Electronics > Beginners

How do i calibrate my multimeters!

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Kleinstein:

--- Quote from: CatalinaWOW on August 15, 2018, 02:42:28 pm ---A tenth of a volt is marginally good enough to prevent overcharging/depletion.  Not good enough to evaluate balance.

--- End quote ---

For balancing it is about resolution, not accuracy. Even the cheap meters read 19.99 volt and thus 1/100 of a volt. For balancing there is not need for calibration.

For those cheap meters it is usually not worth doing an adjustment: usually they are OK with there moderate accuracy (e.g. 0.5% range). If for some reason they are significant off, chances are that there is a real damage and even after adjustment they would not be reliable (not even to the low levels one can expect from a cheap meter). So unless needed for business reasons there is hardly a need for calibration for the cheap meters. Even than calibration would be a check to see of they are still well within specs - if outside, buy new. Just from the money one might even consider to buy new instead of a calibration.

iMo:
It could be the owners of the cheaper multimeters (ie. those $5-$40) are looking for some easy way to check whether their gear actually works. Something like the volnuts do here - they spend years playing with their LTZ1000 stuff, but much faster end cheaper.

Maybe for those "normal cheapo dmms" there is a hint like "do stab two nails made of copper and steel into the lemon, wire the nails to your multimeter, and you should see 0.9453 volts at ambient temperature"  :) 

In fact, I did it few months back - I found a few REF01s in my junkbox (3 legs left, last time used mid 80'), I picked one, wired to 12V and looked at its output with my 3 cheapo multimeters. They showed 9.99, 10.01, 9.99..

mcinque:

--- Quote from: hugo on August 14, 2018, 12:05:47 am ---That would cost more than the two meters combined. ;)

--- End quote ---

In reality it is quite cheap.
For the calibration of a $100 DMMCheck, a $6.500 value device is used.
To calibrate a $300 Rigol DSO, more than $20.000 value devices are used.

rhb:
10 new Rayovac American made alkaline AA cells measured with an HP 34401A.  The meter was  checked with a DMMCheck Plus and reads about 60 uV high. This 34401A  has not been calibrated since it left the factory.  The string in the CAL menu reads 21 August 1995.

1.62424
1.62470
1.62537
1.62462
1.62383
1.62513
1.62546
1.62509
1.62442

So there's a zero cost voltage reference accurate to better than 0.1% if you use one cell which is entirely adequate for calibrating a 3.5 digit DMM.  Ten cells in parallel will reduce the error to around 0.03%.

The 34401A was in 10 Meg input mode.  The cheap Harbor Freight 3.5 digit DMMs have a 1 Meg input.  In this case it doesn't matter, but I have had to correct for it.  This DMM is an older model of the ones they give away.  You can read more about those here:

https://www.eevblog.com/forum/testgear/habor-freight-giveaway-dmm-test/msg1473132/#msg1473132

After setting the trim pot using the 5 V output from the DMMCheck Plus, a 1.62509 cell read 1625 mV on the HF DMM and a cell which read  1.62409 on the 34401A read 1624 on the HF.

I had one cell I pulled from the package which read 1.57382 V  which likely was a cell which was used very briefly and then found its way back into the package with the new cells.  The HF reported it as 1574 mV.

Q.E.D.

N.B.  The list on a 3458A is $9993 and the basic annual cal runs $612/yr with an agreement and $649 without.  A primary standards cal with a Josephson junction array is $1789.

joseph nicholas:
If you're worried about thermal drift over time just buy a new cheap ass DMM every year and compare it to your old cheap ass DMM.  No problem.  Save all the DMMs and keep comparing them until you feel confidant that you have one that does what you want.  This is the perfect way to becoming a volt nut.

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