Patent GB-911975-A (GB)
IPC: G01G9/00
Abstract: 911,975. Determining physical qualities of materials; electric analogue calculating. CURTISSWRIGHT CORPORATION. Feb. 9, 1959 [Feb. 10, 1958], No. 4520/59. Class 37. The weight of continuously produced material comprising two or more ingredients is determined by using a single electrical translating element which gives two responses each jointly in accordance with the weight of one ingredient and the weight of the remaining ingredient(s) and deriving a signal from the combination of the two responses. As shown, a continuouslyproduced strip of paper, cloth or plastics material 30 in which the moisture content and weight of dry material is to be determined is passed between electrodes 18, 20 fed from a radio frequency oscillator 8 via amplifiers 88, 12. The dielectric constant and loss in the material are dependent on both the weight of moisture (m) and weight of dry fibre (f) in the strip 30. Two further electrodes 36, 38 interposed between the strip 16 and the electrode 20 feed radio-frequency energy to a discriminator 6 in which circuits 32, 34 are tuned to frequencies on either side of that of the oscillator 8. Variation in either m or f alters the tuning of the discriminator 6 and results in a rectified output which is fed to a reactance modulator 10 to reset the frequency of oscillator 8 to the new centre frequency of the discriminator 6. A D.C. signal (V am ) dependent on the change in oscillator frequency is provided by a Foster- Seeley discriminator 92. The input to amplifier 12 and the discriminator 92 is maintained constant by a limiter 90, hence the amplitude at the anode of amplifier 12 is dependent on f and m. A D.C. signal (V am ) dependent on amplitude is provided by a detector 60, the output of which is normally set to zero for a strip of standard weight and standard moisture content by means of a control 76. Analogue calculating.-The outputs of detector 60 and discriminator 92 are related to the weight of moisture and of dry fibre by the following equations: where k 1 , k 2 , k 3 , k 4  are constants. It is shown that equations 1, 2 can be solved for m by adding V am  and V fm  in a summing amplifier 107 having input resistors proportioned according to the constants of the equations. The output of amplifier 107 appears on a centre-zero meter 120 in terms of deviation from standard moisture content. f is similarly obtained by adding V am  and V fm  in a summing amplifier 107<SP>1</SP> having a dry weight indicator 120<SP>1</SP>. The output of amplifier 107 is inverted by amplifier 107<SP>11</SP> before being added to that of 107<SP>1</SP> in a further amplifier 107111 to provide an indication of total weight. The amplifier outputs may be used to control the characteristics of the continuouslyproduced strip 30. Amplifiers of the chopper modulator/demodulator type may be used. Modifications.-A heterodyne frequencychanger may be incorporated to enable the amplifier 12 or the discriminator 92 to operate at a different frequency from the oscillator 8. A harmonic generator may be interposed between the oscillator 8 and the frequency changer. An attenuating network as shown in Fig. 1A may be substituted for capacitor 24 to maintain linear response if the deviations of the strip 30 from standard characteristics are large. Specification 591,172 is referred to.