As most chamber-control instruments assume the latent heat of vaporization is constant with temperature, control is problematic (if not impossible). Most instrument measurements are not reliable below freezing, as there is no way to distinguish between supercooled water (evaporation) and ice (sublimation) in your wet bulb, and the differences in vapor pressures. According to my (old and dusty) physics text book, supercooled water can be present as low as -12C, so low-temp control may be possible. So I would suggest performing the test in a controlled atmosphere >90% nitrogen.
Your best bet is to use an environmental chamber must be actively controlled, that uses a controller that does not require an equilibrium to develop, be a positive pressure chamber, have a controlled exhaust manifold, and where the chamber atmosphere exchange rate prevents any significant direct condensation (as this will become a water vapor "sink". I have noted, but not necessarily used, the following instrument, which may used accomplish low-temp measuremnt and control: http://www.sablesys.com/dg1.html Google is your friend. Also, ask this question in the "sci.geo.meteorology" newsgroup. luck, Brian > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of > [email protected] > Sent: Tuesday, November 29, 2005 5:22 AM > To: Emc-Pstc (E-mail) > Subject: Environmental testing help > > > Dear All, > Is it possible to control the humidity at 0 deg. 'C'? > One of our > customer specification lists an environmental testing at 0 > degree 'C' / 7 > % RH. Is there any lab capable of doing this testing? I > request help from > the forum members. > > Sincerely > > K.Balasubramanian > Project Leader - Hardware. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
