Sensor for detecting the direction of a magnetic field in a plane
View Patent ↗The invention relates to a sensor for detecting the direction of a magnetic field in a plane whose direction can be defined by the indication of a polar angle ?. Said sensor comprises a number of n magnetic field sensors (3.0 to 3.7). A measurement axis (8.1 to 8.4) is assigned to each magnetic field sensor in such a manner that the absolute value of the output signal of the magnetic field sensor is largest when the magnetic field runs parallel to the measuring axis. All measuring axes intersect at a common point ( 5 ). The number k of measuring axes is equal to at least three. An operating mode is provided during which two magnetic field sensors are selected for calculating the angle ?. These two magnetic field sensors belong to different measuring axes, and the values of the output signals thereof are less than those of the output signals of the magnetic field sensors belonging to the other measuring axes.
1. A method for detecting a direction of a magnetic field in a plane with a sensor comprising
a number n of magnetic field sensors wherein a measuring axis is assigned to each magnetic field sensor in such a way that an absolute value of an output signal of the magnetic field sensor achieves a maximum when the magnetic field runs parallel to the measuring axis and wherein the number n of measuring axes amounts to at least three; the method comprising the steps of
selecting two magnetic field sensors that belong to different measuring axes and the absolute values of the output signals of which are smaller than the output signals of the magnetic field sensors that belong to the other measuring axes; and
determining the direction of the magnetic field in the plane from the output signals of the two selected magnetic field sensors.
2. The method according to claim 1 , wherein the direction of the magnetic field in the plane is defined by an angle φ, wherein an index m and an angle
Ψ
m
=
m
180
°
n
are assigned to each magnetic field sensor, the index m running from 0 to n−1, wherein an absolute value of the output signal U m of the magnetic field sensor with index in achieves a maximum when the magnetic field runs parallel to the direction of its associated angle ψ m , the method further comprising the steps of
determining the indices of the two selected magnetic field sensors which indices are denoted as p−1. and p;
determining an angle θ from the output signals U p−1 and U p of the two selected magnetic field sensors; and
calculating the angle φ to φ=ψ p−1 +θ.
3. The method according to claim 2 , wherein the angle θ is determined as
θ
=
U
p
-
1
U
p
-
1
-
U
p
.
4. The method according to claim 3 , wherein the ratio
U
p
-
1
U
p
-
1
-
U
p
is determined with an A/D converter, wherein the value U p−1 is fed to a signal input of the A/D converter and the value U p−1 −U p to a reference input of the A/D converter.
5. The method according to claim 3 , wherein the ratio
U
p
-
1
U
p
-
1
-
U
p
is determined by loading a capacitor during a predetermined duration with a current that is proportional to the output signal U p−1 followed by loading or unloading the capacitor in a predetermined number of cycles of the predetermined duration, wherein the sign of the voltage at the capacitor determines whether in the next cycle the capacitor is loaded with a current that is proportional to the output signal U p−1 or unloaded with a current that is proportional to the output signal U p .
6. The method according to claim 3 , wherein two magnetic field sensors belong in pairs to a measuring axis and wherein the angle θ is determined as
θ
=
U
p
-
1
-
U
p
-
1
+
n
2
(
U
p
-
1
-
U
p
-
1
+
n
2
)
-
(
U
p
-
U
p
+
n
2
)
,
wherein the indices
p
-
1
+
n
2
and
p
+
n
2
are to be set modulo n.
7. The method according to claim 6 , wherein the ratio
U
p
-
1
-
U
p
-
1
+
n
2
(
U
p
-
1
-
U
p
-
1
+
n
2
)
-
(
U
p
-
U
p
+
n
2
)
is determined with an A/D) converter, wherein the value
(
U
p
-
1
-
U
p
-
1
+
n
2
)
is fed to a signal input of the A/D converter and the value
(
U
p
-
1
-
U
p
-
1
+
n
2
)
-
(
U
p
-
U
p
+
n
3
)
is fed to a reference input of the A/D converter.
8. The method according to claim 6 , wherein the ratio
U
p
-
1
-
U
p
-
1
+
n
2
(
U
p
-
1
-
U
p
-
1
+
n
2
)
-
(
U
p
-
U
p
+
n
2
)
,
is determined by loading a capacitor during a predetermined duration with a current that is proportional to
U
p
-
U
p
+
n
2
followed by loading or unloading the capacitor in a predetermined number of cycles of a predetermined duration, wherein the sign of the voltage at the capacitor determines whether in the next cycle the capacitor is loaded with a current that is proportional to
U
p
-
U
p
+
n
2
or unloaded with a current that is proportional to
U
p
-
1
-
U
p
-
1
+
n
2
.
9. The method according to claim 2 , further comprising the step of correcting the angle θ by means of a characteristic curve.
10. The method according to claim 3 , further comprising the step of correcting the angle θ by means of a characteristic curve.
11. The method according to claim 4 , further comprising the step of correcting the angle θ by means of a characteristic curve.
12. The method according to claim 5 , further comprising the step of correcting the angle θ by means of a characteristic curve.
13. The method according to claim 6 , further comprising the step of correcting the angle θ by means of a characteristic curve.
14. The method according to claim 7 , further comprising the step of correcting the angle θ by means of a characteristic curve.
15. The method according to claim 8 , further comprising the step of correcting the angle θ by means of a characteristic curve.