A speed sensor is essential for ensuring the proper functioning of several embedded systems. It allows the measurement of the magnetic rotation speed in order to provide a corresponding voltage.

Its most significant application is in the automotive, precision mechanics and aeronautics sectors. This sensor transmits the information to several systems, such as to the Antilock Braking System (ABS) ECU or for vehicle dynamic control (ESP – Electronic Stability Program).

What Are the Types of Speed Sensors?

The speed sensor is needed to control the speed of a combustion or electric motor. The different types of speed sensors are: active sensors (Hall effect or magneto-resistive) and inductive sensors (bipolar or monopolar).

Bipolar inductive sensors have the particularity of being able to transmit a larger electrical signal than that transmitted by monopolar sensors. They are less sensitive to runout.

Monopolar inductive sensors, on the other hand, are magnetic or inductive sensors allowing non-contact measurement of wheel speed. The voltage they produce is called alternating and can have an amplitude that can vary depending on the shape of the tooth, the speed of rotation, the size of the air gap and the materials used.

The so-called active sensors are those that require an external voltage supply to operate. Without this voltage supply, no signal can be provided. A voltage is generated by the sensitive elements (of the hall effect or magneto-resistive type) that compose them, according to the magnetic flux that passes through them. From these types of sensors, the voltage is measured until the wheel comes to a complete standstill, without depending on the speed of rotation of the wheel.

Active hall effect sensors consist of a hall element and an integrated electronic part. Active magneto-resistive sensors consist of a magneto-resistive element and an integrated electronic part.

What is an Active Hall Effect Sensor?

The active Hall-effect sensor generates a voltage that can vary depending on the magnetic flux that passes through it. It is composed of 2 parts: a hall element, that consists of 2 offset Hall effect cells, and an integrated electronic part.

In the case of a wheel speed sensor, a varying magnetic field is generated by the rotation of the wheel. Two alternating signals are thus created. In order to obtain a single signal, it is necessary to subtract the two signals, are then filtered in a differential so that interference is suppressed.

The new signal obtained is amplified and passes through a Schmitt trigger (threshold switch) where it is calibrated and clipped to form a square wave signal. This signal is then passed through two current generators to obtain a “clean” and constant signal that is insensitive to interference.

Note that the output signal of active Hall effect sensors and active magneto-resistive sensors are identical. The same vehicle can carry both, if the design of the sensor allows it.

Cutting and Bending Hall Effect Speed Sensors

Hall effect active speed sensors are typically supplied by manufacturers in strips of hundreds of components. In order for them to be integrated on an electronic circuit, a special machine is required to cut them and thus bend their connection pins. In a minimum amount of time, this automatic machine produces ready-to-use parts that considerably reduces human intervention.

Inexpensive manual devices do exist, but the intervention of an operator is necessary. This can lead to a definite reduction in productivity since the quantity produced per hour is very limited. These devices are better suited for training or product prototyping.

On the other hand, if there is a need to meet greater requirements, the automatic machine is more suitable. Indeed, it allows the rapid production of large quantities of parts with excellent bending and cutting precision. This machine also meets all requirements in terms of cost-effectiveness.