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A study designed to measure the effect of advection(2) required the measurement of evapotranspiration at seventeen sites. Since lysimeters measure evapotranspiration directly, it was decided to install a lysimcter at each site. Because low cost of each unit was paramount in a multiple lysimeter installation, the hydraulic load cell lysimeter was selected. The purpose of this paper is to describe and compare the performance of two types of hydraulic load cell. DESIGN A good review of lysimeters, including the hydraulic load cells, has been provided by Tanner (6). The first attempt by the authors was to support the lysimeter on three bags made from 30-cm diameter butyl-nylon pipe connected to a 3-well differential mercury-water manometer (6) located in a manhole below ground surface. Since it was difficult to space three rectangular bags under a circular tank 0.86 m in diameter and to keep a supply of mercury in the reservoirs if the tank leaned, it was decided to simplify the device by using a coil of 5-cm diameter lay-flat butyl tubing (Figure 1) connected to a single well differential mercury manometer (7). The differential mercury water manometer was temperature sensitive, and correcting for temperature effects did not prove successful.
hydraulic load cell lysimeters
Korven, H.C. and W.L. Pelton 1972. HYDRAULIC LOAD CELL LYSIMETERS. Canadian Agricultural Engineering 14(1):33-36.
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