Zero Power Resistance Value RT (Ω)
RT refers to the resistance value measured at a specified temperature T using a measured power that causes a negligible change in the resistance value relative to the total measurement error.
The relation between resistance value and temperature change of electronic components is as follows:
RT = RN expB(1/T – 1/TN)
RT: NTC thermistor resistance at temperature T (K).
RN: NTC thermistor resistance at rated temperature TN (K).
T: Specified temperature (K).
B: Material constant of NTC thermistor, also known as thermal sensitivity index.
exp: exponent based on a natural number e (e = 2.71828…) .
The relationship is empirical and has a degree of accuracy only within a limited range of rated temperature TN or rated resistance RN, since the material constant B is itself a function of temperature T.
Rated Zero Power Resistance R25 (Ω)
According to the national standard, the rated zero power resistance value is the resistance value R25 measured by the NTC thermistor at the reference temperature of 25 ℃. This resistance value is the nominal resistance value of the NTC thermistor. Usually said NTC thermistor how much resistance value, also refers to the value.
Material Constant (thermal sensitivity index) B value (K)
B values are defined as:
RT1: Zero power resistance at temperature T1 (K).
RT2: Zero power resistance value at temperature T2 (K).
T1, T2: Two specified temperatures (K).
For common NTC thermistors, B value ranges from 2000K to 6000K.
Zero Power Resistance Temperature Coefficient (αT)
The ratio of the relative change in the zero-power resistance of an NTC thermistor at a specified temperature to the temperature change that causes the change.
αT: zero power resistance temperature coefficient at temperature T (K).
RT: Zero power resistance value at temperature T (K).
T: Temperature (T).
B: Material constant.
Dissipation Coefficient (δ)
At a specified ambient temperature, the dissipation coefficient of NTC thermistor is the ratio of the power dissipated in the resistor to the corresponding temperature change of the resistor.
δ : dissipation coefficient of NTC thermistor, (mW/ K).
△ P: Power consumed by NTC thermistor (mW).
△ T: NTC thermistor consumes power △ P, the corresponding temperature change of the resistor body (K).
Thermal Time Constant of Electronic Components (τ)
Under zero power conditions, when the temperature changes abruptly, the thermistor temperature changes the time required for 63.2% of the first two temperature differences. The thermal time constant is proportional to the heat capacity of the NTC thermistor and inversely proportional to its dissipation coefficient.
τ : thermal time constant (S).
C: Heat capacity of NTC thermistor.
δ : dissipation coefficient of NTC thermistor.
Rated Power Pn
The allowable power consumption of a thermistor in continuous operation for a long time under specified technical conditions. Under this power, the resistance body temperature does not exceed its maximum operating temperature.
Maximum operating temperature Tmax: the maximum temperature at which thermistor can operate continuously for a long time under specified technical conditions. That is, T0- Ambient temperature.
Electronic components measure power Pm
At the specified ambient temperature, the resistance value of the resistance body heated by the measurement current can be ignored in relation to the total measurement error. It is generally required that the resistance value change is greater than 0.1%.
Post time: Mar-29-2023