Distributed Control System(DCS) Block Diagram and Architecture

The distributed control system or DCS system is a computerized control system mainly used in a manufacturing plant or any particular process. The name distributed control system implies that the controlling system is distributed among different operators. Here, no centralized control system is involved. So failure in any one operator does not affect the whole system. Of course, the entire system is connected to each other and a central computer is available that can monitor the entire system but the control is distributed to respected supervisory computers.

Distributed Control System(DCS) Block Diagram

Here, you can see a simple block diagram of DCS system.

The parts or components of the DCS system are classified into different levels. Here, we can classify them into five levels,

1. Level 0
2. Level 1
3. Level 2
4. Level 3
5. Level 4

Level 0

All the field or ground devices such as sensors, transducers, and actuators come under this level 0. These devices directly control or interact with the physical world.

Sensors

Sensors are the devices that sense the physical changes around them. For example, a temperature sensor can sense the changes in temperature around it. So the sensor basically acts as an input device. Through these sensors, the DCS system can gather data from the plant.

Transducer

The transducer is a device that either converts the electrical quantity into a physical quantity or converts the physical quantity into an electrical quantity. In a DCS system, the transducer that converts the electrical quantity into a physical quantity can be called an output transducer, and the transducer that converts the physical quantity into an electrical quantity can be called an input transducer. The input transducers act as sensors also, they help to measure and gather data. For example, a pressure transducer(input transducer) helps to measure the pressure. On the other hand, the speaker(output transducer) helps to make an alarm or any announcement.

Actuator

The actuator is a device that makes physical changes when an electrical supply is applied to it. Actuators are the devices used to operate any valve, actuate any lever, etc. For example, the flow of any fluid can be controlled by a solenoid valve.

Level 1

The direct controllers such as microcontrollers, and input/output racks come under this level. All the sensors, actuators, and transducers are directly connected to these devices. The level 1 devices controlled the field devices when they received signals from the supervisory computers. All the converter circuits, controller circuits, and driver circuits come under this level.

Level 2

Supervisory computers where the operators are seated come under level 2. At this level data and information are collected from the field level or plant. The operator controls all the field devices directly from this level. The operators at level 2 are actually the workers who work in the plant for production.

Level 3

The coordinating computers come under this level. It is the production control level. From this level, the process or field devices are not directly controlled. It just monitors the production and makes sure production is ongoing as per the schedule.

Level 4

At this level production schedule is prepared and monitors the whole operation of the systems.

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