1. Zero-power resistance
The zero-power resistance is the resistance value measured under specified temperature conditions, and the self-heating during measurement can be negligible.

2. Resistance at normal temperature
Zero power resistance value of PTC element at 25℃ ambient temperature.

3. Rate resistance at normal temperature
Nominal value of zero-power resistance value of PTC element at 25°C ambient temperature.

4. Curie temperature or switch temperature (T_c )
Cuire temperature is temperature that corresponds to R_Tc =2 ×R₂₅. When the temperature is reached, a step-like increase of PTC thermistor resistance is started. When specifically specified, it can also be defined as the temperature corresponding to the 2xRmin.

5. Rated response temperature or Sensing temperature(T_R)
Sensing temperature is temperature related to a defined resistance value in the steep region of R-T curve. At this temperature point, the system controlled by the PTC element is designed to start the action state, also commonly known as the temperature sensing point, and we control the range of resistance values corresponding to this temperature in the specification.

6.Surface temperature (T_s)
Ts is the temperature reached on the PTCR's surface when it has been operated at specified rated voltage and in a state of thermal equilibrium with the ambient for a prolonged period of time. The specifications in the data sheet section refer to an ambient temperature of 25 °C and are typical values.

7.Rated voltage (V_r)
The rated voltage V_r is the supply voltage lying below V_max.

8. Maximum operating voltage (V_max)
At the specified operating environment temperature, the maximum operating voltage is the highest voltage that continuously applies to thermistor and does not exceed maximum operating current.

9. Maximum link voltage (V_Lmax)
The maximum link voltage V_Lmax is the maximum DC voltage which can occur across the DC link or filter capacitor.

10. Insulation test voltage (For insulated ptc elements only)
The insulation test voltage is applied between the body of the PTCR and its encapsulation for a test period of 5s.

11. Maximum operating current  (I_max)
The maximum operating current I_max is the maximum current that the PTCR can withstand at the ambient temperature specified in the datasheet(still air, steady-state,high-resistance mode). The ambient temperature should fully consider the actual working conditions.

12. Residual current
The residual current is the current developed at applied maximum operating voltage V_max and at thermal equilibrium (steady-state operation). The currents specified in the datasheet refer to 25 °C.

13.Tripping current (I_T) or Switching current 
The tripping current is the lowest current that causes PTCR to trip to high resistance at specified temperature (Specified as 25℃ in the datasheet).

14. Non-tripping current (I_N) or Rated current
The non-tripping current is maximum current that PTCR keeps definitely in its low resistance condition at aspecified ambient temperature (Specified as 25℃ in the datasheet).

15. Switching time(t_s) or Operating time
The switching time is the time it takes at applied voltage for the current passing through the PTCR to be reduced to half of its maximum value. The values apply to 25 °C. it is possible to describe the PTC thermistor's switch-off behavior in terms of switching time.

16.Recovery time (t_r)
The recovery time is the time which the resistance value of PTC recovers to 2 times of R25 after applying specified voltage/time and the turned off. (Specified as 25℃ in the datasheet)

17. Power consumption (P)
The power consumed by the PTC element in the steady-state operating state when the maximum operating voltage is applied at the specified ambient temperature.

18. Withstanding Voltage (V_w)
At normal temperature, the PTC element can briefly withstand a voltage value exceeding the maximum operating voltage.

19. Breakdown voltage(V_BD)
V_BD is the limit voltage which PTC elements can withstand for a short time at specified ambient temperatures. Beyond V_BD the PTC thermistor no longer exhibits its characteristic properties.

20. Heat capacity(C_th)
It is the energy(joule) required for every 1K increase in the body temperature of the PTC element.

21. Thermal dissipation factor (δ)
Thermal dissipation factor refers to the quotient of the change of power dissipation in the PTC element and the temperature change of the corresponding resistor under specified environmental conditions (temperature, medium), expressed in W/K.

22.Response time
a) Response time due to changes in ambient temperature (t_a)
The PTC element temperature changes when the ambient temperature changes.The time required to change between two specific temperatures is the response time caused by changes in the ambient temperature. Such as a PTC temperature sensor.

b) Response time due to power change (t_p)
The response time tP is the time a PTC thermistor requires to recognize the change of power dissipation resulting from a change of the surrounding medium at applied voltage. After this period of time the residual currents assigned to the individual media become effective in the device.

24. Thermal time constant
The thermal time constant (ideal value) of a PTC element is the ratio of its thermal capacity/dissipation coefficient.
a) Thermal time constants caused by changes in the ambient temperature
When the PTC element is affected by the sudden change of the external ambient temperature, the time required for the temperature of the PTC element to change by 63.2% of the temperature difference between the beginning and the end.

b) Thermal cooling time constant
The thermal cooling time constant refers to the time necessary for an unloaded thermistor to vary its temperature by 63.2% of the difference between its mean temperature and the ambient temperature.

25. Operating temperature range
The ambient temperature range in which the PTC element can work continuously at the maximum operating voltage and maximum current.