PR12 4DN Autonics PR12-4DN Inductive Proximity Sensor – 4mm is the most common and affordable solution for no-touch object detection. The most commonly-used proximity sensor is the inductive type, which generates an electromagnetic field to sense metal objects passing close to its face. This is usually the easiest sensing technology to apply in applications where the metal object to be detected is within an inch or two of the sensor face. Note that the standard detecting distance is based on a standard shape approaching the sensor in a standard way. The real detecting distance will vary depending on the shape, thickness, and type of metal being detected and will in general be between 70 to 80% of the standard distance.