Ulrich, when you changed the thermal characteristics around your 10811,
how 'crazy' did it become?
According to your theory, there should be differences in the schematics
of the oven controllers between the single and double oven variants of
the 10811. Last year I picked up a couple of those double oven 10811s
from China that had the outer insulation removed. I wonder if I could
see any anomalies in its operation with no outer insulation and only the
inner oven operating.
Ed
Ulrich Bangert wrote:
I'm not talking about crystal ovens, I'm talking about
timekeeping kit in general: how to filter high frequency
temperature fluctuations out, so the PLL does not have to
deal with them.
Ok, but in this general case you have to accept the fact, that filtering
high temperature fluctuations is only ONE part of the engineering job. The
second task (which I tried to point at) is: When you do already have a
closed loop temperature regulation system inside what you plan to built
around it, then you need to manage the filtering without mal interaction of
the local temperature controller with your additional filtering stuff. The
art is to make the closed temperature loop inside see only smaller
temperature fluctuations but No changes otherwise.
If you apply an overall change in temperature insulation to the ambient you
will make the work of the inside temperature controller a lot harder because
it is not prepared for that. In the aluminium box that i wrote about I have
for an experiment replaced the air between the 10811 and the outer box with
a material that has a significant lower temperature conductivity than
standing air. You can easily watch the temperature controller go crazy with
that. For a second experiment I have replaced the air with a material having
lots more of thermal conductivity than air and you can watch the temperature
controller go crazy with that too. You don't need sophisticated temperature
measurement equipment to see the controller go crazy, just watch the
frequency of the oscillator. This will tell you all about it.
Things are different, if you have an influence on the controller's
regulation parameters (which you do not have with a ready bought device). If
you do have, then your additional provisions for filtering and insulation
can easily be included into the thermal model that the temperature
controller has to handle and will lead to different operation parameters of
the controller. That will of course work and that is why I compared your
suggestions to designing a new oven (for xtal or rubidium or whatever).
Best regards
Ulrich Bangert
-----Ursprungliche Nachricht-----
Von: [email protected]
[mailto:[email protected]] Im Auftrag von Poul-Henning Kamp
Gesendet: Donnerstag, 11. Juni 2009 12:50
An: Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] Thunderbolt stability and ambient temperature
In message <e182724b9fce4b9f9e914bcc4f374...@athlon>, "Ulrich
Bangert" writes:
For PLL steered devices, you want your device enclosed by a
thermal mass which is again enclosed by a layer of thermal
isolation. The goal is to filter/average all rapid (daily ?)
external temperature influences, only letting through such
slow variations (seasonal ?) which the PLL can comfortably
cope with.
My impression with this thread is that two sligthly different things
are being discussed here:
Some posters explain how a crystal oven shall be designed as
Poul-Henning does with his words above. Absolute correct, no doubt
about it!
I'm not talking about crystal ovens, I'm talking about
timekeeping kit in general: how to filter high frequency
temperature fluctuations out, so the PLL does not have to
deal with them.
The above advice applies to GPSDO's and Rb's and Cs's as well
as TCXOs, OCXOs and voltage references.
Poul-Henning
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
[email protected] | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by
incompetence.
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