ZMX40M

• 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

This device ZMX40M 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 ofmagnetic 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 toHy, 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 ZMX40M 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.

When the two peaks are the same amplitude, themagnet  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 30m. By  comparing the two outputs and adding some hysteresis, a large-geometrymagnetic tape reader (for example for a magnetic tape ruler) can be made. By combining both bridg 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.