[time-nuts] Why would Keysight UK uncertainty measuring 1 MHz be as high as 7.6 Hz?

Oz-in-DFW lists at ozindfw.net
Fri Aug 28 18:05:10 EDT 2015

The uncertainly listed seems to be 7.6 mHz (milliHertz, or .0076 Hz.  A
bit better that you mention..

On 8/28/2015 3:48 PM, Dr. David Kirkby (Kirkby Microwave Ltd) 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?
> When they done my VNA last year
> http://www.kirkbymicrowave.co.uk/cal_certificates/Keysight-standard-calibration-with-uncertainties-for-8720D-vector-network-analyzer-16-09-2014.pdf
> the uncertainty on frequency was about 5 orders of magnitude better than
> that. The 10 MHz timebase was measured with an uncertainty of 0.0010 Hz.
> I checked the Keysight UK accreditation (by UKAS) for frequency
> http://www.keysight.com/upload/cmc_upload/All/UKAS_S_2015-08-14_Eng.pdf
> and see over the range 0.1 Hz to 500 MHz, which covers the LCR meter, their
> accreditation is 6.0 in 10^11 + 0.020 nHz.
> I can't believe they are unable to measure better than 7.6 ppm on
> frequency, so are wondering why the uncertainty is so high, even though I
> am sure such an uncertainly is very acceptable for this application.
> It is either an error on the cal certificate, or I am missing something. I
> expect it is the latter, and hoping someone here can fill me in.
> Dave
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