Moisture sensor and switch

Abstract

Soil moisture sensor apparatus includes a housing 10 having an expansion chamber 13 and a piston 20 slidably mounted within the housing 10. Formed through the wall of the housing are electrical lead take-outs 15 through which pass cable tails 16. The piston 20 has a rebate 21 adapted to allow the piston 20 to pass partly by a protruding portion of a fixed contact 22 embedded in the wall of the housing at the upper take-out 15. Bearing on the lower surface of the piston 20 is a moving contact 24, the contact 24 being urged against the piston face by a spring 25 which also serves to bias the piston 20 towards the open end of the housing 10. Disposed across the expansion chamber 13 is a flexible membrane 26 retained in position by an end cap assembly including an annular end cap body member 27, an outer mesh screen portion 32 and a dirt excluding inner fabric portion 33. Contained in the space defined between the fabric portion 33 and the flexible membrane 26 is a water swellable polyacrylamide gel bead composition 34, the expansion and contraction of which moves the piston respectively against and with the bias of the spring to break and make the circuit.

Dependencies are inferred from the claim text.