# A question about MATLAB library "vibration of rotary machinery"

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Si So on 28 Feb 2021
Edited: dpb on 4 Mar 2021
My question is about vibration of rotary machinery:
The author claims the wavforms correponding to input shaft, output shaft, and gear mesh measured by sensors can be reported as:
vfIn = 0.4*sin(2*pi*fPin*t); % Pinion waveform
vfOut = 0.2*sin(2*pi*fGear*t); % Gear waveform
vMesh = sin(2*pi*fMesh*t); % Gear-mesh waveform
A1 sensor can measure vfOut.
A2 sensor can measure vMesh.
But how can you measure vfIn?
dpb on 3 Mar 2021
Edited: dpb on 4 Mar 2021
That's what you get out of an accelerometer in real life, yes.
It responds to whatever happens to it at its base (up to its response frequency, of course); what that resultant waveform is all depends upon the mechanical characteristics of the particular gearbox at the mounting location and, as noted above, the quality of the mount one can manage.
The amplitude of the various parts of the overall response is dependent upon the effective coupling through the mounting components, bearings, lubricants, etc., etc., etc., all as amplified/attenuated by the shape and composition of the components themselves.
"The composite signal generated and analyzed doesn't really try to simulate the responses that would be expected from the two hypothetical accelerometers A1 and A2"
By the above, I didn't mean to imply the signal of the hypothetical accelerometers would not contain these frequencies, I meant that the example didn't try to reproduce a real accelerometer response by modeling the gearbox itself to try to predict the above effects on amplitude and phase of the accelerometers themselves.
This is an idealized example, for sure, but the the basic ideas are there.

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