Electricity: measuring and testing – Magnetic – Displacement
Patent
1986-02-26
1987-12-08
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Magnetic
Displacement
324252, 338 32R, G01B 714, G01R 3302, H01L 4300
Patent
active
047120649
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention is based on a magnetoresistive sensor for emitting electric signals. It is known to use reading heads for scanning magnetic tapes, wherein magnetoresistive measuring strips are provided perpendicular with respect to the magnetic tape through which a measuring current flows. The information which is stored on the magnetic tape consists of small magnetic fields which are disposed in the plane of the magnetoresistive measuring strip and influence the direction of magnetisation in the measuring strip during the passing movement. The resistor of the measuring strip is changed by the magnetic field component which is disposed in the plane of the measuring strip and forms an angle with the direction of the current in the measuring strip. Since the measuring strip is switched through a preresistor to direct voltage, the voltage drop on the measuring strip changes with the resistor being evaluated as a measuring signal (Philips Technische Rundschau 37,1977/78, No. 2/3, page 47 ff). This solution is disadvantageous in that it can be used for scanning weak magnetic fields only which must be applied to a moving carrier. Such a solution principle is unsuitable for a number of sensor applications wherein magnetic fields or magnetic field changes should be detected, because the magnetic tape or another magnetic field carrier must be moved by the reading head practically without an air slot. Moreover, interference fields can falsify the measuring result on the reading head or on the magnetic tape or change the magnetic fields to be detected.
It is an object of the subject solution to provide a magnetoresistive sensor which is stationary mounted and which is substantially insensitive against interference fields as well as against changes and tolerances in the air space between the stationary sensor and a body to be detected.
The inventive solution is advantageous in that the body to be moved passed the sensor does not have to be provided with permanent magnetic fields any longer, but that instead a strong stationary uniform magnetic field penetrates the magnetoresistive measuring strips in such a manner so that the body to be detected is magnetizised by a large component of the uniform field which penetrates perpendicular through the measuring strip, and that a magnetic saturation is obtained in the measuring strip by a magnetic field component which is disposed in the plane of the measuring strip, so that only the change in direction of this magnetic field component causes a voltage change on the measuring strip by means of the ferromagnetic body and interference influences are suppressed. In contrast to known inductive sensors this solution has the advantage that with a static operation, that is, with a shut-down ferromagnetic body its position in the area of the magnetoresistive sensor may be determined. Furthermore, in contrast to the inductive sensors a substantially larger air slot is permissible and no frequency dependent phase frequency characteristic occurs. The sensor in accordance with the invention is substantially less sensitive with respect to vibrations or axial impact of the spur gear than known inductive speed sensors when being used as a speed sensor.
It is particularly advantageous to provide the substrate with the magnetoresistive measuring strip on the front side of a permanent magnet in the area of an edge on the permanent magnet when the ferromagnetic body, preferably a rotating spur gear, moves at a distance along the edge for emitting a speed signal at the output of the sensor. It has been shown to be advantageous to form the edge on the permanent magnet by a groove extending over the total front face of the permanent magnet in the movement direction of the ferromagnetic body or the spur gear for forming a homogenic magnetic field with a magnetic field component which is vertical and horizontal with respect to the measuring strip.
Three exemplified embodiments of the invention are illustrated in the drawings and explained in detail in the following description. The d
REFERENCES:
patent: 4039936 (1977-08-01), Jones et al.
patent: 4361805 (1982-11-01), Narimatsu et al.
patent: 4429276 (1984-01-01), Narimatsu et al.
Eckardt Dieter
Hettich Gerhard
Eisenzopf Reinhard J.
Robert & Bosch GmbH
Snow Walter E.
Striker Michael J.
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