A basic magnetic speed sensor, also known as a magnetic pickup sensor or magnetic Hall effect sensor, is a device used to measure the rotational speed of a moving target equipped with a ferrous metal target or gear. It operates on the principle of detecting changes in a magnetic field caused by the rotation of the target. Here's a description of its operation:
Sensor Construction: The magnetic speed sensor consists of a housing containing a Hall effect sensor or a magnetoresistive sensor and associated electronic components. The sensor is usually encapsulated in a protective casing to shield it from external elements.
Magnet and Target Wheel: The target object, often called the target wheel or gear, is made of ferrous metal and has evenly spaced teeth or protrusions around its circumference. It is usually mounted on the shaft of the rotating object whose speed needs to be measured. This target wheel can have multiple teeth or a single slot, depending on the application.
Magnetic Field Detection: The magnetic speed sensor generates a constant magnetic field, usually from a permanent magnet, within its core. As the target wheel rotates, the teeth or slots on the wheel cause variations in the magnetic field around the sensor.
Hall Effect or Magnetoresistive Sensor: The heart of the magnetic speed sensor is the Hall effect sensor or magnetoresistive sensor. These sensors are sensitive to changes in magnetic fields. When the rotating target wheel moves past the sensor, the magnetic field variations are detected by the Hall effect or magnetoresistive element.
Signal Generation: As the target wheel's teeth pass the sensor, the magnetic field changes are converted into electrical signals. For a Hall effect sensor, the signal voltage will change based on the strength of the magnetic field, and for a magnetoresistive sensor, the resistance will change. These variations in voltage or resistance generate electrical pulses.
Pulse Counting: The electrical pulses generated by the sensor are counted by electronic circuits within the sensor's housing. The frequency of these pulses is directly proportional to the rotational speed of the target wheel. By counting the pulses over a specific time interval, the speed of the rotating object can be accurately calculated.
Output: The sensor typically provides a digital output signal, often in the form of a square wave, with a frequency proportional to the rotational speed. This output can be fed into a speedometer, tachometer, or other control systems for further processing or display.
Magnetic speed sensors are commonly used in automotive applications, industrial machinery, speedometers, and various other speed monitoring systems, due to their simplicity, reliability, and ability to work in harsh environments.