BCMaint (Customer) asked a question.
Question on SC bits
I'm planning to use a click PLC to control water pumps. These pumps are critical to the operation and losing them could be catastrophic. I have two questions.
!. If I use the NC contacts on the C0-04TRS and the module fails, will the pump contactor still pull in?
2, If the module fails, does the SC20 bit turn on?
A lot to consider since "losing them could be catastrophic".
As far as question 1. If the "module" fails, meaning the relay contacts are bad (relay energizes but contacts do not pass current), then , no, the contactor will not pull in thru the N.C. contacts. If the "module" fails, meaning the PLC logic, or I/O communication, fails to energize the relay (and module relay contacts are good), then, yes, the N.C. contacts can pass current, and pull in the contactor thru the N.C. contacts, assuming other components (fuses, circuit breakers, other contacts, contactor) in the circuit are functioning normally
.As far as question 2. If the "module" fails, meaning PLC CPU cannot communicate to the module via the I/O communications, then, yes, SC20 will turn on. If the "module" fails, meaning the relay contacts are bad, but I/O communications are functioning normally to energize the relay, then no, SC20 will not turn on.
But other feedback inputs to the PLC can trigger an alarm if the contactor does not pull in, and run the pump, and generate pressure and/or flow. For example: flow sensors and/or pressure sensors, depending on the application. Also redundant backup systems could be installed to assure water flow. You can add as many inputs as needed to indicate the exact problem.