"Waterproof Cooling Fan" you have to know how much, in fact, DC cooling fans have a lot of equipment above the signal line, here we introduce some of the output signal of DC cooling fan. Fan cooling fan equipment each size can match or RD FG signal line. "Waterproof Cooling Fan" There are two lines, three lines, four lines. Two lines just positive and negative, in addition to the positive and negative poles three signal lines than another, and the signal line, there are two: one is the FG, which is the speed signal is a square wave signal, typically quadrupole "Waterproof Cooling Fan"Signal frequency * 30 = actual speed of the fan, there will be slow to say the actual speed. Another is the RD signal, its function is to operate the fan output is low, the fan does not turn the output high, CPU by detecting this signal to know the fans are running.