A PLC (programmable logic controller) is an industrial digital computer designed for the control of manufacturing processes or robotic devices where reliability control, simple programming and fault diagnosis is necessary. They were originally built to replace electromechanical relay systems in industrial automation.
A CPU (central processing unit) forms part of the PLC system. PLC CPUs are microprocessor-based and act as the electronic circuitry within an industrial computer. They carry out instructions from the computer program, performing basic mathematical, logical, control, input and output operations.
PLC controllers are important for the correct functioning of machinery in manufacturing and industry. They are used in the automation of electromechanical processes, including control of machinery on assembly lines, amusement rides, or lighting fixtures. PLCs are ideal for applications that require constant monitoring of input devices whilst allowing decisions to be made via a custom program. This ultimately enables it to control an output.
Programmable logic controllers are divided into small, medium and large modular categories. Small control systems are robust, compact and mountable on top of or beside the equipment to be controlled. Medium controllers mainly use rack mounting or backplane systems, allowing for simple upgrading via additional function cards. Large systems are necessary for applications where complex control functions are executed, usually in large plants, in machinery requiring constant monitoring, or control of other PLC hardware.
PLCs feature a modular design, making them suitable for use in a wide range of applications. Due to the modular aspect, PLCs can be plugged into numerous setups making them highly versatile.