Interpretation of orbital plots
Interpretation of orbital plots
(OP)
Hi all,
I've been through some training with the standard vibrational plots bode, spectrum, and so on. But most courses I have been on never really went in-depth in how interpretation of orbits or even how time waveform analysis is done.
Does anyone know of any books or documents showing examples of how to interpret these or shows examples of what typical plots look like and their causes ? (similar to how there are spectrum charts to assist in diagnosis).
I've been through some training with the standard vibrational plots bode, spectrum, and so on. But most courses I have been on never really went in-depth in how interpretation of orbits or even how time waveform analysis is done.
Does anyone know of any books or documents showing examples of how to interpret these or shows examples of what typical plots look like and their causes ? (similar to how there are spectrum charts to assist in diagnosis).





RE: Interpretation of orbital plots
Machinery Malfunction Diagnosis and Correction: Vibration Analysis and Troubleshooting for Process Industries by Bob Eisenmann
https://www.amazon.com/Machinery-Malfunction-Diagn...
Fundamentals of Rotating Machinery Diagnostics by Don Bently
https://www.amazon.com/Fundamentals-Rotating-Machi...
Additionally, if you are looking for training, you can take the Machinery Diagnostics course from Bently Nevada (GE).
https://ge-energy.turnstilesystems.com/Programs.as...
RE: Interpretation of orbital plots
I think I did attend that training some years ago. The instructor didn't go much into detail about the different orbitals though.
RE: Interpretation of orbital plots
http://www.maintenance.org/topic/orbit-tutorial#80...
I am unaware of any Wall Charts for orbits.
RE: Interpretation of orbital plots
The problem is that most documents that I can find just say something along the lines of this plot is unbalance or shaft bowing however they don't explain how the orbit forms because of it.
And since I don't really understand how certain orbits form because of certain issues, I find the interpretation to be difficult.
Same with time waveform analysis, most instructors don't go through an example and explain anything. They just say that it is a bit more work to interpret but I don't see how you can reach a conclusion based on an orbit or time waveform with no knowledge of the spectrum.
RE: Interpretation of orbital plots
RE: Interpretation of orbital plots
I 100% agree with that. I just like to understand how certain plots work and how they are formed based on vibration problems. I believe if I am able to visualize what is happening and why an orbital is showing a figure 8 shape for example, I'd be better off in diagnosing problems.
RE: Interpretation of orbital plots
If you have oil whirl giving a whirl frequency at about 0.45X you will see a smaller "loop" hanging off the main unbalance circle and that loop will rotate.
If you have a rub you will see part of the circle is cut off.
If you can visualise the movement of the shaft centreline you are thinking of an orbit. It is an excellent troubleshooting / analysis tool that can help you confirm a spectrum diagnosis.
Ron Frend
http://www.predicon.net
RE: Interpretation of orbital plots
Or like for in your example you had a case of essentially thermal strain due to pipe strain, how would I know if there is excessive loading on the piping which is then being transferred onto a compressor.
RE: Interpretation of orbital plots
In the case of my thermally lengthened inlet pipe the compressor ended up tripping. The cause was that the sun roof had been removed (this was in Oman in the summer at 53C) and the heat from the sun caused the expansion. If you have low values of vibration it makes no sense to analyse the heck out of the orbit (or anything else for that matter). As with anything else in vibration analysis use the amplitude to determine what to analyse and only then should you start looking at detail. Personally I have always used two triggers - 1 an absolute trigger so if the vibration amplitude passed a threshold I analyse, or 2 a rate of change trigger so if something started to change amplitude rapidly I analyse. Don't get hung up on minutae - it's far too easy to get bogged down on inconsequential details.
Ron Frend
http://www.predicon.net
RE: Interpretation of orbital plots