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INDUCTIVE PROXIMITY SENSORS

     

 A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.


                          Principles of Operation for Inductive Proximity Sensors


Inductive proximity sensors are designed to operate by generating an
electromagnetic field and detecting the eddy current losses generated                                                  when ferrous and nonferrous metal target objects enter the field. The
sensor consists of a coil on a ferrite core, an oscillator, a trigger-signal                                              level detector and an output circuit. As a metal object advances into the field, eddy currents
are induced in the target. The result is a loss of energy and a smaller amplitude of                   oscillation. The detector circuit then recognizes a specific change in
amplitude and generates a signal which will turn the solid-state output “ON” or
OFF"






       WORKING

The DC supply generates AC in the internal coil, which in turn causes an alternating magnetic field.
If no conductive materials are near the face of the sensor, the only impedance to the internal AC is due to the inductance of the coil.

If, however, a conductive material enters the magnetic field, eddy currents are generated in the conductive material, resulting in increase in impedance to the AC in the proximity sensor.

A current sensor present in the sensor, detects when there is a drop in the internal AC current due to increased impedance.


The current sensor controls a switch providing the output. Similar to other sensors, proximity sensors also have built in hysteresis. The sensor’s output goes on when a conducting material is inside the sensing range and will goes off if the material just moves away from the sensing range.    






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