Description:
A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation, and looks for changes in the field or return signal.
 
Applications
Due to their reliability and efficiency, inductive proximity switches are used whenever a metal object has to be detected within just a few millimeters:
Presence detection of a machine component
Ultra precise referencing of the zero position of a moving machine component (e.g. in robotics)
Detection of different positions (e.g. limit switches)
Counting metal objects (e.g. in component feed or conveyor technology)
Presence detection of objects in process
Rotary speed measurement on metal gear wheel
 
Specifications: 
Detection distance: 4mm
Voltage: DC 6-36V
Polarity: NPN  NO
current: 150ma
Dimention: 12 x 50mm
Black wire or gray wire Length:about 1m
Package include: 1 x LJ12A3-4-Z/BX