On Wed, 9 Jul 2008 12:10:52 +1000, Jim Palfreyman wrote:

Jim,
have a look into the manual
GPS Disciplined 10 MHz Frequency Standard
by
James Miller G3RUH
http://www.jrmiller.demon.co.uk/projects/freqstd/manual.pdf
he did apply this type and describe the connections.
Good luck!

Regards,

Arnold Tibus

2008/7/9 wje wje@quackers.net:

Also have a look at

http://homepage.sunrise.ch/mysunrise/shegnauer/Z3801A/Power%20Supply/z3801a_power_supply.htm

http://homepage.sunrise.ch/mysunrise/shegnauer/Z3801A/Outer%20Oven%20Controller/z3801a_outer_oven_description.htm

Regards  Juerg

Well, the good news is (if you buy one of these) is that the worst
that can happen is that you unwrap all that 2nd oven junk and
you are left with a 10811 for $50.  I remember when they were
designing that double oven 10811.  There are so many things
wrong with the design that I wouldn't know where to start.
Besides, do you really need more thermal gain for an oscillator
in a benign environment?

Rick Karlquist N6RK

Jim Palfreyman wrote:

From: "Richard (Rick) Karlquist" richard@karlquist.com
Subject: Re: [time-nuts] Double ovened 10811-60158 on ebay
Date: Fri, 11 Jul 2008 20:58:15 -0700
Message-ID: 48782BD7.9050805@karlquist.com

My thought exactly.

Please, let me just grab a cup of coffie, and off you can go...

I keep wondering if not a passive oven (metal box, insulation, metal box)
would be sufficient. Worst case temperature change rates would be significantly
reduced such that the oven loop can track it better. The remaining temperature
shift will be less. Basically acts like a lowpass filter.

What strikes me is the lack of isolation between the oven shells. Oh yes, they
have tried to bring the heating around the outer shell, but never the less.

Well, at least they did not put a fan in that (Z3801A) box.

Cheers,
Magnus

Magnus Danielson wrote:

Magnus

A box with multilayer walls: insulator/metal/insulator/ metal etc does a
much better job of attenuating thermal fluctuations.
The insulator layer only need be significantly poorer at conducting heat
than the metal layer.
Tufnol sheets are OK for the insulator layers, they bond well to
aluminium sheets with epoxy.
You just need to remove the few watts of heat from the OCXO without too
large an internal temperature rise.

Bruce

From: Bruce Griffiths bruce.griffiths@xtra.co.nz
Subject: Re: [time-nuts] Double ovened 10811-60158 on ebay
Date: Sat, 12 Jul 2008 21:16:41 +1200
Message-ID: 48787679.80108@xtra.co.nz

Hej Bruce,

Well, it was not about doing the perfect box in any sense, but just "casing"
an OCXO within a box can have rather noticeable effects on the OCXOs ability
to handle temperature changes. The degree of the filter can then be varied at
need.

Indeed, but the over will not burn as much as it's immediate surrounding is
hotter than if it was sitting there alone in the box.

Providing a too good insulation is certainly a concern. The trick is really
to make the insulation-heatmass-insulation-heatmass stages. Just adding one
such stage can be sufficient.

Cheers,
Magnus

Magnus,

I have been thinking pretty much the same and therefore I built me an
"outer" box for my 10811 that has abt. 2-3 cm of free air between the
outer surface of the 10811 and the inner surface of the box to make the
10811's temperature regulation "look" into the same "thermal leakage
impedance" that the designers may have in mind when they decided for the
controller's parameters.

Then comes 2 cm of massive aluminium which's heat capacity - in
conjunction with the surrounding air's thermal resistance - is expected
to give the desired "lowpass filter" effect.

Due to the nature of my disciplining system I have been able to measure
the overall effect of this shielding quite precise: The lowpass effect
is well defined by

a) an increase of "phase delay" between temperature changes outside and
changes of the oscillator's frequency that is now in the order of some
hours.

b) the frequency changes (as far as they seem to be related to
temperature) appear to be "smoother" and more predictable

Nevertheless I have been a bit disappointed that the overall frequency
changes along the diurnal changes of the surrounding temperature in my
flat have been pretty much the same in terms of amplitude with the above
mentioned phase delay. I have then started to compute what thermal time
constant may be expected from this arrangement. This is not trivial
stuff because in contrast to the aluminium's thermal properties their
counterparts for the surrounding air are not well defined. As far as I
remember, a BEST case assumption gave a result of 2-3 hours that seems
to match the empirical results. If you are out for time constants that
are able to smooth diurnal changes I guess you will have to throw in
MUCH more material.

Best regards
Ulrich

Large metal reflectively lined thermos bottles are worth considering.  You do
end up with a lot of long skinny circuit boards that way.

Peltier based thermoelectric cooler's from Big Box Stores can also be
pressed into
service as temperature cycling oven, or stable temperature environment, with
the addition of proper regulation loop.

See this long outdated paper: http://www.designer-iii.com/cco/HBridge.pdf

http://focus.ti.com/lit/an/slua202a/slua202a.pdf
"Closed-Loop Temperature Regulation Using the UC3638
H-Bridge Motor Controller and a Thermoelectric Cooler".

Next time you have to endure shopping with your wife keep your mind busy by
asking "What can I use 'that' for?" for everything you see...

The Preface to Murphy's Law:
We, the willing,
Lead by the unknowing.
Are doing the impossible for the ungrateful...
We have done so much for so long...
With so little...
We are now qualified to do anything...
With nothing...
Forever!

--
http://www.wearablesmartsensors.com/
http://www.softwaresafety.net/ http://www.designer-iii.com/
http://www.unusualresearch.com/

From: "Ulrich Bangert" df6jb@ulrich-bangert.de
Subject: Re: [time-nuts] Double ovened 10811-60158 on ebay
Date: Sat, 12 Jul 2008 13:09:55 +0200
Message-ID: 769FE70BC9AD430CA6506EEEC90E3B8B@athlon

Ulrich,

Which does not as a big supprice but rather confirms the expected.

Which also matches expected and other measurements done.

Your time-constant for the lowpass filter does not do much to the diurnal
frequency. The temperature changes still go through. The point with the
passive oven is that it does smooth things out, and could potentially make
the oven design inside it an easier task. If temperature changes is the main
problem then it may be all that is needed to get the extra margin. It is
certainly not a perfect solution, but an interesting exercise which may be
of help for some cases.

You would also like to build multiple stages to form a higher degree filter.
The outermost box is really there to create the chamber around the isolating
air and in there your heavy mass (big cap) is gets heated (charged) and chilled
(discharged) through the air and black-body radiation.

Having the heavy mass fairly directly exposed to the surrounding air will
provide better conductivity through drag...

Oh, humidity will change the heat conductivity of the air noticeably.

Cheers,
Magnus

My understanding of thermal regulation is that one of the more difficult
thing to do is precisely to know what is the temperature of the components
you are trying to stabilize.

If you have one oven (even double oven), you have one temperature sensor.
The best you can do is keep the sensor at a constant temperature. Assuming
the temperature sensor is kept at a perfectly stable temperature, how
constant will the temperature of other components be will be a matter of
hardware design and layout. I.e. the components you are trying to stabilize
should be closely thermally coupled to the sensor. Because there are more
than one component to stabilize, not just the crystal, it is a difficult
task.

The issue is not just static regulation, but also regulation in the presence
of a temperature gradient. We understand that if you change the ambient
temperature by X, the oven will react to keep the sensor's temperature
constant, but the distribution of that heat flux will change dynamically
(particularly it will be affected by the masses that are in the way, between
the source of heat and the components that are to be stabilized), and even
if you have perfect static regulation, in most cases there will be a
non-zero dynamic response (a transient).

The designers of the HP E1938 (which never went to full production) went
through pains to try and keep the gradient evenly distributed precisely for
that reason. My guess is that it you take the cover out from the E1938, you
will find a perfectly symmetrical layout around the center, where the
thermistor is located.

A large massive cover over the OCXO will go a long way to reduce the
transient and allow the oven controller loop to react smoothly, but as long
as the time constant is less than the period of variation (a day?), the peak
to peak frequency variations will not change much, but they should be more
predictable and may be compensated by a feed-forward mechanism, or a Kalman
filter.

Didier

By having only one sensor, in the case of the double oven that is obviously
not true, but what I meant was that even with a double oven, you only have
one sensor near the components you try to regulate, the other sensor
regulates the outside temperature of the first oven.

Didier

Didier Juges wrote:

Actually, something like 30,000 E1938A's were built.  Maybe the glass is
not full, but it is not exactly empty.  As I explained in my 1997 FCS
paper, the oven is very symmetrical, etc.  We routinely achieved a
thermal gain of several 100,000.  During design testing, we could often
get the thermal gain up to well over 1 million.    This is the thermal
gain to the crystal.  Of course, the gain to the electronics was less.
The thermal gain of a good 10811 is around 1,000, by comparison.

Rick Karlquist N6RK
E1938A designer