Hello all,

I'm new in the field of condition monitoring and vibration analysis. My main goal is to develop a system which will detect bearing faults in very early stages. For this reason we built bearing test stand and attached four accelerometers and four sensors for acoustic emission on the outer bearing ring.

The test bearing is not standard, it has external gear and is quite big (pitch diameter = 650mm, number of balls = 80). It is slewing ball bearing with extremely low rotational speed (1RPM to 10RPM).

So my question is:
1. What sampling frequency should I use for accelerometers?
2. What sampling frequency should I use for acoustic emission sensors?
3. Do I need analog anti-aliasing filters?

I would be most grateful if whoever could point me in the right direction.

Thank you in advance for any advice.

Mateo

Isn't this like setting up a test on a 100 year bearing? Why? Proper design/setup and lubrication is everything. What is the orientation of the bearing? Shaft's relative position - why not monitor that along with lubrication.

I'm sorry Sam, but I didn't quite understand your answer.

The case is the following:

We have brand new bearing and we have purpose-built laboratory test stand.

A purpose-built laboratory test stand has been manufactured for experimental verification of the carrying capacity and service life of large sized bearings. So, on this test stand we rotating the bearing under the load until the bearing not collapse. One of the objectives of this is to research and develop methods for condition monitoring of large sized bearing, which involves finding suitable measuring methods and studying appropriate techniques for processing and evaluation of signals.

Those bearings are quite big and they are used in such applications that collapse of a bearing could lead to enormous economic damage and potential disastrous consequences for the people. So at this point of view it should be monitored.

I don't now what's wrong with those measurements or maybe I didn't understand you.

Thank you for your answer.

PS.: Sorry for my bad English

Mateo

Sorry; don't mean to be short but aren't you trying to re-invent the wheel! The L-10 life of this bearing without looking it up would probably be 100 years. Generally loads and numbers are published by the OEM. Unsure of your exact application but 1-10 RPM is very slow. You may want to consider eddy current probes so you can monitor shaft's relative position as well as frequency components on the AC side. And not monitor bearing only.

Hello again!

Thanks you Sam for your good advice. It seems that you know a lot about bearing diagnostics. You advised me eddy current probe for monitoring shaft's relative position. My question is: Do you maybe know what measuring range should this transducer have? What displacements should I expect?

The second question is. What did you mean with this part of the sentence: "as well as frequency components on the AC side." What is AC side? (I hope this is not to stupid question).

And I also want to hear, if you (or maybe someone else) anyway have any suggestion about sampling frequencies, which I asked in the beginning.

Regards,
Mateo

PS.: Maybe I'm really trying to re-invent the wheel.

Orientation: vertical! How far from plumb can you have off balance and still be within specification and how much weight will be offset for 1. The OEM brg mfgr. will give max cleanance say 10 mils if you can live with that. The probe will have a DC component and an AC coupled component for measuring frequency. The DC will measure shaft's relative position.

I'm really sorry Sam, but I'm really bad in English. I have read your answer like hundred times already but I still don't understand it.

What's mean: "OEM brg mfgr."

So if I understand you right:
1. The eddy current probe with measuring range with 2mm will be more than enough.
2. AC component of the eddy current probe measure the frequency.
3. DC component of the eddy current probe measure the relative distance.

Sorry to bother you again.

Regards,
Mateo

OEM = Original Equipment Manufacturer
brg mfgr = bearing manufacturer

1 to 10 rpm, 80 balls, 650 mm diameter, are you talking about a rotary table common used in oil drilling equipment?

Mateo,
Read the data at the posted link and it should give you a better understanding of what you may need. http://www.wilcoxon.com/technotes/lowfreq.pdf

Also what is the normal rotational speed of this bearing? Is it the same as the test stand speed or different. Do you manufacture this bearing or are you just testing?

To answer your questions:

We do not manufacture these bearings, we just testing material properties, carrying capacity, service life,.... Our next goal is to find the best way for monitoring these large sized bearings. So for this purpose we are trying to research the widest possible scope of measuring methods and studying appropriate techniques for processing and evaluation of signals that would enable more reliable monitoring and diagnostics of rolling rotational connections in practice.

Bearing, which is at the moment prepared for testing is a bit special. It is prepared specially for our test stand. So is not made to be used in certain application. It is a slewing ring bearing (double row ball bearing with external gearing). I'm attaching a picture of our test stand and our current test bearing.

So any advice about monitoring low speed bearings would be more than appreciated.

Thanks in advance.

Mateo

Test_stand.pdf (182 Kb, 12 downloads) Test stand

Looks like a rotary table to me, which is just a bevel gears set mounted on bearings with a large hole through the ring gear shaft. Works about the same as the rear differential in trucks.
In your case, I don't think that the OEM (probably a machine shop) will have data. But I think that now we understand the application.