CAPACITIVE MOISTURE CONTROL SYSTEM HAVING A PEAK DETECTOR

• US 3,626,286 A
• Filed: 11/20/1968
• Issued: 12/07/1971
• Est. Priority Date: 11/20/1968
• Status: Expired due to Term

• Current Assignee: George P. Rauchwerger
• Original Assignee: George P. Rauchwerger
• Inventors: Rauchwerger, George P.
• Primary Examiner(s): Kubasiewicz, Edward E.
• Application Number:
  US04/777,219
• Time in Patent Office: 1,112 Days
• Field of Search: 324/61M,61UC,61P 239/63,64 73/73
• US Class Current: 324/519
• 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: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825

Abstract

A meter for measuring moisture in soil electronically uses two probes spaced apart with soil between the probes. The probes may be insulated plates of metal or flat insulated cable made of a plurality of conductors. The circuit has an ultrasonic oscillator which transmits a signal to the probes, which function as a variable capacitor depending upon moisture content of the soil. An integrated-circuit peak detector provides a positive DC voltage proportional to input peak voltage, and its output is measured by a microammeter which thus measures moisture. The output of the detector may be used to control an irrigation valve. Several probes and valves may be used in a system. The soil may be contained in a plastic bag and the electrodes applied to opposite sides of the bag.

Claims

1. In a moisture control system wherein the moisture of a medium is sensed and controlled, a pair of probes, insulation means for said probes completely insulating each said probe from said medium and from the other probe, each said probe being flexible, said probes being installable in said medium at selectively varying distances from each other, each said probe being completely surrounded by said medium when imbedded therein, an ultrasonic oscillator providing at its outputs a sinusoidal output signal, one of the outputs of said oscillator electrically connected to one of said probes and the other output tO ground, a positive peak detector having one input connected to the other of said probes and the other input to ground, and means controlled by said detector to sense the capacitance across said probes and thereby to sense the percentage of moisture in said medium.

2. A system according to claim 1 in which said means comprises a comparator circuit comprising adjustable means providing a manually controlled reference voltage and a circuit accepting the outputs of said detector and said reference voltage for comparing the output voltage of said detector against said manually controlled reference voltage, a solid-state switch actuated by said comparator circuit, a solenoid valve controlled by said switch, and a water pipe in which said valve is installed.

3. A system according to claim 2 which further comprises a second pair of probes each completely insulated from said medium and from the other probe and each imbedded directly in a second medium in spaced-apart relation and unsupported except by said medium, one of said second pair of probes connected to the output of said oscillator, a second detector, one input of said second detector connected to the other of said second pair of probes, said means further comprising a second comparator circuit comprising second adjustable means providing a manually controlled second reference voltage and a second circuit accepting the outputs of said second detector and said second reference voltage for comparing the output voltage of said second detector against said second reference voltage, a second solid-state switch actuated by said second comparator circuit, a second solenoid valve controlled by said second switch and a second water pipe in which said second valve is installed, and a logic circuit to turn on only one said valve at a time, said logic circuit including an '"'"''"'"''"'"''"'"'OR'"'"''"'"''"'"''"'"' gate having a plurality of diodes, said gate connected to the output of said comparator circuits, the number of diodes equaling one less than the number of solenoid valves.

4. A system according to claim 2 which further comprises a second pair of probes each imbedded directly in a second medium in spaced-apart relation and insulated from said second medium and from each other, one of the outputs of said oscillator connected to one of said second probes, a second detector, one of the inputs of said second detector connected to the other of said second probes and the other input to ground, an averaging amplifier receiving the output of each said detector, and a valve circuit operable to open said valve when the average moisture sensed by said probes in less than a predetermined percentage.

5. A system according to claim 4 which further comprises individual identical first resistors interposed between the output of each detector and one input of said amplifier, a second resistor between the other input of said amplifier and ground, and a third resistor across said amplifier and wherein there is the following relationship:

said third resistor equals the value of any of said first resistors divided by the number of detectors;

said second resistor equals half said third resistor;

the output of said amplifier equals minus the value of the third resistor times the sum of the outputs of said detectors divided by said first resistor.

6. A system according to claim 1 in which said probe comprises at least one conductor electrically insulated from the exterior in a plastic sheath, one end of said conductor electrically connected to a lead wire for said probe which extends outside said sheath.

7. A system according to claim 1 in which said means comprises a microammeter.

8. A system according to claim 1 in which the signal of said oscillator is approximately of a frequency of 75 kHz. and an amplitude of about 100 V.P.P.

9. In a moisture control system a nonconductive plastic bag, a medium whose moisture is to be controlled filling said bag, said bag when filled being of fixed shape, a first probe on the extErior of said bag, a second probe on the exterior of said bag opposite said first probe, insulation means completely insulating said probes from said medium and from each other, an ultrasonic oscillator providing at its outputs a sinusoidal output signal, one of the outputs of said oscillator electrically connected to one of said probes and the other output to ground, a positive peak detector having one input connected to the other of said probes and the other input to ground, and means controlled by said detector to sense the capacitance across said probes and thereby to sense the percentage of moisture in said medium in said bag.

10. A system according to claim 2 in which each said probe comprises a strip of conductive foil and adhesive to attach said foil to said bag.

11. A system according to claim 2 in which each said probe comprises a strip of conductive compound applied to said bag.