Posted ByDuncan Carter on May 12, 1999 at 15:25:27:
In Reply to: FAQ answer posted byRicardo Garibay García on May 11, 1999 at 11:47:08:
: In the FAQ "Measurment and analysis of diagnosis signal" topic, question 2.2 (asked by SKF people), is answered by Dr. N. Barkova. Unfortunatelly the answer is the same to the question 2.1 (please check it out and you will understand). May somebody answer the question please?. I'm interested because my analyzer uses only HF pass filters for measures of envelope spectrums.
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I have forwarded your question to one of the board moderators, Yury Azovtsev, but I see that it remains unanswered so I will try to give you a preliminary answer.
In diagnostics, we use high frequency demodulated signals that are the result of both friction sources and impact sources within the bearing and we also attempt to control the bandwidth of the signal so that we can relate bearing symptom severity levels to the levels of the envelope spectra lines. Controlling the bandwidth and controlling the relative sensitivities to both friction and impact sources implies that the data be recorded at frequencies away from the friction resonances, which can not be done using just a high pass filter in the general case although it may work for specific cases such as using a kHz cutoff filter with a 10 kHz input bandwidth. Optimum frequencies for the filter are functions of the bearing surface contact velocities so they vary with bearing dimensions and rotating frequencies and may not fit frequencies that can be selected with a simple combination of high pass filter and data bandwidth. We find that it's much more practical to be able to select from a list of relatively narrow band filters and this is especially useful in the case of our automatic diagnostic software, thus allowing the software to optimize the measurement without operator input.
If you will read our articles on bearing diagnostics that are linked to:
http://www.vibrotek.com/ref.htm
I think you will find the answers to you question explained in more detail.