Although the "24V DC Cooling Fan" inverter motor has a high reliability, but it is still mechanical devices, in the long-term use, the speed may be reduced or stopped, so the best fan of running real-time monitoring, facilitate the timely detection of problems. Currently, "24V DC Cooling Fan" own alarm monitoring methods are two types of sensor and speed sensor, alarm sensors can use the fan speed is lower than the alarm signal is given when a certain threshold, and the speed signal output can be achieved Real-time monitoring of fan speeds. From the "24V DC Cooling Fan" alarm signal output circuit have "high" and "low" two states, meaning two levels represented generally in accordance with positive logic system, high indicates "failure" "Low" indicates "normal."