A
programmable logic controller,
PLC, or
programmable controller is a
digital computer used for
automation of typically industrial
electromechanical processes, such as control of machinery on factory
assembly lines,
amusement rides, or
light fixtures. PLCs are used in many machines, in many industries. PLCs are designed for multiple arrangements of digital and analog inputs and outputs, extended temperature ranges, immunity to
electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed-up or
non-volatile memory. A PLC is an example of a "hard"
real-time system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result.