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Abstract

An electromagnetic flowmeter for measuring the flow rate of a fluid passing through a flow tube, the fluid intercepting a magnetic field established by an excitation coil supplied through an excitation circuit with a direct current or a current whose frequency is lower than that of a commercial AC power source. A DC reference voltage is derived from the excitation circuit which is either used in a feedback arrangement to maintain the excitation current constant or in a divider arrangement to correct for the adverse effects of fluctuations in the excitation current of the flow rate signal yielded by the flowmeter. The reference voltage is generated by means of an excitation-current detector that produces a voltage proportional to the excitation current, this voltage being applied to an isolation circuit that modulates the voltage to convert it into an AC voltage whose frequency is higher than the excitation frequency, the AC voltage being fed via a DC isolator into a demodulator which produces the desired DC reference voltage.

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First Claim