Sensor is an important part of various instruments. It is the primary link to realize automatic detection and automatic control. So, what are the types and functions of sensors?
1、 Types of sensors
In production and life, the types of sensors mainly include:
1. Optical sensor
The optical sensor uses the photoconductive effect or photovoltaic effect of semiconductor. Photovoltaic effect is to detect the voltage or current generated at the semiconductor pn junction as an output through light irradiation. Such as photosensitive secondary tube, photosensitive tertiary tube, etc. These effects take advantage of the quantum properties of light. The most common application example is the light controlled lamp.
2. Temperature sensor
Among the physical effects used to detect temperature, in addition to the thermocouple using Seebeck effect, the resistance of metal and oxygen semiconductors such as Pt and W, non oxide semiconductors and organic semiconductors changing with temperature are usually used as temperature sensors. In addition, there are sensors that use the change of current voltage characteristics at PN junction with temperature, the change of magnetic characteristics and dielectric constant near Curie temperature, and the change of dielectric constant and piezoelectric constant to detect the change of resonance frequency, such as the temperature control of common air conditioners.
3. Pressure sensor
Most pressure sensors use some kind of piezoresistive effect. Piezoresistive effect means that when pressure is applied to the resistor, its resistance value will change. This phenomenon is called piezoresistive phenomenon, which is much more obvious than the change of metal resistance, mainly due to the change of electron or hole mobility after pressure. More common applications are electronic scales.
4. Magnetic sensor
The common effects of magnetic sensors are Hall effect and magnetoresistance effect. The element using Hall effect is a Hall element, which applies a current between the two ends of a half conductor sheet. If a magnetic field is applied in the vertical direction of the sheet, the carrier will move in the direction perpendicular to the magnetic field direction under the action of Lorentz force. If an electrode is set in this direction, the voltage (Hall voltage) can be detected. Typical applications, such as speed regulation method of electric vehicle.
5. Gas sensor
The gas sensor is actually a semiconductor gas sensor. It is mainly the adsorption effect of gas. For example, the gas sensor made of semiconductor SnO2 is polycrystalline. When gas molecules are adsorbed on the surface, electron exchange will occur between the gas molecules and the sintered body. The potential barrier at the grain interface controlling the carrier movement will change. If two electrodes are arranged on the sintered body, the resistance between them will increase or decrease with the adsorption of gas molecules. Generally, the resistance value will decrease in reducing gas and increase in oxidizing gas. The most common application example is a variety of smoke alarms.
2、 Function of sensor
What is the function of the sensor? The sensor is actually a functional block, which converts various signals from the outside into electrical signals. The signal detected by the sensor has increased significantly recently, so its variety is also extremely wide.
In order to detect and control a variety of signals, it is necessary to obtain signals that are as simple and easy to process as possible. Such requirements can only be met by electrical signals. Electrical signals can be easily amplified, fed back, filtered, differentiated, stored, remotely operated, etc. Therefore, as a function block, the sensor can be narrowly defined as “a kind of element that converts the external input signal into an electrical signal.”