A basic inductive speed sensor, also known as a proximity sensor or an inductive proximity sensor, is a type of non-contact speed sensor commonly used to detect the speed of rotating equipment. It operates on the principle of electromagnetic induction to sense the presence or absence of a metallic target and determine its rotational speed. Here's a simplified explanation of how it works:
Sensor Construction: The inductive speed sensor consists of a coil wound around a core, typically made of ferrite or other magnetic materials. The coil is energized with an alternating current, creating an electromagnetic field around it.
Target Metal Object: The rotating equipment, such as a gear, shaft, or any metal object, serves as the target for the sensor. The target must be made of a conductive material (e.g., ferrous metals like iron or steel) to work with the inductive sensor.
Electromagnetic Field Interaction: As the target metal object moves closer to the sensor, it enters the electromagnetic field created by the coil. The presence of the conductive metal object disrupts the magnetic field lines around the coil, leading to changes in the magnetic flux.
Eddy Current Induction: The changing magnetic flux induces eddy currents in the metal target. Eddy currents are circular electrical currents that circulate within the conductive material in response to the changing magnetic field.
Impedance Change: The presence of eddy currents in the metal target results in a change in the impedance of the inductive coil. The impedance is the opposition to the flow of the alternating current, and it varies with the speed and distance of the metal target from the sensor.
Sensor Output: The inductive speed sensor's circuitry detects the change in impedance and processes this information to generate an output signal. The output signal can be either a digital pulse or an analog signal that corresponds to the rotational speed of the metal target.
Speed Calculation: By measuring the time between consecutive pulses (for digital sensors) or analyzing the analog signal (for analog sensors), the rotational speed of the target metal object can be calculated.
It's important to note that inductive speed sensors are suitable for applications where the target is metallic and requires non-contact sensing. They are commonly used in industrial applications, automotive systems, and other scenarios where accurate speed sensing of rotating equipment is necessary without direct physical contact with the moving parts.