How a Magnetic Speed Sensor Works

Written by j.t. barett
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How a Magnetic Speed Sensor Works
You can install a magnetic speed sensor on your bike. (bicycle image by Brett Bouwer from

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.


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.


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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