Irrigation control apparatus responsive to soil moisture

Claim 1

An improved irrigation control apparatus for controlling operation of an electrically operated valve in an irrigation system, which comprises: (a) a soil moisture sensor buried at least partially in the ground, wherein the sensor has at least one electrically conductive moisture sensing element which uses electrical power to generate an output signal indicative of the level of moisture in the ground; and (b) a control unit operatively connected to the sensor and to an electrical power source for controlling the operation of the valve in accordance with the level of moisture in the ground, wherein the control unit has control circuit means for applying a relatively short duration pulse of power to the moisture sensing element of the sensor to obtain a sensor output signal only during the pulse, whereby corrosion of the sensor is minimized, wherein the control circuit means includes means for electrically isolating the sensor from the electrical power source whenever the sensor is unpowered, whereby the electrical isolation means protects the sensor from low level leakage of electrical power from the power source, wherein the electrical isolation means includes normally open relay means between the sensor and the electrical power source, which relay means is closed by the application of power to the sensor and is otherwise open, further helping minimize sensor corrosion.