1. US5341673 - Method and device for monitoring of moisture in soil

A system for monitoring the moisture content of soil uses a timing capacitor. The capacitor has several conductive elements adapted for insertion into soil to sense the hydration state capacitance of the soil. A capacitance-to-frequency converter electrically connected to the capacitor has an oscillator circuit. The frequency of the oscillator circuit has a frequency dependent upon the value of the capacitor and independent of the electrical losses in the capacitor. A data logger measures the frequency generated by the capacitance-to-frequency converter, the frequency bearing a known relationship to the dielectric constant and, hence, the water content of the soil. The conductive elements are surrounded by shields of electrical potential substantially equal to that of the timing capacitor.