Abstract: An electromagnetic flow meter which calculates the electric conductivity of a fluid based on the ratio of an output signal generated when electrodes are grounded through short-circuit resistors Rs.sub.1, Rs.sub.2 to an output signal generated when the electrodes are not grounded, and more accurately corrects a flow measurement using the electric conductivity, characterized in that, for reducing measurement errors due to fluctuation in DC offset voltage accompanied by an on/off operation of the short-circuit switch S1, outputs are measured when the short-circuit switch S1 is on and off in a magnetization state, the output are next measured when the short-circuit switch S1 is on and off in a non-magnetization stage, and the outputs in the non-magnetization state are subtracted from the outputs in the magnetization state, thereby removing the influence of "DC offset voltage fluctuation" occurring accompanied by the on/off operation of the short-circuit switch S1.

Abstract: In magnetic induction flow measurement in which a flow rate of a fluid is measured by a DC magnetic field having a periodically reversed polarity, an apparatus is used to compensate a DC offset voltage generated in an amplifying circuit in an electromagnetic flowmeter in which a signal voltage produced across electrodes is sampled and stored in each of a pair of sampling periods where the magnetic field takes a positive polarity and a negative polarity, respectively. A difference between the sampling values is formed as an output signal voltage. The signal voltage is sampled and stored in a compensation period following the pair of sampling periods to produce a compensation voltage to be superimposed onto the signal voltage, and compensation is made on the signal voltage by using the compensation voltage which is held until a succeeding compensation period.