safety relays

[firelient 0]

What is the difference between auto / manual and monitored manual reset on a safety relay?  Thanks

[Joe E. 259]

Brief summary...

A manual reset requires operator action to restore operation, like pushing a "reset" pushbutton. An automatic reset will restore operation as soon as the safety channels and any feedback circuits are closed.

"Monitored" means that the reset circuit (whether it includes a pushbutton or not) is wired through feedback contacts on the devices being controlled. This would typically be normally-closed auxiliary contacts on force-guided contactors. If a contactor sticks closed, the aux contacts remain open and the circuit will not reset. Multiple contactors controlled by the same safety circuit will have their aux contacts wired in series to make sure they all drop out. We have also used redundant pneumatic dump valves with feedback contacts.