I'm measuring the 60Hz potential across a 0.1 ohm shunt from a precision AC current source that has a switching power supply. The 3458A is in ACV SYNC, LF filter ON, RES .002, ACBAND 40, 80. I'm trying to verify a +/- 0.25% accuracy specification. The problem seems to be the triggering of the 3458A. The sample light is not stable, so I assume that the DMM isn't triggering at the same point. This is the way I could looked at the potential output of the shunt, with a 10x passive probe/HP 35670A analyzer. The 60Hz harmonics are >35dB down and the switching supply noise is also >35dB down. I've changed the shunt with a better spec'd one. The harmonics/noise dropped >46dB down and the 3458A performed better, but it was not stable enough. Putting a 10kHz low pass filter on the DMM input made the 3458A readings useable. Had similar results using the Fluke 5790A.
I have two questions. Is the harmonics/noise causing the 3458A TARM (?) to be unstable or is it something else? Is there a way for me to raise the trigger threshold, so I can trigger on only the 60Hz?
I have two questions. Is the harmonics/noise causing the 3458A TARM (?) to be unstable or is it something else? Is there a way for me to raise the trigger threshold, so I can trigger on only the 60Hz?