[time-nuts] High accuracy temp controller ckt

[Bob kb8tq]

Hi

Ok, if it’s a “heat only” design, how about a dewar flask? They aren’t the most rugged items
out there so some sort of padded enclosure would be needed. The real question is:

Does a “single end” design impact your ability to use the resistor? Put another way - do you need
to hit both ends of the device more or less directly? 

There are a variety of eBay sellers that will set you up with parts in a variety of shapes and 
sizes. As far as I can see, their designs would be reasonable for what you are trying to do.

Back a while, the dewar was the enclosure of choice for a high grade OCXO. As people 
learned how to do ovens a bit better and the world decided they needed smaller parts,
that approach fell by the wayside. It’s still a great way to get a reasonable oven that pulls
pretty low power.

Bob

> On Jul 12, 2019, at 7:45 PM, Dr. David Kirkby <drkirkby at kirkbymicrowave.co.uk> wrote:
> 
> On Fri, 12 Jul 2019 at 22:02, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
>> 
>> drkirkby at kirkbymicrowave.co.uk said:
>>> If it could run from a few NiMH cells for 48 hours, that would give the
>>> option of shipping it. I don't know if that's going over the top, but it
>>> would be an interesting exercise.
>> 
>> Shipping a TEC cooler could get interesting.  You need to get rid of the
>> heat
>> somehow.  Cooling fins on a package would be interesting.
> 
> 
> That is why I said that I would avoid a TEC. Running an oven should be less
> problematic.
> 
>> 
>> 
>> The airlines don't like dry ice.  You could try an ice pack/gel.  If it's
>> well
>> insulated, the TEC will be off.  The heater won't take much power.  It's
>> just
>> a matter of how much insulation you need.
> 
> 
> I would not aim to ship by air, although at a push that might be possible.
> 
> In the UK, in theory items can be shipped with batteries by Royal Mail
> subject to some restrictions. Batteries  inside equipment are okay up to
> some capacity. Damaged cells or lose cells are not. In practice a lot of
> staff in post office shops say no to batteries.
> 
> I regularly get alkaline and NiMH batteries delivered from Farnel by UPS.
> The packages are not marked. In contrast, even a coil cell comes in a box
> saying it is batteries, not in transport if the package is damaged etc. So
> Farnell follow all the rules.
> 
> I contacted DHL once about a UK shipment of a battery powered item. That
> was not a problem.
> 
> If the box was much bigger than an OCXO, resistor oven, I don’t believe
> heat would be a problem.
> 
>> 
>> 
>> What's the hysteresis on a resistor?  Is it really important to ship it
>> powered up?
> 
> 
> That I don’t know, but sometimes one does things as a challenge out of
> interest, and to learn. It would be interesting to know if a resistor was
> worth shipping powered up.
> 
> Dave.
> -- 
> Dr. David Kirkby,
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