Microwave moisture measurement using two microwave signals of different ...

United States Patent m

Walker

[ii] Patent Number: 4,727,311 [45] Date of Patent: Feb. 23, 1988

[54] MICROWAVE MOISTURE MEASUREMENT USING TWO MICROWAVE SIGNALS OF DIFFERENT FREQUENCY AND PHASE SHIFT DETERMINATION

[76] Inventor: Charles W. E. Walker, 591 West 57th Avenue #301, Vancouver, B.C., Canada

[21] Appl. No.: 836,964

[22] Filed: Mar. 6,1986

[51] Int. Q." G01R 27/04; G01R 25/04;

Q01N 22/04

[52] U.S. a 324/58.5 A; 324/83 R

[58] Field of Search 324/58 A, 58.5 A, 83 R,

324/83 A

[56] References Cited

U.S. PATENT DOCUMENTS

3,265,967 8/1966 Heald 324/58.5 A

3,348,140 10/1967 Godding 324/58.5 A

3,534,260 10/1970 Walker 324/58.5 A

3,538,434 11/1970 Brown et al 324/58.5 A

3,644,826 2/1972 Cornetet 324/58.5 A

4,123,702 10/1978 Kinanen et al 324/58.5 A

4,326,163 4/1982 Brooke 324/58.5 A

4,499,418 2/1985 Helms et al 324/58.5 A

Primary Examiner—Gerard R. Strecker

Attorney, Agent, or Firm—Klarquist, Sparkman,
Campbell, Leigh & Whinston

[57] ABSTRACT

A microwave measurement apparatus is disclosed for measuring an unknown property of a test material, such as moisture content, by transmitting microwave beams through such material so that a portion of the beam energy is absorbed by the moisture or other property. Two microwave input signals of different frequencies are used to form the microwave beams and the corresponding attenuated received signals are compared in order to compensate for the presence of a component in the test material, such as foundry molding sand, which is not being measured but which also absorbs microwave beam energy. To determine the density of the test material in the event of changes in such density, one of the microwave signals is used to measure the phase shift of the corresponding received signal and produce a phase shift output signal. A single microwave antenna having two microwave signal connections is employed to transmit the two microwave beams of different frequency without interference and another antenna of the same type receives such two beams to produce the two attenuated received signals. The two attenuated received signals of different frequency and the phase shift output signal are combined in a signal processor to produce a percent moisture content signal.

18 Claims, 8 Drawing Figures