With the application and the environment temperature changes, is sometimes necessary to "Waterproof Cooling Fan" to meet the needs of different speed. Some manufacturers specially designed adjustable fan speed cooling fan, manual and automatic modes. Manual is designed to allow users to use a low speed in the winter to get low noise, high speed to get good cooling effect in the summer. Automatic class radiator thermostat with a temperature sensor in general, be able to "Waterproof Cooling Fan" of speed, temperature is high, the current work to improve the speed according to temperature control, low temperature, then reduce speed to achieve a dynamic balance, so that the cooling effect of wind noise and maintain an optimal combination of points. Fan speed is the number of revolutions per minute of the fan blades, the unit is rpm. Fan speed is determined by the motor inside the coil turns, operating voltage, the number of fan blades, tilt, height, diameter and bearing systems. Speed and "Waterproof Cooling Fan" quality is not necessarily linked. Fan speed can be measured by the rotational speed of the internal signal can also be measured by the outside.