Understand a vibration graph of steam turbine

[Adam001]

There was a problem with a steam turbine and some vibration expert study it using a software calling vibro sight . A graph is called trend analysis and it is between time on x- axis and displacement on y-axis. The displacement starts from 0 , 10 , 20 , 30 , 40 , 50 and 60 and at each displacement value there is a sin wave . I know that each measuring sensor on turbine reads different frequencies and combine them to one frequency . Does these waves on the graph represents the amplitude of each single wave from the same sensor or something else ? there is an attachment picture

 

[Strong]

It was hard to see all details of the image. The graph looks like the overall vibration level on four different sensors (perhaps 2 on each turbine bearing) versus time (about 25-days). You need to read about fundamental of vibrations to gain a better understanding of this graph and others (such as waveforms and spectra) that you may be presented. Why not ask the vibration expert to sit down with you and explain his/her analysis and how diagnostic conclusions were reached?

Walt

 

[Adam001]

The experts came and they did there analysis and I was watching the curves on their computer and they were focusing and I didn't want to disturb them of such a question as all I need to know is what they represent not their physical meaning , The image is not clear as it is from the net and the curve on their computer is very similar to that , so you expect it is the reading from each sensor ? as far as I know the results from the two sensors on each bearing are combined on one wave ?

 

[Strong]

"so you expect it is the reading from each sensor ?"
Yes, 4 non-contact proximity probes (2 on each bearing) gives 4 traces; like a strip chart recorder. Probably the two lower amplitude traces are from the same bearing, and the two higher amplitude traces are from the other bearing. This would be quite easy to identify, if the image you presented was readable!

"as far as I know the results from the two sensors on each bearing are combined on one wave ?"

The traces on the graph/plot are not waves or waveforms, since they represent overall displacement level (typically in units of mils or micron peak-to-peak). Signals from two sensors of the same bearing may be combined into Orbit plots that show the shaft vibration within the bearing housing. Your Consultant may have made Orbit plots, but you have not presented them.

"I know that each measuring sensor on turbine reads different frequencies and combine them to one frequency ."
Simply not true!

Walt

 

[Adam001]

"I know that each measuring sensor on turbine reads different frequencies and combine them to one frequency ." this means that on each bearing I have 2 probes in different axis , each measures a reading and then combine the readings of two into one graph which is time vs displacement , as I saw on control room each bearing has only one vibration value wheither it is relative or absolute ?