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Thermal Dissipation Constant

The thermal dissipation constant δ indicates the amount of power required for a thermistor to heat itself up by 1℃ when it is energized in still air (mW/℃).
When a power W is applied to the thermistor at an ambient temperature Ta and the temperature of the thermistor finally reaches a temperature T, the following equation is established.

Applying a power equivalent to the thermal dissipation constant makes a thermistor heat itself up by 1℃. This causes an error between the measured and the actual ambient temperatures.
Therefore, it is necessary to design circuitry to minimize the power to be applied so that measurement errors caused by thermistor’s self-heating are eliminated.
The thermal dissipation constant δ is determined by a balance between “self-heating” and “heat dissipation.” As a result, it varies substantially depending on the thermistor’s surroundings.
Placing materials that have a high thermal conductivity around the thermistor promotes heat release and increases the constant δ.
On the contrary, the construction allowing heat to accumulate decreases it. Therefore, it is essential to select appropriate materials in assembling your thermistor.
It is also important, after assembling your thermistor, to measure the constant δ in its operation environment (air, water, oil, hot plate etc.) to see that the constant meets your requirement.

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