DUAL MAGNETIC FIELD SENSOR
DESCRIPTION
This device is a special tangential field difference
sensor with two AMR (Anisotropic Magneto-Resistive)
bridges for field movement measurements or field
comparative measurements.
The ZMX40M contains two extremely sensitive magnetic
sensor chips, mounted parallel to each other in an SM8
package, employing the magneto-resistive effect of thin
film permalloy. It allows the measurement of magnetic
fields or the detection of magnetic parts. The sensors each
consist of a chip covered with thin film permalloy stripes
which form a Wheatstone bridge, whose output voltage is
proportional to the magnetic field component Hy. A field
Hx, which is perpendicular to Hy, is necessary to suppress
the hysteresis and to bias the sensors into the linear
region. This field Hx is provided by an internal permanent
magnet.
The chips are mounted in the package 3mm apart. If a
magnet travels horizontally above the sensor, each chip
will give an output which will peak as the magnet passes
above it and the two peaks will be spatially separated by
3mm.
FEATURES
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ISSUE 1 - MARCH 2004
Output voltage proportional to magnetic field Hy
across each chip
Both chips are in the same orientation and chip
centres are 3mm apart in Y direction
Magnetic fields vertical to the chip level Hz are not
effective
Disturbing fields Hx up to 30 kA/m are allowed
Extremely small chip distance from the top side of
package for accurate measurement
Internal magnet each chip for creation of auxiliary
field Hx
PINOUT
Top View
1
When the two peaks are the same amplitude, the magnet
must be mid-way between the two chips. Therefore this
double sensor can be used to measure position of, for
example, a wheel tooth very accurately for automotive
and machine-tool applications. With calibration to allow
for the tolerances on the bridge outputs being slightly
different, the ZMX40M has been used in machine tool
applications to resolve distances down to 30µm. By
comparing the two outputs and adding some hysteresis,
a large-geometry magnetic tape reader (for example for a
magnetic tape ruler) can be made. By combining both
bridge outputs a current sensor can be also made by
adding an external current loop over or under the
ZMX40M. This loop is outside the package and therefore
provides excellent galvanic isolation.
APPLICATIONS
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DEVICE MARKING
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CONNECTION DIAGRAM
AMR chip 1: supply voltage between +Vb1 and -Vb1
AMR chip 2: supply voltage between +Vb2 and
Linear position measurement for process control,
door interlocks, proximity detectors and precision
machine tools
H-field movement measurement for a magnetic
tape recognition
High voltage isolated current measurement up to
many amps range by using a suitable current loop
over or under the IC
Detection of rotating magnets in the presence of a
disturbing field by comparisons of maximum
values of individual sensors
ZMX40M
output voltage of bridge between
+V
-Vb2 output voltage of bridge between
+V
out
out
1 and -V
2 and -V
out
out
1
2
S E M I C O N D U C T O R S
ZMX40M