[time-nuts] uC ADC resolution (was: Poor man's oven)
jimlux at earthlink.net
Wed Jun 7 23:04:46 EDT 2017
On 6/7/17 7:35 PM, Bob kb8tq wrote:
> Metal actually makes things a bit worse since it has a lower thermal resistance than glass.
> This is also why a high performance dewar is made from glass rather than metal. Yes, you
> can go to weird stuff like titanium (it has been done). You can’t afford that ….
> If you fill the entire dewar with a heat conductor you make things worse still. The idea is to
> *block* heat flow out of the heated area. Even without fill, the wall of the dewar goes from the outside
> world to the heart of the heated area. It is the perfect “sneak" path into the oven. Actually
> it’s not that much of a sneak path since it’s a well known effect :)
> Again, none of this is particularly original. Take a hammer to any dewar based OCXO and
> the details are going to be similar.
And the wires provide a thermal path - you've got to get power to it and
the oscillator signal out.
In dewar OCXOs (like the USOs made by APL), the leads are essentially
the only thermal path in/out.
BTW, you don't want to do oil filled. All oil filled electronics (unless
welded closed) inevitably leaks, oozes, or otherwise puts oil on the
outside. If you *must* have oil, then use solid, uninsulated wires to
penetrate the surface of the oil. Otherwise you'll gain new appreciation
for what capillary action is.
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