Said and Björn,
saidj...@aol.com wrote:
Hello Bjoern,
that would work well for static acceleration (tilt) but for vibration
resistance the crystal must be low-g, or complexly compensated with wide loop
bandwidths such as the FEI papers describe.
It could work for low-frequency compensation, as it would take a bit
more analysis to figure out the impulse response needing of
compensation/equalisation.
Initial Calibration would also be tricky, and having an algorithm to
measure one result (frequency) against five inputs (aging, tempco, X, Y, Z
acceleration) and more (crystal jumps, retrace) is also quite sophisticated :)
But hey, we are time-nuts, arn't we? :)
Also, Mems, or other accelerometers have inherent noise, and to
compensate a crystal that has say +/-2E-09 per g sensitivity means one would have to
add up to +/-2E-09 in offset statically. That's a lot of deviation, and
any noise from the mems would find its way into the Allan
Variance/phase-noise.
Which is scaled by the g-sensitivity of the crystal. If you have a
g-sensitivity of 2E-6 of the crystal and then compensate that with a
noise of 2E-9 you would end up with a 4E-15 noise contribution. Right?
Now, that was assuming white-noise... the 1/f noise sources needs to be
estimated for real performance, as they behave differently in ADEV.
For vibration compensation, the compensation could easily go up to
+/-1.2E-08 and more (for up to +/-6G vibration to be canceled).
Very interesting topic, and I would love to hear what folks think about
this, or have come up with in terms of solutions.
At the high-end of the spectrum of the technology is the gun-barrel
launched artillery shell with crystal oscillator built-in, that has to withstand
and operate with 10,000 to 20,000 g acceleration!
Hence the military and related industry have worked alot on figuring out
how to handle it. Using two crystal blanks in opposite direction to
subtract the vector-field of the g-sensitivity is one way. The patents
for that is available.
One caveat for the artillery shell: commercial GPS would likely not work
due to the 1000 Knots verlocity limit.
Not an issue for military receivers, but they need to be built for it
not to break at the moment of fire rather than the moment of impact.
Cheers,
Magnus
_______________________________________________
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.
