Basic PLC scan cycle

A PLC executes an initialization step when placed in run mode, then repeatedly executes a scan cycle sequence.

PLC scan cycle

The basic PLC scan cycle consists of three steps

  1. An input scan
  2. A user program scan
  3. An output scan

The total time for one complete program scan is a function of processor speed, I/O modules used, and length of user program

Typically, hundreds of complete scans can take place in 1 second or less.

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Study in detail about Scan Cycles

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