What is a Distributed Control System? Over the years, the term DCS has evolved from the original description for the acronym as a “Distributed Control System” to the use of the term “Decentralized Control System” and they seem to be somewhat interchangeable nowadays.Regardless of which description is used, we are discussing a structure that, at the high-level view, is a system that coordinates and supervises an entire plant of many varying processes. PLCs, traditionally, were used forsingle batch or high-speed control, have a relatively simple, low-cost design, and are the core of the system. Their design is flexible and generic but completely customizable.Processing time for tasks are typically very fast,operators usually interact and control the system using some sort of graphical display such as SCADA. At the next level, you have the master controllers that supervise the individual processors as well as I/O modules.These controllers are also responsible for providing the data to the servers, which in turn, supply the data for the graphical interface.Industrial Ethernet is typically used for communication with the previous level. Fiber Optic may be used here when Ethernet cabling runs would be too long. A DCS would be better used in an environment where there are large I/O counts with many continuous processes, a processor failure in one section of the plant is not a problem for production, or risk assessment has determined that an integrated package would be the best option.

1. DISTRIBUTED CONTROL SYSTEM
Eng Mahdi Rasoulian

2. What is a Distributed Control System? Over the years, the term DCS has
evolved from the original description for the acronym as a “Distributed
Control System” to the use of the term “Decentralized Control
Control System” and they seem to be somewhat interchangeable
interchangeable nowadays.
Regardless of which description is used, we are discussing a structure that,
at the high-level view, is a system that coordinates and supervises an entire
plant of many varying processes.
WHAT IS DCS? (DISTRIBUTED CONTROL SYSTEM)

3. Briefly, as a point of the historical review, when PLCs were invented, they
were really good at handling single processes and were primarily used for
repetitive, discrete control.
The advent of the DCS was for controlling many autonomous controllers
that handled many continuous operations, mainly using analog control.
Through time and innovation, the lines have blurred a bit between the two
systems but each, in the current day, has some principal differences.

4. PLCs, traditionally, were used for
single batch or high-speed control,
have a relatively simple,
low-cost design,
and are the core of the system.
Their design is flexible and generic but completely customizable.
Processing time for tasks are typically very fast,
operators usually interact and control the system using some sort of
graphical display such as SCADA.

5. PLCs, traditionally, were used for
single batch or high-speed control,
have a relatively simple,
low-cost design,
and are the core of the system.
Their design is flexible and generic but completely customizable.
Processing time for tasks are typically very fast,
operators usually interact and control the system using some sort of
graphical display such as SCADA.

6. A DCS is used for continuous, complex controls, have an integrated
control center much like a SCADA, which is the core of the system versus
the processors in a PLC system.
The DCS has a number of predefined functions that come ready to
customize and deploy for various applications.

7. A DCS is used for continuous, complex controls, have an integrated
control center much like a SCADA, which is the core of the system versus
the processors in a PLC system.
The DCS has a number of predefined functions that come ready to
customize and deploy for various applications.

8. DCS also have a claim that when safety is a top priority, it is the most reliable
system.
The reason for this:
is because the manufacturer supplies both the control and supervisory
equipment as an integrated package.
The risks of integration errors are greatly reduced.
Automation Pyramid:
The Automation Pyramid is a pictorial representation of the
layers of automation within a typical factory, comprising five
layers of integrated devices and technology.

9. There are indeed scenarios in which a PLC system would be the best
option such as smaller sized processes where you could employ redundant
components to negate the possibility of process shutdowns.
Without redundancy, you risk production halts due to the nature of a single
processor controlling an entire plant.
Redundancy may be deployed in either the PLC or DCS applications. We
will talk more about redundancy in a future article.
Just as there are circumstances for a PLC system, the use of DCS would
be for larger, more complex processes that require a lot of interaction
between many processors.
Now that we’ve touched on some of the differences in the systems, let’s
focus on the DCS and some of its components.
The DCS is a process-oriented system that uses closed-loop control.

10. 1. Operator Stations
A typical plant starts with a centralized operator
typically called Operator Stations.
Operator Stations, in a DCS, are the heart of the
This is where the operator can observe the
view process warnings and alarms, monitor
Basic Components of a Typical DCS Network

11. 1. Operator Stations
A typical plant starts with a centralized operator
typically called Operator Stations.
Operator Stations, in a DCS, are the heart of the
This is where the operator can observe the
view process warnings and alarms, monitor
Basic Components of a Typical DCS Network

12. 2. Servers, Archiving and Engineering Computers
The next level of components may contain servers, archiving computers, and
Communications with the Operator Station level is typically Industrial Ethernet.
Servers are used for the collection of data at the processor level.
They are responsible for the data that moves between the Operator Station and
floor.
Archiving computers are used for storing historical data that may be used for
trends or compliance.
Engineering stations are used for creating the projects on which the processes
run. This includes;
– Hardware configurations
– Logic for tasks
– Graphical displays for operator interaction
– Administration of all of those tasks through installed software packages.
This is the station that is used to download the projects to the processors and
Basic Components of a Typical DCS Network

13. 3. DCS Controllers
At the next level, you have the master controllers that supervise
processors as well as I/O modules.
These controllers are also responsible for providing the data to
turn, supply the data for the graphical interface.
Industrial Ethernet is typically used for communication with the
Optic may be used here when Ethernet cabling runs would be too
At this level, the processor executes the logic and does what it
control the process.

14. 3. DCS Controllers
At the next level, you have the master controllers that supervise
processors as well as I/O modules.
These controllers are also responsible for providing the data to
turn, supply the data for the graphical interface.
Industrial Ethernet is typically used for communication with the
Optic may be used here when Ethernet cabling runs would be too
At this level, the processor executes the logic and does what it
control the process.
Cc-pcnt01 Honeywell Dcs C300 Controller Module C300 Io

15. 4. Field Devices
The next level is the field device level. Communications between
processor level can be nearly any type that may be compatible
Those include Industrial Ethernet, Profibus DP, EtherCAT, Fiber
proprietary communication protocols.
Components at this level would be devices such as transmitters,
motors, remote or distributed I/O, etc.

16. 4. Field Devices
The next level is the field device level. Communications between
processor level can be nearly any type that may be compatible
Those include Industrial Ethernet, Profibus DP, EtherCAT, Fiber
proprietary communication protocols.
Components at this level would be devices such as transmitters,
motors, remote or distributed I/O, etc.
Honeywell Process Solutions
Field Instruments | Honeywell

17. A DCS would be better used in an environment where there are large I/O counts with
many continuous processes, a processor failure in one section of the plant is not a
problem for production, or risk assessment has determined that an integrated package
would be the best option.
Summary