Electronics Technology


New MR sensors deliver highly accurate and robust performance

19 November 2003 Electronics Technology

Philips Semiconductors offers magneto-resistive (MR) sensors with coils integrated into the housing that compensate for both temperature drift and sensor offset. Magnetic field sensors are commonly used to measure the earth's field, for compass and navigation systems in the automotive industry. They are also increasingly popular in traffic detection and flow control systems, where their sensitivity is high enough to allow identification of individual vehicle types. Another application is in compensation circuits, which automatically eliminate geometry errors produced by changes in the magnetic environment around TVs and monitors.

Available through Arrow Altech Distribution, the KMZ51 sensor, by eliminating the need for external coils, simplifies system design in applications requiring the measurement of weak magnetic fields, allowing the inherent sensitivity, stability and high accuracy of the magnetoresistive effect to be cost-effectively exploited.

The integrated coils have an excellent magnetic coupling factor, so the KMZ51 also has very low power consumption, allowing it to operate from a 5 V supply. Uniquely, even operating at this low supply voltage the sensor requires no DC-to-DC up-converter to provide sufficient coil currents, as required by some sensors with integrated coils under the same conditions.

Compensation for temperature drift and sensor offset is essential in weak-field measurements, otherwise the magnetic effects they produce can completely swamp the target magnetic field. The flipping coil periodically applies brief (3 to 5 µs) magnetic pulses to the sensor, first in one direction, then the other, which 'flips' over the output characteristic of the sensor (which is bi-stable). After rectification and smoothing, the time-averaged output signal is then free from sensor offset. The compensation coil uses an electromagnetic feedback loop to ensure the sensor always operates at its 'null-point', where both sensor offset and signal characteristic are unaffected by temperature fluctuations.

For more information contact Rodney Farrow, Arrow Altech Distribution, 011 923 9600, rfarrow@arrow.altech.co.za



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