Micro Cooling Fan actual speed

"Micro Cooling Fan" tachometer signal is generally output from the three-wire plug, three leads, yellow and black, respectively + 12V power and ground, another color of the line is the line speed signal output. It should be noted that some three-lead Lead is not a fan of the third speed signal output line, but the speed control signal line, through which the "Micro Cooling Fan" input speed control signal. Some fan speed signal is not output from the fan's 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 the 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, and data were then compared.