EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: GregDunn on September 07, 2018, 07:39:34 pm
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Rather than clutter up the TEA thread, I thought I'd make this separate. It's really nice having a handful of DMMs when troubleshooting; just last week I was fixing an audio amplifier and needed to simultaneously see line voltage (variac), PS voltage, channel DC offset and bias current. Seriously, something was defective and if I didn't monitor everything, it would have been way easy to fry something in the input diff amp stage - I did actually cook a resistor because the current got too high on one stage while the others looked within spec, so another DMM went on the test point there to monitor it. At one point I realized I had ALL my DMMs connected! Anyway, I found the problem (bad cap) and all is well.
So while cleaning up the bench and getting ready for another project, I thought perhaps I should just do a spot check on my meters - I had them all out anyway, right? I know I don't have a cal source, but even relative accuracy is good to know about. I ended up testing with two separate power supplies: an old kit 5V analog supply which is pretty stable and quiet, and my newly acquired HP6236B. Results at 5, 10, 20 and 40VDC were comparable, so I'm just showing the 5VDC test.
Interestingly, ALL the Fluke DMMs tracked beautifully (the 73 iii is not shown because it honestly didn't have enough resolution to compare with the others, but it was OK within the digits it was capable of displaying). I calculated about 0.02% difference among the 3 of them, even at the 40VDC level. The BK read a little lower, then the Dana, and the Ideal still lower but only about 0.1% off the Flukes. Of course, I have no idea which (if any) are close to being accurate, so the Ideal may well have been spot on. :-DD
The point being that they're all close enough to each other for what I'm doing. I'd love to have some kind of traceable reference just out of curiosity, but frankly it wouldn't affect my use of the instruments. I suspect, but can't prove, that they're all within spec or darn close - but as I said, the correct voltage may have been significantly higher or lower than any of them showed. My opinion is that the Flukes are closest, but that carries no weight in the real world. ;)
Meanwhile, the search for a reasonably priced cal source continues, because I'd just like to know...
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https://www.eevblog.com/forum/testgear/group-buy-proposal-voltagestandard-dmmcheck-plus/ (https://www.eevblog.com/forum/testgear/group-buy-proposal-voltagestandard-dmmcheck-plus/)
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Looks like they sold the last batch already, but I'll show my face in case Malone decides to make another run...