Inductive Proximity Sensors

Inductive Proximity sensors find wide application in the field of industrial instrumentation.  These sensors are extremely popular as they are reliable, robust and have a simple construction.  Inductive Proximity sensors are used to measure speed, detect motion and sense the position of objects.

The inductive proximity sensor consists of an oscillator, a coil and a detector.  The oscillator develops a high frequency signal which is fed to the coil. 

The high frequency signal develops a corresponding high frequency magnetic field at
the tip of the sensor.  When a metallic object comes in front of the sensor, eddy currents are induced in the object.  This acts as a load on the oscillator and the amplitude of the high frequency output drops.  This drop in the voltage is detected by the detector unit which causes the switching on or off of a transistor.  This results in a change of voltage level which is interpreted as a digital signal 0 or 1.

The inductive proximity principle can also be applied to speed sensors.  In speed measurement, the inductive proximity sensor is placed near the rim of a rotating object. The rotating object has a number of teeth along its rim.  When a tooth passes near the inductive proximity sensor, a pulse is produced. 

This sequence of pulses can be converted into an analog signal can be measured as the speed of the device.