PLC Fault Routine in CompactLogix

[Tweeker]

I am using a CompactLogix system and our customer wants to turn on two devices by default should the PLC fault. Can a Fault Routine turn on an output when the processor faults? How long will the output stay on if so?

 

[DBLD99]

Would only be one scan, So you would have to latch the outputs.

 

[Steve Bailey]

Have the PLC output control a relay. In the PLC logic, keep the output on at all times. When the PLC stops, the output will turn off. Use a NC contact from the relay to energize the two devices you want to turn on. If the devices are anything more than simple indicator lights, make sure there is some way to turn them off regardless of the state of the PLC.

 

[daba]

Steve Bailey has suggested a workable solution, but in answer to your post, it is not possible for CompactLogix to turn an output ON if the processor faults. If the processor faults, or communication with the controller is lost, then the output modules will turn all outputs OFF

ControlLogix output modules have the option to turn OFF, retain last state, or turn ON, for each output channel, but not CompactLogix output modules.

The given approach seems to be the best solution - hold some outputs true with an unconditional rung, and if the processor faults the relays will drop out. Use the n/c contacts on the relays to drive the "outputs" that must come on. When the processor restarts, the relays will be energised again, and the n/c contacts will open.

 

[jdbrandt]

Steve Bailey has suggested a workable solution, but in answer to your post, it is not possible for CompactLogix to turn an output ON if the processor faults. If the processor faults, or communication with the controller is lost, then the output modules will turn all outputs OFF

ControlLogix output modules have the option to turn OFF, retain last state, or turn ON, for each output channel, but not CompactLogix output modules.

The given approach seems to be the best solution - hold some outputs true with an unconditional rung, and if the processor faults the relays will drop out. Use the n/c contacts on the relays to drive the "outputs" that must come on. When the processor restarts, the relays will be energised again, and the n/c contacts will open.

Actually, the 1769-L16 has the "output state in fault" option on its embedded I/O.
And, technically speaking, the 1769-L16 is a Compact Logix.

 

[daba]

Actually, the 1769-L16 has the "output state in fault" option on its embedded I/O.
And, technically speaking, the 1769-L16 is a Compact Logix.

There's always one.... lol (or maybe more...)

Perhaps I should have said "If your chosen Logix5000 Output module allows it, you can ........."

 

[jdbrandt]

There's always one.... lol (or maybe more...)

Perhaps I should have said "If your chosen Logix5000 Output module allows it, you can ........."

Yeah...I get that a lot.