Inductive pressure sensor to detect metal objects, common application for mechanical positioning; Capacitive pressure sensor can detect metal and non-metallic objects (including liquid), commonly used for liquid level detection, etc.; By using infrared photoelectric sensor as the light source, has the reaction speed, high precision, detection distance, the characteristics of common application for conveyor belt object detection, etc.; Optical fiber sensor is composed of optical fiber amplifier and fiber catheter, have characteristics such as testing method, more accurate detection of many specifications, commonly used in the occasion of the high precision and small objects. A variety of different sensors advantage, choose need combined with specific application environment in the process of choosing appropriate stability of the sensor.