[time-nuts] uC ADC resolution (was: Poor man's oven)
kb8tq at n1k.org
Wed Jun 7 18:18:50 EDT 2017
Consider that a lot of the heat flow is through the glass wall of the
vacuum gizmo. You want to tie your heater(s) to it in order to create
an iso-thermal “wall”. Often this is done by gluing the whole assembly
In addition, you probably also want a foam plug in the end
of the beast to keep from creating an even more non-uniform (= very
directional) heat flow. Yes, the directivity issue is inherent in the design
approach. It’s not clear that you want to exaggerate it ….
> On Jun 7, 2017, at 6:03 PM, Attila Kinali <attila at kinali.ch> wrote:
> On Wed, 7 Jun 2017 22:20:50 +0100
> Peter Vince <petervince1952 at gmail.com> wrote:
>>> Additionally: if I would set out to build my own OCXO today, I would
>>> go and buy one of those lunch thermos flasks to house everything. Their
>>> isolation is higher than anything you can easily build yourself,
>>> especially at that size. I would place the (inner) oven at the bottom,
>>> probably using a puck design similar to the E1938, place the electronics
>>> on top of it and close the lid using an aluminium plate which forms
>>> the outer oven.
>> Might there be a problem that a thermos flask is TOO well insulated, and
>> even the minimal heat generated in the electronics would be more than could
>> escape through the vacuum, and so the unit would cook?
> That's why the top of the flask is closed with an aluminium plate.
> Assuming the plate on the top is around 5x5cm, that should give a
> thermal resistance in the order of 20-40°C/W. That's not low, but
> should be enough to support 100-400mW of heat generated inside
> with a moderate temperature differential. If it turns out not to
> be enough, making the plate bigger and attaching a few fins, or
> having a small fan blowing lightly on it should solve the problem.
> Attila Kinali
> You know, the very powerful and the very stupid have one thing in common.
> They don't alters their views to fit the facts, they alter the facts to
> fit the views, which can be uncomfortable if you happen to be one of the
> facts that needs altering. -- The Doctor
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