive     and   process   information
        simultaneously, and the modules themselves detect faults. One of the
        significant methods of fault detection is comparison of communication
        messages at the module external interfaces. Upon detection of a fault,
        self-diagnostics are run by both modules to determine which module is
        defective. The non-defective module then assumes control without
        affecting normal system operations.


                  To further ensure reliable communications, the fault-tolerant
        control processor performs error detection and address verification tests
        in its Nodebus and Fieldbus interfaces. For enhanced reliability during
        maintenance operations, the Control Processor is equipped with a
        recessed reset button. This feature provides for manually forcing a
        module power off and on (reboot) without removing the module from the
        enclosure.


        3.3.2 Diagnostics


                  The Control Processor uses three types of diagnostic tests to detect
        and/or isolate faults:
             •    Power-up self-checks
             •    Run-time and watchdog timer checks
             •    Off-line diagnostics
                  Power-up self-checks are self-initiated when power is applied to
        the control processor. These checks perform sequential tests on the
        various control processor functional elements. Red and green indicators at

                                                                                    38
Distributed Control System and Programmable Logic Control



        the front of the control processor module reflect the successful (or non-
        successful) completion of the various phases of the control processor
        startup sequence.
                The run-time and watchdog timer checks provide continuous
        monitoring of control processor functions during normal system
        operations. The operator is informed of a malfunction by means of
        printed or displayed system messages.
                Off-line diagnostics are temporarily loaded into the system for the
        purpose of performing comprehensive tests and checks on various system
        stations and devices. Using the off-line diagnostics, a suspected fault in
        the control processor can be isolated and/or confirmed.


        3.4 Engineering Interface


                The   engineering     interface,   i.e.     Application   Processor,   is
        microprocessor-based application processor/file server stations. They
        perform two basic functions:
            •   As application processor (computer) stations, they perform
                computation intensive functions.
            •   As file server stations, they process file requests from tasks within
                themselves or from other stations. Bulk storage devices used with
                the Application Processors include floppy disk drives, hard disk
                drives, streaming tape drives, and CD-ROMs.


                The Application Processors operate in concert with other system
        stations (such as communication processors, workstation processors, and
        control processors), which provide the necessary means for data
        input/output and operator interfacing. A smaller system can utilize a
        single Application Processor, while a larger system can incorporate

                                                                                       39
Distributed Control System and Programmable Logic Control



        several Application Processors, each configured to perform specific
        functions. Some functions can be performed by individual Application
        Processors, while others can be shared by two or more Application
        Processors in the same network.
               For all models of the Application Processor, applications range
        from minimal functions, such as the storage of memory images, alarm
        events, and historical data, to larger-scale applications such as database
        management and program development.


        3.4.1 Application Processor Functions


               The following sections describe the major functions performed by
        the Application Processors.


        3.4.1.1 System and Network Management Functions

               The    Application     Processors     perform    system   management
        functions, which include collecting system performance statistics, data
        reconciliation,    performing      station   reloads,   providing   message
        broadcasting, handling all station alarms and messages, and maintaining
        consistent time and date in all system stations. The Application Processor
        also performs network management functions, which comprise that
        portion of system management functions which deal with the network.


        3.4.1.2 Database Management

               Database management involves the storage, manipulation, and
        retrieval of files containing data received and/or produced by the system.
        The Application Processors utilize the industry-standard Relational Data
        Base Management System.

                                                                                40
Distributed Control System and Programmable Logic Control



        3.4.1.3 File Requests


               Each Application Processor contains a file manager, which
        manages all file requests associated with bulk memory attached to the
        Application Processor. Each Application Processor also supports a
        remote file system that allows tasks in one station to share files in
        another.


        3.4.1.4 Historical Data


               The Application Processors can be configured to contain the
        Historian function, which maintains a history of application messages and
        continuous and discrete I/O values. These values may represent any
        parameters such as measurements, setpoints, outputs, and status switches
        from stations that have been configured to collect data and send it to a
        Historian. In addition, the Historian computes and stores a history of
        averages, maximums, minimums, and other derived values. This
        information is maintained for display, reporting, and access by
        application programs. An archiving facility saves the data on removable
        media, where applicable.


               The Application Processors can be configured to maintain a history
        of errors, alarm conditions, and selected operator actions. The occurrence
        of errors, alarms, and events in other stations can be stored (for later
        review and analysis) by sending a message defining the event to the
        Historian in one or more Application Processors.




                                                                               41
Distributed Control System and Programmable Logic Control



        3.4.1.5 Graphic Display Support


                The Application Processor supports graphic displays by storing and
        retrieving display formats, by providing access to objects stored on the
        Application Processor, and by storing tasks which execute in a
        workstation processor. Application Processors not only provide storage of
        information and file management for displays, but also execute programs
        that perform display and trend service.


        3.4.1.6 Production Control Software


                Production control software represents a large range of packages
        that require varied Application Processor resources. The following is a
        list of packages provided:
            •   DBMS
            •   Historian
            •   Spreadsheet
            •   Physical Properties Library
            •   Mathematics Library
            •   BATCH
        The operation and performance of the production control software are
        determined by the particular Application Processor configuration.


        3.4.1.7 Configuration


                Configuration refers to the process of entering or selecting
        parameters to define what a software package does, or to define the
        environment for a software package. The Application Processors support
        configuration functions by providing bulk storage for configuration
        parameters and by executing some of the configuration processes.

                                                                               42
Distributed Control System and Programmable Logic Control



        3.4.1.8 Application Development Facilities


                Application development tools are provided to build programs for
        all system stations. These include tools to document, enter, translate, link,
        test, and maintain programs written in several programming languages.
        The Application Processor supports program development for all stations
        (workstation processors, control processors, and so forth).
                Assembly language, FORTRAN, and C programs can be written on
        the Application Processor using standard operating system tools. An
        optional package is available including text editors, debuggers, linkers,
        revision control, and compilers, plus execution statistics functions.


        3.4.1.9 User Application Program Execution


                The Application Processors also execute user application programs.
        These may be application packages such as special optimizations, test
        data collections, special data reductions, or other packages that you may
        have already developed. The allocation of resources reserved for user
        application varies with each Application Processor.


        3.4.2 Diagnostics


                The Application Processors utilize three types of diagnostic tests to
        detect and/or isolate faults:
            •   Power-up self-checks
            •   Run-time and watchdog timer checks
            •   Off-line diagnostics
                Power-up self-checks are initiated when power is applied to the
        Application Processor. These checks perform sequential tests on the

                                                                                  43
Distributed Control System and Programmable Logic Control



        various Application Processor functional elements. Any malfunction
        detected during the power-up self-checks is reported by means of
        messages printed or displayed on a directly connected printer or terminal.
                The run-time and watchdog timer checks provide continuous
        monitoring of Application Processor functions during normal system
        operations. For any processor model, you are informed of a malfunction
        by means of printed or displayed system messages. Off-line diagnostics
        are temporarily loaded into the system for the purpose of performing
        comprehensive tests and checks on various system stations and devices.
                Using the off-line diagnostics, a suspected fault in the Application
        Processor can be isolated and/or confirmed.


        3.4.3 Workstation Components


                The workstation components provide user interface to all System
        CRT display functions. A selection of workstation components is
        available for command and data entry, along with CRT pointer
        manipulation and control. These components interact with software
        resident in versions of the system Workstation Processors (WPs) and
        Application Workstation Processors (AWs). Many of these components
        (displays and keyboards) are "common" and allow interchangeability and
        simplicity in mixed technology configurations.
        Workstation components include:
            •   Alphanumeric Keyboard
            •   Annunciator and Annunciator/Numeric Keyboards
            •   Workstation Display (with/without Touchscreen)
            •   Mouse
            •   Trackball
            •   Industrial Pointing Device

                                                                                  44
Distributed Control System and Programmable Logic Control



            •   Workstation Processor or Application Workstation Processor
            •   Personal Workstation
            •   Modular Industrial Console
                Selection of the touch screen, mouse, trackball or industrial
        pointing device is required for picking display objects on the CRT. The
        touch screen has sufficient resolution for all functions normally
        associated with a process operator. Only the mouse or trackball provides
        the picking resolution necessary for engineer-related functions (for
        example, building graphic displays). The touch screen associated with
        Workstation Display and the annunciator type keyboards connects to a
        Graphics Controller Input Output (GCIO) interface unit located beneath
        the workstation display. The GCIO interfaces to the Workstation
        Processor and/or Application Workstation that provide secure, high-
        speed, bidirectional data flow. The alphanumeric keyboard and trackball
        connect together in a functional grouping via a serial communications
        link to the processors. Personal Workstations (PW) utilize separate serial
        communication links for alphanumeric keyboard and mouse/trackball.
        These buses allow a variety of component connections.




                               Figure 3.5 Table- Workstation Components.



                                                                               45
Distributed Control System and Programmable Logic Control



        3.4.3.1 Alphanumeric Keyboard


               The alphanumeric keyboard is used any time text is entered into the
        system. It consists of the full set of alphanumeric keys plus punctuation
        and special symbol keys laid out in the standard format, and a numeric
        data entry pad (with cursor control).




                                  Figure 3.6 Alphanumeric Keyboard

        3.4.3.2 Annunciator Keyboard


               The Annunciator Keyboard Figure 3.7 is an array of LED/switch
        pairs. It also contains a horn silence switch and a lamp-test switch. Each
        LED, under control of the processor software, may be ON, OFF, or
        FLASHING as determined by the process conditions. The LEDs, when
        used in conjunction with the unit's audible annunciator, form an effective
        means of calling a user's attention to specific areas of the system. The
        switch associated with each LED can be used to invoke any pre-
        configured displays or operator responses..




                                   Figure 3.7 Annunciator Keyboard

        3.4.3.3 Workstation Display with/without Touchscreen


               The workstation display is an analog cathode ray tube (CRT) color
        monitor supporting ultra-high resolution applications. The monitor is
        suitable for mounting onto a Modular Industrial Workstation or on a


                                                                               46
Distributed Control System and Programmable Logic Control



        desktop. The monitor can include a touchscreen optional feature. Figure
        3.8 shows the monitor with a tilt and swivel base mounted on the GCIO
        interface unit. The GCIO interface supports the touchscreen, annunciator
        and annunciator/ numeric keyboard, and audible horn options.




                                Figure 3.8 Table-Top Workstation Display

               The optional touch screen is bonded to the front surface of the CRT
        monitor. The user selects display objects by touching them on the screen.
        The touch screen senses the action and sends a data signal to the
        workstation processor's software indicating the position of the selection.
        3.4.3.4 Trackball


               The trackball is a stationary component that contains a rotatable
        sphere. The trackball can be located on a table top. Rotation of the sphere
        causes CRT pointer movement analogous to the mouse action. Buttons
        are also provided for user selections/manipulations. See Figure 3.9




                                          Figure 3.9 Trackball

        3.4.3.5 Modular Industrial Console

               Modular      Industrial      Consoles        provide        flexible   mounting
        arrangements of components. They allow users to configure centralized
        or distributed control centers tailored to the functional requirements of
        each interaction point in the plant. The modular console furniture

                                                                                           47
Distributed Control System and Programmable Logic Control



        described herein may incorporate a mix of equipment - console displays,
        input devices, processors, Fieldbus Modules, data storage devices, and so
        on. Alternately, only display-specific equipment can be incorporated.
        Modular Industrial Consoles (MICs) are ideal for supporting powerful
        multiple-screen, real-time display software interactions. This combination
        allows console resources to be optimally allocated to meet changing day-
        to-day needs.


        3.5 Operator Interface


               Operating in conjunction with human interface input/output
        components, the workstation processors serve as a link between the
        operator and other distributed processor modules. They receive graphic
        and textual information both stored internally or from application
        processors and generate signals to display the information on a
        workstation display. Display formats and data files are available from
        bulk storage. Live display information (distributed data objects) is
        available from any control -processor, or from shared system global data.
        The video information displayed can include free form combinations of
        text, graphic illustrations, charts, and control displays.
               The workstation processors display textual information as 80 text
        characters per line, with four fonts. The processors provide resizable and
        restackable windows. Displays for all of the workstation processors may
        also be developed using the system software running in a compatible
        personal computer.
        A workstation processor, together with its workstation monitor and input
        components, can be configured with combinations of peripherals to suit
        functions and user preferences.


                                                                               48
Distributed Control System and Programmable Logic Control



        3.6 Gateways


               The architecture of the DCS permits it to be connected to other
        foreign systems using a gateway module for adapting different
        communication protocols. See figure 3.10.




                                Figure 3.10 Field Automation Subsystem




        3.7 Role Play


        Each trainee should introduce one of the main components:
            1. Communication Bus
            2. Control Processor.
            3. Application Processor
            4. Operator Interfaces and Gateways




                                                                           49
Distributed Control System and Programmable Logic Control




                                         Chapter 4
                                     DCS Hardware

        4.1 Learning Objectives


        • Define fieldbus communication.
        • Illustrate system components of level 1 control.
        • Demonstrate interconnection between different components.
        • Develop knowledge base of foundation fieldbus technology.


        4.2 Fieldbus Modules


                Fieldbus Modules provide connection of digital I/O, analog I/O,
        and Intelligent Transmitters to control processors. There are two types of
        Fieldbus Modules: Main and Expansion. Some main modules can be
        expanded using an expansion module.


                A wide range of Fieldbus Modules is available to perform the
        signal conversion necessary to interface the control processor with field
        sensors and actuators.


        4.3 Fieldbus Interconnection


            The Control Processor is used in three different configurations, which
        provide broad flexibility in Fieldbus implementation:
            •   Local Fieldbus (Figure 4.1) - Used only within the enclosure.
                Fieldbus Modules attach directly to the redundant local bus.



                                                                                50
Distributed Control System and Programmable Logic Control




                                            Figure 4.1 Local Fieldbus

            •   Twinaxial (Dual-Conductor Coaxial) Fieldbus Extension (Figure
                4.2) - Using twinaxial cable, the Fieldbus can optionally extend
                outside of the enclosure. Fieldbus Modules attach to the extended
                bus through Fieldbus isolators. The twinaxial Fieldbus extension
                may be redundant.




                                Figure 4.2 Twinaxial Fieldbus Extension

            •   Fiber Optic Fieldbus Extension (Figure 4.3) - The fiber optic
                Fieldbus can optionally extend the distance as well as add
                application versatility and security.




                                Figure 4.3 Fiber Optic Fieldbus Extension




                                                                              51
Distributed Control System and Programmable Logic Control



        All three Fieldbus configurations use serial data communication
        complying with Electronic Industrial Association (EIA) Standard RS-485.


        4.4 Cluster I/O Subsystem Interfacing


               The Control Processor interfaces with the Fieldbus Cluster
        Input/Output Subsystem that consists of the Fieldbus, a multi-slot chassis
        configuration of a Fieldbus Processor, analog/digital Fieldbus Cards
        (FBCs), and power supply and power monitor card. These Cluster I/O
        subsystems meet the needs of applications where a high number of
        channels per card are required. Figure 4.4 shows a typical twinaxial
        Fieldbus configuration.




                  Figure 4.4 Twinaxial Fieldbus Cluster I/O Subsystem Interface Configuration


        4.5 Fieldbus Cluster I/O Subsystem


               The Fieldbus Cluster Input/Output Subsystem provides full support
        for analog measurement, digital sensing, and analog or discrete control
        capabilities. The Subsystem integrates with the Control Processor or
        Personal Workstation via the Fieldbus, and includes a multi-slot chassis
        configuration made up of a Fieldbus Processor, Analog/Digital Fieldbus
        Cards (FBC), subsystem main power supply, and power monitor card.



                                                                                                52
Distributed Control System and Programmable Logic Control



                The Fieldbus Cluster I/O Subsystem is configurable, gathering
        analog measurements, while simultaneously handling analog and digital
        input and output channels. The Fieldbus Cluster I/O Subsystem is offered
        in both non-redundant and redundant configurations. Each in a redundant
        pair is individually addressable on the Fieldbus with a unique logical
        address. In a redundant configuration, the FBPs provide switchover from
        the primary FBP to the redundant FBP and back again automatically. The
        FBCs are suitable in applications where a high number of channels per
        card are required. They are ideal for non-isolated and isolated input signal
        gathering and data acquisition systems where high quantities of "points
        per cluster" areas are desired. The FBCs may be optionally connected as
        redundant pairs. Various input cards are available with one of the
        following three levels of isolation:
            •   Non-isolated - Each channel is referenced to ground and the card
                itself is referenced to ground.
            •   Group-isolated - Electrically separate card-to-card but not channel-
                to-channel on the same card.
            •   Isolated - Each channel is electrically separated from any other
                channel, card, group, building, site, etc.


        4.6 Fieldbus Processor


                The Fieldbus Processor (FBP) module provides communication
        between the Fieldbus Cards (FBCs) and the Control Processor. Optionally
        available is redundancy for the FBP module. Each FBP module is
        individually addressable via the Fieldbus. If the primary FBP fails or is
        taken off-line, the secondary FBP automatically assumes control. It
        remains in control until the primary FBP returns on-line (figure 4.5).


                                                                                  53
Distributed Control System and Programmable Logic Control




                                      Figure 4.5 FBP Overview

        4.7 Fieldbus Cards


               The Fieldbus Cards support a variety of analog and digital I/O
        signals. The FBCs convert electrical I/O signals used by field devices to
        permit communication with these devices via the Fieldbus.
               The FBCs can be connected in a redundant configuration via the
        hardware. The redundant FBCs must be in adjacent slots and they are
        connected via a hardware adapter at the interface to the field devices. In
        an FBC redundant configuration, the FBP determines which FBC of the
        redundant pair is to supply the data to the Control Processor. This is done
        in the software by a predetermined set of conditions.


        4.7.1 Analog FBCS


               The analog FBCs support analog signal types and control functions
        equipped with accurate signal conditioning circuitry, the analog cards
        interface between process sensors and actuators.
               To input an analog voltage (into DCS) the continuous voltage value
        must be sampled and then converted to a numerical value by an A/D

                                                                                54
converter. Figure 4.6 shows a continuous voltage changing over time.
There are three samples shown on the figure. The process of sampling the
data is not instantaneous, so each sample has a start and stop time. The
time required to acquire the sample is called the sampling time. A/D
converters can only acquire a limited number of samples per second. The
time between samples is called the sampling period T, and the inverse of
the sampling period is the sampling frequency (also called sampling rate).
The sampling time is often much smaller than the sampling period.




                       Figure 4.6 Sampling an analog voltage

      Analog outputs are much simpler than analog inputs. To set an
analog output an integer is converted to a voltage. This process is very
fast, and does not experience the timing problems with analog inputs.
But, analog outputs are subject to quantization errors. Figure 4.7 gives a
summary of the important relationships. These relationships are almost
identical to those of the A/D converter. Assume we are using an 8 bit D/A
converter that outputs values between 0V and 10V. We have a resolution
of 256, where 0 results in an output of 0V and 255 results in 10V. The
quantization error will be 20mV. If we want to output a voltage of
6.234V, we would specify an output integer of 159, this would result in
an output voltage of 6.235V. The quantization error would be 6.235V-
6.234V=0.001V. The current output from a D/A converter is normally
limited to a small value, typically less than 20mA.
Figure 4.7 D/A converter



4.7.2 Digital FBCS


      The digital FBCs consist of 32- and 64-channel types. Inputs can
be either voltage monitoring or contact sensing.
      Contact inputs must convert a variety of logic levels to the 5Vdc
logic levels used on the data bus. This can be done with circuits similar to
figure 4.8. Basically the circuits condition the input to drive an
optocoupler. This electrically isolates the external electrical circuitry from
the internal circuitry. Other circuit components are used to guard against
excess or reversed voltage polarity.




                          Figure 4.8 Contact input circuitry.

      Contact outputs must convert the 5Vdc logic levels on the DCS
data bus to external voltage levels. This can be done with circuits similar
to figure 4.9. Basically the circuits use an optocoupler to switch external
circuitry. This electrically isolates the external electrical circuitry from
the internal circuitry. Other circuit components are used to guard against
excess or reversed voltage polarity.




                         Figure 4.9 Contact output circuitry.




4.8 Other Modules


   • 0 to 20 mA Input/Output Interface
   • Pulse Input, 0 to 20 mA Output Interface
   • Thermocouple/ Millivolt Input Interface
   • RTD Input Interface
   • High Power Contact/dc Input/Output Interface


4.9 Foundation Fieldbus Technology


      FOUNDATION fieldbus is an all-digital, serial, two-way
communications system that serves as the base-level network in a plant or
factory automation environment.




                      Figure 4.10 Foundation Fieldbus Network
Figure 4.11 Historical development of field devices technology.



      It's ideal for applications using basic and advanced regulatory
control, and for much of the discrete control associated with those
functions. Two related implementations of FOUNDATION fieldbus have
been introduced to meet different needs within the process automation
environment. These two implementations use different physical media
and communication speeds.
  •   H1 works at 31.25 Kbit/sec and generally connects to field devices.
      It provides communication and power over standard twisted-pair
      wiring. H1 is currently the most common implementation and is
      therefore the focus of these courses.
  •   HSE (High-speed Ethernet) works at 100 Mbit/sec and generally
      connects input/output subsystems, host systems, linking devices,
      gateways, and field devices using standard Ethernet cabling. It
      doesn't currently provide power over the cable, although work is
      under way to address this.




                            Figure 4.12 Field Device Capacity.
Conventional analog and discrete field instruments use point-to-
point wiring: one wire pair per device. They're also limited to carrying
only one piece of information -- usually a process variable or control
output -- over those wires. As a digital bus, FOUNDATION fieldbus
doesn't have those limitations.


   • Multidrop wiring. FOUNDATION fieldbus will support up to 32
      devices on a single pair of wires (called a segment) -- more if
      repeaters are used. In actual practice, considerations such as power,
      process modularity, and loop execution speed make 4 to 16 devices
      per H1 segment more typical.


That means if you have 1000 devices -- which would require 1000 wire
pairs with traditional technology -- you only need 60 to 250 wire pairs
with FOUNDATION fieldbus. That's a lot of savings in wiring (and
wiring installation).




                        Figure 4.12 Fieldbus wiring diagram.
• Multivariable instruments. That same wire pair can handle
      multiple variables from one field device. For example, one
      temperature transmitter might communicate inputs from as many as
      eight sensors -- reducing both wiring and instrument costs.


Other benefits of reducing several devices to one can include fewer pipe
penetrations and lower engineering costs.


   • Two-way communication. In addition, the information flow can
      now be two-way. A valve controller can accept a control output
      from a host system or other source and send back the actual valve
      position for more precise control. In an analog world, that would
      take another pair of wires.
   • New types of information. Traditional analog and discrete devices
      have no way to tell you if they're operating correctly, or if the
      process information they're sending is valid.


But FOUNDATION fieldbus devices can tell you if they're operating
correctly, and if the information they're sending is good, bad, or
uncertain. This eliminates the need for most routine checks -- and helps
you detect failure conditions before they cause a major process problem.


   • Control in the field. FOUNDATION fieldbus also offers the
      option of executing some or all control algorithms in field devices
      rather than a central host system. Depending on the application,
      control in the field may provide lower costs and better performance
      -- while enabling automatic control to continue even if there's a
      host-related failure.
FOUNDATION fieldbus is covered by standards from three major
organizations:
   •   ANSI/ISA 50.02
   •   IEC 61158
   •   CENELEC EN50170:1996/A1


       The technology is managed by the independent, not-for-profit
Fieldbus Foundation, whose 150+ member companies include users as
well as all major process automation suppliers around the globe.
Some suppliers have even donated fieldbus-related patents to the Fieldbus
Foundation to encourage wider use of the technology by all Foundation
members.


       Interoperability simply means that FOUNDATION fieldbus
devices and host systems can work together while giving you the full
functionality of each component.


4.10 Role Play


Each trainee should introduce one of the main components:
   5. Fieldbus Module and Interconnection
   6. Fieldbus Processor and Clusters.
   7. Foundation Fieldbus technology
Chapter 5
                            DCS Software

5.1 Learning objectives


• To be familiar with main software components of DCS.
• Understand main tasks for each application.


5.2 Standard Application Packages
5.2.1 System Management
Features include:
   •   Display of equipment information for the station and its associated
       input/output devices, buses, and printers.
   •   Capability for change actions directed to the associated equipment.
   •   Processing of station alarm conditions and messages.
5.2.2 Database Management
Features include:
   •   Storage, retrieval, and manipulation of system data files.
   •   A run-time license for the embedded use of the Relational Database
       Management System.
   •   A spreadsheet package.


5.2.3 Historian
Features include:
   •   Maintenance    of   a    history   of   values   for   process-related
       measurements that have been configured for retention by the
       Historian.
•   Maintenance of a history of application messages that have been
       sent to the Historian.
   •   Maintenance of a history of alarms and error conditions which
       generate messages for the Historian.
   •   Access to all Historian data by display and report application
       programs.


5.2.4 View Display Manager
Features include:
   •   Presentation of the operating environment.
   •   Setting of the overall operating environment according to the type
       of user. Process engineers, process operators, and software
       engineers have access to specialized functions and databases suited
       to their specific requirements and authorizations.
   •   Dynamic and interactive process graphics.
   •   Display and processing of current process alarms.
   •   Group and default displays for control blocks.
   •   Execution of embedded trending within displays.


5.2.5 Draw Display Builder
Features include:
   •   Graphical display configuration for viewing and control of process
       operation.
   •   Access to graphical object palettes allowing easy inclusion of
       pumps, tanks, valves, ISA symbols, and similar complex objects.
   •   Ready modification of existing displays using a mouse pointer,
       menu items, and quick-access toolbars.
   •   Association of process variables with objects in the displays.
•   Dynamic variation of object attributes such as fill level, color,
       position, size and visibility with changes in the associated process
       variable.
   •   Inclusion of operator control elements such as pushbuttons and
       sliders into displays.
   •   A library of faceplates which may be configured by simply
       specifying the compound and block name of the block to which the
       faceplate is to be connected.


5.3 Alarm System




                                Figure 5.1 Alarm manger

       Alarm Manager provides an easy-to-use graphical interface of
preconfigured alarm displays for viewing and quickly responding to
process alarm conditions. The alarm display windows present alarm
messages initiated by the control blocks and related to digital input, state
change, absolute analog, deviation, rate of change, device status
mismatch, and other alarm conditions.
Accessible from any environment, the Alarm Manager Display windows
provide:
•   Quick, easy access to the most recent alarm messages via the Most
       Recent Alarm display or Current Alarm display
   •   Alarm status and value information dynamically updated from the
       control station
   •   Color-coded priority and status indicators that allow you to quickly
       focus in on critical alarms
   •   Summary displays for different views of the alarm database based
       on alarm status
   •   An historical list of alarms
   •   The capability to view subsets of alarms based on specific user-
       defined criteria
   •   The capability to silence or temporarily mute workstation and
       annunciator horns.
   •   Secured access to alarming functions dependent on user or system
       responsibility
This set of resizable alarm displays providing a variety of current and
historic views of the process alarm database includes:
   •   A multi-page list of all the current alarms
   •   A single page of the most recent, active, unacknowledged alarms
       with dynamically updating value and status fields
   •   Three summary displays specific to alarm status also with updating
       values and statuses:
          o   all active, unacknowledged alarms
          o   all unacknowledged alarms that have returned to normal
          o   all active, acknowledged alarms
   •   A list of historized alarms related to the selected historian database
   •   An operations display for silencing horns, temporarily muting
       horns, changing environments
These displays allow you to respond to alarm conditions, filter and
analyze specific alarm data, and maintain alarm message files for
reporting purposes.
   The Process or Alarm button in the Display Manager (DM) window
indicates    the     presence   of   alarms   (both   acknowledged    and
unacknowledged) and provides access to Alarm Manager Displays.
Initially, the Current Alarm Display (CAD) appears and the other
displays are easily accessible from the CAD via its default Displays
menu:
   •    Most Recent Alarm display (MRA)
   •    New Alarm display (NEWALM)
   •    Unacknowledged Alarms display (UNACK)
   •    Acknowledged Alarms display (ACKALM)
   •    Alarm History display (AHD)
   •    Operations display (OPR)
These easy-to-use displays support the following features:
   •    A pre-configured number of alarms per screen or page
   •    Pre-configured alarm message information and formatting per
        alarm type
   •    A status area for indication of current Alarm Manager and display
        status, such as horns muted, match active, display paused, initial
        call-up time
   •    Buttons for responding to alarm conditions, such as acknowledging
        or clearing alarms, and for accessing additional alarm information
        and process displays
   •    Pull-down menus for editing, viewing, and filing functions
   •    A pull-down menu for accessing other displays
   •    Pop-up menus for quick access to commonly used functions
•   A scroll bar and Go To Page option for moving easily through the
       alarm list
Although a preconfigured set of alarm displays is provided, many aspects
of the displays and alarm message content are user configurable to
accommodate different process control applications and operational
needs. See the section on Alarm/Display Manager Configurator.


5.4 Historian


       The Historian collects, stores, processes, and archives process data
from the control system to provide data for trends, Statistical Process
Control (SPC) charts, logs, reports, spreadsheets, and application
programs. The Historian software is an easy-to-use data collection tool
that allows the user to organize and enforce a plant data collection
philosophy. The Historian provides extensive data collection and
management functions, and data display functions for use by process
engineers or operators.
       Typical historical data are process analog and/or digital variables
(points). The Historian can also collect and display application generated
messages. You can use the Historian to collect data in support of the
following production control functions:
   •   Cost accounting
   •   Equipment performance analysis
   •   Historical trending
   •   Information retrieval
   •   Inventory management
   •   Legal record maintenance
   •   Lost time analysis
•   Maintenance reporting
   •   Material accounting
   •   Process analysis
   •   Production reporting
   •   Quality control
The Historian can:
   •   Retrieve variables from process databases or accept data from
       production control databases maintained by user application
       programs.
   •   Perform built-in calculations on the collected data.
   •   Store calculated (reduced) data in a real time, relational database.
Application software in a plant-wide control system can access the
Historian database to obtain historical data for process control, production
control, and management information reporting.
You can use SPC chart displays of Historian data to monitor process
variables on-line via the Statistical Process Control Package (SPCP).
You can build displays for trending historical data via the Display Builder
and Display Configurator with Trending software.
Using the Report Writer, you can generate detailed reports of historical
data for management information.
Examples of Industrial Software that interface with the Historian are:
   •   Batch Plant Management
   •   Data Validator
   •   Display Manager
   •   Display Configurator with Trending
   •   Object Manager (for process data histories)
   •   Operator Action Journal
   •   Operator Message Interface
   •   Real-Time Data Base Manager
•   Spreadsheet
   •   Statistical Process Control Package
   •   System Monitor
   •   Report Writer


5.5 Draw




                                Figure 5.2 Draw

       Draw is a display builder and configurator that allow you to create
and maintain dynamically updating process displays. Displays can
represent the plant, a process area or a detailed portion of the process.
You can draw basic objects using Draw's toolbars, menu items and
shortcut keys. You assign graphic attributes such as color and line style to
the objects, and then configure them to reflect process variable changes or
operator actions. Draw includes numerous palettes of objects such as
operator buttons, pumps, tanks, pipes, motors, valves and ISA symbols.
You can also create your own palettes for storing complex objects and
company-standard symbols. Displays can include faceplates, trends and
bitmapped images. You can easily edit your displays to reflect changes in
the process control scheme or to maximize operating efficiency and
security.
5.5.1 Configuration


There are two ways of configuring a display object. You can:
   1. Choose the Dynamic Update tab to connect one of the object's
       attributes, such as visibility or fill level, to a process variable or a
       file. With this type of configuration, changes in an attribute are
       triggered dynamically by changes in the process variable. No
       operator intervention is necessary.
   2. Choose the Operator Action tab to connect the entire object to an
       action, such as opening a display or executing a command. An
       operator triggers the action by selecting the object.
An individual object can have both types of connections, although it can
have only one operator action.


5.5.2 Operator Actions


       In a display configured for operator action, an operator can trigger
events by selecting an object (typically a button), moving a slider, or
typing text or a numeric value. In response to an operator action,
variables can be modified, a new display can open or an overlay can
appear.


       While you can configure only one operator action for each display
object, you can trigger two or more events with a single operator action
by configuring an object with a View display command script.
Operator Actions include:
   •   Open Display
   •   Open Overlay
   •   Close Display/Overlay
•   Display Command
   •   Relative Pick
   •   Momentary Contact
   •   Ramp
   •   Connect Variable
   •   Move Horizontal or Vertical
   •   Numeric/Text Entry


5.5.3 Faceplates
       A faceplate is a dynamic representation of control block
parameters. Draw provides a complete library of faceplates, ready to be
connected to any control block in the control database. In addition, you
can build your own faceplates using the standard Draw drawing tools.
To configure a faceplate, you need only define the Compound:block to
which the faceplate is connected. Draw automatically determines the
proper configuration attributes for the associated Compound:block.


5.5.4 Trends
       Trend areas represent changing data values from the real-time
database and historian database. A data is displayed as a series of plotted
points connected by straight lines and scaled according to the high and
low limits configured for each trend line.


5.5.5 Group Displays
       Group displays allow you to group faceplates and trends into
unique layouts to meet changing operational needs.
5.6 View




                                  Figure 5.3 View

       View is a window into the system software, providing a user-
friendly interface to the total process. You can interact with any or all of
the real-time plant, field, and process data available in the system.
View provides:
   •   Direct access to dynamic process displays.
   •   Entry into user-configurable operating environments specific to
       each user - the process engineer, process operator, and software
       engineer.
   •   Execution of embedded real-time and historical trending.
   •   Service and display of process alarms via the Alarm Manager.
   •   An overview of the compounds and blocks in the control database
       and access to block default detail displays via Select.
   •   Access to other applications, such as:
          o   Draw software for building and configuring dynamic user
              graphics.
          o   System Management Displays for monitoring system
              equipment health.
          o   Integrated Control Configurator for configuring the control
              database.
          o   Historian for configuring the historization of data and system
              messages.
o   Access to the four most recently used displays.
Additionally, with View you have:
   •   Flexibility in customizing environments to conform to your site
       requirements.
   •   Rapid access to View while in other applications.
   •   Screen print utility.
   •   Window sizing options.
The multi-window capability of Solaris and Windows NT operating
systems allows you to monitor the information on a process control
display as well as access other applications without closing any window.


5.6.1 View Window


View Window contains the following features:
   •   A top menu bar for accessing displays, configurators, and other
       applications as specified by the environment.
   •   A display bar of named display buttons or eight "thumbnail" mini-
       display buttons for directly accessing process displays.
   •   A system bar with System and Process alarm buttons indicating
       system and process health; a message bar with a dropdown list of
       the latest messages; display of the current date and time.
   •   A status bar indicating the current display name, current operating
       environment, Operator Action Journal logging name, printer
       logging name, Historian name.


Using the control window menu, you can:
   •   Resize the View window automatically or manually.
   •   Move the window.
5.6.2 Operating Environments


      A collection of programs, utilities, and displays related to user
tasks is provided for each of the following: process operator, process
engineer, and software engineer. These environments, including menu
bars, menu content, and Display Bar content, can be modified to conform
to your site requirements. You can easily switch from one configured
environment to another. To secure environments against unauthorized
use, environment passwords can be configured and menu entries disabled
based on the environment.


5.7 Operator Action Journal


      The Operator Action Journal is a record of specific operator actions
taken during process control operations. These actions generally consist
of manipulating certain Control Processor, and gateway parameters as
well as Application Processor, Application Workstation, and Workstation
Processor shared variables. Actions of this type are the ramping or direct
data entry of point values, toggling points, changing block statuses,
acknowledging block alarms, and horn muting. Operator action reporting
is limited to operator actions from the Display Manager, View, and
Alarm Manager. Also logged are environment change actions, scripts,
applics, and invoking other applications such as configuration.


      When the Operator Action Journal feature is enabled, all operator
actions within the Display Manager, View, and the Alarm Manager that
change parameters in the process database are logged to a printer and/or
to the specified Historian database. These operator actions include
toggling points, ramping or direct data entry of new point values,
changing block statuses, acknowledging block alarms, and other actions
such as horn muting.


Information logged as a result of each database change includes:
    •      Name of the Display Manager, FoxView, or Alarm Manager that
           requested the database change.
    •      Compound:Block.Point for which the change was made.
    •      The "old value" TO "new value" text for non-packed Boolean.
    •      Current mask and data value for packed Boolean/long.
Following is an example of an Operator Action Journal Report.

Operator Action Journal Report


Tue Aug    1 1997 17:04:05 Page   1
08-02-97   07:57:08 GC3E31 SCRIPT /usr/fox/hi/init.cmds
08-02-97   07:57:15 GC3E31 ChgEnv Init_Env ->Init_env
08-02-97   07:58:19 GC3E31 ChgEnv Init+Env ->Proc_Eng_Env
08-02-97   08:00:34 CG3E31 UC01_LEAD :SINE .OUT 16.18      to 46.18
08-02-97   08:00:54 GC3E31 UC01_LEAD :SINE .MA Manual to Auto
08-02-97   08:00:57 GC3E31 UC01_LEAD :SINE .LR Remote to Local
08-02-97   08:01:01 GC3E31 UC01_LEAD :SINE .MA Auto       to Manual



5.8 Control Configuration


           Process control for DCS is based on the concepts of compounds
and blocks. A compound is a logical collection of blocks that performs a
control strategy. A block is a member of a set of algorithms that performs
a certain control task within the compound structure. Figure 7.4 shows
the compound/block relationship.
The compound provides the basis for the integration of:
    •      Continuous control
    •      Ladder logic
    •      Sequential control.
Within this structure, any block in any compound can be connected to
any other block in any other compound in the system. The entire
compound structure can be viewed through the workstation display.
The block contains parameters that have values of the types: Real,
Boolean, Packed Boolean, Boolean Long, Integer, or String.




                      Figure 5.4 Compound/Blocks relationship


5.8.1 Compound Functions


The compound supports the following functions for the related blocks:
   •   Process alarm priority, alarm inhibiting, and alarm grouping
   •   Sequence status notification (see Sequential Control section)
   •   Phasing for execution load leveling at execution time.


5.8.2 Compound/Block Process Alarming


       Alarms and status messages are generated by specific alarm blocks
and by alarm options in selected blocks. Alarms have five levels of
priority, 1-5, (where 1 = highest priority) that enable you to quickly focus
on the most important plant alarm conditions. An alarm priority of 0
indicates the absence of any alarm. These are summarized in a single
alarm summary parameter for each compound. This parameter contains
the priority of the highest current alarm in that compound. To reduce
nuisance alarms, alarms can be inhibited at the compound level on a
priority level basis. Alarms can also be inhibited at the block level, on
either an alarm type basis, or an overall basis.
        Alarms are initiated by the blocks within the compound. Alarm
messages are then sent to groups of stations or applications (for example,
Workstations, Historians, Printers) according to configured alarm groups.
The UNACK alarm acknowledge output parameter allows the user to
propagate alarm acknowledge actions to all blocks in a compound.
Stations, applications, and devices corresponding to various alarm
destination groups are configured at the compound level or at the station
level in the case of station compounds.
Group numbers for individual block alarm types are configured at the
block level.
5.8.3 Compound/Block Phasing
        A user-defined phase number can be assigned to each compound
using a range of integer values that varies with assigned period. Phasing
allows the starting time of one compound/block to lead or lag the starting
time of another compound/block, thereby leveling the block processor
load.


5.8.4 Compound Attributes
The compound has the following attributes:
   • Name: User-defined name that must be system-unique and no more
        than 12 characters in length. The name can be any mix of numeric
        (0 to 9), upper case alphabetic (A to Z), and the underscore (_).
   • Descriptor: 32-character field for user-defined identification.
   • On/Off: Parameter that enables or disables the execution of all
        blocks within the compound, where: 1 = on; 0 = off.
5.8.5 Compound/Block Parameters


      Compound and block parameters contain values that are of one of
the types Real, String, Integer, Short Integer, Long Integer, Boolean,
Packed Boolean, Packed Long, or Character. Additionally, parameters are
defined as being configurable, and either connectable/settable, not
connectable/not settable, or a combination that is dependent upon the
compound, block, and state.


5.8.5.1 Configurable Parameters


      Configurable parameters are those parameters that can be defined
through the Integrated Control Configurator. They can be displayable
only, or displayable and editable.


5.8.5.2 Connectable Parameters


      Connectable parameters are those parameters of the user interface
in which secured, change-driven connections may be made between
network stations, or as local direct connections within the same station.
Each connection consists of a connectable source and a connectable sink.
Output parameters (all outputs are connectable) are sources, while a
connectable input may be a sink or a source, or both.
Certain parameters that may be considered functional inputs (such as SPT
in the PID blocks, and RATIO in the RATIO block) are settable but not
connectable. A connectable parameter has a value record that contains the
parameter's value, its status, and its designated value type (Real, Boolean,
or Integer).
5.8.5.3 Input Parameters


      Input parameters are connectable types that are the receivers of
data from other connectable parameters via a path connection.
If no source path is specified during configuration, then the resident data
of the value record is the actual "source" of data. It can be either the
initial default or configured value, or a new value through a SET call to
the input parameter.
If a source path is specified, then the data value is an output parameter of
the same or another block, or a shared variable, thereby securing the
input. By linking a shared variable to a block input during configuration,
the user can establish a long-term secured connection between a remote
application program and the block input.


5.8.5.4 Output Parameters


      All output parameters are connectable data sources that have value
records. There are two types: settable and nonsettable. The settability of a
settable output is controlled by the secured status of the value record. The
secured status is dependent on whether the block's operational mode is in
Auto or in Manual. In either Auto or Manual, nonsettable output
parameters cannot be written by any other source under any conditions.


      Settable outputs may be conditionally released by the block
algorithm in the Manual mode. In Manual, the block unsecures settable
output parameters. They can then be written by other tasks via SET calls.
When the block switches to Auto, the block secures and updates its
output parameter(s).
5.8.5.5 Nonconnectable Parameters


      Nonconnectable parameters have no value records and are not
linkable. They mainly consist of string-type variables like NAME, or
nonsettable parameters that are used in the configurator only, for
example,   block     options.   Local   algorithm   variables   are   also
nonconnectable. Nonconnectable parameters are generally accessible
through GET calls.
There is also a class of nonconnectable input parameters that comprise the
block user interface which can be manipulated through SET calls. An
example is an alarm deadband.


5.9 Role Play
Each trainee should introduce one of the main applications:
   8. System Management.
   9. Historian
   10.Graphics Applications.
   11.Control Configurator.
   12.Operator Journal
   13.Alarm System.
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Dcscourse doc

  • 2. Distributed Control System and Programmable Logic Control Course Aim The aim of this training course is to build up the procedural and declarative knowledge required to be recognized by projects engineer that don not have past background of DCS or PLC. This will help them to supervise projects dealing with control systems with a strong background. In this course, the training cycle is divided in five steps that necessitate the cooperation between the instructor and the trainees. These steps are shown in figure below, they are summarized as follows: 1. Define the knowledge and skills required to be developed. 2. Define the elements of each knowledge or skill. 3. Formulate a verbal phrase for the learning objective of each element. 4. Choose an adequate instructional activity to present each element. 5. Set up an indicator to measure the outcomes of the course and modify the training skills to adapt the vocational needs. Define Knowledge Determine & Skills Elements Measure Learning & Correction Objectives Instruction Activity Training Cycle. 1
  • 3. Knowledge and Elements  Illustrate DCS & PLC Benefits, Usage and History.  Overview of control system history.  Control system benefits and usage.  Types of control  Develop Knowledge of DCS Components (Hardware & Software).  Infrastructure [Communication Bus, Interfaces, Controllers, Gateways, RTU, Others].  Hardware and technologies.  Software [Configuration, Graphics, Alarming, Trending, System Management, Others].  Extend Knowledge of DCS installation and Maintenance.  Site Installation, Commissioning and Startup.  Diagnostics, Spares, Tools and Power Distribution.  Maintenance [Backup, Replacements and System Installation].  Develop Knowledge of PLC Components.  PLC fundamentals.  PLC Logic.
  • 4. Table of Contents Section I Chapter 1 Introduction Chapter 2 Regulatory Control Section II Chapter 3 DCS Infrastructure Chapter 4 DCS Hardware Chapter 5 DCS Software Section III Chapter 6 Installation Chapter 7 Maintenance Chapter 8 Power Distribution Section IV Chapter 9 PLC Fundamentals. Chapter 10 Ladder Logic And SFC Appendices A Electrical Relay Diagram And P&ID Symbols B Serial Communication C Networking D Software Engineering
  • 5. Distributed Control System and Programmable Logic Control 4
  • 6. Distributed Control System and Programmable Logic Control Chapter 1 Control Systems 1.1 Automation System Structure Although applications differ widely, there is little difference in the overall architecture of their control systems. Why the control system of a power plant is not sold also for automating a brewery depends largely on small differences (e.g. explosion-proof), on regulations (e.g. Food and Drug Administration) and also tradition, customer relationship. The ANSI/ISA standard 95 defines terminology and good practices Level 4 Business Planning & Logistics Enterprise Resource Plant Production Scheduling Operational Management, etc. Level Manufacturing 3 Operations & Control Dispatching Production, Detailed Product Manufacturing Execution Scheduling, Reliability Assurance,... Level 2,1,0 Batch Continuous Discrete Control & Command Control Control Control 1.1.1 Large Control System Hierarchy • Administration: Production goals, planning • Enterprise: Manages resources, workflow, coordinates activities of different sites, quality supervision, maintenance, distribution and planning. 5
  • 7. • Supervision: Supervision of the site, optimization, on-line operations. Control room, Process Data Base, logging (open loop) • Group (Area): Control of a well-defined part of the plant. closed loop, except for intervention of an operator) o Coordinates individual subgroups o Adjusting set-points and parameters o Commands several units as a whole • Unit (Cell): Control (regulation, monitoring and protection) of a small part of a group (closed loop except for maintenance). o Measure: Sampling, scaling, processing, calibration. o Control: regulation, set-points and parameters o Command: sequencing, protection and interlocking • Field: Sensors & Actors, data acquisition, digitalization, data transmission, no processing except measurement correction and built-in protection. 4 Planning, Statistics, Finances administration 3 Workflow, Resources, Interactions enterprise SCADA supervisi on Supervisory Supervisory 2 And Data Group Control Unit Control 1 Field Sensors T & Actors A V 0 Primary Figure 1.1 Large control system hierarchy
  • 8. 1.1.2 Response Time and Hierarchical Level Planning ERP (Enterprise Level Resource Planning) MES Execution (Manufacturing Level Execution System) SCADA (Supervisory Control Supervisory and Data Acquisition) Level DCS (Distributed Control System) Control Level PLC (Programmable Logic Controller) ms seconds hours days weeks month years Figure 1.2 Response Time And Hierarchical Level 1.2 What is DCS?  A DCS is an integrated set of modules with distributed functions. – Multi-loop controllers (10’s-100’s) that connect to field devices – Supervisory coordinating controllers – Multi-loop operator stations and engineering stations – Servers for system data management – Control network for intercommunication – External connections
  • 9. Supervisory Operator System Stations Remote Users Controller www Server Engineering Station Remote Server Control Network Multi-loop Controller Direct I/O Module Other Industrial Devices Figure 1.3 DCS Hierarchy  A DCS, throughout the whole system, must provide: – Performance: control must be faster than the process. – Determinism: control must always take the same time. – Fault tolerance: redundancy; must fail to a known state. – Security: must have access restrictions/controls. Even though performance, ease of use, and interoperability are key evaluation criteria for any control system software package, the following is intended to provide the manufacturing engineer with a concise list of control system software evaluation criteria. 1. INTEROPERABILITY. This refers to the interaction of all control system hardware and software components at all levels. 2. INTERCONNECTIVITY. This criterion is concerned with the transmission medium, which is constrained by the network topology and how efficiently the system’s components communicate with each other.
  • 10. 3. DISASTER PROCESSING. This component is defined by the efficiency with which the software provides the operator with system failure information and the ease at which the operator is permitted to bring the system back to maximum operation after system failure. 4. DATABASE. This refers to the software’s ability to maintain the system’s database. 5. PROCESSES/DATA. This criterion is concerned with the variety of processes and data that can be controlled by the SCADA package. 6. DIAGNOSTICS. The SCADA package’s ability to assist in the resolution of system failures is evaluated by this diagnostic utility. 7. SECURITY. This component is concerned with the levels of security provided by the software. 8. MONITORING/CONTROL Monitoring of a given process in real-time and control of that process, within preset parameters, is evaluated by this criteria. 9. ALARM MANAGEMENT/LOGGING. This is the category for detecting, annunciating, managing, and storing alarm conditions. 10. STATISTICAL PROCESS CONTROL. This is the portion of the SCADA package that evaluates the process data. Production and quality is greatly effected by this data. 12. OPERATOR INTERFACE. The graphical user interface (GUI) is evaluated using this criterion.
  • 11. 13. TRENDING. The software’s ability to display trending plots using historical and current data is considered in this category. 14. REPORT GENERATION. The production of logs and reports using current real-time data and data retrieved from historical files is evaluated under this category. Due to the advancements in computer technology and low cost, a personal computer-based distributed control system can be installed for a fraction of the cost required just a few years ago. However, prior to selecting any piece of DCS equipment, first examine the existing equipment, in particular the smart controllers, for network compatibility. Then, examine and select the software to be employed. 1.3 What is PLC? A programmable logic controller, also called a PLC or programmable controller, is a computer-type device used to control equipment in an industrial facility. The kinds of equipment that PLCs can control are as varied as industrial facilities themselves. Conveyor systems, food processing machinery, auto assembly lines…you name it and there’s probably a PLC out there controlling it. In a traditional industrial control system, all control devices are wired directly to each other according to how the system is supposed to operate. In a PLC system, however, the PLC replaces the wiring between the devices. Thus, instead of being wired directly to each other, all equipment is wired to the PLC. Then, the control program inside the PLC provides the “wiring” connection between the devices.
  • 12. The control program is the computer program stored in the PLC’s memory that tells the PLC what’s supposed to be going on in the system. The use of a PLC to provide the wiring connections between system devices is called soft-wiring. Let's say that a push button is supposed to control the operation of a motor. In a traditional control system, the push button would be wired directly to the motor. In a PLC system, however, both the push button and the motor would be wired to the PLC instead. Then, the PLC's control program would complete the electrical circuit between the two, allowing the button to control the motor. Figure 1.4 PLC development A PLC basically consists of two elements: • The central processing unit • The input/output system 1.3.1 The Central Processing Unit The central processing unit (CPU) is the part of a programmable controller that retrieves, decodes, stores, and processes information. It also executes the control program stored in the PLC’s memory. In
  • 13. essence, the CPU is the “brains” of a programmable controller. It functions much the same way the CPU of a regular computer does, except that it uses special instructions and coding to perform its functions. The CPU has three parts: • The processor • The memory system • The power supply The processor is the section of the CPU that codes, decodes, and computes data. The memory system is the section of the CPU that stores both the control program and data from the equipment connected to the PLC. The power supply is the section that provides the PLC with the voltage and current it needs to operate. Figure 1.5 Microprocessor Hardware 1.3.2 The input/output (I/O) system It is the section of a PLC to which all of the field devices are connected. If the CPU can be thought of as the brains of a PLC, then the I/O system can be thought of as the arms and legs. The I/O system is what actually physically carries out the control commands from the program stored in the PLC’s memory.
  • 14. The I/O system consists of two main parts: • The rack The rack is an enclosure with slots in it that is connected to the CPU. • I/O modules I/O modules are devices with connection terminals to which the field devices are wired. Together, the rack and the I/O modules form the interface between the field devices and the PLC. When set up properly, each I/O module is both securely wired to its corresponding field devices and securely installed in a slot in the rack. This creates the physical connection between the field equipment and the PLC. In some small PLCs, the rack and the I/O modules come prepackaged as one unit. Figure 1.6 I/O Racks
  • 15. 1.4 How is a DCS different from a PLC system? DCS PLC Mfr sells a complete system of integrated Mfr sells some components; an SI components. acquires others and engineers the system. Mfr supports the system. Mfr supports the components. On-line repair/ maintenance are the norm. Off-line repair/ maintenance are the norm. System management built-in. System management designed per project. Users expect to evolve/upgrade/expand a System is a one-off project (like a house). system over 10/20/30 years. Upgrades / expansions are new projects. 1.5 Redundancy and Fault Tolerance 1.5.1 Redundancy • Hardware redundancy – add extra hardware for detection or tolerating faults • Software redundancy – add extra software for detection and possibly tolerating faults 1.5.2 Fault Tolerance • Error Detection • Damage Confinement • Error Recovery • Fault Treatment 1.5.2.1 Error Detection • Ideal check – Check should be independent from system – Check fails if system crashes
  • 16. • Acceptable check – Cost – Reasonable check, e.g. monitor rate of change • diagnostics – Performed “by system on system components” – E.g. power-up diagnostics 1.5.2.2 Damage Confinement • Error might propagate and spread • Identify boundaries to state beyond which no information exchange has occurred 1.5.2.3 Error Recovery • Backward recovery – State is restored to an earlier state – Requires checkpoints – Most frequently used – Recovery overhead • Forward recovery – Try to make state error-free – Need accurate assessment of damage – Highly application-dependent 1.5.2.4 Fault Treatment • If transient fault: restart system, goto error-free state • System repair – On-line, no manual intervention, (automatic) – Dynamic system reconfiguration – Spare (hot or cold)
  • 17. 1.5.2.5 Fault Coverage • Measure of system’s ability to perform: – Fault detection – Fault location – Fault containment – (and/or fault recovery) • Note: – Recovery implies that the system as a whole is operational – This does not imply that a “repair” occurred – E.g. duplex system with benign fault can recover to continue operation on one non-faulty processor 1.5.2.6 Hardware Redundancy • Passive (static) – Uses fault masking to hide occurrence of fault – No action from the system is required – E.g. voting • Active (dynamic) – Uses comparison for detection and/or diagnoses – Remove faulty hardware from system => reconfiguration • Hybrid – Combine both approaches – Masking until diagnostic complete – Expensive, but better to achieve higher reliability 1.5.2.7 Passive Hardware Redundancy • N-Modular Redundancy (NMR) – N independent modules replicate the same function
  • 18. • Parallelism – Results are voted on requirements: N >= 3 • TMR (Triple Modular Redundancy) 1.5.2.8 Fault tolerant structures Fault tolerance allows continuing operation in spite of a limited number of independent failures. Fault tolerance relies on work redundancy. 1.5.2.9 Static redundancy: 2 out of 3 • Workby of 3 synchronised and identical units. – All 3 units OK: Correct output. – 2 units OK: Majority output correct. – 2 or 3 units failure: Incorrect output. – Otherwise: Error detection output. Process input sync sync Voter Process output Figure 1.7 (2 out of 3) Redundancy 1.5.2.10 Dynamic Redundancy • Redundancy only activated after an error is detected. – Primary components (non-redundant) – Reserve components (redundancy), standby (cold/hot standby)
  • 19. Input Primary unit Standby unit Switch Output Figure 1.8 Dynamic Redundancy 1.5.2.11 Workby and Standby Workby Hot standby Cold standby sync sync on-line workby on-line standby =? Both computers are doing Standby is no operational Standby is not computing the same calculations Error detection needed. Error detection needed. at the same time Long switchover period Easy switchover in case Comparison for easy with loss of state info. of failure. error detection. Easy repair of reserve unit. No aging of reserve unit. Comparator needed. Non- redundant continuation in case of failure? Figure 1.9 Workby and Standby 1.5.2.12 Workby Fault-Tolerance for Integrity and Persistency input input synchronization synchronization Worker Co E Worker Co E W-orker D W-orker D Matching Matching Output Output comparator commutator disjunctor output output INTEGER PERSISTENT Figure 1.10 Workby Fault-Tolerance for Integrity and Persistency
  • 20. 1.5.2.13 Hybrid Redundancy Mixture of workby (static redundancy) and standby (dynamic redundancy). work- work- work- stand- stand- by by by by by voter Reconfiguration work- work- work- stand- failed (self-purging by by by by redundancy) voter Figure 1.11 Hybrid Redundancy 1.6 Microprocessor Control For simple programming the relay model of the PLC is sufficient. As more complex functions are used the more complex VonNeuman model of the PLC must be used. A computer processes one instruction at a time. Most computers operate this way, although they appear to be doing many things at once. Consider the computer components shown in Figure 1.12. Figure 1.12 Simplified Personal Computer Architecture
  • 21. Input is obtained from the keyboard and mouse, output is sent to the screen, and the disk and memory are used for both input and output for storage. (Note: the directions of these arrows are very important to engineers, always pay attention to indicate where information is flowing.) This figure can be redrawn as in Figure 1.13 to clarify the role of inputs and outputs. Figure 1.13 An Input-Output Oriented Architecture In this figure the data enters the left side through the inputs. (Note: most engineering diagrams have inputs on the left and outputs on the right.) It travels through buffering circuits before it enters the CPU. The CPU outputs data through other circuits. Memory and disks are used for storage of data that is not destined for output. If we look at a personal computer as a controller, it is controlling the user by outputting stimuli on the screen, and inputting responses from the mouse and the keyboard. A PLC is also a computer controlling a process. When fully integrated into an application the analogies become; • Inputs - the keyboard is analogous to a proximity switch input circuits - the serial input chip is like a 24Vdc input card
  • 22. • Computer - the 686 CPU is like a PLC CPU unit • Output circuits - a graphics card is like a triac output card • Outputs - a monitor is like a light • Storage - memory in PLCs is similar to memories in personal computers It is also possible to implement a PLC using a normal Personal Computer, although this is not advisable. In the case of a PLC the inputs and outputs are designed to be more reliable and rugged for harsh production environments. 1.7 Role Play Each trainee should act a role play on the following: 1. Automation system structure. 2. What DCS and PLC and their differences? 3. Redundancy and fault tolerance.
  • 23. Chapter 2 Regulatory Control 2.1 Learning Objectives • Introduce Regulatory Control. • Understanding PID control. • Differentiate between various control loops. 2.2 Introduction Most of the applications of industrial control process used simple loops which regulated flows, temperatures, pressures and levels. Occasionally ratio and cascade control loops could be found. There are many benefits for using regulatory control. One of the most important is simply closer control of the process. Process control is one part of an overall control hierarchy that extends downwards to safety controls and other directly connected process devices, and upward to encompass process optimization and even higher business levels of control such as scheduling, inventory management. Most control engineers would recognize the form of response shown in figure 2.1. Actually the response could be determined by solving a differential equation. It is more important to have a good understanding of the physical response than to be able to predict the solution by solving the differential equation.
  • 24. Figure 2.1 Response of simple dynamic process to step input change Instrumentation, control and process engineers abstract the pictorial form of the process into an iconographic diagram called "Piping and Instrumentation Diagram", i.e. P&ID. Figure 2.2 is an example of the P&ID. Figure 2.2 Control loop representation used on P&IDs. For description and analysis of a control loop, without referring to whether it is implemented with analog or digital hardware, a block diagram as shown in figure 2.3 is beneficial. Figure 2.3 Simplified block diagram representation of process control loop.
  • 25. 2.3 PID Control 2.3.1 Feedback Control The principle of feedback is one of the most intuitive concepts known. An action is taken to correct a less satisfactory situation then the results of the action are evaluated. If the situation is not corrected then further action takes place. Feedback control can be classified by the form of the controller output. One of the simplest forms of output is discrete form, also called on-off or two position control. An example of this is the household thermostat, which activates heating unit if the temperature is below the setting, or deactivates the unit if the temperature is above the setting. Figure 2.4 On-Off Control. The idea of two position control can be extended to multi-position control; an example is commercial air-conditioning refrigeration equipment which is operated by loading and unloading compressor cylinders. The ultimate extension is infinite number of positions which is called modulating control; an example is the process controller output that can drive a valve to any position between 0 and 100 percent, as shown in figure 2.5.
  • 26. Figure 2.5 Flow versus position, infinite position Control. 2.3.2 Modes of Control Feedback controllers use one, two, or three methods to determine the controller output. These methods, called the modes of control, including the following: • Proportional (P) • Integral (I) • Derivative (D) In general these modes can be used singly or in combination. 2.3.2.1 Proportional Mode With a controller containing only the proportional mode, the controller output is proportional to the measurement value only. Neither history of the measurement value nor consideration to the rate of change is utilized. Adjustment, i.e. tuning, of the controller is simple because there is only one adjustment as shown in figure 2.6.
  • 27. Figure 2.6 Relationship between input and output for proportional control. Figure 2.7 illustrates a proportional control system. The rate of fluid flow into the tank represents the load. To be in equilibrium, the outflow must be the same as the inflow. The outflow is achieved by a particular valve position where the fixed mechanism between the float, pivot and link attain. Figure 2.7 Proportional control. 2.3.2.2 Integral Mode An integrator is the ideal device for automating the procedure for adjusting the controller output bias. It is called the automatic reset. 2.3.2.3 Derivative Mode The derivative is used to anticipate the effect of load changes by adding a component to the controller output that is proportional to the rate of change of the measurement. See figure 2.8.
  • 28. Figure 2.8 PID control. 2.3.3 Control Loop Structure For microprocessor control system, control strategy is configured by a series of software function blocks. Just like a set of hardware modules require interconnections to form a complete control system, a set of software function blocks also acquire interconnections, i.e. soft-wiring. Figure 2.9 shows a simple feedback loop with the software portion consists of three function blocks: • An analog input block that causes the analog to digital converter to convert the incoming 4-20mA signal to an analogous value. The value is deposited in a memory register. • A PID control block which obtains the measurement value from the analog input block and compares it with the setpoint then it executes a PID algorithm to calculate the output. • An analog output block that obtains from the PID block the required valve position value. The value is converted by a digital to analog converter to 4-20mA signal.
  • 29. Figure 2.9 Control loop hardware/software structure. 2.3.4 Control Loop Tuning The power of PID control is that by good choice of control parameters the controller can be adjusted to provide the desired behavior on a wide variety of process applications. Determining acceptable values of these parameters is called tuning the controller. A good criterion for acceptable performance is the "quarter cycle decay" shown in figure 2.10. Figure 2.10 quarter cycle decay criterion Most loops are tuned by experimental techniques, i.e. trial and error. Figures 2.11 and 2.12 give a tuning map for adjusting control parameters.
  • 30. Figure 2.11 Gain and Reset effects. Figure 2.12 Derivative effects. 2.4 Control Loop Types 2.4.1 Ratio Control Figure 2.13 shows the P&ID of a process heater in which the fuel flow is measured and multiplied by the required air-to-fuel ratio; this results in the required air flow rate, which is introduced as a setpoint of the feedback controller. The required air-to-fuel ratio is automatically adjusted as the output of the stack O2 controller.
  • 31. Figure 2.13 ratio Control.. 2.4.2 Cascade Control In figure 2.14 the temperature controller cascades a steam flow controller. The temperature controller would react to outlet temperature drop by increasing the setpoint of the steam flow controller, which in turn would increase the signal to the valve. The flow will quickly respond to increased demand from the temperature controller and thus reaching the desired setpoint of the outlet temperature stream. Figure 2.13 Cascade Control. 2.4.3 Feedforward Control With feedforward control, the objective is to drive the controlling device from a measurement of the disturbance that is affecting the process, rather than from the process variable itself. In figure 2.14, the
  • 32. application was analyzed the variation in process inlet temperature was the principle of disturbance. Hence, a feedforward controller is used to drive the fuel flow controller by sensing the inlet temperature. Figure 2.14 Feedforward Control. 2.4.4 Selector (Override) Control There are several ways of using selector switches in control strategies. One way is to select the higher (or lower) of several measurement signals to pass the process variable to a feedback controller. For example, the highest of several process temperatures may be selected automatically to become the controlling temperature as shown in figure 2.15. Figure 2.15 Override Control.
  • 33. 2.4.5 Split Range Control Split range control when one process variable such as plant inlet pressure is used to manage two different output devices such as plant bypass control valve and flow control loop for fractionation area. The 4- 12 mA signal is used to control the flow control loop. If the plant cannot handle all incoming feed, the 12-20 mA signal control the plant bypass valve to direct extra feed to the outside of the plant. 2.5 Role Play The trainees are required to play roles about: 1. Introducing regulatory control. 2. Introducing modes of control. 3. Intruding control loop types.
  • 34. Distributed Control System and Programmable Logic Control 33
  • 35. Distributed Control System and Programmable Logic Control Chapter 3 DCS Infrastructure 3.1 Learning Objectives • Introduce system infrastructure interoperability and interconnectivity. • Illustrate system components of level 2 control. 3.2 Communication Bus Figure 3.1: Communication Bus The communication bus, i.e. the Nodebus, interconnects stations (Control Processors, Application Processors, Application Workstations, and so forth) in the system to form a process management and control node. Depending on application requirements, the node can serve as a single, stand-alone entity, or it can be configured to be part of a more extensive communications network. Operating in conjunction with the Nodebus interface electronics in each station, the Nodebus provides high-speed, redundant, peer-to-peer communications between the stations. The high speed, coupled with the redundancy and peer-to-peer characteristics, provide performance and security superior to that 34
  • 36. Distributed Control System and Programmable Logic Control provided by communication media used in conventional computer-based systems. Station interfaces to the Nodebus are also redundant, further ensuring secure communications between the stations. The Nodebus can be implemented in a basic, non-extended configuration or it can be extended through the use of Nodebus Extenders and Dual Nodebus Interface Extenders. 3.2.1 Nodebus Interface The Nodebus Interface is a module which allows direct connection of a personal workstation (PW), with appropriate Nodebus connector card and software, to the Nodebus figure 3.2. In this configuration, the PW functions as a station on the node. The Nodebus Interface allows connection of a station application workstation hosting an Ethernet configuration to Nodebus. See figure 3.2. Figure 3.2 Nodebus Interface Implementation (Typical) 35
  • 37. Distributed Control System and Programmable Logic Control An Attachment Unit Interface (AUI) cable, connects the PW or an Ethernet hub configuration to the Nodebus via a Nodebus Interface. A coaxial cable (ThinNet) connects an Ethernet daisy chain configuration to the Nodebus via a Nodebus Extender. The Nodebus Interface is non- redundant, and can be used in any of the Nodebus configurations described. 3.2.2 Dual Nodebus Interface The Dual Nodebus Interface (DNBI) is a module which allows direct connection of stations to the appropriate Nodebus. Connection between the DNBI and station is made via an AUI cable. For data transmission security, a separate (RS-423) control cable connects between the station and the DNBI to allow switching between the two redundant Nodebus cables. Switching of the Nodebus cables is controlled by the station, which transmits commands to the DNBI via the control cable. Figure 3.3 shows connection of a station to the Nodebus using a DNBI. Figure 3.3 Local Connection of Station 3.2.3 Dual Nodebus Interface Extender The Dual Nodebus Interface Extender (DNBX) is functionally similar to the DNBI, but provides a greater cabling distance. The 36
  • 38. Distributed Control System and Programmable Logic Control principal transmission medium used is a coaxial Ethernet cable directly connected to the station end by a standard Ethernet transceiver. Figure 3.4 remote connection of a station to the Nodebus using a DNBX. Figure 3.4 Remote Connection of Station 3.3 Control Processor The Control Processor performs regulatory, logic, timing, and sequential control together with connected: • Fieldbus Modules (FBMs) • Fieldbus Cluster I/O Cards (FBCs) It also performs data acquisition (via the Fieldbus Modules), alarm detection and notification, and may optionally serve as an interface for one or more Panel Display Stations. The non-fault-tolerant version of the Control Processor is a single-width processor module. The fault-tolerant version consists of two single-width processor modules. 3.3.1 Enhanced Reliability The Control Processor offers optional fault- tolerance for enhanced reliability. The fault-tolerant control processor configuration consists of two parallel-operating modules with two separate connections to the Nodebus and to the Fieldbus. 37 37
  • 39. Distributed Control System and Programmable Logic Control The two control processor modules, married together as a fault- tolerant pair, are designed to provide continued operation of the unit in the event of virtually any hardware failure occurring within one module of the pair. Both modules receive and process information simultaneously, and the modules themselves detect faults. One of the significant methods of fault detection is comparison of communication messages at the module external interfaces. Upon detection of a fault, self-diagnostics are run by both modules to determine which module is defective. The non-defective module then assumes control without affecting normal system operations. To further ensure reliable communications, the fault-tolerant control processor performs error detection and address verification tests in its Nodebus and Fieldbus interfaces. For enhanced reliability during maintenance operations, the Control Processor is equipped with a recessed reset button. This feature provides for manually forcing a module power off and on (reboot) without removing the module from the enclosure. 3.3.2 Diagnostics The Control Processor uses three types of diagnostic tests to detect and/or isolate faults: • Power-up self-checks • Run-time and watchdog timer checks • Off-line diagnostics Power-up self-checks are self-initiated when power is applied to the control processor. These checks perform sequential tests on the various control processor functional elements. Red and green indicators at 38
  • 40. Distributed Control System and Programmable Logic Control the front of the control processor module reflect the successful (or non- successful) completion of the various phases of the control processor startup sequence. The run-time and watchdog timer checks provide continuous monitoring of control processor functions during normal system operations. The operator is informed of a malfunction by means of printed or displayed system messages. Off-line diagnostics are temporarily loaded into the system for the purpose of performing comprehensive tests and checks on various system stations and devices. Using the off-line diagnostics, a suspected fault in the control processor can be isolated and/or confirmed. 3.4 Engineering Interface The engineering interface, i.e. Application Processor, is microprocessor-based application processor/file server stations. They perform two basic functions: • As application processor (computer) stations, they perform computation intensive functions. • As file server stations, they process file requests from tasks within themselves or from other stations. Bulk storage devices used with the Application Processors include floppy disk drives, hard disk drives, streaming tape drives, and CD-ROMs. The Application Processors operate in concert with other system stations (such as communication processors, workstation processors, and control processors), which provide the necessary means for data input/output and operator interfacing. A smaller system can utilize a single Application Processor, while a larger system can incorporate 39
  • 41. Distributed Control System and Programmable Logic Control several Application Processors, each configured to perform specific functions. Some functions can be performed by individual Application Processors, while others can be shared by two or more Application Processors in the same network. For all models of the Application Processor, applications range from minimal functions, such as the storage of memory images, alarm events, and historical data, to larger-scale applications such as database management and program development. 3.4.1 Application Processor Functions The following sections describe the major functions performed by the Application Processors. 3.4.1.1 System and Network Management Functions The Application Processors perform system management functions, which include collecting system performance statistics, data reconciliation, performing station reloads, providing message broadcasting, handling all station alarms and messages, and maintaining consistent time and date in all system stations. The Application Processor also performs network management functions, which comprise that portion of system management functions which deal with the network. 3.4.1.2 Database Management Database management involves the storage, manipulation, and retrieval of files containing data received and/or produced by the system. The Application Processors utilize the industry-standard Relational Data Base Management System. 40
  • 42. Distributed Control System and Programmable Logic Control 3.4.1.3 File Requests Each Application Processor contains a file manager, which manages all file requests associated with bulk memory attached to the Application Processor. Each Application Processor also supports a remote file system that allows tasks in one station to share files in another. 3.4.1.4 Historical Data The Application Processors can be configured to contain the Historian function, which maintains a history of application messages and continuous and discrete I/O values. These values may represent any parameters such as measurements, setpoints, outputs, and status switches from stations that have been configured to collect data and send it to a Historian. In addition, the Historian computes and stores a history of averages, maximums, minimums, and other derived values. This information is maintained for display, reporting, and access by application programs. An archiving facility saves the data on removable media, where applicable. The Application Processors can be configured to maintain a history of errors, alarm conditions, and selected operator actions. The occurrence of errors, alarms, and events in other stations can be stored (for later review and analysis) by sending a message defining the event to the Historian in one or more Application Processors. 41
  • 43. Distributed Control System and Programmable Logic Control 3.4.1.5 Graphic Display Support The Application Processor supports graphic displays by storing and retrieving display formats, by providing access to objects stored on the Application Processor, and by storing tasks which execute in a workstation processor. Application Processors not only provide storage of information and file management for displays, but also execute programs that perform display and trend service. 3.4.1.6 Production Control Software Production control software represents a large range of packages that require varied Application Processor resources. The following is a list of packages provided: • DBMS • Historian • Spreadsheet • Physical Properties Library • Mathematics Library • BATCH The operation and performance of the production control software are determined by the particular Application Processor configuration. 3.4.1.7 Configuration Configuration refers to the process of entering or selecting parameters to define what a software package does, or to define the environment for a software package. The Application Processors support configuration functions by providing bulk storage for configuration parameters and by executing some of the configuration processes. 42
  • 44. Distributed Control System and Programmable Logic Control 3.4.1.8 Application Development Facilities Application development tools are provided to build programs for all system stations. These include tools to document, enter, translate, link, test, and maintain programs written in several programming languages. The Application Processor supports program development for all stations (workstation processors, control processors, and so forth). Assembly language, FORTRAN, and C programs can be written on the Application Processor using standard operating system tools. An optional package is available including text editors, debuggers, linkers, revision control, and compilers, plus execution statistics functions. 3.4.1.9 User Application Program Execution The Application Processors also execute user application programs. These may be application packages such as special optimizations, test data collections, special data reductions, or other packages that you may have already developed. The allocation of resources reserved for user application varies with each Application Processor. 3.4.2 Diagnostics The Application Processors utilize three types of diagnostic tests to detect and/or isolate faults: • Power-up self-checks • Run-time and watchdog timer checks • Off-line diagnostics Power-up self-checks are initiated when power is applied to the Application Processor. These checks perform sequential tests on the 43
  • 45. Distributed Control System and Programmable Logic Control various Application Processor functional elements. Any malfunction detected during the power-up self-checks is reported by means of messages printed or displayed on a directly connected printer or terminal. The run-time and watchdog timer checks provide continuous monitoring of Application Processor functions during normal system operations. For any processor model, you are informed of a malfunction by means of printed or displayed system messages. Off-line diagnostics are temporarily loaded into the system for the purpose of performing comprehensive tests and checks on various system stations and devices. Using the off-line diagnostics, a suspected fault in the Application Processor can be isolated and/or confirmed. 3.4.3 Workstation Components The workstation components provide user interface to all System CRT display functions. A selection of workstation components is available for command and data entry, along with CRT pointer manipulation and control. These components interact with software resident in versions of the system Workstation Processors (WPs) and Application Workstation Processors (AWs). Many of these components (displays and keyboards) are "common" and allow interchangeability and simplicity in mixed technology configurations. Workstation components include: • Alphanumeric Keyboard • Annunciator and Annunciator/Numeric Keyboards • Workstation Display (with/without Touchscreen) • Mouse • Trackball • Industrial Pointing Device 44
  • 46. Distributed Control System and Programmable Logic Control • Workstation Processor or Application Workstation Processor • Personal Workstation • Modular Industrial Console Selection of the touch screen, mouse, trackball or industrial pointing device is required for picking display objects on the CRT. The touch screen has sufficient resolution for all functions normally associated with a process operator. Only the mouse or trackball provides the picking resolution necessary for engineer-related functions (for example, building graphic displays). The touch screen associated with Workstation Display and the annunciator type keyboards connects to a Graphics Controller Input Output (GCIO) interface unit located beneath the workstation display. The GCIO interfaces to the Workstation Processor and/or Application Workstation that provide secure, high- speed, bidirectional data flow. The alphanumeric keyboard and trackball connect together in a functional grouping via a serial communications link to the processors. Personal Workstations (PW) utilize separate serial communication links for alphanumeric keyboard and mouse/trackball. These buses allow a variety of component connections. Figure 3.5 Table- Workstation Components. 45
  • 47. Distributed Control System and Programmable Logic Control 3.4.3.1 Alphanumeric Keyboard The alphanumeric keyboard is used any time text is entered into the system. It consists of the full set of alphanumeric keys plus punctuation and special symbol keys laid out in the standard format, and a numeric data entry pad (with cursor control). Figure 3.6 Alphanumeric Keyboard 3.4.3.2 Annunciator Keyboard The Annunciator Keyboard Figure 3.7 is an array of LED/switch pairs. It also contains a horn silence switch and a lamp-test switch. Each LED, under control of the processor software, may be ON, OFF, or FLASHING as determined by the process conditions. The LEDs, when used in conjunction with the unit's audible annunciator, form an effective means of calling a user's attention to specific areas of the system. The switch associated with each LED can be used to invoke any pre- configured displays or operator responses.. Figure 3.7 Annunciator Keyboard 3.4.3.3 Workstation Display with/without Touchscreen The workstation display is an analog cathode ray tube (CRT) color monitor supporting ultra-high resolution applications. The monitor is suitable for mounting onto a Modular Industrial Workstation or on a 46
  • 48. Distributed Control System and Programmable Logic Control desktop. The monitor can include a touchscreen optional feature. Figure 3.8 shows the monitor with a tilt and swivel base mounted on the GCIO interface unit. The GCIO interface supports the touchscreen, annunciator and annunciator/ numeric keyboard, and audible horn options. Figure 3.8 Table-Top Workstation Display The optional touch screen is bonded to the front surface of the CRT monitor. The user selects display objects by touching them on the screen. The touch screen senses the action and sends a data signal to the workstation processor's software indicating the position of the selection. 3.4.3.4 Trackball The trackball is a stationary component that contains a rotatable sphere. The trackball can be located on a table top. Rotation of the sphere causes CRT pointer movement analogous to the mouse action. Buttons are also provided for user selections/manipulations. See Figure 3.9 Figure 3.9 Trackball 3.4.3.5 Modular Industrial Console Modular Industrial Consoles provide flexible mounting arrangements of components. They allow users to configure centralized or distributed control centers tailored to the functional requirements of each interaction point in the plant. The modular console furniture 47
  • 49. Distributed Control System and Programmable Logic Control described herein may incorporate a mix of equipment - console displays, input devices, processors, Fieldbus Modules, data storage devices, and so on. Alternately, only display-specific equipment can be incorporated. Modular Industrial Consoles (MICs) are ideal for supporting powerful multiple-screen, real-time display software interactions. This combination allows console resources to be optimally allocated to meet changing day- to-day needs. 3.5 Operator Interface Operating in conjunction with human interface input/output components, the workstation processors serve as a link between the operator and other distributed processor modules. They receive graphic and textual information both stored internally or from application processors and generate signals to display the information on a workstation display. Display formats and data files are available from bulk storage. Live display information (distributed data objects) is available from any control -processor, or from shared system global data. The video information displayed can include free form combinations of text, graphic illustrations, charts, and control displays. The workstation processors display textual information as 80 text characters per line, with four fonts. The processors provide resizable and restackable windows. Displays for all of the workstation processors may also be developed using the system software running in a compatible personal computer. A workstation processor, together with its workstation monitor and input components, can be configured with combinations of peripherals to suit functions and user preferences. 48
  • 50. Distributed Control System and Programmable Logic Control 3.6 Gateways The architecture of the DCS permits it to be connected to other foreign systems using a gateway module for adapting different communication protocols. See figure 3.10. Figure 3.10 Field Automation Subsystem 3.7 Role Play Each trainee should introduce one of the main components: 1. Communication Bus 2. Control Processor. 3. Application Processor 4. Operator Interfaces and Gateways 49
  • 51. Distributed Control System and Programmable Logic Control Chapter 4 DCS Hardware 4.1 Learning Objectives • Define fieldbus communication. • Illustrate system components of level 1 control. • Demonstrate interconnection between different components. • Develop knowledge base of foundation fieldbus technology. 4.2 Fieldbus Modules Fieldbus Modules provide connection of digital I/O, analog I/O, and Intelligent Transmitters to control processors. There are two types of Fieldbus Modules: Main and Expansion. Some main modules can be expanded using an expansion module. A wide range of Fieldbus Modules is available to perform the signal conversion necessary to interface the control processor with field sensors and actuators. 4.3 Fieldbus Interconnection The Control Processor is used in three different configurations, which provide broad flexibility in Fieldbus implementation: • Local Fieldbus (Figure 4.1) - Used only within the enclosure. Fieldbus Modules attach directly to the redundant local bus. 50
  • 52. Distributed Control System and Programmable Logic Control Figure 4.1 Local Fieldbus • Twinaxial (Dual-Conductor Coaxial) Fieldbus Extension (Figure 4.2) - Using twinaxial cable, the Fieldbus can optionally extend outside of the enclosure. Fieldbus Modules attach to the extended bus through Fieldbus isolators. The twinaxial Fieldbus extension may be redundant. Figure 4.2 Twinaxial Fieldbus Extension • Fiber Optic Fieldbus Extension (Figure 4.3) - The fiber optic Fieldbus can optionally extend the distance as well as add application versatility and security. Figure 4.3 Fiber Optic Fieldbus Extension 51
  • 53. Distributed Control System and Programmable Logic Control All three Fieldbus configurations use serial data communication complying with Electronic Industrial Association (EIA) Standard RS-485. 4.4 Cluster I/O Subsystem Interfacing The Control Processor interfaces with the Fieldbus Cluster Input/Output Subsystem that consists of the Fieldbus, a multi-slot chassis configuration of a Fieldbus Processor, analog/digital Fieldbus Cards (FBCs), and power supply and power monitor card. These Cluster I/O subsystems meet the needs of applications where a high number of channels per card are required. Figure 4.4 shows a typical twinaxial Fieldbus configuration. Figure 4.4 Twinaxial Fieldbus Cluster I/O Subsystem Interface Configuration 4.5 Fieldbus Cluster I/O Subsystem The Fieldbus Cluster Input/Output Subsystem provides full support for analog measurement, digital sensing, and analog or discrete control capabilities. The Subsystem integrates with the Control Processor or Personal Workstation via the Fieldbus, and includes a multi-slot chassis configuration made up of a Fieldbus Processor, Analog/Digital Fieldbus Cards (FBC), subsystem main power supply, and power monitor card. 52
  • 54. Distributed Control System and Programmable Logic Control The Fieldbus Cluster I/O Subsystem is configurable, gathering analog measurements, while simultaneously handling analog and digital input and output channels. The Fieldbus Cluster I/O Subsystem is offered in both non-redundant and redundant configurations. Each in a redundant pair is individually addressable on the Fieldbus with a unique logical address. In a redundant configuration, the FBPs provide switchover from the primary FBP to the redundant FBP and back again automatically. The FBCs are suitable in applications where a high number of channels per card are required. They are ideal for non-isolated and isolated input signal gathering and data acquisition systems where high quantities of "points per cluster" areas are desired. The FBCs may be optionally connected as redundant pairs. Various input cards are available with one of the following three levels of isolation: • Non-isolated - Each channel is referenced to ground and the card itself is referenced to ground. • Group-isolated - Electrically separate card-to-card but not channel- to-channel on the same card. • Isolated - Each channel is electrically separated from any other channel, card, group, building, site, etc. 4.6 Fieldbus Processor The Fieldbus Processor (FBP) module provides communication between the Fieldbus Cards (FBCs) and the Control Processor. Optionally available is redundancy for the FBP module. Each FBP module is individually addressable via the Fieldbus. If the primary FBP fails or is taken off-line, the secondary FBP automatically assumes control. It remains in control until the primary FBP returns on-line (figure 4.5). 53
  • 55. Distributed Control System and Programmable Logic Control Figure 4.5 FBP Overview 4.7 Fieldbus Cards The Fieldbus Cards support a variety of analog and digital I/O signals. The FBCs convert electrical I/O signals used by field devices to permit communication with these devices via the Fieldbus. The FBCs can be connected in a redundant configuration via the hardware. The redundant FBCs must be in adjacent slots and they are connected via a hardware adapter at the interface to the field devices. In an FBC redundant configuration, the FBP determines which FBC of the redundant pair is to supply the data to the Control Processor. This is done in the software by a predetermined set of conditions. 4.7.1 Analog FBCS The analog FBCs support analog signal types and control functions equipped with accurate signal conditioning circuitry, the analog cards interface between process sensors and actuators. To input an analog voltage (into DCS) the continuous voltage value must be sampled and then converted to a numerical value by an A/D 54
  • 56. converter. Figure 4.6 shows a continuous voltage changing over time. There are three samples shown on the figure. The process of sampling the data is not instantaneous, so each sample has a start and stop time. The time required to acquire the sample is called the sampling time. A/D converters can only acquire a limited number of samples per second. The time between samples is called the sampling period T, and the inverse of the sampling period is the sampling frequency (also called sampling rate). The sampling time is often much smaller than the sampling period. Figure 4.6 Sampling an analog voltage Analog outputs are much simpler than analog inputs. To set an analog output an integer is converted to a voltage. This process is very fast, and does not experience the timing problems with analog inputs. But, analog outputs are subject to quantization errors. Figure 4.7 gives a summary of the important relationships. These relationships are almost identical to those of the A/D converter. Assume we are using an 8 bit D/A converter that outputs values between 0V and 10V. We have a resolution of 256, where 0 results in an output of 0V and 255 results in 10V. The quantization error will be 20mV. If we want to output a voltage of 6.234V, we would specify an output integer of 159, this would result in an output voltage of 6.235V. The quantization error would be 6.235V- 6.234V=0.001V. The current output from a D/A converter is normally limited to a small value, typically less than 20mA.
  • 57. Figure 4.7 D/A converter 4.7.2 Digital FBCS The digital FBCs consist of 32- and 64-channel types. Inputs can be either voltage monitoring or contact sensing. Contact inputs must convert a variety of logic levels to the 5Vdc logic levels used on the data bus. This can be done with circuits similar to figure 4.8. Basically the circuits condition the input to drive an optocoupler. This electrically isolates the external electrical circuitry from the internal circuitry. Other circuit components are used to guard against excess or reversed voltage polarity. Figure 4.8 Contact input circuitry. Contact outputs must convert the 5Vdc logic levels on the DCS data bus to external voltage levels. This can be done with circuits similar to figure 4.9. Basically the circuits use an optocoupler to switch external circuitry. This electrically isolates the external electrical circuitry from
  • 58. the internal circuitry. Other circuit components are used to guard against excess or reversed voltage polarity. Figure 4.9 Contact output circuitry. 4.8 Other Modules • 0 to 20 mA Input/Output Interface • Pulse Input, 0 to 20 mA Output Interface • Thermocouple/ Millivolt Input Interface • RTD Input Interface • High Power Contact/dc Input/Output Interface 4.9 Foundation Fieldbus Technology FOUNDATION fieldbus is an all-digital, serial, two-way communications system that serves as the base-level network in a plant or factory automation environment. Figure 4.10 Foundation Fieldbus Network
  • 59. Figure 4.11 Historical development of field devices technology. It's ideal for applications using basic and advanced regulatory control, and for much of the discrete control associated with those functions. Two related implementations of FOUNDATION fieldbus have been introduced to meet different needs within the process automation environment. These two implementations use different physical media and communication speeds. • H1 works at 31.25 Kbit/sec and generally connects to field devices. It provides communication and power over standard twisted-pair wiring. H1 is currently the most common implementation and is therefore the focus of these courses. • HSE (High-speed Ethernet) works at 100 Mbit/sec and generally connects input/output subsystems, host systems, linking devices, gateways, and field devices using standard Ethernet cabling. It doesn't currently provide power over the cable, although work is under way to address this. Figure 4.12 Field Device Capacity.
  • 60. Conventional analog and discrete field instruments use point-to- point wiring: one wire pair per device. They're also limited to carrying only one piece of information -- usually a process variable or control output -- over those wires. As a digital bus, FOUNDATION fieldbus doesn't have those limitations. • Multidrop wiring. FOUNDATION fieldbus will support up to 32 devices on a single pair of wires (called a segment) -- more if repeaters are used. In actual practice, considerations such as power, process modularity, and loop execution speed make 4 to 16 devices per H1 segment more typical. That means if you have 1000 devices -- which would require 1000 wire pairs with traditional technology -- you only need 60 to 250 wire pairs with FOUNDATION fieldbus. That's a lot of savings in wiring (and wiring installation). Figure 4.12 Fieldbus wiring diagram.
  • 61. • Multivariable instruments. That same wire pair can handle multiple variables from one field device. For example, one temperature transmitter might communicate inputs from as many as eight sensors -- reducing both wiring and instrument costs. Other benefits of reducing several devices to one can include fewer pipe penetrations and lower engineering costs. • Two-way communication. In addition, the information flow can now be two-way. A valve controller can accept a control output from a host system or other source and send back the actual valve position for more precise control. In an analog world, that would take another pair of wires. • New types of information. Traditional analog and discrete devices have no way to tell you if they're operating correctly, or if the process information they're sending is valid. But FOUNDATION fieldbus devices can tell you if they're operating correctly, and if the information they're sending is good, bad, or uncertain. This eliminates the need for most routine checks -- and helps you detect failure conditions before they cause a major process problem. • Control in the field. FOUNDATION fieldbus also offers the option of executing some or all control algorithms in field devices rather than a central host system. Depending on the application, control in the field may provide lower costs and better performance -- while enabling automatic control to continue even if there's a host-related failure.
  • 62. FOUNDATION fieldbus is covered by standards from three major organizations: • ANSI/ISA 50.02 • IEC 61158 • CENELEC EN50170:1996/A1 The technology is managed by the independent, not-for-profit Fieldbus Foundation, whose 150+ member companies include users as well as all major process automation suppliers around the globe. Some suppliers have even donated fieldbus-related patents to the Fieldbus Foundation to encourage wider use of the technology by all Foundation members. Interoperability simply means that FOUNDATION fieldbus devices and host systems can work together while giving you the full functionality of each component. 4.10 Role Play Each trainee should introduce one of the main components: 5. Fieldbus Module and Interconnection 6. Fieldbus Processor and Clusters. 7. Foundation Fieldbus technology
  • 63. Chapter 5 DCS Software 5.1 Learning objectives • To be familiar with main software components of DCS. • Understand main tasks for each application. 5.2 Standard Application Packages 5.2.1 System Management Features include: • Display of equipment information for the station and its associated input/output devices, buses, and printers. • Capability for change actions directed to the associated equipment. • Processing of station alarm conditions and messages. 5.2.2 Database Management Features include: • Storage, retrieval, and manipulation of system data files. • A run-time license for the embedded use of the Relational Database Management System. • A spreadsheet package. 5.2.3 Historian Features include: • Maintenance of a history of values for process-related measurements that have been configured for retention by the Historian.
  • 64. Maintenance of a history of application messages that have been sent to the Historian. • Maintenance of a history of alarms and error conditions which generate messages for the Historian. • Access to all Historian data by display and report application programs. 5.2.4 View Display Manager Features include: • Presentation of the operating environment. • Setting of the overall operating environment according to the type of user. Process engineers, process operators, and software engineers have access to specialized functions and databases suited to their specific requirements and authorizations. • Dynamic and interactive process graphics. • Display and processing of current process alarms. • Group and default displays for control blocks. • Execution of embedded trending within displays. 5.2.5 Draw Display Builder Features include: • Graphical display configuration for viewing and control of process operation. • Access to graphical object palettes allowing easy inclusion of pumps, tanks, valves, ISA symbols, and similar complex objects. • Ready modification of existing displays using a mouse pointer, menu items, and quick-access toolbars. • Association of process variables with objects in the displays.
  • 65. Dynamic variation of object attributes such as fill level, color, position, size and visibility with changes in the associated process variable. • Inclusion of operator control elements such as pushbuttons and sliders into displays. • A library of faceplates which may be configured by simply specifying the compound and block name of the block to which the faceplate is to be connected. 5.3 Alarm System Figure 5.1 Alarm manger Alarm Manager provides an easy-to-use graphical interface of preconfigured alarm displays for viewing and quickly responding to process alarm conditions. The alarm display windows present alarm messages initiated by the control blocks and related to digital input, state change, absolute analog, deviation, rate of change, device status mismatch, and other alarm conditions. Accessible from any environment, the Alarm Manager Display windows provide:
  • 66. Quick, easy access to the most recent alarm messages via the Most Recent Alarm display or Current Alarm display • Alarm status and value information dynamically updated from the control station • Color-coded priority and status indicators that allow you to quickly focus in on critical alarms • Summary displays for different views of the alarm database based on alarm status • An historical list of alarms • The capability to view subsets of alarms based on specific user- defined criteria • The capability to silence or temporarily mute workstation and annunciator horns. • Secured access to alarming functions dependent on user or system responsibility This set of resizable alarm displays providing a variety of current and historic views of the process alarm database includes: • A multi-page list of all the current alarms • A single page of the most recent, active, unacknowledged alarms with dynamically updating value and status fields • Three summary displays specific to alarm status also with updating values and statuses: o all active, unacknowledged alarms o all unacknowledged alarms that have returned to normal o all active, acknowledged alarms • A list of historized alarms related to the selected historian database • An operations display for silencing horns, temporarily muting horns, changing environments
  • 67. These displays allow you to respond to alarm conditions, filter and analyze specific alarm data, and maintain alarm message files for reporting purposes. The Process or Alarm button in the Display Manager (DM) window indicates the presence of alarms (both acknowledged and unacknowledged) and provides access to Alarm Manager Displays. Initially, the Current Alarm Display (CAD) appears and the other displays are easily accessible from the CAD via its default Displays menu: • Most Recent Alarm display (MRA) • New Alarm display (NEWALM) • Unacknowledged Alarms display (UNACK) • Acknowledged Alarms display (ACKALM) • Alarm History display (AHD) • Operations display (OPR) These easy-to-use displays support the following features: • A pre-configured number of alarms per screen or page • Pre-configured alarm message information and formatting per alarm type • A status area for indication of current Alarm Manager and display status, such as horns muted, match active, display paused, initial call-up time • Buttons for responding to alarm conditions, such as acknowledging or clearing alarms, and for accessing additional alarm information and process displays • Pull-down menus for editing, viewing, and filing functions • A pull-down menu for accessing other displays • Pop-up menus for quick access to commonly used functions
  • 68. A scroll bar and Go To Page option for moving easily through the alarm list Although a preconfigured set of alarm displays is provided, many aspects of the displays and alarm message content are user configurable to accommodate different process control applications and operational needs. See the section on Alarm/Display Manager Configurator. 5.4 Historian The Historian collects, stores, processes, and archives process data from the control system to provide data for trends, Statistical Process Control (SPC) charts, logs, reports, spreadsheets, and application programs. The Historian software is an easy-to-use data collection tool that allows the user to organize and enforce a plant data collection philosophy. The Historian provides extensive data collection and management functions, and data display functions for use by process engineers or operators. Typical historical data are process analog and/or digital variables (points). The Historian can also collect and display application generated messages. You can use the Historian to collect data in support of the following production control functions: • Cost accounting • Equipment performance analysis • Historical trending • Information retrieval • Inventory management • Legal record maintenance • Lost time analysis
  • 69. Maintenance reporting • Material accounting • Process analysis • Production reporting • Quality control The Historian can: • Retrieve variables from process databases or accept data from production control databases maintained by user application programs. • Perform built-in calculations on the collected data. • Store calculated (reduced) data in a real time, relational database. Application software in a plant-wide control system can access the Historian database to obtain historical data for process control, production control, and management information reporting. You can use SPC chart displays of Historian data to monitor process variables on-line via the Statistical Process Control Package (SPCP). You can build displays for trending historical data via the Display Builder and Display Configurator with Trending software. Using the Report Writer, you can generate detailed reports of historical data for management information. Examples of Industrial Software that interface with the Historian are: • Batch Plant Management • Data Validator • Display Manager • Display Configurator with Trending • Object Manager (for process data histories) • Operator Action Journal • Operator Message Interface • Real-Time Data Base Manager
  • 70. Spreadsheet • Statistical Process Control Package • System Monitor • Report Writer 5.5 Draw Figure 5.2 Draw Draw is a display builder and configurator that allow you to create and maintain dynamically updating process displays. Displays can represent the plant, a process area or a detailed portion of the process. You can draw basic objects using Draw's toolbars, menu items and shortcut keys. You assign graphic attributes such as color and line style to the objects, and then configure them to reflect process variable changes or operator actions. Draw includes numerous palettes of objects such as operator buttons, pumps, tanks, pipes, motors, valves and ISA symbols. You can also create your own palettes for storing complex objects and company-standard symbols. Displays can include faceplates, trends and bitmapped images. You can easily edit your displays to reflect changes in the process control scheme or to maximize operating efficiency and security.
  • 71. 5.5.1 Configuration There are two ways of configuring a display object. You can: 1. Choose the Dynamic Update tab to connect one of the object's attributes, such as visibility or fill level, to a process variable or a file. With this type of configuration, changes in an attribute are triggered dynamically by changes in the process variable. No operator intervention is necessary. 2. Choose the Operator Action tab to connect the entire object to an action, such as opening a display or executing a command. An operator triggers the action by selecting the object. An individual object can have both types of connections, although it can have only one operator action. 5.5.2 Operator Actions In a display configured for operator action, an operator can trigger events by selecting an object (typically a button), moving a slider, or typing text or a numeric value. In response to an operator action, variables can be modified, a new display can open or an overlay can appear. While you can configure only one operator action for each display object, you can trigger two or more events with a single operator action by configuring an object with a View display command script. Operator Actions include: • Open Display • Open Overlay • Close Display/Overlay
  • 72. Display Command • Relative Pick • Momentary Contact • Ramp • Connect Variable • Move Horizontal or Vertical • Numeric/Text Entry 5.5.3 Faceplates A faceplate is a dynamic representation of control block parameters. Draw provides a complete library of faceplates, ready to be connected to any control block in the control database. In addition, you can build your own faceplates using the standard Draw drawing tools. To configure a faceplate, you need only define the Compound:block to which the faceplate is connected. Draw automatically determines the proper configuration attributes for the associated Compound:block. 5.5.4 Trends Trend areas represent changing data values from the real-time database and historian database. A data is displayed as a series of plotted points connected by straight lines and scaled according to the high and low limits configured for each trend line. 5.5.5 Group Displays Group displays allow you to group faceplates and trends into unique layouts to meet changing operational needs.
  • 73. 5.6 View Figure 5.3 View View is a window into the system software, providing a user- friendly interface to the total process. You can interact with any or all of the real-time plant, field, and process data available in the system. View provides: • Direct access to dynamic process displays. • Entry into user-configurable operating environments specific to each user - the process engineer, process operator, and software engineer. • Execution of embedded real-time and historical trending. • Service and display of process alarms via the Alarm Manager. • An overview of the compounds and blocks in the control database and access to block default detail displays via Select. • Access to other applications, such as: o Draw software for building and configuring dynamic user graphics. o System Management Displays for monitoring system equipment health. o Integrated Control Configurator for configuring the control database. o Historian for configuring the historization of data and system messages.
  • 74. o Access to the four most recently used displays. Additionally, with View you have: • Flexibility in customizing environments to conform to your site requirements. • Rapid access to View while in other applications. • Screen print utility. • Window sizing options. The multi-window capability of Solaris and Windows NT operating systems allows you to monitor the information on a process control display as well as access other applications without closing any window. 5.6.1 View Window View Window contains the following features: • A top menu bar for accessing displays, configurators, and other applications as specified by the environment. • A display bar of named display buttons or eight "thumbnail" mini- display buttons for directly accessing process displays. • A system bar with System and Process alarm buttons indicating system and process health; a message bar with a dropdown list of the latest messages; display of the current date and time. • A status bar indicating the current display name, current operating environment, Operator Action Journal logging name, printer logging name, Historian name. Using the control window menu, you can: • Resize the View window automatically or manually. • Move the window.
  • 75. 5.6.2 Operating Environments A collection of programs, utilities, and displays related to user tasks is provided for each of the following: process operator, process engineer, and software engineer. These environments, including menu bars, menu content, and Display Bar content, can be modified to conform to your site requirements. You can easily switch from one configured environment to another. To secure environments against unauthorized use, environment passwords can be configured and menu entries disabled based on the environment. 5.7 Operator Action Journal The Operator Action Journal is a record of specific operator actions taken during process control operations. These actions generally consist of manipulating certain Control Processor, and gateway parameters as well as Application Processor, Application Workstation, and Workstation Processor shared variables. Actions of this type are the ramping or direct data entry of point values, toggling points, changing block statuses, acknowledging block alarms, and horn muting. Operator action reporting is limited to operator actions from the Display Manager, View, and Alarm Manager. Also logged are environment change actions, scripts, applics, and invoking other applications such as configuration. When the Operator Action Journal feature is enabled, all operator actions within the Display Manager, View, and the Alarm Manager that change parameters in the process database are logged to a printer and/or to the specified Historian database. These operator actions include toggling points, ramping or direct data entry of new point values,
  • 76. changing block statuses, acknowledging block alarms, and other actions such as horn muting. Information logged as a result of each database change includes: • Name of the Display Manager, FoxView, or Alarm Manager that requested the database change. • Compound:Block.Point for which the change was made. • The "old value" TO "new value" text for non-packed Boolean. • Current mask and data value for packed Boolean/long. Following is an example of an Operator Action Journal Report. Operator Action Journal Report Tue Aug 1 1997 17:04:05 Page 1 08-02-97 07:57:08 GC3E31 SCRIPT /usr/fox/hi/init.cmds 08-02-97 07:57:15 GC3E31 ChgEnv Init_Env ->Init_env 08-02-97 07:58:19 GC3E31 ChgEnv Init+Env ->Proc_Eng_Env 08-02-97 08:00:34 CG3E31 UC01_LEAD :SINE .OUT 16.18 to 46.18 08-02-97 08:00:54 GC3E31 UC01_LEAD :SINE .MA Manual to Auto 08-02-97 08:00:57 GC3E31 UC01_LEAD :SINE .LR Remote to Local 08-02-97 08:01:01 GC3E31 UC01_LEAD :SINE .MA Auto to Manual 5.8 Control Configuration Process control for DCS is based on the concepts of compounds and blocks. A compound is a logical collection of blocks that performs a control strategy. A block is a member of a set of algorithms that performs a certain control task within the compound structure. Figure 7.4 shows the compound/block relationship. The compound provides the basis for the integration of: • Continuous control • Ladder logic • Sequential control.
  • 77. Within this structure, any block in any compound can be connected to any other block in any other compound in the system. The entire compound structure can be viewed through the workstation display. The block contains parameters that have values of the types: Real, Boolean, Packed Boolean, Boolean Long, Integer, or String. Figure 5.4 Compound/Blocks relationship 5.8.1 Compound Functions The compound supports the following functions for the related blocks: • Process alarm priority, alarm inhibiting, and alarm grouping • Sequence status notification (see Sequential Control section) • Phasing for execution load leveling at execution time. 5.8.2 Compound/Block Process Alarming Alarms and status messages are generated by specific alarm blocks and by alarm options in selected blocks. Alarms have five levels of priority, 1-5, (where 1 = highest priority) that enable you to quickly focus on the most important plant alarm conditions. An alarm priority of 0 indicates the absence of any alarm. These are summarized in a single alarm summary parameter for each compound. This parameter contains the priority of the highest current alarm in that compound. To reduce
  • 78. nuisance alarms, alarms can be inhibited at the compound level on a priority level basis. Alarms can also be inhibited at the block level, on either an alarm type basis, or an overall basis. Alarms are initiated by the blocks within the compound. Alarm messages are then sent to groups of stations or applications (for example, Workstations, Historians, Printers) according to configured alarm groups. The UNACK alarm acknowledge output parameter allows the user to propagate alarm acknowledge actions to all blocks in a compound. Stations, applications, and devices corresponding to various alarm destination groups are configured at the compound level or at the station level in the case of station compounds. Group numbers for individual block alarm types are configured at the block level. 5.8.3 Compound/Block Phasing A user-defined phase number can be assigned to each compound using a range of integer values that varies with assigned period. Phasing allows the starting time of one compound/block to lead or lag the starting time of another compound/block, thereby leveling the block processor load. 5.8.4 Compound Attributes The compound has the following attributes: • Name: User-defined name that must be system-unique and no more than 12 characters in length. The name can be any mix of numeric (0 to 9), upper case alphabetic (A to Z), and the underscore (_). • Descriptor: 32-character field for user-defined identification. • On/Off: Parameter that enables or disables the execution of all blocks within the compound, where: 1 = on; 0 = off.
  • 79. 5.8.5 Compound/Block Parameters Compound and block parameters contain values that are of one of the types Real, String, Integer, Short Integer, Long Integer, Boolean, Packed Boolean, Packed Long, or Character. Additionally, parameters are defined as being configurable, and either connectable/settable, not connectable/not settable, or a combination that is dependent upon the compound, block, and state. 5.8.5.1 Configurable Parameters Configurable parameters are those parameters that can be defined through the Integrated Control Configurator. They can be displayable only, or displayable and editable. 5.8.5.2 Connectable Parameters Connectable parameters are those parameters of the user interface in which secured, change-driven connections may be made between network stations, or as local direct connections within the same station. Each connection consists of a connectable source and a connectable sink. Output parameters (all outputs are connectable) are sources, while a connectable input may be a sink or a source, or both. Certain parameters that may be considered functional inputs (such as SPT in the PID blocks, and RATIO in the RATIO block) are settable but not connectable. A connectable parameter has a value record that contains the parameter's value, its status, and its designated value type (Real, Boolean, or Integer).
  • 80. 5.8.5.3 Input Parameters Input parameters are connectable types that are the receivers of data from other connectable parameters via a path connection. If no source path is specified during configuration, then the resident data of the value record is the actual "source" of data. It can be either the initial default or configured value, or a new value through a SET call to the input parameter. If a source path is specified, then the data value is an output parameter of the same or another block, or a shared variable, thereby securing the input. By linking a shared variable to a block input during configuration, the user can establish a long-term secured connection between a remote application program and the block input. 5.8.5.4 Output Parameters All output parameters are connectable data sources that have value records. There are two types: settable and nonsettable. The settability of a settable output is controlled by the secured status of the value record. The secured status is dependent on whether the block's operational mode is in Auto or in Manual. In either Auto or Manual, nonsettable output parameters cannot be written by any other source under any conditions. Settable outputs may be conditionally released by the block algorithm in the Manual mode. In Manual, the block unsecures settable output parameters. They can then be written by other tasks via SET calls. When the block switches to Auto, the block secures and updates its output parameter(s).
  • 81. 5.8.5.5 Nonconnectable Parameters Nonconnectable parameters have no value records and are not linkable. They mainly consist of string-type variables like NAME, or nonsettable parameters that are used in the configurator only, for example, block options. Local algorithm variables are also nonconnectable. Nonconnectable parameters are generally accessible through GET calls. There is also a class of nonconnectable input parameters that comprise the block user interface which can be manipulated through SET calls. An example is an alarm deadband. 5.9 Role Play Each trainee should introduce one of the main applications: 8. System Management. 9. Historian 10.Graphics Applications. 11.Control Configurator. 12.Operator Journal 13.Alarm System.