Measuring and testing – Volume or rate of flow – By measuring electrical or magnetic properties
Patent
1992-03-31
1995-03-21
Chilcot, Jr., Richard E.
Measuring and testing
Volume or rate of flow
By measuring electrical or magnetic properties
7386112, G01F 500
Patent
active
053985532
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electromagnetic flowmeters of the kind in which a liquid having an electrolytic property is caused to flow through a tube on a z axis intersected by an alternating or pulsating magnetic field on a y axis so that a potential difference between electrodes can be measured for the velocity of flow to be estimated according to the Faraday effect, the electrodes being mounted on opposite sides of the tube on an x axis perpendicular to the y and z axes. Changes in the strength or distribution of the magnetic field or changes in the contact impedance between adjoining pipes and the liquid can result in inaccurate flow velocity measurements.
An effect of the alternating or pulsating magnetic field is to produce an eddy current in the liquid, whether flowing or not, which has an electric field with E.sub.z and -E.sub.z components respectively adjacent the two electrodes.
It is, therefore, a main object of the present invention to introduce into an electromagnetic flowmeter a self-calibration function that compensates for any magnetic field changes and for changes in contact impedance between adjoining pipes and the liquid, which compensation is virtually insensitive to velocity profile effects in the liquid.
According to one aspect of the invention an electromagnetic flowmeter assembly comprises an insulating tube arranged for an electrolytic liquid to flow therethrough while the velocity of the passing liquid is determined, a magnet arranged for producing a periodically changing magnetic field on an axis (y) substantially perpendicular to the tube axis (z) and electrodes on opposite sides of the tube positioned according to a transverse axis (x) substantially intersecting the tube axis and passing though the magnetic field when produced by the magnet, characterised in that on one side of the tube there are two of said electrodes mounted side-by-side, being equidistantly spaced from said transverse axis (x) on a line substantially perpendicular thereto, and on the other side of the tube at least one electrode positioned in predetermined relationship to the said two electrodes, and that conductors extend individually from the electrodes whereby, in the operation of the assembly, the potential difference between the two side-by-side electrodes due to an axial component of an eddy current electric field in the liquid can be determined for self-calibration purposes in compensating automatically for any extraneous change in said magnetic field and the potentials of all the electrodes can also be determined to derive the velocity of flow of the liquid.
According to another aspect of the invention an electromagnetic flowmeter assembly comprises an insulating tube arranged for an electrolytic liquid to flow therethrough while the velocity of the passing liquid is determined, a magnet arranged for producing a periodically changing field on an axis (y) substantially perpendicular to the tube axis (z) and electrodes on opposite sides of the tube positioned according to a transverse axis (x) substantially intersecting the tube axis and passing through the magnetic field when produced by the magnet, characterised in that on one side of the tube there are two of said electrodes mounted side-by-side, being equidistantly spaced from said transverse axis (x) on a line substantially perpendicular thereto, and on the other side of the tube at least one electrode positioned in predetermined relationship to the said two electrodes, and that conductors extend individually and respectively from said electrodes and from a current to voltage converting device responsive to the periodically changing magnetic field to phase-detecting means for providing self-calibration in compensating automatically for any extraneous change in said magnetic field to means whereby the potentials of all the electrodes can also be determined to derive the velocity of flow of the liquid.
In order that the invention may be clearly understood and readily carried into effect flowmeters in accordance therewith will now be described, by way
REFERENCES:
patent: 2722122 (1952-05-01), Soffel
patent: 3372589 (1968-03-01), Mannherz
patent: 3942377 (1976-03-01), Ginzburg et al.
patent: 4308752 (1982-01-01), Appel et al.
patent: 4329879 (1982-05-01), Appel et al.
International Search Report; PCT/GB90/01442; Dec. 12, 1990; European Patent Office.
Examiner's report to the Comptroller under Section 17 (The Search Report); Application No. 8921702.2; Examiner H. Collingham; Dec. 13, 1989; UK Patent Office.
Biegel R.
Chilcot Jr. Richard E.
The Foxboro Company
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