Chapter 1 part 1

BEE 4363 DISTRIBUTED CONTROL
SYSTEMS
DISTRIBUTED CONTROL SYSTEMS
BEE4363
Maziyah Mat Noh
Room: E10-C28

SYSTEMS
CHAPTER ONE
INTRODUCTIONTO DCS

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LEARNING OUTCOMES
• Describe the concept of Distributed Control
System
• Explain the functions of every layer in ISO/OSI
reference model.
• Explain the networking concept
• Identify the advantages and disadvantages of
networking
• Select the suitable network based on networks
selection criteria

SYSTEMS
INTRODUCTIONTO DCS
1.1 Background
1.2 ISO/OSI Reference Model
1.3 Networking and its benefits
1.4 Basic networking concept
1.5 Network selection criteria

SYSTEMS
CHAPTER 1 - PART 1
1.1 Background
1.2 ISO/OSI Reference Model

SYSTEMS
1.1 BACKGROUND
• Distributed control systems (DCSs) are
dedicated systems used to control manufacturing
processes that are continuous or batch-oriented,
such as oil refining, petrochemicals, central
station power generation, fertilizers,
pharmaceuticals, food and beverage
manufacturing, cement production, steelmaking,
and papermaking.

SYSTEMS
1.1 BACKGROUND
• Prior 1960
o Early minicomputers were used in the control of industrial
processes since the beginning of the 1960s.
Example: IBM 1800, was an early computer that had
input/output hardware to gather process signals in a plant for
conversion from field contact levels (for digital points) and
analogue signals to the digital domain.
o Control hardware comprised pneumatic or electronic
analog devices
o Equipment which worked with continuous. E.g: relay
o Limited usage – anything more than a few additions or
multiplications of signals involved complex circuit – expensive,
potentially inaccurate, subject to calibration drift which made
them unreliable.

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• Early 70s
o Why the idea of DCS came about
o Increased availability of
microcomputers
o Abundance of microprocessors in the
world of process control.
o DCS was introduced in 1975 by
Honeywell (TDC2000) and Yokogawa
(CENTUM)

SYSTEMS
• Early 70s
o Originally introduced for the larger plants – e.g
petroleum refining and petrochemical industries
o To distribute the computing power geographically
around the plant.
o Before - use a single computer (or a pair of
computers when redundancy was used to improve
reliability).
o Early minicomputers were used in the control of
industrial processes since the beginning of the 1960s.
o Reduced hardware costs, increased reliability & speed
of computers.

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Objective of DCS
• Safe operation of plant
• Lowest cost of generation
• Longest equipment life
• Minimum environmental effect
• Maximum efficiency
• Energy conversation

BEE 4363 DISTRIBUTED
CONTROL SYSTEMS
What is DCS??
Distributed Control System (DCS) is one
composed of several autonomous devices which
operate in achieving an overall goal.The
intelligent devices are capable of supporting
processes which coordinate their activities of
exchange of information by means of a
communication network
.

CONTROL SYSTEMS
A distributed control system (DCS) refers to a
control system usually of a manufacturing system,
process or any kind of dynamic system, in which the
controller elements are not central in
location (like the brain) but are distributed
throughout the system with each component
sub-system controlled by one or more controllers.
The entire system of controllers is connected by
networks for communication and monitoring.

CONTROL SYSTEMS
A distributed control system (DCS) is a control
system for a process or plant, wherein control
elements are distributed throughout the system.
This is in contrast to non-distributed systems, which
use a single controller at a central location.

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DCS vs Conventional Controller

Other
devices
Input/Output
devices
Motor starter
Drive
Motor controller
Bar code
scanner
Sensor
Pushbutton
cluster
Controller
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A Conventional production cell control system

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Features of Conventional control system
• Centralised control system.
• All components are connected to a central controller.
• Central controller responsible for coordinating the
operation of the production cell.
• Different control components will be mounted in different
geographical locations.
• Numerous wires must be run around the production/process
cell.
• Cell complexity increases so does the wiring complexity.
• Difficult for troubleshooting due to complexity of the wiring.
• Greater cost.

Drive
Motor
controller
Bar code
scanner
Sensor Pushbutton
cluster
Controller
Other
devices
Input/Output
devices
Motor
starter
Network
Device
Configuration
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A typical DCS production cell

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Features of DCS
• Decentralised Control System
• All components are connected to the same
fieldbus, a shared communication medium.
• Enable to develop a low cost microcontroller
with advancement of IT.
• Only a single set of wires needs to be routed
around the cell, often including power cables.
• Less physical connectors are required

SYSTEMS
Features of DCS
• Reduce overall cost.
• Easy to install new devices.
• Better diagnostics and fault finding mechanism
can be implemented
• Greater flexibility and the ability for controllers
to operate over larger geographical areas.
• Only one basic standard interface may be
required.

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Basic configuration of a DCS
DCS consists minimum of the following components.
• Field Control station (FCS)
– It consists of input/output modules, CPU and communication
bus.
• Operator station:
– It is basically human interface machine with monitor, the
operator man can view the process in the plant and check if
any alarm is presents and he can change any setting, print
reports, etc.
• Engineering station:
– It is used to configure all input & output and drawing and any
things required to be monitored on Operator station
monitor.
• Communication network

SYSTEMS
Basic configuration of a DCS system
Process
Plant
monitoring
Communication
network

SYSTEMS
Basic configuration of a DCS system
Sensors, Transmitters, control
valves and field of network
Batch controllers, continuous
controllers, Discrete Controller
and process monitoring
Supervisory controllers and
primary operators interface
The production control,
optimizing control, process
history and windows domains
-Site business planning
-Site accounting

SYSTEMS
ADVANTAGES OF DCS
 High reliability – reduce human error
 Improved response time
– allowing easier identification of bottle-necks
 Improve operator interface to plant
– better production scheduling, making
maximum use of the production facilities
 Improve accessibility of plant data to
engineering & management personnel
- Faster identification of faults in both product
and processing machinery

SYSTEMS
ADVANTAGES OF DCS
• Greater flexibility in response to changes in
design, customer requirements and competition.
• Shorter ‘lead times’ in designing product.
• Historical storage & retrieval system
• Ability to identify deterioration in equipment
before actual failure,
• Reducing production ‘down time’.

SYSTEMS
1.2 ISO/OSI REFERENCE MODEL

SYSTEMS
THE NEED FOR STANDARDS
• Over the past couple of decades many of the networks that
were built used different hardware and software
implementations, as a result they were incompatible and it
became difficult for networks using different specifications to
communicate with each other.
• To address the problem of networks being incompatible and
unable to communicate with each other, the International
Organisation for Standardisation (ISO) researched various
network schemes.
• The ISO recognised there was a need to create a NETWORK
MODEL that would help vendors create interoperable
network implementations.

SYSTEMS
ISO - ORGANISATION FOR
STANDARDISATION
• The International Organisation for Standardisation (ISO) is
an International standards organisation responsible for a
wide range of standards, including many that are relevant to
networking.
• In 1984 in order to aid network interconnection without
necessarily requiring complete redesign, the Open
Systems Interconnection (OSI) reference model
was approved as an international standard for
communications architecture.

SYSTEMS
• Open Systems Interconnection
(OSI) is a set of internationally
recognised, non-proprietary
standards for networking and for
operating system involved in networking
functions.
OSI REFERENCE MODEL

SYSTEMS
OSI REFERENCE MODEL
• Provides useful way to describe and think about
networking (how information or data makes its
way from application programmes through a
network medium (such as wire) to another
application programme located on another
network.
• Breaks networking down into series of
related tasks
• Each aspect is conceptualised as a layer
• Each task can be handled separately

SYSTEMS
All
People
Seem
To
Need
Data
Processing
Seven Layers of OSI Reference Model

SYSTEMS
ISO/OSI Message Construction
Application
Layer 7
Presentation
Layer 6
Session
Layer 5
Transport
Layer 4
Network
Layer 3
Data Link
Layer 2
Physical
Layer 1
Application
Layer 7
Presentation
Layer 6
Session
Layer 5
Transport
Layer 4
Network
Layer 3
Data Link
Layer 2
Physical
Layer 1
Provides service that directly support
the application
Transforms data to a negotiated
standard form
Syncronises interactions between
Applications
Provides reliable end-to-end system
data transfer
Routes messages over multiple
intermediate subnetworks
Construct data frames and detects
errors in them
Electrically encodes data and
transfers data over physical link
Physical Medium
Examples of Layer Functions
Application A Processes Application B Processes

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Tasks involved in sending letter

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OSI Reference Model Structure
 Each layer of OSI model communicates and
interacts with layers immediately above and
below it
 Each layers is implemented independently
 Each layer responsible for different aspect of
data exchange / responsible for a specific
subtask

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Relationships Among OSI Layers

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Advantages of Layering
• Helps simplify networking protocols.
• Protocols can be designed for interoperability
– Software that uses Layer n can talk to software
running on another machine that supports Layer
n, regardless details of the lower layers.
Example: a network layer protocol can work with an
Ethernet network and a token ring network.

SYSTEMS
Application Layer - Layer 7
• Enables the user, whether human or software,
to access the network
• Provide user interfaces for applications to
access variety of networked services such as:
– File transfer
– E-mail message handling
– Database query processing

SYSTEMS
The layer responsibilities include:
• Provide complete addresses for ‘named’ remote application
processes.
• Control of security
• Check the authenticity and authority of the communications
link end systems.
• Error control and recovery
• In general, provides all services required for the support of
the application process e.g transfer management.
• This layer makes use of services provided by all the lower
layers.
Application Layer - Layer 7

SYSTEMS
Presentation Layer - Layer 6
• The presentation layer ensures that the information
that the application layer of one system sends out is
readable by the application layer of another system.
• If necessary, the presentation layer translates
between multiple data formats by using a common
format.
• Provides encryption and compression of data.
• Examples :- JPEG, MPEG, ASCII, EBCDIC, HTML.

SYSTEMS
Session Layer - Layer 5
• Manages dialogues between two computers/machines
by establishing, managing, and terminating
communications
• Formal dialogue between a service requester and a
service provider. eg.: user login and logout
• Provides synchronisation services on both ends
• Determines which side transmits data, when, and for
how long

SYSTEMS
• dialogues
can take
three
forms:
– Simplex
– Half
duplex
– Full duplex

SYSTEMS
Transport Layer - Layer 4
• Responsible for process-to-process delivery
of the entire message
– Ensures that the whole message arrives intact
and in order.
– Include port address - Network layer gets each
packet to the correct computer ; transport layer
gets the entire message to the correct process
on that computer
– Segmentation & reassembly: reassemble the
message correctly upon arrival at the destination
and to identify & replace packets that were lost
in the transmission.

SYSTEMS
Network Layer - Layer 3
• Responsible for the source-to-destination
delivery of a packet across multiple network
– Defines logical addressing so that any endpoint
can be identified
– Decides how to route transmissions from
source to destination
– Defines how to fragment a packet into smaller
packets to accommodate different media
– Delivery individual packets : does not recognize
any relationship between those packets. Each
packet belonged to separate message.

SYSTEMS
Data Link Layer - Layer 2
• Responsible for transmitting frames from one
node to the next (creates data frames )
– Divides no of bits received into manageable data
units called frames
– Add header to the frame to define the
sender/receiver of the frame for multiple stations
– Error controller : detect & retransmit damaged or
lost frames. Prevent duplication of frames.

CONTROL SYSTEMS
• Responsible for flow control
– to cope with the problems inherent with a fast sender
sending messages to a slow receiver.
• Responsible for Link Management
– deals with the rules that a sender and receiver must follow
in order to exchange information.
• Responsible for Medium Access Control (MAC)
– Controls access to the transmission medium itself to cope
with the problem of two or more station sending data at
the same time; either by preventing the problem from
happening, or by recognising a ‘data collision’ (two stations
trying to send messages on the transmission medium at the
same time), and resolving the problem so that data and
messaged are not lost.
Data Link Layer - Layer 2

SYSTEMS
Physical Layer - Layer 1
• Defines the characteristics of the interface
between the devices and transmission media
– Converts bits into signals for outgoing messages and
signals into bits for incoming messages
– Defines duration of a bit (no. of bits sent each
second)
– Synchronisation of bits : sender & receiver clocks
must be synchronized

SYSTEMS
Physical Layer - example
Process that allows the clock of the receiver in a digital system
to operate at the same frequency (and phase) as the clock
used to transmit the bits. Ensuring this criteria is called
Synchronisation

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Layers 1-4 are concerned with the flow of data from end to
end through the network and Layers 5-7 are concerned
with services to the applications.

Actions of Each layer of
OSI Reference Model
SYSTEMS

Advantages of using OSI model
SYSTEMS
• Provides a common language or reference point
between network professionals
• Divides networking tasks into logical layers for easier
comprehension
• Allows specialisation of features at different levels
• Aids in troubleshooting
• Promotes standards interoperability between networks
and devices
• Provides modularity in networking features (developers
can change features without changing the entire
approach)

Disadvantages of OSI model
SYSTEMS
• OSI layers are theoretical and do not actually perform
real functions
• Industry implementations rarely have a layer-to-layer
correspondence with the OSI layers
• Different protocols within the stack perform different
functions that help send or receive the overall message
• A particular protocol implementation may not represent
every OSI layer (or may spread across multiple layers)

SYSTEMS
Hardware

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Connecting Networks
• Repeater / hub: physical layer
• Bridge / switch : data link layer
• Router: network layer
• Gateway: network layer and above.

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Repeater
• Receives a signal and, before it becomes too
weak or corrupted,
– Copies bits from one network to another
– Regenerates the original bit pattern
– Extend the network physical length

SYSTEMS
Hub
• Device that enables more than one computer
(host)/devices to interconnect on a network.

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Bridge
• Connects multiple network segments at the data link layer (layer
2) of the OSI model.
• Bridges are similar to repeaters or network hubs
• But bridge has filtering capability
– Check destination address of a frame and decide if the frame
should be forwarded or dropped
• A bridge works : copying a data frame from one network to the
next network along the communications path.
BRIDGE

SYSTEMS
Switches
• Connect multiple links and route traffic from one link
to another
• appear nearly identical to network hubs, but a switch
generally contains more intelligence than a hub
End-user
equipment
End-user
equipment
End-user
equipment
End-user
equipment
Switch

SYSTEMS
Router
• To examine the
network
address of the
data packets
and decide the
route that the
data should
take place

SYSTEMS
Gateways
• A gateway is a network point that acts as
an entrance to another network. On the
internet, in terms of routing, the network
consists of gateway nodes and host
nodes.

SYSTEMS
What is the difference between?
• Bridge: device to interconnect two LANs that use
the SAME logical link control protocol but may use
different medium access control (MAC) protocols.
• Router: device to interconnect SIMILAR networks,
e.g. similar protocols and workstations and servers
• Gateway: device to interconnect DISSIMILAR
protocols and servers, and Macintosh and IBM LANs
and equipment

SYSTEMS
What you have learned so far?
• Describe the DCS
• Differentiate DCS n CENTRALISED
• Advantages of DCS
• ISO/OSI reference model
• Advantages and disadvantages of ISO/OSI
• Types network connectors
1
2

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