A basic inductive speed sensor, also known as an inductive proximity sensor or an inductive proximity switch, is a type of sensor that detects the presence or absence of a target object (usually a metal target) and can be used to indirectly measure the speed of rotating equipment. It works based on electromagnetic principles and does not require physical contact with the target.
Here's how it typically works:
Principle of Inductance: When a conductive metal target comes into the proximity of the inductive sensor, it induces eddy currents in the target material due to electromagnetic field variations. These eddy currents generate their own magnetic fields, which interact with the original electromagnetic field from the sensor.
Oscillating Circuit: The inductive sensor has an internal oscillating circuit that generates a high-frequency electromagnetic field around the sensor coil. This oscillating field induces voltage changes in the coil itself.
Target Presence Detection: When a metal target comes within the sensing range of the inductive sensor, the eddy currents induced in the target cause a dampening effect on the original oscillating field of the sensor. This dampening effect is detected by the sensor, causing changes in the voltage and current in the sensor's coil.
Signal Processing: The inductive sensor is connected to electronic circuitry that processes the changes in the coil's voltage and current. These changes are used to determine the presence or absence of the metal target within the sensor's range.
Speed Detection: When the inductive sensor is positioned near rotating equipment, such as a gear, shaft, or wheel, a metal portion of the equipment passes in front of the sensor's sensing range as the equipment rotates. As the metal portion moves closer to the sensor, the sensor detects its presence and triggers an output signal. As the metal portion moves away from the sensor, the signal changes again. By counting these changes in the output signal over time, you can indirectly calculate the speed of the rotating equipment.
Output Signal: The inductive sensor typically provides a digital output signal, usually a simple on/off signal, indicating whether the metal target is present within its sensing range or not. This signal can be used to infer the rotational speed of the equipment based on the frequency of the on/off transitions.
It's important to note that the accuracy and resolution of speed measurement using such sensors can be limited, especially for high-speed applications, due to factors such as the response time of the sensor, the size of the metal target, and the electronics used for signal processing. For more precise speed measurement, more advanced sensors and methods might be necessary.