DC fan monitoring and protection

　　Despite the frequency motor has a high reliability, but it is still mechanical devices, while long-term use, the speed may be reduced or stopped, so it is best to fan running status in real-time monitoring, to facilitate the timely detection of problems.

　　Currently, there are ways to monitor the fan's own alarm sensor and speed sensor are two types of alarm sensors can use the fan speed is lower than an alarm signal when a certain threshold, and the speed signal output can achieve real-time monitoring of fan speeds .

　　Fan circuit alarm signal output from the "High" and "Low" two states, meaning two levels represented in accordance with generally positive logic system, high "failure", "Low" represents "normal."

　　Fan speed signal output from the circuit is typically in the form of pulses, each wave is represented with the fan turned around, this signal may be provided directly to the host for display via the data bus. Some fan speed signal is not output from the fan's speed, but the speed of a multiple, for example once per revolution and two, four or six pulses, must be treated in order to reflect the formation of a true fan speed signal. To discern the true speed of the fan speed is still a factor, you can use the tachometer to measure the actual speed, and then compare the data show. Fan

　　Fan speed signal is generally from three lead plug output, three yellow and black leads are + 12V power and ground, another color line is the speed signal output lines. It should be noted that some of the three leads a third fan speed signal is not output lead line, but the speed control signal line, through which the input speed control signal to the fan motor.