| Technical information |
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| Definitions: |
What is an NTC Thermistor ? --- Negative Temperature Coefficient Thermistor. |
NTC Thermistors are electronic components which reduce the resistance when the temperature increases. |
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| Feautures: |
Sintered ( upto1400℃ ) non-oxide 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. |
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| 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/T-1/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. |
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| Four constants that determine thermistor characteristics: |
Basically, characteristics of a thermistors is represented by four constants: resistance R, B constant B, thermal dissipation constant and thermal time constant . |
| Zero-power resistance ( R T ) |
| The zero-power 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 zero-power resistance ( R25 ) |
| The rated zero-power resistance is the nominal value at the standard temperature of 25℃ no other specified.. |
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| 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/T-1/T0) R: Resistance when ambient temperature is T(K), R0: resistance when the ambient temperature is T0 (K) |
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| 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. |
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| 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 zero-power conditions in thermally stable environments. |
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