[ntp:questions] Re: HowTo calibrate system clock frequency using NTP

Richard B. Gilbert rgilbert88 at comcast.net
Mon Feb 6 16:19:49 UTC 2006


Daniel Kabs wrote:
> Hello Hal!
> 
> Hal Murray wrote:
> 
>> What sort of accuracy are you expecting?
> 
> 
> I hoped to measure the time drift within (or better than) 1 PPM
>

To what purpose?  The drift will vary with the temperature and you are 
not planning to operate these devices at a controlled temperature.  If 
they MUST keep the correct time then you have two choices as I see it:

1.  Use a much better clock; e.g. an Oven Controlled Crystal Oscillator 
(OCXO) or a Temperature Compensated Crystal Oscillator (TCXO).  OCXO is 
the better of the two.  The "oven" part is not what you would bake a 
pizza in, it's a tiny thing, thermostatically controlled, to maintain 
the temperature of the oscillator (especially the crystal) at a constant 
value that will always be greater than the ambient temperature.

2. Correct the clock periodically: ntpd, sntp, rdate, or set it by hand.
If the devices do not have a network connection or dialup capability, 
you are pretty much limited to setting the clock by hand.

The clocks will be in error no matter what you do!  All you can control 
is whether they are off by microseconds, milliseconds, seconds, minutes, 
etc.

<snip>




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