Technical information 


Definitions: 
What is an NTC Thermistor ?  Negative Temperature Coefficient Thermistor. 
NTC Thermistors are electronic components which reduce the resistance when the temperature increases. 

Feautures: 
Sintered ( upto1400℃ ) nonoxide ceramic made of manganese (Mn) , nickel (Ni) , cobalt (Co) , and other 
element are used as the material of NTC Thermistors. An electrode is formed in this ceramic. 
The lead type and chip type are common appearance shapes. 

Resistance  Temperature Characteristic: 
The resistance value of NTC Thermistors decreases exponentially to the temperature increases, as shown in 
the following figue. 
Since the resistance value of NTC Thermistors can be expressed by the following formula, it is widely used as 
a temperature sensor. RT=R0expB(1/T1/T0) 
In the formula, RT is the resistance value when the ambient temperature is T (K) ,R0 is the resistance when 
the ambient temperature is T0 (K) , and B is the constant called the B constant. In addition, the B constant 
indicates a slope of the change in resistance value of the NTC Thermistor due to a temperature change , 
and is the basic characteristic of an NTC Thermistor. 
Note that since the B constant changes slightly with the temperature, the value of the B constant changes by 
the defined temperature. 


Four constants that determine thermistor characteristics: 
Basically, characteristics of a thermistors is represented by four constants: resistance R, B constant B, thermal dissipation constantand thermal time constant. 
Zeropower resistance ( R T ) 
The zeropower resistance is the value of a resistance when measured at a specified temperature, under conditions such that the change in resistance due to the internal generation of heat is negligible with respect to the total error of measurement. 
Rated zeropower resistance ( R25 ) 
The rated zeropower resistance is the nominal value at the standard temperature of 25℃ no other specified.. 

B Constant 
The constant which shows the change in the resistance calculated by the following formula using the resistance at 2 points at a specified ambient temperature. B=ln (R/R0) / (1/T1/T0) R: Resistance when ambient temperature is T(K), R0: resistance when the ambient temperature is T0 (K) 

Dissipation constant ( δ ) 
The dissipation constant is the quotient (in W/K), at a specified ambient temperature in a specified medium of a change in power dissipation in a thermistor to the resultant body temperature change. 

Thermal time constant ( τ ) 
The time (in sec) required for a thermistor to change its body temperature by 63.2% of a specific temperature span when the measurements are made under zeropower conditions in thermally stable environments. 

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