MICROWAVE MOISTURE MEASUREMENT USING TWO MICROWAVE SIGNALS OFDIFFERENT FREQUENCY AND PHASE SHIFT DETERMINATIONABSTRACT OF THE DISCLOSUREA microwave measurement apparatus is disclosed for measuring anunknown property of a test material, such as moisture content, bytransmitting microwave beams through such material so that a portion of thebeam energy is absorbed by the moisture or other property. Two microwaveinput signals of different frequencies are used to form the microwave beamsand the corresponding attenuated received signals are compared in order tocompensate for the presence of a component in the test material, such asfoundry molding sand, which is not being measured but which also absorbsmicrowave beam energy. To determine the density of the test material inthe event of changes in such density, one of the microwave signals is usedto measure the phase shift of the corresponding received signal and producea phase shift output signal. A single microwave antenna having twomicrowave signal connections is employed to transmit the two microwavebeams of different frequency without interference and another antenna ofthe same type receives such two beams to produce the two attenuatedreceived signals. The two attenuated received signals of differentfrequency and the phase shift output signal are combined in a signalprocessor to produce a percent moisture content signal.
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