[time-nuts] TECs in cooling below ambient

[Bruce Griffiths]

You could always use a TEC as the heart of a dewpoint sensor by optically sensing the temperature required for dew to form on a cooled mirror.
In practice the temperature at which the dew vanishes is typically used.
A collimated light beam together with a photodiode is typically used to sense the presence of dew droplets on the mirror.

Bruce
> On 24 December 2020 at 08:57 ed breya <eb at telight.com> wrote:
> 
> 
> This recent TEC talk reminded of some of my long term planned projects, 
> and related issues. I have at least four "someday" projects involving 
> TECs, to regulate device temperatures near or below "normal" room 
> temperature, including a high precision DC voltage standard, a sub-fA 
> electrometer circuit, a constant temperature block for nonlinear analog 
> computing elements, and a small general purpose heat/cool box for device 
> and circuit testing. Each has its own particular system, application, 
> and environment issues, but common to all is the lower limit of running 
> temperature, based on the local climate conditions and dew point. I plan 
> to estimate the lowest possible operating temperatures for expected 
> conditions, that avoids condensation, and not having to resort to 
> special packaging.
> 
> An essential thing for this is a dew point calculator. I found lots 
> online, but this is my favorite so far. It's slider-based, so you don't 
> even have to enter numbers.
> 
> http://www.dpcalc.org/
> 
> The harder part is finding the normal range of local climate conditions.
> 
> Ed
> 
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