A Programmable Logic Controller (PLC) is an industrial digital computer specialized for manufacturing processes, such as assembly lines, robotic devices, or any activity requiring high-reliability control. They were first developed in the automobile industry to provide flexible sequencing and process control. Early PLCs were expensive and difficult to program, but their use has spread because programming can be done quickly with ladder logic diagrams.

Ladder logic is a graphical language that resembles a ladder with two vertical rails between which rungs containing switches are strung. When current flows through the switch contacts at the top of each rung, it energizes coils located further down the rung on one of two output “rails.” Output coils may also be used as input coils by reversing their position on the rail so that they are energized when current flows through them from an external source rather than activated by contact closure within the PLC’s circuitry.

A programmable logic controller is a type of computer used for industrial automation. It is designed to be rugged, durable, and easy to use and program. PLCs are used in various industries, including automotive, food and beverage, pharmaceuticals, oil and gas, petrochemicals, pulp and paper, water treatment plants, and more.

PLCs were first developed in the 1960s by General Motors Corporation (GM) to replace relays in automobile manufacturing plants. Today’s PLCs are much more sophisticated than the early versions; they can be programmed to perform complex tasks such as monitoring process variables such as temperature or pressure; controlling motors; sequencing production steps; communicating with other devices on networks; or even making decisions based on data from sensors.

PLC programming can be done using ladder logic diagrams which resemble electrical relay circuits. This makes it easy for people familiar with electrical wiring diagrams to learn how to program PLCs. Other programming languages, such as C++ or Java, can also be used, but ladder logic is still the most popular method among engineers and technicians.