Glossary of PTC Thermistor

Resistance-Temperature characteristic (R-T) characteristic： Resistance-temperature characteristic means the relation of zero power resistance of PTC thermistor to PTC thermistor body temperature under a specified voltage

Rated zero power resistance: resistance value of PTC thermistor measured at 25℃,
Minimum resistance （Rmin）: the minimum resistance in temperature curve starting from temperature25℃, and the corresponding temperature is Tmin corresponding to Rmin.
Switch temperature: The temperature at which the resistance value of PTC thermistor increases to twice Rmin, also called Curie temperature. From the switch temperature, resistance increases sharply.
Maximum operating voltage (Vmax): The maximum voltage that PTC thermistor can continuously endure at maximum permissible ambient temperature.
Maximum current （Imax）: The maximum current permissible to flow through PTC thermistor under maximum operating voltage.
Non trip current (Int):The maximum current that won’t cause PTC thermistor into high resistance state at the stipulated time and temperature, also called rated current, or hold current.
Trip current (It): The minimum current that causes PTC thermistor into high resistance sharp increasing under stipulated time and temperature.
Temperature range under maximum voltage: Operating ambient temperature range that PTC thermistor can continuously operate under maximum voltage.
Dissipation factor （δ）: The ratio of power dissipation change to corresponding temperature change mw/℃. δ=P/（T-Tr）
Breakdown voltage: The maximum voltage that PTC thermistor can bear under stipulated time and temperature. PTC thermistor will breakdown exceeding this voltage.
Thermal Time Constant （τ） is the time required for PTC thermistor to change 63% of the difference between its initial and final temperature. τ= C/δ
Residual current ( Ir)： current under heat balance state, after PTC thermistor resistance increases sharply, under maximum operating voltage.

T₁、T₂ corresponding to R₁、R₂,10℃,25℃higher than curie temperature separately.
Temperature at minimum resistance （TRmin）： Temperature corresponding to minimum resistance.
Upper category temperature: Maximum ambient temperature that PTC thermistor can operate continuously.
Low category temperature: Minimum ambient temperature that that PTC thermistor can operate continuously.

Voltage-Current characteristics
Voltage-current characteristic means the relation of voltage across PTC thermistor to current under stable condition with thermal balance. (As shown in the following fig.)

Insulation thermistor: thermistor that satisfy stipulated insulation resistance and voltage test requirement.
Non-insulation thermistor: thermistor that does not require insulation voltage and insulation resistance test.
Ininital current (Iin): the current that appears instantaneously in circuit switch starting to closing.

Peak-peak value of initial current.
Current-Time characteristic means current change characteristics vs. time with voltage on.