Magnetic sensor system

#The invention described and claimed hereinbelow is also described in PCT/EP 2005/050063, filed on Jan. 7, 2005 and DE 102004011809.4, filed Mar. 11, 2004. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d).

#The present invention relates to a magnetic sensor system, in particular for sensing the motion of elements moved in a linear or rotary manner.

#It is known per se that sensors that are sensitive to magnetic fields are used in many applications where contactless detection of motion is desired. The motion can be rotary or linear. A distinction must be made here between two fundamentally different measurement principles. In one case, one or more magnetic dipoles are mounted, as the active elements, on the element to be detected, and the motion is determined directly via the magnetic field, which changes with respect to time, at the point where the sensor is located. In contrast, with passive transmitter elements, which are made of a soft-magnetic material, the magnetic field is produced by a working magnet that is permanently connected with the sensor. The sensor measures the change in the magnetic field of the working magnet caused by the motion of the transmitter elements.

#Exemplary embodiments of the present invention are explained with reference to the drawing.

#FIG. 1 Shows a schematic illustration of a magnetic sensor system with two permanent magnets, each of which is diametrically opposed to a magnetoresistive sensor element in a gradiometer system,

#FIG. 2 Shows a system that is refined relative to FIG. 1, with homogenization plates,

#FIG. 1 shows a schematic illustration of a magnetic sensor system 1 that includes two permanent magnets 2 and 3, the respective magnetic fields B of which are oriented with lines of flux shown in this illustration in the direction toward a sensor 4. In this case, sensor 4 is designed as an XMR sensor and has two magnetoresistive sensor elements 5 and 6. Sensor elements 5 and 6 are shown in a gradiometer system with gradiometer separation GM; they detect the changes in the particular field gradient caused, e.g., by 5 a metallic transmitter element, e.g., a toothed wheel shown in FIG. 5, that passes by magnetic sensor system 1.

#The optimum working point of sensor 4 is adjusted via distance a between magnets 2 and 3 and can be adapted to the gradiometer separation GM of sensor elements 5 and 6. Furthermore, the courses of the lines of flux depend on the dimensions h, b and t of permanent magnets 2 and 3. Given a fixed gradiometer separation GM, e.g., 2.5 mm, the size, material and arrangement, for example, of permanent magnets 2 and 3 can be determined in this case such that sensor 4 functions in an offset-free manner and can therefore detect the smallest possible signals in order to obtain the greatest possible distance away from a transmitter element.

#In the absence of a transmitter element, e.g., a toothed wheel, that is moved past externally, the magnetic lines of flux of magnetic sensor system 1 extend such that a small “in-plane” component toward the outside exists at the location of sensor elements 5 and 6. The use, e.g., of a mobile toothed wheel, causes the magnetic field to vary, the “in-plane” components being modulated around the zero position, so that an offset-free signal is produced by the gradiometer system.