Patent ID: 7426874

Claim:
An electromagnetic flowmeter comprising: a measuring tube through which a fluid to be measured flows; an electrode which is placed in said measuring tube and detects an electromotive force generated by a magnetic field applied to the fluid and a flow of the fluid; an exciting unit which applies, to the fluid, a time-changing magnetic field asymmetrical to a first plane which includes said electrode and is perpendicular to an axial direction of said measuring tube; a signal conversion unit which extracts a ∂A/∂t component irrelevant to a flow velocity of the fluid from a resultant electromotive force of an electromotive force based on the ∂A/∂t component and an electromotive force based on a v×B component originating from the flow velocity of the fluid; and a flow rate output unit which removes a variable factor for a span as a coefficient by which a magnitude V of a flow velocity of the v×B component in the resultant electromotive force is multiplied, on the basis of the extracted ∂A/∂t component, and calculates a flow rate of the fluid from a result obtained by removing the variation factor, wherein said exciting unit applies the magnetic fields to the fluid while switching exciting frequencies, said signal conversion unit obtains an amplitude and phase of the resultant electromotive force in each of at least two excitation states in which the exiting frequencies differ from each other, and extracts the ∂A/∂t component on the basis of the amplitude and phase of the resultant electromotive force, and said flow rate output unit removes a variation factor for a span contained in a v×B component in a resultant electromotive force at a given exciting frequency on the basis of the extracted ∂A/∂t component, and calculates a flow rate of the fluid from a result obtained by removing the variation factor.