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Control System Nomenclature

There are a few acronyms used to describe industrial computer control systems.

DCS – Distributed Control System

A DCS is typically used to describe a system that controls a process; that is, something that involves moving fluids, like a waste water treatment plant or a refinery.

SCADA – Supervisory Control And Data Acquisition

This usually describes the control system for an automated manufacturing facility like an assembly line for a furniture maker.

PLC – Programmable Logic Controller

This is the computer that receives data from sensors and controls machinery. It can perform as the core processor for a DCS or a SCADA system.

Popular PLCs are Rockwell (Allen-Bradley), Siemens, Modicon and Delta V.

PAC – Programmable Automation Controller

This is Rockwell’s new for their ControlLogix computers.

HMI – Human Machine Interface

An HMI is a terminal that is used by plant operators to control the plant. It typically shows a graphic representation of the plant and allows the operator to start and stop motors, look at tank levels, etc. The graphics are usually very similar to the P&ID drawings of the plant.

An HMI is part of a SCADA or a DCS.

Typical HMIs are based on RSView32, FactoryView (Rockwell) or Wonderware. Other PLC manufacturers have their own HMI software.

OIT – Operator Interface Terminal

This device is a self-contained screen that is located near the equipment that it controls. All OITs are HMIs, but not necessarily vice-versa.