Magnetic flow sensor and method
First Claim
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1. A flow sensor for measuring a flow rate component, along a selected direction, of a fluid flowing in a flow direction relative to a sensing head, the sensor comprising:
- at least one stationary magnet arranged to have its magnetic axis generally orthogonal to the flow direction and to the selected direction;
at least one pair of electrodes wetted by the fluid when it is present, the electrodes of the at least one pair thereof spaced apart from one another along a line generally orthogonal to both the selected direction and to the magnetic axis;
at least one switching device having at least two states, the switching device, when in the first state, directly electrically connecting each electrode to a respective reference voltage;
the switching device, when in a second state, connecting a voltage measurement circuit between an electrode of the at least one pair thereof and that other electrode with which it is paired;
wherein the voltage measurement circuit is adapted to measure a voltage between the electrodes of the at least one pair thereof and to provide therefrom an output representative of the flow rate component.
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Abstract
A magnetic flow sensor is configured to compensate for electrode related drifts by connecting the electrodes either to each other or to a reference voltage during most of an operating duty cycle. Some versions of the invention use multiple sensing heads in a single sensor to increase the magnitude of the flow related signal, either by interconnecting ones of the electrodes or by externally summing the signals. Additionally, some versions of the sensor can be used with weakly electrically conducting flow conduits, such as blood vessels.
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Citations
31 Claims
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1. A flow sensor for measuring a flow rate component, along a selected direction, of a fluid flowing in a flow direction relative to a sensing head, the sensor comprising:
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at least one stationary magnet arranged to have its magnetic axis generally orthogonal to the flow direction and to the selected direction;
at least one pair of electrodes wetted by the fluid when it is present, the electrodes of the at least one pair thereof spaced apart from one another along a line generally orthogonal to both the selected direction and to the magnetic axis;
at least one switching device having at least two states, the switching device, when in the first state, directly electrically connecting each electrode to a respective reference voltage;
the switching device, when in a second state, connecting a voltage measurement circuit between an electrode of the at least one pair thereof and that other electrode with which it is paired;
wherein the voltage measurement circuit is adapted to measure a voltage between the electrodes of the at least one pair thereof and to provide therefrom an output representative of the flow rate component. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A flow sensor for measuring a flow rate at which a fluid flows, the sensor comprising:
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at least one stationary magnet arranged to have a magnetic axis generally orthogonal to a direction in which the fluid flows adjacent the at least one magnet;
at least two pairs of electrodes wetted by the fluid when it is present, the two electrodes of each of the at least two pairs spaced apart from one another along a respective line generally orthogonal to both the direction in which the fluid flows between them and to the magnetic axis;
the two pairs of electrodes spaced apart from each other along the flow direction;
at least one switching device for switching each of the at least two pairs of electrodes between a respective open circuit state in which a respective voltage between the electrodes of the respective pair thereof is representative of the fluid flow and a closed circuit state in which each of the electrodes of the respective pair thereof is directly electrically connected to one of a respective reference voltage and that electrode with which the each of the electrodes is paired; and
a voltage measurement circuit connected by the at least one switching device to each of the pairs of electrodes when that pair of electrodes is in its respective open circuit state. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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18. A method of operating a magnetic flow sensor in which a fluid flows in a flow direction orthogonal to a magnetic field, the flow sensor comprising at least one pair of electrodes spaced apart from each other along a selected direction orthogonal to the magnetic field, the flow sensor further comprising at least one voltage measurement circuit for measuring an electric voltage between the at least one pair of electrodes, the electric voltage proportional to a component of the flow rate that is orthogonal to both the selected direction and to the magnetic field, the method comprising the steps of:
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operating at least one electric switching device to switch, for a first selected interval, each of the at least one pair of electrodes into a closed circuit state in which the each of the electrodes is directly electrically connected to one of a respective reference voltage and that electrode with which the each of the electrodes is paired;
operating the at least one electric switching device to connect, for a second selected interval each of the at least one pair of electrodes to a voltage measurement circuit; and
measuring the electric voltage during the second selected interval. - View Dependent Claims (19, 20, 21, 22)
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23. A flow sensor for measuring a flow rate at which a fluid flows through a tube having a weakly electrically conductive wall, the sensor comprising:
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a housing having an external concave surface shaped so as to receive the tube;
at least one permanent magnet fixedly disposed in the housing so that its magnetic axis is generally orthogonal to a direction of flow through the tube when the tube is received in the housing;
at least one pair of electrodes spaced apart on the external concave surface of the housing so as to contact an external surface of the tube when the tube is received in the housing and so that a line between the two electrodes making up the at least one pair thereof is generally orthogonal to both the direction of flow in the tube and the magnetic axis;
at least one switching device disposed in the housing, the switching device for switching each of the pairs of electrodes between a respective open circuit state in which a voltage between the electrodes of the respective pair thereof is representative of the fluid flow and a closed circuit state in which each of the electrodes is directly electrically connected to one of a respective reference voltage and that electrode with which the each of the electrodes is paired; and
a voltage measurement circuit disposed in the housing, the voltage measurement circuit for measuring the respective voltage representative of the flow rate. - View Dependent Claims (24, 25, 26, 27)
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28. Apparatus for measuring a flow rate of a fluid in a tube, the apparatus comprising:
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at least two pairs of electrodes spaced apart a selected distance along the tube, each of the electrodes wetted by the fluid when the fluid is in the tube, each of the electrodes spaced apart from that other electrode with which it is paired along a line generally orthogonal to the tube;
at least two stationary magnets spaced apart by the selected distance along the tube so that at least one magnet is respectively adjacent each pair of electrodes, each of the at least two magnets for providing a respective magnetic field orthogonal both to the tube and to the respective line along which the two electrodes of the adjacent pair thereof are spaced;
a piece of ferromagnetic material extending the selected distance along the tube so as to extend between two of the at least two magnets; and
at least one voltage measurement circuit for measuring a voltage difference between each of the electrodes and that other electrode with which it is paired. - View Dependent Claims (29, 30, 31)
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Specification