This Tube Type Inductive Proximity Sensor Detection Switch NPN DC6-36V 4mm Normally Open switch LJ12A3-4-Z/BX is a component widely used in automatic control industry for detecting, controlling, and non-contact switching. When the proximity switch is close to some target object, it will send out control signal.
 
When the metal approaches near-proximity switch sensing area, an Edy Current is induced in metal. Which in turn disturbs the magnetic field produced by the Inductive Proximity Sensor. This change is sensed by the sensor.
 
This 4mm proximity sensor can detect a variety of metals, miniature size, long life, low price, shielded type installation, anti-interference ability, 1mm detection distance, using for precise positioning of molds, precision machine tools, and robots.