Have you visited my previous blogs of What is PLC? How does it work? Application, Advantages, Brands, etc. and What is SCADA Software? Top Feature of SCADA.
In this blog, I am going to cover detail information about Distributed Control System.
Let’s Start Then,
What is a Distributed Control System?
Nowadays, there are lots and lots of smart field devices and use of protocols like Profibus, Profinet, Modbus makes the large and complex industrial process very easy to control. This is often referred to as a Distributed Control System (DCS) or DCS System, which gives better efficiency in production, provides the most effective quality and improves reliability.
A DCS is used in several industries currently like oil and gas, refinery, power plants, water treatment plant, automobiles industries, etc.
Basic Overview of Distributed Control System(DCS)
Distributed Control System is defined by Wikipedia,
“A distributed control system (DCS) is a computerized control system for a process or plant usually with many control loops, in which autonomous controllers are distributed throughout the system, but there is no central operator supervisory control. The DCS concept increases reliability and reduces installation costs by localizing control functions near the process plant, with remote monitoring and supervision.”
A simple definition of DCS:
Distributed Control System(DCS) is a specially designed control system to manage complicated, giant and geographically distributed control systems throughout the complete plant space.
It is different from a centralized control system where a single controller at a central location serves the control process.
Distributed Control System Architecture
In the DCS, a dedicated controller is assigned for each machine or group of machines to control the process. Here the smart field devices or instruments are directly connected with the dedicated controller as well as operator station via high-speed communication.
In the DCS, we have seen that the distribution of control systems, which are very small sets of control systems is connected as a subsystem. These subsystems are connected with high-speed communication buses. Some of the subsystems are divided to do,
- Data Acquisition
- Data Presentation
- Process Control and Supervision
- Report Generation
Components of Distributed Control System
The main elements of the DCS system are Operator station or HMI, Engineering station, Process control unit or Local control unit, Smart field devices, Communication system.
This is the main station from where all the distributed controllers, as well as field devices and operator stations, can be configured. This station can be a PC or any other system.
This station is additionally used to configure new controller, modifying control logic of controller, to configure smart field devices, to create a new logic, to store the information, to create a new input or output point, etc.
Operator Station or HMI
This is the station from where an operator can monitor the entire plant equipment in a graphical illustration. An operator can also operate the equipment as well as see the trends, alarm, and reports.
Sometimes multiple stations are used to perform this task like Trends, Alarms, Report, Recipe in a different station.
Process Control Unit or Local Control Unit
This is also called a distribution controller or process station. It is placed near to the field devices or a suitable location from where all the field devices can connect with it.
This process station incorporates one or more distributed controllers. There is a CPU, I/Os, communication Module and I/Os expansion module in the controller.
The field devices like sensors, actuators, transmitters are directly connected with the I/Os of this unit. Some field devices can be directly connected with the controller using fieldbuses without any I/O module, which can be termed as smart field devices.
The controller receives the instructions from the engineering station like set point and other parameter and also acquire the information from the various input devices.
The CPU analyzes all the inputs and processes it based on the user program and then sends the output signal via output modules to control the devices.
It can sense and control both analog and digital inputs/outputs by analog and digital I/O modules. These modules are extendable according to the number of inputs and outputs.
It collects the information from discrete field devices and sends this information to operating and engineering stations.
The communication system is the most important part of the Distributed Control System or DCS System, which is used to connect all the engineering stations, process stations, control units, and smart field devices.
The common protocol used in DCS as communication protocols are Ethernet, Profibus, Modbus, DeviceNet, etc.
However it is not compulsory that only a single protocol can be used in DCS, we can use a different protocol for different levels.
As an example in the below figure, Profibus is used to connect all the smart field devices with process control unit and Process stations or HMIs and Engineering stations are connected with Ethernet.
Advantages of DCS
Handle complex structure
PLC is used to control the industrial process in a very high-speed requirement. However, due to the limitation of Input/Output devices, PLC can’t handle a more complex structure.
DCS has an inbuilt distributed controller for each different control operation, and even when we want to expand I/Os, it’s very easy to configure or modify controller in DCS. This makes it suitable for complex structures.
DCS facilitates system redundancy at entry-level. Redundancy rises system reliability by maintaining system operation endlessly during the time of some abnormalities even when the system is in operation.
DCS can give a facility to monitor and control the equipment of the entire plant area through HMI. Data logging and an Alarming facility can give the operator to better understand the physical overview of the process.
The structure of DCS can be easily scalable just by adding some more control units or process units. I/Os can be easily expanded by just adding some I/O modules to the controller.
Distributed Control System design offers a perfect secured system to handle system functions for better factory automation control. Security is also provided at different levels such as engineer level, entrepreneur level, operator level, etc.
Popular Brand of DCS System
- Emerson Electric
- Honeywell International
- Yokogawa Electric
- General Electric
- Mitsubishi Heavy Industries
- Rockwell Automation
- Schneider Electric
- Toshiba International
This is all the basic information about the Distributed Control System. If you like this article, please share this article with your friends, colleagues. If you any queries then hit your question in the comment section below. Thanks, Enjoy your day.