That's a great question and I'm afraid I don't have a good answer 

Volker, That's a great question and I'm afraid I don't have a good answer for you. If pressed, I would estimate less than 100ps. The error of this measurement contributes to the error in our final measurement which has many components. I haven't worked out an error budget for each contributor. Our goal is a final error of less than 10ns. But a few contributors are already expected to be around 1ns, so this error really needs to be less than 1ns, preferably less than 100ps. Cheers, Paul On Tuesday, 4 December 2012, Volker Esper wrote: > I agree. Since Paul want's to use an SR620 I presume he needs precision. > Otherwise almost any TIC with a fairly stable osc would do, for example > one with a battery backup. So I further presume that he needs nearly the > full accuracy / stability. But that's just speculation, surely Paul can > answere this question? -- Paul DeStefano

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