An electromagnetic flowmeter includes a measuring tube through which a fluid to be measured flows, electrodes which detect an electromotive force generated by a magnetic field applied to the fluid. An exciting coil applies, to the fluid, a time-changing magnetic field asymmetrical to a plane (PLN) w
An electromagnetic flowmeter includes a measuring tube through which a fluid to be measured flows, electrodes which detect an electromotive force generated by a magnetic field applied to the fluid. An exciting coil applies, to the fluid, a time-changing magnetic field asymmetrical to a plane (PLN) which includes the electrodes and is perpendicular to the axial direction of the measuring tube. A signal conversion unit extracts a ∂A/∂t component from the resultant electromotive force of the electromotive force. A flow rate output unit removes a variation factor for a span as a coefficient applied to the magnitude of the flow velocity on the basis of the ∂A/∂t component, and calculates the flow rate of the fluid from the result obtained by removing the variation factor.
대표청구항▼
The invention claimed is: 1. 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 ex
The invention claimed is: 1. 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. 2. An electromagnetic flowmeter according to claim 1, characterized in that said exciting unit comprises an exciting coil placed at a position spaced apart by an offset from the first plane which includes said electrode and is perpendicular to the axial direction of said measuring tube, and a power supply unit which supplies an exciting current to the exciting coil while switching exciting frequencies, said signal conversion unit obtains an amplitude and phase of the resultant electromotive force in each of a first excitation state and a second excitation state in which the exciting frequencies differ from each other, and extracts an electromotive force difference between a resultant electromotive force in the first excitation state and a resultant electromotive force in the second excitation state as the ∂A/∂t component on the basis of the amplitudes and phases of the resultant electromotive forces, and said flow rate output unit removes a span variation factor contained in a v��B component in a resultant electromotive force in the first excitation state 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. 3. An electromagnetic flowmeter according to claim 1, characterized in that said exciting unit comprises a first exciting coil placed at a position spaced apart by a first offset from the first plane which includes said electrode and is perpendicular to the axial direction of said measuring tube, a second exciting coil which is placed at a position spaced apart by a second offset from the first plane so as to face the first exciting coil through the first plane, and a power supply unit which supplies exciting currents to the first exciting coil and the second exciting coil which switching a phase difference between the exciting current supplied to the first exciting coil and the exciting current supplied to the second exciting coil and exciting frequencies of the exciting currents, said signal conversion unit which obtains amplitudes and phases of the resultant electromotive forces in three excitation states including a first excitation state in which a phase difference between a first magnetic field generated by the first exciting coil and a second magnetic field generated by the second exciting coil is Δθ3, and an exciting angular frequency is ω0, a second excitation state in which the phase difference between the first magnetic field and the second magnetic field in the first excitation state has changed from Δθ3 to Δθ3+π, and a third excitation state in which the exciting angular frequency in the second excitation state has changed to ω1, and extracts an electromotive force difference between the resultant electromotive force in the second excitation state and the resultant electromotive force in the third excitation state as the ∂A/∂t component on the basis of the amplitudes and the phases, and said flow rate output unit removes a variation factor for a span contained in a v��B component in a resultant electromotive force in the first excitation state on the basis of the ∂A/∂t component, and calculates a flow rate of the fluid from a result obtained by removing the variation factor. 4. An electromagnetic flowmeter according to claim 1, characterized in that said exciting unit comprises an exciting coil which applies a magnetic field to the fluid and a power supply unit which supplies an exciting current to the exciting coil while switching exciting frequencies, said electrode comprises a first electrode placed at a position spaced apart by a first offset from a second plane which include an axis of the exciting coil and is perpendicular to an axial direction of said measuring tube, and a second electrode which is placed at a position spaced apart by a second offset from the second plane so as to face the first electrode through the second plane, said signal conversion unit obtains amplitudes and phases of electromotive force differences between first resultant electromotive forces detected by the first electrode and second resultant electromotive forces detected by the second electrode in a first excitation state and a second excitation state in which the exciting frequencies differ from each other, and extracts a difference between the electromotive force differences in the first excitation state and the second excitation state as the ∂A/∂t component on the basis of the amplitudes and phases of the electromotive force differences, and said flow rate output unit removes a variation factor for a span contained in a v��B component in an electromotive force sum of the first resultant electromotive force and the second resultant electromotive force in the first excitation state. 5. An electromagnetic flowmeter according to claim 1, characterized in that said exciting unit comprises an exciting coil which applies a magnetic field to the fluid and a power supply unit which supplies an exciting current to the exciting coil while switching exciting frequencies, said electrode comprises a first electrode placed at a position spaced apart by a first offset from a second plane which include an axis of the exciting coil and is perpendicular to an axial direction of said measuring tube, and a second electrode which is placed at a position spaced apart by a second offset from the second plane so as to face the first electrode through the second plane, said signal conversion unit obtains amplitudes and phases of electromotive force sums of first resultant electromotive forces detected by the first electrode and second resultant electromotive forces detected by the second electrode in a first excitation state and a second excitation state in which the exciting frequencies differ from each other, and extracts a difference between the electromotive force sums in the first excitation state and the second excitation state as the ∂A/∂t component on the basis of the amplitudes and phases of the electromotive force sums, and said flow rate output unit removes a variation factor for a span contained in a v��B component in an electromotive force difference between the first resultant electromotive force and the second resultant electromotive force in the first excitation state on the basis the extracted ∂A/∂t component, and calculates a flow rate of the fluid from a result obtained by removing the variation factor. 6. 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 generates magnetic fields with the same exciting frequency from a plurality of exciting coils and applies the magnetic fields to the fluid while switching a phase difference between the magnetic fields generated from the respective exciting coils, 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 phase differences differ from each other, and extracts a resultant electromotive force in a specific excitation state in which the phase difference is a predetermined value as 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 in another excitation state which differs from the specific excitation state on the basis of the extracted ∂A/∂t component. 7. An electromagnetic flowmeter according to claim 6, characterized in that said exciting unit comprises a first exciting coil placed at a position spaced apart by a first offset from the first plane which includes said electrode and is perpendicular to the axial direction of said measuring tube, a second exciting coil which is placed at a position spaced apart by a second offset from the first plane so as to face the first exciting coil through the first plane, and a power supply unit which supplies exciting currents with the same frequency to the first exciting coil and the second exciting coil while switching a phase difference between the exciting current supplied to the first exciting coil and the exciting current supplied to the second exciting coil, said signal conversion unit which obtains amplitudes and phases of the resultant electromotive forces in two excitation states including a first excitation state in which a phase difference between a first magnetic field generated by the first exciting coil and a second magnetic field generated by the second exciting coil is substantially zero, and a second excitation state in which the phase difference between the first magnetic field and the second magnetic field in the first excitation state is substantially π, and extracts a resultant electromotive force in the second excitation state as the ∂A/∂t component on the basis of the amplitude and phase of the resultant electromotive force, and said flow rate output unit which removes a variation factor for a span contained in a v��B component in a resultant electromotive force in the first excitation state 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.
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이 특허를 인용한 특허 (2)
Rogers, Steven Bruce; Smith, Joseph Alan, Integrally molded magnetic flowmeter.
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