The programmable controller has eliminated much of the hardwiring associated with conventional relay control circuits. Other benefits include easy programming and installation, high control speed, network compatibility, troubleshooting and testing convenience, and high reliability.

The programmable logic controller is designed for multiple input and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs for the control and operation of manufacturing process equipment and machinery are typically stored in battery-backed or nonvolatile memory.

A PLC is an example of a real-time system since the output of the system controlled by the PLC depends on the input conditions.


The programmable logic controller is, then, basically a digital computer designed for use in machine control.

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Sources: Programmable Logic Controllers-Frank D Petruzella