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This article in AJ

  1. Vol. 61 No. 4, p. 597-601
    Received: Jan 9, 1969



Simultaneous Cycling of Peltier Thermocouple Psychrometers for Rapid Water Potential Measurements1

  1. G. J. Hoffman,
  2. W. N. Herkelrath and
  3. R. S. Austin2



An automatic system was built to record the output from Peltier-effect thermocouple psychrometers. The system consists of a scanner, capacitors, voltmeter, and a recorder. The scanner, built from inexpeusive commercial components, is of solid-state circuitry and contains only one moving mechanism, a stepping relay. The system automatically reads and stores the initial emf, cools as many as six psychrometers simultaneously, reads and stores the final emf, and heats the measuring junction of the psychrometers. For a 30-second cooling period, six psychro~neters can be read in 2½ minutes. By adding a stepping relay, as many as 150 psychrometers can be read in an hour. The standard deviations for recorded calibration outputs were ±0.04 µv for soil and intact leaf thermocouple psychrometers. Under actual experimental conditions, the values obtained with the automatic system were as accurate as measurements made manually.

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