A basic inductive speed sensor, often referred to as an "inductive proximity sensor" or "inductive proximity switch," detects the speed of rotating equipment using electromagnetic principles. These sensors are commonly used in industrial applications to monitor the speed of rotating machinery, such as motors, conveyors, and other equipment.
Here's how a basic inductive speed sensor works:
Principle of Induction: The sensor operates based on the principle of electromagnetic induction. When a conductive or metallic target approaches the sensor's sensing area, it causes changes in the electromagnetic field around the sensor.
Sensor Construction: The sensor consists of a coil of wire wound around a ferrite core. This coil is connected to an oscillator circuit, which generates a high-frequency alternating current (AC) in the coil. The coil and its core are encased in a non-conductive housing.
Detection Zone: The sensor has a detection zone or sensing area in front of it. When a metallic target enters this zone and moves within the sensor's range, it affects the sensor's electromagnetic field.
Eddy Currents: As the metallic target (such as a gear tooth or a rotating shaft) enters the detection zone, it cuts across the sensor's electromagnetic field. This action induces eddy currents in the metallic target. Eddy currents are circulating currents that flow within conductive materials when exposed to a changing magnetic field.
Frequency Shift: The presence of the eddy currents in the metallic target causes changes in the impedance (resistance to alternating current) of the coil. This, in turn, alters the sensor's oscillation frequency.
Frequency Detection: The sensor's electronics monitor the oscillator's frequency. The frequency changes caused by the eddy currents are proportional to the speed at which the metallic target is moving. The faster the target moves, the higher the frequency shift.
Output Signal: The sensor's electronics process the frequency shift and convert it into an electrical signal that represents the speed of the rotating equipment. This signal can be in the form of a voltage or a digital signal (e.g., high/low logic level).
Output Connection: The output signal is then sent to external devices, such as programmable logic controllers (PLCs) or other control systems, which can use this information to monitor and control the speed of the rotating machinery.
In summary, a basic inductive speed sensor detects rotating equipment speed by generating a high-frequency electromagnetic field and monitoring the changes in the field caused by the induction of eddy currents in a metallic target moving within its sensing zone. The resulting frequency shift is then converted into a usable speed signal for further processing and control.