Although the motor fan has high reliability, it is stil […]
Although the motor fan has high reliability, it is still a mechanical device. When it is used for a long time, its speed may drop or even stop. Therefore, the fan's running status is monitored in real time to facilitate timely detection of problems. The alarm sensor provides an alarm signal when the fan speed is below a certain threshold, while the speed signal output enables real-time monitoring of the fan speed.
The alarm signal output from the fan circuit has two states of "high level" and "low level". The meanings of the two levels generally follow a positive logic system, and the high level indicates "fault" and "low level". Indicates "normal". The speed signal output from the fan circuit is usually in the form of a pulse. Each wave head indicates that the fan has rotated one turn. Such a signal can be directly provided to the host for display through the data bus.
The speed signal output by some fans is not the actual speed of the fan, but a multiple of the speed. For example, two, four or six pulses are generated per revolution, and must be processed to form a true speed signal reflecting the fan. To tell if the fan speed is a true speed or a multiple, use the tachometer to measure the actual speed and compare it to the displayed data.
The speed measurement signal of the fan is generally output from the three-lead plug. The yellow and black of the three leads are respectively +12V power supply and ground, and the other color line is the speed signal output line. It should be noted that the third lead of some three-lead fans is not a speed signal output line, but a speed control signal line through which a speed control signal is input to the fan motor.