So far there are alarm sensors and the speed sensor are two types of "220V Cooling Fan" self-monitoring methods, the use of the alarm sensor in the fan speed is lower than an alarm signal when a certain threshold, and the fan speed signal output can be realized Real-time monitoring of speeds. "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. " To distinguish "220V Cooling Fan" Speed is real or a multiple speed, tachometer may be used to measure the actual speed, and data were then compared.