Hello,
The calibration certificate does not indicate that the measurements were
done with the frequency counters referenced to the 5071A at the time of
calbiration (if so, it would be listed under the Calibration Equipment
Used table). It says that the 53132A were calibrated against the 5071A.
If for your calibration they have used 53132A witout the oven oscillator
option it is very probable that its uncertainity is 7.6ppm as indicated
in the certificate. Since the maximum error tolerable for the LCR meter
is 100ppm (+/-100Hz @ 1MHz), it makes sense to perform the measurement
with an instrument with an uncertainity of 7.6ppm, and not to use the
better counter in the lab for that purpose.
Regards,
Javier
On 28/08/2015 22:48, 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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