Another thing to watch out for is circulating currents due to thermal
emfs with the aluminium to steel contacts.
Such thermoelectric currents will in turn generate a magnetic field.
Bruce
Bob Camp wrote:
Hi
The big hitters for heat outside the physics package seem to be the RF excitation and the
microwave generation "stuff". The regulators will warm things up if you run
high voltage into them, but I would probably not do that.
I don't believe that putting multiple swimming pools into the basement, mercury filled or
otherwise was ever a real candidate for a solution. It is kind of interesting to see just
how big the "jug of water" would have to be.
Right now my leading candidate is a multi layer aluminum / steel enclosure with a "point short"
between each of the layers to keep the heat rise under control. Cool the "baseplate" with
recirculating water and a cheap (< $50) pump. Throw in a fan and radiator to cool the water to room
temperature. Servo the temperature with "what ever" at the point shorts. Monitor the temperature as
best you can.
The main "what ever" still in there are TE coolers. A quick look suggests that
+12 heats and -12 cools. In between the two it's not clear that much happens (maybe it
does ...). Even if it does not, I haven't dug deep enough to see if something like
current drive takes care of the dead band issue.
Some math. It's late, but I think this is about right:
1) 4 layers
2) Shorts at 2 C/W
3) 10 W "inside"
4) 80 C heat rise - not going to work
If I stick with 4 layers, 10 W, and a 15 C rise then the shorts need to be ~
0.38 C/W. A 15C rise gets me to 40C which looks reasonable based on the app
notes I have read on the rubidiums.
If the basement moves up 5 C then I'm cold pumping 1/3 of the 10W. Same thing
in reverse if the basement drops 5 C. Both are unlikely to happen as long as
there isn't a catastrophic failure of the HVAC.
If I go to a air cooled baseplate heat sink, it's thermal resistance is going
to have to come out of the budget. My *guess* is that's going to be more
involved than a simple pump and some plastic tubes.
Bob
On Dec 24, 2009, at 10:46 PM, Hal Murray wrote:
li...@cq.nu said:
The original intent was to simply take an existing "cheap" rubidium
and do simple things to it. Tearing it into pieces and redesigning
parts of it was not anything I originally contemplated. The tight
integration of the physics package to the electronics would make this
a fairly involved process.
Sure, but if we are discussing digging a hole big enough for a ton of
mercury, then taking apart a tightly integrated package seems worth
considering.
I expect the packaging might be reasonable for this purpose. After all, the
designers probably wanted to keep that heat away from the electronics.
--
These are my opinions, not necessarily my employer's. I hate spam.
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