[time-nuts] Looking for RTC or some combination of MPU/crystal for 0.1ppm accuracy.
bruce.griffiths at xtra.co.nz
Sun Sep 13 00:37:57 UTC 2009
> It seems like you have given plenty of information for me to give you two possible suggestion.
> Here is an almost no extra cost solution, (just takes care and helps if you have done it before)
> Take a pretty standard xtral osc with EFC, buffer its output real good,
> give it good clean power from preferable its own regulator,
> put a little insulted house around it so that it is not effected by direct air flow and quick temperature changes,
> Add a processor controlled PLL a driving a Dac to control it freq,
> Update the PLL loop with the time beacon, (assuming it is good to better than 1us) to correct the Phase offset error,
> and it is pretty easy to get much better than 0.1 PPM with this.
> I did about the same thing using the 1PPS of my GPS and could get around 1e-8 accuracy.
> The most important things are if using a cheap $5 osc like I was is to isolate real well it from the effects of PS,
> load and temperature, and have of low noise reference voltage to provide a settable coarse freq tuning and use the Dac just for fine adj.
> Or of course you could just buy a better osc TCXO and save a lot of development time, but that's not as much fun.
> Depends how may you want to build, Anything below say 50 units the TCXO is going to be the cheaper solution if time is money.
That is probably an unnecessarily expensive solution that doesn't
address the fundamental problem of synchronising the RTC associated with
each sensor to a common time base.
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