Industrial Control System (ICS): Functional Components & Uses

Instructor: Archna Khubchandani

Archna has a professional post graduate diploma in system management for programming, system analysis, & design.

This lesson explores functional Industrial Control System (ICS) components. You will mainly explore the functions and uses of Programmable Logic Controllers (PLCs), Remote Terminal Units (RTUs), and Communication Gateways.

Industrial Control Systems

ICS include several types of control systems to either operate or automate industrial processes. The control system includes a collection of devices, systems, networks, and controls.

Each ICS functions differently based on the industry and is built to electronically manage tasks efficiently.

ICS can be configured to operate in three ways:

  1. Open loop, where the output is controlled by established settings, such as in automatic washing machines and traffic signal systems.
  2. Closed loop, where the output regulates input to a set point without human interaction, such as in air conditioning systems and servo voltage stabilizers.
  3. Manual mode, where the system is controlled completely by humans.

Components of an ICS

Figure 1 shows the basic components and operation of an ICS.


Figure 1: Basic Operations in ICS
Basic Operations in ICS


A typical ICS contains several control loops, remote diagnostics, maintenance tools, and human interfaces built on layered network architectures using an array of network protocols. Let us learn more about some of the terms used in ICS.

A process consists of series of activities to achieve the desired output.

A control loop utilizes sensors, actuators, and controllers or PLCs to automatically adjust the value of output to the desired set-point.

A sensor detects changes in its environment and sends information as controlled variables to the controller.

The controller uses target set point and control algorithms to generate required output variables and transmits them to the actuators.

Actuators or movers are components of a machine for moving or controlling a mechanism such as control valves, breakers, switches, and motors.

Human interfaces are utilities used to display process status information and to monitor and configure parameters in the controller.

Remote Diagnostics and maintenance applications do real-time diagnosis and maintenance operations like identification, prevention and recovery from abnormal operations or failures remotely.

A Data Historian is a centralized database storing all process information within an ICS environment. The logged data is exported to the corporate Information Systems (IS) for process data analysis, control and planning.

A Communications Gateway device provides communication to a remote network such as internet or an autonomous system that is out of bounds for the host network nodes. The gateway is implemented through hardware or software. It directs the traffic of the network and may block certain traffic to protect it from malicious attack. It also grants or denies access to computers within the network to the outside world.

Intelligent Electronic Device (IED) is a device for protection, control, monitoring, metering and communication with the capability of serial communication with other devices like microprocessor-based voltage regulators, protection relays, and circuit breaker controllers.

Field Devices receive supervisory commands from remote stations and control local operations.

Remote Terminal Unit (RTU)

RTU is a microprocessor-controlled field device specially designed to manage remote substations and power systems, integrating them into different types of ICS. Its primary task is to control and acquire data from process equipment at the remote location and to transfer this data back to Master Terminal Unit (MTU). RTUs gather telemetry data over large geographical areas, because they use wireless communication and hence are referred to as Remote Telemetry Units.

Programmable Logic Controller (PLC)

PLC is a type of computer used in ICS as a control component of an overall system. PLCs have a user-programmable memory for the purpose of storing instructions and for implementing specific functions. A basic PLC system consists of

  • Input/ Output Section: Input devices like sensors, switches and output devices like motor or a lamp or a heater, whose functioning is controlled by varying the input signals.
  • CPU or Central Processing Unit: It carries out all the processing based on the control program.
  • Programming Device: It is the platform where the control logic is written. It can be a handheld device or a computer itself.
  • Power Supply
  • Memory

In Supervisory Control and Data Acquisition systems a PLC works as an RTU. In Distributed Control Systems PLCs are used as local controllers. In smaller control system configurations, PLCs are implemented as primary components as in automobile assembly lines and amusement rides.

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