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Programmable Logic Controllers (PLC) in Industrial Networks: Definition, Applications & Examples

Instructor: Vignesh Sivabalan

Viignesh has an MS in information technology.

Programmable Logic Controllers (PLC) are special computers designed for industrial automation and control. Let us get introduced to PLCs and learn their industrial applications and working with examples in this lesson.

What is a Programmable Logic Controller?

In simple terms, a PLC (Programmable Logic Controller) is a computer with one microprocessor but lacking keyboard, monitor or mouse. A PLC is an industrial control computer system which continuously monitors the state of input devices, processes this input using custom programs, the output of which is used to control the states of output devices. The design of PLC is such that it can withstand harsh industrial operations and PLC can rightly be called as a special type of computer for industrial control systems. PLCs are robust in construction and have special features such as reliable control, easy-to-use hardware, sequential control, counters and timers.

Use of PLCs in Industrial Automation and Industrial Networks

Industrial Automation uses control devices and systems like robotics and computers to automate industrial machinery and their operations which eliminates the need for human operators. Industrial automation saves time, eliminates human errors, cuts costs and improves performance. Once we program PLCs, they perform events in sequence, triggered by the stimuli called inputs. The inputs are received through time delays or counted occurrences. To keep pace with the increasing demands of industrial standards, PLCs are designed to withstand extreme vibration, heat, humidity, temperatures and noise.

PLCs are of great use in various industries such as automobile industry, steel industry, chemical industry, energy sectors and so on. Based on the technologies followed in industries, the application of PLCs varies. Let us discuss a few industries where PLCs help in automation and control.

Paper Industry

In the paper industry, PLCs are used in various applications including machine control and monitoring. For example, PLC controls and automates the speed of the machine that prints books or offset web pages.

Travel Industry

In the travel industry, such as in airports, PLCs are used to operate lifts and monitor safety control systems.

Glass Industry

PLCs have been used in the glass industry for decades to control material ratios and to process production of large sheets of glass. PLC is used in both analog and digital mode in the glass industry. Analog mode is used for data recording and digital mode for position and digital quality control.

Medicine

PLCs are used in injection molding, corrugation machine control applications, silo feeding and coal-fire boiler systems in hospitals.

Cement Manufacturing Industries

The important part of quality cement manufacturing involves mixing of correct raw materials in proper proportions. The end product greatly depends on this process of mixing and processing. The distributed control systems using PLC controls ball milling, shaft kiln and coal kiln. The PLC ensures accuracy of data to measure right quantity and quality of raw materials in cement manufacturing.

Other Industrial Applications

PLCs can be used in, but not limited to, mobile automation, the food industry for filling machine control, water tank quenching in the aerospace industry as well as batch washing machines control and shrinkage systems in the textile industry.

Why are PLCs used in Industries and not normal computers?

PLCs are special computers designed for industrial applications and they differ from normal PCs in that:

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