I heard taht there's a Poor man's method to doing ODS. Anybody has any idea on this?

I've heard of the poor man's modal. Universal Technologies called it curl.

V102_General_Mode_Shape_Plot_Procedure.pdf (256 Kb, 191 downloads) Poor Man's Modal

Wookp,

I prefer to say "low cost" rather than poor man's ODS method! I use a 2-channel analyzer, but I save money on mode animation software. I use MS Excel to plot static mode shapes. This is adequate for most common machinery vibration problems. One can plot an ODS mode shape with a 1-channel analyzer if the vibration of interest is at 1xSS and a tachometer is used for a phase reference. Failure to get good data is truely a "poor man's method"!

Walt

lawrencep,
Thanks for the information.

walt,
Yeah. That's what i have heard that you could plot on MS Excel. But I am having problems on how to plot it, formulas involved , plotting method. And I am using a CSI2130 so getting amplitude and phase data should not be a problem.

Walt, I have seen the end process of the Excel mode shapes but am unsure how to generate this myself in Excel, any help?

I have used Excell spreadsheets to record amplitude and = or - phase angle. This spreadsheet gives specific machine location ie.. northeast side, bottom of frame. I then transfer my amplitudes to another spreadsheet making each number = or - according to phase direction. After all data is entered, press F11. This will create a graph. You can then use the tools to change the type of graph or shading.

insert a + where you see = above. Always forget to proof read!!

ODS_Example.ppt (111 Kb, 78 downloads)

How do you use phase in this method?

Do the tach and accelerometer need to be in the same orientation (plane)?

FWIW, attached is an example I developed of animation of magnitude and phase data taken along a line (top graph).

You can see that in that for this particular data (which happens to be ficticious), it creates quite a different picture than if you had just plotted the magnitudes only (bottom graph). The deflection shape including the phase in this case is much more flexible (more bending) than the shape suggested by the magnitudes alone. This particular shape has some characteristics of a traveling wave vs a simple standing wave.

A simple standing wave would correspond to the case where the phase was the same everywhere along the length (with exception of 180-degree phase shifts on either side of the nodes of a standing wave), and in that case (standing wave), animation would not be necessary to interpret the shape.

How important is it to take phase data and do animations for ODS in practical real world situations? I would think in most practical cases you can normally get a pretty good idea from the magnitudes alone, but I would be interested to hear others' comments on that aspect.

This message has been edited. Last edited by: electricpete,

SimpleModeAnimate.xls (34 Kb, 86 downloads)

Is there a Scilab toolbox for doing ods work?

Aubrey

Webcruiser829
I use the "Adv. Cross Channel" feature on my 2130, and use a roving accellerometer. My fixed accellerometer is in the same plane as i take my data.

Measuring phase and magnitude for the purpose of doing a phase analysis or Operational Deflection Shape analysis (ODS) is only half the battle. It's just as important to resolve what is going on with the machine when evaluating the test results. I have nothing against "poor man's" methods. I've used some of the techniques mentioned in the postings. I know that depending on the machine shape or when many points are collected it becomes more and more difficult to use a poor man's method to evaluate the test results.

The attached movie is a 300 point ODS of a vertical pump operating at a speed exciting torsional resonance of the vertical structure. Most route based analyzers have the capability to make the phase and magnitude measurements for this kind of a test. The only other thing required to get ODS animation is a $3000 software program.

Everyone has problem machines. It would cost much more than $3000 to have one plant meeting to discuss what might be wrong with a problem machine. With ODS there is no doubt. Very little is left to the imagination. Two great advantages of ODS and Modal software often left unmentioned are:
1) Everyone viewing the animation can "see things" and understand the problem displayed in the movie. You can't say the same about spectrums and waveforms.
2) what's not happening in he animation is just as important as what is happening. For example, in the attached movie, there is no looseness between the floor (black), concrete (grey) or sole plate (pink) so any doubt about that question is erased.

Some of the techniques used to measured ODS data are:

Single Channel Frequency Based Techniques using one sensor and a tachometer:
Order Tacked phase and magnitude.
Route based phase and magnitude.

Cross Channel Frequency Based Techniques using two sensors (no tachometer):
Cross channel phase and magnitude.
Cross Channel transmissibility measurements that can be saved to analyzer memory, downloaded to the computer and imported into ODS software.

Time Based ODS Techniques:
Multi channel time waveform aquisitions using a DAT tape recorders or a time capture instument such as CSI's XP32 or LDS Focus II. No phase reference is required for time based ODS because all of the signals are acquired simultaneously.

Please call me if you are interested in purchasing ODS/Modal software or public and on-site ODS/Modal training courses, mentoring and consulting serivce.

Pump_ODS.avi (574 Kb, 80 downloads) Pump ODS

quote:

I have nothing against "poor man's" methods.

Except that if everyone used 'poor man's methods' then you wouldn't have anything to sell.

I looked at the 300 point (how long did that take?) ODS. Assuming that this is a pump with a vibration problem that needs to be solved, then I cannot see what a simple set of phase and amplitude measurements correctly plotted out would not achieve when compared to a fully blown ODS

A quick 'above and below' measurement across any interface identifies looseness

Brickbat,
Thanks for the answer.
I have no training in this area. Anybody have links to modal/ODS? Introductory stuff would be especially appreciated. When time allows, I will do a search. Not today, I'm too busy turning wrenches!

Buzz,

Assuming you can get around a machine without having to climb ladders, etc. about three measuremets per minute can be collected using a single channel or dual channel analyzer. Nine to twelve points per minute can be measured using a four channel analyzer (fixed single channel reference sensor and roving tri-axial sensor).

The Pump ODS was made with a dual channel analyzer. It took about 1.5 hours to collect the data.

I think most would agree with Buzz that we can certainly check stationary support looseness without ODS software. But I can certainly see there can be benefits to using ODS software to display animated 3-d deflection shapes:
1 - It might extend our ability to visualize what's going on just a little bit. Especially when we are doing a complex 3d shape. And especially when presented to others helping with the troubleshooting that may not be able to interpret phase/magnitude info readily.
2 - It looks cool.

It would be really cool if you could animate a certain frequency component of the bump test results and compare them to the running ODS animation. Unfortunately, I'm pretty sure that would require a helluva lot more effort and/or equipment.

Out of curiosity, I have questions on the video posted:
Is the pump impeller just above the light blue vertical cyclinder, or down below out of sight?
What was the frequency (1x? bladepass?) and excitation for the torsional oscillation?
Why does the top of the motor appear to be tilted toward the viewer?

Electricpete,

Thanks for your input and questions.

1. You asked about animating a certain frequency of the bump test and comparing it to the ODS animation. If you do a modal and and ODS the comparison is easily made within a ME'scope project. You probably know that the modal test takes much longer to complete than the ODS test. To get around the time issue, the modal test could contain fewer points. The same structure drawing can be used for both the ODS and Modal projects. I do about ten ODS projects for every one modal job. The reason is that the modal test requires the machine to be off-line during testing. Most modal jobs take a whole day to complete and there are fewer opportunities for a machine to be off-line that long.

2. The pump impeller is 56 feet below the building floor. The ODS animation frequency was 51 Hertz. When the pump was operated at 775 rpm (86% of speed), electrical line frequency of the VFD (3088 cpm or 51.4 Hz.) was exciting a twisting mode in the machine structure above the building floor.

3. The motor isn't really tilting towards the viewer. I guess it's an illusion seen in the 3D view. I've attached a top down view of the ODS. Besides the twisting motion, the top view shows pure side to side motion of the motor.

Note: When playing ODS or Modal animations turn on the "Repeat" or "Loop" function on the movie player. It also helps to make the animation window full screen on your monitor.

Pump_ODS_Top_View.avi (544 Kb, 43 downloads) Top View

Thanks Tony. That answers a lot of my questions well. From the top, it looks like the bottom of the motor is twisting. That's what I'd expect with an oscillating torque applied to the stator and exciting a resonance of the supporting structure below. But the top of the motor looks like it's swinging back and forth instead of twisting. Do you have any idea why that would be?

Also makes me wonder about how the apparently purely tangential direction movement at the bottom of the motor was captured. Triaxial accelerometer? Tangential mounting?

This message has been edited. Last edited by: electricpete,

The excel spreadsheets are great for movement in one plane but the ODS software will interpolate three degrees of freedom (V,H & A) giving you a better indication of the vibration.