Precision Lysimetry in Franceby Philippe Grebet, INRA, Thiverval-Grignon, France,
Abstract: After a definition of the parameters to be measured, a possible reasoning is presented for the construction of a weighing lysimeter. A number of factors have to be taken in account: the soil inertia, the sensitivity of the whole data acquisition system (from the sensors to the recorder), the disturbance of the medium by the equipment, and, finally, the manufacturing and installation costs of the lysimeter. The final design depends on the importance attributed to each of these factors. After testing various weighing system such as floating on a zinc chloride solution, hydraulic systems (with rubber bolsters) and an entirely electronic system, we decided, in the end, to use only the last one. The lysimeter was made up of: 1/ An outer iron tank forming a watertight container and supporting bottom. 2/ A double triangular frame for holding three load cells (one on each corner of the triangles). 3/ An inner iron tank filled with the soil to be weighed. 4/ Initially a strip-chart recording system and currently a more sensitive digital recorder For improved sensitivity and precision we also used a mechanical-electronic weighing system.
Subject Headings: Measuring instruments | Water resources | Data collection | Evapotranspiration | Water tanks | Iron compounds | Parameters (statistics) | Terminology and definition | France | Europe
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