[time-nuts] Considerations When Using The SR620

Volker Esper ailer2 at t-online.de
Mon Dec 17 16:07:03 UTC 2012

I'm curious, which way you went and which accuracy you achieved... :-)
Can you tell us?

Am 06.12.2012 19:10, schrieb Paul DeStefano:
> On Tuesday, 4 December 2012, Tom Van Baak wrote:
>>> We are using the SR620 to measure the interval between 1PPS signals from
>>> two clocks. One is the Septentrio PolaRx4 GPS receiver and the other
>>> is a
>>> Rubidium clock.
>>> Many Thanks,
>>> Paul
>> 1) If you are making frequency measurements, the warm-up of the
>> internal oscillator is the major factor limiting accuracy. ...
>> Plotting digits of precision as a function of warm-up time would make
>> a very educational graph you could tape to the top of your SR620.
>> 2) If you are making time interval measurements and using an external
>> standard, the warm-up time will also affect the accuracy of your TI
>> measurements, but to a far lesser degree. Here are informal results
>> for TI (time interval) mode after a 5 minute power-down (see also
>> attached plots):
>> - if you need 1 ns accuracy, you can use the SR620 immediately after
>> power-up
>> - if you need 100 ps accuracy, wait 2+ minutes
>> - if you need 10 ps accuracy, wait 15+ minutes
>> - if you need 1 ps accuracy, you need a seriously stable lab
>> environment or a different counter.
>> Given that you plan to use the SR620 with high-end GPS gear I would
>> suggest you try this quick experiment for yourself to see what *your*
>> SR620 does, with *your* inputs, in *your* environment. Your numbers
>> will come out different than mine; but the methodology is the same.
>> Your procedures can then be based on measurement and confidence
>> instead of guesswork and folklore.
> Tom & Co.,
> Thank you! These plots are excellent and will be very helpful. You are
> quite right; we should do the test ourselves. We will definitely do
> that. Obviously, there is not need to worry, as we can characterize the
> instrument behavior ourselves, which is probably necessary anyway if
> we're going to publish these measurements with error values.
> Many Thanks,
> Paul

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