Thermistor

A thermistor is a thermally sensitive semiconductive resistor whose resistance changes with its temperature.

    Negative Temperature Coefficient Thermistor

NTC thermistor is a kind of ceramic semiconductive thermal sensitive crystal sintered from manganese, cobalt, nickel-based variety of metal oxides, whose zero-power resistance decreases while its temperature increases.

    Zero-power Resistance(R_T)

The zero-power resistance of a thermistor is the direct current resistance value measured at a specified temperature “T” with power dissipation by the thermistor low enough that any further decrease in power will result in less than 0.1% change in resistance.

    Material Constant(B)

B constant is a value calculated by the following formula under two specified ambient temperature (Expressed in degrees kelvin K):

B=Ln(R₁/R₂)/(1/T₁-1/T₂)

The reference temperature used in this formula for determining B constant of QAM thermistor is 298.15K and 323.15K or 358.15K.Generally B=2000～6000K, the greater the B constant is, the greater the resistance change rate per 1℃ is.

    Dissipation Factor (δ)

The dissipation factor is the required power which makes the NTC thermistor body temperature raise 1℃ through self-heated, normally expressed in milliwatts per degree Celsius (mW/℃). It can be calculated by the following formula:

δ = V×I / (T-T₀)

    Thermal Time Constant(τ)

The thermal time constant is the time required for a thermistor under zero-load condition to change 63.2% of total difference between its initial and final body temperature when the ambient temperature changed dramatically, normally expressed in second(S).