Hi If it is an un-compensated crystal oscillator (I’d bet it is) there will be a maximum temperature slope to the part. In order to have absolute calibration, you would need to know both the frequency read *and* the temperature of the inside of the device. I’d bet somebody did the math, looked at the “rated” temperature control in the cal lab area and came up with a proper number for the ambiguity of the calibration. If the slope is 2 ppm / C then the number you have implies a 3.5C temperature control in the area. That seems pretty tight. A 1 ppm / C number gets you to 7.6 C. That seems about right for the room plus the ambiguity in the internal temperature rise inside the box.
Bob > On Aug 28, 2015, at 4:48 PM, 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? > > 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 > _______________________________________________ > 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. _______________________________________________ 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.
