Distributed Control Systems (DCS)

DCS were initially developed to support large process industries such as refineries and chemical plants. The DCS controllers are distributed throughout the plant; hence the name distributed control system. They are typically deployed at site facilities over the plant or control area.

DCS are different from a centralized control system where a single controller handles the control functions from a central location. DCS has each machine or group of machines controlled by a dedicated controller. These distributed individual automatic controllers are connected to the field devices.

The biggest advantage of DCS is its ability to have multiple controllers dividing tasks, because DCS is best suited for large-scale processing or manufacturing plants where a large number of continuous control loops need to be monitored and controlled. The biggest advantage to multiple controllers dividing the control tasks is if any part of DCS fails, the plant can continue to operate irrespective of the failed area.

Due to the distribution of control system's architecture of DCS, it has become prominent in large and complex industrial processes. They include:

• Papermaking

• Fixed Chemical

• Water Treatment

• Rail Transit

• Power Stations

• Petrochemical

• Biopharmaceutical

Through a proper command structure and information flow, the DCS architecture unites sub-systems. This includes the basic elements, such as engineering workstation, operating station, smart devices, and communication system.

SCADA v DCS

Today the functionality of Supervisory control and data acquisition (SCADA) and DCS systems are very similar, but DCS tends to be used on large continuous process plants where high reliability and security is important, and the control room is not geographically remote, though, key comparison points are:

• HIM/PLC software is integrated within the DCS. For SCADA environments, this may have to be purchased seperately and for each vendor of PLC/RTU.

• SCADA has a slight advantage for time-sensitive processes due to quicker processing times.

• SCADA infrastructure also supports a wider range of communications protocols as opposed to a more limited number for DCS.