how do you calibrate a dvm with 6.5 digits?

[J-R]

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.

[TheDefpom]

Unfortunately, all three of the top references/standards that I would suggest for a typical hobbyist to consider are currently out of stock:
https://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-2-mini-detail

I believe Ian is currently building some more PDVS2 Mini's so he may have stock soon, he did a video on it the other day.

[tautech]

Unfortunately, all three of the top references/standards that I would suggest for a typical hobbyist to consider are currently out of stock:
https://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-2-mini-detail

I believe Ian is currently building some more PDVS2 Mini's so he may have stock soon, he did a video on it the other day.

I hear he might be short of caps after he sent a booby prize package to you. 

[TheDefpom]

I hear he might be short of caps after he sent a booby prize package to you. 

I still need to sit down and start sorting those out...

[Tony_G]

I need to revisit my TEA cred, I haven't tried to acquire one of Ian's standards because I had the DMMCheck (along with an uncalibrated 5200A & a working 5440B).

I still need to sit down and start sorting those out...

Should probably get onto that, assuming you haven't run him out of the "Cap Game" DefPom.

TonyG

[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. 

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.

[David Hess]

I have been thinking of

https://voltagestandard.com/shop/ols/products/pentaref

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]

It only goes up to 10V, not sure how you plan to scale it up to 100x.

Easy! You buy 100 of them and connect them in series.

[David Hess]

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.

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.

[GigaJoe]

yeah been there ... any instability multiplied by x100 ,  self- heating divider sucks even with 10ppm resistors,   noise  multiply by x100  ... need rare capacitors at least 600V in serial ...

im end up to build 2 fixed sources on 250V and 2 variable 90-200 , 250-350,   so you can connect in ser and adjust

in overall cheapest solution - get a trusted one , ask performance paper, no adjustment, then do value transfer adjusting against performance report. so target is - to acquired \ build all necessary sources for value transfer.

[J-R]

Fully calibrating/adjusting any DMM is no trivial task as you'll typically need access to high voltage AC and DC signals.  The path I've taken frequently is to use another DMM along side the DMM that needs calibration/adjustment and then carefully dial in the source.  For example, I recently needed 1kV DC, which required about an hour of tinkering and waiting for the Spellman DC-DC converter to stabilize, then within about a 5 second window I quickly stored the calibration point while observing the value on another DMM that I had calibration data for.  The results are acceptable for a hobbyist, not so much for a volt-nut perhaps.

For AC, I use a function generator with a transformer.  When that limit is reached, I've been known to insert an amp in between to push the voltage higher.  I recently acquired some additional custom transformers to see if I can get better results especially for higher frequencies.

I have also acquired some vintage gear that has helped with providing stable sources.  The Fluke 515A is pretty handy, although one issue is that it has reduced specs when using a DMM with a 10M input.  Another nifty bit of gear is the Advantest R6144.  Both took many months of searching to find at a reasonable price point.

[coromonadalix]

when you have many meters, you make one calibrated and serve as a reference   ...

but if you do serious stuff  .... other than hobbyist   

you know what to do even if its costly ...

[David Hess]

yeah been there ... any instability multiplied by x100 ,  self- heating divider sucks even with 10ppm resistors,   noise  multiply by x100  ... need rare capacitors at least 600V in serial ...

If the resistor temperature coefficients match, then a string of resistors can be used in an isothermal environment to improve tracking.  Using a string makes sure that the voltage and current of each resistor is the same.  If the voltage and current is the same, then the power is the same and the temperature of each resistor should be the same.

If the voltage coefficients of resistance match, then the resistor string can be tested and verified at low voltage.

Noise and instability would be multiplied in any design using a low voltage reference.  In a good design the noise and drift from the reference dominates, so that means using a better reference, like a buried zener, or multiple references in series/parallel.  While that would be nice, I could change the reference later if it is a problem.

[GigaJoe]

I'm really had no idea how it goes, so such high voltage source was my first attempt to  learn things.   at first shot it more less acceptable.  would be great if would be some discussion about.