Moisture sensor and control system

• US 5,570,030 A
• Filed: 04/17/1995
• Issued: 10/29/1996
• Est. Priority Date: 05/07/1993
• Status: Expired due to Term

• Current Assignee: William E. Wightman
• Original Assignee: William E. Wightman
• Inventors: Wightman, William E.
• Primary Examiner(s): Regan, Maura K.
• Application Number:
  US08/423,555
• Time in Patent Office: 561 Days
• Field of Search: 324/715, 324/724, 324/664, 324/694, 361/280, 361/281, 137/78.5, 73/73, 340/602
• US Class Current: 324/694
• CPC Class Codes: G01N 27/043 of a granular material
• CPC Class Codes: G01N 27/048 for determining moisture content of the material
• CPC Class Codes: Y10T 137/1939 Atmospheric

Abstract

A sensor for measuring moisture changes in soil and having an electrically insulating cylindrical body along which bare electrical conductors are placed. A transmitter produces constant alternating current which is supplied to the sensor. The voltage which this current creates in the soil is detected by the electrical conductors on the sensor and is fed to a receiver. The receiver consists of electronic circuitry for determining the necessity for allowing irrigation to occur, and if so, switches on a solenoid controlling the water supply. When the sensor indicates sufficient irrigation has occurred, the electronic controls switch the irrigation off. A tube sensor comprising rigid metal tubes of equal length and secured by end members such that no two tubes touch is also provided, for example to measure moisture content changes of any granular material. A plurality of the tube sensors are connected in series with insulated electrically conducting cables to form a string of tube sensors, thereby providing a means to obtain an average moisture content of large surface areas or volumes of material.

Claims

1. A method of measuring soil moisture, comprising;

providing a moisture content sensor having a first and a second rigid and electrically insulating body member, said first and second body members being physically spaced apart to define a sensor length parameter and to define an open space between said first and second body members, a plurality of electrically uninsulated and rigid electrical electrodes, each of said electrodes having a first end and a second end, said first end of each electrode being mechanically fastened to different physically spaced points on said first body member, said electrodes passing between said first and second body members in a manner such that said electrodes do not physically touch, and said second ends of each electrode being mechanically fastened to different physically spaced points on said second body member, said plurality of electrodes thereby forming a unitary physical assembly with said first and second body members having said open space between said first and second body members,

connecting current transmitter means to one of said ends of first ones of said electrodes,

connecting voltage receiver means to one of said ends of different second ones of said electrodes, said voltage receiver means providing an output indicative of moisture content, and

placing said sensor in soil whose moisture content is to be measured.

2. The method of claim 1 including the step of;

selecting said plurality of electrodes from the group two, three and four electrodes.

3. The method of claim 2 including the step of;

providing said current transmitter means as an oscillating current transmitter means.

4. The method of claim 3 including the step of;

providing said oscillating current transmitter means as a constant oscillating current transmitter means.

5. The method of claim 1 wherein said electrodes are metal electrodes selected from the group hollow metal rods and solid metal rods.

6. The method of claim 2 including the step of;

coating said metal electrodes with an electrically conductive material selected to protect said metal electrodes from chemical effects present in soil.

7. The method of claim 2 including the steps of;

providing said first ones of said metal electrodes as cylindrical rods having a relatively small diameter, and

providing said different second ones of said metal electrodes as cylindrical rods having a relatively large diameter.

8. The method of claim 1 wherein said plurality of electrodes comprise an even number, and including the step of;

connecting electrical resistance means between pairs of said first ones and said different second ones of said electrodes.

9. The method of claim 1 including the step of;

providing a plurality of said sensors, said plurality of sensors including a first sensor and a last sensor,

connecting said first ones of said electrodes within said plurality of sensors in electrical series circuits,

connecting said current transmitter means to said one end of said first ones of said electrodes that are within said first sensor,

connecting said different second ones of said electrodes within said plurality of sensors in electrical series circuits,

connecting voltage receiver means to said one end of said different second ones of said electrodes that are within said first sensor, said voltage receiver means providing an output indicative of moisture content, and

placing said plurality of sensors in soil whose moisture content is to be measured.

10. The method of claim 9 wherein said electrodes are metal electrodes selected from the group hollow metal rods and solid metal rods.

11. The method of claim 10 wherein said plurality of electrodes within said plurality of sensors comprise the same even number of electrodes within each of said sensors, and including the step of;

connecting electrical resistance means between pairs of said first ones and said different second ones of said electrodes within said last sensor.

12. The method of claim 11 including the steps of;

providing said first ones of said metal electrodes as cylindrical rods having a relatively large diameter, and

providing said different second ones of said metal electrodes as cylindrical rods having a relatively small diameter.

13. The method of claim 12 including the step of;

coating said metal electrodes with an electrically conductive material selected to protect said metal electrodes from corrosive chemical effects present in soil.

14. A device adapted for the measurement of soil moisture, comprising;

a first and a second rigid and electrically insulating body member, said first and second body members being physically spaced apart to define a physically open soil volume therebetween,

first, second, third and fourth electrically uninsulated and rigid electrodes, each of said four electrodes having a first end and a second end,

means fastening said first ends of each of said four electrodes to different physically spaced points on said first body member in the sequence first, second, third and fourth electrode,

said four electrodes then passing through said open space between said first and second body members in a manner such that said four electrodes do not physically touch,

means fastening said second ends of each of said four electrodes to different physically spaced points on said second body member in the sequence first, second, third and fourth electrode, to thereby form a unitary assemble with said first and second body members wherein said four electrodes occupy only a portion of said open soil volume,

current transmitter means connected to first body member and to said first ends of first and second electrodes, and

voltage receiver means connected to said first body member and to said first ends of said second and third electrodes, said voltage receiver means providing an output indicative of soil moisture content.

15. The device of claim 14 wherein said current transmitter means is an oscillating current transmitter means.

16. The device of claim 15 wherein said oscillating current transmitter means is a constant oscillating current transmitter means.

17. The device of claim 14 wherein said electrodes are metal electrodes selected from the group hollow metal rods and solid metal rods.

18. The device of claim 14 wherein said first and second electrodes are cylindrical rods having a relatively large diameter, and said third and fourth electrodes are cylindrical rods having a relatively small diameter.

19. The device of claim 18 including an external surface coating on said metal electrodes of an electrically conductive material selected to protect said metal electrodes from chemical effects present in soil.

20. The device of claim 14 including;

first resistance means connected from said second end of said first electrode to said second end of said fourth electrode, and

second resistance means connected from said second end of said second electrode to said second end of said third electrode.

21. A device adapted for the measurement of soil moisture, comprising;

a plurality soil moisture sensors, each sensor having

a first and a second rigid and electrically insulating body member, said first and second body members being physically spaced apart to define an open space therebetween,

first, second, third and fourth electrically uninsulated and rigid electrodes, each of said electrodes having a first end and a second end,

means fastening said first ends of each of said four electrodes to different physically spaced points on said first body member in the sequence first, second, third and fourth electrode, with successive electrodes being adjacent to each other,

said four electrodes then passing between said first and second body members in a manner such that said four electrodes do not physically touch, and

means fastening said second ends of each of said four electrodes to different physically spaced points on said second body member in the sequence first, second, third and fourth electrode, to thereby form a unitary assemble of said four conductors and said first and second body members with said open space being between said first and second body members,

first circuit means connecting said first electrodes of said plurality of sensors in a series circuit from a first sensor to a last sensor,

second circuit means connecting said second electrodes of said plurality of sensors in a series circuit from said first sensor to said last sensor,

third circuit means connecting said third electrodes of said plurality of sensors in a series circuit from said first sensor to said last sensor,

fourth circuit means connecting said fourth electrodes of said plurality of sensors in a series circuit from said first sensor to said last sensor,

current transmitter means connected to said first sensor and to said first ends of first and second electrodes at said first body member thereof, and

voltage receiver means connected to said first sensor and to said first ends of said third and fourth electrodes at said first body member thereof.

22. The device of claim 21 wherein said current transmitter means is an oscillating current transmitter means.

23. The device of claim 22 wherein said oscillating current transmitter means is a constant oscillating current transmitter means.

24. The device of claim 21 wherein said electrodes of said plurality of sensors are selected from the group hollow metal rods and solid metal rods.

25. The device of claim 21 wherein said first and second electrodes are cylindrical metal rods having a relatively large diameter, and wherein said third and fourth electrodes are cylindrical metal rods having a relatively small diameter.

26. The device of claim 25 including an external surface coating on said electrodes of a material selected to chemically protect said electrodes.

27. The device of claim 21 including;

first resistance means connected to said first and second electrodes at a position spaced from said first sensor, and

second resistance means connected to said third and fourth electrodes at a position spaced from said first sensor.

28. The device of claim 21 including;

first resistance means connected to said last sensor and to said second ends of said first and fourth electrodes at said second body member thereof, and

second resistance means connected to said last sensor and to said second ends of said second and third electrodes at said second body member thereof.

29. A device adapted for the measurement of soil moisture, comprising;

a first and a second rigid body member, said first and second body members being physically spaced apart to define a physically open soil volume therebetween for occupancy by soil,

a plurality of electrically uninsulated and rigid electrodes, each of said electrodes having a first end and a second end,

means fastening said first ends of each of said plurality of electrodes to different physically spaced points on said first body member and in a given sequence,

said plurality of electrodes passing between said first and second body members in a manner such that said four electrodes do not physically touch, in a manner to leave said open soil volume generally unobstructed for said occupancy by soil, and

means fastening said second ends of each of said plurality of electrodes to different physically spaced points on said second body member and in said given sequence.

30. The device of claim 29 wherein said plurality of electrodes is selected from the group two, three or four electrodes.

31. The device of claim 29 wherein said electrodes are generally parallel metal electrodes selected from the group hollow metal rods and solid metal rods.

32. The device of claim 31 wherein said plurality of electrodes comprise a first group of metal rods having a relatively large cross sectional area, and a second group of metal rods having a relatively larger cross sectional area.

33. The device of claim 31 including an external surface coating on said metal rods of an electrically conductive material selected to protect said metal electrodes from chemical effects present in soil.

34. The device of claim 29 wherein said plurality of electrodes comprise an even number X of electrodes, and including;

X/2 resistance means, one of said resistance means being connected from said second end of an electrode in said first group to-said second end of an electrode in said second group.

35. The device of claim 29 including;

a plurality of resistance means, one of said resistance means being connected from said second end of an electrode in said first group to said second end of an electrode in said second group.

36. A device adapted for the measurement of soil moisture, comprising;

a plurality soil moisture sensors, each sensor having

a first and a second rigid and electrically insulating body member, said first and second body members being physically spaced apart to define an open space therebetween for occupancy by soil,

a plurality of electrically uninsulated and rigid electrodes, each of said electrodes having a first end and a second end,

means fastening said first ends of each of said plurality of electrodes to different physically spaced points on said first body member in the sequence from a first of said plurality to a last of said plurality,

said plurality of electrodes then passing through a portion of said open space between said first and second body members in a manner such that said electrodes do not physically touch, and

means fastening said second ends of each of said plurality of electrodes to different physically spaced points on said second body member in the said sequence, to thereby provide a remainder of said open space to be occupied by soil, and to thereby form said plurality of electrodes and first and second body members into a unitary physical assembly, and

a plurality of means connecting said electrodes of said plurality of sensors in a plurality of series circuit from a first sensor to a last sensor.

37. The device of claim 36 wherein said electrodes of said plurality of sensors are selected from the group hollow metal rods and solid metal rods.

38. The device of claim 37 wherein certain ones of said plurality of electrodes are cylindrical metal rods having a relatively large diameter, the remainder of said plurality of electrodes being cylindrical metal rods having a relatively small diameter.

39. The device of claim 38 including an external surface coating on said electrodes of a material selected to chemically protect said electrodes.

40. A plural-sensor device adapted for the measurement of soil moisture, comprising;

a plurality of soil moisture sensors, each of said sensors having rigid electrically insulating first and second body members that are physically spaced apart to define an open space therebetween, a plurality of electrically uninsulated electrodes, each of said electrodes having a first end and a second end, means fastening said first ends of each of said plurality of electrodes to different physically spaced points on said first body member in a sequence from a first of said plurality of electrodes to a last of said plurality of electrodes, said plurality of electrodes then passing through a first portion of said open space between said first and second body members in a manner such that said electrodes do not physically touch, and means fastening said second ends of each of said plurality of electrodes to different physically spaced points on said second body end in said sequence, to thereby form said plurality of electrodes and said first and second body members into a unitary assembly having a second portion of said open space that is unoccupied by said plurality of electrodes, and

a plurality of electrical connection means connecting said electrodes of said plurality of sensors in a plurality of series circuits from a first of said plurality of sensors to a last of said plurality of sensors.

41. The device of claim 40 including an external surface coating on said electrodes of a material selected to protect said electrodes from chemical effects within the soil.

42. The device of claim 40 including;

a first pair of electrical conductors at said first sensor connected to a first group of said plurality of electrodes at said first sensor, said first pair of electrical conductors being adapted to be connected to current transmitter means, and

a second pair of electrical conductors at said first sensor connected to a second group of said plurality of electrodes at said first sensor, said second pair of electrical conductors being exclusive of said first pair of electrical conductors, and said second pair of electrical conductors being adapted to be connected to voltage receiver means.

43. The device of claim 42 including;

a plurality of resistance means at one of said plurality of sensors exclusive of said first sensor, each individual one of said resistance means being connected from one of said first group of electrodes to one of said second group of electrodes.