I'm measuring inrush current with a current probe ( tektronix P6303) that is connected with an amplifier between, which is powered by an AC line before it's connected to an oscilloscope.
I got some struggle with my measurement so I changed oscilloscope to another oscilloscope of the same model, suddenly I realized that despite the setup is the same it gives totally different result in amplitude and shape.
So I changed the power cord between the oscilloscopes with the result that they displayed the same result as the other part did before the change.
After this I rotated the contacts in the AC line with the result that it for one oscilloscope resulted in half the amplitude still same shape and for the other one another totally new shape.
There is only one possible earth loop and it's between the current amplifier and the oscilloscope not against the DUT. I can't really see why it in this case should matter that much.
Have anyone else experienced this before and how did you proceed to get a "true" measurement?
I inserted a isolation transformer to the osilloscope, in this config it seem to give a consistent result, even if I change the power cords rotation and oscilloscope. Maybe I've found a solution.
Current inrush Measurement with isolation transformer
White = with min voltage
Yellow = with max voltage