Answer / thowsif_csm team_emerson

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

For Details log on to:-
http://en.wikipedia.org/wiki/Programmable_logic_controller

Answer / bela shree

The main difference from other computers is that PLCs are armored for severe conditions (such as dust, moisture, heat, cold) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC.

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