Hardware vrs Software Safety Resets

I have some AB saftey relays. The main system has all of the estops wired through the safety relay with a hardwired pushbutton to reset the relay. This kills the power to all drives when the estop is pressed. No problems here.

There is some support conveyors that also go through its on safety relay. At first it was wired to auto reset.

It now been changed not to auto reset. The operator has to push the fault reset on the PanelView and then restart each conveyor from the screen as needed.

Does anyone know if this setup is OK as far as standards go using a software reset vrs a hardwired pushbutton?

I don't know why at first the support conveyors where set to a auto reset. One of the inverters died and right before I heard a pop in the cabinet, the safety reset chattered a bunch of times and I think this blew on of the inverters.

Hi there,
I think the present setup is better then the previous one.
Because if emergency has been pressed then the cause for it needs to be diagnosed before resetting the relay. Auto resetting wont allow this. Also alarm will get registered in Panel view allowing maintenance personal to view the exact time of occurrence of fault/emergency stop.

Resetting the relay through Panel View/PLC is I think have no safety issue, but tripping of safety relay should not have any software element in it. Only thing is Panel view should not loose communication in case of emergency stop for obvious reasons.

Resetting safety relays with a PLC output is perfectly acceptable. The auto-reset of a safety relay should be addressed in the risk assessment of the machine/process; sometimes its fine, sometimes it can create an unsafe condition.

Your safety relay should reset on the falling edge of the reset pulse (most do, including the AB safety relays). That means that your PLC will turn the output on, then turn it offa, and safety system resets as it turns off - so you have confidence that the reset device, whether it is a P.B. or a PLC is functioning. I prefer having the PLC do the reset, even if the logic amounts to little more than output:=input so that the estop system cannot be reset if the PLC is not functioning.