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Agronomy Journal Abstract -

Four-terminal Peltier Type Thermocouple Psychrometer for Measuring Water Potential in Nonisothermal Systems1


This article in AJ

  1. Vol. 62 No. 6, p. 705-708
    Accepted: June 26, 1970

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  1. A. A. Millar,
  2. A. R. G. Lang and
  3. W. R. Gardner2



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 #v/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.

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