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how do you calibrate a dvm with 6.5 digits?
NoisyBoy:
Of the three standards, I like DMMCheck the best because it checks more than voltage, but other functions such as AC/DC voltage/current, resistance, frequency, and duty cycle as well. I noticed they now have an add-on LC reference module.
This would be my pick for a sanity check reference if I suspect the DMM is acting up. The key is understanding what its name implies - Check, it is a validation reference, not a calibration reference, and definitely not for 6.5 digit meters. But it may be good enough to be used to calibration cheap handheld DMMs with calibration pots.
I like all three suggestions, good picks.
--- Quote from: J-R on May 02, 2023, 03:16:51 am ---Be sure to cruise the Metrology forum. There are a lot of conversations about this topic over there.
My top comment is: don't forget to observe accuracy specifications. For example, with the HMC8012 a 10V DC input could display between 9.9972-10.0028 and still be within the 1 year spec. It also requires a 90 minute warm-up period. So you probably could get away with sanity checking it against a $175USD 50,000 count DMM in this case.
This next thought was mentioned in passing, but start building a small collection of references/standards that you can use to check your equipment regularly. It's better to ship those out than the equipment itself. Only if your test equipment shows evidence of being out of spec would you then have it calibrated/adjusted.
Unfortunately, all three of the top references/standards that I would suggest for a typical hobbyist to consider are currently out of stock:
https://dmmcheckplus.com/shop/ols/products/dmmcheck-plus-without-enclosure
https://voltagestandard.com/shop/ols/products/pentaref
https://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-2-mini-detail
Also, it's good to have some precision resistors for checking resistance functions, but also for various Ohm's law calculations. This can help you generate additional inputs for your equipment in order to check things from different directions.
Used/vintage gear can be popular due to stability from aging. You could mix vintage for stability along with new for modern features like ethernet and big, color screens.
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David Hess:
I have been thinking of
--- Quote from: J-R on May 02, 2023, 03:16:51 am ---https://voltagestandard.com/shop/ols/products/pentaref
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I have been thinking of getting the Pentaref with a set of voltages that I can accurately multiply up to higher voltages like 19 (9.5x2), 190 (9.5x20), and 950 volts (9.5x100) for calibrating higher ranges.
NoisyBoy:
It only goes up to 10V, not sure how you plan to scale it up to 100x. I doubt a 9V battery driven reference will provide you anything stable at higher voltages to reliably check 6.5 digit meters.
Fungus:
--- Quote from: NoisyBoy on May 03, 2023, 08:16:29 pm ---It only goes up to 10V, not sure how you plan to scale it up to 100x.
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Easy! You buy 100 of them and connect them in series.
David Hess:
--- Quote from: NoisyBoy on May 03, 2023, 08:16:29 pm ---It only goes up to 10V, not sure how you plan to scale it up to 100x. I doubt a 9V battery driven reference will provide you anything stable at higher voltages to reliably check 6.5 digit meters.
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I plan to scale it up with a precision high voltage gain stage. A gain of 2 is easy, but there are other higher gain values which are not too difficult. The tricky parts are self heating and the voltage coefficient of resistance of the resistive divider which take place at higher voltages, but for specific values of gain these can be handled.
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