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Title: Vibration Analysis Certification Exam Preparation Package Certified Vibration Analyst Category I: Fault Analysis and Correction (Part 5)

Series: CAT I PREP I SERIES PRACTICE TESTS FOR CVA (Link)

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

Regards- Ali M. Al-Shurafa

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Original Post

Please comment on the below practice question (sample) for vibration analysis certification exam. Is this suitable for Level 1, 2 or 3? 6, 18 or 36 months experience, respectively. Or maybe not suitable at all.

The intent of many of the questions in the booklets is to trigger the attention to a possible misunderstanding in a concept or its application. However, based on previous posts and some private messages, the level of difficulty of some practice questions was controversial.

Perhaps, the language clarity also adds another barrier.

Regards- Ali M. Al-Shurafa

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From a language view, speed and frequency are mixed in the question.  I tend think of cpm as a frequency and rpm (perhaps frequency or speed) as a type of speed or angular velocity.

Additionally, I would take Hz as a frequency, not a speed.  50 Hz is the frequency of the line.  Synchronous implies something is related (synchronized) to something else.  Most who are around motors are likely to take this as to the line frequency.

Have a fluid drive that can lock-up, and the story of what is synchronous changes - would be a motor to line frequency or the driver to the driven?

William_C._Foiles posted:

I tend think of cpm as a frequency and rpm (perhaps frequency or speed) as a type of speed or angular velocity.

Additionally, I would take Hz as a frequency, not a speed.  50 Hz is the frequency of the line.  Synchronous implies something is related (synchronized) to something else.  Most who are around motors are likely to take this as to the line frequency.

I think as all rotational speed is frequency cyles/time, rpm, rpm or Hz.... Apparently people like to think only hz are frequency....

fburgos posted:
William_C._Foiles posted:

I tend think of cpm as a frequency and rpm (perhaps frequency or speed) as a type of speed or angular velocity.

Additionally, I would take Hz as a frequency, not a speed.  50 Hz is the frequency of the line.  Synchronous implies something is related (synchronized) to something else.  Most who are around motors are likely to take this as to the line frequency.

I think as all rotational speed is frequency cyles/time, rpm, rpm or Hz.... Apparently people like to think only hz are frequency....

I agree with Bill on this, frequency is most often Hz or cpm.

”Fburgos”, if you handed me a spectrum and I pointed to some peak and asked what is that frequency, would you replay it is “X” rpm?

When I shared this question previously, I received different kinds of comments. The majority were interesting but some were conflicting.

• Some readers disliked having two questions in one question. For them, this could be confusing or too much to ask in one question. (Others liked this format).
• Some readers emphasized that the two questions are not relevant in real life. Furthermore, some mentioned that no need to know the synch speed for analysis.
• The term synchronous speed for an induction motor was a subject of debate. Some argued that this term is not valid and some suggested other terms like magnetic field frequency etc.
• The units were also a subject of argument. Some accepted rpm, cpm, rps and Hz for speed and frequency. Some did not agree.
• Difficulty. A very wide range of comments was received, from a pre-requesit to Cat I to suitable to Cat III.

Perhaps, one of the reasons for these discrepancies is that the responders had different levels of formal training/education on vibration analysis and they have varying exposure to the ISO requirements for Cat I.

Regards- Ali M. Al-Shurafa

Welcome to the real world :-) in my book RPM, Hz are only different ways to describe the the same thing whatever it may be that is suitable and have no inherent meaning of what it is... I think a ISO training should conform to the ISO definition of things if there are one and not invent anything else.... Only my view. You also in detail know my view on the other thing about none existing synch... :-) also in my view and every physics trained IMHO....