IC-ML Datasheet, PDF (7/17 Pages) IC-Haus GmbH – HALL Position Sensor / Encoder

iC-ML
HALL Position Sensor / Encoder
The sensor principle
Rev A3, Page 7/17
In conjunction with a magnetic tape iC-ML can be used
to create a complete linear encoder system. With a
Hall sensor pitch of 1.28 mm, the iC-ML is taylored
to work with a magnetic tape having a pole pitch of
2.56 mm (5.12 mm magnetic periode). At a resolution
of 8 bit, the digital increment represents a linear dis-
tance of 20 µm. In the same way, pole wheels can also
be used together with the iC-ML.
Magnetic tapes (or pole wheels) with a smaller pitch
than 2.56 mm can be used by skewing the iC-ML with
respect to the tape direction and thus adjusting the pro-
jected sensor pitch to the tape pitch.
iC-ML has four Hall sensors which are used pairwise
to generate sine- and cosine signals. Each Hall sen-
sor pair detects the magnetic tape at a lateral distance
of half of a magnetic periode. From the difference of
the hall voltages, each Hall sensor pair generates ei-
ther the sine or the cosine signal. Due to the differen-
tial sensing, the resulting signal voltages are insensitve
to external homgenious magnetic fields and pole with
variations.
From the physical principal, the Hall sensors are also
insensitive to magnetic fields parallel to the chip sur-
face.
Arrangement and signal outputs
Figure 5 shows the arrangement of the iC-ML to the
magnetic tape. Both chip and magnetic tape are paral-
lel aligned to each other. The coordinate system is de-
fined in the way that the z-coordinate is perpendicularly
to the surface of the magnetic tape and the x-direction
lies in direction of travel. The four HALL sensors are
located at the upper edge of the chip and should be
centered to the magnetic tape for optimized magnetic
sensing.
Figure 6: Sensing of a pole wheel at the surface us-
ing iC-ML
Figure 5: Arrangement of iC-ML to the magnetic
tape
Magnet wheels are scanned depending upon their di-
rection of magnetization either on the surface or at the
periphery. The sensing radius must be chosen accord-
ingly to match the magnetic pitch to the sensor pitch.
For further consideration, the reference position of the
chip is selected in such a way that the x-position of the
outmost left hall sensor coincides with the zero point
of the magnetic tape, which is located at the center of
an arbritrally chosen north pole of the magnetic tape.
Then, as shown in figure 8, the corresponding output
signals in the analog operation mode (S-Sensor) will
be available as a function of the lateral shift x_d. The
electrical signals exhibit the same periodicity as the
magnetic field of the magnetic tape, showing extremes
at the poles (Vcos) or at the pole gaps (Vsin).