Hi All,
I am doing a project that is a fan to control the speed of a video. The fan that I am going to use has three speeds. I wonder how can I detect the current speed? What sensor should I use?
The fan is 120 AC, 60 Hz.
Tricky - an isolated current sensor (current transformer) perhaps in the supply lead? You might get
better information from the phase difference between voltage and current though.
Do you need to measure the power supply, or is some other sensor acceptable ?
You can open the finger guard.
In the center is a large cover, you could mount a reflective sensor under there.
I'm assuming the blades are a single part or at least a single color.
Attach a sticker or a small layer of paint (matte would be best) of a high contrasting color.
So if the fan blade is one piece white, put some matte black paint on it.
Adjust the sensor to see the tag each rotation.
Now you can tell exactly how fast it spins, by counting the pulses received from the sensor, or measuring the average of those pulses.
Requires a 3 or 4 wire cable to be run along the finger guard for your sensor.
Neither voltage nor current can be used to measure fan speed. As MAS3 states, you need to count actual revolutions. You don't need to apply anything to the blades however. Simply place an LDR or other form of photo sensor on the front or rear of the fan guard and an LED to the rear opposite the LDR. You will then get a pulse at 3 times fan running speed. In fact you might not even need to use an LED as ambient light might produce a detectable signal on the sensor
Mount an encoder onto the shaft of the fan. It'll take some work and time. But it'll measure the speed for sure.
Other than a 3-way switch which provides a VERY crude form of speed control to the simple shaded pole motor how important is it that the fan's selected speed remains constant.