A Distributed Control System (DCS) refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location but are distributed throughout the system with each component sub-system controlled by one controller. Distributed Control Systems (DCSs) are used in industry 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 may employ one or several workstations and can be configured at the workstation or by an off-line personal computer. Local communication is handled by a control network with transmission over twisted pair, coaxial, or fiber optic cable. A server and/or applications processor may be included in the system for extra computational, data collection, and reporting capability. The entire system may be networked for communication and monitoring. The computer network and field buses will connect the distributed controllers with the central controller and finally to the Human-Machine Interface (HMI) or control consoles.
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. Instead of being hardwired, field devices can also be connected via the latest communication protocols such as Foundation Fieldbus or Profibus. Today’s controllers have extensive computational capabilities and, in addition to proportional, integral, and derivative (PID) control, can generally perform logic and sequential control.
Figure 1: DCS SCADA Architecture