[time-nuts] temperature sensor

EWKehren at aol.com EWKehren at aol.com
Mon Jul 21 09:02:12 EDT 2014

Hi Tom
I agre the educational aspect of time nuts is great and I have learned a  
lot but it would be even more useful if discussions include what can be 
attained  and what may be in the reach of time nuts. I used to have a HP 2804A 
with  matched probe prom only used it once when developing a super efficient 
boat air  condition system running on batteries. After that used it to sort 
of calibrate  my YSI probes and sold the unit. I do not think I need any 
accuracy better than  0.1 C and feel comfortable having it. But if time nuts 
find a way to get an  affordable solution I would get one.
We use fan speed temperature control and at one time I did use it on a  
Tbolt. May revisit it discarded it because of my concern of fan noise  
transferring to the XTAL in the OCXO. 
We use it successfully with NTC embedded in the base plate of FRK's and  
using a separate sensor see 0.01C. Also use heat pipes. In all cases we use  
voltage control do to my lack of PIC programming experience. In our work the  
OCXO is not in the Rb  but Rb , fan and OCXO all have vibration isolation.  
The challenge is reliable fan start at low voltage if you want the unit  
stay constant over an ambient change of 10 C. Members have talked about u  
processor control but I have not seen any thing that works, many of the heat  
pipes used in laptop do have digital speed control, some one please step up 
to  the plate.
Back to the Tbolt it is tempting but right now I have to many things on my  
plate. I suggest controlling temperature in an enclosure within 0.1 C along 
with  added mass to the unit, reduce other heat sources in the unit. An 
other approach  would be a heat pipe again more thermal mass and all sides with 
thermal  isolation to reduce ambient temperature. influence. I have an 
analog fan conrtol  board and the plan is to make one available for those that 
buy a FE 5680A kit.  Again maybe some one steps to the plate and designs a 
digital control.
Bert Kehren
In a message dated 7/21/2014 3:17:16 A.M. Eastern Daylight Time,  
tvb at LeapSecond.com writes:

> What I am  missing in all these discussions is what do we want to  
>  or is this an other paper only  discussion. I am used to  starting  out 
with a 
> goal, and tackle the challenge from there.
> We have  a saying in German "Papier ist geduldig.  Translate You  can 
> any thing on paper.  
> Bert Kehren

Hi  Bert,

Let me answer in two parts.

1) The issue of precision  temperature sensing is so key to the field of 
precise time & frequency  that any thread that attracts more information, 
anecdotes, and wisdom from the  group is very welcome. Quartz is such an amazing 
substance that its use as a  precision sensor is every bit as interesting 
as its use as a precision  timekeeper.

Not everything has to be goal oriented. Some discussions on  this list are 
pure enjoyment, others highly educational, and some simply plant  seeds. 
Starting with concrete goals is good for a business but when working  with 
precision timing as a hobby, as most of us are, goals are sometimes  secondary 
to just learning or playing around.

2) If you want an example  of a specific goal related to temperature, try 

There have been  several discussions over the years about variable fan 
speed based temperature  control. I can't explain it, but I've always been 
suspicious of this  technique. It seems to me still air is inherently better than 
moving air.  Passive (no fan) is better than active (fan). And constant 
velocity is better  than turbulence is better than variable velocity. But I 
don't know for sure.  That's where experiments and measurement come in.

To satisfy my  curiosity and get actual data I'd like to place 6 or more 
tiny analog  high-resolution temperature sensors all around the OCXO of a 
Trimble  Thunderbolt. That's high-resolution both in temperature and in time. In 
other  words, no fake accuracy "averaging" allowed. The goal is to observe 
thermal  gradients in real-time and see how good, or how bad, the 
correlation is among  crystal temperature, case temperature, and DS1620 temperature 
sensor (which is  mounted a considerable distance from the OCXO). The same 
technique, and maybe  even the same conclusions, might apply to  Rb.


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