Definition and calculation formula of thermal time constant of NTC thermistor.Microwave Sensor Manufacturing

　　As defined by IEC 60539, an NTC (Negative Temperature Coefficient) thermistor is a thermally sensitive semiconductor resistor whose resistance decreases as the temperature increases. It has a very large negative temperature coefficient, and the resistance value varies with ambient temperature or self-heating due to passing current. Using this feature, the NTC thermistor can be used to determine the corresponding temperature by measuring its resistance value, so as to achieve the purpose of detecting and controlling the temperature. 

　　3 main features of NTC thermistor:

　　1. Determine the sensitivity to temperature.

　　2. Sensitivity to power input.

　　3. Sensitivity to changes in thermal conductivity.

　　Definition of thermal time constant of NTC thermistor:

　　Under zero conditions, the time it takes for a thermistor temperature sensor to change 63.2% of the total difference between the initial and final temperature; when subjected to a step function temperature change. How long it takes for a thermistor to recover to 50% of its original resistance.

　　The thermal time constant is proportional to the thermal capacity of the NTC thermistor and inversely proportional to its dissipation factor.

　　The formula for calculating the thermal time constant of NTC resistors:

　　τ: Thermal time constant (S).

　　C: Thermal capacity of the NTC thermistor.

　　δ: Dissipation coefficient of NTC thermistor.

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