[Observium] Alert question for Cisco Nexus FEX PSU

Hello

Last night one of our Cisco Nexus FEX's PS went down and i realized that we don't have alarm to check the status of the FEX's PS.

I would like to write one. I found a graph about this fault PS. Normally the value 2 but after that is went to fault state the value is 4. I attached the picture.

So the question is in this case what is Entity Match that i have to use? I tried this but it doesn't work:

sensor_value equal 4 hostname match *sw* sensor_class equals PowerOperType

The "PowerOverType" came from the attached picture RRD name (it was just a try :) Or what is the normal way to find the sensor name for the alert?

Thanks

BR Laszlo