MEASURING CHARACTERISTICS OF MATERIALS BY USING SUSCEPTIVE AND CONDUCTIVE COMPONENTS OF ADMITTANCE

• US 3,746,975 A
• Filed: 08/20/1971
• Issued: 07/17/1973
• Est. Priority Date: 08/20/1971
• Status: Expired due to Term

• Current Assignee: Frederick L. Maltby
• Original Assignee: Frederick L. Maltby
• Inventors: Maltby, Frederick L.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/173,538
• Time in Patent Office: 697 Days
• Field of Search: 324/65R,61R 73/34C
• US Class Current: 324/720
• CPC Class Codes: G01N 27/048 for determining moisture content of the material

Abstract

A system for measuring a condition of a material using an admittance probe or probes which are immersed in or placed in proximity to the material, in which both the susceptive and conductive components of admittance exhibited by the probes are utilized to provide measurements of the desired characteristic which are substantially free from errors due to variations in other characteristics of the materials.

Claims

3. In a system for measuring the dry weight of a aterial having a variable moisture content, an admittance probe adapted for association with said material, means for deriving first and second signals respectively representative only of the susceptive and the conductive components of admittance exhibited by said rpobe, said susceptive component varying with the weight of said material and also varying with the moisture content thereof, said conductive component varying only with the moisture content of said material, and means for combining said first and second signals to yield a signal primarily representative of variations in weight of said material and substantially independent of variations with moisture content.

4. In a system for measuring the conductivity between spaced points o a coating applied to a relatively non-conductive substrate, a pair of spaced electrodes positioned in proximity to said substrate on the side thereof opposite said coating, means for deriving first and second signals respectively representative only of the susceptive and conductive components of admittance exhibited by said electrodes, and means for operating on said first and second signals to produce a quantity representative of the conductivity of said coating between said spaced electrodes.

5. A system according to claim 4 in which said last means comprises:

means for squaring said first signal, means for dividing said squared signal by said second signal, ane means for adding the signal resulting from said division to said second signal to provide a signal representative of said conductivity.

6. A system according to claim 1 in which said combining means comprises means for subtracting said second signal from said first signal. 7. A system according to claim 1 including means for modifying at least one of said signals prior to combination with the other of said signals in a manner to render the variation of both said signals with said second characteristic of substantially the same form.

8. A system according to claim 7 in which said signal modiyfing means comprises a capacitor in series with said probe.

9. A system according to claim 7 in which said signal modification is effected by using an insualted probe.

10. A system according to claim 7 including means for dividing said second signal by said first signal, a function generator for producing a signal which is a predetermined function of the quotient signal produced by said division, means for multiplying said last-named signal by said first signal, and means for subtracting the resultant product signal from said first signal to produce a signal primarily representative of variations in said first characteristic and substantially independent of variations in said second characteristic.

11. A system according to claim 10 in which the signal produced by said function generator is such that, when multiplied by said first signal, the resultant product signal is similar in mathematica form to said first signal.

12. In a system for measuring a first characteristic of a material, means including an admittance probe adapted for association with said material for deriving a signal having components respectively representative only of the susceptive and conductive components of admittance exhibited by said probe, said susceptive component varying with said first characteristic and also varying with a second characteristic of said material, said conductive component varying only with said second characteristic of said material, and a phase-sensitive detector supplied with said signal and phased to produce an output representative of the difference between said susceptive and conductive components.

13. In a system for measuring a first characteristic of a material, means including a capacitive probe adapted for association with said material for deriving a signal having components respectively representative only of the susceptive and conductive components of admittance exhibited by said probe, said susceptice component varying with said first characteristic and also varying with a second characteristic of said material, said conductve component varying only with said second characteristic of said material, and a phase-sensitive detector supplied with said signal and phased to produce an output representative of the difference between said susceptive component and the product of a constant times the conductive component.

14. In a system for measuring the level of a conducting material in a vessel, an admittance probe adapted for immersion into said material, said material tending to produce a coating on aid probe, means for deriving a signal having components represnetative only of the susceptive and conductive components of admittance exhibited by aid probe, said susceptive component varying with said level and also varying by reason of adherence of said material to said probe when the level of said material changes, said conductive component varying only by reason of said adherence of material to said probe, and a phase snesitive detector supplied with said signal and phased to produce an output representative of the difference between said susceptive and conductive components.