I received a call from and old friend who is trying to get his system up and running. His company recently updated an older PLC to a new PLC. He stated that the wire logic is Negative logic. The problem he is trying to resolve is that the sensors that count the items continue to burn up and in a random order...not the same sensor each time...A total of (5). These sensors send the negative input to the PLC and receive a constant (+)24vdc. There is no fuse or surge within the system other than the main breaker. He also mentioned that they replace some of the ice cube relays a lot that are 120vac that run the stepper motors. My first thought was to advise him to put in some sort of surge and fuse the sensors minimally. My main concern would be to discover where the over-current is coming from? Do you guys have any recommended trouble shooting ideas I could pass along to him to try and find his over-current? I also believe that the new PLC is just a coincidence unless something got mis-wired. Not sure how to advise him to continue his trouble shooting effort. Any ideas would be appreciated.
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