Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
2001-04-19
2003-10-21
Deb, Anjan K. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
C324S11700H, C324S244000, C324S251000
Reexamination Certificate
active
06636029
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
Applicant claims priority under 35 U.S.C. §119 of German Application No. 198 38 536.6 filed Aug. 25, 1998. Applicant also claims priority under 35 U.S.C. §365 of PCT/EP99/06109 filed Aug. 20, 1999. The international application under PCT article 21(2) was not published in English.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device and a method for creating one or a plurality of magnetic field gradients through a current conductor that is straight in the site where the magnetic field is measured.
The one or the plurality of magnetic field gradients so created are to be used preferably for the potential-free measurement of the current in the addressed conductor, which is preferably straight in the site where the magnetic field is measured.
2. The Prior Art
It is known to measure currents potential-free by recording their magnetic field with the help of the Hall-effect (Proceedings PCIM Hong Kong, October 1997, pages 129 ff). However, the Hall-transducers commercially available at the present time require relatively expensive and, especially when higher currents are measured, also voluminous iron or ferrite cores for concentrating the magnetic flux in the areas of the respective transducer that are sensitive to the magnetic field (FIG.
1
).
Said circumstance, which has to be ascribed to the low magnetic field-sensitivity of the commercially available Hall-transducers mentioned above, has led to the development of more sensitive Hall-converters and other equipment for measuring magnetic fields.
For example, devices are known in the field of Hall transducers or Hall sensors that contain on a silicon substrate of the size of only a few square millimeters both a layer sensitive to magnetic fields, and also flux concentrators [EPFL/Sentron, Highly Sensitive Hall Sensor, shown at the Hannover Messe Industrie (Hannover Industrial Exposition, 1998); and H. BLANCHARD ET AL, Cylindrical Hall Device, Proc. International Electron Devices Meeting (IEDM) 1996), San Francisco, USA, Dec. 8-11, 1996].
Furthermore, a whole series of other methods exists for measuring the magnetic field, which, by virtue of their sensitivity, are suitable for pot potential-free current measurements without iron or ferrite cores as well.
For example, devices for measuring the magnetic field are known since a longer time that operate on the basis of magnetoresistive effects such as the anisotropic magnetoresistive effect (AMR) (Magnetoresistive Sensors III, Final Report of the Combined Project IMOMAG, BMFT Promotion ID 13 MV 0109-0120, chapter 6.1, Magnetic Field Sensor with Integrated Compensation Line MSK 6), or such as the gigantic magnetoresistive effect (GMR) (Magnetoresistive Sensors IV, Symposium and Status Seminar held on Mar. 11 and 12, 1997, in Wetzlar, chapter “MR Sensors with Giant Resistance Materials: Potencies and Problems”).
Furthermore, it seems to be conceivable also in the future to produce such sensor systems on the basis of the colossal magnetoresistive effect (CMR)(loc.cit. page 7 f).
However, all sensor systems possessing a magnetic sensitivity that permits them to measure currents potential-free without the use of voluminous iron cores, have in common that they have high sensitivity to interference fields. Said circumstance is counteracted at the present time, for example in that by arranging the magnetoresistive materials employed in the respective measuring device in a special way, magnetic field gradiometers are produced that have a lower sensitivity to homogeneous fields of interference.
For example, DE 43 00 605 C2 describes a sensor chip that functions especially on the basis of the anisotropic magnetoresistance effect (AMR). Said sensor chip is capable of measuring current potential-free by recording the magnetic field gradient. Devices are also known, of course, that operate based on the GMR effect (Magnetoresistive Sensors IV, symposium and Status Seminar on Mar. 11 and 12, 1997, in Wetzlar, chapter “MR Sensors with Giant Resistance Materials: Potencies and Problems”, page 4 ff) or other magnetic field-sensitive effects, such devices being devised as gradiometers.
The devices introduced above, and also the particularly sensitive Hall sensors with integrated soft-magnetic flux concentrators (EPFL/Sentron, Highly Sensitive Hall Sensor, shown at the Hannover Industrial Exposition in 1998) can be basically devised as gradiometers as well. It is only necessary for said purpose to apply, for example two magnetic field-sensitive surfaces on a silicon substrate, and to then evaluate the two generated Hall voltages in a suitable manner.
A drawback of the principle described above lies in the circumstance that of a magnetic field gradient has to be provided.
DE 43 00 605 C2 and U.S. Pat. No. 5,548,208 propose for said purpose, for example the U-shaped design of the current conductor through which the primary current to be measured is passed (FIG.
2
). In both of said published documents, the actual magnetic field gradiometer is preferably applied to a carrier material separating the potential, said carrier material itself being secured on the U-shaped primary conductor.
However, the drawbacks of said principle are obvious: it is necessary to pass the current normally flowing in straight current conductors through a U-shaped primary conductor. For this purpose, massive current conductors or flat cables are interrupted especially in the high-current sector, and the conductor ends are connected in a suitable form to the connections of the U-shaped primary conductor. This method requires relatively much expenditure and it is difficult to reconcile it, most of all, with the manufacturing methods usually employed in the field of machine and vehicle manufacturing.
Therefore, an arrangement is known as well that permits with the use of at least two magnetic field measuring devices, measurements of the current without voluminous iron or ferrite cores in a manner that is relatively insensitive to homogenous fields of interference: in conjunction with DE 44 34 4177 A1, particularly two absolute-field measuring devices are arranged preferably on two sides of a straight conductor opposing each other (parallel with the direction of flow of the current) (FIG.
3
). It is assured in this way that the circular magnetic field of the straight conductor penetrates the two measuring devices in the reverse direction. The output signals of both measuring devices are subtracted from each other, so that the interfering components of homogeneous interference fields are largely omitted.
Said invention, however, has inherent drawbacks as well. First of all, two magnetic field measuring devices and two potential-separating carrier substrates have to be used, as opposed to the gradiometric principle shown herein. Furthermore, the spacing between the two magnetic field measuring devices is not freely selectable because such spacing is particularly dependent upon the diameter of the primary conductor.
Said spacing, however, is decisive for the sensitivity of the arrangement to interference fields because the latter naturally change with the spacing. With simple mathematical means such as subtraction, the influences of said interference fields in the evaluation of the output signals of the absolute-field measuring devices can be minimized adequately only if such measuring devices are penetrated by approximately equal interference fields. When gradiometers are employed, the meaning of the term “basic width of the gradiometer”, with respect to the sensitivity of said device versus interference fields, conforms to the spacing of the absolute-field measuring devices explained above.
The fact that the spacing between the absolute-field measuring devices is dependent on the cross section of the primary conductor in conjunction with DE 44 34 417 A1, is disadvantageous especially in the high-current area, which is characterized by both large primary conductor cross sections and high interference fields.
The invention eliminates the drawbacks of th
Kunze Jürgen
Schepp Gunter
Weber Jan
Collard & Roe P.C.
Deb Anjan K.
Lust Antriebstechnik GmbH
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