[time-nuts] temperature sensor
EWKehren at aol.com
EWKehren at aol.com
Mon Jul 21 09:02:12 EDT 2014
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
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
> 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
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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