Single-winding magnetometer with Schmitt trigger output circuit

Details Single-winding magnetometer with Schmitt trigger output circuit Single-winding magnetometer with Schmitt trigger output circuit

1985-06-10

1988-03-22

Strecker, Gerard R.

Electricity: measuring and testing

Magnetic

Magnetometers

33361, G01R 3304, G01L 1728

Patent

active

047331810

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a magnetometer with time coded output of measured magnetic fields, as defined by the preamble background: The use of magnetometers with time coding for measuring the earth's magnetic field is already known from German Pat. 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, at 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 with the resistor-capacitor element and the comparator, the evaluation circuit is relatively expensive. Furthermore, the resistor-capacitor element causes damping of the signal voltage that is to be evaluated, and the measuring accuracy is affected by the temperature-dependent capacitance of the resistor-capacitor element.
With the present invention, the object is to simplify the evaluation circuit.


The Invention

The magnetometer according to the invention has the advantage that the measurement voltage, without being damped by a resistor-capacitor element, is converted directly into a pulse length modulated rectangular signal by the limit-value switch, and a linear relationship between the duty cycle of the rectangular signal at the output of the circuit and the measured magnetic filed is attained. A further advantage is that by using the limit-value switch, the measurement voltage need not have any pronounced extreme values, thereby also enabling greater tolerances in terms of the requirements for the form taken by the sensor core and its properties.
Advantageous further developments and improvements are attainable by means of other features of the invention. A particular advantage is attained if the limit-value switch comprises a Schmitt trigger with switching limits that are symmetrical with respect to one another. A particularly simple arrangement can be attained by providing that merely a single winding disposed on the core serves to generate both the auxiliary alternating field and the measurement voltage. In so doing, in order to generate the auxiliary alternating field a triangle (wave shape) generator is connected to the winding via a current source connected to its output and controlled by the voltage of the triangle generator, with one connection of the triangle generator and of the winding being connected to a reference voltage. To amplify the measurement voltage induced in the winding, the end of the winding that is not connected to reference voltage is connected to one input of a subtracting amplifier, and the output of the triangle generator that is not connected to reference voltage is connected to the other input of the subtracting amplifier. The output of the subtracting amplifier is then connected directly to the input of the Schmitt trigger.


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 geomagnetic field, using an electronic compass having a magnet ometer;
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

REFERENCES:
patent: 3197880 (1965-08-01), Rice et al.
patent: 3461382 (1969-08-01), Anderson
patent: 3568052 (1971-03-01), Anderson
patent: 3812428 (1974-05-01), Trenhler
patent: 3936949 (1976-02-01), Devaud
patent: 4290018 (1981-09-01), Rhodes

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