[time-nuts] 10811 crystal orientation

Magnus Danielson magnus at rubidium.dyndns.org
Sun Jul 12 21:21:04 UTC 2009


SAIDJACK at aol.com wrote:
> 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 :)

This is indeed a very good point. Blindfoldingly adding some 
compensation scheme could end up worse than it was originally. Still, 
some quantization noise may be tolerable than the much higher and not 
tolerable acceleration deviation. Thought, it is always good to get the 
extra margin. Far too many design become a hurdle due to a too small 
initial assumption on dynamics.

> 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.

Depends on what large-scale means. For some it could be 100-1000 units a 
year.

It's not mobiles or something we are discussing. Yet.

Cheers,
Magnus



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