The working principle of NTC negative temperature coefficient NTC is the abbreviation of negative temperature coefficient, which means negative temperature coefficient, generally referring to semiconductor materials or components with large negative temperature coefficient. NTC thermistor is a negative temperature coefficient device. It is made of manganese, cobalt, nickel, copper and other metal oxides by ceramic technology. These metal oxide materials have semiconductor characteristics because they are completely similar to semiconductor materials such as germanium and silicon in conductivity. When the temperature is low, the number of carriers (electrons and holes) in these oxide materials is small, so their resistance value is high; With the increase of temperature, the number of carriers increases, so the resistance decreases. The temperature range of NTC thermistor at room temperature is 10O~ 100000 ohm, and the temperature coefficient is -2%~-6.5%. NTC thermistor can be widely used in temperature measurement, temperature control, temperature compensation and other fields. NTC negative temperature coefficient NTC (negative temperature coefficient 1 factor) refers to the thermistor phenomenon and the exponential decrease of resistance with the increase of temperature, which has a negative temperature coefficient. The material is made of manganese, copper, silicon, cobalt, iron, nickel, and semiconductor ceramics made by fully mixing two or more metal oxides such as zinc, molding and sintering. Thermistors with negative temperature coefficient (NTC) can be manufactured. Resistivity and material constant vary with material ratio, sintering atmosphere, sintering temperature and structural state. Now there are non-oxide NTC thermistor materials represented by silicon carbide, tin selenide and tantalum nitride. NTC thermistor ceramics are mostly oxide ceramics with spinel structure or other structures, which have negative temperature coefficient. The resistance value can be approximately expressed as: in the formula, RT and RT0 are the resistance values at temperatures t and T0, respectively, and Bn is the material constant. The resistivity of ceramic particles varies with temperature, which is determined by the characteristics of semiconductors. The development history of NTC negative temperature coefficient NTC thermistor has gone through a long period. In 5438+0834, scientists first discovered that silver sulfide has a negative temperature coefficient. 1930, scientists found that cuprous oxide-copper oxide also has a negative temperature coefficient, and it was successfully applied to the temperature compensation circuit of aviation instruments. Subsequently, due to the continuous development of transistor technology, the research of thermistor has made great progress. NTC thermistor was developed in 1960. The negative temperature coefficient temperature range of NTC is-10 ~+300℃, and it can also be -200 ~+ 10℃. It can even be used for temperature measurement at +300 ~+ 1200℃. The accuracy of negative temperature coefficient thermometer can reach 0. 1℃, and the temperature sensing time can be as short as 10s. It is not only suitable for granary thermometers, but also for grain storage, medicine and health, scientific breeding, ocean, deep well, high altitude, glaciers and so on.

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NTC characteristic curve [1]

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The technical term of NTC negative temperature coefficient, zero-power resistance value RT (ω) RT, refers to the resistance value measured with the measuring power that makes the change of resistance value negligible relative to the total measurement error at the specified temperature T. The relationship between resistance and temperature change is: rt = rnexpb (1/t–1/TN) rt: the resistance value of NTC thermistor at temperature T (K). Rn: resistance of NTC thermistor at rated temperature TN (k). T: specified temperature (k). The material constant of NTC thermistor is also called thermal sensitivity index. Exp: Exp based on natural number e (e = 2.7 1828 …). This relationship is an empirical formula, which has certain accuracy only in the limited range of rated temperature TN or rated resistance value RN, because the material constant B itself is also a function of temperature T. According to national standards, rated zero power resistance R25(ωω) is the resistance R25 measured by NTC thermistor at the reference temperature of 25℃, which is the nominal resistance value of NTC thermistor. What is the resistance of NTC thermistor? It also refers to this value. Material constant (thermal sensitivity index) b value (K) B value is defined as zero power resistance (k) at RT 1: temperature T 1. RT2: Zero power resistance at temperature T2 (K). T 1, T2: two specified temperatures (k). For commonly used NTC thermistors, the range of B value is generally between 2000 K and 6000 K. Zero power resistance temperature coefficient (α t) The ratio of the relative change of zero power resistance value of NTC thermistors to the temperature change value that causes this change at a specified temperature. αT: temperature coefficient of zero power resistance at temperature T (K). RT: zero power resistance at temperature T (K). T: temperature (t) B: material constant. Dissipation coefficient (δ) At the specified ambient temperature, the dissipation coefficient of NTC thermistor is the ratio of the power dissipated in the resistor to the corresponding resistance temperature change. Dissipation coefficient of NTC thermistor, (mW/ K). △ p: power consumed by NTC thermistor (mW). △ T: the temperature change corresponding to NTC thermistor when it consumes power△ P (K). Under the condition of thermal time constant (τ) and zero power, when the temperature suddenly changes, the temperature change of thermistor is 63.2% of the previous two temperature differences. The thermal time constant is directly proportional to the thermal capacity of NTC thermistor and inversely proportional to its dissipation coefficient. τ: thermal time constant (s). Thermal capacity of NTC thermistor. Dissipation coefficient of NTC thermistor. Rated power Pn The power that the thermistor can work continuously for a long time under the specified technical conditions. At this power, the temperature of the resistor itself will not exceed its maximum working temperature. Maximum operating temperature Tmax The maximum temperature allowed for long-term continuous operation of thermistors under specified technical conditions. I.e. T0- ambient temperature. Measuring power Pm thermistor At the specified ambient temperature, the resistance change caused by the resistance heated by the measuring current can be ignored compared with the total measurement error. Generally, the resistance change is required to be greater than 0. 1%, so the measured power Pm at this time is: resistance temperature characteristic. The temperature characteristics of NTC thermistor can be approximately expressed by the following formula: where: RT: zero power resistance at temperature t: coefficient related to physical characteristics and geometric dimensions of thermistor material. B: b value. T: temperature (k). A more accurate expression is: where: RT: zero power resistance value of thermistor at temperature t: absolute temperature value, k; A, b, c and d are specific constants. The negative temperature coefficient R-T characteristic B of NTC has the same value, but the R-T characteristic curves with different resistance values are the same. The R-T characteristic curves of NTC thermistors with different B values are schematic diagrams of temperature measurement and control. NTC thermistor shape structure epoxy package series NTC thermistor glass package series NTC thermistor application circuit schematic diagram temperature measurement (Wheatstone bridge circuit) temperature control application design electronic thermometer, electronic calendar, electronic clock temperature display, electronic gift; Heating and cooling equipment, heating thermostat; Automobile electronic temperature measurement and control circuit; Temperature sensor, temperature instrument; Medical electronic equipment, electronic toilet equipment; Mobile phone batteries and charging equipment.

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