1. Zero-power resistance value
　　The resistance value measured when the self-heating effect of a PTC element is negligible or very small during measurement at the specified ambient temperature.
　　
　　2. Room-temperature resistance value
　　The zero-power resistance value of the PTC component at an ambient temperature of 25°C.
　　
　　3. Rated Room-Temperature Resistance Value
　　The nominal value of the zero-power resistance of a PTC component at an ambient temperature of 25°C.
　　
　　4. Curie Temperature (also known as the Switching Temperature)
　　The temperature at which the resistance of a PTC element begins to increase sharply is defined as the temperature corresponding to twice the zero-power resistance at 25°C. When specifically specified, it may also be defined as the temperature corresponding to twice the minimum resistance value.
　　
　　5. Rated Operating Temperature (TR)
　　The nominal temperature at the step region of the resistance–temperature characteristic curve is the temperature at which the PTC element–controlled system is designed to begin operating; this temperature is also commonly referred to as the temperature-sensing point, and the specification typically defines a range for the resistance value corresponding to this temperature.
　　
　　6. Surface Temperature
　　The temperature reached by a PTC device when it has attained thermal equilibrium with its surrounding environment under the specified voltage is typically referenced in the datasheet to an ambient temperature of 25°C.
　　
　　7. Operating Voltage (also known as Rated Voltage)
　　It is typically equal to the line-supplied voltage and is lower than the PTC element’s maximum operating voltage.
　　
　　8. Maximum Operating Voltage
　　Under the specified ambient operating temperature, the maximum voltage that may be continuously applied to the PTC element without exceeding its maximum operating current is permitted.
　　
　　9. Maximum DC Link Voltage VLmax
　　The maximum voltage that may appear across the filter capacitor in surge current suppression applications at power-up.
　　
　　10. Insulation Voltage (applicable only to insulated PTC elements)
　　The maximum peak voltage that may be applied between the insulating protective layer/housing of a PTC device and any conductive surface under continuous operating conditions.
　　
　　11. Maximum Operating Current
　　The maximum current that a PTC device is permitted to carry under the specified operating ambient temperature when subjected to the maximum operating voltage.
　　
　　12. Residual Current
　　Under the specified ambient temperature (preferably 25°C), the current value of the PTC element when it reaches steady state, unless otherwise specified, is measured at the maximum applied voltage.
　　
　　13. Operating Current
　　The minimum current required to trigger the thermistor into a high-resistance state within a specified time, under the prescribed ambient temperature (preferably 25°C).
　　
　　14. Non-operation current
　　The maximum current that can be continuously passed through a thermistor while keeping it in a low-resistance state, under the specified ambient temperature (typically 25°C).
　　
　　15. Action Time
　　The time interval, at an ambient temperature of 25°C, from the moment current is applied to the PTC element until the current through the PTC element decreases from its maximum value Is to 0.5 times Is.
　　
　　16. Recovery Time
　　The time interval from the moment the PTC element is de-energized in its steady state at the maximum operating voltage, to the moment its resistance drops to twice its room-temperature resistance, under an ambient temperature of 25°C.
　　
　　17. Power Consumption
　　The power consumed by a PTC device in its steady-state operating condition when the maximum operating voltage is applied at the specified ambient temperature.
　　
　　18. Short-time overvoltage (also known as withstand voltage)
　　Under ambient temperature conditions, the voltage value that a PTC device can temporarily withstand exceeding its maximum operating voltage.
　　
　　19. Breakdown Voltage
　　At room temperature, the PTC element can withstand a maximum voltage for a short period; exceeding this voltage may cause the PTC element to fail.
　　
　　20. Heat Capacity
　　The amount of energy (in joules) required to raise the body temperature of a PTC element by 1 K.
　　
　　21. Dissipation coefficient (δ)
　　Under specified environmental conditions (temperature and medium), the ratio of the change in power dissipation in a PTC element to the corresponding change in its resistance temperature is defined as the dissipation coefficient (δ), expressed in watts per kelvin (W/K).
　　Response time
　　a) Response time (ta) caused by ambient temperature changes
　　When the ambient temperature changes, the temperature of the PTC element also changes. The time required for this change to occur between two specified temperatures is defined as the response time to ambient temperature variations.
　　b) Response time (tp) caused by power variation
　　Under two specified power-input conditions, the response time is the duration required for the PTC element’s temperature to transition between the two defined states, corresponding to the power-change-induced thermal response.
　　
　　22. Thermal Time Constant
　　The thermal time constant of a PTC element (in the ideal case) is the ratio of its thermal capacitance to its dissipation coefficient.
　　a) Thermal time constant caused by ambient temperature variations
　　When a PTC device is subjected to a sudden change in ambient temperature, the time required for its temperature to change by 63.2% of the total temperature difference between its initial and final states.
　　b) Thermal time constant due to cooling
　　The time required for a PTC element to cool in still air from its overtemperature condition to 63.2% of that overtemperature.
　　
　　23. Operating Temperature Range
　　The ambient temperature range in which the PTC component can operate continuously at its maximum operating voltage without exceeding the maximum operating current.