On 28 August 2015 at 21:48, Dr. David Kirkby (Kirkby Microwave Ltd) < drkir...@kirkbymicrowave.co.uk> wrote:
> My LCR meter came back from Keysight UK last week, where it was > calibrated. This instrument works at various frequencies from 20 Hz to 1 > MHz, so obviously has some sort of oscillator in it. But I don't think the > absolute accuracy on frequency is important on this, as it does not even > have the ability to set to an arbitrary frequency. There are only 8000 or > so steps, and at the high end, some of those steps are more than 100 kHz > apart!!! So clearly frequency accuracy on this instrument is not that > important. > > Anyway, the cal certificate, a copy of which I put here > > > http://www.kirkbymicrowave.co.uk/cal_certificates/Keysight-standard-calibration-with-uncertainties-for-4284A-precison-LCR-meter-18-08-2015.pdf > > shows on page 5 that it was checked at 1, 8, 20, 80, 400 kHz, and 1 MHz. > But the uncertainty reported (7.6 Hz) seems extremely high, given they used > a 53132A counter as a working standard, and a 5071A primary frequency > standard. Why should the uncertainty be so high? Am I missing something? > I don't know if this thread is closed, but I did get a telephone call from someone at Keysight today, in response to my query on this matter. Essentially 1) At the particular calibration centre in the UK, the frequency counter used would have been locked to an external reference, as are all the counters they use at that particular calibration centre in the UK. The reference is an old HP 5071 cesium, which is regularly compared with GPS. Their best uncertainty is 5 x 10^-13. 2) The LCR meter tolerance on the 1 MHz is +/- 100 Hz. This means it does not need a particularly good counter. 3) To enable Keysight to use one calibration procedure world-wide, that calibration procedure is written to allow the uncertainty to be as high as the worst case with a counter running on its own internal oven. So in essence, the meter when calibrated in the UK would have been measured to far better than the +/- 7.6 Hz indicated on the calibration certificate. but by specifying +/- 7.6 Hz, it allows the same procedure to be used anywhere in the world. Dave _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.