1. US5224769 - Method and device for non-invasive monitoring of hydration state of plants

A system for the non-invasive monitoring of the hydration state of a plant comprising the elements: PA0 a timing capacitor comprising a plurality of conductive elements adapted for mounting on a plant part to sense the hydration state capacitance of the plant part; PA0 a capacitance-to-frequency converter electrically connected to the timing capacitor comprising an oscillator circuit having a frequency dependent upon the value of the timing capacitor and independent of the electrical losses in said timing capacitor; PA0 means for supplying electrical power to the capacitance-to-frequency converter; PA0 means for measuring 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 plant part; and PA0 devices for electrically guarding the circuit generated by the elements from capacitance extraneous to the plant part comprising means for surrounding the elements with shields of electrical potential substantially equal to that of the timing capacitor.