The optical sensing of despoint by dew-on-the-mirror was used in a device designed at the Whirlpool Research labs in St. Joseph, MI. It apparently never made it into production, but a number of units were built and sold or given away (I'm not sure). I know about this because I interned at the lab during college summer breaks, and on one occasion I was asked to replace the Peltier (TEC) module in one of these units. These units had a thermocouple buried under the cold mirror's surface, and use of the device required that the user provide the instrument to read the thermo- couple's temperature.
I've long wondered how this system dealt with the fact that the desired operating point of the loop is on a sharp corner of the light versus temperature curve where dew is just beginning to form, and there is no "negative dew" on the warm side of that point. I hadn't thought of this complication when I was working with this thing, however, or I would have asked. Oh, well, an opportunity missed. Sigh! Dana On Wed, Dec 23, 2020 at 6:53 PM Bruce Griffiths <[email protected]> wrote: > 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 <[email protected]> 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 > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
