[time-nuts] Low-long-term-drift clock for board level integration?

Bill Woodcock woody at pch.net
Sun Feb 19 23:56:43 UTC 2012


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Hi. This is my first posting to this list, and I'm not a timekeeping engineer, so my apologies in advance for my ignorance in this area. 

I'm building a small device to do one-way delay measurements through network.  Once I'm done with prototyping, I'm planning a production run of several hundred of the devices. They'll have a GPS receiver, probably a Trimble Resolution SMT, and they have a bit of battery so they can initially go outdoors for ~30 minutes to get a good fix, but then they get taken indoors and plugged into the network, and probably never get a clear view of a GPS or GLONASS satellite again.  

- From that point forward (and we hope the devices will have an operational life of at least ten years) they'll be dependent on their internal clock and NTP, but we really need them to stay synchronized to within 100 microseconds. 10 microseconds would be ideal, but 100 would be acceptable. And in order to be useful, they need to stay synchronized at that level of precision essentially forever. 

My plan, such as it is, was just to get the best clock I could find within budget, integrate it onto the motherboard we're laying out as the system clock, and depend on NTPd to do the right thing with it.  

Anyone have any thoughts or advice on clocks I could use that would be, say, under USD 300 in quantity 500, and would be optimized for minimal long-term drift?  Power-use is not particularly constrained.  It needs to be integrated onto our board, but space isn't too constrained either. 

I'm also happy to pay for a few consulting hours if people want to give me detailed advice on a professional basis. 

Thanks,

               -Bill
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