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Isolated ground with 6528


I've got following problem:

I want to use an output of my Ni 6528 card for swithing on vacuum valve. So... I've connected a relay to one of the output of my card, just so as it is on the picture(then the relay swithes next circuit with 24V vacuum valve). 19825iEDF7E4DB6EF989EF

Now, the documentation of the Ni 6528 shows follownig circuit with an isolated ground:



I am not sure if by connecting 0V om my power supply, there is already isolated ground connected to PX.Y- or not? How can I check it, or what would be "isolated ground" in my circuit?


As powersupply I use this

24V 9A


As the relay I use Finder relays 55.33 series :


I've observed recently(unfortunatelly), that one of my outputs is demaged and it doesn't work any more. I am not sure what is the reason of this. The current of the coil of the relay is much lower then 150mA(what is when the relay swithes on?). 6 other outputs with same relays works fine. I will appreciate any hints. Many thanks in advance for your help.





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Dear Martin,


yes, connecting your source as you described should be OK. The isolated output means that the sources are different and are not connected. The ground is isolated as long your power source is not connected to the same ground as your card. As described in the datasheet of your power source, the outputs are isolated, so they are not connected to the ground of the electrical system. Basically, the output acts as a relay (as mentioned on page 18 of the documentation you referenced).


As for your second question, I am afraid I cannot help you without further information. Did problems with the output appear before your current application? Have you tried using the output in a different application or measuring its voltages? Have you tried changing the used relay? Have you tried measuring the current for both on and off states?


Sorry for the late reply, I hope I helped you and I am looking forward to any further questions you might have.


Have a nice day!

Zenon Kuder
Applications Engineering
National Instruments
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