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IC-MZ Datasheet, PDF (9/11 Pages) IC-Haus GmbH – DIFFERENTIAL HALL SWITCH | |||
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iC-MZ
DIFFERENTIAL HALL SWITCH
APPLICATION EXAMPLES
Gear wheel scanning
Logging the position and rotation of a gear wheel with
iC-MZ requires that the gear wheel is made of a soft
magnetic basic material with which a magnetic ï¬eld
applied externally through the gear geometry can be
modulated. The strength of the modulation is greatest
at the gear rim, calling for iC-MZ to be placed at the
shortest possible operating distance to the gear wheel.
The necessary external bias ï¬eld is generated by a
back bias magnet placed behind iC-MZ. The magnet
should be positioned central to the package so that the
two Hall sensors are impinged by equal magnetic ï¬eld
strengths and a ï¬eld strength offset is avoided; the lat-
ter would make a greater difference in modulation ï¬eld
strength necessary for switching purposes. Field ho-
mogeneity can be improved by placing a pole piece
between the magnet and iC-MZ.
The strength of the magnetic ï¬eld modulation depends
not just on the operating distance and the intensity of
the bias ï¬eld but also on the module and addendum
of the gear wheel. The distance of the teeth along the
perimeter of the wheel stipulates the cycle with which
the magnetic ï¬eld strength is modulated. An optimum
modulation depth is achieved when the gear wheel ge-
ometry is selected so that the two Hall sensors on the
chip are opposite a tooth or a gap and the sensors pro-
vide signals in antiphase. With the given iC-MZ sensor
distance of 2 mm a tooth distance of about 4 mm is ad-
vantageous but not imperative. Even if the geometry of
the wheel is not adapted to suit the sensor, the signals
generated by the two Hall sensors share a ï¬xed phase
relation.
Figure 9 illustrates the typical course of magnetic in-
duction B = µ0 · H at the two Hall sensors, dependent
on angle of rotation Ï of the gear wheel. In an ensuing
ampliï¬cation process analog signals VA and VNA are
formed from the differential signal; digital signals VD
and VND are generated by the back-end comparator
with hysteresis.
Rev A2, Page 9/11
gear wheel
P
B1
B2
S1
S2
iC-MZ
N
bias magnet
S
B
B2
B1
bias
field
B1-B2
BT,hi
P
BT,l o
0
P/2
V
VNA
VA
0
P/2
P
VD
3P/2
Vdc
3P/2
VB
VND
P/2
P
VB
3P/2
P/2
P
3P/2
Figure 9: Gear wheel scanning
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