NTC thermistor is a kind of semiconductor ceramic assembly made of transition metal oxide as the main raw material by sintering at high temperature. Its resistance value changes with the change of ambient temperature, that is, under a certain measurement power, the resistance value decreases rapidly with the rise of temperature. Using this characteristic, the temperature of NTC thermistor can be determined by measuring its resistance value, so as to achieve the purpose of temperature monitoring and temperature controlling. So, what are the main technical parameters to refer to when selecting NTC thermistor?

First, zero-power resistance value(R_T)

At specified temperature, the value of resistance measured using the measured power that causes the change in resistance to be negligible in relation to the total measurement error.

Second, zero-power resistance R₂₅

This refers to the zero power resistance value measured at 25℃. Unless otherwise noted, it is the design resistance value of the thermistor and is also the nominal resistance value.

Third, B value is the thermal index of the NTC thermistor, which is defined as the ratio of the difference of the natural logarithm of the zero power resistance value at two temperatures to the difference of the reciprocal of the two temperatures.

Among them, R₁ is the zero power resistance at T₁, R₂ is the zero power resistance at T₂, T₁= 2731.5K +(T₁℃), T₂= 2731.5K +(T₂℃)

Unless otherwise noted, the B value is calculated from the zero-power resistance values at25℃ (298.15K) and 50℃ (323.15K), and is not a strict constant over the operating temperature range.

Fourth, dissipation factor(δ)

δ=ΔP/ΔT (mW/℃)

At specified temperature, the ratio of the rate of change of the thermistor's dissipated power to the corresponding temperature change. It represents the power consumed to raise the temperature of the thermal resistor body by 1℃. δ varies with the ambient temperature in the operating temperature range.

Fifth, thermal time constant (τ)

Under condition of zero power, the time required for the temperature difference between the beginning and the end of the thermistor temperature change when the temperature change occurs. τ is directly proportional to the heat capacity of thermistor C, and inversely proportional to its dissipation coefficient δ, i.e.:

τ=C/δ

Sixth, power rating

Rated power = dissipation factor δ × (maximum operating temperature T_max － 25℃)

Seventh, resistance/temperature characteristic

The resistance of NTC thermistor varies with temperature as follows:

R₁ is resistance value at absolute temperature T₁(K)

B is B value constant

T (K) =T (℃) + 273.15

EXSENSE Electronic Technology Co., Ltd. is a high-tech private enterprise specializing in the research, production, development and sales of various NTC thermistor, NTC thermistor chip and related materials. We can produce customized NTC thermistor according to customer requirements.