[volt-nuts] High precision calibration for the poor man

[Marvin E. Gozum]

IMHO if you are not calibrating these devices officially for an 
organization [and thus need strict procedures to pass] you needn't 
really adjust the 5500a to output 10.000 000 Vdc.

What is most critical is a output voltage stable enough to complete the 
test procedure, sufficient for the range under calibration such as a 1nV 
if required, and an equally good calibrated meter, such as 3458a, to 
confirm that.  You adjust your DUT to match the readout of the 3458a. 
Your DUT is effectively calibrated against the 3458a.

A good DMM is linear throughout its ranges, and a measurement taken 
beyond the recommended calibration voltage can be extrapolated anywhere 
in the range under test, and should measure 10.000 000V when given such 
a voltage even if adjusted at 10.000 0073 V.  Luckily calibration rarely 
involves adjustment but just comparison of readings against a reference, 
in this case the 3458a.

I fear that if you made some circuit to reduce the voltage without 
confirmed testable precision, that you'd risk more inaccuracy that if 
you simply take the stable output of the 5500a confirmed against the 3458a.




On 10/20/2010 5:54 PM, Samuel DEMEULEMEESTER wrote:
> Hi guys,
>
> I love your level of knowledge and I would like to get your thought about a
> way to achieve a calibration of a high precision meter without a high
> precision calibrator. Let me explain myself. I have many 6.5&  7.5 digits
> meter and only two calibrated and certified tools: a Fluke 5500A calibrator
> and an HP 3458A meter. The 5500A is very stable but can only achieve 5.5
> digits precision. The idea is to source a known stable voltage with the
> calibrator, then use the 3458A to correct (lower) the offset in order to
> feed a 6.5 or 7.5 digits meter in calibration mode.
>
> Example : I need 10.00000V +/-  25µV. I set the 5500A (or any other very
> stable voltage source) to 10.0000V. I get 10.000073V, according to the
> known-good 3458A. I’m now looking for a very precise way to step-down the
> voltage (-70 µV) in order to achieve the rated accuracy needed to calibrate
> the meter. That accuracy doesn’t need to be maintained for more than one or
> two minutes.
>
> Is it a stupid idea? What can I use to add a very small and very stable,
> variable negative offset to a known voltage? A variable resistor should not
> be able to meet the required accuracy without a drift. So, perhaps a high
> precision aop ?
>
> Any idea greatly appreciated :-)
>
> ---------------------
> Samuel DEMEULEMEESTER
> Presse Non Stop - Canard PC
> http://www.canardpc.com
> Tel : +33.6.13.73.4003
> MSN : sam at x86.fr
>
>
>
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