Rain detector for irrigation control

Claim 1

In a rain sensor system, for controlling irrigation, the combination comprising (a) a heat diffusion sensor comprising a thermistor having a tip exposed to the atmosphere and characterized in that relatively higher heat loss created by collection of water adjacent the sensor reduces its electrical resistance, and relatively lower heat loss created by absence of such water collection increases the sensor electrical resistance, and (b) circuitry means operatively connected with the sensor for controlling an actuator for an irrigation valve, (c) there being a water collector tray having an interior wherein the thermistor is exposed to water collecting in the tray to be cooled by such water, the tray located above ground, (d) said thermistor and circuitry means connected to initiate irrigation when water is absent from the tray, (e) the top of the thermistor located in the tray at a substantial distance below the top level of the tray and above but near (rear) bottom level of the tray interior, whereby water filling the tray must evaporate from the tray down to the level of the thermistor before the thermistor will initiate irrigation via the circuitry means to actuate said valve, (f) there being a body supporting the tray and in which said circuitry means is protectively located, whereby the body, tray and thermistor and circuitry means form a single unit.