PLC Operation

PLC Operation

If you are trying to understand a PLC system better, it will be beneficial to learn how a PLC controller operates once the program is written and the appropriate I/O modules are selected. The programmable logic controller will process the given information (inputs), execute the instruction from the program, and deliver the results (outputs) based on the provided information and written logic. PLCs operate in a repeating loop once the user determines the inputs and outputs.

The four basics steps in PLC operation are:

1. Input Scan - Detects the state of input devices connected to the PLC

2. Program Scan - Executes program created by user

3. Output Scan - Operate all output devices connected to the PLC

4. Housekeeping - Communicates with other devices and runs diagnostics

Scan time is the Time required to read the I/P, Process the logic and update the output in one cycle. Typically it is less than 10 ms. It depends on the complexity of logic.