Seeking help with AB PLC issues
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The AB PLCs used in the oxidation furnaces on site have been in use for many years without any problems. Recently, however, two control valves have shown significant fluctuations in their performance, and the actuator of one of these control valves keeps burning out. Control valves use a current of 4–20 MA. There are fluctuations in the current measured at the PLC’s output terminal. The 4-output module was replaced just last year. I would like to ask the experts: what could be causing this? Is it possible that there is a problem with the channels on the PLC’s backplane?
It is recommended to add an isolator or safety barrier to this circuit.