Capacitance Measurements

Capacitive sensors measure the resonant frequency of an inductance-capacitance (LC) tuned circuit where the soil located in between two flat waveguides is the dielectric material. The inductance is kept constant and the resonant frequency f measured and therefore the capacitance can be calculated from

2n ^ e

where Le is the inductance and Ce is the capacitance. The capacitance Ce is a measure of the relative bulk dielectric constant of the soil and is a function of the water content of the soil (Veenstra et al., 2005). As with all dielectric moisture-based sensors, calibration is necessary for an accurate determination of the water content. Starr and Paltineanu (2002) give an overview of the current capacitance methods, their instrumentation and procedures.