[time-nuts] Temperature stability for Thunderbolt: results

Bob Camp lists at rtty.us
Wed Jan 26 17:36:53 UTC 2011


There are a bunch of cheap little USB thermometers out there ($10 or so). If
you plug one into the back of your PC you can get a "guess" at what the room
is doing. Just as you found with the power supply and fan - it's only a
guess. Between that data and LH's EFC plot you should have some pretty good
information on just how much the temperature control is helping.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Achim Vollhardt
Sent: Wednesday, January 26, 2011 3:12 AM
To: time-nuts at febo.com
Subject: [time-nuts] Temperature stability for Thunderbolt: results

After some tweaking of the temperature controlled fan setup (not always 
to the better), I finally settled on a setup with great results.

- Peak-peak variations in stable environments are down to 0.02K.
- opening window for few minutes disturbs only 0.03K down.
- TBolt sits now nice and stable at 36 degC.

Summarizing the important points (and please if somebody wants to 
add/correct, feel free!):

- Using Lady Heather's temperature controller helps A LOT.
- Using a too small fan results in too small control range. Large 
temperature disturbances cannot be compensated.
- Direction of flow DOES make a difference. First attempt blew the air 
from the (warmer) power supply to the TBolt.. which make you kind of 
wondering why the temperature shoots up while the fan is running 100%.
- I minimized the thermal mass *between* the fan and the TBolt. It is 
still in his own case, but no passive shielding around. Slows down the 
control loop and seems to make things worse. Some thermal mass around 
the fan control loop might be a different story.
- Once the temperature has settled, 'ka4' optimizes the controller 
parameters. Another improvement in response speed and temperature residuals.

A big thank you to Warren and Mark for implementing this feature (sorry 
if I forgot somebody) and all others who helped in this list. I think 
this feature is a must-have for all TBolt setups out there..

73s Achim, DH2VA

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