ceilingwalker
Lifetime Supporting Member
Hello. Throughout the years, getting support on this forum, I have always been taught that safety systems such as a process furnace overtemp circuit should be wired outside of PLC control, just in case power is lost, the heating elements would shut down, for example.
I was told in a meeting that it is acceptable now to run these safety systems through a PLC. It is for the circumstance I mentioned above, the overtemp condition, and I want a separate stand-alone controller that will kill power to the heating elements and shut Hydrogen and HF process gas flow. We had a situation many years ago in which case a PLC-5 was controlling a CVD system. It was using a Remote I/O module for mass flow controllers, scrubbers, etc.... . The PLC just died, in the middle of a run, with HF and Hydrogen flowing. It launched our Scrubber like the space shuttle.
I just wanted to get opinions here please, to see if what I am being told is true or false. Have PLC's come a long way to where we can trust it keep human and machine safe, in this overtemp scenario? If my question needs more information, let me know and I will respond. Thank you
I was told in a meeting that it is acceptable now to run these safety systems through a PLC. It is for the circumstance I mentioned above, the overtemp condition, and I want a separate stand-alone controller that will kill power to the heating elements and shut Hydrogen and HF process gas flow. We had a situation many years ago in which case a PLC-5 was controlling a CVD system. It was using a Remote I/O module for mass flow controllers, scrubbers, etc.... . The PLC just died, in the middle of a run, with HF and Hydrogen flowing. It launched our Scrubber like the space shuttle.
I just wanted to get opinions here please, to see if what I am being told is true or false. Have PLC's come a long way to where we can trust it keep human and machine safe, in this overtemp scenario? If my question needs more information, let me know and I will respond. Thank you
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