Thermistor is widely used in measuring the rate of energy flow in micro wave beams. The beams fall on a thermistor and heats it. A relatively small rise in temperature results in a very large change in resistance because, for a thermistor alpha is very high. By measuring the change in resistance, we can accurately measure micro wave power.
In a radio circuit, there will be several heater elements in series. A sudden change in the current through the circuit will damage the device. To prevent such a sudden surge of current, we place a thermistor with a high negative temperature coefficient of resistance, in series in the circuit. Initially, the thermistor is at cold state and hence has a very high resistance. This prevents the current to moderate level. Later, as the thermistor gets heated, its resistance decreases and it allows normal flow of current through the heater elements there by preventing surge. A thermistor can also be used as a thermostat.
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