How does a PLC control a circuit?

The interface between the PLC and the electrical circuit is accomplished through the input and output section (I/O).The I/O module integrates the PLC's I/O circuitry, with input stubs reflecting the input signal state and output points reflecting the output latch state.The input module converts electrical signals into digital signals into the PLC system, and the output module does the opposite. The input module converts electrical signals into digital signals into the PLC system, and the output module is the opposite.I/O is divided into switching input (DI), switching output (DO), analog input (AI), analog output (AO) and other modules to control external intermediate relays, solenoid valves and so on.