Programmable Logic Controller PLC Systems - SCADA Systems

A PROGRAMMABLE LOGIC CONTROLLER (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices.

The primary difference between a PLC (or Programmable Logic Controller) and SCADA (Supervisory Control and Data Acquisition) is the fact that a PLC is hardware and SCADA is (generally) software, though some would argue that SCADA is a plant's overall control system using hardware and software elements.