What are the principles and characteristics of the sensitive resistor in the sensitive element
What are the principles and characteristics of the sensitive resistor in the sensitive element
Sensitive element is an important part of sensor. It is a special electronic element that can sensitively feel some physical, chemical and biological information and convert it into electrical information.
Such components are usually made by using some sensitive effect of materials. Sensitive elements can be named according to the input physical quantities, such as thermal (see thermistor), photosensitive, (electric) pressure (pressure) force sensitive, magnetic sensitive, gas sensitive and humidity sensitive elements. Using sensitive elements in electronic devices to sense external information can achieve or exceed the function of human sensory organs. The sensitive element is the core element of the sensor. With the rapid development of computer and information technology, the importance of sensitive components is increasing.
Sensitive resistor is a kind of sensitive element. Most of these resistors are particularly sensitive to certain physical conditions. As soon as the physical conditions change, the resistance value will change. It can usually be used as a sensor, such as photosensitive resistance, humidity sensitive resistance, magnetoresistance and so on. Thermistors and varistors are widely used in circuit design, which are often used as protective devices.
In terms of thermistors, PTC is a positive temperature coefficient resistor. There are usually two kinds: one is ceramic material, called CPTC, which is suitable for high voltage and high current occasions; The other is high polymer material, called PPTC, which is suitable for low voltage and low current occasions.
Ceramic PTC, whose resistance material is a kind of polycrystalline ceramics, is sintered from a mixture of barium carbonate, titanium dioxide and other materials. PTC temperature coefficient has strong nonlinearity. When the temperature exceeds a certain threshold, the resistance will become large, which is equivalent to an open circuit, so it can play the role of short circuit and overcurrent protection.
The second is varistor, which is usually metal oxide varistor, namely metal oxide varistor (MOV). Its resistance material is zinc oxide particles and ceramic particles mixed and sintered together. The characteristic of MOV is that when the voltage exceeds a certain threshold, the resistance drops rapidly and can pass large current, so it can be used for surge protection and overvoltage protection.
A multilayer varistor, MLV, is made of zinc oxide ceramics by a process similar to MLCC. MLV package is small, usually in sheet form, and its rated voltage and current capacity are much smaller than mov. It is suitable for low-voltage DC occasions.
In addition, there are photosensitive resistors. Photosensitive resistor refers to a sensitive element whose resistance value changes with the intensity of incident light (generally refers to visible light).
Generally, when the incident light is enhanced, the resistance value decreases. The response of photosensitive resistor to incident light is related to the wavelength of light and the material used.
The materials used to make photosensitive resistors are mainly cadmium compounds, such as cadmium sulfide, cadmium selenide and their eutectic - cadmium sulfide selenide. Secondly, there are germanium, silicon, zinc sulfide, etc. Photosensitive resistors are used in light intensity control, light electric automatic control, light electric switch, light electric counting, light electric safety protection and smoke alarm.