Quadrature-voltage balancing circuit or electromagnetic flowmeter

Claim 1

In combination with an electromagnetic flowmeter wherein a fluid whose flow rate is to be measured is conducted through a metallic flow tube to intersect a transverse alternatingcurrent magnetic field whereby a signal representing flow rate is induced in first and second diamEtrically-opposed electrodes projecting into said tube; a balancing circuit for coupling said electrodes to the respective input terminals of an amplifier while compensating for the quadrature voltage induced in the leads extending from said electrodes, said circuit comprising: A. a transformer assembly having first and second sections each having a primary and a secondary, and B. first and second coaxial cables each having an inner conductor surrounded by an outer shielding conductor, said first and second electrodes being respectively connected through said first and second inner conductors in series with the secondaries of said first and second sections to the input terminals of said amplifier, the primaries of said first and second sections being connected through said outer conductors to external points on the circumference of said metallic flow tube whereby quadrature voltage induced in said outer conductors and applied to said primaries acts in opposition to quadrature voltage induced in said inner conductors and applied to said secondaries, whereby the signal applied to said amplifier is substantially free of a quadrature voltage component.