Geometrical instruments – Indicator of direction of force traversing natural media – Magnetic field responsive
Patent
1989-07-13
1991-09-10
Cuchlinski, Jr., William A.
Geometrical instruments
Indicator of direction of force traversing natural media
Magnetic field responsive
33361, 324247, G01C 1728
Patent
active
050462601
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an electronic compass with sensors, the output signal of which is dependent on the magnitude and direction of the magnetic fields permeating them and to which a coil for an exciter field, supplied with a clock voltage, is assigned.
BACKGROUND OF THE INVENTION
Such-electronic compass is known from the Technische Information [Technical Information]No. 840323 of the firm VALVO. The magnetoresistive sensors of the type KMZ 10A therein described are a passive component with a slide-wire bridge to which an operating voltage has been applied. The alignment of the bridge changes in relation to the magnitude of a magnetic field permeating the sensor in its longitudinal direction. Thus a voltage can be head off at the diagonal of the bridge, its sign depending on the direction and its magnitude on the magnitude of the incident magnetic field. In this connection it is known to dispose two such sensors offset from each other by 90.degree. which, in this manner, evaluate the components of the incident magnetic field in two directions which are perpendicular to each other. By means of these two components, i.e. by the output voltages of the two sensors, the magnetic field is unequivocally defined as to its magnitude and direction.
Such sensors have an unavoidable offset voltage, i.e. a direct voltage component present in the output signal, which in particular is generated by an imperfect adjustment of the bridge and other environmental influences. At, for example, .+-.10-20 mV, this offset voltage is considerably greater than the signal voltage in the range of a few .mu.V.
To compensate for this offset voltage, it is known to assign a coil to the sensors which is controlled by a clock voltage and which generates in the sensors a reversed exciter field oriented perpendicular to the direction of sensitivity. By means of this exciter field the direction of sensitivity of the sensors is periodically reversed with the frequency of the clock voltage. Then the output signal of the sensors is not a direct voltage but an alternating voltage having the frequency of the clock voltage. This makes it possible to separate the actual information signal from the offset voltage.
However, the information signals emitted by the sensors have to be amplified for further processing. On the one hand, their amplitude is insufficient for further processing of the signals. On the other hand, the ground field considerably changes regionally, so that the amplification must be correspondingly adapted and controlled. Because small differences in the amplification of the individual signals determine the result of the measurements and because in particular during the control of a plurality of amplification paths it is practically impossible to attain uniformity of the amplification for the signals of the two sensors, relatively large inaccuracies in measurement occur which limit the use of such magnetoresistive sensors.
SUMMARY OF THE INVENTION
It is an object of the invention to reduce such scattering and dependence on the adjustment of sensors and other parameters and to increase the accuracy of the compass equipped with such sensors.
This object is attained by means of the invention as described below.
The invention is based on the following realizations and considerations. When disposing three identical sensors at an angle of 120.degree. from each other, the sum of the output signals of the three sensors exposed to the same magnetic field equals zero. This is based on the fact that the sum of the three instantaneous values of a sinusoidal voltage spaced at 120.degree. is always zero. This is equivalent to the fact that the output signals of the three sensors, offset from each other by 120.degree. and turned inside a constant magnetic field, always is zero, independent of the magnitude of this magnetic field, assuming that the three output signals offset by 120.degree. have the same amplitude. Then, if the output signals of the three sensors are each scanned in short succession, their sum also
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Cuchlinski Jr. William A.
Wirthlin Alvin
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