I have two iron pipes, one bent and cracked, and one whole. On one end Ive attached a vibration motor (200hz) and on the other end Ive attached a vibration sensor.
I do a fft and then get out the amplitudes of the different frequencies I pick up.
Question: I want to compare the signal picked up from the broken pipe to the signal from the whole pipe, how?
At the moment I calculate the "total" energy in the signal, by summing the amplitudes. However, this sometimes fail, especially if im testing a very broken pipe. I can reliably detect smaller damages to the pipes.
Correlation does not work, due to the shape of the signal would be similar, but there would be small variations in the harmonics of the main signal. Also the vibration motor is 200 hz +/- 10hz approximately. Suggestions? Visual check doesnt work as I want to build a completely automated system, where a LED light turns on if the difference in the signal is above some treshhold.