Hi One of the (many) parts of the EG&G empire made a dew on the mirror setup and (apparently) sold quite a few of them. It was one of the few gizmos that could reliably tell you about very low temperature (like -50C) dew points.
Bob > On Dec 23, 2020, at 8:37 PM, Dana Whitlow <[email protected]> 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 <[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. _______________________________________________ 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.
