Moisture sensing electronic irrigation control

• US 5,749,521 A
• Filed: 05/22/1996
• Issued: 05/12/1998
• Est. Priority Date: 05/22/1996
• Status: Expired due to Fees

• Current Assignee: Lore Parker
• Original Assignee: Lore Parker
• Inventors: Lattery, Jerome E.
• Primary Examiner(s): Taylor, Dennis L.
• Application Number:
  US08/651,740
• Time in Patent Office: 720 Days
• Field of Search: 405/37, 405/36, 405/52, 137/78.3, 239/63, 239/64, 239/67, 239/68, 47/1.01 R, 340/604, 324/664
• US Class Current: 239/64
• CPC Class Codes: A01G 25/167 Control by humidity of the soil itself or of devices simulating soil or of the atmosphere; Soil humidity sensors
• CPC Class Codes: Y02A 40/22 Improving land use; Improving water use or availability; Controlling erosion
• CPC Class Codes: Y10T 137/189 Soil moisture sensing

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.

Claims

1. An apparatus for comparing the amount of moisture in soil with a reference setting and controlling the application of irrigation water, comprising:

an electronic means for generating periodic electrical current pulses that pass through the soil between two conductive electrodes fixed upon a nonconductive support and disposed beneath the surface of the soil, said electrical current being in the form of a unipolar pulse of the briefest practical duration followed immediately by a unipolar pulse of the same duration and current amplitude having opposite polarity,

an electronic comparator means that compares the voltage potential difference produced by said electrical current pulses between said conductive electrodes with a voltage potential expressing a reference setting,

an electronic sensor means for measuring temperature of the air or soil and applying a correction to said voltage potential that expresses said reference setting, equal to the effect from change with temperature of the apparent electrical resistance in the soil medium,

an electronic switching means that completes an electrical circuit for electrically controlled irrigation valves when the voltage potential difference produced by said electrical current between said conductive electrodes exceeds said voltage potential expressing the reference setting,

and an electronic means that detects the presence of an external control signal and that causes cessation of said periodic electrical current pulses during the presence of said external control signal.

3. The apparatus of claim 1 further comprising;

a weather proof housing that encloses the several electronic means and,

a control panel that supports the electrical controls and connection points at locations convenient to the user.

4. The apparatus of claim 1 wherein the electronic sensor means for measuring temperature is a thermistor device disposed in the soil near to the soil moisture probe.

5. The apparatus of claim 1 wherein the electronic sensor means for measuring temperature is a thermistor device disposed in the air at a place typifying the outdoor ground surface temperature of the area over which irrigation control is intended.

2. An apparatus for measuring the amount of moisture in soil and controlling the application of irrigation water comprising a cooperative arrangement of electronic components, that generate periodic electrical current pulses in the form of a unipolar pulse of the briefest practical duration followed immediately by a unipolar pulse of the same duration and current amplitude having opposite polarity, that pass between two conductive electrodes, disposed beneath the surface of said soil,

that compare the voltage potential difference produced by said electrical current pulses between said conductive electrodes with a voltage potential expressing a reference setting,

that measure the temperature of the air or soil and apply a correction to said voltage potential that expresses said reference setting, equal to the effect from change with temperature of the apparent electrical resistance the soil medium,

that complete an electrical circuit path for an external electrical circuit,

that detect the presence of an external control signal and that cause cessation of said periodic electrical current pulses during the presence of said external control signal.