Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
1999-01-13
2001-04-10
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
C324S127000
Reexamination Certificate
active
06215296
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an alternating or direct current measuring arrangement for generating a magnetic field from the current to be measured, a device for sensing the generated magnetic field, and a measuring circuit which determines the current.
BACKGROUND
There are already known measuring arrangements which generally use a grip current tester or a torus which may or not be opened and which fully closes about a cable in which the current to be measured is flowing.
Now it is known that the presence of discontinuities in the magnetic circuit, as produced by an air gap, a winding, an opening of the grip current tester for tightly enclosing the cable, the insertion of the sensor or the like creates zones on torus which exhibit a greater sensitivity to magnetic fields of external origin, i.e., a parasitic field thereby altering or making false the measurement of the current.
The usual measures for decreasing these external influences consist either in reducing these discontinuities to the utmost or in modifying the geometry of the parts present in this sensitive zone or in adding a shield or screen in the vicinity of this zone.
These different measures for solving the problem caused by the discontinuities are the major inconveniences likely to change the design of the measuring equipment and of adding difficulties during its manufacture.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a measuring arrangement which copes with the inconveniences of the state of the art which have just been stated.
To reach this goal, the arrangement according to the invention includes means for reducing the external influences comprising a device for sensing the parasitic field and a circuit for the correction of the external influences by applying a correction to the aforesaid measuring circuit.
According to one feature of the invention, when the parasitic field is a parasitic magnetic field, the device for sensing the parasitic field comprises at least one magnetic field sensor disposed in the vicinity of the zone sensitive to the parasitic magnetic field.
According to another feature of the invention, the correction circuit comprises means for sensing the measured parasitic field and for applying the measured parasitic field in reverse state at a predetermined point of the measuring circuit.
According to still another feature of the invention, a correction sensor is disposed at the same angle with respect to parasitic field lines as a measuring sensor with respect to the lines of a magnetic field to be measured.
According to still another feature of the invention, when the current to be measured is established by reducing to zero the magnetic field which generates it, a correction is applied to a current amplifier mounted in a circuit of a field annulment coil.
According to still another feature of the invention, when a current is established through measurement of the magnetic field generated by it, the correction is applied to the input of an operational amplifier mounted in a measuring circuit.
REFERENCES:
patent: 5459395 (1995-10-01), Berkcan
patent: 6005383 (1999-12-01), Savary et al.
patent: WO9011529 (1990-10-01), None
Arnoux Axel
Genter Claude
Piaud Didier
Chauvin Arnoux
Kerveros J
Leydig , Voit & Mayer, Ltd.
Metjahic Safet
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