A PLC (Programmable Logic Controller) uses a cyclic sequence referred to as the scan cycle, which includes the following fundamental steps:
Input Scan
The PLC checks the status of all input devices linked to it, including sensors, switches & other signals. This information is saved in the memory as input status.
Program Execution
Using the input data, the PLC executes the logic program stored in its memory. The software chooses what actions to execute by comparing the input conditions to programmed instructions (such as timers, counters, or arithmetic operations).
Output Scan
After running the program, the PLC changes the status of its output devices, such as motors, valves, & actuators, based on the program logic.
Maintenance Tasks (Housekeeping)
This step includes communication, diagnostic, and memory management operations to ensure that the PLC system runs smoothly.
The entire procedure is repeated in a loop, and the time it takes to complete one cycle is referred to as the scan time.
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