On Sat, 29 Nov 2008 19:27:34 -0500, "Mike Monett" <[EMAIL PROTECTED]> 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. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
