A basic magnetic speed sensor, also known as a magnetic speed pickup or magnetic speed encoder, is a device used to measure the rotational speed of a shaft or wheel. It is commonly used in various applications, such as automotive speedometers, industrial machinery, and speed control systems. The principle behind its operation is based on the detection of magnetic field changes caused by rotating ferromagnetic materials.
Here's a description of the operation of a basic magnetic speed sensor:
Sensor Construction: The sensor consists of a magnetic core and a coil winding. The magnetic core is usually made of a ferromagnetic material like iron or ferrite, and the coil winding is wrapped around it.
Mounting: The sensor is mounted in close proximity to the rotating target object, which could be a toothed gear, a slotted disc, or any other ferromagnetic element attached to the shaft or wheel whose speed is to be measured.
Magnetic Field Variation: As the ferromagnetic target rotates, it induces changes in the magnetic field near the sensor. The magnetic field strength around the sensor fluctuates as the target's teeth or slots pass by the sensor's core.
Electromagnetic Induction: The changing magnetic field induces a voltage across the coil winding due to the principle of electromagnetic induction. The magnitude and frequency of this induced voltage are directly related to the speed of the rotating target.
Signal Processing: The induced voltage is typically a sinusoidal signal whose frequency corresponds to the rotational speed of the target. To obtain a clean and usable speed signal, the raw voltage signal may go through signal conditioning and amplification circuits.
Output: The processed speed signal is then sent to the relevant control or display system. For example, in automotive applications, it can be used to drive the speedometer gauge, while in industrial applications, it might be used for process control or monitoring.
Speed Calculation: The receiving system can interpret the frequency of the signal and convert it into rotational speed using calibration factors or lookup tables, thus providing an accurate measurement of the target's speed.
The main advantage of magnetic speed sensors lies in their simplicity, reliability, and ability to work in harsh environments where optical sensors might struggle due to dirt, dust, or moisture. They are also suitable for measuring both low and high rotational speeds. However, the precision and resolution of the measurement can vary depending on the design and application of the sensor. More advanced speed sensors, such as Hall effect sensors or optical encoders, can provide higher accuracy and resolution but may be more complex and expensive.