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How a Magnetic Speed Sensor Works

Updated October 29, 2018

Many electronic speed sensors use a magnetic principle called the Hall Effect. The Hall Effect device registers the presence of a nearby magnet. A computer counts how many times the magnet passes by and determines speed.

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Hall Effect Device

A magnetic speed sensor consists of a stationary Hall Effect device and a moving magnet. The device has no moving parts and can measure very high speeds. Whenever the magnet passes by it, it produces a small voltage pulse.

Magnet

The speed sensor's magnet rides on a rotating wheel, such as the inside of a car's wheel. For every revolution of the wheel, the magnet moves past the Hall Effect sensor, which sends an electrical pulse to a computer.

Computer

A simple computer measures the time between pulses from the Hall Effect sensor. Using this data and the diameter of the wheel, it calculates the vehicle's speed.

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About the Author

Chicago native John Papiewski has a physics degree and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."

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