Absolute-reading soil moisture and conductivity sensing method

摘要

A method of sensing moisture based on propagation-delay provides absolute readings of volumetric water content in a moisture-bearing medium without calibrating the sensor or its readings for the conductivity or temperature of the medium. A fast transition is launched on a transmission line that is immersed in the medium to be measured. The amplitude of the resultant waveform is analyzed at precise, programmable time increments by using a high-speed latching comparator. Firmware in a controlling microprocessor facilitates the successive reconstruction of the significant characteristics of the returning waveform. The microprocessor analyzes these characteristics to provide an accurate determination of propagation delay and conductivity, even for severely distorted waveforms. The moisture content of the medium is derived from the propagation delay.