[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.
(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such. I don't always see new messages very quickly. If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)
timekeepingdude AT c3energy.com
More information about the questions