Ground potential difference

[gary36]

I have a system consisting of two PCBs connected via Flat ribbon connectors. Checked the continuity of the ground and it is ok. Resistance is around 0.6 ohms. When I power ON, I see that there is 100mV potential difference between the two PCB grounds. What could be the reasons? I am unable to post the layout or the schematics at this point of time. I would highly appreciate if someone can explain the potential reasons, why the ground might lift up?

 

[betwixt]

Possibly there is 166mA flowing along the ground wire. Ohms Law says V=I*R so 0.166A * 0.6 Ohms gives 0.1 volts.

If power return is also along the same ground wire it is entirely reasonable to see that much voltage. To measure 0.6 Ohms accurately you would need a four-wire measurement so if you used a normal DVM I would be suspicious about its accuracy.

Quick check - temporarily add a second similar sized wire in parallel with the existing ground wire, if the voltage halves it would prove it was nothing more than drop along the resistance of the wire and connectors.

Brian.

 

[gary36]

Hi
Tried your method but mysteriously the problem does not disappear. It remains the same.

 

[KlausST]

Hi,

Then I guess there is soemething that you did not tell.
Show us a photo of the situation.

Klaus

 

[Easy peasy]

You may have higher frequencies present upsetting your DVM reading - put a scope on it - and reference to one point only ....