[time-nuts] V standards

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Nov 30 01:39:29 UTC 2008


Mike Monett wrote:
> 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




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