| Autor: |
Jack J. C. Hsieh, Frank P. Hungate |
| Rok vydání: |
1970 |
| Předmět: |
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| Zdroj: |
Soil Science. 110:253-257 |
| ISSN: |
0038-075X |
| DOI: |
10.1097/00010694-197010000-00005 |
| Popis: |
A SIMPLE FIELD MODEL PSYCHROMETER WITH BUILT-IN TEMPERATURE COMPENSATION FOR MEASURING WATER POTENTIAL IN SOIL OR PLANT TISSUES IS DESCRIBED. THE ADVANTAGE OF THE DEVICE IS THAT WHILE AS ACCURATE AS OTHER PSYCHROMETERS IN MEASURING WATER POTENTIAL UNDER STABLE TEMPERATURE CONDITIONS, IT SIGNIFICANTLY IMPROVES ACCURACY WHEN ABRUPT CHANGES OCCUR. THE COMPENSATION IS ACHIEVED BY TWO IDENTICAL (25-MICRON DIAMETER CONSTANTAN-CHROMEL WIRE CONTAINED IN A TEFLON CAVITY WITH AN INTERNAL DIAMETER OF ABOUT 6MM) THERMOCOUPLES CONNECTED ELECTRICALLY IN SERIES BUT IN OPPOSITE POLARITY. MOST OF THE CURRENT GENERATED BY AMBIENT TEMPERATURE CHANGES ARE THEREBY AUTOMATICALLY CANCELLED. DURING A 51-MIN RECORDING SESSION IN WHICH CHAMBER AIR TEMPERATURE WAS CYCLED BETWEEN 20.1 AND 20.9 DEG C EVERY 5 MIN, THE MAGNITUDE OF FLUCTUATION IN THE UNCOMPENSATED PSYCHROMETER WAS 4.8 MICROVOLTS, EQUIVALENT TO A WATER POTENTIAL OF 11 ATM, WHILE UNDER IDENTICAL CONDITIONS THAT OF THE COMPENSATED DEVICE WAS 1.2 MICROVOLTS (2.8 ATM). ANOTHER ADVANTAGE OF THE NEW DEVICE IS THAT A NULL SETTING CAN BE ACHIEVED ON A MORE SENSTIVE SCALE. CHARACTERISTICS OF EMF VARIATIONS WITH ABRUPT AND CONTINUOUS TEMPERATURE CHANGES ARE DISCUSSED WITH REFERENCE TO THE DESIGN OF AND EFFECTS IN THE COMPENSATED PSYCHROMETER. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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