IC-MHM Datasheet, PDF (17/63 Pages) IC-Haus GmbH – 14-BIT ABSOLUTE ANGLE HALL ENCODER

iC-MHM
14-BIT ABSOLUTE ANGLE HALL ENCODER
HALL SENSORS: Principle of Operation
Rev D1, Page 17/63
The iC-MHM contains four Hall sensors equally spaced
on a 2.42 mm diameter circle for sensing the field of a di-
ametrically magnetized, cylindrical permanent magnet
as shown in Figure 9.
By subtracting the Hall voltages from opposite sensors,
the effects of homogeneous stray fields are eliminated
and two differential Hall signals are generated. As
shown in Figure 11, these signals are proportional to
the sine and cosine of the magnet angle, α.
Figure 9: Hall Sensor Locations
This sensor arrangement allows a very tolerant align-
ment of the iC-MHM to the rotational axis of the magnet.
Each of the four sensors produces a voltage (the Hall
voltage) proportional to the magnetic field strength at
the position of the sensor. As shown in Figure 10, only
the Z component of the magnetic field (the component
perpendicular to the surface of the iC-MHM) is sensed.
Figure 11: Sine and Cosine Hall Signals
These two signals are used by the interpolator to de-
termine the angular position of the magnet. The zero
position (α = 0) of the system is where the South pole of
the magnet is over the PCOS sensor (the one closest
to pin 1 of the iC-MHM) as shown in Figure 12.
Figure 12: Zero Position of the Magnet
Figure 10: Sensor Principle
Note: The field direction for each sensor is opposite
to that of the sensor directly opposite to it. Thus, oppo-
site sensors generate opposite polarity Hall voltages.
Optimum sensor signals are generated by a diametri-
cally magnetized, cylindrical permanent magnet with a
diameter, D, of 4 mm and an axial length, L, of 4 mm.
Magnets of neodymium iron boron (NdFeB) or samar-
ium cobalt (SmCo) are very well suited to the iC-MHM
and are hardly influenced by external stray fields. Dif-
ferent size magnets can be used with the iC-MHM, but
the length-to-diameter ratio, L/D, of the magnet should
be between 0.3 to 2 to ensure sufficient field strength.