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

Bob Camp kb8tq at n1k.org
Sat Aug 29 22:02:59 EDT 2015


Hi

Well, since we all have made our totally uninformed guesses, the only 
thing to do now is to give Keysight a call and see what the real answer 
is. 

Bob


> On Aug 29, 2015, at 1:46 PM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkirkby at kirkbymicrowave.co.uk> wrote:
> 
> 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
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