If your system had four such inputs, then the wiring diagram would again show an array of input devices displayed in ladder fashion. But this time, they wouldn’t share L1. Instead, each would be ...

If you see a different reading, there may be a problem with the input device, the wiring, or the PLC input module. Add your perspective. Help others by sharing more (125 characters min.) ...

If they do, the problem is on the processor side of the input module. Next, watch the PLC logic for a corresponding change. If it doesn't happen, then the signal isn't making it from the input module ...