A basic magnetic speed sensor, also known as a magnetic speedometer sensor or magnetic pickup, is a type of sensor that measures the rotational speed of a target object using the principle of magnetic induction. It is commonly used in automotive applications to measure the speed of rotating components such as wheels, crankshafts, or camshafts. Here's a description of its operation:
Sensor Construction: The magnetic speed sensor consists of a permanent magnet and a coil. The permanent magnet is typically mounted in a fixed position near the target object (e.g., a rotating wheel), and the coil is located close to the magnet, but not in direct contact with it.
Target Wheel with Teeth: The target object, such as a wheel, has teeth or notches on its outer circumference. These teeth create fluctuations in the magnetic field as they pass by the magnetic sensor.
Magnetic Field Fluctuations: As the teeth on the target wheel rotate past the permanent magnet, they disturb the magnetic field around the sensor. When a tooth approaches the sensor, it causes an increase in the magnetic field strength, and when it moves away, the field strength decreases.
Induced Voltage: The magnetic fluctuations induce a voltage in the coil of the sensor. The induced voltage is proportional to the rate at which the teeth pass by the sensor, which is directly related to the rotational speed of the target object.
Signal Output: The induced voltage is processed and amplified by electronic circuitry within the sensor. It is then converted into an electrical signal that represents the rotational speed of the target object.
Output Signal Interpretation: The output signal can be in various formats, such as a variable voltage or a square wave signal with frequency proportional to the rotational speed. This signal can be further processed by the vehicle's electronic control unit (ECU) or other systems to display the speed on the speedometer or use it for various control purposes, like anti-lock braking systems (ABS) and traction control.
In summary, the magnetic speed sensor works by detecting the changes in the magnetic field caused by the teeth on the rotating target object. These changes induce a voltage in the coil, and the resulting electrical signal is used to determine the rotational speed of the object.