[time-nuts] OCXO sensitive to gravity

[Tom Van Baak]

Although we time-nuts prize quartz oscillators that are highly-stable
and well-insulated from environmental effects there is an entire
industry doing the exact opposite -- using quartz as a sensor.

Some of the best thermometers are based on quartz oscillators
(hp 2804A) cut to maximize, rather than minimize, their tempco.

And billions of accelerometers (from air bag sensors to Wii game
controllers to the iPod touch and iPhone) have been produced in
the past decade. Google words like MEMS Quartz Accelerometer.
Also for Quartz Rate Sensor QRS.

I've seen quartz resonators used to measure to impurities in the
making of semiconductor wafers -- they measure the change in
frequency of an exposed quartz resonator as atoms fall on the
exposed crystal and change its frequency. Note that a 1 mm
quartz crystal is only about a million molecules thick. So adding
a layer of only 1 atom will change the frequency in the ppm range.
We can measure a thousand or million times better than that.

As you feel your heart beat, google for Quartz Pressure Sensor

Quartz is really quite amazing. It's almost a shame to shield it
from everything so all they have left to do is try to measure time!

One other note: rubidium vapor frequency standards are much
more sensitive to magnetic fields than cesium beam standards.
I've heard that military sub-hunting sea planes use deliberately
un-shielded rubidium clocks to detect hidden submarines. Google
for words like Rubidium Magnetometer ASW P-3 Zeeman

As always, one man's error is another man's signal...

/tvb
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