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turbokinetic · Junior 2 Joined: 21 Oct 2012 Posts: 23

Got a question. We have a PLC which uses the 1756-IB16D modules for input. One circuit is getting spurious signals which are causing it to see an input "on" when it should not be on.

I am trying to determine if an excess of leakage current is coming through he device providing the signal to the PLC. The device providing the signal is another electronic module. We are going to see what the voltage is at the input channel, in the off-state.

What I can't find in the Rockwell documentation is the actual threshold voltage where the input channel "sees" an "on" state. I would expect somewhere around 8V based on other experience, but I would like to know from someone who has tested. I'm not at the site and can't do a test myself.

This system has worked fine for about 2 years and this problem has gradually cropped up and become more frequent as time passes. It seems like something has shifted in value and is now hovering right around the on-state sensing threshold for that channel.

Thanks in advance for any information.
Sincerely,
David