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
--
Paul DeStefano
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
