Magnetometer with time coded output of measured magnetic fields

Details Magnetometer with time coded output of measured magnetic fields Magnetometer with time coded output of measured magnetic fields

1985-06-10

1988-03-01

Eisenzopf, Reinhard J.

Electricity: measuring and testing

Magnetic

Magnetometers

33361, G01R 3304, G01C 1728

Patent

active

047288884

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a magnetometer with time coded output of measured magnetic fields. Background: The use of magnetometers with time coding for measuring the earth's magnetic fields is already known from German Patent No. 16 23 577. The magnetometer includes a sensor having a magnetizable rod-shaped core, on which two windings are arranged. One winding serves to generate an auxiliary alternating field, by being connected to an alternating voltage by means of which the core is magnetized in alternation up to and into saturation. At the other winding, a measurement voltage is picked up, which serves to ascertain the magnetic field that is to be measured. To this end, the measurement voltage is differentiated with a resistor-capacitor element. By means of the magnetic field that is to be measured, which acts in the direction of the sensor axis, a time shift of the extreme values of the measurement voltage is effected, the magnitude of the shift being a measure for the intensity of the measured magnetic field. Via a comparator, the differentiated measurement voltage can be converted into a digital value corresponding to the intensity of the magnetic field. This arrangement has the disadvantage, however, that the magnetizable core must have two windings electrically separated from one another, and the measurement voltage must be delivered to a differentiating element before it can be evaluated further. Also, an hourglass-pinched magnetic core is used, which is expensive to manufacture.
With the present invention, the object is to reduce the expense of generating the evaluatable measurement voltage, while attaining good magnetometer measuring accuracy.
The magnetometer according to the invention has the advantage that only one winding needs to be disposed on the magnetizable core of the sensor, and hence the heretofore-required second winding can be omitted. A further simplification and an improvement in the measuring accuracy are attained by eliminating the differentiation stage, in which as a rule a temperature-dependent capacitor was required.
Advantageous further developments and improvements are attainable with certain preferred features. It is particularly advantageous if, in order to generate the auxiliary alternating field, the alternating current source is controlled by the voltage of a triangle (wave shape) generator. The result is a triangular premagnetizing current. The measurement voltage that can be picked up at the coil is composed of the voltage dropping at the copper (wire) resistance of the winding in order to generate the premagnetizing current, and the voltage induced in the winding by means of the change in flux in the rod-shaped core. However, it is particularly effective to use only the voltage induced in the winding in order to ascertain the intensity of the magnetized unidirectional field. To this end, by means of a subtracting amplifier, the auxiliary alternating voltage of the triangle generator is subtracted from the measurement voltage to such an extent that at its output, only an amplified induction voltage then appears. One output of the triangle generator and one end of the winding are connected to a common reference voltage, preferably ground. To amplify the voltage induced in the winding, the end of the winding that is not connected to reference voltage is connected to one input of the subtracting amplifier, and the output of the triangle generator that is not connected to reference voltage is connected to the other end of the subtracting amplifier.


DRAWING

One exemplary embodiment of the invention is shown in the drawing and described in further detail below.
FIG. 1 shows a motor vehicle in which the driving direction is ascertained by measuring the earth field, using an electronic compass having a magnetometer;
FIG. 2 shows the circuit of a magnetometer for measuring a magnetic field component detected by a sensor; and
FIG. 3 shows the course of the voltage at various points in the circuit of FIG. 2.


DESCRIPTION OF THE EXEMPLARY EMBODIMENT

In FIG. 1, a motor vehicl

REFERENCES:
patent: 3812428 (1974-05-01), Trenkler
patent: 3936949 (1976-02-01), Devaud
patent: 4290018 (1981-09-01), Rhodes
patent: 4314200 (1982-02-01), Marck
Heineche, "Fluxgate Magnet-Meter . . . " Conference in Precision Electromagnetic Measurements, 1978, pp. 89-90.

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