Programmable logic controller (PLC) or programmable controller is a real-time digital computer system used for industrial automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. Typical applications of Programmable logic controllers (PLC) are automotive manufacturing industry, steel plants, power plant smart grids, mineral and chemical processing, water and waste treatment, and petroleum collection and distribution.

Programmable Logic Controller (PLC) Hardware

Unlike general-purpose computers, the PLC hardware is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programmable logic controllers are usually designed with microprocessors, microcontrollers, or digital signal processors (DSP). Programmable logic controller (PLC) take inputs from many input devices such as sensors and limit switches using data acquisition system. Programmable logic controllers (PLC) operate electric DC motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, some other mechatronic actuators.

Programmable Logic Controller (PLC) Software

Programmable logic controller (PLC) software programmes are usually written in assembly language instructions, and C-language programs. Few real-time operating systems (RTOS) are also available as opensource free software, which suitable to certain microcontroller-based hardware configurations. Software programs to control machine operations are typically stored in battery-backed or non-volatile memory such as EEPROM or Flash memory. PLCs can be programmed using application software on personal computers connected to the PLC through Ethernet, RS-232, RS-485 or RS-422 cabling.

Programmable Logic Controller (PLC) Communications

Programmable Logic Controllers (PLC) have built in communications ports, usually 9-pin RS-232, but optionally EIA-485 or Ethernet. Modbus, BACnet or DF1 is usually included as one of the communications protocols. Other options include various fieldbuses such as DeviceNet or Profibus. Other communications protocols that may be used are listed in the List of automation protocols. Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system or web browser. PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between processors.