Hall effect sensor applications

A Hall effect sensor detects a magnetic field. Its reading depends on the component of the field along the direction to which the sensor is sensitive. As the sensor turns relative to the field, that component can change.

Monitoring orientation

A Hall effect sensor fixed to an object can help monitor the object's orientation, or attitude, relative to a magnetic field. If the field remains unchanged while the object turns, a change in the sensor reading indicates a change in its orientation relative to the field.

For example, the detected component is greatest when the sensor's sensitive direction is aligned with the field and zero when it is perpendicular to the field. Turning the sensor between these orientations changes its reading.

A single magnetic field reference does not uniquely determine the object's complete attitude. For example, an object can rotate about the direction of the field without changing its orientation relative to that field.

Measuring rotational speed

A tachometer measures rotational speed. A Hall effect tachometer detects repeated changes in magnetic field as an object rotates. For example, a magnet fixed to the rotating object can pass the sensor once per revolution, producing one signal each time it passes.

The number of signals counted over a known time gives the rotational speed, provided the number of signals per revolution is known:

If time is measured in seconds, the result is in revolutions per second. Multiply it by $$60$$ to obtain revolutions per minute.

For example, if the sensor counts $$120$$ signals in $$10$$ seconds and produces $$2$$ signals per revolution, the object makes $$60$$ revolutions in that time. Its speed is therefore $$6$$ revolutions per second, or $$360$$ revolutions per minute.