A basic magnetic speed sensor, also known as a magnetic pickup or magnetic hall effect sensor, is a device used to measure the speed or RPM (revolutions per minute) of a rotating object. It works on the principle of detecting changes in magnetic fields due to the rotation of a ferromagnetic target, such as a gear tooth or a metal toothed wheel.
Here's how a basic magnetic speed sensor operates:
Sensor Construction: The magnetic speed sensor consists of a magnet and a Hall-effect sensor. The magnet is a permanent magnet that generates a magnetic field, and the Hall-effect sensor is a semiconductor device that detects changes in the magnetic field.
Mounting: The sensor is typically mounted near the rotating target, so the magnetic field from the target can influence the Hall-effect sensor.
Target Wheel: A ferromagnetic target wheel or gear is attached to the rotating shaft whose speed we want to measure. This target wheel contains evenly spaced teeth or magnetic markers.
Detection: As the target wheel rotates, its teeth or markers pass in close proximity to the magnetic sensor. This changes the magnetic field around the sensor.
Hall Effect: When the magnetic field around the Hall-effect sensor changes, the sensor generates a voltage proportional to the strength of the magnetic field. The Hall-effect sensor is designed to output a voltage in response to the changes in the magnetic field.
Signal Processing: The voltage output from the Hall-effect sensor is then processed and converted to a digital signal by electronic circuits. The frequency of the digital signal is directly proportional to the speed of the rotating target. The signal is then sent to a display unit, a control system, or any other device that needs to measure and use the speed information.
Speed Calculation: The receiving device can calculate the speed of the rotating object by counting the number of pulses (signal transitions) within a specific time interval. By knowing the number of teeth or markers on the target wheel and the gear ratio, the rotational speed can be converted into RPM.
The key advantages of magnetic speed sensors include their simplicity, reliability, and ability to work in harsh environments, such as those with dirt, oil, or other contaminants. They are commonly used in various applications, including automotive systems (e.g., speedometers), industrial machinery, and other equipment where accurate speed measurement is required.