What about magnetic position sensor reliability?

July 20, 2015 // By Mark Donovan
A stubborn question about the reliability of magnetic position sensors lingers in the minds of some automotive and industrial system designers. Yet complete stray field immunity is possible in contactless magnetic position sensing, claims Mark Donovan of AMS AG.

Magnetic position sensors are an electronics industry’s technological success.
In automotive and industrial applications in particular, the magnetic sensor’s ability to withstand the dust, dirt, grease, vibration and humidity that commonly disable optical encoders – the best known alternative contactless type of position sensor – is highly valued. Like optical encoders, the potentiometer – the industry’s most familiar device for measuring linear or angular displacement, also suffers from the effects of mechanical wear, a common source of premature failure.

By contrast with both the optical encoder and the potentiometer, a magnetic position sensing system is far more durable, and operates far more reliably no matter how dirty, damp or unstable the operating conditions.

And yet, a stubborn question about the reliability of the magnetic position sensor lingers in the minds of some automotive and industrial system designers.
Since they often design systems for use in an environment containing powerful sources of magnetism, such as motor drives and high-voltage power transmission lines, they are wary of magnetic position sensors.

They fear the huge magnetic forces unleashed by these systems – for instance, in the enclosed space of a car body or wind turbine – will swamp the weak field generated by the target magnet with which a Hall Effect sensor is paired.

That’s partly true.

Magnetic position sensors can be sensitive to the paired target magnet field, and also to unintended magnetic stray fields, which can impair the accuracy of the magnetic position sensor’s output by reducing the signal-to-noise ratio (SNR) to unacceptable levels within the device.

If the issue of unintended stray fields is not addressed, a sensor sub-system could yield inaccurate results, potentially leading to reduced system performance and safety issues.

Stray fields are of particular concern in industrial and automotive applications where high levels of electromagnetic interference (EMI) are commonly found.

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