Ron Frazier (NTP) wrote:
On 2/13/2012 3:25 PM, Chris Albertson wrote:
On Mon, Feb 13, 2012 at 10:59 AM, Chuck Swiger<cswi...@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.
My most recent PC is from about 7 years ago. All the
systems that I've checked seem to have a 14.31818 MHz
crystal. Some of the older systems even have a jumper
to use an external source.
David
Ron
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