I’ve been using a Hantek CC-650 current clamp to measure welding current. So the answer probably is , “serves you right, there’s your problem: cheap Chinese rubbish”. And that might be the case, but I wonder if there’s any other reason why my results are skewed as if there’s an inconsistent DC Bias.
I let the clamp warm up, zeroed it a couple of times, checked it read zero at the start of the run and confirmed it read zero afterwards (with no current). Bur the zero Amp axis seems to be way out and not consistent in that another run might give different results.
The zero axis should be where I have placed the top horizontal cursor, giving a symmetric waveform. But the displayed zero axis is where the bottom cursor is. So the waveform is lifted up by some 40A.
I have a 20A Fluke clamp and, though it clips at higher amps, it has confirmed beyond a reasonable doubt that the zero amps axis should be right down the middle of the waveform.
Any ideas? I switched from DC coupling to AC, and, of course, that had no effect. So other than being advised to only use decent hardware in future, is there anything I could be overlooking?