[volt-nuts] Traveling Standards - Measuring Protocol

[Bob Smither]

WarrenS wrote:
> Bob
> 
> First I'd like to say that what your doing is a great idea and could be 
> a great benefit to the Volt nut group.
> Now for some comments that I hope you will find useful to get the most 
> from this exercise.
> 
> I'm still hoping you will post more details and if need be get 
> suggestions for the measurement that YOU should make before sending the 
> TS out.

Good point - I am very open to suggestions about what I should do to 
characterize the TS before it is shipped around.

> When doing short term stability testing better to do it at a Higher 
> resolution than 1.7 PPM / count.
> One way to do that is to put your 6 digit voltmeter on the 1V or better 
> yet,
> the 0.1V range and measure the difference between the Device you're 
> testing and
> a similar stable non-effected voltage such as a second device of the 
> same type that is not being subject to the things you're testing for.
> Then taking into consideration that noise measurements are the RMS sum 
> of the two devices and Drift measurements are the Difference between 
> devices,
> it is possible to greatly increase the accuracy of the measurements.
> 
> Also very useful to measure the actual Temperature Coefficient of the 
> devices so that the temperature readings have more meaning.
> 
> When evaluation precision voltage references,
> I find it very helpful to make a High Resolution strip chart recording, 
> be it Analog or Digital,
> Preferable showing Both temperature and voltage.
> For an example of how I get much better than 0.1 PPM resolution using 50 
> year old technology,
> See attached plot comparing two 10 volt devices, using a slow, dual 
> channel analog Rustrak recorder and Fluke 845A/B null meter
> 
> Just my two cents worth to the bigger picture.
> It is hard to properly evaluate a precision Voltage source unless you 
> first know the measurement uncertainties 'aka noise' including any 
> Temperature Coef.
> AND if the temperature coef is known and not zero (over the measurement 
> temperatures), why not add a simple compensating voltage to reduce the 
> effect of temperature to insignificant levels?

Hi Warren,

Thanks for the great suggestions!  I will follow up on them as I have 
time.  Looks like my plate is pretty full on this project:

1.  Repackage it to avoid being visited by the Gestapo :-).
2.  Wire up a second LM199AH for the offset measurement.
3.  Measure the TC of both LM199AHs using difference technique.
4.  Measure the TC of the MAX6350 using difference technique.

I will be working towards the above.  In the meantime I will post some 
very preliminary TC measurements (not high resolution) when they are 
completed.

Best regards,

Bob Smither

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