[time-nuts] 10811 crystal orientation

[SAIDJACK at aol.com]

Hi Magnus,
 
Agree with all your points.
 
On the added noise due to an accelerometer, my thoughts are that this needs 
 to be carefully designed so as not to add more error than we are actually  
removing (due to phase shifts between crystal sensitivity and the 
accelerometer  response for example, and due to random noise).
 
For example, if we do the compensation in the digital domain, and use a 10  
bit ADC on the accelerometer, and a full-scale compensation is say 2E-09, 
then  the quantization noise itself (1/2 of 1 LSB on average, or about 4E-013 
just due  to the quantization noise) may already be considerable. So we 
need to use a good  ADC, and very low noise accelerometer :)
 
While building and carefully calibrating a unit for  Time-Nuts enjoyment is 
possible, I would think bringing such technology  into large-scale mass 
production is quite a challenge.
 
bye,
Said
 
 
In a message dated 7/12/2009 03:08:41 Pacific Daylight Time,  
magnus at rubidium.dyndns.org writes:


>  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?