Meaning 220V Cooling Fan signal

"220V Cooling Fan" circuit outputs an alarm signal from the "high" and "low" states, meaning two levels represented by the general system in accordance with positive logic, high indicates "failure", " low "for" normal. " DC fan speed signal output from the circuit is typically pulses, each wave DC fan turned his head in a circle, so that a signal can be provided directly to the host for display via the data bus. Some "220V Cooling Fan" output speed signal is not true DC fan speed, but the speed of multiples, such as once per revolution and two, four or six pulses, must be treated in order to form reflected in the DC fan real speed signal. To distinguish "220V Cooling Fan" Speed is real or a multiple speed, tachometer may be used to measure the actual speed, then the data were compared.