[time-nuts] V standards
Predrag Dukic
stijena at tapko.de
Thu Dec 11 14:25:37 UTC 2008
John,
Yes, that is a common practice. Both scale factor TC and balance TC
are inside the cell body.
Usually it is a device similar to foill strain gage, (but made of
nickel or balco alloy) and glued to the cell near the sg bridge.
Micromeasurements.com (Vishay) has a lot on that topic.
Predrag Dukic
At 15:03 11.12.2008, you wrote:
>On Sat, 29 Nov 2008 19:27:34 -0500, "Mike Monett" <XDE-L2G3 at myamail.com>
>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:)
>
>Because it's still an analog world out there. One instance that immediately
>comes to mind are truck scales, especially the enforcement ones. I recently
>serviced one that had a 200,000 lb capability, a 5 lb resolution and nailed my
>personal body weight to within the resolution with no last digit dithering.
>That indicates to me better than 2.5 lb internal resolution.
>
>Calibration of this particular scale is done in the digital world - roll a
>50,000 lb calibrated trailer onto the scale, tell the scale processor that it
>weighs 50,000.0 lbs and it figures out its own conversion factors. HOWEVER.
>Servicing the thing means working down in the kind of precision levels we're
>talking about.
>
>I have the 4 lightning-struck load cells and the matched summing box in my
>shop ($10,000 from the scale company) so when I get time I can see how they do
>it that precise with so few parts and with the load cells and summing box out
>in the weather. There are only 4 wires coming from each load cell so the
>temperature compensation has to be built into the mechano-electrical design
>and not externally compensated.
>
>John
>--
>John De Armond
>See my website for my current email address
>http://www.neon-john.com
>http://www.johndearmond.com <-- best little blog on the net!
>Tellico Plains, Occupied TN
>In theory, there is no difference between theory and practice. In
>practice, there is.
>
>
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