초록 ▼

An electromagnetic flowmeter includes a measuring tube, an electrode, an exciting unit, a signal conversion unit, and a flow rate calculating unit. The signal conversion unit extracts a ∂A/∂t component irrelevant to a flow velocity of the fluid and a v��B component originating from the f

An electromagnetic flowmeter includes a measuring tube, an electrode, an exciting unit, a signal conversion unit, and a flow rate calculating unit. The signal conversion unit extracts a ∂A/∂t component irrelevant to a flow velocity of the fluid and a v��B component originating from the flow velocity of the fluid from a resultant electromotive force of an electromotive force ∂A/∂t, with A, t, v, and B respectively representing a vector potential, a time, a flow velocity, and a magnetic flux density. The flow rate calculating unit extracts a variation component dependent on a parameter from the ∂A/∂t component, corrects a span which is a coefficient applied to a magnitude V of the flow velocity of the v��B component, and calculates the flow rate of the fluid from the v��B component whose span is corrected.

대표청구항 ▼

What is 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

What is 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 and a v��B component originating from the 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 the v��B component, with A, t, v, and B respectively representing a vector potential, a time, a flow velocity, and a magnetic flux density; and a flow rate calculating unit which extracts a variation component dependent on a parameter from the ∂A/∂t component extracted by said signal conversion unit, corrects a span which is a coefficient applied to a magnitude V of the flow velocity of the v��B component input from said signal conversion unit on the basis of the variation component, and calculates the flow rate of the fluid from the v��B component whose span is corrected, the parameter being at least one of a characteristic and state of the fluid and a state in said measuring tube which are independent of the flow rate of the fluid. 2. A flowmeter according to claim 1, wherein said flow rate calculating unit comprises a state quantifying unit which extracts a variation component dependent on a parameter from the ∂A/∂t component extracted by said signal conversion unit, and quantifies the parameter on the basis of the variation component, and a flow rate correcting unit which corrects a span of the v��B component input from said signal conversion unit on the basis of the parameter quantified by the state quantifying unit, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 3. A flowmeter according to claim 2, wherein the state quantifying unit comprises a state storage unit which stores in advance a relationship between a parameter and a variation component dependent on the parameter, and a state output unit which extracts a variation component dependent on the parameter from the ∂A/∂t component extracted by said signal conversion unit, and obtains the parameter corresponding to the extracted variation component on the basis of the relationship stored in the state storage unit, and said flow rate correcting unit comprises a span storage unit which stores in advance a relationship between a parameter and a variation component of a span of a v��B component, and a flow rate output unit which obtains a variation component of a span corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in the span storage unit, corrects a span of the v��B component input from said signal conversion unit on the basis of the variation component of the span, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 4. A flowmeter according to claim 3, wherein said signal conversion unit extracts a ∂A/∂t component and a v��B component from a resultant electromotive force detected by said electrode, obtains a v��B component obtained by normalizing the extracted v��B component with the extracted ∂A/∂t component, and outputs the normalized v��B component as a v��B component as a correction target to the flow rate output unit. 5. A flowmeter according to claim 3, wherein said exciting unit applies magnetic fields to the fluid to provide a plurality of exciting frequencies at one of a simultaneous timing and an alternative timing, and said signal conversion unit extracts a ∂A/∂t component and a v��B component by obtaining amplitudes and phases of a plurality of frequency components, of the resultant electromotive force detected by said electrode, which are obtained, at one of a simultaneous timing and an alternative timing. 6. A flowmeter according to claim 5, wherein said exciting unit comprises an exciting coil placed at a position spaced apart by an offset from a first plane which includes said electrode and is perpendicular to an axial direction of said measuring tube, and a power supply unit which supplies an exciting current to the exciting coil to provide two different exciting frequencies including a first frequency and a second frequency at one of a simultaneous timing and an alternative timing, said signal conversion unit obtains amplitudes and phases of two frequency components with the first frequency and the second frequency of the resultant electromotive force detected by said electrode, extracts an electromotive force difference between the two frequency components as a ∂A/∂t component on the basis of the amplitudes and the phases, and extracts a v��B component of the resultant electromotive force by removing the extracted ∂A/∂t component from the first frequency component of the resultant electromotive force, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a magnitude of a variation component of a span of a v��B component, and the flow rate output unit obtains a magnitude of a variation component of a span corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in the span storage unit, corrects a span of a v��B component input from said signal conversion unit on the basis of the magnitude of the variation component of the span, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 7. A flowmeter according to claim 5, wherein said exciting unit comprises an exciting coil placed at a position spaced apart by an offset from a first plane which includes said electrode and is perpendicular to an axial direction of said measuring tube, and a power supply unit which supplies an exciting current to the exciting coil to provide two different exciting frequencies including a first frequency and a second frequency at one of a simultaneous timing and an alternative timing, said signal conversion unit obtains amplitudes and phases of two frequency components with the first frequency and the second frequency of the resultant electromotive force detected by said electrode, extracts an electromotive force difference between the two frequency components as a ∂A/∂t component on the basis of the amplitudes and the phases, extracts a v��B component of the resultant electromotive force by removing the extracted ∂A/∂t component from the first frequency component of the resultant electromotive force, and obtains a v��B component as a correction target by normalizing the extracted v��B component with the extracted ∂A/∂t component, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a ratio between a magnitude of a variation component of a span of a v��B component and a magnitude of a variation component of a ∂A/∂t component, and the flow rate output unit obtains a ratio corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in the span storage unit, corrects a span of the v��B component input from said signal conversion unit on the basis of the ratio, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 8. A flowmeter according to claim 5, wherein 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 to provide two different exciting frequencies including a first frequency and a second frequency at one of a simultaneous timing and an alternative timing 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 obtains amplitudes and phases of two frequency components with the first frequency and the second frequency of the resultant electromotive force detected by said electrode in an 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 p, extracts, as a first ∂A/∂t component, an electromotive force difference between the two frequency components in an excitation state in which the phase difference between the magnetic fields is substantially p on the basis of the amplitudes and the phases, obtains amplitudes and phases of the two frequency components in an excitation state in which the phase difference between the magnetic fields is substantially 0, extracts, as a second ∂A/∂t component, an electromotive force difference between the two frequency components in an excitation state in which the phase difference between the magnetic fields is substantially 0 on the basis of the amplitudes and the phases, and extracts a v��B component by removing the extracted second ∂A/∂t component from the first frequency of the resultant electromotive force detected by said electrode in an excitation state in which the phase difference between the magnetic fields is substantially 0, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the first ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a magnitude of a variation component of a span of a v��B component, and the flow rate output unit obtains a magnitude of a variation component of a span corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in the span storage unit, corrects a span of a v��B component input from said signal conversion unit on the basis of the magnitude of the variation component of the span, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 9. A flowmeter according to claim 5, wherein 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 to provide two different exciting frequencies including the first frequency and the second frequency at one of a simultaneous timing and an alternative timing 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 obtains amplitudes and phases of two frequency components with the first frequency and the second frequency of the resultant electromotive force detected by said electrode in an 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 p, extracts, as a first ∂A/∂t component, an electromotive force difference between the two frequency components in an excitation state in which the phase difference between the magnetic fields is substantially p on the basis of the amplitudes and the phases, obtains amplitudes and phases of the two frequency components in an excitation state in which the phase difference between the magnetic fields is substantially 0, extracts, as a second ∂A/∂t component, an electromotive force difference between the two frequency components in an excitation state in which the phase difference between the magnetic fields is substantially 0 on the basis of the amplitudes and the phases, extracts a v��B component by removing the extracted second ∂A/∂t component from the first frequency of the resultant electromotive force detected by said electrode in an excitation state in which the phase difference between the magnetic fields is substantially 0, and obtains a v��B component as a correction target by normalizing the extracted v��B component with the first ∂A/∂t component, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the first ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a ratio between a magnitude of a variation component of a span of a v��B component and a magnitude of a variation component of a ∂A/∂t component, and the flow rate output unit obtains a ratio corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in the span storage unit, corrects a span of the v��B component input from said signal conversion unit on the basis of the ratio, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 10. A flowmeter according to claim 5, wherein 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 to provide two different exciting frequencies including a first frequency and a second frequency at one of a simultaneous timing and an alternative timing, said electrode comprises a first electrode placed at a position spaced apart by a first offset from a second plane which includes an axis of the exciting coil and is perpendicular to an axial direction of said measuring tube, and a second electrode 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 a first resultant electromotive force detected by the first electrode and a second resultant electromotive force detected by the second electrode, obtains an electromotive force difference between identical frequency components of the first resultant electromotive force and the second resultant electromotive force for each of the first frequency and the second frequency on the basis of the amplitudes and the phases, extracts a difference between the electromotive force difference at the first frequency and the electromotive force difference at the second frequency as a first ∂A/∂t component, obtains an electromotive force sum of identical frequency components of the first resultant electromotive force and the second resultant electromotive force for each of the first frequency and the second frequency, extracts a difference between the electromotive force sum at the first frequency and the electromotive force sum at the second frequency as a second ∂A/∂t component, and extracts a v��B component by removing the second ∂A/∂t component from the electromotive force sum at the first frequency, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the first ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a magnitude of a variation component of a span of a v��B component, and the flow rate output unit obtains a magnitude of a variation component of a span corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in said the span storage unit, corrects a span of a v��B component input from said signal conversion unit on the basis of the magnitude of the variation component of the span, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 11. A flowmeter according to claim 5, wherein 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 to provide two different exciting frequencies including a first frequency and a second frequency at one of a simultaneous timing and an alternative timing, said electrode comprises a first electrode placed at a position spaced apart by a first offset from a second plane which includes an axis of the exciting coil and is perpendicular to an axial direction of said measuring tube, and a second electrode 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 a first resultant electromotive force detected by the first electrode and a second resultant electromotive force detected by the second electrode, obtains an electromotive force difference between identical frequency components of the first resultant electromotive force and the second resultant electromotive force for each of the first frequency and the second frequency on the basis of the amplitudes and the phases, extracts a difference between the electromotive force difference at the first frequency and the electromotive force difference at the second frequency as a first ∂A/∂t component, obtains an electromotive force sum of identical frequency components of the first resultant electromotive force and the second resultant electromotive force for each of the first frequency and the second frequency, extracts a difference between the electromotive force sum at the first frequency and the electromotive force sum at the second frequency as a second ∂A/∂t component, extracts a v��B component by removing the second ∂A/∂t component from the electromotive force sum at the first frequency, and obtains a v��B component as a correction target by normalizing the extracted v��B component with the extracted first ∂A/∂t component, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the first ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a ratio between a magnitude of a variation component of a span of a v��B component and a magnitude of a variation component of a ∂A/∂t component, and the flow rate output unit obtains a ratio corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in the span storage unit, corrects a span of the v��B component input from said signal conversion unit on the basis of the ratio, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 12. An flowmeter according to claim 3, wherein 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 to provide two excitation states in which phase differences between first magnetic fields generated by the first exciting coil and second magnetic fields generated by the second exciting coil differ from each other, and said signal conversion unit extracts a ∂A/∂t component by obtaining an amplitude and phase of the resultant electromotive force detected by said electrode in one of the excitation states, and extracts a v��B component on the basis of the extracted ∂A/∂t component and an amplitude and phase of the resultant electromotive force detected by said electrode in the other excitation state. 13. An flowmeter according to claim 12, wherein said signal conversion unit extracts a ∂A/∂t component by obtaining an amplitude and phase of a resultant electromotive force detected by said electrode in an excitation state in which a phase difference between the first magnetic field and the second magnetic field is substantially p, and extracts a v��B component by obtaining an amplitude and phase of a resultant electromotive force detected by said electrode in an excitation state in which the phase difference between the first magnetic field and the second magnetic field is substantially 0, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a magnitude of a variation component of a span of a v��B component, and the flow rate output unit obtains a magnitude of a variation component of a span corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in the span storage unit, corrects a span of a v��B component input from said signal conversion unit on the basis of the magnitude of the variation component of the span, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 14. An flowmeter according to claim 12, wherein said signal conversion unit extracts a ∂A/∂t component by obtaining an amplitude and phase of a resultant electromotive force detected by said electrode in an excitation state in which a phase difference between the first magnetic field and the second magnetic field is substantially p, extracts a v��B component by obtaining an amplitude and phase of a resultant electromotive force detected by said electrode in an excitation state in which the phase difference between the first magnetic field and the second magnetic field is substantially 0, and obtains a v��B component as a correction target by normalizing the extracted v��B component with the extracted ∂A/∂t component, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a ratio between a magnitude of a variation component of a span of a v��B component and a magnitude of a variation component of a ∂A/∂t component, and the flow rate output unit obtains a ratio corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in the span storage unit, corrects a span of the v��B component input from said signal conversion unit on the basis of the ratio, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 15. A flowmeter according to claim 3, wherein 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, said electrode comprises a first electrode placed at a position spaced apart by a first offset from a second plane which includes an axis of the exciting coil and is perpendicular to an axial direction of said measuring tube, and a second electrode 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, and said signal conversion unit obtains an amplitude and phase of each of a first resultant electromotive force detected by the first electrode and a second resultant electromotive force detected by the second electrode, extracts a ∂A/∂t component from an electromotive force difference between the first resultant electromotive force and the second resultant electromotive force on the basis of the amplitudes and the phases, and extracts a v��B component from an electromotive force sum of the first resultant electromotive force and the second resultant electromotive force. 16. A flowmeter according to claim 15, wherein said signal conversion unit obtains an amplitude and phase of each of a first resultant electromotive force detected by the first electrode and a second resultant electromotive force detected by the second electrode, extracts a ∂A/∂t component from an electromotive force difference between the first resultant electromotive force and the second resultant electromotive force on the basis of the amplitudes and the phases, and extracts a v��B component from an electromotive force sum of the first resultant electromotive force and the second resultant electromotive force, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a magnitude of a variation component of a span of a v��B component, and the flow rate output unit obtains a magnitude of a variation component of a span corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in said the span storage unit, corrects a span of a v��B component input from said signal conversion unit on the basis of the magnitude of the variation component of the span, and calculates the flow rate of the fluid from the v��B component whose span is corrected. 17. A flowmeter according to claim 15, wherein said signal conversion unit obtains an amplitude and phase of each of a first resultant electromotive force detected by the first electrode and a second resultant electromotive force detected by the second electrode, extracts a ∂A/∂t component from an electromotive force difference between the first resultant electromotive force and the second resultant electromotive force on the basis of the amplitudes and the phases, extracts a v��B component from an electromotive force sum of the first resultant electromotive force and the second resultant electromotive force, and obtains a v��B component as a correction target by normalizing the extracted v��B component with the extracted ∂A/∂t component, the state storage unit stores in advance a relationship between a parameter and one of a magnitude and phase of a variation component dependent on the parameter, the state output unit extracts one of a magnitude and phase of a variation component dependent on a parameter from the ∂A/∂t component extracted by said signal conversion unit, and obtains a parameter corresponding to one of the magnitude and phase of the extracted variation component on the basis of the relationship stored in the state storage unit, the span storage unit stores in advance a relationship between a parameter and a ratio between a magnitude of a variation component of a span of a v��B component and a magnitude of a variation component of a ∂A/∂t component, and the flow rate output unit obtains a ratio corresponding to the parameter obtained by the state output unit on the basis of the relationship stored in the span storage unit, corrects a span of the v��B component on the basis of the ratio, and calculates the flow rate of the fluid from the v��B component whose span is corrected.