Method for the measurement of a position of a magnet by means of a sensor arrangement with an increased external magnetic field robustness, taking into account the signal-to-noise ratio
An arrangement has a sensor pair and a magnet mounted to move relative thereto. Magnetic flux density per spatial coordinate per sensor is measured. A non-differential alteration of position of the magnet per the measured magnetic flux density is calculated. Differences of the measured magnetic flux densities per spatial coordinate are calculated. A differentially calculated alteration of position of the magnet from the calculated magnetic flux densities is calculated. Non-differentially and differentially calculated alterations of position of the magnet based on a null position thereof are normalised. Differences of the differentially calculated alteration of position of the magnet and the non-differentially calculated alterations of position thereof are calculated. A weighting factor based on the calculated differences is calculated. An average value, weighted by the calculated weighting factor, of the normalised non-differentially and differentially calculated alterations of position of the magnet is calculated to obtain an adjusted alteration of position.
1 . A method for processing sensor signals to determine a physical position of a magnet based on signals from a magnet-sensor arrangement ( 1 ), wherein the magnet-sensor arrangement ( 1 ) comprises at least one sensor pair ( 3 ) and a magnet ( 2 ) mounted such that it can move relative to the latter, comprising the following steps:
a) measurement, by the at least one sensor pair ( 3 ), of the magnetic flux density per spatial coordinate per sensor;
b) non-differential calculation of an alteration of position of the magnet ( 2 ) for each magnetic flux density measured in step a);
c) calculation of the differences of the measured magnetic flux densities per spatial coordinate;
d) differential calculation of an alteration of position of the magnet ( 2 ) from the magnetic flux densities calculated in step c);
e) normalisation of the non-differentially and differentially calculated alteration of position of the magnet ( 2 ) on the basis of a null position of the magnet ( 2 );
f) calculation of the differences between the differentially calculated alteration of position of the magnet ( 2 ) and the non-differentially calculated alterations of position of the magnet ( 2 ) indicative of deviations caused by external magnetic field influences;
g) calculation of a weighting factor based on the differences calculated in step f) to adaptively combine the non-differentially and differentially calculated alterations of position; and
h) calculation of an average value, weighted by the weighting factor from step g), of the non-differentially and differentially calculated alterations of position of the magnet ( 2 ) normalised in step e) to obtain a corrected alteration of position of the magnet relative to the magnet-sensor arrangement as a physical position of the magnet that compensates for external magnetic field influences while maintaining signal-to-noise ratio.
2 . The method of claim 1 , wherein the movable magnet ( 2 ) is pivotably mounted about at least one pivot axis and the alteration of position is measured in the form of a deflection angle.
3 . The method of claim 2 , wherein the deflection angle is calculated using a trigonometric function from the measured magnetic flux densities.
4 . The method of claim 2 , wherein the differentially calculated deflection angle is calculated using a trigonometric function from the differences of the measured magnetic flux densities.
5 . The method of claim 1 , wherein the weighted average value is formed from one of the non-differentially calculated alterations of position and the differentially calculated alteration of position, and wherein the total calculated alteration of position is calculated using the average value of the weighted average values.
6 . The method of claim 1 , wherein the normalisation in accordance with step e) is performed using a multi-point adjustment.
7 . The method of claim 6 , wherein an external magnetic field influencing the measurements is determined from the difference between the two differently calculated alterations of position, and wherein these alterations of position are corrected by the multi-point adjustment.
8 . The method of claim 6 , wherein the multi-point adjustment is a 9-point adjustment.
9 . The method of claim 6 , wherein the multi-point adjustment is a 15-point adjustment.
10 . The method of claim 1 , wherein an external magnetic field influencing the measurements is determined from the difference between the two differently calculated alterations of position, and wherein these alterations of position can be corrected by comparing them with a measurement under laboratory conditions.
11 . The method of claim 1 , wherein, when calculating the weighting factor, a predefinable constant A max is taken into account, which describes the degree of deviation between the differentially and non-differentially calculated alteration of position, from which the signal is used exclusively from the differentially calculated alteration of position in accordance with step d) for the calculation of the alteration of position.
12 . The method of claim 1 , wherein a pre-definable constant O diff is taken into account when calculating the weighting factor to specify a percentage of the differential signal to be used for calculating the alteration of position.