Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
1999-10-20
2002-04-02
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
C324S126000, C324S127000
Reexamination Certificate
active
06366076
ABSTRACT:
The present invention aims at providing a device for measuring the intensity of electrical current passing through a conductor which allows measurement, with great accuracy, of continuous current as well as high frequency current, i.e., a device having a passband from zero to more than 10 MHz.
To this end, the device according to the invention is characterized in that it comprises, on one hand, a measuring coil closed on itself, without a magnetizable core, surrounding at least partially the said conductor and adapted to provide a first measurement signal and, on the other hand, at least one measuring resistor traversed by the current to be measured or at least one magnetic field detector arranged in proximity to said conductor, adapted to provide a second measurement signal, the measuring device comprising a circuit for processing said first and second measurement signals so as to provide an output signal which is an image of the current to be measured.
The invention seeks moreover to enable miniaturization of the measuring device, and, according to a preferred embodiment, measurement without galvanic coupling between the current and the output signal.
Particular embodiments of the device according to the invention are indicated in the claims
2
to
13
and other aspects, objectives and advantages of the invention will become apparent from the description which follows and from the annexed drawings.
Measuring methods using a Rogowski's coil are already known, for example from the publication “Rogowski Transducers for High Current Measurement” by W. F. Ray, “IEE Colloquium on Low Frequency Power Measurement and Analysis, London, 1994, pg. 10/1-10/6, and the documents FR-A-2695482 and U.S. Pat. No. 5,442,280, these methods however not permitting the measurement of continuous current or of continuous current components.
Other known methods for measuring current use the measurement of the magnetic field created by a conductor through which the current flows, by means of field detectors such as Hall detectors or magneto-resistive elements (cf. DE 36 05 719 and DE 35 17 095, and the publication by L. Ghislanzoni “MAGNETIC COUPLED CURRENT SENSING TECHNIQUES FOR SPACECRAFT POWER SYSTEMS”, Proceedings of the European Space Power Conference Oct. 2-6, 1989, Madrid, Spain). Without channelling the flux by means of magnetic materials with high permeability, the corresponding measurement signals are however very weak. Thus, the capacitive coupling and the parasitic fields may generate signals of an amplitude attaining a multiple of that of the measurement signal, for example in the case of switching by semi-conductor switches leading to rates of voltage variation in the order of several thousands of volts per micro-second. To increase the measurement signal as well as the signal
oise ratio, the conductor may be surrounded by a magnetic circuit with an air-gap. One measures in this case the magnetic field inside the air-gap, for example by means of a compensating device regulating the flux in the magnetic circuit to zero with the help of a supplementary winding. Nevertheless, the upper frequency limit of such current sensors with compensation is generally less than 1 MHz. Moreover, the cross-section of the magnetic circuit that is needed increases with the intensity of the current and therefore reduces the scope of miniaturization.
In methods in which one measures the voltage drop on conductors or resistors traversed by the current, the losses which increase proportionally with the effective value of the current, the conductive coupling between the measurement signal and the current to be measured, as well as the costly mechanical design that these methods imply, represent major inconveniences. A method of this type is the subject of a publication by Adolf Schwab “Die Berechnung der Bandbreite und der Anstiegszeit rohrförmiger koaxialer Messwiderstände unter Berücksichtigung der Stromverdrängung” (ETZ—A vol. no. 89, pg. 604 ff).
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Hofer-Noser Patrick
Karrer Nicolas
Brown Glenn W.
Browning Clifford W.
Hamdan Wasseem H.
Liaisons Electroniques-Mecaniques LEM SA
Woodard Emhardt Naughton Moriarty & McNett
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