Hello again. If you have read and replied to my prev post about laser alignment on a piece of equiptment, I would like to share some "raw" data with you all to maybe help me understand what I am seeing. Some backgound info, I am a maintenance mechanic (tech) working in the food processing industry. All our vibrations analysis is done from a outside contractor. I have always been interested with data collecting and analysis and trying to persuade the company to invest in our own equiptment and train some people. Anyway, while looking thru the tool cabinets, I found a old and dusty Vitec 654cs. I charged up the battery, and read thru the manuals that where still with it.. (thats the first ). This is a tablet size device with a lcd readout for values. It has a knob to select g's, in/sec, and mills. Scale of 2, 20, and 200. It also has a filter device (vibration frequency (CPM) readout) with a low and high switch setting and a rotory knob to increase the values. Ok, so now it time to see what this thing does. I when down to the extruding machine that was prev flagged for misalignment to see what this device would read. I selected filter off, and selected the mills range. I then placed the magnetic probe on the r/h side (horizontal) of DE motor. Read out showed 3.37. Next at top of DE motor (vertical). Read .76. Went to ODE of motor, r/h side read 5.35. ODE motor top read .5. I tried to take readings as close to the bearings as possiable. There is also a cooling fan houseing mounted on top of this motor. I placed the pick up on the DE r/h side and read 13. DE top read 6.05. ODE r/h side read 15.6 and ODE top read 7.01. Again I want to stress that this is my first time ever useing this device (and from the looks of it, nobody else has used it)..

I went to another extruder the was also running and took some reading from that. DE motor r/h read 1.16. DE top read .8. ODE motor r/h read 2.0. ODE top read .9. Went to cooling fan.. DE r/h read 3.9. DE top read 3.8. ODE r/h read 4.2. ODE top read 2.8. Now they also had shut this extruder down for a few minutes and I was able to take reading of just the cooling fan running while motor was off. DE r/h cooling fan read .5. DE top read .5. Values for the ODE of cooling fan where the same .5.

So now back to the first extruder machine.. My first look at the values , I notice the cooling fan is higher than the second machine. Could the cooling fan be the problem that is causeing the machine to be flagged? I do not have a copy of the data from the vibration report, but I recall him staying a horizontal movement to int he r/h direction and a value of 11. But i don't know if that was the cooling fan or motor or both...

Added info. The motor is a 250 HP DC GE motor. 1725 rpm. The cooling fan assembly has two motors inside it, 3600 rpm. Each motor is driving two squirrel cage fans..

First post about alignment can be located here >>>> Alignment Post

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

It sounds like you are looking at an "overall amplitude" reading, which is not the best for diagnostics. Vibration data can contain many frequencies at various amplitudes. Performing a diagnosis from an overall is not something that I would recommend. You see, that amplitude of, say 0.5 Mils on the cooling fan, might be at 1X RPM (which might be from imbalance) or it could be at 2X RPM (might be looseness). It is great that you have an interest in this technology and I would encourage you to learn as much as you can, but you just don't have the tools required.

I would like to suggest that since you are PAYING another company to provide you with vibration analysis, you approach them with your desire for more information. Tell your service company that you want details, FFT's with notations and trending plots. Ask them to explain more clearly what the problems are and what they feel would resolve them. Vibration analysis is one of many excellent diagnostic tools, but unless the information can be used, the dollars spent are pretty much wasted.

If the company that your are paying is NOT willing to provide further assistance, there are hundreds of us out here that would love the opportunity to do so. (Personally, I would love a chance to come up there to my old stomping grounds.)

Take Care,

If you give use two readings from the same point in different units (for example mils and ips), then we could make an educated GUESS as to the frequency assuming that there is only one frequency present.

For example if you tell me it is 2 mils and 0.2 ips, than I would guess the frequency is 1800cpm.

But often times there is more than one frequency present and the highest one is not necessarily the one that tells you the most info.

So bottom line, Chris is right. Trying to diagnose from an overall would be kind of like trying to tackle Shaun Alexander with your eyes closed. (is that what the panthers were doing?)

It sounds like this is actually a tunable-filter analyzer. In the "filter out" position, you are reading overall levels as Pete and Chris suggested. As Pete explained, you can estimate the predominant frequency present by comparing displacement, velocity and acceleration and a little math. This is in fact the basis of the instruments Spintelligent Labs sells....we add a little magic so make the calculations and display the results in a simple format.

The instrument you have can also read the peaks at individual frequencies. If you have a machine that turns at 1800 RPM, you should have peaks at 1800 RPM (or 1800/60 = 30 Hz), 3600, and higher multiples of rotation rate. There are also particular "forcing frequencies" associated with each machine. If a pump has 5 vanes on the impeller there may be a strong peak at 5 x 1800 = 9,000 CPM (cycles per minute), a peak at maybe 12x roation rate depending on the number of vanes on the motor cooling fan and so on.

A tunable filter analyzer can tell you everything an FFT analyzer can - it just takes longer...a lot longer. Try this proceedure:

1. Take a "filter out" reading and record the level. Velocity (IPS) is probably the best bet. Say you read 0.5 ips.

Now we want to determine the source of the high level.

2. Set the analyzer to "filter in" and tune the filter to 1800 RPM. The level displayed is the energy at roation rate. If it's close to 0.5 ips, you've identified the source of high vibration as a rotation-rate frequency. This could indicate an imbalance problem if measured in the vertical or horizontal direction, or a misalignment problem if measured in the axial direction.

3. If the level is much lower than the overall level, continue the search by tuning the filter to 2x, 3x and so on. If you know the forcing frequencies of the machine, check these frequencies first. A strong signal at 5x in the case of the above machine ("pump vane rate") indicates poor flow through the pump.

For some simple guidance on vibration analysis, check out this document on our web page:

http://www.spintelligentlabs.com/spin-diag.html

There are many other documents in the library section about selecting measurement locations and other info you may find useful.

A tunable-filter analyzer is far from state-of-the-art, but it can be used to determine machinery condition and the underlying causes. Everything you learn using it applies directly to understanding FFT-based vibration signatures, so it will be a valuable learning tool.

Just remember...vibration analysis is easy - it's the exceptions to the rules that take a while to understand....20...ah, better make that 25 years and I'm still learning them!

Jon
www.spintelligentlabs.com

I went back took some more readings and recorded them on a spread sheet for your viewing. From the sheet, 1= l/h or ODE. 2= DE. For the cooling fan, since it is encased in a retangle houseing on top of motor, the readings where read as if it where a motor. ( Vert, Horiz, Axial).

Thanks for your input.

test.xls (18 Kb, 12 downloads) Spread sheet of readings