This sensor is a widely used in automatic control industry for non-contact detecting metal at the front tip of the sensor barrel. The signal would then switch a transistor to pull current into the black wire (NPN sinking type control). This sensor is an inductive type proximity switch. This sensor is commonly used for the axis limit switch (home position) as well as the auto-focus position sensor.
Specifications:
Signal Polarity: NPN Detection
Wire Type: 3 Wire Type (Brown=Voltage, Blue=GND, Black=Signal)