[ntp:questions] how do I lock in average frequency correction

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Tue Feb 14 06:20:10 UTC 2012

On 2/13/2012 3:25 PM, Chris Albertson wrote:
> On Mon, Feb 13, 2012 at 10:59 AM, Chuck Swiger<cswiger at mac.com>  wrote:
>>>> You might be able to improve the stability of the crystal by ensuring good
>>>> airflow and cooling via HVAC as needed.  And I suppose you could adjust the
>>>> rate by changing the HVAC set-point, but I don't think the benefit is worth it.
> For temperature stability, I just finished building a fan controller.
>   There is a temperature sensor on the end of a 18" cable.  Glue the
> sensor onto anything you like.  Then when the sensor matches a set
> point the fan comes on.    I think this should work as long as you
> keep the set point above the room temperature.     I've not tried it
> yet.  It is simple enough to make.  The TMP36 sensor outputs a voltage
> of 10mV per degree.  That goes to one side of an LM311 comparator.
> The lm311 switches a transistor that drives the fan.   It looks like
> holding the sensor temp to +- 1/2 degree is easy.    Holding to only
> 0.5 C is not hard and might help.       Actually this controller is
> going on a Rubidium oscillator, not an XO.   but if it works well I'll
> build a few more.
>   The idea is about the same is an ovenized XO but slightly more crude.
>   Just aim the fan at the part you want to control and insulate the
> sensor from airflow.     I'll know if this work in a few weeks
> Chris Albertson
> Redondo Beach, California

Perhaps a silly question, but, does the "tick" that drives the OS 
software clock originate from the RTC or from the CPU master clock at 2 
GHz or whatever?  Just trying to understand how this stuff works.



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Ron Frazier
timekeepingdude AT c3energy.com

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