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Four‐terminal Peltier Type Thermocouple Psychrometer for Measuring Water Potential in Nonisothermal Systems 1
Author(s) -
Millar A. A.,
Lang A. R. G.,
Gardner W. R.
Publication year - 1970
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1970.00021962006200060006x
Subject(s) - hygrometer , thermocouple , water vapor , bar (unit) , calibration , thermoelectric effect , analytical chemistry (journal) , chemistry , materials science , thermodynamics , humidity , composite material , meteorology , mathematics , environmental chemistry , physics , statistics , organic chemistry
The construction, calibration, and tests of a miniature four‐terminal thermocouple psychrometer are described. Improved thermal stability under nonisothermal conditions is the main feature of this new type of psychrometer. This is achieved using a separate thermocouple to cool and condense water vapor on the sensing thermocouple. The sensitivity for this thermocouple psychrometer is about 0.4 μv/bar ‐ at 25C, and is operable at temperature fluctuations of about 0.5C during the course of a measurement. In situ measurements of water potential in onion leaves under a cloudy day differed by 0.5 to 1 bar from measurements on detached leaves. With greater temperature fluctuations, water potentials obtained by the two methods differed by as much as 2 to 3 bars.