Thermistor is a sensitive component that has been developed early, with many types and more mature development. The thermistor is composed of semiconductor ceramic materials, and the principle is that temperature causes resistance to change. Because the semi-superconductor thermistor has a common function, it can be used as a measurement component (such as measuring temperature, flow, liquid level, etc.) because of the range in use, and it can also be used as a control component (such as a temperature sensor, a current limiter) and Path to make up components. Thermistors are widely used in household appliances, wind power, light industry, communications, military superstitions, aerospace and other fields, and their development prospects are extremely broad. Thermistor products mainly include: two series including negative temperature coefficient NTC thermistor and positive temperature coefficient PTC thermistor. We specialize in the production of KTY81, KTY83, KTY84, LPTC-2000, LPTC-1500, LPTC-1200, LPTC-1000, LPTC-500, LPTC-200 and other thermistor positive temperature sensor products, but there are often customers who consult our NTC thermal Sensitive resistance, so we make a distinction here:
PTC (Positive Temperature Coeff1Cient) refers to the thermistor phenomenon or material that has a positive temperature coefficient and a sharp increase in resistance at a certain temperature, which can be used as a temperature sensor. The material is a sintered body with BaTiO3 or SrTiO3 or PbTiO3 as the main component, which is doped with a small amount of oxides such as Nb, Ta, Bi, Sb, Y, and La for atomic valence control to make it semiconducting. Semiconductorized BaTiO3 and other materials are referred to as semiconducting (bulk) porcelain for short; at the same time, oxides of Mn, Fe, Cu, Cr and other additives that increase the positive temperature coefficient of resistance are added, and they are formed by general ceramic technology. High temperature sintering makes platinum titanate and its solid solution semiconducting, thereby obtaining a positive temperature thermistor material. Its temperature coefficient and Curie point temperature vary with the composition and sintering conditions (especially the cooling temperature).
Barium titanate crystal belongs to the perovskite structure, it is a ferroelectric material, and pure barium titanate is an insulating material. Adding trace rare earth elements to the barium titanate material, after proper heat treatment, the resistivity sharply increases by several orders of magnitude near the Curie temperature, resulting in the PTC effect. This effect is related to the ferroelectricity of BaTiO3 crystals and near the Curie temperature. The phase change of the material is related. Barium titanate semiconducting porcelain is a polycrystalline material, and there are inter-grain interfaces between the crystal grains. When the semiconducting porcelain reaches a certain temperature or voltage, the crystal grain boundary changes, and the resistance changes sharply.
The PTC effect of barium titanate semiconducting porcelain originates from grain boundaries (grain boundaries). For conducting electrons, the interface between the grains is equivalent to a potential barrier. When the temperature is low, due to the action of the electric field in the barium titanate, the electrons can easily cross the barrier, and the resistance value is small. When the temperature rises to near the Curie point temperature (that is, the critical temperature), the internal electric field is destroyed, which cannot indicate that the conductive electrons have crossed the barrier. This is equivalent to an increase in the potential barrier and a sudden increase in the resistance value, resulting in the PTC effect. The physical models of the PTC effect of barium titanate semiconducting ceramics include the sea view surface barrier model, the barium absence model of Daniels et al., and the superimposed barrier model. They provide reasonable explanations for the PTC effect from different aspects.
The PTC thermistor appeared in 1950, and then in 1954, a PTC thermistor with barium titanate as the main material appeared. PTC thermistors can be used for temperature measurement and control in industry, as well as for temperature detection and adjustment of certain parts of automobiles. They are also widely used in civilian equipment, such as controlling the water temperature of instantaneous boilers, air conditioners and cold storage, Use its own heating for gas analysis and wind speed machine and other aspects.
In addition to being used as a heating component, the PTC thermistor can also function as a "switch". It has three functions: a sensitive component, a heater, and a switch, and is called a "thermal switch." After the current passes through the component, the temperature rises, that is, the temperature of the heating element rises. When the Curie point temperature is exceeded, the resistance increases, thereby increasing the current, so the decrease of the current causes the temperature of the component to decrease, and the decrease of the resistance value makes the circuit The current increases, the temperature of the component rises, and it repeats itself, so it has the function of keeping the temperature in a specific range, and it also acts as a switch. Use this resistance to temperature characteristics to make a heating source, as heating components, heaters, electric soldering irons, drying wardrobes, air conditioners, etc., can also play a role in overheating protection for electrical appliances.
NTC (Negative Temperature Coeff1Cient) refers to the thermistor phenomenon and material whose resistance decreases exponentially as the temperature rises and has a negative temperature coefficient. The material is a semiconductor ceramic made of two or more metal oxides such as manganese, copper, silicon, cobalt, iron, nickel, zinc, etc., which are fully mixed, formed, and sintered, and can be made into a negative temperature coefficient (NTC) thermistor. Its resistivity and material constants vary with the material composition ratio, sintering atmosphere, sintering temperature and structural state. Now there are non-oxide NTC thermistor materials represented by silicon carbide, tin selenide, tantalum nitride, etc.
The development of NTC thermistor has gone through a long stage. In 1834, scientists discovered for the first time that silver sulfide has a negative temperature coefficient. In 1930, scientists discovered that cuprous oxide-copper oxide also has the performance of a negative temperature coefficient, and successfully used it in the temperature compensation circuit of aeronautical instruments. Subsequently, due to the continuous development of transistor technology, the thermistor research has made significant progress. NTC thermistor was developed in 1960, which is widely used in temperature measurement, temperature control, temperature compensation, etc.
Its measuring range is generally -10～+300℃, and it can also reach -200～+10℃.
The accuracy of the thermistor thermometer can reach 0.1°C, and the temperature sensing time can be as short as 10s or less. It is not only suitable for granary thermometers, but also for temperature measurement in food storage, medicine and health, scientific farming, oceans, deep wells, high altitudes, glaciers, etc.
The characteristics of NTC (negative temperature coefficient) thermistors are:
·No power consumption resistance
·The resistance decreases as the temperature rises
The response of NTC resistance to temperature changes is usually linear. When it is necessary to continuously linearly change the resistance and temperature, such as temperature compensation, temperature control system and inrush current limit, it is more appropriate to choose NTC thermistor.
The characteristics of PTC (Positive Temperature Coefficient) Thermistor are:
·No power consumption resistance
·The resistance increases with temperature
The PTC resistance will change slightly with the increase in temperature until it reaches the "switching point", after which the resistance value will increase by several orders of magnitude. PTC is generally suitable for fuse and heater applications with self-reset function.