[time-nuts] Double ovened 10811-60158 on ebay

[Ulrich Bangert]

Magnus,

> 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.

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   



> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Magnus Danielson
> Gesendet: Samstag, 12. Juli 2008 11:06
> An: time-nuts at febo.com; richard at karlquist.com
> Betreff: Re: [time-nuts] Double ovened 10811-60158 on ebay
> 
> 
> From: "Richard (Rick) Karlquist" <richard at 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 at karlquist.com>
> 
> > 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.
> 
> My thought exactly.
> 
> > 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?
> 
> 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
> 
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