Explanation of terms related to power type NTC thermistor
Zero power resistance value RT (Ω)
When the RT is at the specified temperature T, the resistance value measured by the measured power that causes the change in the resistance value to be negligible relative to the total measurement error is used.
Zero-power resistance temperature coefficient (αT)
The ratio of the relative change in the NTC thermistor's zero-power resistance value to the temperature change value that caused the change at a specified temperature.
The maximum power dissipation P(max)
The maximum power dissipation is the maximum power that the thermistor can apply for a long time at an ambient temperature of 25 degrees Celsius.
Rated zero power resistance R25(Ω)
The rated zero-power resistance is the zero-power resistance measured at an ambient temperature of 25 °C.
Dissipation coefficient δ
The ratio of the rate of change of the thermistor's dissipated power to its corresponding temperature change at the specified ambient temperature. It represents the power required to raise the thermal resistor by 1 °C. In the operating temperature range, δ varies with ambient temperature.
Where: UTH is the terminal voltage of NTC; ITH is the current flowing through NTC; Tb is the self-heating stable temperature; Ta is the indoor temperature.
It can be seen that the rise in NTC temperature refers to the self-heating temperature. From another point of view, the temperature rise caused by self-heating can be calculated using δ.
Generally speaking, the larger the value, the better the heat dissipation performance. Its unit mW / ° C, which means the power required to increase the temperature of the thermistor by 1 ° C.
Regardless of whether you use NTC resistors for temperature measurement, temperature control, temperature compensation, or suppression of inrush current, the greater the dissipation factor, the better the heat dissipation and the faster the response speed.
Thermal time constant τ
Thermal time constant τ at zero power, when the temperature changes suddenly,
The temperature of the thermistor body changes the time required for 63.2% of the difference between the temperature and the temperature. τ is proportional to the heat capacity C of the thermistor and inversely proportional to its dissipation coefficient δ