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

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 29 August 2015 at 12:59, Javier Herrero <jherrero at hvsistemas.es> wrote:

> 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


I would find it a bit hard to believe they would use a counter without an
oven in their lab, as it would seriously restrict what they can do with it,
making it more difficult to replace one counter with another. I would have
thought that within reason it best to have the lab have reasonably high
spec kit, so more than one instrument could be done on the same line. They
did for example use a pair of 3458As, despite I'm sure the voltage accuracy
requirements could be met with a multimeter with far greater uncertainty
than an expensive 3458A. It makes more sense (within reason) to have 3458As
in the cal lab, as it allows a wider range of instruments to be calibrated.

Also, if you consider the spec on the 53132A without an oven, it is 3 x
10^-7 per month. So after 12 months that could be 12 * 3 10^-7 or 3.6
10^-6, so if it did drift the maximum amount each month for a year, the
uncertainty would higher than it actually is.

I intended to contact Keysight about the calibration for a couple of other
reasons

1) I would like to know if it was adjusted or not. That is not clear from
the cal certificate, since the

* As received condition  - Not applicable, as this calibration certificate
applies to the initial calibration of a new, refurbished or upgraded
equipment.
* Action taken  - The equipment was upgraded.

I doubt it has seen a cal lab in ages.

The upgrade was just a software one, to enable cable lengths of 2 m and 4 m
(option 006) to be used to connect the DUT, which they kindly provided free
of charge, on the condition I paid for the calibration.

2) They never put any stickers over the screws that prevent the covers
being removed, which struck me as a bit odd.

Since I was going to ask about those two issues, I will ask about the
uncertainty on frequency too. It will be interesting what response I get.
I'm just interested -  I realize that this instrument does not demand much
of the counter used to calibrate it. The demanding calibration devices
would be the resistance and capacitance standards.

Dave