A programmable logic controller, or PLC, is a rugged industrial computer designed for the control of manufacturing processes. PLCs monitor input devices and make decisions based on the program installed by the operator. These decisions control the state of output devices.
PLCs perform three primary functions: receive information from connected devices like buttons, switches, sensors, networks, and even other PLCs; process that information according the installed program; and executing commands by activating outputs.
PLCs have evolved to accept five programming languages, provide sequential relay control, perform advanced networking tasks, and handle data between thousands of inputs and outputs. Because of this, PLCs have been widely adopted as high-reliability automation controllers suitable for harsh environments.