[time-nuts] HP10811 dual oven

[WarrenS]

Mark Posted
>I laid out a through-hole version of Warren's board in Eagle
>and had OSHPARK fab up three of them.
>I sent one to Warren and am using the other two.
>The one mod I made was to use a single darlington TO-220 instead
>of the two transistor stage that Warren used.
>They seem to work quite well.

I tested Mark's through-hole PC board Dual oven controller and
it worked very well and was well laid out.    **(see attached)**
The only changes I made to Mark's PCB where:
R1(Temperature Adj) ~ 35K  and R4 = 1K

Dan Kemppainen also laid out a nice looking, very small surface
mount dual oven control board, but I was not able to test it.

This outer oven controller is able to hold the inner oven's temperature
to within 0.1C over normal room temperature variations,
The effect is the HP10811's frequency change due to temperature variation
(aka temp coeff) is reduced by more than 60 to 1,
from 6e-11/C to under 1e-12 /C

<http://www.mail-archive.com/time-nuts%40febo.com/msg59680.html>
<http://www.febo.com/pipermail/time-nuts/attachments/20100223/c94d5eec/attachment-0001.gif>

As has pointed out in response to the above nut posting,
if the osc is already being disciplined at shorter time constants,
then the improvement is not nearly as great, and may not be helpful.
The big improvement is seen when the osc is in holdover or running
open loop or running with a very long disciplined time constants >1000
seconds.

The reason I designed the linear dual oven controller to run on
15V power is that unlike the standard HP10811, the dual
oven 10811's inner oven can run at 15V, So a single 15 volt PS
followed by a 12V regulator makes it a single supply design.

Is a outer oven needed? Yes, but only if you are a freq nut.
Note that adding an outer oven is generally easier to do than
burying the osc in a pool of underground mercury or most of the
other nut things that have been suggested in the past to reduce the
effect of temperature variation.


ws

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