Ball Bearing Order Tracking
Ball Bearing Order Tracking
(OP)
I am looking for any information or person who has worked on using order tracking to evaluate NVH characteristics of ball bearings. Any help would be great.
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Ball Bearing Order Tracking
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RE: Ball Bearing Order Tracking
RE: Ball Bearing Order Tracking
RE: Ball Bearing Order Tracking
We used to use this technique on Navy shipboard turbine driven pumps and blowers because their governors often did not control speed very precisely. Rolling element bearings did not always create a lot of energy when they have defects and if the speed variations during data acquisition created "smearing" the bearing defects were sometimes lost in the noise. This was in the days when all the data was tape recorded before being "processed" so we needed all the help we could get. Even though our real time analyzers had 72 db dynamic range, the analog tape recorders only had about 40 dB dynamic range, so it was important to preserve any of the amplitude near the noise floor that we had, and "Order Tracking" helped us do that. The data was used for planning an overhaul period that was 6-12 months in the future so detecting a developing bearing fault was important.
When using this technique and setting up for data acquisition you define the FFT range in number of "orders" rather than a frequncy range like 0-1000 Hz or 0-60,000 CPM. Typically, you would define an FFT range as 0 - 20 orders and maybe a second higher frequency range such as 0 - 60 orders, depending on the characteristics of the machine. The problem was that you need to have the tach signal, so setup time to get the data was longer. Sometimes when we could not record a tach signal we could generate one from the vibration signal if the 1X RPM vibration signal was strong enough and we band-pass filtered it so that the 1XRPM signal actually appeared to the instrument to be a pulse train that it could track in the tach input channel.
I hope this helps for your application.
Skip Hartman
http://www.machinerywatch.com
RE: Ball Bearing Order Tracking
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RE: Ball Bearing Order Tracking
I think it is mostly a transportation industry term.
Skip Hartman
http://www.machinerywatch.com
RE: Ball Bearing Order Tracking
RE: Ball Bearing Order Tracking
I think with extended time synchronous averaging the amplitude of the non-integer harmonics like 3.67X, 11.23X, etc average downward, and the true 1,2,3X etc remain.
RE: Ball Bearing Order Tracking
The process I described (Order Tracking) is not time synchronous averaging (TSA). You are right that TSA reduces the amplitude of any non-synchronous peaks in the FFT, but TSA is a very different process, than Order Tracking.
TSA essentially times the start of each digitized time block of data acquired so that each block of time data is synchronized with some event. This event is usually the passing of some triggered part of a rotating shaft, but it can be some other event like a trigger based on the AC power supplied to a motor. The multiple blocks of digitized time domain data acquired are then averaged. The block of data that is the result of the averaging is then converted to an FFT that typically only shows harmonics of the trigger event.
The Order Tracking (OT) is quite another process. It does not eliminate the non-synchronous frequencies from the FFT. With OT, the "smearing" associated with a normal FFT captured on machines that are varying in speed results in a much reduced amplitude displayed in the spectrum because the energy at a specific "order of shaft rotation" keeps moving across several lines of FFT resolution. Order tracking varies the sample rate of the analyzer/digitizer at a rate linked to the shaft speed. This results in specific number of samples per shaft rotation rather than a specific number of samples per second. The FFT yields frequency energy that is locked into the same FFT lines instead of smearing across several FFT lines, so it is a much better representation of the true amplitude, even if it is a non-synchronous frequency.
Because the data must be captured with a speed trigger many people make the mistake of thinking OT is the same process as TSA. It most definitely is not the same!
Skip Hartman
http://www.machinerywatch.com
RE: Ball Bearing Order Tracking
"For example, the prestigious Sound and Vibration magazine (a freebe for qualified engineers)..."
It's also free to unqualified ones!
LOL!
RE: Ball Bearing Order Tracking
Skip Hartman
http://www.machinerywatch.com
RE: Ball Bearing Order Tracking
Sounds interesting, but coming from Michigan Tech, it may or may not have any practical application!.
LOL!