The method still appears to be in use: http://www.michell.com/nl/documents/Optidew_Vision_97144_NL_Datasheet-V6.pdf
Bruce > On 24 December 2020 at 14:37 Dana Whitlow <k8yumdoo...@gmail.com> wrote: > > > 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 <bruce.griffi...@xtra.co.nz> > 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 <e...@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 > > > > > > _______________________________________________ > > > time-nuts mailing list -- time-nuts@lists.febo.com > > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > > and follow the instructions there. > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.