An Electronic Sensor for Vapor-Pressure Deficit of the Air1
- W. C. Johnson and
- R. G. Davis2
The parameter of vapor-pressure deficit (VPD) is used in several methods of calculating potential evapotranspiration. This note describes an electronic sensor for measuring VPD whose principle of operation is based on wet and dry-bulb psychrometry and utilizes thermistors and silicon diodes as wet and dry-bulb probes. These probes produce two voltages which, when multipled together by an inexpensive, commercially available, analog multiplier, result in an output voltage proportional to VPD that can be recorded continuously on a strip chart recorder. The VPD sensor has shown good reliability in actual field tests with accuracy that would not be a limiting factor in calculating potential evapotranspiration. Detailed information on construction and operation of the sensor is available from the authors and will be mailed on request.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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