Digital or Distributed Control System. DCSs historically refers to larger analog control systems traditionally used for PID control in the process industries, whereas PLCs were used for discrete or logic processing. However, PLCs are gaining capability and acceptance in doing PID control while the DCS has come to mean the system of input/output devices, control devices and operator interface devices which execute the stated control functions and permit transmission of control, measurement, and operating information to and from multiple locations, connected by a communication link. The DCS is specifically separate from the safety instrumented system (SIS) in that there are no meaningful random common mode failures between the two systems.

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