For the front unit control system information collection, the role of the sensor is more and more important. As the signal processing technology and the rapid development of the microprocessor and computer technology and wide application, sensor as the measurement and control system structure of key components, its importance and the technical development degree is becoming more and more obvious, need to be in the development of sensor synchronous progress.

From a general point of view, sensor is a kind of can convert physical or chemical quantity to can handle the use of electrical devices. As defined by the international electrotechnical commission, the sensor measurement system is a front unit, its role is to convert the input variables available for measurement signal. Sensor is a part of the sensor system, is by measuring signal input of the first entry.

Many technical requirement is defined for the sensor, there is universally applicable to all sensor requirements, there are only apply to the special requirements of specific type sensor. The working principle and structure of the sensor in different occasions must meet the following requirements: high sensitivity, anti-jamming, linear, school approval of practicability, high precision, high reliability, no hysteresis effect, good durability, repeatability, anti-aging, high response speed, strong ability to resist environmental impact, optional, security, compatibility, low cost, wide measuring range, small volume, etc. From the point of energy conversion, sensors can be divided into boom in yellow and check Michael chu assisted two kinds. Passive sensors can not directly convert form of energy, but can control from another input input excitation energy; Active sensor can transform one form of energy into another form, does not need external energy.

According to the working principle of the sensor can be divided into two major categories of passive sensors and active sensors. Physical sensors is the application principle of physical effects, such as pressure effect and magnetostrictive phenomenon, thermoelectric, photoelectric and magnetoelectric effect, through these effects will be small changes in the quantity of measured signal into electrical signal; Chemical sensors including chemical adsorption, electrochemical reaction to the phenomenon such as sensors for the transformation relations, will be small changes in the measured signal into electrical signal. These sensors according to its USES can be roughly divided into gas sensors, vacuum sensor, biosensor, moisture sensor, magnetic sensor, acceleration sensor, ray radiation sensor, vibration sensor, thermal sensor, acceleration sensor, speed sensor, energy consumption of sensor, liquid level sensor, pressure sensor, position sensor, etc. If according to the output signal as a standard, and can be divided into: analog sensor, is used to convert the non-electric quantity being measured into analog signals; Digital sensors, used to convert measured the amount of the electrical signal into digital output signals; Switch sensor, when a measured signal reaches a certain threshold, the sensor output accordingly a set of low level or high level signal.