[time-nuts] SRS SR620 External Source Issue -- Help Request -- A thought

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Feb 21 22:48:48 EST 2007


TheInfamousFlavio at hotmail.com wrote:
>> ...if my model is correct the apparent offset in the
>> mean will be increased by a factor of 10 over that for a a 1 second gate
>> time.
>>
>> Bruce
>>     
>
>
> Looks like you're right Bruce.  I did both 1, 0.1 and 0.01 gate times and 
> the error increased by a factor of 10.
>
> And it doesn't sound like this is a fixable in any easy sort of manner, 
> right? 
>
>
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>   
Flavio

If the SR620 can do some simple arithmetic before displaying the result, 
then this calibration problem is easily corrected.
Otherwise you will have to do the corrections on a PC (or hand held 
calculator).
The correction will vary with time and temperature so you will need to 
measure it periodically.

Corrected frequency = measured frequency*(nominal gate time)/(nominal 
gate time + differential delay).
In your case the differential delay appears to be about 150 picoseconds.

Bruce



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