hat is NTC Thermistor?

NTC:Negative Temperature Coefficient

    負溫度係數(shù)

Thermistor:Thermally Sensitive Resistor      [A]、非線性的溫度特性       [B]、Y軸爲(wèi)對數(shù)座標(biāo)時

    熱敏電阻                                                           接近實際的溫度特性

NTC特性：NTC的阻值隨溫度升高而減小。 

NTC熱敏電阻是一種以過渡金屬氧化物爲(wèi)主要原材料經(jīng)高溫?zé)Y(jié)而成的半導(dǎo)體陶瓷元件，它具有大的負溫度係數(shù),電阻值隨環(huán)境溫度或因通過電流而産生自熱而變化，即在的測量功率下，電阻值隨著溫度上升而下降。利用這一特性，可將NTC熱敏電阻通過測量其電阻值來確定相應(yīng)的溫度，從而達到檢測和控制溫度的目的。

Thermistor is a semiconduing ceramic resistor produced by sintering the materials at high temperature and made mainly from metal oxide. NTC thermistors are resistors with large negative temperature coefficient. Change in resistance of the NTC thermistors can be brought about either externally by a change in ambient temperature or internally by self-heating resulting from a current flowing through the device. At certain measure power, its resistance reduce rapidly while the temperature getting increase. Taking advantage of this charaeristic, it can achieve the deteing and controlling temperature purpose.

1. 功率電阻值R_T  Zero-power resistance (R_T)

在規(guī)定溫度下，採用引起電阻變化相對於總的測量誤差來說可以忽略不計的測量功率測得的電阻值。

The zero-power resistance is the value of a resistance when measured at a specified temperature, under conditions such that the change in resistance due to the internal generation of heat is negligible with respe to the total error of measurement.

2、功率電阻R₂₅    Rated zero-power resistance R₂₅

指25℃時測得的功率電阻值。除非特別指出，它是熱敏電阻器的設(shè)計電阻值，也是標(biāo)稱電阻值。The rated zero-power resistance is the nominal value at the standard temperature of 25℃unless otherwise specified.

3、B值   B constant in Kelvin’s (K)  

B值是負溫度係數(shù)熱敏電阻器的熱敏指數(shù)，它被定義爲(wèi)兩個溫度下功率電阻值的自然對數(shù)之差與兩個溫度倒數(shù)之差的比值。

B constant is an index of the thermal sensitivity expressed by the formula:

R_T1--溫度爲(wèi)T₁時的功率電阻Resistance in ohms ( ) at temperature T1

R_T2--溫度爲(wèi)T₂時的功率電阻值Resistance in ohms ( ) at temperature T2

T₁=298.15k +( T₁℃), T₂=358.15k(T₂℃)

除非特別指出，B值是由25℃（298.15K）和50℃（323.15K）的功率電阻值計算而得到的，B值在工作溫度範(fàn)圍內(nèi)並不是一個嚴格的常數(shù)。

4、耗散係數(shù)δ   Dissipation faor(δ)

δ=ΔP/ΔT(mW/℃)

即：在規(guī)定的環(huán)境溫度下，熱敏電阻器耗散功率變化率與其相應(yīng)溫度變化之比。它表示使熱能電阻體升高1℃溫度所需消耗的功率。在工作溫度範(fàn)圍內(nèi)，δ隨環(huán)境溫度變化而有所變化。

Dissipation faor (δ) is power in milliwatts required to raise thermistor temperature 1℃.Measured with thermistor suspended by its leads in a specified environment.

5、熱時間常數(shù)τThermal time constant (τ)

在功率條件下，當(dāng)溫度發(fā)生突變時，熱敏電阻體溫度

變化了始末溫度差的63.2%所需的時間。τ與熱敏電阻

器的熱容量C成正比，與其耗散係數(shù)δ成反比，即：

τ=C/δ

Thermal time constant (τ) is the time required by a thermistor to change 63.2% of the difference between its initial and final temperature. Measured with thermistor suspended by its leads in specified environment.

6、額定功率P_r      Power rating

  額定功率=耗散係數(shù)δ×（使用溫度T_max－25℃）

Rated power=heat dissipationfaorδ×(maximum operating temperature－25℃)

7、阻-溫特性Resistance/temperature charaeristic

The relationship between the zero-power resistance of a thermistor and its body temperature. The resistance law follow approximately the formula:

熱敏電阻的阻值隨溫度變化的規(guī)律，大體如下：

R1 :在絕對溫度T1(K)下的阻值

                       Resistance value at absolute temperature T1 (K)

B :B常數(shù)

B constant

T(K)=T(℃)+273.15

(1)B值相同，阻值不同                          (2)相同阻值，B值 不同