What's digital Voltmeter read for 24Vdc PNP sourcing output when DO is OFF

[danw]

A voltmeter connected from the DO output to the DO common for a sourcing digital output will read close to the DC power supply (less whatever the drop across the transistor is) when the DO is in the ON state.

What's the voltage reading for that same 24Vdc PNP sourcing output when DO is in the OFF state?

 

[Mickey]

I'll bite. It depends on the load.

Very close to zero with an inductive or resistive load.

Slightly less then the applied power source with a electronic load ( led or an input to an electronic board)

 

[bernie_carlton]

Assuming your output card is a solid state (transistor) output rather than a relay (as your diagram suggests) you should remember that a solid state output doesn't become an open circuit when off. It becomes a very large resistance. Thus the voltage seen at the output depends on the resistance of the load.

 

[GaryS]

If there is no load connect to it, it will read close to the 24VDC source with a good meter
you need the load to pull the voltage down. as stated solid state devices leak they are never completely ON or OFF. (semiconductor)
If you using a solid state output to drive a solid state input on another device you may have to put a load resistor in the get it to work. I have run into this quite a few times.

 

[danw]

Thanks. I was thinking it depends on the load impedance.

I'll put a meter on the outputs in a couple days when I'm there.

Dan

 

[shooter]

It can be anything. I have seen snubber circuits over the contact, so it can also be a problem with relaiscircuits.