RHEINTACHO Messtechnik GmbH | Measurement, control and indication of rotational speed

Hall-effect sensors

Hall-effect sensors are suitable for proximity rotational speed recording on gears with a small module and high resolution. The various models can be used in a wide range of applications, even under extreme conditions. SH type rotational speed sensors are used in a wide variety of applications in mechanical engineering, vehicles and mobile working machines, as well as in hydraulic drives.

The sensor detects the movement of ferromagnetic structures such as gears using the change in the magnetic flux. The sensor is biased using a permanent magnet. Teeth and gaps which moves past the sensor affect the magnetic field in different ways. This changes the Hall voltage on a hall-effect sensor.
This means the changes to the magnetic field can be converted to electrical values, and then filtered and processed. The output signal of the sensor is a square wave voltage which reflects the change in the magnetic field.

A Hall generator is a semiconductor which is dependent on the magnetic field, and its function is based on the effect discovered by Edwin Hall. The Hall effect is caused by the Lorentz force, which acts on moving charge carriers in the magnetic field. The semiconductor board has four connections. A constant current (I) flows through two opposite connections. In the neutral state, there is no difference in voltage between the other two connections. (Fig. 1) However, if the Hall plate is exposed to a magnetic field with the induction B, the current (I) is deflected by the Lorentz force. (Fig. 2) The charge carriers are forced to the side, so that an electric field is generated between the edges to counteract the Lorentz force. This gives rise to a difference in voltage at the two opposite sides; this is known as the Hall voltage. This voltage is proportional to the current (I) and the magnetic induction B acting at 90 degrees to the plate.

How it works
The sensor detects the movement of ferromagnetic material, such as gears, using changes in the magnetic flux. The tooth of a gear affects the magnetic field of the sensor in different ways as it enters or leaves the field. The sensor element measures a change in the Hall voltage. This means the change in the magnetic field can be converted into an electrical value, then filtered and turned into an output signal to reflect the rotation of the gear.