Thermistors change resistance with a change in temperature. They do not amplify, rectify, polarize or generate a signal. The thermistor temperature may be changed by the surrounding temperature or by self-heating the thermistor by passing a current through it.Most applications such as temperature measurement and control or copper coil compensation require that the power dispersed in a thermistor be kept to a minimum so as not to perceptibly self-heat the thermistor. Other applications depend entirely on the self-heating effect. When the surrounding temperature is fixed, the resistance of a thermistor is largely a function of power being dispersed within it, raising its temperature above its environment. Under these operating conditions, the temperature may rise 100 °C to 200 °C [121 °F to 392 °F] and the resistance may be lowered to 1/1000th of its original value at low current.This self-heating characteristic provides a whole field of uses for the thermistors. In the self-heat state it is thermally sensitive (its resistance will be changed) to any condition, changing the rate at which heat is conducted away from it. If the rate of heat removal is ideally fixed, then the thermistor is sensitive to power input and suited for use in voltage or power level control applications.