Speed signal "Micro Cooling Fan" circuit output from the usual form of pulses, each wave head in DC fan turned around, this signal may be provided directly to the host for display via the data bus. Some DC fan speed signal is not output from the real DC fan speed, but the speed multiples, such as 2 per revolution, four or six pulses, must be treated in order to form a true reflection of a DC fan speed signal . To identify the "Micro Cooling Fan" Speed is real or a multiple speed, tachometer can be used to measure the actual speed, then the data were compared. So far, the fan has its own way of monitoring alarm sensors and speed sensors of two types, the use of an alarm signal to the alarm sensor in "Micro Cooling Fan" speed is below a threshold value, and the output speed signal can be realized Real-time monitoring of fan speed.