Weird DMM experience

Last night while I was hacking together an adapter from a 6 pin header to wires to a SOIC test clip, I was using my Fluke 179 in ohmmeter mode to check that I’d made the connections I wanted to make and not the ones I didn’t want to make. I’d put the probes on something right after I’d soldered it, and got a steady -0.2 ohms.

I was surprised. Seeing a negative value in the ohmmeter mode usually means there’s voltage in the circuit. I shorted the probes together and got a less-surprising 0.4 ohms or something like that. Then, when I put the probes back on the connections under test, I got a similar, small positive value.

And then I realize what had happened: while the connections under test were cool enough for the solder to be solid, things were hot enough to be noticeably exhibiting the Seebeck effect, like thermocouples intended for this purpose.

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