Negative temperature coefficient thermistor

NTC negative temperature coefficient thermistor works(Metal Oxide Varistor)

NTC Negative Temperature Coefficient of abbreviations, the meaning of a negative temperature coefficient, refers to the negative temperature coefficient of semiconductor materials or components, the so-called NTC thermistor is a negative temperature coefficient thermistor device. It is based on metal oxides, such as manganese, cobalt, nickel and copper as a main material, and the ceramic manufacturing process made. These metal oxide materials have semiconductor properties, because the conductive way completely similar germanium, silicon and other semiconductor materials. The temperature is low, the number of these oxide material carriers (electron and hole) less, so its resistance value is high; as the temperature increases, the number of carriers increases, so the resistance value is lowered. The range of variation of the NTC thermistor at room temperature 10O ~ 1000000 ohms, the temperature coefficient of -2% to -6.5%. NTC thermistor NTC thermistors are widely used for temperature measurement, temperature control, temperature compensation.

NTC negative temperature coefficient thermistor(Metal Oxide Varistor)

NTC (Negative Temperature Coefficient) refers to the reduced resistivity exponential relationship, with a temperature rise phenomenon and material having a negative temperature coefficient thermistor. The material is sufficiently mixed with manganese, copper, silicon, cobalt, iron, nickel, zinc, and the like of two or more metal oxides, molding and sintering process is made of a semiconductor ceramic having a negative temperature coefficient, can be made (NTC) thermistor. Ratio, sintering atmosphere, sintering temperature, and the structural state of the resistivity and material constants with the material composition varies. Now also appears to the silicon carbide, selenium, tin, tantalum nitride, etc. as the representative of the non-oxide-based NTC thermistor material.

NTC thermistor semiconductive porcelain mostly spinel structure or other structure of the oxide ceramics, having a negative temperature coefficient, the resistance value can be approximated as:

Formula RT RT0 is the temperature T, T0 when the resistance value, Bn is a material constant. Ceramic grain changes due to temperature changes in the resistivity, which is determined by the semiconductor properties.

NTC negative temperature coefficient thermistor History

The NTC thermistor experienced long stage. 1834, the first time scientists have found that the characteristics of the negative temperature coefficient of silver sulfide. In 1930, scientists found that the cuprous oxide - copper oxide has a negative temperature coefficient of performance and the success of the use of in aviation instrument temperature compensation circuit. Subsequently, due to the continuous development of transistor technology, thermistor made significant progress. NTC thermistor developed in 1960.

NTC negative temperature coefficient thermistor temperature range

Its measurement range is generally -10 ~ +300 ℃, can also be done from -200 to +10 ° C, and even can be used for temperature measurement with +300 ~ +1200 ℃ environment.

The negative temperature coefficient thermistor thermometer accuracy can reach 0.1 ° C temperature sensing less time to 10s. It is not only applicable to the granary thermometer, also can be used in food storage, medicine and health, scientific farming, marine, deep wells, high-altitude, glacier temperature measurement.

Edit this paragraph NTC characteristic curve

  NTC characteristic graph

NTC characteristic graph(Metal Oxide Varistor)

[1]

Edit this paragraph jargon

NTC negative temperature coefficient thermistor jargon

Zero-power resistance value RT (Ω)

RT refers to the predetermined temperature T, caused by changes in the resistance value can be ignored without taking into account the measured power of the measured resistance values ​​with respect to the total measurement error.

The resistance value and the temperature changes in the relationship of the formula:

RT = RN expB (1 / T - 1/TN)

RT: NTC thermistor resistance when the temperature T (K).

RN: NTC thermistor resistance rated temperature TN (K).

T: predetermined temperature (K).

B: NTC thermistor material constant, known as thermal index.

exp: natural number e base index (e = 2.71828 ...).

This relationship is the empirical formula, only within the limited range of the nominal or rated temperature TN resistance RN having a reasonable degree of accuracy, because the material constant B itself is also a function of the temperature T.

Rated zero power resistance value of R25 (Ω)

Rated zero power resistance value of the NTC thermistor resistor R25 measured at the reference temperature of 25 ℃, the resistance value is NTC thermistor nominal resistance value according to the provisions of the GB. Commonly referred to as the NTC thermistor much resistance, and also refers to the value.

Material constants (thermal index) B value (K)

B value is defined as:

RT1: zero-power resistance value when the temperature T1 (K).

RT2: zero-power resistance value when the temperature T2 (K).

T1, T2: two specified temperature (K).

Common NTC thermistor B value range between 2000K ~ 6000K.

Zero power temperature coefficient of resistance (αT)

Zero Activity of relative change of the power resistance value of the NTC thermistor at a predetermined temperature, causing the ratio of the value of the temperature change of the change.

αT: zero power when the temperature T (K) resistance temperature coefficient.

RT: zero-power resistance value when the temperature T (K).

T: temperature (T).

B: material constants.

Dissipation factor (δ)

, NTC thermistor dissipation factor is the ratio of the corresponding temperature change of the power dissipated in the resistance change and the resistance body in a predetermined ambient temperature.

δ: NTC thermistor dissipation factor (mW / K).

The △ P: NTC thermistor consumption of power (mW).

△ T: the NTC thermistor consumption power △ P, the corresponding temperature change of the resistance body (K).

Thermal time constant (τ)

Zero-power conditions, When mutations temperature, the temperature of the thermistor changes the time required in the beginning not two temperature difference of 63.2%, the thermal time constant and the NTC thermistor is proportional to the thermal capacity, and its dissipation coefficient inversely proportional.

τ: thermal time constant (S).

C: NTC thermistor heat capacity.

δ: NTC thermistor dissipation coefficient.

Rated power Pn

Thermistor technical conditions prescribed long-term continuous work allowed power consumption. In this power, the resistor body temperature does not exceed its maximum operating temperature.

Maximum working temperature Tmax

Thermistor technical conditions prescribed long-term continuous work the maximum temperature allowed. Namely:

T0-ambient temperature.

Measuring power Pm

Thermistor at a predetermined ambient temperature of the resistive element by measuring current of the resistance change caused by heating with respect to the total measurement error is negligible power consumption.

General requirements for the resistance change is greater than 0.1%, then the measured power Pm is:

Resistance temperature characteristic

NTC thermistor temperature characteristics can be approximated by:

Formula:

RT: temperature T, the zero-power resistance value.

A: with the the thermistor material physical characteristics and geometry of the coefficient.

B: B values.

T: temperature (k).

The more accurate expression:

Formula:

RT: thermistor temperature T, the zero-power resistance value.

T: absolute temperature value, K;

A, B, C, D: for a specific constant.

R-T characteristics of the NTC negative temperature coefficient thermistor

B the same value, different resistance RT characteristic curve diagram

Same resistance and B value of the NTC thermistor RT characteristics curve diagram

Temperature measurement and control with NTC thermistor

Overall structure

Epoxy package series NTC thermistor

The glass encapsulation Series NTC thermistor

Application circuit schematics

Temperature measurement (Wheatstone bridge circuit)

Temperature control

Application Design

Electronic thermometer, electronic calendar, electronic clock temperature display, electronic gifts;

Heating and cooling equipment, heating thermostat electrical appliances;

Automotive electronic temperature measurement and control circuit;

Temperature sensor, temperature instrumentation;

Medical electronic equipment, electronic washing equipment;

Mobile phone batteries and charging appliances.(Metal Oxide Varistor)