Micro Cooling Fan pulse signal

Speed signal "Micro Cooling Fan" output from the circuit is typically in the form of pulses, each of said fan is turned around the first wave, such signal may be displayed directly to the host via the data bus. Some fan speed signal is not output from the actual rotational speed of the fan, but the speed ratio, for example, 2 per revolution, four or six pulses, must be treated to form reflected "Micro Cooling Fan" in real rpm signal. To distinguish the true speed or fan speed is a factor, you can use the tachometer to measure the actual speed, and then display and compare data. Fan tachometer signal output is generally from three wire plug, three leads in yellow and black, respectively + 12V power and ground, the other is a color line speed signal output lines. It should be noted that some of the three-lead "Micro Cooling Fan" in a third speed signal output line does not lead, but the speed control signal line through which an input speed control signal to the fan motor.