Distributed control system

A distributed control system (DCS) refers to a control system usually of a
manufacturing system or process, in which the controller element is not central in
location (like the brain) but are distributed throughout the system with each component
sub-system under the control of one or more controllers. The entire system may be
networked for communication and monitoring.Distributed control systems (DCS) are used in industrial and civil engineering applications to monitor and control distributed equipment with or without remote human intervention; the nomenclature for the former ‘manual control’ and the latter ‘automated control’.


A DCS typically uses computers (usually custom designed processers) as controllers and
use both proprietary interconnections and protocols for communication. Input & output
modules form component parts of the DCS. The processor receives information from
input modules and sends information to output modules. The input modules receive
information from input instruments in the process (aka field) and output modules
transmits to the output instruments in the field. Computer buses or electrical buses
connect the processor and modules through multiplexer/demultiplexers. They also
connect the distributed controllers with the central controller and finally to the Human-
Machine Interface (HMI) or control consoles.


Distributed Control Systems (DCSs) are dedicated systems used to control manufacturing
processes that are continuous or batch-oriented, such as oil refining, petrochemicals,
central station power generation, pharmaceuticals, food & beverage manufacturing,
cement production, steelmaking, and papermaking. DCSs are connected to sensors and
actuators and use setpoint control to control the flow of material through the plant. The
most common example is a setpoint control loop consisting of a pressure sensor,
controller, and control valve. Pressure or flow measurements are transmitted to the
controller, usually through the aid of a signal conditioning Input/Output (I/O) device.
When the measured variable reaches a certain point, the controller instructs a valve or
actuation device to open or close until the fluidic flow process reaches the desired
setpoint.


A typical DCS consists of functionally and/or geographically distributed digital
controllers capable of executing from 1 to 256 or more regulatory control loops in one
control box. The input/output devices (I/O) can be integral with the controller or located
remotely via a field network. Today’s controllers have extensive computational
capabilities and, in addition to proportional, integral, and derivative (PID) control, can
generally perform logic and sequential control.