[time-nuts] High accuracy temp controller ckt

[Bob kb8tq]

Hi

Airlines tend to have issues with various battery types as well. Not clear 
what the rules are on “powered up in the hold” are. My guess is that ground
transportation gets the nod pretty quickly. 

TEC’s are good for some limited temperature delta and then you need to go to
cascaded “layers” of them. In cascade, the power requirements just go up and up.
If your shipping container could be on a hot runway / parking lot or in an un-heated 
hold at  40,000 feet ….. the design could get really “interesting”. 

A whole other set of questions might reasonably be asked about pressure, 
humidity, shock and vibration. No idea about the answers on a precision resistor. 
On other devices they certainly *do* pop up.

One traditional answer for things like running Cs standards was to have a 
“minder” (or two or three) accompany the device on it’s trip to the destination
lab. It traveled as close to them as practical ( = in the passenger compartment)
to minimize the issues. That also made hooking it to power while in transit
a bit easier. Even with that level of pampering, the story seems to be that the
trip was not always successful. 

Bob

> On Jul 12, 2019, at 4:38 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> drkirkby at kirkbymicrowave.co.uk said:
>>> If you do go the TEC route, plan on a fairly big power source :).
>> I'm particularly keen to avoid the requirement for high power, as I was
>> thinking to make this in such a way it can be shipped and powered up all the
>> time. 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.
> 
> 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.
> 
> What's the hysteresis on a resistor?  Is it really important to ship it 
> powered up?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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