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 IChapter 1 IntroductionChapter 2 Regulatory Control Section IIChapter 3 DCS InfrastructureChapter 4 DCS HardwareChapter 5 DCS Software Section IIIChapter 6 InstallationChapter 7 MaintenanceChapter 8 Power Distribution Section IVChapter 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
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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 administration3 Workflow, Resources, Interactions enterprise SCADA supervisi on Supervisory Supervisory2 And Data Group Control Unit Control1 Field Sensors T & Actors A V0 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 Level1.2 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 keyevaluation criteria for any control system software package, the followingis intended to provide the manufacturing engineer with a concise list ofcontrol 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 thesoftware provides the operator with system failure information andthe ease at which the operator is permitted to bring the system backto maximum operation after system failure.4. DATABASE.This refers to the software’s ability to maintain the system’sdatabase.5. PROCESSES/DATA.This criterion is concerned with the variety of processes and datathat can be controlled by the SCADA package.6. DIAGNOSTICS.The SCADA package’s ability to assist in the resolution of systemfailures is evaluated by this diagnostic utility.7. SECURITY.This component is concerned with the levels of security providedby the software.8. MONITORING/CONTROLMonitoring of a given process in real-time and control of thatprocess, within preset parameters, is evaluated by this criteria.9. ALARM MANAGEMENT/LOGGING.This is the category for detecting, annunciating, managing, andstoring alarm conditions.10. STATISTICAL PROCESS CONTROL.This is the portion of the SCADA package that evaluates theprocess 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, apersonal computer-based distributed control system can be installed for afraction of the cost required just a few years ago. However, prior toselecting any piece of DCS equipment, first examine the existingequipment, 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 orprogrammable controller, is a computer-type device used to controlequipment in an industrial facility. The kinds of equipment that PLCs cancontrol are as varied as industrial facilities themselves. Conveyorsystems, food processing machinery, auto assembly lines…you name itand there’s probably a PLC out there controlling it. In a traditional industrial control system, all control devices arewired directly to each other according to how the system is supposed tooperate. In a PLC system, however, the PLC replaces the wiring betweenthe devices. Thus, instead of being wired directly to each other, allequipment is wired to the PLC. Then, the control program inside the PLCprovides the “wiring” connection between the devices.
The control program is the computer program stored in the PLC’smemory 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 systemdevices is called soft-wiring. Lets say that a push button is supposed to control the operation ofa motor. In a traditional control system, the push button would be wireddirectly to the motor. In a PLC system, however, both the push button andthe motor would be wired to the PLC instead. Then, the PLCs controlprogram would complete the electrical circuit between the two, allowingthe button to control the motor. Figure 1.4 PLC developmentA PLC basically consists of two elements: • The central processing unit • The input/output system1.3.1 The Central Processing Unit The central processing unit (CPU) is the part of a programmablecontroller that retrieves, decodes, stores, and processes information. Italso executes the control program stored in the PLC’s memory. In
essence, the CPU is the “brains” of a programmable controller. Itfunctions much the same way the CPU of a regular computer does, exceptthat it uses special instructions and coding to perform its functions. TheCPU has three parts: • The processor • The memory system • The power supplyThe processor is the section of the CPU that codes, decodes, andcomputes data. The memory system is the section of the CPU that storesboth the control program and data from the equipment connected to thePLC. The power supply is the section that provides the PLC with thevoltage and current it needs to operate. Figure 1.5 Microprocessor Hardware1.3.2 The input/output (I/O) system It is the section of a PLC to which all of the field devices areconnected. If the CPU can be thought of as the brains of a PLC, then theI/O system can be thought of as the arms and legs. The I/O system is whatactually physically carries out the control commands from the programstored 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 thefield devices and the PLC. When set up properly, each I/O module is bothsecurely wired to its corresponding field devices and securely installed ina slot in the rack. This creates the physical connection between the fieldequipment and the PLC. In some small PLCs, the rack and the I/Omodules come prepackaged as one unit. Figure 1.6 I/O Racks
1.4 How is a DCS different from a PLC system? DCS PLCMfr sells a complete system of integrated Mfr sells some components; an SIcomponents. 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 Tolerance1.5.1 Redundancy • Hardware redundancy – add extra hardware for detection or tolerating faults • Software redundancy – add extra software for detection and possibly tolerating faults1.5.2 Fault Tolerance • Error Detection • Damage Confinement • Error Recovery • Fault Treatment126.96.36.199 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 diagnostics188.8.131.52 Damage Confinement • Error might propagate and spread • Identify boundaries to state beyond which no information exchange has occurred184.108.40.206 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-dependent220.127.116.11 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)
18.104.22.168 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 processor22.214.171.124 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 reliability126.96.36.199 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)188.8.131.52 Fault tolerant structures Fault tolerance allows continuing operation in spite of a limitednumber of independent failures. Fault tolerance relies on workredundancy.184.108.40.206 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) Redundancy220.127.116.11 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 Redundancy18.104.22.168 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 Standby22.214.171.124 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
126.96.36.199 Hybrid RedundancyMixture 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 Redundancy1.6 Microprocessor Control For simple programming the relay model of the PLC is sufficient.As more complex functions are used the more complex VonNeumanmodel of the PLC must be used. A computer processes one instruction ata time. Most computers operate this way, although they appear to bedoing many things at once. Consider the computer components shown inFigure 1.12. Figure 1.12 Simplified Personal Computer Architecture
Input is obtained from the keyboard and mouse, output is sent to thescreen, and the disk and memory are used for both input and output forstorage. (Note: the directions of these arrows are very important toengineers, always pay attention to indicate where information is flowing.)This figure can be redrawn as in Figure 1.13 to clarify the role of inputsand 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 theright.) It travels through buffering circuits before it enters the CPU. TheCPU outputs data through other circuits. Memory and disks are used forstorage of data that is not destined for output. If we look at a personalcomputer as a controller, it is controlling the user by outputting stimuli onthe screen, and inputting responses from the mouse and the keyboard. A PLC is also a computer controlling a process. When fullyintegrated 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 computersIt 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 outputsare designed to be more reliable and rugged for harsh productionenvironments.1.7 Role PlayEach 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 Control2.1 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 simpleloops which regulated flows, temperatures, pressures and levels.Occasionally ratio and cascade control loops could be found. There aremany benefits for using regulatory control. One of the most important issimply closer control of the process. Process control is one part of anoverall control hierarchy that extends downwards to safety controls andother directly connected process devices, and upward to encompassprocess optimization and even higher business levels of control such asscheduling, inventory management. Most control engineers would recognize the form of responseshown in figure 2.1. Actually the response could be determined bysolving a differential equation. It is more important to have a goodunderstanding of the physical response than to be able to predict thesolution by solving the differential equation.
Figure 2.1 Response of simple dynamic process to step input change Instrumentation, control and process engineers abstract the pictorialform of the process into an iconographic diagram called "Piping andInstrumentation Diagram", i.e. P&ID. Figure 2.2 is an example of theP&ID. Figure 2.2 Control loop representation used on P&IDs. For description and analysis of a control loop, without referring towhether it is implemented with analog or digital hardware, a blockdiagram as shown in figure 2.3 is beneficial. Figure 2.3 Simplified block diagram representation of process control loop.
2.3 PID Control2.3.1 Feedback Control The principle of feedback is one of the most intuitive conceptsknown. An action is taken to correct a less satisfactory situation then theresults of the action are evaluated. If the situation is not corrected thenfurther action takes place. Feedback control can be classified by the formof the controller output. One of the simplest forms of output is discreteform, also called on-off or two position control. An example of this is thehousehold thermostat, which activates heating unit if the temperature isbelow the setting, or deactivates the unit if the temperature is above thesetting. Figure 2.4 On-Off Control. The idea of two position control can be extended to multi-positioncontrol; an example is commercial air-conditioning refrigerationequipment which is operated by loading and unloading compressorcylinders. The ultimate extension is infinite number of positions which iscalled modulating control; an example is the process controller outputthat can drive a valve to any position between 0 and 100 percent, asshown 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 determinethe 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.188.8.131.52 Proportional Mode With a controller containing only the proportional mode, thecontroller output is proportional to the measurement value only. Neitherhistory of the measurement value nor consideration to the rate of changeis utilized. Adjustment, i.e. tuning, of the controller is simple becausethere 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 offluid flow into the tank represents the load. To be in equilibrium, theoutflow must be the same as the inflow. The outflow is achieved by aparticular valve position where the fixed mechanism between the float,pivot and link attain. Figure 2.7 Proportional control.184.108.40.206 Integral Mode An integrator is the ideal device for automating the procedure foradjusting the controller output bias. It is called the automatic reset.220.127.116.11 Derivative Mode The derivative is used to anticipate the effect of load changes byadding a component to the controller output that is proportional to the rateof 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 configuredby a series of software function blocks. Just like a set of hardwaremodules require interconnections to form a complete control system, a setof software function blocks also acquire interconnections, i.e. soft-wiring.Figure 2.9 shows a simple feedback loop with the software portionconsists 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 controlparameters the controller can be adjusted to provide the desired behavioron a wide variety of process applications. Determining acceptable valuesof these parameters is called tuning the controller. A good criterion foracceptable performance is the "quarter cycle decay" shown in figure 2.10. Figure 2.10 quarter cycle decay criterionMost 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 Types2.4.1 Ratio Control Figure 2.13 shows the P&ID of a process heater in which the fuelflow is measured and multiplied by the required air-to-fuel ratio; thisresults in the required air flow rate, which is introduced as a setpoint ofthe feedback controller. The required air-to-fuel ratio is automaticallyadjusted 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 flowcontroller. The temperature controller would react to outlet temperaturedrop by increasing the setpoint of the steam flow controller, which in turnwould increase the signal to the valve. The flow will quickly respond toincreased demand from the temperature controller and thus reaching thedesired 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 controllingdevice from a measurement of the disturbance that is affecting theprocess, rather than from the process variable itself. In figure 2.14, the
application was analyzed the variation in process inlet temperature wasthe principle of disturbance. Hence, a feedforward controller is used todrive 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 controlstrategies. One way is to select the higher (or lower) of severalmeasurement signals to pass the process variable to a feedback controller.For example, the highest of several process temperatures may be selectedautomatically to become the controlling temperature as shown in figure2.15. Figure 2.15 Override Control.
2.4.5 Split Range Control Split range control when one process variable such as plant inletpressure is used to manage two different output devices such as plantbypass 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 cannothandle all incoming feed, the 12-20 mA signal control the plant bypassvalve to direct extra feed to the outside of the plant.2.5 Role PlayThe trainees are required to play roles about: 1. Introducing regulatory control. 2. Introducing modes of control. 3. Intruding control loop types.
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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. 18.104.22.168 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. 22.214.171.124 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 126.96.36.199 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. 188.8.131.52 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 184.108.40.206 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. 220.127.116.11 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. 18.104.22.168 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 22.214.171.124 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. 126.96.36.199 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 188.8.131.52 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 184.108.40.206 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 units audible annunciator, form an effective means of calling a users 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 220.127.116.11 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 processors software indicating the position of the selection. 18.104.22.168 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 22.214.171.124 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 thedata is not instantaneous, so each sample has a start and stop time. Thetime required to acquire the sample is called the sampling time. A/Dconverters can only acquire a limited number of samples per second. Thetime between samples is called the sampling period T, and the inverse ofthe 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 ananalog output an integer is converted to a voltage. This process is veryfast, and does not experience the timing problems with analog inputs.But, analog outputs are subject to quantization errors. Figure 4.7 gives asummary of the important relationships. These relationships are almostidentical to those of the A/D converter. Assume we are using an 8 bit D/Aconverter that outputs values between 0V and 10V. We have a resolutionof 256, where 0 results in an output of 0V and 255 results in 10V. Thequantization error will be 20mV. If we want to output a voltage of6.234V, we would specify an output integer of 159, this would result inan 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 normallylimited to a small value, typically less than 20mA.
Figure 4.7 D/A converter4.7.2 Digital FBCS The digital FBCs consist of 32- and 64-channel types. Inputs canbe either voltage monitoring or contact sensing. Contact inputs must convert a variety of logic levels to the 5Vdclogic levels used on the data bus. This can be done with circuits similar tofigure 4.8. Basically the circuits condition the input to drive anoptocoupler. This electrically isolates the external electrical circuitry fromthe internal circuitry. Other circuit components are used to guard againstexcess or reversed voltage polarity. Figure 4.8 Contact input circuitry. Contact outputs must convert the 5Vdc logic levels on the DCSdata bus to external voltage levels. This can be done with circuits similarto figure 4.9. Basically the circuits use an optocoupler to switch externalcircuitry. This electrically isolates the external electrical circuitry from
the internal circuitry. Other circuit components are used to guard againstexcess 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 Interface4.9 Foundation Fieldbus Technology FOUNDATION fieldbus is an all-digital, serial, two-waycommunications system that serves as the base-level network in a plant orfactory automation environment. Figure 4.10 Foundation Fieldbus Network
Figure 4.11 Historical development of field devices technology. Its ideal for applications using basic and advanced regulatorycontrol, and for much of the discrete control associated with thosefunctions. Two related implementations of FOUNDATION fieldbus havebeen introduced to meet different needs within the process automationenvironment. These two implementations use different physical mediaand 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 doesnt 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. Theyre also limited to carryingonly one piece of information -- usually a process variable or controloutput -- over those wires. As a digital bus, FOUNDATION fieldbusdoesnt 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 wirepairs with traditional technology -- you only need 60 to 250 wire pairswith FOUNDATION fieldbus. Thats a lot of savings in wiring (andwiring 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 pipepenetrations 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 theyre operating correctly, or if the process information theyre sending is valid.But FOUNDATION fieldbus devices can tell you if theyre operatingcorrectly, and if the information theyre sending is good, bad, oruncertain. This eliminates the need for most routine checks -- and helpsyou 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 theres a host-related failure.
FOUNDATION fieldbus is covered by standards from three majororganizations: • ANSI/ISA 50.02 • IEC 61158 • CENELEC EN50170:1996/A1 The technology is managed by the independent, not-for-profitFieldbus Foundation, whose 150+ member companies include users aswell as all major process automation suppliers around the globe.Some suppliers have even donated fieldbus-related patents to the FieldbusFoundation to encourage wider use of the technology by all Foundationmembers. Interoperability simply means that FOUNDATION fieldbusdevices and host systems can work together while giving you the fullfunctionality of each component.4.10 Role PlayEach 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 Software5.1 Learning objectives• To be familiar with main software components of DCS.• Understand main tasks for each application.5.2 Standard Application Packages5.2.1 System ManagementFeatures 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 ManagementFeatures 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 HistorianFeatures 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 ManagerFeatures 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 BuilderFeatures 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 ofpreconfigured alarm displays for viewing and quickly responding toprocess alarm conditions. The alarm display windows present alarmmessages initiated by the control blocks and related to digital input, statechange, absolute analog, deviation, rate of change, device statusmismatch, and other alarm conditions.Accessible from any environment, the Alarm Manager Display windowsprovide:
• 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 responsibilityThis set of resizable alarm displays providing a variety of current andhistoric 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 andanalyze specific alarm data, and maintain alarm message files forreporting purposes. The Process or Alarm button in the Display Manager (DM) windowindicates the presence of alarms (both acknowledged andunacknowledged) and provides access to Alarm Manager Displays.Initially, the Current Alarm Display (CAD) appears and the otherdisplays are easily accessible from the CAD via its default Displaysmenu: • 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 listAlthough a preconfigured set of alarm displays is provided, many aspectsof the displays and alarm message content are user configurable toaccommodate different process control applications and operationalneeds. See the section on Alarm/Display Manager Configurator.5.4 Historian The Historian collects, stores, processes, and archives process datafrom the control system to provide data for trends, Statistical ProcessControl (SPC) charts, logs, reports, spreadsheets, and applicationprograms. The Historian software is an easy-to-use data collection toolthat allows the user to organize and enforce a plant data collectionphilosophy. The Historian provides extensive data collection andmanagement functions, and data display functions for use by processengineers or operators. Typical historical data are process analog and/or digital variables(points). The Historian can also collect and display application generatedmessages. You can use the Historian to collect data in support of thefollowing 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 controlThe 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 theHistorian database to obtain historical data for process control, productioncontrol, and management information reporting.You can use SPC chart displays of Historian data to monitor processvariables on-line via the Statistical Process Control Package (SPCP).You can build displays for trending historical data via the Display Builderand Display Configurator with Trending software.Using the Report Writer, you can generate detailed reports of historicaldata 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 Writer5.5 Draw Figure 5.2 Draw Draw is a display builder and configurator that allow you to createand maintain dynamically updating process displays. Displays canrepresent the plant, a process area or a detailed portion of the process.You can draw basic objects using Draws toolbars, menu items andshortcut keys. You assign graphic attributes such as color and line style tothe objects, and then configure them to reflect process variable changes oroperator actions. Draw includes numerous palettes of objects such asoperator buttons, pumps, tanks, pipes, motors, valves and ISA symbols.You can also create your own palettes for storing complex objects andcompany-standard symbols. Displays can include faceplates, trends andbitmapped images. You can easily edit your displays to reflect changes inthe process control scheme or to maximize operating efficiency andsecurity.
5.5.1 ConfigurationThere are two ways of configuring a display object. You can: 1. Choose the Dynamic Update tab to connect one of the objects 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 canhave only one operator action.5.5.2 Operator Actions In a display configured for operator action, an operator can triggerevents by selecting an object (typically a button), moving a slider, ortyping text or a numeric value. In response to an operator action,variables can be modified, a new display can open or an overlay canappear. While you can configure only one operator action for each displayobject, you can trigger two or more events with a single operator actionby 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 Entry5.5.3 Faceplates A faceplate is a dynamic representation of control blockparameters. Draw provides a complete library of faceplates, ready to beconnected to any control block in the control database. In addition, youcan build your own faceplates using the standard Draw drawing tools.To configure a faceplate, you need only define the Compound:block towhich the faceplate is connected. Draw automatically determines theproper configuration attributes for the associated Compound:block.5.5.4 Trends Trend areas represent changing data values from the real-timedatabase and historian database. A data is displayed as a series of plottedpoints connected by straight lines and scaled according to the high andlow limits configured for each trend line.5.5.5 Group Displays Group displays allow you to group faceplates and trends intounique 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 ofthe 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 operatingsystems allows you to monitor the information on a process controldisplay as well as access other applications without closing any window.5.6.1 View WindowView 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 usertasks is provided for each of the following: process operator, processengineer, and software engineer. These environments, including menubars, menu content, and Display Bar content, can be modified to conformto your site requirements. You can easily switch from one configuredenvironment to another. To secure environments against unauthorizeduse, environment passwords can be configured and menu entries disabledbased on the environment.5.7 Operator Action Journal The Operator Action Journal is a record of specific operator actionstaken during process control operations. These actions generally consistof manipulating certain Control Processor, and gateway parameters aswell as Application Processor, Application Workstation, and WorkstationProcessor shared variables. Actions of this type are the ramping or directdata entry of point values, toggling points, changing block statuses,acknowledging block alarms, and horn muting. Operator action reportingis limited to operator actions from the Display Manager, View, andAlarm 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 operatoractions within the Display Manager, View, and the Alarm Manager thatchange parameters in the process database are logged to a printer and/orto the specified Historian database. These operator actions includetoggling points, ramping or direct data entry of new point values,
changing block statuses, acknowledging block alarms, and other actionssuch 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 ReportTue Aug 1 1997 17:04:05 Page 108-02-97 07:57:08 GC3E31 SCRIPT /usr/fox/hi/init.cmds08-02-97 07:57:15 GC3E31 ChgEnv Init_Env ->Init_env08-02-97 07:58:19 GC3E31 ChgEnv Init+Env ->Proc_Eng_Env08-02-97 08:00:34 CG3E31 UC01_LEAD :SINE .OUT 16.18 to 46.1808-02-97 08:00:54 GC3E31 UC01_LEAD :SINE .MA Manual to Auto08-02-97 08:00:57 GC3E31 UC01_LEAD :SINE .LR Remote to Local08-02-97 08:01:01 GC3E31 UC01_LEAD :SINE .MA Auto to Manual5.8 Control Configuration Process control for DCS is based on the concepts of compoundsand blocks. A compound is a logical collection of blocks that performs acontrol strategy. A block is a member of a set of algorithms that performsa certain control task within the compound structure. Figure 7.4 showsthe 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 toany other block in any other compound in the system. The entirecompound 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 relationship5.8.1 Compound FunctionsThe 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 blocksand by alarm options in selected blocks. Alarms have five levels ofpriority, 1-5, (where 1 = highest priority) that enable you to quickly focuson the most important plant alarm conditions. An alarm priority of 0indicates the absence of any alarm. These are summarized in a singlealarm summary parameter for each compound. This parameter containsthe priority of the highest current alarm in that compound. To reduce
nuisance alarms, alarms can be inhibited at the compound level on apriority level basis. Alarms can also be inhibited at the block level, oneither an alarm type basis, or an overall basis. Alarms are initiated by the blocks within the compound. Alarmmessages 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 topropagate alarm acknowledge actions to all blocks in a compound.Stations, applications, and devices corresponding to various alarmdestination groups are configured at the compound level or at the stationlevel in the case of station compounds.Group numbers for individual block alarm types are configured at theblock level.5.8.3 Compound/Block Phasing A user-defined phase number can be assigned to each compoundusing a range of integer values that varies with assigned period. Phasingallows the starting time of one compound/block to lead or lag the startingtime of another compound/block, thereby leveling the block processorload.5.8.4 Compound AttributesThe 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.