Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1998-11-30
2001-06-05
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S072000, C324S095000, C324S658000
Reexamination Certificate
active
06242911
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a field sensor comprising means for measuring a magnetic field and/or an electric field as well as a corresponding method.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is based on the object of providing a field sensor of the aforementioned type with which electric or magnetic fields may be measured simultaneously or successively in any direction, and a respective device as well as a corresponding method.
A field sensor is provided with at least six capacitor plates which are arranged in a cube and in the space thus formed a means for measuring the magnetic field is provided which means is three-dimensionally aligned and consists for example of coils, Hall-effect sensors, magnetoresistors or the like.
The capacitor plates serve in this connection for measuring the electric field three-dimensionally and simultaneously generate in the interior of their spatial arrangement a field-free space. The latter is provided with the measuring means which enables a three-dimensional detection of the magnetic field without interference by the electric field.
Thus, an electric and a magnetic field can simultaneously be measured three-dimensionally, however, without affecting each other.
In an advantageous embodiment of the invention, three annular and/or cylindrical coils are provided which are arranged on the x-, y- or z-axis and the coils are surrounded by the capacitor plates every two of which are arranged in parallel to each other.
According to an alternative embodiment, the capacitor plates are partially or completely arranged within a space which is formed by the components of a magnetometer. In a magnetometer consisting of coils, e.g., the coils extend partially or completely beyond the capacitor plates. The size of the capacitor plates and their distance from each other is selected as a function of the size of the magnetometer components such that an electric and a magnetic field may simultaneously be measured three-dimensionally, their mutual interference being preferably low. Preferably, the edge length of the capacitor plates is low with respect to the outer dimensions of the magnetometer components. The ratio between the edge length of the capacitor plates and for example the diameter of a magnetic field coil is in the range of 1 to 100 up to 100 to 1. The capacitor plates may be displaced up to 30% of the coil diameter to the inside.
In other words, in the alternative embodiments, the space formed by the capacitor plates and the space formed by the means for measuring the magnetic field are aligned with each other and both systems intersect with each other three-dimensionally while having a common reference point.
In a further preferred embodiment of the invention, the coils are fitted into each other annularly with an almost identical diameter.
Thus, the magnetic field may uniformly be measured in all three directions.
It has also turned out to be quite advantageous if, according to a further embodiment of the invention, each coil has a couple of capacitor plates which are provided in parallel to the respective coil outside the coil arrangement.
Thus, the coils are perfectly screened by the capacitor plates.
According to an embodiment of the invention it is also very advantageous to provide the capacitor plates with a high-resistance coating.
It is, however, also possible according to a further embodiment of the invention that the capacitor plates consist of a high-resistance material.
In both embodiments, any interference with the magnetic field to be measured is excluded.
A further embodiment of the invention is characterized in that the capacitor plates are arranged in couples and each of the respective inner plates is electronically connected to a common earth terminal.
Thus, any interference of the coils, Hall-effect sensors or magnetoresistors with the electric field is excluded.
According to a further embodiment of the invention, it has turned out to be very advantageous to provide the electric terminals of the capacitor plates at their edge. Thus, any influence of the current within the lines on the measuring result is avoided.
The present invention further relates to a device for measuring electric fields which comprises a field sensor with at least one capacitor-plate couple whose output voltage is applied to the non-inverting and the inverting input of a differential amplifier, a capacitor being connected between the two inputs of the differential amplifier. This measuring device may in particular be used with the field sensor described above. The measuring device works on the following basic principle. An arrangement of two capacitor plates leads to a voltage drop in the electric field at the capacitor; this voltage drop is decoupled by earthing via a differential amplifier preferably with a high resistance and preferably with a low input capacity. The relatively high current through the capacitor minimizes the coupling of interference voltages by the measuring amplifier as well as the field intensity between the capacitor plates. The measuring device may preferably be used for measuring electric and/or magnetic fields with a frequency of 1 Hz to 30 GHz, particularly preferred are 5 Hz to 400 kHz. The measuring device is in particular advantageous in that it may be designed as a hand tool which takes measurements both as a stationary tool and when moved with electrically conducting lines and the resulting measuring errors are minimized.
A further preferred feature is the use of thin wires as connections between the measuring device and the capacitor-plate couple. The advantage thereof is that on account of the small cross-section of the wires the interference with the field is low as compared with the plate size of the capacitor-plate couple. Preferably, two wires each are twisted for being connected with one capacitor-plate couple. Thus, magnetic fields generated within the wires on account of a current counterbalance each other such that the resulting magnetic field is kept low and a reverse effect is reduced.
Preferably, the distance between the field plates and the measuring amplifier is so large that the interference of the measuring device with the electric field to be measured is low.
It is particularly preferred that the area of the capacitor and the differential amplifier is small as compared with the area of the capacitor plates in order to further avoid the interference of the measuring device with the electric field to be measured. The method according to the present invention for measuring electric and/or magnetic fields is preferably carried out with a combination of the above-described field sensor and the respective measuring device. In particular, measuring errors caused by the person taking the measurement or the electric lines can be kept within tolerable limits with the present method depending on the measurement set-up. This is in particular achieved by measuring the electric and the magnetic field simultaneously at one point. Moreover, the smallest possible sensors are used to avoid errors on account of field inhomogeneities.
Furthermore, the smallest possible sensors have the advantage that averaging is avoided when measuring an electric or magnetic field. Moreover, the object to be measured may be appreciated.
In particular by using sensitive sensors, the present invention fulfils the electromagnetic compalitrility (EMC) standards.
A simultaneous three-dimensional measurement of electric and magnetic fields moreover avoids possible measuring errors which may occur in one-dimensional measurements when searching the maximum field.
On account of a larger distance between the person taking the measurement and the measuring device as well as technical measures at the measuring device for providing a high-resistance set-up as well as a small capacity between sensor and display unit, the measuring accuracy in particular of the electric field is improved.
With the method according to the present invention, electric and magnetic fields may be measured simultaneously. Prefe
Andersen Henry S.
Birch & Stewart Kolasch & Birch, LLP
Patidar Jay
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