Recirculating apparatus for testing hygrometers
Arnold Wexler · Journal of research of the National Bureau of Standards · 1950
An appa ra t us t hat was developed fo r produ cin g at mosph eres of known r elat ive humidi ty is described.It was des ig ned, principally, for research on and calibrat ion of radiosond e hyg rom eter elem ents a t t emperatures ab ove freez in g, b ut is equally useful at te mpe ra t ures down to -40° C. It o perates by sa t ura t.in g air a t one te mpe rat ure and t hen raisin g the a ir te mpera turc suffi cient ly to g ive an y desired relati ve humidity.The ail' is rec irculated co n t inu o usly in a closed syste m .Four iden t ical, bu t in de penden t, recircula tin g sy ste ms a re employed.Discrete cha nges in humidi ty and te mperat ure are obtain ed by m eans of a novel pn euma t ic valve t ha t per mits t he hyg rom eters und er t est to be sw itched, ea sily , from system to syste m.C hec ks on t he pe rforman ce of t he appa rat us b y means of t he g ra v im e t ric m ethod of mois t ure determina t ion and the psychrom et.ri c method sho w an a verage difference in relative humidi ty of ± 1.2 percent.