Hi Owen,

Sorry for the slow reply, I’ve been wrestling with the issue because it seems quite nuanced.

Thank you for finding the issue with 8kHz buffered graphs in the beta firmware, I’ll investigate this.

Regarding the meat of the problem, measuring AC voltages in such a noisy environment: I will repeat some information you probably already know for the benefit of others who might come across this post. The Mooshimeter defaults to 4kHz sample rate and 256 samples to do its AC RMS math. Internally, the low pass filters on the input start to cut off around 20kHz (that number is rough and off the top of my head, but sufficient for this discussion).

The meter who’s datasheet you sent me has filters built in to cut off everything above 60Hz or so (one of the features listed is “Filter to isolate 50/60Hz fundamental from harmonics). Could this be part of the discrepency in readings? The meter you’re used to using shows you RMS of the fundamental, but the Mooshimeter is showing you the RMS of all the harmonics up to 2kHz or so. I recognize this does not address the magnetic pickup issue, but I think there may be multiple factors at play here.

A way to test this might be to manually lower the sample rate of the Mooshimeter, eg. selecting “Voltage AC”, then setting the sample rate to 500Hz instead of 4kHz. This may cause slight aliasing, but the number you get out should do a much better job rejecting all the higher harmonics.

Regarding magnetic pickup – You mentioned zeroing your other meter’s AC reading to compensate for the ambient field (in your May 12 post). If AC zeroing was added to the Mooshimeter, would that solve the issue?

Thanks for the detailed descriptions, sorry if I’m misunderstanding the problem. Screenshots might be helpful if I’m still not getting it. Best
~James