A Programmable Logic Controller (PLC) is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis. PLCs are designed to be used by engineers without a programming background, and they can automate a specific process or machine function. They can monitor and record run-time data such as machine productivity or operating temperature, automatically start and stop processes, generate alarms if a machine malfunctions, and more.
PLCs are input-output systems, which means that each unit both accepts inputs and controls outputs. The logic programming, which happens in the CPU, controls the systems functions using the internal logic programmed into it. The first PLC was invented by Dick Morley in 1968, and it was the Modicon 084, designed for General Motors.
PLCs are a flexible and robust control solution, adaptable to almost any application. They are different from industrial PCs, microcontrollers, and other industrial control solutions because of their key features:
- Ruggedized design for harsh environments
- High reliability and fault tolerance
- Ease of programming
- Ability to monitor and record run-time data
- Compatibility with a variety of programming languages
Most PLC programming software offers programming in Ladder Logic, which is the traditional programming language. It mimics circuit diagrams with "rungs" of logic read left to right, and each rung represents a specific action controlled by the PLC, starting with an input or series of inputs (contacts) that result. While Ladder Logic is the most commonly used PLC programming language, it is not the only one.
