What is your answer to the below vibration question and *** why ***?

This page is from "Fault Analysis and Correction". Part 5 of Vibration Analysis Certification Exam Preparation Package: https://lnkd.in/eKv4TyF

Drop me a private message, if you are interested in more details about purchasing the booklets.

Regards- Ali M. Al-Shurafa

#certification #rotatingequipment #conditionmonitoring #vibrationanalysis #reliability #machinery #machines #vibration #diagnosis

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Vibration Certification Exam Practice Question Certified Vibration Analyst Cat I Fault Analysis Diagnosis
Original Post

Is the purpose of those questions to search for knowledge or to confuse people? Why the same line form on both plots? Doesn't make any sense. I stay convinced that those formal exams doesn't make consultants any better, just to learn how to avoid some paper tricks.

John from PA posted:
Becar posted:

Why the same line form on both plots? Doesn't make any sense.

Are you sure?  What if I had a proximity probe signal and decided to display it in two methods, one AC coupled and one DC coupled?

I’m not saying this is the answer to Ali’s question.

Very strange to get the same curve when one scale is in seconds and the other in miliseconds, don't you agree?

Becar posted:
John from PA posted:
Becar posted:

Why the same line form on both plots? Doesn't make any sense.

Are you sure?  What if I had a proximity probe signal and decided to display it in two methods, one AC coupled and one DC coupled?

I’m not saying this is the answer to Ali’s question.

Very strange to get the same curve when one scale is in seconds and the other in miliseconds, don't you agree?

Agree, also must say looking at data on a phone leaves a lot to be desired!

Becar posted:

Is the purpose of those questions to search for knowledge or to confuse people? [....] I stay convinced that those formal exams doesn't make consultants any better, just to learn how to avoid some paper tricks.

Becar,

For sure, the question (in my post) is not intended to confuse. Why should I? I'm sorry if it confused anybody. WRT consultants, this question is not really for them and definitely not to make them better. It is for Level 1.

The purpose of posting the question here to test it and challenge its validity/suitability for its objective by having comments like yours. Please consider a possible language barrier here.

Do formal vibration certification exams make better consultants? I guess this has been a subject for numerous debates and hot arguments, for the past two decades. Though this isn't the topic of this thread, my opinion is that these exams have some merits but they are not perfect.

On the technical part of this question, I'd like to avoid commenting now to avoid spoiling the question or letting other posters be biased.

Regards- Ali M. Al-Shurafa

 

John from PA posted:
Agree, also must say looking at data on a phone leaves a lot to be desired!
 

Thanks, John for the comments and mentioning the phone version of the page. I'm not sure how to fix it but perhaps the pdf file (already on the OP) should work fine.

Regards- Ali M. Al-Shurafa

A comment on plot 1:  I have seen this too many times, where the units are not properly labeled.  mils p-p, mils 0-p, mils r.m.s - TIR?  I have seen this from consultants and data takers.

I have inquired as to what their instrument reads and how - true r.m.s.?  Too often, the user does not know.  Instruments have gotten inexpensive enough from many to buy and go into business.  Training, including some reading, could help.  

This series of books does give people some examples to review.  Prior to looking into the books, it might be helpful to do some training, even if one does it by them self.  

 

William_C._Foiles posted:

A comment on plot 1:  I have seen this too many times, where the units are not properly labeled.  mils p-p, mils 0-p, mils r.m.s - TIR?  I have seen this from consultants and data takers. 

Bill, 

How about shaft axial position? Have you seen any one reporting it in "mils pp"?

Regards- Ali M. Al-Shurafa 

Normally it will display the axial pos in whatever you like to see it displayed parts of mm or inches or even % of something if you don't know what you are doing and that is kind of normal and that is the DC signal so rectification like p-p, RMS do technically not apply IMHO. However if you can get hold of the AC signal, that do exist,  the axial shaft vibration of the axial bearing target plate, movement can be measured and that is a standard eddy probe AC signal with all it's limitations and you can display it as whatever you like with what filtering, rectification you like, using the correct calibration but no orbit IMHO..... unless you move the sensors mounting to be 90 Deg apart...... never seen that anyway. So everything is possible :-).

I have advocated for looking at axial vibration from the thrust probes for a long time.  This can be valuable information that is often ignored.

The big issue is that (some) manufacturers do not provide a surface with low runout.  One compressor vendor can't get the runout as low as we did at GE on Frame 9F turbines (on the steam turbines it was lower), which are far larger - tremendously larger.  

When I get crazy units, like mil pp, on axial, I inquire if I can.  I am trying not to be too cynical as I get more mature, but I have often found sloppy data and data from untrained and inexperienced people, which is enough to make one jaded.  Fortunately, there are many who give it their best and try to get better - not all by far.  

Some learn from their mistakes; others repeat the same mistakes.  Those who learn from their and other's mistakes, gain much.  

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