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What is a PLC?

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A Programmable Logic Controller (PLC) is an industrial digital computer used for control of electromechanical devices such as control of industrial machinery, pumps, lighting etc. A PLC will be connected to inputs. The PLC processes the inputs in real time based on the logic stored in it and switches the outputs on or off.

In other words, Programmable logic controllers, also called programmable controllers or PLCs, are solid-state members of the computer family, using integrated circuits instead of electromechanical devices to implement control functions. They are capable of storing instructions, such as sequencing, timing, counting, arithmetic, data manipulation, and communication, to control industrial machines and processes. Figure 1-1 illustrates a conceptual diagram of a PLC application.

• PLC is an electronic device. It is an application of microcontroller.
• PLC is a Logic Controller - It controlls machines / electro mechanical devices based on a defined logic.
• PLCs are Programmable - The PLC's logic or program can be altered instantly and easily without any rewiring. The programs are typically stored in battery-backed or non-volatile memory.

A more formal definition of PLCs is:

A PLC is an industrial computer - unlike general-purpose computers, the PLC is designed for the industrial environment and requirements. The key differences are as follows:

1. PLCs are much compact that general purpose computers or industrial computers. Most of the time, PLCs are cost effective than computers.
2. PLCs have multiple digital and analog inputs and output arrangements.
3. PLCs are designed to work in industrial temperature ranges - ?? to ?? degress typically.
4. PLCs have to be immune to electrical noise and interference from nearby loads or devices and be resistance to vibration and shock.
5. Unlike a computer, the PLC can boot up in less than a second and does not need any shutdown - thus making it practical for industrial use.

What is a PLC? - Video:

PLC - Presentation: