Patent ID: 7408364

Claim:
A method of determining a moisture content value and a salinity value of a soil, the method comprising: providing a sensor, the sensor comprising a probe conducting structure to be placed in the soil to form a capacitor, a soil moisture circuit comprising a high frequency oscillator for applying a first electrical stimulus to the probe structure, a reference capacitor connected in series to the high frequency oscillator, and a first voltage meter located between the high frequency oscillator and the reference capacitor, and a soil salinity circuit comprising a low frequency oscillator for applying second electrical stimulus to the probe structure, a reference resistor connected in series to the low frequency oscillator, and a second voltage meter located between the low frequency oscillator and the reference resistor, wherein the low frequency oscillator is substantially lower in frequency than the high frequency oscillator, wherein the soil salinity circuit and the soil moisture circuit connect between the reference capacitor and the reference resistor, at which point the soil moisture circuit and the soil salinity circuit are connected to the probe structure and a third voltage meter; measuring voltages V 1 , V 2 , and V 3 , wherein V 1 is the output voltage measured by the first voltage meter when the low frequency oscillator and the high frequency oscillator are inactive, V 2 is the output voltage measured by the second voltage meter when the low frequency oscillator and the high frequency oscillator are inactive, and V 3 is the output voltage measured by the third voltage meter when the low frequency oscillator and the high frequency oscillator are inactive; measuring voltages V 2 ′ and V 3 ′, wherein V 2 ′ is the output voltage measured by the second voltage meter when the low frequency oscillator is active and the high frequency oscillator is inactive, and V 3 ′ is the output voltage measured by the third voltage meter when the low frequency oscillator is active and the high frequency oscillator is inactive; measuring voltages V 1 ′ and V 3 ″, wherein V 1 ′ is the output voltage measured by the first voltage meter when the low frequency oscillator is inactive and the high frequency oscillator is active, and V 3 ″ is the output voltage measured by the third voltage meter when the low frequency oscillator is inactive and the high frequency oscillator is active; calculating a capacitance of the soil as a function of (V 3 ″−V 3 )/(V 1 ′−V 1 ) to obtain a soil moisture content value; and calculating a resistance of the soil as a function of (V 3 ′−V 3 )/V 2 ′−V 2 ) to obtain a soil salinity value.