The dissipation constant is the amount of power dissipation in a given thermistor (expressed in milliwatts) that will result in a ~1° Celsius increase in the thermistor body temperature due to power dissipation when the sensor is in still air. The dissipation constant for standard Littelfuse thermistors is noted on the product data sheet and is typically 1-2 milliwatts per degree C. The dissipation constant increases substantially (up to 400%) when the sensor is encased in a probe assembly, mounted to a thermally conductive surface, and/or subjected to an environment such as moving air or water. When using thermistors for temperature measurement and control applications, consideration must be made to limit the power dissipation to a level whereby the body temperature isn’t significantly increased due to “Self-Heating”. Excessive self heating occurs when the power dissipated in the sensor results in an unacceptable temperature rise above the ambient. Littelfuse’s application engineers can provide the dissipation constant data for any Littlefuse thermistor or thermistor probe assembly.