Inductive Proximity Sensor Principle

Inductive Proximity Sensor/Switch which is the most frequently used position/proximity sensor in many applications. Inductive proximity sensors can be used to recognize any conducting metal target. Inductive proximity sensors make use of electromagnetic field that penetrates through the target. An inductive proximity sensot consists of an oscillator that generates a high frequency electromagnetic field. This field is radiates from the sensing face of the system. When this field contacts a conducting metal target, a small current is induced within the metal target.

These currents will generate their own electromagnetic field that interferes with the field originating from the system. This causes a change in the amplitude of the oscillations of the signals from the system. The output voltage can be calibrated to this change. When the system is closer to the target, the more current reacts with the field originating from the system and the output is greater.

The material and size (also the thickness) of the target is an important factor for inductive proximity sensors. Generally there are two types of target materials for inductive sensors; ferrous and nonferrous. Ferrous materials (iron and most steel materials) are magnetic in nature while nonferrous materials (zinc, aluminum, copper and brass) are nonmagnetic.

Note that some inductive sensors will work with both ferrous and nonferrous target materials while others will work only with one type of material, and most inductive proximity sensors are independent of the material in the gap between the probe and the target (they can be used in hostile environments where oil or other liquids may appear in the gap).

Since the output voltage (and current) of an inductive sensor is directly proportional to the distance between the sensor and the target (the voltage and current represent the absolute measured values corresponding to the distance), inductive proximity sensors are widely used in numerous applications.