[ntp:questions] NTP offset doesn't change.

Charles Swiger cswiger at mac.com
Fri Feb 13 00:48:37 UTC 2015


On Feb 12, 2015, at 4:02 PM, William Unruh <unruh at invalid.ca> wrote:
>> You're describing a TCXO; using a temperature sensor to compensate for thermal
>> drift would gain perhaps a factor of 5 accuracy.
> 
> No, that is a hardware solution. There are software solutions-- a
> termistor to meaure the temperature of the crystal ( or somethign
> nearby) which feeds that measurement to the OS. the revised ntp then
> reads the temperature, and corrects the drift rate as a function of that
> temperature.

Anything which measures temperature to provide a compensation for XO frequency
is a "TCXO" which is an acronym for "Temperature Compensated Crystal Oscillator".

There are details which matter; see: [1].

> This is all without controlling the temperature of the oscillator (TCXO)
> but rather measuring that temperature-- much cheaper.

Something which controls the temperature of the oscillator is an OCXO,
which is an "Oven Controlled Crystal Oscillator".

Regards,
-- 
-Chuck

[1]: If you wanted to distinguish between a precalibrated analog feedback circuit
commonly included within the package and external compensation via a digital
temp sensor (perhaps located on the motherboard chipset) and a lookup table,
ie, ATCXO vs DCXO, fine.  Good definitions here:

http://www.radio-electronics.com/info/data/crystals/tcxo.php

The lookup mechanism described above would be adjusting the kernel's tick values
(ie, how many ticks it counts per second) and not providing a voltage change--
aka VCXO-- to change the actual crystal oscillation frequency.



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