Humidity sensor

• US 20070132542A1
• Filed: 12/12/2005
• Published: 06/14/2007
• Est. Priority Date: 12/12/2005
• Status: Active Grant

• Current Assignee: Sensitron
• Original Assignee: Sensitron
• Inventors: Beck, David, Sindt, John, Danielson, Thomas
• Granted Patent: US 7,573,365 B2
• Time in Patent Office: Days
• US Class Current: 338/35
• CPC Class Codes: G01N 27/048 for determining moisture content of the material

Abstract

A system and method for a resistor for detecting the relative level of moisture content in a humid environment. The resistor has a first layer of conductive material on a top surface of a substrate having a bend. The conductive material is exposed to atmospheric conditions. The first layer of conductive material has a static condition moisture content and a measurable electrical resistance that changes predictably when the amount of moisture content in contact with the first layer of conductive material changes from the static condition. The change of resistance of the first layer of conductive material corresponds to a change in the moisture content in contact with the first layer of electrically conductive material.

Claims

1. A humidity sensitive resistor comprising:

a substrate having a first surface and a second surface spaced from and generally opposite to said first surface, said substrate being in a configuration having at least one permanent bend;

a first layer of electrically conductive material disposed on said substrate in a desired configuration having a first end and a second end, said first layer of electrically conductive material exposed to atmospheric conditions and having a static condition moisture content, said first layer of electrically conductive material having an electrical resistance that changes predictably from said static condition moisture content when an amount of moisture content in contact with said first layer of conductive material changes from said static condition;

a second layer of electrically conductive material electrically connected to a first end of said first layer of conductive material; and

a third layer of electrically conductive material electrically connected to a second end of said first layer of conductive material.

2. The humidity sensitive resistor of claim 1 wherein said electrical resistance is dependent upon both the resistance of the first layer of electrically conductive material and the resistance of the moisture content in contact with said first layer of electrically conductive material.

3. The humidity sensitive resistor of claim 1 wherein said first layer of electrically conductive material, said second layer of electrically conductive material and said third layer of electrically conductive material are located on the top surface of said substrate.

4. The humidity sensitive resistor of claim 3 wherein a longitudinal x-axis extends along the length of said substrate and said permanent bend is in a direction that is generally in a negative y-direction relative to said longitudinal x-axis.

5. The humidity sensitive resistor of claim 1 further comprising an apparatus for holding said deflectable resistor in a fixed position, wherein said permanent bend is achieved by affixing said deflectable resistor to said apparatus.

6. The humidity sensitive resistor of claim 1 wherein said change of resistance of said first layer of conductive material reflects the amount of moisture content in the environment surrounding said deflectable resistor.

7. The humidity sensitive resistor of claim 1 wherein said static configuration moisture content is 0% relative humidity.

8. The humidity sensitive resistor of claim 7 wherein said change from said static configuration moisture content is greater than 0% relative humidity.

9. The humidity sensitive resistor of claim 8 wherein said change of electrical resistance between said static condition moisture content and said different moisture content in contact with said first layer of electrically conductive material corresponds to a relative humidity value.

10. The humidity sensitive resistor of claim 1 wherein said first layer of conductive material is a conductive ink.

11. The humidity sensitive resistor of claim 10 wherein said second layer of conductive material and said third layer of conductive material is made of a soft conductive metal.

12. The humidity sensitive resistor of claim 11, wherein said soft conductive metal is a silver or a silver alloy.

13. The humidity sensitive resistor of claim 1 wherein said permanent bend in said substrate widens a number of cracks in said first layer of conductive material, said cracks being wide enough for receiving said moisture content.

14. The humidity sensitive resistor of claim 13 wherein said moisture content comprises molecules of water.

15. The humidity sensitive resistor of claim 13 wherein a plurality of said cracks in said first layer of conductive material fill with moisture droplets as the amount of moisture content in contact with said first layer of conductive material increases and said electrical resistance measured between said first end and said second end decreases accordingly.

16. The humidity sensitive resistor of claim 1 further comprising:

a first connector means coupled to said second layer of conductive material for interconnection to external electrical components; and

a second connector means coupled to said third layer of conductive material for interconnection to external electrical components.

28. The humidity sensitive resistor of claim 1 wherein said second layer of electrically conductive material is coated with anti migration material to inhibit the migration of material of said second layer of electrically conductive material to and between second layer of electrically conductive material and said third layer of electrically conductive material.

29. The humidity sensitive resistor of claim 28 wherein said third layer of electrically conductive material is coated with anti migration material to inhibit the migration of material of said third layer of electrically conductive material to and between second layer of electrically conductive material and said third layer of electrically conductive material.

30. The humidity sensitive resistor of claim 28 wherein said second layer of electrically conductive material and said third layer of electrically conductive material are made of a precious metal.

31. The humidity sensitive resistor of claim 29 wherein said precious metal is silver.

32. The humidity sensitive resistor of claim 28 wherein said anti migration material is carbon.

33. The humidity sensitive resistor of claim 1 further comprising a fourth layer positioned over said second electrically conductive material and said third electrically conductive material, said fourth lawyer being made of a material to inhibit the movement of moisture there through.

34. The humidity sensitive resistor of claim 33 wherein said fourth layer is positioned over the substrate excluding the first electrically conductive material.

35. The humidity sensitive resistor of claim 34 wherein said fourth layer is a dielectric.

36. The humidity sensitive resistor of claim 34 wherein said fourth lawyer is an ink which is curable by ultraviolet rays.

37. The humidity sensitive resistor of claim 36 wherein said fourth layer is comprised of a first coat of said ink which is cured by ultraviolet rays and a second coat of ink which is cured by ultraviolet rays.

38. The humidity sensitive resistor of claim 37 wherein said first coat and said second coat together have a thickness from about 0.3 mil to about 0.8 mil.

39. The humidity sensitive resistor of claim 1 wherein said second layer of electrically conductive material is coated with anti migration material, wherein said third layer of electrically conductive material is coated with said anti migration material, said anti migration material being of the type to inhibit the migration of material of said second layer of electrically conductive material and said third layer of electrically conductive material to and between second layer of electrically conductive material and said third layer of electrically conductive material.

40. The humidity sensitive resistor of claim 39 further comprising a fourth layer positioned over said second electrically conductive material and said third electrically conductive material, said fourth lawyer being made of a material to inhibit the movement of moisture there through.

17. A humidity sensitive resistor comprising:

a substrate having a first surface and a second surface spaced from and generally opposite to said first surface, said substrate being in a configuration having at least one permanent bend;

a first layer of electrically conductive material disposed on said substrate in a desired configuration having a first end and a second end, said first layer of electrically conductive material exposed to atmospheric conditions, said first layer of electrically conductive material having a first resistance and a second resistance, said first resistance corresponding to a first condition having an amount of moisture content in contact with said first layer of electrically conductive material and said second resistance corresponding to a second condition having an amount of moisture content in contact with said first layer of electrically conductive material that is different than said first condition, the difference between said first resistance and said second resistance representing a change in moisture content in contact with said first layer of electrically conductive material.

18. The humidity sensitive resistor of claim 17, wherein said first condition has no moisture content.

19. The humidity sensitive resistor of claim 18, wherein said atmospheric condition associated with said first condition is 0% relative humidity.

20. The humidity sensitive resistor of claim 17, wherein said substrate has a length with a longitudinal x-axis extending along said length and wherein said permanent bend is in a direction in a negative y-direction relative to said longitudinal x-axis.

21. The humidity sensitive resistor of claim 17, further comprising:

a second layer of electrically conductive material electrically connected to said first end of said first layer of conductive material; and

a third layer of electrically conductive material electrically connected to said second end of said first layer of conductive material.

22. The humidity sensitive resistor of claim 21 wherein said second layer of electrically conductive material and said second layer of electrically conductive material are made of a soft conductive metal.

23. The humidity sensitive resistor of claim 22 wherein said soft conductive metal is a silver or a silver alloy.

24. The humidity sensitive resistor of claim 22 wherein said soft conductive metal is a carbon or a carbon compound.

25. The humidity sensitive resistor of claim 17 further comprising:

a first connector means coupled to said first end of said first layer of electrically conductive material for interconnection to external electrical components; and

a second connector means coupled to said second end of said first layer of electrically conductive material for interconnection to external electrical components.

26. A method for varying the resistance in an electrical circuit exposed to a humid environment, said method comprising:

providing a substrate having a first surface and a second surface spaced from and generally opposite to said first surface, said substrate being in a configuration having at least one permanent bend;

providing a first layer of electrically conductive material disposed on said substrate in a desired configuration having a first end and a second end, said first layer of electrically conductive material exposed to atmospheric conditions and having a static condition moisture content, said first layer of electrically conductive material having an electrical resistance that changes predictably from said static condition moisture content when an amount of moisture content in contact with said first layer of conductive material changes from said static condition;

providing a connector means for connection to external electrical components and said first and second end of said first layer of electrically conductive material;

connecting said connector means to said first and second end of said first layer of conductive material and said external electrical components in said electrical circuit;

applying an electrical signal to said first and second end of said first layer of conductive material; and

measuring a change of resistance of said first layer of conductive material to determine said amount of moisture content in contact with said first layer of electrically conductive material different than said static moisture content.

27. The method of claim 26 further comprising:

connecting a second layer of electrically conductive material electrically to a first end of said first layer of conductive material; and

connecting a third layer of electrically conductive material electrically to a second end of said first layer of conductive material.

41. A humidity sensor comprising:

a substrate having a width and a length configured with a bend along its length;

a first electrical conductor disposed on said substrate, said first electrical conductor having a first end and a second end opposite said first end with a length therein between oriented in general alignment to the length of said substrate, said first electrical conductor being exposed to a gas having a variable humidity and being formed of electrically conductive material having an electrical resistance that changes predictably with the change of the humidity of said gas;

a second layer of electrically conductive material electrically connected to a first end of said first layer of conductive material; and

a third layer of electrically conductive material electrically connected to a second end of said first layer of conductive material.