Plant irrigation system water content sensor - using thermal pulse probe in defined earth sample

摘要

A measurement sensor for determination of water in the earth is designed for sufficient accuracy for control of automatic irrigation installations. The probe uses the thermal pulse principle of moisture measurement applied to a known volume of sample earth with known characteristics. The sample earth (1) is enclosed in a fine net (2) placed in the soil (5). A thermal probe (3) with heating and temp. measurement windings is inserted into the sample and connected to further equipment via a cable (4). The moisture content of soil and sample earth are in equilibrium. The sample moisture content is periodically measured by recording the temp. of the probe before and directly after applying current to the heating coil for a short time. The temp. difference is a measure of the moisture content.