NTC Temperature Characteristics Symbol:
R = Ro exp {B (I / T-I / To)}
R: resistance value at temperature T (K)
Ro: Resistance value at temperature T0 (K)
B: B value
* T (K) = t (ºC) +273.15
In fact, the B value of the NTC thermistor is not constant,Its size varies depending on the material composition,Maximum up to 5K / ° C.So in the larger temperature range should be used when the formula 1,There will be some error between the measured value.
Here, when the value of B in Equation 1 is calculated using the temperature function of Equation 2,It can reduce the error between the measured value,It can be considered approximately equal.

(Equation 2) BT = CT2 + DT + E

In the above formula, C, D, E are constants.In addition, the fluctuation of the B value due to the difference in the production conditions causes the constant E to change,But the constant C, D unchanged.Therefore, when discussing the fluctuation of the B value,Just consider the constant E.

• Calculation of constants C, D, and E The constants C, D, and E can be expressed by four (temperature, resistance) data (T0, R0). (T1, R1). (T2, R2) and (T3, R3) Calculated by formulas 3 to 6.
First, by the pattern 3 according to T0 and T1, T2, T3 resistance to find B1, B2, B3, and then into the following models.


• NTC resistance value calculation example:
According to NTC thermistor - temperature characteristics table,The NTC resistance at 25 ° C is 5 (kΩ)，B value deviation of 50 (K) thermistor in the 10 ° C ~ 30 ° C resistance.
• Steps
(1) According to the resistance - temperature characteristics table, find the constant C, D, E.
To = 25 + 273.15 T1 = 10 + 273.15 T2 = 20 + 273.15 T3 = 30 + 273.15
(2) into BT = CT2 + DT + E + 50, seeking BT.
(3) substituting a value R = 5exp {(BTI / T-I / 298.15)}, seeking R.
* T: 10 + 273.15 ~ 30 + 273.15

• NTC resistance-temperature characteristics shown in Figure 1