A basic magnetic speed sensor, often referred to as a magnetic speed encoder or a magnetic proximity sensor, is a device used to measure the speed or rotational motion of a target object. It relies on the principles of magnetism and induction to function. Here's how it typically operates:
Sensor Construction: The sensor itself consists of a housing or casing containing a coil of wire wound around a magnetic core. The magnetic core enhances the sensitivity of the sensor to changes in magnetic field strength.
Magnetized Target Object: The target object, usually a rotating gear, wheel, or shaft, is equipped with a small magnet or a magnetic field generator. This magnet generates a magnetic field that can be detected by the sensor as it moves in proximity to the sensor.
Inductive Principle: As the magnetized target object rotates, the magnetic field around it changes in strength and orientation. This changing magnetic field induces a small electric current in the coil of wire within the sensor. The magnitude and frequency of this induced current are directly proportional to the speed at which the magnetized object is moving.
Signal Generation: The induced current in the coil generates an electrical signal. This signal is typically a sinusoidal or square wave voltage pattern with a frequency proportional to the rotational speed of the target object. The faster the object rotates, the higher the frequency of the generated signal.
Signal Processing: The generated electrical signal is then passed through signal conditioning circuitry within the sensor. This circuitry may involve amplification, noise filtering, and signal shaping to ensure accurate and reliable speed measurement.
Output: The final processed signal is output from the sensor as a digital or analog electrical signal that can be interpreted by external devices such as microcontrollers, PLCs (Programmable Logic Controllers), or displays. The output can then be used for various applications such as speed control, monitoring, or feedback in machinery and systems.
Advantages of Magnetic Speed Sensors:
They can be used in various environments, including dirty or dusty conditions, as the magnetic field is less affected by contaminants.
They are relatively robust and durable.
They can provide accurate speed measurements for a wide range of rotational speeds.
Limitations of Magnetic Speed Sensors:
They require a magnetized target object, which might add complexity to the equipment design.
They might be affected by strong external magnetic fields, potentially leading to inaccuracies.
They generally provide relative speed measurements and might need calibration for precise speed values.
In summary, a basic magnetic speed sensor utilizes changes in magnetic fields induced by a rotating magnetized object to generate an electrical signal that represents the speed of the object's rotation. This signal is then processed and used for various control and monitoring purposes.