[time-nuts] TEC party file format?

Tom Van Baak tvb at LeapSecond.com
Tue Jun 28 18:59:08 UTC 2011

> Coming into this late so I have a very basic question.   What level if
> resolution is required?   Are variations in the line frequency
> expected to be at the 1% level or is this parts per million?    Can we
> measure the frequency by averaging many cycles or are we looking for
> transients where the frequency jumps?


The NERC is not really talking about changing frequency. I
mean, it will still be 60 +/- 0.05, or whatever. The proposal is
about eliminating the time error correction (TEC). This is a
more gradual process, a steering of sorts. Ok, I know time
and frequency are related, but the point is what you really
want to monitor is the time error, that is the accumulated
phase drift. Especially over days and weeks.

In a case like this recording time error and then calculating
frequency, or average frequency, is likely better than trying
to make a bunch of periodic frequency measurements and
then stitching them all together to guess the accumulated time.

Around here the mains time drifts by a couple of seconds
over the coarse of a day. Because of TEC it tends to head
back to zero, on average. Note that a couple of seconds is
a couple hundred cycles. So it's trivial to monitor this if you
just count cycles and compare then to a reference. The
reference should be accurate to better than 1ppm.


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