Hi Bill -- Normally, they do close the loop at the end of the trip by comparing the traveling standard again with the home reference. In the quartz days, you would use the difference to determine the daily drift over the length of the trip (assuming the oscillator didn't get bumped too hard) and you could take that into account in the calculations Tom described. Today closing the calculation with a traveling Cs is more of a sanity check that nothing went wrong.
John On Jan 8, 2012, at 12:55 PM, "Bill Hawkins" <b...@iaxs.net> wrote: > Tom, > > I had to look up "traveling clock synchronization" to get a > better understanding, and found this link: > > http://www.newtonphysics.on.ca/einstein/chapter9.html > > The idea that Qz (time on the quartz clock, no?) drops out in > the subtraction seems to me to require Qz to be invariant. > That seems beyond the capability of quartz at the required > error of one microsecond during the many hours that it will > take to transport Q between CERN and LNGS. Plenty of time > for cracks to propagate or chips fall off. > > Why do you say we can ignore such effects? > > Thanks for any enlightenment. > > Bill Hawkins > > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Tom Van Baak > Sent: Sunday, January 08, 2012 9:11 AM > To: iov...@inwind.it > Cc: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Question re neutrinos and GPS > >> what about swapping the Cs clocks between CERN and LNGS without re- >> synchronizing them, and repeating the neutrino test? >> >> Antonio I8IOV > > Right, typically when you perform a traveling clock experiment > you don't touch the clocks -- you don't need to synchronize or > resynchronize anything. The key point is the difference in time > from A to B, or A to B to A. This is accomplished with a time > interval counter and you do the subtraction with a calculator. > > Imagine that you have two Rb in your house and wish to compare > their times. If they are too far apart to use a long cable, one trick > is to use a "traveling" quartz clock and TIC. You measure Rb1-Qz > and then walk to the other clock in order to measure Rb2-Qz. > > Ignoring effects like drift in quartz or counter, the time of the > quartz drops out of the calculation of Rb2-Rb1. Make sense? > > So there's no mathematical requirement for synchronization of > the traveling clock. And there's also a practical reason why you > don't precisely synchronize or resynchronize -- most Cs have > a 100 ns granularity on their 1PPS sync input. > > /tvb > > > _______________________________________________ > 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. > > > _______________________________________________ > 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. _______________________________________________ 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.
