I have a system which is composed of 3 Rotating components • Motor i.e. Shaft (running at around ~7rev/s) • 3 Gears of x16 teeth mounted in series • shaft hold Bearings (number of rolling elements unknown)
I am doing an FFT using Matlab on the accelerometer readings, mounted over the shaft holding bearing.
i stack these FFTs and plot them in time(called sample in the image) and get the image below
Now my questions are 2:
This is the main question: what is the source of vibration indicated in frequency range 200-250Hz, since i know the gear meshing frequency ~120Hz (clear in the FFTs image), i can eliminate it being the gears. But maybe it is the gear in the middle meshing with the 2 other gears on each side? or is it just noise ? any help on this one be much appreciated
second question: Why do the frequencies drift to the right, i.e. the meshing frequency seems to be increasing. my take on this is the motor heating up after running and so drawing less current, therefore less torque is applied and then the motor runs at higher speed ?