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Asset Condition ManagementPosts About vibration/alignment/balance
CTA - Cyclic Time Average (SKF)/Contribution Profile
Registered Member Thanks John, I am using @ptitude Analyst from SKF. This is a tool for analysis gear tooth defects.But i am not sure about the interpretation. following the tecknical paper about. https://skftechnicalsupport.ze...-SKF-ptitude-Analyst [ more ]
Registered Member I am not really familiar with the software you are using but can you do multiple revolutions of the circular plot? I’m used to seeing about 8 revolutions. If they lay more or less on top of each other it is an indicator of something related to the rotor. In the case of a gear, perhaps something related to the hob. If the pattern constantly rotates, then perhaps related to a bearing on the rotor. [ more ]
Registered Member In this shaft 33. Please look at the picture. Thanks. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Omnitrend Help
Registered Member Dave, yes, watched it. There are things in Omnitrend that are very bothersome and I’m beginning to think it is the fault of using Microsoft Access. Emonitor is still the best by far, and they use a commercial third party database , like Gupta. If you change a collection spec, they all change. Could not duplicate that in OT. I built an alarm band spec in the alarm editor and it looked great. I went back out to look at the data and the RMS bands at the higher frequencies had all shifted! I’ve... [ more ]
Registered Member https://www.youtube.com/watch?v=4dOUlxYDgHM Came across this hour long video, may have what you are looking for Dave [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Subsynchronous vibration multistage high pressure centrifugal pump
Registered Member @Registered Member Hey Ayman, thanks for replying. I haven't got the critical speed data from factory and haven't been able to check it myself on site [ more ]
Registered Member @Registered Member Hey Ralph, thanks again for replying. I attached the wrong files, my bad. Attached the sectional drawing. For the trouble in viewing images have you try to re-login? For the spectrum, as I could tell there is no sidebands, at first I thought I saw sidebands too, but turns out it is subsynchronous peak at 69 Hz, pump 1X is at 88.9 Hz. For change in operation, as you can see in my other attachment files, there is change in flow and pressure but it was affected by the speed... [ more ]
Registered Member I am totally confused as to what is wrong with this thread and the replies and why I can not see all the the replies,or my last image I posted. I am posting the image again. Seems as though, somehow, I have been partially block out of the thread or there may be something wrong with my computer.???????????????????????? Thanks for any help on why this might be happening. If I am "blocked-out", tell me and I will cease to question this problem. Here is the image I posted earlier. Thanks. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Oscillating overall vibration of Motor
Registered Member Many good suggestions have already been given by the forum members. What I advise is to compile the suggestions into a checklist to systematically go through them. In order to eliminate some of the mentioned possibilities, there is a need to take additional measurements with specic configurations or perform more tests. For example, to verify the sidebands and confirm the frequencies, I would take high-resolution data with a high number of averages say 50. I would also perform a shutdown test... [ more ]
Registered Member Thinh, Hello, I have a couple of questions. See the M2V Point Spectrum image. Referencing to Point # M2V The sideband frequency appears to be of a low frequency range, similar to, # of poles times slip frequency, {(1800 –1780)}x 4 = 80 cpm/60 Hz = 1.33 Hz. But this particular pattern could be because you captured this spectrum at just the “right” time to give the impression of electrical problems. Have you more data, on a different day, on this point M2V? But on the other hand, if this is a... [ more ]
Registered Member The beat, in my opinion, is coming from: loose bearing fit to shaft/housing in motor, soft foot, worn coupling or the 2 running pumps are beating with each other. The imbalance from 1 pump eventually lines up with the imbalance from pump 2 then eventually the separate again runs smoother. Your recent plot, thank you, shows a "skirt" just to the left of 1x rpm, this is typically a natural frequency. So when the pump starts, just before full speed, the vibration will increase, then drop... [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Multiple speed correction calculation Required
Registered Member There are balance software that can use multiple speeds. I gather that the high-speed balance machine doesn't consider mulitple speeds. [ more ]
Registered Member When you use the term "operating speed" are you referring to the test speed in the balancing tunnel which can at times be different than the final machine operating speed? [ more ]
Registered Member Here, https://www.maintenance.org/to...ackage-rotor-balance [ more ]
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Asset Condition ManagementPosts About Asset Condition Management
How to detect Centrifugal Compressor Liquid Carryover
Registered Member The effects of carryover liquid: impeller can be broken, very high vibration. posible causes: heat exchanger broken, the water traps damaged. Regards. [ more ]
Registered Member Thank you for the reply gents. What effect liquid entrainment will have on compressor suction and discharge temperature, pressure and flows keeping in view centrifugal compressor? [ more ]
Registered Member Greetings team, Very interesting question and appreciated the answer from Mr. Al- Shurafa. 1. Centrifugal compressor is oil compressed and separated the pressure gas or air is released oil free. 2. If liquid carry over, the oil drum level increases and no pressure gas or air is released. The high level alarms of oil drum is an indication of some liquid entered in compressor system. 3. The liquid can emulsify the oil system, if that is not liquified gases. 4. If such risks are there system... [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Alarm Ge
Registered Member I know a place or two where they have one of those installed [ more ]
Registered Member I added these measurements to an online system that had permanently mounted accelerometers (stud mounted and properly torqued) and STILL did not get repeatable results. [ more ]
Registered Member SKF has mentioned in the past (if I remember) that this is extremely sensitive to sensor position and mounting. This requires faith in a technology that I do not have. I've seen some case histories purported to support this. I wonder how many case histories do not support this. I have seen material supporting/promoting the use on fluid film bearings. ???? [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Electrical Motor vibration Issue
Registered Member Re: Electrical Motor vibration Issue [ more ]
Registered Member Abu Nafi, Thanks for the reply. Sounds like maybe, if it running good now, it is best to leave it alone for now, huh? Thanks, Ralph [ more ]
Registered Member I still look for the relation, but seems no relation, in the meanwhile I confirm that the Fs .79 What does "Fs .79" Refer to? I think, .79 Hz refers to Slip frequency, Speed 428.4 and we have Speed in the plate 425 RPM So, we have difference of 3.4 RPM, Fs=Slip#No.pole/60 = .79 HZ Actually, there is a question had slipped my mind days ago, can we distinguish the type of loading that the bearing exposed to (radial or axial?) from the spectrum? if so, how? I am not sure about the "load" from... [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Vertical thermal offset for wind turbines
Registered Member Correct. It is a fixture that rotates so you don' t need to rotate the gearbox shaft, which would be almost impossible, considering the blades would still be out there sitting in the wind! [ more ]
Registered Member In a planetary arrangement (fixed annulus/ring) the gearbox may also have an alignment fixture so check with the OEM. [ more ]
Registered Member The results are in !!! 2.0 mm offset was dialed into the laser with the wind turbine cold. Ran for 1 hour to come to temperature and the final offset was just 0.11 mm!!! I love it when science works. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
High axial vibration in a centrifugal fan
Registered Member Is this fan fed from both ends? If yes, then this is usually the result of uneven damper settings, and/or the fan is not centered in the fan housing. [ more ]
Registered Member Strange; 9 mm/sec is 10 divisions? Why not 9 divisions? [ more ]
Registered Member Hi John, that's 9 mm/s RMS, values at discrete frequencies can be roughly estimated from this value. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
How to calculate residual unbalance from vibration data after balancing
Registered Member Balance grade as defined in ISO 21940-11 is in mm/s. If you read the standard, it should answer your questions. 1. There used to be an Annex (if I recall correctly) in an old ISO 1940 that reminded one that it was not possible to relate vibration to balance grade. 2. 2.5 mm/s - See ISO 21940-11. 3. Question not well defined. Basicly the balacne grade, G, is the permissible mass eccentricity multiplied by the rotational speed (max) in rad/sec. More in ISO. [ more ]
Registered Member https://www.hornusa.com/filead...ical_Info_-_2015.pdf [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Electric Motor Sub 1X Vibration
Registered Member They changed the compressor and noticed after that. But who knows, maybe it has always been like that but wasn´t noticed until replacement of compressor. This motor has 6316 bearings. And in evening the technical manager sent me these pictures. It seems the axle is damaged ( Grey Area ) but bearing seems ok. [ more ]
Registered Member Has it always exhibited this phenomenon or is this new? If you zoom in, is it exactly 30 Hz or something slightly below 30? VFD? On 60 cycle rating is 290 kW (388 HP). Does it have rolling element bearings or fluid film bearings? [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Balancing of flexible rotor on hard bearing balancing machine.
Registered Member Probably I've just seen the small turbine rotors [ more ]
Registered Member If you are talking about field balancing, the end planes may be more accessable. I have seen center planes on steam and gas turbines accessable in the field (not always so easy). I think there are paractical reasons to use the end planes. I remember trying to get the field guy to open a port for a center plane on a steam turbine. He tried for a good while but the port was frozen by rust. We made due with the end planes. This must have be a first mode problem--don't really recall the... [ more ]
Registered Member Bill, I've seen many rotors (stream turbine) that have groves for balancing only at at their ends (first and last wheels), are this places choosed at design because of the modal characteristics expected for the rotor, or a more simple approach because it's easy to work with [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
High vibration at 1×BPFI at Motor DE Axial during no load condition
Registered Member To make it easier for the readers, it's better if the spectrum x-axis is expressed in order while the speed is accurately configured. WRT the intermittent/unstable vibration, one of the possible reasons is the unstable lubrication (oil flow, dirt in the lubricant, unstable grease location, etc.). Another possible reason is the thermal effects either from the process side or from the metal expansion/contraction. Clearances can be sensitive to temperature due to the dimensions of the machine's... [ more ]
Registered Member thank you @Registered Member, @Registered Member for valuable comment and sorry for late reply. in continuation with above problem we have taken motor solo run trial (Without pump coupled) on 25.04.2022 and then coupled with pump. Overall vibration again increased drastically on motor both end in axial direction at 1X and 2X. interestingly without any work done and without pump stoppage this vibration again reduced with dominant peak at around 12K CPM at motor NDE axial and at 14560 CPM at... [ more ]
Registered Member "I am still wondering why this does not excite 1X vibration ?" Perhaps just a misunderstanding of terminology. Vibration at 1xSS is the result of an excitation force such as rotor unbalance or shaft misalignment. The foundation does not excite vibration, but it can amplify the vibration response. Several factors with the "loose motor base" can occur, such as change in natural frequency, change in damping, change in vibration transfer from motor frame into foundation, change in hammer contact... [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Orbit Plot Reverse Precision
Registered Member Alright sir i will try and send you the same 🙏 [ more ]
Registered Member At least with my hardware, visually looking at the plots you've provided is challenging. I can't resolve amplitudes or the actual shapes and characteristics of the plots. I suggest you learn to use the screen copy feature within System 1 and paste the data into a Word document, then save as a PDF. As an example of what I see I saved one of your plots and inserted it into a Word document. The attached image is what I see, very blurry and unable to read any of the associated text. One thing of... [ more ]
Registered Member Please let me know if I can provide you any other information 🙏 [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Motor High vibration 1X
Registered Member Ramanathan, Thanks for the reply. Based on the data you posted, quote: "We found in the FFT 1X with pole pass frequency side band (amplitude 0.37 mm/sec RMS) in the motor and I zoomed the 90 to 120 order 2xRBPF frequency with 2 line frequency and found 675 cpm(0.375X )side band in the mentioned frequencies." sounds like you may have a rotor with rotor bar problems, if the frequency of these " pole pass " sidebands you are referring to, are equal to the number of poles times the slip... [ more ]
Registered Member Thanks for for reply Mr. Ralph, We found in the FFT 1X with pole pass frequency side band (amplitude 0.37 mm/sec RMS) in the motor and I zoomed the 90 to 120 order 2xRBPF frequency with 2 line frequency and found 675 cpm(0.375X )side band in the mentioned frequencies. Thanks RS [ more ]
Registered Member Ramanthan, Can you take a high resolution (6400 lines) spectrum from, 0 to 120 orders and zoom in from 0 to 10 orders, and also zoom in on the data from, 90 to 120 orders and measure the sidebands, if any exists, in these 2 areas, not displaced in orders, but displayed in Hz? Thanks, Ralph [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Feedwater Pump High Vibration at Partial Load Range
Registered Member To add more clarity (I hope ) and to be more specific: 1. No, I have not heard of a situation like this before. Typical problems with a recirc line occur when we deviate far from the BEP....which I am sure you are already aware. Most of the problems I have seen are at one extreme or the other and not at partial recirc flow as you indicate. ASSUMING a good design up front; hence my asking about whether it was always like this or something new, perhaps changes to the flow path. 2. I did have... [ more ]
Registered Member Your statement, "Vibration is normal at low load - when Automatic Recirculation Valve (ARV) is close and at full load - when ARV is fully open" , is confusing. Let's change this discussion from "load" to "flow" and show us what this means on the pump's head curve which will be much more useful and informative. It would also be helpful to the members here if you can provide background information (e.g. Has this issue always been a problem? <--suggesting a design issue OR something that... [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Standard query ANSI/ASA S2.75 alignment
Registered Member Might be of interest; https://oaktrust.library.tamu....ce=1&isAllowed=y [ more ]
Registered Member These are "different alignments" With a spacer shaft (CML) as in your document, there are two flexible planes, the spacer shaft (CML, middle shaft) splits the angle between the shafts (driver and drivem) in two, the tolerance between shafts (driver and driven) is twice as much when compared to a simple coupling (pin-bush, gear, grill, etc) at each flexible plane the offset between the spacer and shaft (driver or driven) is zero, therefore you only have one angle tolerance at each of this... [ more ]
Registered Member I would be using the distance between the teeth on the two hubs. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
2140 balancing issue
Registered Member Check the RPM using the rpm option from analyze mode, it will show the FFT of the tech pulse, change the plot type it will show you the time waveform of the tech pulse, look at the volt peak level and adjust the trigger accordingly, default trigger is 2 volts and it is correct for photo tech, speed vue works with a different way, and can change the trigger point/location/phase angle if the shaft has more reflection/scratches. I suggest changing the trigger level to 4 volts for the peak vue... [ more ]
Registered Member Afaik peakvue send an analog output that depends on external factors therefore there's no trigger level for all conditions. [ more ]
Registered Member It was the trigger level. Never had to raise it that high in the past. Not sure what changed, but something did. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
accelerometer in rotating disc perimeter
Registered Member interesting Walt, for sure another mass 180 degrees apart is necessary to cancel the unbalance of the sensor Then you answered one of my concerns. Setting up the sensor in the rotary part perimeter, tangential, axial and radial for the triaxial sensor, it is possible to still read an amplitude and phase value and perform a balancing. I will take in mind and try to do if I have the opportunity i thought, beeing the unbalance 1x synchronous component and with a constant rotating speed (no... [ more ]
Registered Member My understanding is that two tangential accelerometers, 180-degrees apart, are needed to cancel (by subtraction) the lateral motion from pure torsional motion. I would be more convinced with the Erbessed-Instrument "experiment" if another direct measure of torsional vibration was used for comparison. Perhaps for that experiment the torsional motion was dominant compared to lateral motion. I use the optical encoder method (located for high torsional displacement/velocity) and the Binsfeld... [ more ]
Registered Member thanks! so, I would measure torsional vibrations by placing the accelerometer in an eccentric position... [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
EMERSON CSI 2140 WATERFALL
Registered Member You can choose the axis units either speed or orders, in VA tab just right click the axis or plot, if using plot data is somewhere but can't remember [ more ]
Registered Member Sounds like what you want is what is termed a cascade plot. I'm not into Emerson/CSI equipment but the video at Collect Cascade Measurements might be of help. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Vibration limits for centrifugal fan
Registered Member That fan category is BV-3 and in the limits chart it is suggested "See ISO 10816-3". When you go to that specification, specifically section 5, the logic behind setting limits is discussed extensively. At least that is true in the version I have, the 1st edition dated 1998-05-15. You'll find that many of the "steps" build on a 25% factor. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
High harmonics (2.5X, 3X and 3.5X) in Journal Bearing of GEN
Registered Member Unfortunately my resources, which are quite old, don't have any info on a 18 cylinder "V" arrangement. You could probably get the information from the engine OEM; ask for the "major and minor" orders. They might also be able to supply a torsional analysis which might have been done when the machine was purchased. [ more ]
Registered Member It is an 18-cylinder V. engine, the ignition sequence is as follows: A1-B1-A3-B3-A5-B5-A7-B7-A9-B9-A8-B8-A6-B6-A4-B4-A2-B2. We do not have long time trends. However, the trends of these previous months are shown below. We have recommended to check the elastic mounting where the engine is supported. However, we have not yet received any news of such a check. Apologies for only just answering but I have been out of the office. [ more ]
Registered Member At 18 cylinders, probably inline. Can you provide the firing order and I might be able to look up the “major” and “minor” orders. You also mentioned the engine is “resiliently mounted on springs”. Do you mean spring as in the traditional sense (a piece of steel wound in a coil) or the type with rubber elements. The rubber type do age over time so check for a recommended replacement interval. Do you have any trend data to support an upward climb in amplitudes. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Square Orbit Plot, what would possibly?
Registered Member I add here a simple orbit simulator from RITEC. It allows for 3 frequency inputs (amp. and Phase), plots blank-bright/bright-blank once per rev trigger mark, accommodates different prox. probes and keyphasor orientations, and machine speed/direction of rotation can be altered. The X/Y time waveforms are also plotted. https://www.ritec-eg.com/Libra...-Plot-Simulator.html [ more ]
Registered Member In your early data you showed the DE orbit marked with the notation "5 Revolutions". I suggest you look at the NDE data but only view a single revolution. Step through the revolutions if possible to establish a clearer picture of the orbit shape. It might not be as random as you might think. When you view the attached, note the similarity of the DE orbit overall shape to the inside of the NDE orbit. What might prove interesting is a comparison of the DE and NDE single revolution orbits. [ more ]
Registered Member The data looks the same for each plot. However, one is an A vs. B, and the other is a B vs. A. Could this be a feature of the box used, perhaps an option? [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Belt Frequency
Registered Member I add here a Belt Frequency Calculator by RITEC. https://www.ritec-eg.com/Libra...ency-Calculator.html [ more ]
Registered Member Belt Frequency = 2*pi*R1*F1 / BeltLength where F1 = frequency of rotation of larger pulley BeltLength ~ 2*C + 2*1.57*(R1+R2)+[(R1-R2)^2]/C C = center-to-center distance between pulleys R1 = radius of smaller pulley, R2 = radius of larger pulley "Belt Frequency" above is inverse of the time it takes the belt to travel rotate once. It is not the belt natural frequency. See attached for derivation of an alternate calculation of belt length * Edited to correct the message/attachment by dividing... [ more ]
Registered Member 3.142 x sheave pitch diameter x sheave rpm, divided by belt length. [ more ]
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Asset Condition ManagementFor PdM Beginners Only
How to calculate belt frequency
Registered Member I add here a Belt Frequency Calculator by RITEC. https://www.ritec-eg.com/Libra...ency-Calculator.html [ more ]
Registered Member HOW TO IDENTIFY RESONANCE AND WHAT TO DO IF RESONANCE HAPPENS? WHAT IS THE USE OF BUMP TEST? [ more ]
Registered Member On-line calculator at https://www.ctconline.com/fileup/VIBCALC.lzx.swf . Just watch the selected units ("Imperial" or "metric"). John from PA [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
shaft alignment rim face method using simple excel sheet programme
Registered Member I add here Shaft Alignment Calculators by RITEC. In these calculator, one could generate numerical and graphical results based on machine information and dial readings. A PDF report can be generated as well. Reverse Method EU (Mils/Inches): https://www.ritec-eg.com/Libra...nches-Angle-pdf.html Reverse Method SI (mm/cm): https://www.ritec-eg.com/Libra...cm-mm-Angle-pdf.html Face & Rim (Mils/Inches): https://www.ritec-eg.com/Libra...nches-Angle-pdf.html Face & Rim SI (mm/cm): ... [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Reverse dial indicator to laser alignment conversion formula
Registered Member I add here Shaft Alignment Calculators by RITEC. In these calculator, one could generate numerical and graphical results based on machine information and dial readings. A PDF report can be generated as well. Reverse Method EU (Mils/Inches): https://www.ritec-eg.com/Libra...nches-Angle-pdf.html Reverse Method SI (mm/cm): https://www.ritec-eg.com/Libra...cm-mm-Angle-pdf.html Face & Rim (Mils/Inches): https://www.ritec-eg.com/Libra...nches-Angle-pdf.html Face & Rim SI (mm/cm): ... [ more ]
Registered Member "People, not lasers and dials, move equipment!" What a great quote! What I noticed is that there is a lot of emphasis on the measuring instruments and calculations that is way more than what is given to the feild needs like cleanliness of surfaces, inspection of possible cracks or restrictions, correct way installation of shims etc. The know how in such aspects is extremely essential but unfortunately these aspects are given less attention in the literature. But that is only my thought and I... [ more ]
Registered Member From the first link I provided “...However, when it gets down to the correction in the field, one must get down to hard rock fundamentals. The cold alignment will be done with measuring devices in the field by machinists, technicians, and/or engineers. Several know how to determine the moves. Very few know how to move the machines graciously and accurately! Piotrowski recently said, "People, not lasers and dials, move equipment!". [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
alignment programs
Registered Member I add here Shaft Alignment Calculators by RITEC. In these calculator, one could generate numerical and graphical results based on machine information and dial readings. A PDF report can be generated as well. Reverse Method EU (Mils/Inches): https://www.ritec-eg.com/Libra...nches-Angle-pdf.html Reverse Method SI (mm/cm): https://www.ritec-eg.com/Libra...cm-mm-Angle-pdf.html Face & Rim (Mils/Inches): https://www.ritec-eg.com/Libra...nches-Angle-pdf.html Face & Rim SI (mm/cm): ... [ more ]
Registered Member John the OP, Following up on Stan's comments: Search: android app for shaft alignment https://play.google.com/store/...turlaser.dials&hl=en Search: iPhone app for shaft alignment https://itunes.apple.com/us/ap...alc/id364490317?mt=8 Some additional resources: "This online shaft alignment software helps you to align machinery using the reverse indicator method. Just enter the indicators' readings to obtain the plot of the relative position of the shafts centerlines and the corrections... [ more ]
Registered Member There are now smart phone apps that can do both rim and face and reverse dial. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
reverse indiactor alignment: a simple excel programme
Registered Member I add here a Reverse Method Shaft Alignment Calculator by RITEC. In this calculator, one could generate numerical and graphical results based on machine information and dial readings. A PDF report can be generated as well. EU (Mils/Inches): https://www.ritec-eg.com/Libra...nches-Angle-pdf.html SI (mm/cm): https://www.ritec-eg.com/Libra...cm-mm-Angle-pdf.html [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
energy correction factor of hanning window?
Registered Member I add here a simple Windowing Demo from RITEC. In this simulator, the user can generate single or dual frequency signals, and apply several different types of windows on them to view the effects of non-bin-centered data, whereby leakage of energy to adjacent bins occurs; a result of processing finite-duration records. There are several types of windows available in this simulator including: Hann (Hanning / Raised Cosine), Bartlett, 4-term Blackman-Harris, Flat-Top, and Hamming windows. The... [ more ]
Registered Member Thanks for your help. [ more ]
Registered Member Pete, The definition and methods of computing Fourier transforms vary. In mathematics it is often useful to scale the transform so that it is a unitary operator - or in plain speak the spectrum has the same norm (rms value) as the time based signal (functions on a circle [Fourier series vs World Series] or on the real line). Look at the terms of a Fourier series as +/- frequencies (i.e. sine and cosine series vs complex number series); the 0th term has a different scaling factor from the... [ more ]
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Asset Condition ManagementFor PdM Beginners Only
Need some help understanding FFT amplitude scaling
Registered Member I add here a simple Windowing Demo from RITEC. In this simulator, the user can generate single or dual frequency signals, and apply several different types of windows on them to view the effects of non-bin-centered data, whereby leakage of energy to adjacent bins occurs; a result of processing finite-duration records. There are several types of windows available in this simulator including: Hann (Hanning / Raised Cosine), Bartlett, 4-term Blackman-Harris, Flat-Top, and Hamming windows. The... [ more ]
Registered Member Dear Post it on vibration/alignment/balance board. Then It may be answered by an expert if he can.... Zaheer [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Calculated Overall - Hanning vs Flattop
Registered Member I add here a simple Windowing Demo from RITEC. In this simulator, the user can generate single or dual frequency signals, and apply several different types of windows on them to view the effects of non-bin-centered data, whereby leakage of energy to adjacent bins occurs; a result of processing finite-duration records. There are several types of windows available in this simulator including: Hann (Hanning / Raised Cosine), Bartlett, 4-term Blackman-Harris, Flat-Top, and Hamming windows. The... [ more ]
Registered Member Ron, From your sales experience, do you have an opinion whether most of the major vibe box vendors calculate the peak-overall from the spectra using square root sum squares w/ correction factors (as Pete explained above)... or do some pick the overall directly off the time domain with a peak detector? A friend who uses a different vibe equipment vendor than us said he is able to choose. We don't have a choice... our box just calculates from the spectra. If we want "true-peak", we must just... [ more ]
Registered Member I guarantee you will have fun playing with a shaker and your analyzer. It will also be very instructive. I used to sell FFT analyzers and did the same exercise with a signal generator. It allowed me to better understand window functions, how they affected the data, and that the software correctly adjusted for the actual signal amplitudes. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Hanning or flat top window
Registered Member I add here a simple Windowing Demo from RITEC. In this simulator, the user can generate single or dual frequency signals, and apply several different types of windows on them to view the effects of non-bin-centered data, whereby leakage of energy to adjacent bins occurs; a result of processing finite-duration records. There are several types of windows available in this simulator including: Hann (Hanning / Raised Cosine), Bartlett, 4-term Blackman-Harris, Flat-Top, and Hamming windows. The... [ more ]
Registered Member Noise 'skirts' around even a 'pure' sine wave can often be phase noise. See: http://en.wikipedia.org/wiki/Phase_noise A/D converter jitter, time base jitter, and the signal itself will all contribute to these time-domain sampling 'jitters' that result in phase noise. Then add to that all the FFT math limitations from truncated numeric operations and you can easily get noise of the kind described. [ more ]
Registered Member Then try the measurement again at 12800 lines with the flat top window and the hannning window as a backup and see if the greater resolution helps enough. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
filtered orbit plots
Registered Member I add here a simple orbit simulator from RITEC, which is free and immediately ready to use. It allows for 3 frequency inputs (amp. and Phase), plots blank-bright/bright-blank once per rev trigger mark, accommodates different prox. probes and keyphasor orientations, and machine speed/direction of rotation can be altered. The X/Y time waveforms are also plotted. https://www.ritec-eg.com/Libra...-Plot-Simulator.html [ more ]
Registered Member Agree, but the orientation of the transdures matter, too. Sometimes one may have non-orthogonal probe locations; these can be corrected for orbits. When properly plotted, the orbit is the orbit, with or without a taco, bing, mark. Relative phase is inherent in the plot if done correctly. Some may remember Charlie Jackson placing his oscilloscopes on 2x4's (I am sure there is a metric equivalent.) at 45 degrees. This way the orbits and physical vibration aligned (with or without bings) when... [ more ]
Registered Member Gary, do a find (here) on "orbit tutorial". You should find a good document by Steve Schultheis, formerly BN. [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
ORBIT PLOT
Registered Member I add here a simple orbit simulator from RITEC, which is free and immediately ready to use. It allows for 3 frequency inputs (amp. and Phase), plots blank-bright/bright-blank once per rev trigger mark, accommodates different prox. probes and keyphasor orientations, and machine speed/direction of rotation can be altered. The X/Y time waveforms are also plotted. https://www.ritec-eg.com/Libra...-Plot-Simulator.html [ more ]
Registered Member John, Thanks for the attachment & rules. Actually i have it in my notes from Bently Book which i had read before but i dont have it now. Let me also also add the axis are measured perpendicualr to the probes (3. At any given frequency the larger of the forward or reverse component defines precession for that frequency.) This was what im asking. In the figure 8, the Full FFT showing somewhat equal 1X & clearly higher 2X but the trigger dot clearly looks forward. I was expecting it to... [ more ]
Registered Member Based on what you are asking, I think you are making reference to the figure 8 shaped orbit but I'm not sure of what you are asking when you state "Should the orbit show the same". Can you clarify? The four smaller box are predefined orbit shapes. I've attached a PDF that shows each case and the relative amplitudes used in the generation of the orbit. Keep in mind a few basic rules of full spectrums. 1. At any given frequency the sum of the forward and reverse components is the major axis of... [ more ]
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Asset Condition ManagementPosts About vibration/alignment/balance
Software for creating orbit
Registered Member As explained above, there are numerous ways to plot orbits for simulation purposes. I add one more from RITEC, which is free and immediately ready to use. It allows for 3 frequency inputs (amp. and Phase), plots blank-bright/bright-blank once per rev trigger mark, accommodates different prox. probes and keyphasor orientations, and machine speed/direction of rotation can be altered. The X/Y time waveforms are also plotted. https://www.ritec-eg.com/Libra...-Plot-Simulator.html [ more ]
Registered Member OK, Thanks for all the replys, I have been up the garden path and got a little lost. Mathematically I understand what needs to be done in general terms. However I am still missing the details. I know I have to convert the acceleration data ( in .wav files) to displacement. I then need to combine the horizontal & vertical components into to produce the orbit. However I don't know how to convert the wave files (.wav format) into a file format I can use? I don't know the formula to convert... [ more ]
Registered Member Bently Nevada has a training CD called Machine Library in which there is a module called "Orbit Simulator". The software can add in, I guess, up to 4 vibration signals. Each signal consists of X and Y discrete/spectral components (amplitude, phase and frequency). It is very good tool for illustrating the effect of any components. Attached is a print screen of a sample. (I'm not affiliated with Bently Nevada) Important note: creating a real orbit requires two time waves running... [ more ]
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Asset Condition ManagementPosts About Motor Testing
Electric Motor RPM drop
Registered Member I think the possibilities in order of likelihood are: 1. Miswired motor (makes the effective voltage lower). If the motor is supposed to be run in delta and you have it running in wye, then it will see sqrt(3) less voltage on the windings and it will develope a factor of 3 less torque, which may allow it to stall at a lower speed and possibly not trip on overloads. (Obvious way to investigate that: was the motor worked on since the last time you checked speed?) 2. Does the motor have a vfd... [ more ]
Registered Member Change in VFD output to motor, motor shorted phase to phase, broken rotor bars, motor connected incorrectly, two speed motor, all can cause the motor to "slow down". You provide no details of your application to go any further..... Dave [ more ]
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