I am working on a project where I need to measure the displacement of a vibrating device. The device vibrates back and forth from a set center location at a constant frequency of set between 20Hz and 50Hz. I know that the net distance it moves will be less than 0.5 inches max - probably less. The sensor will be placed about 4 inches away from the device. My budge per sensor is less than $30.
I need a sensor that will measure the farthest and closest distances the vibrating device moves. It needs to be high precision with low range. I've looked into ultrasonic and optical sensors. Optical sensors have higher precision and lower ranges, but I can't find one with high enough precision.
Thinking out loud: Could you mount the sensor on a track and traverse it back and forth? Use it like a regular break beam. Run the sensor in to where the DUT just breaks the beam, record this point then advance until the beam is never seen and record that point. Distance between the two points is displacement.
At least for a sinusoidal vibration, you can calculate the maximum displacement from the instantaneous maximum acceleration, measured using an accelerometer.
If you used that from 4 inches away, you will end up with approximately 1.6-1.8 voltage output for .5 inch movement.
Voltage divide that in half, set analog reference voltage to 1volt and you will end up with approximately 200 increments for the arduino to measure for that distance.
I recall there are versions of that sensor for closer range having greater sensitivity. But are they fast enough to follow this movement accurately? You'd need at least 500 Hz output for a 50 Hz movement.
1/2" movement at up to 50 Hz - that's gonna be quite an acceleration! Sorry, too lazy to try and calculate how much, will leave that to someone else. Mounting anything to that will disturb the movement. An accelerometer may be shaken off, or at least the wires that connect it won't last long with that kind of movement.
