How does a plc operate?

There are four basic steps in the operation of all PLCs; Input Scan, Program Scan, Output Scan, and Housekeeping. These steps continually take place in a repeating loop.

Four Steps In The PLC Operations

• Input Scan 

                    Detects the state of all input devices that are connected to the PLC 

• Program Scan

                   Executes the user-created program logic 

• Output Scan 

                  Energizes or de-energize all output devices that are connected to the PLC. 

• Housekeeping 

                 This step includes communications with programming terminals, internal diagnostics, etc...
 

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