GB992554A - Means for converting the ratio of two alternating electrical signals into a direct current or voltage signal - Google Patents

Abstract

992,554. Induction flowmeters. GEORGE KENT Ltd. Dec. 14, 1962 [Dec. 14, 1961], No. 44907/61. Heading G1N. [Also in Division G4] A circuit for measuring the ratio of two alternating electrical signals, which may be indicative of the field current and generated e.m.f. in an electromagnetic flow meter, includes a Hall plate H to an input of which one of the two signals, Ia, is applied, an A.C. amplifier A and a demodulator D. The direct current output from the demodulator, Id, is applied to the other input of the Hall plate and the A.C. output from the plate is opposed to the other of the two alternating signals, the error signal thus derived being fed to the amplifier and thence to the demodulator. The demodulator output current Id gives a measure of the required ratio of the two alternating signals. As shown in Fig. 1 the A.C. signal Ia is applied directly to the plate, while the D.C. signal Id controls the magnetic field across the plate, but this order may be reversed (Fig. 2 not shown). If the two initial alternating signals are slightly out of phase, a quadrature feedback circuit may be included to eliminate the out of phase component. This circuit includes a second demodulator sensitive to the out of phase component supplying a D.C. input to a second Hall plate, whose other input is provided by a signal related to the initial A.C. input, but phase shifted through 90 degrees. The second Hall plate output is then applied to one input of the amplifier A to suppress any quadrature input (Fig. 3 not shown).