Measuring and testing – Volume or rate of flow – By measuring electrical or magnetic properties
Reexamination Certificate
2002-04-04
2004-10-26
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring electrical or magnetic properties
Reexamination Certificate
active
06807867
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetoinductive flowmeter for moving fluids, incorporating a measuring tube, a magnet serving to generate a periodically alternating magnetic field that extends in a direction at least essentially perpendicular to the axis of the measuring tube, and two measuring electrodes positioned along a connecting line that extends in a direction at least essentially perpendicular to the axis of the measuring tube and to the vector of the magnetic field. The invention further relates to a magnetoinductive flow-measuring process for measuring the flow rate of a fluid moving through a measuring tube which is equipped with two measuring electrodes positioned along a connecting line that extends in an at least essentially perpendicular direction relative to the axis of the measuring tube, in which process a periodically alternating magnetic field is generated that extends in a direction at least essentially perpendicular to the axis of the measuring tube and perpendicular to the connecting line of the measuring electrodes, a voltage differentiated from a reference potential is collected at one or both of the measuring electrodes and the direct-current component of the voltage differentiated from the reference potential and collected at one or both of the measuring electrodes is quantified.
2. Description of the Prior Art
The basic principle of magnetoinductive flowmeters and of magnetoinductive flow-measuring techniques has been well known for some time and has been variously employed in a range of different applications. The underlying concept of a magnetoinductive flowmeter for moving fluids goes back to Faraday who in 1832 postulated the applicability of the principle of electrodynamic induction in the measurement of flow rates. According to Faraday's law of induction, a moving fluid that contains charge carriers and flows through a magnetic field will develop an electric field intensity perpendicular to the direction of flow and perpendicular to the magnetic field. A magnetoinductive flowmeter utilizes Faraday's law of induction by virtue of the fact that a magnet, usually consisting of two magnetic poles each with a field coil, generates a magnetic field perpendicular to the direction of the flow through the measuring tube. Within this magnetic field, each volume element of the fluid traveling through it and containing a certain number of charge carriers contributes its field intensity generated in that volume element to a measuring voltage that can be collected by way of measuring electrodes. In conventional magnetoinductive flowmeters, the measuring electrodes are so designed as to make conductive or capacitive contact with the moving fluid. A salient feature of magnetoinductive flowmeters is the proportionality between the measuring voltage and the flow rate of the fluid averaged across the diameter of the measuring tube, i.e. between measuring voltage and volumetric flow.
As stated above, a periodically alternating magnetic field is generated. In prior art, this has been accomplished following a variety of approaches. For example, a magnetoinductive flow measurement can be obtained using an alternating magnetic field for which purpose the field coils of the magnet are typically fed a sinusoidal 50/60 Hz line voltage directly off the power mains. However, transformation-induced noise and line interference compromise the measuring voltage derived from the flow between the measuring electrodes. Therefore, it is now common practice in magnetoinductive flow measurements to employ a polarity-reversible constant magnetic field. A polarity-reversible constant magnetic field is obtained by feeding to the field coils of the magnet a current with a sequential square-wave pattern which changes in periodically alternating fashion. Magnetoinductive flow measurements are also possible by means of a pulsed constant field which is obtainable by feeding to the field coils of the magnet a sequential square-wave current of unchanging polarity only at periodic intervals.
The magnetoinductive flowmeter and the magnetoinductive flow measuring technique referred to above have been described for instance in U.S. Pat. No. 5,677,496. According to that publication, the constant voltage component of the voltage collected on one or both of the measuring electrodes and differentiated from a reference potential is quantified for the purpose of subtracting its value from a flow-derived voltage that is composed of a value for the flow of the moving fluid through the measuring tube and a value for the said constant-voltage component. In this fashion, a voltage value is obtained which, now no longer error-prone due to the constant-voltage potential, provides a direct measure of the flow rate of the moving fluid through the measuring tube.
SUMMARY OF THE INVENTION
It is the objective of this invention to provide a magnetoinductive flowmeter and a magnetoinductive flow-measuring process, both as referred to above, which provide to the user specific information in addition to the flow rate.
Based on the concept of the magnetoinductive flowmeter described above, the magnetoinductive flowmeter according to this invention which achieves the stated objective is characterized in that it features an output device which displays a value representing the constant-current component of the voltage differentiated from the reference potential and collected at one or both of the measuring electrodes to the user, and/or makes that value available to the user for further processing.
The invention thus utilizes the fact that, apart from the magnetic-field-induced voltage, another voltage potential is generated at the measuring electrodes, that being the electrochemical noise voltage from which the user of the magnetoinductive flowmeter can derive additional, and additionally beneficial, information. These additional benefits, available to the user by virtue of this invention, are explained in detail further below in connection with the description of preferred embodiments of this invention.
The electrochemical noise voltage, utilized according to this invention, originates in contact potentials generated by the contact between the moving fluid and the measuring electrodes and resulting from the different chemical potentials of the moving fluid and the material of the measuring electrodes, respectively. Thus, according to the invention, the contact potentials which normally constitute a noise factor are utilized for providing to the user the possibility, in addition to flow-rate data, to derive quantitative information which is indicative of other parameters of the fluid, such as its conductivity or its charge-carrier concentration. In one example, a change in the electrochemical noise potential indicates a change of fluids in the measuring tube.
The above statement whereby an output device is provided for indicating a value for the constant-voltage component of the voltage collected, more specifically refers to an output which represents either the actual value of the constant-voltage component itself or a mean value for the constant-voltage component, or a value based on and derived from the constant-voltage component, such as the pH value of the fluid passing through the measuring tube.
In principle, each measuring electrode can have its own reference potential and the difference between the reference potential and the potentials of the individual measuring electrodes, the moving fluid, the measuring tube, etc. may be of any arbitrary magnitude. However, in a preferred embodiment of the invention, the reference potential employed is the earth potential. Especially when the earth potential is used as the reference potential, but in the case of other reference potentials as well, both measuring electrodes should preferably use the same reference potential. If, specifically, both measuring electrodes jointly use the earth potential as the reference potential, the structural design of the magnetoinductive flowmeter becomes quite uncomplicated and
Cesari & McKenna LLP
Krohne Messtechnik GmbH & Co. KG
Lefkowitz Edward
Thompson Jewel
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