Everything You Need to Know About the Speed Sensor

The speed sensor, an essential component for the operation of several on-board systems, allows the magnetic rotation speed to be measured in order to provide a voltage corresponding to the rotation speed.

It is widely used in the aeronautics, automotive and precision engineering sectors. In the automotive sector, a wheel speed sensor is required. An example of its use is it can be mounted on the wheel to transmit information to various systems, such as the ABS (anti-lock braking system) or ESP (Electronic Stability Program) computer for dynamic vehicle control.

 

Different Types of Speed Sensors

 

The use of speed sensor is also necessary for controlling the speed of an electric or thermal motor. There are different types of speed sensors: inductive sensors that can be monopolar or bipolar and active sensors that can be magneto-resistive and Hall effect.

  • Monopolar inductive sensors are inductive or magnetic sensors that measure wheel speeds without contact. They produce a so-called alternating voltage with an amplitude that can vary according to the speed of rotation, the shape of the prong, the materials used or the size of the gap.
  • Bipolar inductive sensors have a particular feature which is to transmit a larger electrical signal than that transmitted by monopolar sensors. They are also less sensitive to warps.

The final two types of speed sensors are active sensors. They are called active because they must be powered by an external voltage in order to operate. Without a power supply, they cannot provide any signals. Depending on the magnetic flux that passes through it, the sensitive elements that it is composed of generate a voltage. These elements are of magneto-resistive or hall effect types. The voltage to be measured from these types of sensors does not depend on the rotational speed of the wheel since it can be measured until it stops completely. This is not the case for inductive sensors.

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

 

A Detailed Look at the Active Hall Effect Sensor

 

The active hall speed sensor consists of two parts: an integrated electronic part and a hall element which consists of two offset hall effect sensors. It generates a voltage that can vary according to the magnetic flux that passes through it.

For example, in the case of a wheel speed sensor, the rotation of the wheel generates a magnetic field that varies, creating two alternating signals. In order to obtain a single signal, the two signals are subtracted and filtered to suppress interference. The new signal obtained is amplified and then passed into a threshold switch (or Schmitt trigger) where it is clipped and calibrated to form a square signal. Finally, the latter passes through two power generators. The objective of these generators is to obtain a so-called “clean” and constant signal that is not sensitive to interference.

It is good to know that the output signal of active magneto-resistive sensors and active hall effect sensors are identical and if the design of the sensor allows it, it is then possible to mount them on the same vehicle.

A Machine for Cutting and Bending Hall Effect Speed Sensors

 

Generally, manufacturers supply speed sensors of the active hall effect type in strips of hundreds of components. In order to integrate them into an electronic circuit, it is necessary to use a machine to cut them and bend the connection pins. This automatic machine makes it possible to obtain ready-to-use parts in a short amount of time, therefore minimizing the need for human intervention.

There are, of course, less expensive manual devices, but they require the intervention of an operator. Productivity can be extremely low, as the quantity produced per hour is very limited. These types of devices are more suitable for product prototyping or training.

On the other hand, for more important needs, the use of an automatic machine allows to obtain parts in large quantities very quickly. Furthermore, you are also benefiting from an excellent cutting and bending precision and a better profitability.

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