Moisture measurement device

• US 4,932,243 A
• Filed: 09/05/1989
• Issued: 06/12/1990
• Est. Priority Date: 07/12/1985
• Status: Expired due to Term

• Current Assignee: Kawata Mfg. Co., Ltd.
• Original Assignee: Axiomatics Incorporated (Axiomatics AB)
• Inventors: Lee, Thomas H., Waldman, Francis A., Chin, Douglas M., von Turkovich, Richard E., Suh, Nam P.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): WORTH, WILLIE M
• Application Number:
  US07/402,963
• Time in Patent Office: 280 Days
• Field of Search: 73/73, 324/61 R, 324/61 P, 361/282, 361/286, 364/556, 364/557, 364/568, 374/115, 374/142
• US Class Current: 73/73
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825

Abstract

A method of determining the moisture content of a material in which the material is caused to flow continually through a sensor region, the spatially averaged temperature of the material being continually determined independently of the dynamic thermal response of the material. The loss and capacitance of the sensor is also continually determined, the moisture content of the material than being determined in response to the spatially averaged temperature and the loss and capacitance determinations independently of changes in the packing density of the material as it continually flows through the sensor region.

Claims

1. A method of determining the moisture content of a continually flowing material comprising the steps of

causing said material to flow continually through a region defined by an operating sensor capacitance element;

continually determining the spatially averaged temperature of said material as said material flows through said region using a plurality of temperature sensors, each of said temperature sensors being configured so that the thermal response characteristics thereof substantially approximate the thermal response characteristics of the flowing material;

continually determining therefrom the loss and capacitance of said operating sensor capacitance element as said material flows through said region; and

continually determining the moisture content M of said material in response to said spatially averaged temperature determination and said loss and capacitance determination regardless of changes in the packing density of said material as said material flows through said region in accordance with the following relationship;

##EQU3## where Lm is the dielectric loss, T is the spatially averaged temperature, C is the capacitance, Bo, Bt, Bm, Btm, Ko, Kt, Km and Ktm are predetermined coefficients, Cor is the pre-determined capacitance of a reference sensor capacitance element when no material is present in the region defined by said reference sensor capacitance element and Com is the capacitance of said operating sensor capacitance element when no material is present in the region defined by said operating sensor capacitance element.

2. A method in accordance with claim 1 and further wherein said region is made sufficiently large to permit the determination of the temperature of said flowing material at a plurality of points within said region so that the spatially averaged temperature of a relatively large sample of said flowing material can be determined at any one time.

3. A method in accordance with claim 1 and further wherein said region is made sufficiently large to avoid restriction of material flow.

4. A method in accordance with claim 1 and further wherein said region is made sufficiently small to permit the accurate determination of said loss and capacitance by providing a certain minimum capacitance.

5. A method in accordance with claim 4 wherein said minimum capacitance lies within a range of approximately 10-20 picofarads.

6. A method in accordance with claim 1 wherein the steps of continually determining the loss and capacitance and average temperature and thereby continually determining the moisture content are performed at a position which is remote from the material flowing through said sensor element.

7. An apparatus for determining the moisture content of a continually flowing material comprising

a sensing capacitance means defining a region through which said material can continually flow and including a plurality of temperature sensing means for continually sensing the spatially averaged temperature of said material, wherein the dynamic thermal response of said temperature sensing means matches the dynamic thermal response of said material as said material continually flows through said region, said sensing capacitance means further including a plurality of concentrically mounted cylindrical members interconnected by a plurality of spaced radial struts, at least one of said temperature sensing means being positioned on each of said struts;

means for continually determining the dielectric loss and capacitance of said sensing capacitance means as said material continually flows through said region; and

means responsive to said spatially averaged temperature and to said dielectric loss and capacitance for continually determining the moisture content of said material regardless of changes in the packing density of said material as it flows through said region.

8. An apparatus in accordance with claim 7 wherein said plurality of temperature sensor elements are positioned at different radial points on said struts and at different elevation points within said region.

9. An apparatus in accordance with claim 7 wherein at least one of said cylindrical members comprises a plurality of separate cylinders mounted one above the other on said struts.

10. An apparatus in accordance with claim 7 and further wherein at least one of said struts has at least two temperature sensor elements mounted thereon at different elevations of said sensing means.

11. An apparatus in accordance with claim 7 wherein the thickness of said cylindrical members is substantially smaller than the distance between them so as to minimize resistance to the continual flow of said material through said sensing means.

12. An apparatus in accordance with claim 7 and further including shield members mounted on each side of and spaced from each temperature sensing means on each said strut.

13. An apparatus in accordance with claim 7 wherein said moisture content determining means comprises a microprocessor means.

14. An apparatus in accordance with claim 13 wherein said microprocessor means responds to said spatially averaged temperature, dielectric loss and capacitance for continually determining said moisture content in accordance with the following relationship:

##EQU4## where M is the moisture content, Lm is the dielectric loss, T is the spatially averaged temperature, C is the capacitance, and Bo, Bt, Bm, Btm, Ko, Kt, Km and Ktm are predetermined coefficients.

15. An apparatus in accordance with claim 13 wherein said microprocessor means responds to said spatially averaged temperature, dielectric loss and capacitance for determining said moisture content when using different sizes for said sensing capacitance means in accordance with the following relationship:

##EQU5## where M is the moisture content, Lm is the dielectric loss, T is the spatially averaged temperature, C is the capacitance, Bo, Bt, Bm, Btm, Ko, Kt, Km and Ktm are predetermined coefficients, Cor is the capacitance of a reference sensing capacitance means having a first size, Cor being the capacitance when no material is present in the region defined by said reference sensing capacitance means and Com is the capacitance of any other sensing capacitance means having a different size than that of said reference sensing capacitance means, Com being the capacitance when no material is present in the region defined by said other sensing capacitance means.

16. An apparatus in accordance with claim 12 wherein each of said temperature sensing means comprises

a thermally sensitive element;

a stainless steel collar member in which said element is mounted, the electrical leads from said element extending through said collar member, said leads being encapsulated with a high temperature epoxy material, at least a selected portion of said element being exposed to said continually flowing material, the amount of exposure of said selected portion being arranged so that the thermal response characteristics of said device substantially matches the thermal response characteristics of said continually flowing material, whereby the spatially averaged temperature of the flowing material is determined in accordance with the dynamic thermal response of the flowing material.

17. An apparatus in accordance with claim 13 wherein said microprocessor means further responds to said spatially averaged temperature measurement so as to determine a temporally compensated temperature which is compensated for the dynamic thermal response of said material.