Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1985-07-31
1988-03-22
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Magnetic
Magnetometers
33356, G01R 3302, G01C 1738
Patent
active
047331798
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention relates to a method of calibrating an electronic compass for measuring magnetic fields in vehicles, the compass being provided with a magnetometer of the type in accordance with the main claim. For measuring planetary magnetic fields it is already known from DE-PS No. 16 23 577 to use a magnetometer with a time code. The magnetometer contains a probe with two horizontally disposed magnetiseable rod like cores which are penetrated by an alternating field and the component of the magnetic earth's field being in the direction of the rod axis. Furthermore, it is known to establish the X-component or the Y-component of the earth's field with respect to the longitudinal axis of the vehicle by means of two measuring coils which are offset with each other by 90.degree. and to establish therefrom the size and direction of the applied magnetic field. However, the disadvantage exists that the earth's field to be determined superimposes with an interfering field generated in the vehicle, whereby the measuring accuracy can be considerably influenced. In navigation it is known to eliminate the interfering field directly on the compass, in that a counter directed field of the same strength is generated.
With the subject solution an effort is being made to determine an interfering field generated in the vehicle in accordance with size and direction measured with the compass, so that it can be considered as a correcting size for measuring the earth's field or for the further evaluation in the electronic compass.
ADVANTAGES OF THE INVENTION
The process in accordance with the invention and with the characterizing features of the main claim has the advantage that the size and the direction of a magnetic interference field in the motor vehicle is determined from two measurements of the size and direction of a constant magnetic field which already are to be made by the electronic compass. A further advantage consists in that no further measuring devices are required. Furthermore, it is possible in a simple manner to electronically store the measured values by actuating a standard calibration key in the two 180.degree. deviating positions of the vehicle.
Advantageous further embodiments and improvements of the features stated in the main claim are possible by the measures stated in the subclaims. It is particularly advantageous when the vehicle in order to determine the interfering field is rotated by 360.degree.. Thereby, the extreme values of the uniform field which are offset by 180.degree. being measured by the magnetometer are picked up by a circuit and the interference field is determined in its size by arithmetic means from the two measured values, whereby the direction of the interference field is provided by the position of the maximum steady or constant field. The determined interference field of the vehicle is also stored in a storage as a correcting size by a previous actuating of a standard key and when determining the driving direction of the vehicle the interference field is subtracted from the constant field measured on the magnetometer in accordance with the size and the direction.
DRAWING
One exemplified embodiment of the invention is illustrated in the drawing and is explained in detail in the following description. The drawings show:
FIG. 1 a motor vehicle, wherein the drive direction is determined by measuring the magnetic earth's field by means of an electronic compass with a magnetometer,
FIG. 2 the circuit of a magnetometer for measuring a magnetic field picked up by a probe,
FIG. 3 the voltage path at different points of the circuit in accordance with FIG. 2, and
FIG. 4 the vectors of the interference field, the earth's field and the constant field composed therefrom being picked up by the probe when calibrating the compass.
DESCRIPTION OF THE EXEMPLIFIED EMBODIMENT
A motor vehicle 10 is illustrated in plan view in FIG. l. For determining the drive direction the motor vehicle 10 is provided with an electronic compass consisting of a magnetometer 11 and an evaluati
REFERENCES:
patent: 3683668 (1972-08-01), Baker et al.
patent: 3991361 (1976-11-01), Mattern et al.
Bauer Harald
Hettich Gerhard
Eisenzopf Reinhard J.
Robert & Bosch GmbH
Snow Walter E.
Striker Michael J.
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