Distributed Control system as its name indicates is a control system specifically works with manufacturing systems. Like all the control systems it controls and monitors the distributed equipment. But a distributed control system is primarily designed to support voluminous industrial applications. A DCS is device or combination of devices that command and regulate the distributed equipment.

DCS Components

A typical distributed control system consists of a single computer. It serves as a controller of the network that can contain sensors such as thermocouple elements, operator terminals, actuators, or other controllers. The interconnections are proprietary. Distributed control systems may also contain ADC, DAC, multiplexers, demultiplexers, and HMIs (human machine interfaces).

DCS Implementation

In a bigger picture all the control systems use two types of controls to perform their functionality. One is logic controls and the other is linear / feedback control. Some systems also use the combination of these controls.

Feedback Controls

A feedback control uses a feedback path from output to input. So in the systems deploying such controls, the process is kept within an acceptable hour. One example of such implementation is thermostat. When the temperature goes below the reference voltage, control operates like furnace gets on in household thermostats.

Logic Controls

Logic control designs are similar to Boolean logic system design. They are easy to apply and suitable for sequential mechanical applications. For example they work fine in elevators or in factory applications. They are poor at continuous applications such as in steel mills or oil refineries.

Programmable Logic Controller (PLC)

Mostly both logic control systems and feedback controls are designed through Programmable Logic Controllers (PLCs). A programmable logic controller serves as a control hub for many automated systems. PLCs contain transistors and relays. Depending upon the inputs and other circuitry these transistors and relays serve as switches to control equipment. PLCs also support multiple inputs and outputs. The proprietary languages are available to program PLCs using standard computer interfaces.

PLC Specifications

Important specifications associated with PLCs are number o inputs and outputs, programming options, and programming languages. Input and output choices for programmable logic controllers are thermocouple, AC, DC, RTD, frequency, pulse, interrupts, and transistor I /Os. The programming options refer to the way PLCs are programmed. These include computer interface, front panel, or through handheld devices.

PLC Programming Languages

Here is a variety of programming languages are available for programmable logic controllers. These include RLL (relay ladder logic), LD (ladder diagram), ST (structured text), flow chart, SFC (sequential function chart), FBD (function block diagram), IEC 61131 – 3, C language, and visual basic. Moreover IEC 61131 – 3 software supports five PLC programming languages that are instruction list, SFC (sequential function chart), FBD (function block diagram), LD (ladder diagram), and ST (structured text).