Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Patent
1996-09-17
1998-10-20
Karlsen, Ernest F.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
324127, G01R 3300
Patent
active
058251758
DESCRIPTION:
BRIEF SUMMARY
The invention relates to magnetic sensors.
Magnetic sensors find application in fields in which remote sensing of magnetic fields or electrical current is required.
In a typical application, magnetic sensors, such as Hall effect sensors, are used in hand-held measuring devices. Such a hand-held measuring device might typically include a pair of jaws which can be opened and closed so as to admit the passage of an electrical conductor therebetween. With the electrical conductor in place, the jaws are closed and one or more magnetic sensors situated within the jaws are arranged to generate an electrical output which is dependent upon a current flowing through the conductor.
In devices of the type described above, the sensors are generally positioned adjacent to at least one end face of the jaws. By necessity, the sensor must not be shielded magnetically from the electrical conductor held in the space defined by the closed jaws. In this respect, it is usual for end faces of the jaws, where the sensors, which may be in the form of integrated circuits or chips, are located, to be simply covered by a plastic cap. Unfortunately however, having the sensor covered in such a manner means that not only is it influenced by magnetic fields generated by the conductor, but it can also be influenced by stray fields from outside of the region defined by the closed jaws and so give false or inaccurate readings.
German patent application DE-4-3,817,299 discloses a magnetic sensor arrangement forming part of an electrical measuring device having means for being fitted around an electrical conductor for the measurement of a property associated with the conductor, wherein the sensor arrangement is at least partially shielded from one or more sources of interference. This is achieved by locating a current sensor element within a recess of a core material and covering the current sensor with an earthing element and a cover plate.
According to a first aspect of the invention, a magnetic sensor arrangement forming part of an electrical measuring device, the device having means for being fitted around an electrical conductor for the measurement of a property associated with the conductor and, wherein the sensor arrangement comprises at least one sensor mounted in a recess formed in an end face of one of a pair of arms of a given material the arms being mounted for movement towards and away from one another, said arms forming said means for being fitted around an electrical conductor and being characterised in that said end faces are exposed such that with the arms in a closed position a continuous loop of the material is formed to thereby shield the, or each, sensor from one or more sources of interference.
The interference may be magnetic interference.
A pair of sensors may be provided.
Preferably, the, or each, sensor is mounted on or within the means for being fitted around an electrical conductor.
The arms are preferably mounted on a body member for movement with respect to the body member.
The arms, or the loop, preferably comprise magnetically permeable material.
The material may be formed from a number of laminations.
Alternatively, the material may comprise a strip wound core.
If the material is a strip wound core, then the recesses may be formed by milling. If the material comprises a number of laminations, then the form of the laminations may be arranged so as to provide the recess, or recesses.
The recesses are preferably formed such that the, or each, sensor is exposed to a magnetic field generated by the electrical conductor, but is shielded from stray fields.
Preferably, electrical windings are provided around the arms and the, or each, sensor forms part of a control circuit, whereby a primary current flowing in the electrical conductor, induces a first magnetic flux within the material of the arms, and an output from the, or each, sensor, is used to control a secondary current flowing in the windings. Preferably, the secondary current is arranged to induce a secondary flux in the material, which is opposed to the prima
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patent: 4283677 (1981-08-01), Niwa
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patent: 5349289 (1994-09-01), Shirai
patent: 5473244 (1995-12-01), Libove et al.
Karlsen Ernest F.
Lem Heme Limited
Phung Anh
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