I have a boiler feed pump that has a very speed specific 3x VPF peak of which approaches 5.5 G's. This peak is out at around 1595 HZ.
I use the medium sized PCB Modal hammer that I think everyone who takes vibe data has (sorry, I don't know the model number off hand) which comes with the 4 tips.... brown, grey, red, and black (Black being the hardest).
This peak certainly behaves like resonance.... very directional and speed specific. I have even considered the possibility of acoustic resonance.
I have attached a force spectrum from this hammer using the black hammer tip..... please take a look... I have attached the same spectrum in both log and linear scale.
I don't believe I can excite that frequency range with the tip that I have (based on the spectrum I attached).
I have a few questions:
- I know there is the 10 or 20 dB drop off practice.... my software shows LBS Force RMS... what is the drop off rule for this?
- Has anyone had to excite a frequency range anywhere around 1595 Hz? What did you use for excitation?
- Does the amount of force input have anything to do with the frequency range/response? Meaning could I put more force into the impact and possibly get out to the required range?
- What would you suggest for this case?
Thanks for your help and please let me know if you have any questions!