OK. I accept everything, and take back my suggestion.
We can simply tell the students to copy the hardwired diagram, with both N/O and N/C switches represented by N/O contacts, and use actual switches (i.e., N/O or N/C types) for PLC inputs.
Actually, the best thing would be not to think in terms of hardwired diagram. A PLC program should be viewed as a computer program, even though initially PLC was invented to replace relay logic.
The concept of internal relays associated with each input and output is the right approach. This has already been explained in this thread.
Am I right now?
