The PRF series is a 0603 chip-size overheat-sensing PTC thermistor from Murata Manufacturing. The resistance value is 470 Ohm at 25°C and maintains an almost constant resistance value over normal room temperatures. From the above graph, you can see that as the temperature of the POSISTOR® increases, its resistance value ramps up to 4.7 kOhm on to 47 kOhm sharply. The sensing temperature is selected by the choice of Murata part number.