Products > Test Equipment

Easy way to test the calibration of a DMM (Fluke 45)?

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shabaz:
"but don't suggest anything further."

I don't see that I suggested anything dangerous. I caveated each time that one cannot rely on it as a calibration.

shabaz:
LM399 has low drift hence the price, but there are other ICs with higher initial accuracy (higher drift). REF50xx could be an option (sub-$5) that would easily determine if a meter had a 20mV discrepancy (at the spot(nominal) voltage of the chip).

shapirus:

--- Quote from: J-R on April 02, 2024, 11:21:03 pm ---So it's more dangerous to have one than not. Fine, if you're bored and want to play around with them go ahead, but don't suggest anything further.

--- End quote ---
As usual, they may be useful if you know what you're doing and understand the limitations.

For example, I bought one of those Chinese LM399 boards and measured it with my then freshly purchased Brymen BM869s and used that measurement as a reference point. They still stay in agreement today, after 3 years or so, which may mean one of: a) neither of them have drifted; b) they both have drifted by the same amount. By comparing this to my other meters I conclude that the former is much more likely, and that's more than good enough for my hobby. Of course I'd like to re-measure that LM399 thingy with a more precise meter, but I don't have access to any.

The important point here is that I had a known-good meter to compare that reference against.

In the case of two meters, neither of which is known-good, such a board wouldn't work, especially given that there are reports of bogus values on the stickers that some people received, especially when those stickers are printed. Mine was hand-written, which kinda invites to trust it a little more.

KungFuJosh:
Here's some simple solutions.

Buy a $20 ref, and pay $100 (plus shipping) to have it calibrated (after hundreds of hours of runtime to confirm stability).

Or buy a $140 ref that comes calibrated and reliable.

Or spend a lot more money, build a ref yourself, and still need to send it out for calibration (after hundreds of hours of runtime to confirm stability).

Or just send both meters out for calibration. Simple. 😉

Fungus:

--- Quote from: CalibrationGuy on April 02, 2024, 09:24:52 pm ---No, I'm not missing the point. Without traceability, those numbers mean NOTHING. I have friends who have boards like these and the numbers were the same for every board. Your usability claims have no credibility because there is no verification of said values.

--- End quote ---

OTOH lots of people have a good one where the numbers are good.

eg. Me. I've measured mine on a few different high-end multimeters and the numbers seem good to at least three decimal places.

Traceability or not, that's very unlikely to be luck.

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