Also known as linear sensor, displacement sensor is a device that belongs to the metal induction linear sensor is used to convert various measured quantities to electricity. In the process of production, displacement measurement generally divided into two physical dimensions and mechanical displacement measurement. According to the measured variable transformation, different kind of displacement sensor can be divided into analog and digital two kinds. Can be divided into the physical properties and structural analog two kinds. Displacement sensor is commonly used in the majority with analog structured, including the potentiometer displacement sensor, inductive displacement sensor, selsyn, capacitive displacement sensor and electric eddy current displacement sensor and hall displacement sensor, etc. An important advantage of digital displacement sensor is to facilitate the signal directly into a computer system. This kind of sensor has been developing rapidly, the application is becoming more and more widely.