Dual Magnetic Field Sensor – more accurate than Hall Effect devices

Containing two highly sensitive magnetic field sensors, the ZMX40M from Zetex can be used for accurately measuring linear position and high voltage current.

This magneto-resistive device provides a measurement sensitivity many times greater than that of traditional Hall Effect devices. Thin film permalloy stripes covering each sensor chip form a Wheatstone bridge providing an output voltage proportional to the magnetic field (Hy) running the length of the SM8 package. Internal permanent magnets create a perpendicular field (Hx) that suppresses hysteresis and biases the sensors in their linear region. Mounted in parallel and separated by precisely 3mm in the Y plane, the two sensors can accurately measure the position of a magnetic object. A magnet moving above the package stimulates an output from each sensor that peaks as the magnet passes directly above. When the two peaks are of the same amplitude, the magnet is exactly mid-way between the two chips.

With calibration to allow for tolerance differences between the sensor bridge outputs, the ZMX40M can resolve distances down to 30µm in toothed wheel automotive and machine tool applications. By comparing the outputs and adding some hysteresis, a large geometry magnetic tape measure can be created.

By combining both bridge outputs and locating an external current loop above or below the ZMX40M , a high voltage current sensor can also be created. Since the current loop sits outside of the dual magnetic field sensor package, complete galvanic isolation is assured.

Zetex PLC, Oldham, Lancs OL9 9TY, UK.

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