Vibration Analysis Know-How: Quick Intro to Vibration Analysis

hello and welcome to this quick presentation on spectrum analysis time waveform analysis and phase analysis my name is Jason Tranter the founder and managing director of Mobius Institute Mobius Institute provides vibration training and accredited certification so first let's take a quick look at spectrum analysis the spectrum is generated by the time waveforms from the machine we'll take a closer look at time waveforms in just a moment but in basic terms each component in the machine generates a single frequency and the spectrum makes each frequency easier to see and we can also see harmonics and sidebands in the spectrum that tells us that the motion within the machine and the forces that are involved and so on are more complex and simple vibrations or simple single frequency vibrations so if we were to look out of the raw signal from a vibration sensor perhaps placed on this bearing here or any one of the bearings it would appear quite complicated but what we're going to do is just break it down into a few simple areas so first I'm going to click this button which turns on the vibration from this gray shaft and the gray pulley now all the vibration we're about to see comes from this bearing here imagine that there's a nacelle Ramat is sitting on this bearing here but this is the a single source of vibration if we speed the Machine up a little then the frequency increases in the waves become close together and if we increase the amplitude we see higher amplitude or lower amplitude now that is one source of vibration that we might see from this machine another source of vibration we see would be from the bearing itself now the measurements taken on the bearing but within the bearing there are rolling elements and there are three different frequencies primary frequencies generated but things very simple we're just going to represent the bearing as having one unique frequency which happens to be a higher frequency than that once per revolution gray vibration that we saw before so there is the green vibration from the bearing at a different frequency to the turning of the shaft and we can see that you know the bearing was actually in good condition we wouldn't see any unique vibration from the bearing that as the fault develops and the amplitude increases at that frequency as I say in reality bearing vibration is more complicated than that let's just turn off that for a second and say what about the vibration generated by the fan itself now there's the once per revolution vibration we saw but if they will say ten blades on that fan then as each blade goes past our reference location the vibration transmits through the shaft to this point here on the bearing and it's kind of like hearing yeah phoom phoom phoom phoom from 10 times per revolution and therefore we actually have 10 cycles per one cycle of this vibration so there are three sources of vibration the orange vibration from the orange fan the green vibration from the green bearing and the gray vibration from the gray shaft and pulley so if we turn them all on we end up with something well you can see the three sources of vibration and you can see that there's you know no problem with the bearing and so on but in reality we don't see this we see this this red signal is the combination of all three if we look at them and in reality the vibration will be more complicated than that but what we're going to do is look at this in 3d so what we are seeing here is basically what we saw just before there's the gray vibration the green vibration in the orange vibration now what I'm going to do is rotate our view this is the passage of time this is amplitude but we've actually got a sort of a three-dimensional picture here because now we've separated the three waveforms that we've been talking about in terms of frequency so there's the frequency of the shaft turning is a lower frequency higher frequency the green vibration from the bearing and in this particular case the orange vibration from the fan is a higher frequency still so we've separated them into their three frequencies now instead of looking at it from this side and seeing the waveforms or the summation of the waveforms what if we looked at from this side and just looked at the ends of the spectrum well that is basically what the FFT or the spectrum does and there it is there's those three peaks if you like now as part of the FFT we chop off the bottoms we do some you know changes as part of the calculation but there you see whoops there's my higher orange vibration or green vibration in fact here we can see it a little more clearly you know if I've got vibration from the fan that's where I'm going to see it vibration from the bearing that's where I'm going to sit and vibration from from just from the ones for revolution vibration now if we had more unbalanced or we'd get higher vibration lower vibration good healthy bearing we don't see any of that vibration a bit of a bearing problem we see some more so there's lots more we could talk about in terms of spectra but that's the basic idea and you know if the vibration was normal we expect we always expect some vibration at the running speed but hey you know in a ideal world we wouldn't see any other vibration if there was unbalance though that vibration would be higher if there's misalignment well we might see 2x or 3x or 4x or 5x it's a different story looseness for rotating looseness we might see lots of these Peaks which are called harmonics in the case of bearing faults we see a lot of these Peaks again harmonics but this time of the the bearing frequency we might see little Peaks on either side as well they're called side bands in resonance we might see a high 1x peak but a broader base so there's lots of things we can look at in terms of the individual fault conditions but the spectrum how the spectrum changes tells us about the nature of the problem and just what amplitudes are achieved that tells us the severity so I mentioned that all this comes from the time wave form and the time wave form itself is very useful that's the raw signal from the sensor so in this example we're looking at you know we've already seen some waveforms in this case it's a little bit more complicated not really though as these teeth mesh together we see this cycle of vibration each tooth mesh gets an additional wave in this wave form and so if I had 21t fare let's say well then I'll have 21 of these little cycles per revolution of the shaft now if there was a problem with the gear let's say a broken tooth well each time that broken tooth goes through the mesh we get an extra spike now we're not trying to talk about give gearbox faults particularly the point is that the time waveform gives us some information which would be harder to see in a spectrum you know it's very clear what's happening in this case but in a spectrum it's more deep difficult and here is an actual example as this little damaged area goes through the mesh then we get this big spike of vibration here here here here and so on the vibration in between is what the mesh vibration should look like it should look like that now it's a different scale you know what we're looking at in between the big spikes is is this here so yes there's some variation but if I sort of tone my form like that normally I think everything's fine a few caveats to that but it's when I see big spikes or you know rises and falls in in the signal but time waveform analysis is therefore very important particularly if I've got impacts gearbox folds rolling element bearing faults and so on now phase analysis is an additional type of analysis that tells us much more about the motion of the machine if a machine is you know if the road is moving in a sort of a circular motion because of unbalanced phase tells us that if there was misalignment different sorts of forces different sort of motion phase tells us that a centricity bent shaft cocked bearing and so on the phase readings tell us what sort of motion the machine is going through and therefore we can tell what forces are causing that motion and therefore what sort of fault condition exists there's a couple of ways to measure phase the simplest technically but not the simplest way to measure it is that we put one sensor on the machine to measure the vibration and we have a once per revolution tachometer signal so this could be a laser tack or a photo tech there's other ways of doing it as well but once per revolution when it sees that white tape go by we get a pulse and that's like a timing reference and we can see where the peak of vibration is relative to that the easier way to do it is with to a seller ah meters you tell them analyser what the speed is and it says okay I can therefore see the motion so for example if we look at my little simulator here I'll put the reflective tape up on the shaft I'll put the photo tech there we'll start the machine and that's what the signal looks like from our laser tack or photo tech and then we put the sensor up on the machine and we can not only see what the waveform looks like but we can get a phase reading and then I can move the sensor and say well okay it's zero when I place or close enough when I place it up on top oops it's changed by about 90 degrees that might indicate unbalance and there's lots of things we can do we can compare the the phase reading there to the phase reading on the two phases see if we've got misalignment we can compare the top there to the top there to see if we've got will misalignment again or looseness and lots of things or we can stop the machine we don't want to hurt our fingers here take that away and instead use two Acela meters you know to channel analyzer and do the same sort of thing we can see a 90 degrees phase shift that's minus 90 just because I can swap those around it's now back to just 90 and we can do all the same sorts of tests it's easier to do this way we don't have to stop the machine so we can also use a strobe so if we start the machine if we were to look at that in slow motion we can see that red bolt well what I'm going to do is cause the strobe to flash once per revolution and it appears as if the shaft stops cause it doesn't stop and therefore you don't want to touch it but we can for example pop a sensor on the machine as we move the sensor it appears as if the shaft slowly turns in this case it turned by a quarter of rotation the bolt moved from the top to the side and that might indicate unbalance there's all sorts of things we can do with the with the strobe to use it properly and learn things but this isn't the presentation to really explain that but there are many applications you know we can see the belts flapping and all sorts of things with the stroke and Wayne in conclusion spectrum analysis is the most commonly used vibration analysis tool the peaks usually relate to the components within the machine so we can see what's happening with the unbalance with the fan blades with the gear teeth with the rolling elements in the bearing and so on it does help us diagnose a number of fault and it does help us to determine if there is a problem that we need to look at more closely time wait the time waveform is used to create the spectrum but it is also a very useful analysis tool and should be used particularly on gearboxes but also rolling element earrings and and other types of components you should be able to use time waveforms and phase analysis helps us understand the motion of the machine it can help distinguish between unbalance and misalignment and there centricity and bent shaft and other sorts of faults it is very important to understand the machine the fault conditions and the measurements setup in other words a little bit about signal processing so that you have an intuitive feel for not only how to take the measurement properly in the first place but when the vibration changes you'll understand what's happening inside the machine rather than just looking at a wall chart and hoping that what it looks like on the wall chart is what's actually wrong with your machine life is far more complicated than a wall chart ok well thank you very much for viewing this presentation I hope you found it useful and if you have any questions please send us an email you

Channel: LUDECAINC

Views: 75,204

Rating: 4.9408865 out of 5

Keywords: vibration analysis

Id: ZyIyWrHVFkA

Length: 14min 20sec (860 seconds)

Published: Mon Nov 30 2015