Distributed control system (DCS) involves a computer that communicates with control elements (machine, process controller and PLCs) distributed throughout the plant or process, through high-speed communication network and displays gathered data.
The Basic Elements Comprised in a Distributed Control System (DCS) Include:
- Engineering Workstation, Operating Station or Human Machine Interface (HMI)
- Process Control Unit or Local Control Unit
- Field devices or Smart instruments
- Communication system
Engineering Workstation, Operating Station or Human Machine Interface (HMI)
It is a supervisory controller over the entire DCS. It is used to Operate, Monitor and Control plant parameters. It can be a PC or any other computer that has dedicated engineering software.
Process Control Unit or Local Control Unit
Process control unit or local control unit of distributed control system (DCS) acquire the information from various sensors via input module, analyze and process it based on the control logic implemented and sends the output signals via output modules to controllers.
Field devices or Smart Devices
Field devices or smart instruments are capable of communicating with PLC’s or other controllers while interacting with real-world parameters like temperature, pressure, etc.
Communication system in Distributed control system (DCS) is used to interconnects the engineering workstation, operating station or HMI and smart devices with one another. It carries the information from one station to another. The common communication protocols used in Distributed control system (DCS) include Ethernet, Profibus, Foundation Field Bus, Device Net, Modbus, etc.
Operation of Distributed Control System (DCS)
Sensors sense the process information and send it to the local I/O modules, to which actuators are also connected to control the process parameters.
Information or data from these remote modules is send to Process Control Units via field bus.
If smart field devices are used, the sensed information is directly transferred to Process Control Unit via field bus.
The collected information is further processed, analyzed and produces the output results based on the control logic to controller.
The results or control actions are then carried to the actuator devices via field bus.
Advantages of Distributed Control System (DCS)
- It gives a facility to monitor and control the equipment of the entire plant area through Human Machine Interface (HMI).
- Data logging and an alarming facility can give the operator to better understand of the physical overview of the process.
- System reliability by maintaining system operation endlessly during the time of some abnormalities even when the system is in operation.
- It offers a perfect secured system to handle system functions for better factory automation control.