It probably isnt the right forum section, but I wasnt sure where to post.
I recently did a retrofit of an old ABB plc with an s7-1200 with ET200s. The ABB plc had quite a few inductive proximity sensors, oparating at 110Vac. As there arent available input modules with 8DI at 110Vac, I did the following: I wired the proximities to a relay (Relpol RM85 or RM84 if I can recall correctly), and I then wired the relay contact at the 24Vdc inputs of the ET200s. After about 2 weeks I get the following fault:
The only two IFM proximities, SOMETIMES fail to triger the relay and subsequently the input of the ET200.
I havent been to site yet to determine if the problem comes from the contact or if it comes from the coil. Replacing the relay though solves the problem.
Now Is it possible that the contact is damaged? The plc input is not a great deal of a load, nor it is an inductive load.
Is it possible that the IFM proximity sensor damages the relay coil? All relay coils have an overvoltage limitation (Relpol M93R I think) and LED.
Any help will be highly appreciated.