Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Patent
1997-03-26
1999-08-03
Strecker, Gerard
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
324 99, 324126, 324252, G01R 1900, G01R 1710, G01R 33025, G01R 3309
Patent
active
059330031
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a device for measuring an electric current flowing through a current conductor with an electric control circuit comprising a measuring component in the form of a measuring bridge of magnetoresistive measuring resistors. This type of measuring bridge is constructed as a Wheatstone bridge, to which is applied an electric bridge voltage and from which is tapped a measuring voltage for measuring the strength of a magnetic field produced by the current in the vicinity of the current conductor. The measuring voltage of the measuring bridge controls a compensating current that flows in a compensating conductor, which is selected such that the magnetic field strength of the compensative current measured by a measuring component is so that the compensating current is proportional to the current.
A measuring device for determining magnetic field strength is employed to facilitate the potential-free measurement of the current strength of the electric current, which generates the magnetic field. Since in the vicinity of a magnetic field that is measured in this manner there is already large-area interference magnetic fields, it is obvious to differentiate the interfering field with the help of magnetic field gradients between the magnetic field to be measured and the interference magnetic field.
Such a measuring device is known from the Offenlegungsschrift DE 43 00 605, also published as U.S. Pat. No. 5,621,377, in which a sensor, which is equipped with a measuring bridge of magnetoresistive laminated strips and a thin laminated microstrip that functions as a conductor for the compensating current are structurally provided. The output signal is independent from the interference field, is proportional to the current being measured and is neither temperature nor auxiliary magnetic field dependent. However, in the prior art it is necessary that the measuring device be provided with an intermediate element integral with the current conductor. Thus, the current conductor must for this purpose be cut and must be connected on both sides of the intermediate element, if one wants to avoid expressing a portion of the current conductor in order to be able to mount the measuring device. When measuring large currents a busbar alone is practical as the intermediate element, on which the measuring device has already been mounted and calibrated, in order to be able to control the influence of the geometric dimensions on the turns ratio.
SUMMARY OF THE INVENTION
The basic purpose of the invention is therefore to overcome these disadvantages and to construct a measuring device of the type identified in detail in the beginning such that it can be connected at any time to the current conductor, which remains unchanged, and can, if needed, also be easily again removed without that the advantages already realizable in such measuring devices--potential-free, interference-field independent, temperature independent and auxiliary magnetic field independent measuring--would have to be abandoned.
The measuring device of this invention includes two parallel connected measuring bridges or measuring bridge halves that are subjected to the electric bridge voltage so as to function as a measuring component. The measuring bridges each consist of four magnetoresistive measuring resistors arranged in a measuring bridge. A measuring bridge half consists of two magnetoresistive resistors and the measuring resistors in the measuring bridges or measuring bridge halves are arranged in one common bridge plane. Each measuring bridge or measuring bridge half has a compensating line, and the sum of the compensating currents through the compensating lines of the measuring bridges or measuring bridge halves is proportional to the flowing current.
The invention takes advantage of the fact that on both sides of a current conductor the magnetic field produced along the conductor acts in opposite direction and is either strengthened or weakened in a homogeneous interference field so that these interference field
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Ruhl et al; "Stromsensor als Microsystem", Electronic vol. 42, No. 5, Oct. 1993 Munchen, DE, pp. 42-44.
Hebing Ludger
Kunze Juergen
Lust Karl-Heinz
Lust Antriebstechnik GmbH
Strecker Gerard
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