M
I would like to hear opinions regarding placing an "master power" control relay in the supply path to a PLC output module.
The PLC in question is an Allen Bradley PLC 5 utilizing a number of discrete (not relay) output modules. The racks (1771) are set up to fail off. An associate claims that the plc can "stop processing", as opposed to fault, etc, and leave outputs set. Thus the need for an emergency power disconnect relay in the supply to the module.
I have created every type of recoverable plc failure I can think of and all outputs always go off, both in the local rack and in associated ControlNet connected remote racks. I recognize that a failed output channel (shorted) could leave an output active. I also recognize that there is potential for failure of the added "protective" relay.
Opinions? (flame minimization mode = ON)
Dave McConnell
The PLC in question is an Allen Bradley PLC 5 utilizing a number of discrete (not relay) output modules. The racks (1771) are set up to fail off. An associate claims that the plc can "stop processing", as opposed to fault, etc, and leave outputs set. Thus the need for an emergency power disconnect relay in the supply to the module.
I have created every type of recoverable plc failure I can think of and all outputs always go off, both in the local rack and in associated ControlNet connected remote racks. I recognize that a failed output channel (shorted) could leave an output active. I also recognize that there is potential for failure of the added "protective" relay.
Opinions? (flame minimization mode = ON)
Dave McConnell