Anyone got any good ideas for testing long circuits of input devices connected in series? A customer has a problem with something in a long string of devices tripping their plant, but doesn’t know which one is causing it - they only feed the final connection into the PLC, not each individual device. It’s an intermittent problem which makes testing really difficult.
I thought at first of testing continuity at the mid-point of the line to see which half contained the tripped device, but I realised this would effectively short out half of the devices, so I couldn’t do this when running - this is a safety circuit. I then thought of using spare terminals on each relay (if available) to wire a second loop and do the testing on that, but that would be very time consuming to install.
Any other approaches I’m missing?