spark controller dropping voltage in reverse

[Ether]

Originally Posted by dlsmith

I don't recall for sure the models but we tried a couple of different meters. I think one was a Fluke. While it was measuring you could see that it was trying to "lock onto" the signal somehow (showed moving bars constantly) and it wasn't doing a good job averaging the voltage I suspect. Could be that we didn't have all the right modes selected as it seemed like "average voltage" should be possible somehow.

With a cheap $3 DVM from Harbor Freight I am able to accurately measure the PWM signal voltage and the PWM output voltage. So I would imagine your Fluke (a very reputable brand) ought to have a way to do the same.

Cheap DVMs use averaging; expensive are selectable averaging or true RMS.

Cheap DVMs on AC scale use a diode to rectify the signal, average the rectified half wave, and then multiply that by some fudge factor (based on an assumed sine waveform). It works OK for sine waves but gives nonsense readings for square waves or PWM.

Expensive DVMs (your Fluke might be one such) with true RMS do not assume a sine wave, do not throw half the wave away by rectifying, and can measure the actual rms value of any periodic AC waveform (within reason).