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

Magnus Danielson magnus at rubidium.dyndns.org
Sat Aug 29 07:09:12 EDT 2015


On 08/29/2015 10:01 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> On 28 Aug 2015 23:05, "Oz-in-DFW" <lists at ozindfw.net> wrote:
>> The uncertainly listed seems to be 7.6 mHz (milliHertz, or .0076 Hz.  A
>> bit better that you mention..
> No, please look again.
> The first line does show an uncertainty of 7.6 mHz, but that is when the
> LCR meter was set to 1 kHz. The last line shows an uncertainty of 7.6 Hz
> (1000x higher) when measuring 1 MHz, which is obviously 1000x higher in
> frequency than 1 kHz. So the original uncertainty I quoted was correct.
> The uncertainty rises proportionately with frequency.

I agree. That's how I read it too, and it is very obvious as you look at 
the table.

The calibration is in line with Chapter 10 of the manual:

It might be that the 7.6 ppm number was a practical uncertainty measure 
found in deeper analysis along the lines of GUM and was added to the 
calibration chart afterwards. For the peak-error of 100 ppm, this 
provide a good margin anyway.

So, it's the instrument and the way it behaves, nothing in their 
test-setup which is way better than needed for this particular instrument.

In short, don't worry about it, it's OK.


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