Programmable Logic Controller (PLC)

     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 devices connected as outputs.

        Almost any production line, machine function or process can be automated using a PLC. The speed and accuracy of the operation can be greatly enhanced using this type of control system. But the biggest benefit in using a PLC is the ability to change and replicate the operation or process while collecting and communicating vital information.

 

         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.

A PLC consists of following main parts:

What is a PLC input/output?

INPUT	OUT
Sensing Devices	Valves
Switches and Push buttons	Solenoids
Proximity Sensors	Motor
Limit Switches	Actuators
Pressure Switches	Pumps

 

 PLC Operations consist of four steps

            1. Input Scan: Scans the state of the Inputs
            2. Program Scan: Executes the program logic
            3. Output Scan: Energize/DE-energize the outputs
            4. Housekeeping