Moisture sensor probe with at least two groups of resistive arrays

• US 4,801,865 A
• Filed: 01/19/1988
• Issued: 01/31/1989
• Est. Priority Date: 01/19/1988
• Status: Expired due to Fees

• Current Assignee: California Sensor Corp.
• Original Assignee: California Sensor Corp.
• Inventors: O'Brien, Kent, Miller, Ralph W.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): REGAN, MAURA K
• Application Number:
  US07/144,957
• Time in Patent Office: 378 Days
• Field of Search: 324/65 R, 324/65 P, 340/602, 338/34, 73/336.5, 361/78
• US Class Current: 324/696
• CPC Class Codes: G01N 27/048 for determining moisture content of the material
• CPC Class Codes: G01N 33/246 for water content for control of watering A01G25/167

Abstract

A probe for sensing the moisture content in a porous medium such as soil. The probe includes an array of a multiplicity of conductors and resistors formed on a substrate, with contact pins or electrodes connected to one end of each resistor, typically extending outwardly from the substrate. The resistor array is preferably divided into at least two groups, providing a separate output for each group. An appropriate voltage source and indicator means are connected to the resistor array in a circuit to provide indication of soil moisture. The transfer characteristic of the apparatus is such that the probe has improved sensitivity in the area of primary interest, that is at, between 80 and 100% of saturation.

Claims

1. A probe for sensing moisture content in a porous medium, said probe comprising:

a substrate;

an array of at least a first and a second group of resistors formed on said substrate, there being a multiplicity of resistors in each said group;

first conductor means formed on said substrate interconnecting one end of all of said multiplicity of resistors in said first group together in a partial parallel configuration;

first output terminal means connected to said first conductor means;

a first electrode connected to the other end of each said resistor in said first group of resistors;

second conductor means formed on said substrate interconnecting on end of all of said multiplicity of resistors in said second group together in a partial parallel configuration;

second output terminal means connected to said second conductor means;

a second electrode connected to the other end of each said resistor in said second group of resistors, said first and second electrodes being adjacent and electrically isolated within said probe; and

encapsulating material sealing said resistors, conductors and electrodes, said encapsulating material protecting all but the ends of each said first and second electrode from the environment.

2. The probe recited in claim 1, wherein said first and second output terminal means are adapted to be selectively connected to circuitry comprising a voltage source and indicator means, whereby said probe, pursuant to voltage applied thereto, produces output signals representative of moisture content in the medium, the indicator means providing moisture content indication in response to the output signals.

3. The probe recited in claim 1, wherein said first and second output terminal means are adapted to be selectively connected to circuitry comprising a voltage source and an irrigation control system, whereby said probe, pursuant to voltage applied thereto, produces output signals representative of moisture content in the medium, said control system controlling the amount of fluid applied to the medium in response to the output signals.

4. The probe recited in claim 1, wherein at least two groups of resistors and first electrodes are connected to said first output terminal means.

5. The probe recited in claim 1, wherein:

at least two groups of resistors and first electrodes are connected to said first output terminal means; and

at least two groups of resistors and second electrodes are connected to said second output terminal means.

6. The probe recited in claim 5, wherein said first group of resistors and first electrodes are electrically isolated and physically closely adjacent said second group of resistors and second electrodes.

7. The probe recited in claim 6, wherein said first group of first electrodes is arranged in physically alternating fashion with said second group of second electrodes.

8. A method for measuring moisture content of a porous medium, said method comprising the steps of:

placing a multiplicity of contact points in contact with the medium, said contact points being arranged in at least two groups;

applying a voltage to said contact points;

inserting a predetermined electrical resistance between each of said contact points and the voltage source, at least one group of said contact points being spaced from and electrically separate from the other groups; and

determining the moisture content in the medium as a function of the number of said contact points being wetted and being connected through the moisture to at least one other of said contact points.

9. The method recited in claim 8, wherein the resistance value between two contact points unconnected by moisture and the resistance value of each predetermined electrical resistance is several higher than is the resistance value between two contact points connected by moisture.