Electromagnetic flowmeters and methods for measuring flow
AssigneeNational Research Development Corporation
InventorsJohn Hemp, Yousif A. H. Al-Khazraji
Life of this patent
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Abstract
An electromagnetic flowmeter for measuring the mean velocity of a fluid flowing through a duct is described. In one embodiment the electrodes are shaped to provide a uniform weighting function relating fluid velocity distribution over the duct cross section to flowmeter output voltage representative of mean velocity. Flowmeters are described in which using large insulated electrodes sensitivity is made independent of velocity profile by either ensuring that the applied magnetic field is uniform and the virtual current in the duct is two dimensional, or vice versa.
Claims18
A flowmeter comprising
- a duct for a fluid, the duct having a substantially circular cross-section,
- means for applying a magnetic field to a fluid in the duct, the magnetic field having at least one component which is generally normal to the direction of fluid flow, and
- two electrodes each having an appreciable area as compared with a point electrode and being insulated from fluid in the duct, the electrodes being positioned adjacent to the inner surface of the duct, opposite one another across the duct, to ensure that a virtual current between the electrodes would have at least a component generally normal to both the direction of fluid flow and the magnetic field, the distance between the longitudinal axis of the duct and each electrode increasing with increasing distance around the periphery of the inner surface of the duct from the center of the electrode in order to minimize the effect of fluid velocity profile in the duct on the voltage generated between the electrodes when fluid flows in the duct,
- and the said voltage being representative of the mean velocity of fluid flowing through the duct.
A magnetic flowmeter for measuring the flow rate of a fluid conducted through a pipe having a longitudinal axis Z, the field intercepting a magnetic field having at least one component substantially parallel to a transverse axis X which is normal both to axis Z and a diametric axis Y, said flowmeter further comprising:
- a pair of electrode assemblies mounted on the pipe on opposite sides of the Y axis in the region of the magnetic field;
- and
- the voltage generated between the electrode assemblies being substantially proportional to flow rate and being substantially immune to the influence of a non-axisymmetric flow profile, said electrode assemblies being out of contact with the fluid and being capacitively coupled thereto to detect potential .phi. present on the fluid surface, the effective coupling capacitance of the assemblies so decreasing with increase in angle .PSI.=90.degree.-.theta. with respect to the Y axis that the effect of fluid velocity profile in the pipe on the said voltage is minimized.
A magnetic flowmeter for measuring the flow rate of a fluid conducted through a pipe having a longitudinal axis Z, the fluid intercepting a magnetic field whose lines of flux are essentially parallel to a transverse axis X, which is normal both to axis Z and a diametric axis Y, said flowmeter further comprising:
- A. a pair of electrode assemblies mounted on the pipe on opposite sides of the X axis in the region of the magnetic field;
- and
- B. a converter whose input terminals are connected to the electrode assemblies to produce a signal which is proportional to flow rate and is substantially immune to the influence of a non-axisymmetric flow profile, said electrode assemblies being out of contact with the fluid and being capacitively coupled thereto to detect a potential present on the fluid surface, the effective coupling capacitance of the assemblies decreasing in a manner substantially proportional to the cosine of an angle defined with respect to the Y axis.
Dependencies are inferred from the claim text.