GB1105572A - An electromagnetic flow-meter - Google Patents

Abstract

1,105,572. Induction flowmeters. COMPAGNIE GENERALE d'ELECTRONIQUE INDUSTRIELLE LEPAUTE. May 18, 1965, No. 21100/65. Heading G1N. In an electromagnetic flowmeter, a tube 16 carrying the liquid to be measured has a magnetic field applied across it by coils 5a, 5b, and pick-up electrodes 7a, 7b, are connected via a two-core screened cable, B, to a transistorized, differential, feedback amplifier, A, a feedback loop of which contains the capacity of the cable. The arrangement maintains a high input impedance to the amplifier, the outputs from electrodes 7a, 7b being fed to cable conductors 1 and 2 and thence to the amplifier inputs 24, 25, while the screens 1a, 2a of the respective cable conductors are connected to feedback lines 27, 26 of the amplifier. An overall cable screen 3 is connected to a third, reference, electrode, 18, on the tube 16, and to the amplifier earth line. A signal proportional to the applied magnetic field is derived by a circuit, D, from the A. C. source 17 which supplies the coils 5a, 5b, and this signal appears at 14 where it is compared with the output signal, at 13, of the amplifier in a comparison means (not shown); this eliminates the effect of field variations upon the flow measurement signal. Correction is also applied to the output of the electrodes 7a, 7b, by a circuit consisting of resistors 6a, 6b and a coil 4 mounted inside the flowmeter casing 8 with an associated moving core 21, this circuit serving to compensate for noise signals introduced, by the field, in the connecting leads to the electrodes.