[time-nuts] Making a HP 10811 better

Tom Van Baak tvb at LeapSecond.com
Mon Mar 29 00:49:39 UTC 2010


Warren,

No, measuring an oscillator every second will not help.

The change in g = ~9.81 m/s due to tides is about 1e-7 over
part of a day. So g changes by about 1e-8 per hour; that's
about 1e-12 per second.

Now df/dg for a 10811 is on the order of 1e-9. So the tidal
effect of the sun/moon will change a 10811's frequency by
about 1e-12 x 1e-9 = 1e-21 per second, which is about a
billion times below the short-term noise level of a 10811.

Now the reason pendulum clocks can "detect" tides (and
only a few of the world's best have ever done so) is that
their frequency is directly dependent on g. That is, df/dg
for a pendulum clock is 0.5! By contrast df/dg for a 10811
quartz oscillator is around 0.000000001.

/tvb




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