A basic inductive speed sensor, also known as an inductive proximity sensor or an inductive encoder, detects the speed of rotating equipment by utilizing the principle of electromagnetic induction. This type of sensor is commonly used in industrial applications to measure rotational speed and monitor the operation of machinery. Here's how it works:
Principle of Electromagnetic Induction: Electromagnetic induction is a phenomenon where a change in magnetic field induces a voltage in a nearby conductor. In the context of an inductive speed sensor, the sensor generates a magnetic field, and any nearby metallic object moving at a certain speed will cause changes in this magnetic field.
Sensor Construction: An inductive speed sensor typically consists of a coil of wire wound around a core. This coil is connected to an oscillator circuit that generates an alternating current (AC) signal, typically in the radio frequency (RF) range.
Magnetic Field Generation: When the oscillator circuit is powered, it generates an alternating magnetic field around the coil and the core. This magnetic field extends a short distance from the sensor's surface.
Metallic Target: As the equipment's rotating metallic target (such as a gear tooth, shaft, or gearwheel) passes near the sensor's active face, it causes disturbances in the sensor's magnetic field due to the conductive properties of the metal.
Eddy Currents: As the metal target moves through the sensor's magnetic field, it induces eddy currents within the metal. These eddy currents generate their own magnetic fields that oppose the original magnetic field produced by the sensor. This opposition causes a change in the sensor's coil impedance, which is detected by the sensor's electronics.
Frequency Change: The change in impedance leads to a change in the oscillator's frequency. The sensor's electronics can then convert this frequency change into an electrical signal that corresponds to the speed of the rotating equipment. The frequency change is directly proportional to the speed of the equipment.
Signal Processing: The sensor's electrical signal is often conditioned and processed to produce a usable output. This might involve amplification, filtering, and signal conditioning to ensure accuracy and reliability.
Output: The processed signal can be sent to a controller, display, or monitoring system to provide information about the rotational speed of the equipment. This information can be used for various purposes, such as controlling the equipment's operation, ensuring safe operation, or monitoring maintenance needs.
Inductive speed sensors are known for their robustness and durability in harsh industrial environments. They can detect a wide range of rotational speeds and are often used in applications such as conveyor systems, motor control, and rotational speed monitoring in manufacturing processes.