Products > Test Equipment
Easy way to test the calibration of a DMM (Fluke 45)?
shabaz:
"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, spend $5! and not send it for calibration, nor wait hundreds of hours (a ridiculous suggestion) because it will immediately tell you which of the two multimeters has the 20 mV discrepancy. Then, you know which multimeter might actually be functioning, and you can send it for a cal, at less than the cost of a calibrated reference.
shapirus:
--- Quote from: shabaz on April 02, 2024, 11:30:20 pm ---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).
--- End quote ---
Now, this lengthy discussion has finally produced a second result that may be useful not only to the OP.
To answer this:
--- Quote from: Fried Chicken on March 30, 2024, 04:42:41 am ---Are there any reliable around-the-house ways I can test these multimeters? Reliable resistors? Pencil lead? The nicest resistor I have laying around?
--- End quote ---
REF50xx is specified (standard grade) at +/- 0.1%, which is, for REF5050 that outputs 5V, +/- 0.005V, which is almost good enough for the initial problem. If we get a high grade type (the "I" suffix), then precision is 0.05% which I think gets rid of the "almost".
This can be considered, I think, an acceptable solution for an in-house basic verification of DMMs to what, say ~10 mV uncertainty? Doesn't sound too bad!
Is there anything better than REF50xx and still reasonably cheap?
shapirus:
--- Quote from: Fungus on April 02, 2024, 11:34:35 pm ---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.
--- End quote ---
Yeah but still you don't know if you received a good one or a bad one until you measure it with a known-good meter. That was the point. Once you do such a measurement, whatever its accuracy is, you have a decent reference point (of a long-term stability that remains unclear though) with about that accuracy. But if you don't have a known-good meter to do it, then the reference is useless.
shabaz:
I've not kept up-to-date on the latest reference chips unfortunately, but I do have a few REF50xx parts here (not kept sealed though, they are a few years old), I could check a few samples of them, if a lashed-up circuit would in practice have that accuracy, I think there's a chance they would, those are excellent chips for ADC references. I could check at 4.5V and possibly 2.048V (I think those are the ones I've got). But there may be better chip options than this at a similar price.
Fungus:
--- Quote from: shapirus on April 02, 2024, 11:46:02 pm ---Yeah but still you don't know if you received a good one or a bad one until you measure it with a known-good meter. That was the point.
--- End quote ---
Correct, but what's the worst thing that could possibly happen? That you have to return it?
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