DC Fan speed control problem

"DC Fan" operation with the changed conditions of heat, operate at a slower speed, a DC fan will produce less noise and consumes less energy. In most design requirements, after a few hours running speed DC fans air temperature is usually lower than the maximum design temperature values. Position sensors installed on the choice should pay attention to the sensor in the proper position, as far as possible so that the sensor can be clamped directly in the surface to be cooled. In operation, a temperature-controlled fan will run at a faster rate if the thermistor feel at higher temperatures; while at lower temperatures, it will operate at low speed; in these higher and lower intermediate, fan speed will hardly due to temperature change. When the temperature changes slow the fan speed of the fan also changes slowly, not suddenly change the fan speed and noise. The reaction time depends mainly on the length of its sensor for sensing heat sensitivity.