Hello,

As you have probably guessed from my previous posts, im relatively new to this game. Im at the stage where reading lots of material on vibration doesnt really help unless I can ask direct questions!

I would like to know about enveloping the acceleration data and how it points out frequencies that relate to bearings. I would really appreciate anyone's help.

Can I just look at the acceleration spectrum and divide the peak frequencies to see if there are any trends at high frequency compared to low frequency? My software (Commtest Ascent) puts little red arrows across the graph when I click one peak so i can see if there are any related to it.

If Demodulation shows peaks that might have been "drowned out" by background noise, how do I calculate the frequency on the acceleration spectrum that this is occuring? Is it as simple as just adding the frequency on the demod graph taking into account the bandwidth and range the demodulation is showing??

Any input is much appreciated,

Stevebob

To go into a full discussion here would take some time. However, if you use the "search" feature on the FIND tab, you will find many previous threads that discuss this feature extraction, including how it works, setup parameters, etc.

Then, if those previous discussions dont answer your question, then you could post again.
Hope this helps

Jim P

Steve,

Jim is right, it might take a long post to reply.

If no one gives any thing soon and the link below doesn't help, email me and Alert might can give a little help.

Look here at CSI's 750 explanation.

Thanks guys, im trawling through that csi 750 explaination. Maybe I just need the right kind of literature and not just a google search on the subject!

By the way, would any of you have examples of real life (ie warts and all) of a few machines that have been correctly diagnosed using vibration analysis? ill try searching the posts for ones too.


Cheers,

DLI has some decent low level content at http://www.dliengineering.com/published/TECH-Demodulation.pdf

John from PA

Steve,
The Commtest site has some guides on basic vibration and an explaination of Demodulation. You should still take high frequency acceleration readings and trend these also. The 6 Pak give you a basic idea how to setup common readings. Fault frequencies are avaiable in the software if you know the bearing brand and number.
Four Stages of Bearing Failure
Stage 1. Earliest detectable indication of bearing failure using vibration analysis. Signals appear in the ultrasonic frequency bands around 250 KHz to 350 KHz. At this point, there is approximately 10 to 20 percent remaining bearing life.

Stage 2. Bearing failure begins to "ring" at its natural frequency, (500 to 2,000 Hz) signal appears at the first harmonic bearing frequency. Five to 10 percent remaining bearing life.

Stage 3. Bearing failure harmonics of the fundamental frequency are now apparent. Defects in the inner and outer race are now apparent and visible on vibration analysis of the noise signal. Temperature increase is now apparent. One to five percent of remaining bearing life.

Stage 4. Bearing failure is indicated by high vibration. The fundamental and harmonics begin to actually decrease, random ultrasonic noise greatly increases, temperatures increase quickly. Remaining life one hour to one percent.
Hope this helps

demod_guide.pdf (75 Kb, 19 downloads)