[time-nuts] V standards

[WarrenS]

Mike

> So my questions to the group are
>1) what kind of things do you do that require high precision in voltage measurements?
>2)  I wonder why extreme accuracy is needed in measuring voltage?

That is two different questions.
Bruce already answered the precision question
I'll make attempt at answering the accuracy question.

Voltmeters with the ability to measure extremely accuracy voltages are 
needed all the time and everywhere to measure the voltages of extremely accurate
things  that are used as voltage standards. These standard are used to calibrate 
and test less extremely accurate voltmeters.
Everything else, including  dace's, bridges, resister testers etc depend on extreme precision 
or accurate voltage ratios not extreme absolute voltage accuracy.
The only other time I know of that you would need any true absolute voltage accuracy is 
to measure a Joseph voltage standard. If you had one of those you wanted to check, 
I guess you'd need a extremely accurate absolute voltmeter,  AND if you saw that your 
extreme accurate voltmeter read something different than expected, you would know 
it was time to have the voltmeter recalibrate, which you could do right then and there.

So to answer your second question, the only things that really requires high accuracy in 
voltage measurements are all the things that are used to calibrate accurate voltmeters. 
Everything else is it would seem is actually done with precisions voltage ratios.

WarrenS
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----- Original Message ----- 
From: "Mike Monett" <XDE-L2G3 at myamail.com>
To: <time-nuts at febo.com>
Sent: Saturday, November 29, 2008 4:27 PM
Subject: Re: [time-nuts] V standards


> This discussion of voltage standards is very informative and useful, and my
> thanks to all who are contributing. 
> 
> It is clear why precise frequency standards are needed - there are
> innumerable applications such as GPS, VLBI, secure spread spectrum radio,
> deep space navigation using doppler, and so on.
> 
> But I wonder why extreme accuracy is needed in measuring voltage? Don't get
> me wrong - I have a HP 3456A, and I would love to have a 3458. But the
> prices on eBay can reach $6k, and I can't see spending that much money for
> two more digits. As Bill would say, six digits should be enough for
> everyone:)
> 
> As well as the HP, I have a number of other DMM's. But the one I use the
> most is a simple 3 1/2 digit Walmart special. You have to switch ranges
> manually, but it provides a reading much faster than the other units which
> are all autoranging. Most of the time, I am concerned with the supply
> voltages. If they are correct, then CMOS and ECL logic pretty much have to
> have the correct swing, and you have to use a scope to see the pulses
> anyway.
> 
> So my question to the group is what kind of things do you do that require
> high precision in voltage measurements?
> 
> Regards,
> 
> Mike Monett
> 
Mike

In testing high resolution DACs (20+ bits) used in GPSDOs etc a high
resolution DVM (or equivalent) with low noise and good short term
stability is useful if not essential.
Monotonicity and perhaps linearity together with good short term
stability are generally more important than absolute accuracy.
Higher resolution is usually accompanied with higher accuracy.
DVMs like the 3457A. 3456A etc dont have sufficiently low noise or good
enough short term stability for testing DACs with 24 bit resolution.

Bruce