| abstract |
An apparatus for soil irrigation control comprising a control unit, a soil probe, and a temperature probe. The function of the invention is to provide day-to-day soil moisture measurement and control of the irrigation system it is attached to, usually a timer operated system. During operation, the control circuitry periodically measures the apparent electrical resistance between the two electrodes of the soil probe. A signal related to the measured resistance is then compared to a reference set by the user and functions to close or open an electrical switch that ultimately controls the application of irrigation water. The apparatus has a temperature sensor to compensate for effects upon the moisture sensor due to changes in soil temperature, and to also suspend irrigation when freezing conditions are pending. The apparatus also detects the presence of a external timer signal and sustains irrigation through completion of the timer cycle even though the moisture sensor may become wetted during the cycle. The apparatus is capable of a wide range of adjustment to accommodate soils having vastly different characteristics and moisture content, attained by having a novel logarithmic current pulse generator. |