Doing a test and don’t have a tachometer? Or don’t have time to instrument a tachometer? Have a system in which it is impossible to measure the RPM?
No problem! Simcenter Testlab has you covered!
With the Offline RPM-Extraction add-in (Tools -> Add-ins -> Offline RPM Extraction, 20 tokens), it is possible to extract a RPM trace from the vibration or acoustic throughput data you collected.
1. Choose the throughput files of the signal you would like to track and replace in the input basket. Selected data could be a vibration or acoustic signal.
2. Go to the Time Data Selection workbook. Ensure the “Data Source” is set to “Input Basket” then click “Replace”. The throughput channels that were put in the input basket in Step 1 will appear in the Data Set.
3. Go to the RPM Extraction workbook. Select “Make trace list” to import the throughput data into this workbook from the Time Data Selection workbook. Select which channel to use to calculate the time-tracked colormap by checking the box in the “Selected” column (a blue box will appear). Then click “Calculate spectral map”. In the resulting colormap, it is desired to see a strong order that can be traced to determine the rpm. If necessary, change the processing setting for your map under “Settings…” until the desired order content appears.
4. Extracting the RPM:
4.A: Place the cross-hair cursor on an order.
4.B: Click “Accept Point”. This will accept this point for the order calculation.
4.C: Click “Predict Curve”. This will estimate the order trace and a black line will appear on the colormap where the order trace is estimated.
4.D: Enter the order number of the order the cursor is placed on. This is essential to get the correct RPM trace.
4.E: Click “Calculate RPM”.
4.F: The RPM trace will appear.
NOTE: Under the “Processing” area, there are three method options: the “One point method”, “Two points method”, and “Multiple points method”.
Try playing around with these different settings to see how they differ.
5. Using the “Save” button, a new run will be created in the Navigator. Offline RPM extraction will not store data back into the original throughput run. So, if you want all of your original throughput channels to save into the run created in RPM Extraction, you must add all the throughput channels to the input basket and import all the throughput channels into RPM Extraction (Steps 1 and 2).
5.A: Name the run.
5.B: Save the data.
6. View the data in the Navigator workbook. The data will be stored in a folder with the run name that was typed in the RPM Extraction workbook. The extracted trace will always be named channel “5555: RPM Extr”. Drag the extracted RPM into a plot to see what it looks like.
For this example, the actual tachometer data was also recorded. Below is the actual tacho data compared with the extracted RPM. You can see they are nearly identical.
Questions? Post a reply or email jacklyn.kinsler@siemens.com.
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Good afternoon friend!
I have a question respect the RPM extraction.
I'm reading this tutorial for practice this option in the LMS Test.lab, also I have the signal for the turbodata1 and when analyze the option RPM extraction, I'm a little confused respect to the values of the RPM results.
Show a follow figure:
I know that to convert RPM to Hertz the convertion factor is 60, so, for the same time point (7,13) I obtain 86,36 Hz in the spectral map and 1287,86 RPM in the RPM curve, but 86,36 Hz equals to 5181,6 RPM and not 1287,86 RPM, like the RPM curve. Im a little confused about that, please help me.
Grettings
Alvaro
Hello Alvaro,
In order to use Offline RPM extraction you need to be able to identify a dominant order in the waterfall / colormap and know what the order number is. For example, the black curve you've drawn is it 1st, 2nd, 3rd, or 4th order ? You've entered 4th order and we use that calculate the RPM. So the speed is calculated as ~ (86.36 Hz (cycles/sec) * 60 (sec/minute)) / 4 (your order specified).
If you specify 1st order and re-calculate the RPM you would get the speed you expect based on 1st order.
Kevin
Very thanks Kevin.
Well, is a nice tool to know the RPM and I understanded now about this option, but is necessary to know the order dominant. what happen if the dominat order isn't RPM of the motor? because I did an experimental test of a motor and the the owner of the motor said me that the RPM is 1800 RPM, but I don't see anyone peaks at this frecuency (I installed 4 sensores) in my FFT's spectrums, the RPM of the motor always will be the order dominant?
Hello Alvaro, if the order is very quiet or does not vibrate much it may not be the dominant order. If you can hear it, can you use a microphone rather than an accelerometer? I would be very suprised if 1800 RPM is the speed of the motor that 30 Hz or it's harmonics do not show up at all.
If you are following the tutorial, you can determine the RPM using 1st, 2nd and 4th order of the engine if I remember correctly and later in the tutorial you can determine the speed of the turbo using 1st or 2nd order of the turbo signal.
Kevin
Hello Kevin
The motor information indicates revolutions at 1770 RPM, however, analyzing the spectrum of accelerometers installed in the motor housing (horizontal and vertical directions) it is not possible to identify peaks or harmonics at that speed of rotation (ie, equivalent in frequency). However, there are peaks identified in other frequencies that would be related to faults in the bearings, belts, etc. But to be sure, it is necessary to determine the rotation of the motor in the FFT. We have not bought a tachometer, would it be better to buy it in these cases? Is it possible that the motor's axis is well balanced and the corresponding peak can not be identified in the FFT?
Grettings
Alvaro
Hello
Since i don't have a tacho, but i want to extract the RPM and predict the order. I know that my machine runs at 800+/- 10 rpm. How should i collect this data? Should i run a signature analysis using stationary as tracking methos and then follow the steps you have shown?
Hello HrushikeshPatil,
We just noticed that nobody replied to your question. To use offline RPM extraction the input is a throughput file (time history) with at least one channel that has a dominant order and you need to know what that order is.
You can use Signature Acquisition using either the Stationary tracking method or Tracked on Time.
Since you know the operating speed that helps. So, measure the throughput data, then in Offline RPM extraction calculate the spectral map. You can tweak the Settings to increase or decrease the frequency resolution and frame size if needed to improve the colormap. You then draw a curve on it using the one point, two point or multiple point methods as shown above.
Then specify the order and predict the rpm. If the rpm is not close to 800 rpm in your case, then the order is incorrect. Try a different order number until you get the rpm you expect and the save the run. You can then process the saved run.
Hello Alvaro12,
We just noticed you did not get a reply. Similar to the other question here, it helps that you know the speed is 1770 RPM. If you can draw a curve on it using the one point, two point or multiple point methods as shown above. You can then specify an order number, calculate the speed and compare it to 1770 rpm. Iterate on that until you find an order number and a line on the colormap that corresponds to 1770 rpm. You can then save that. If you know the test article well enough, hopefully you can track the order number back to something physical.
A tachometer is always useful test equipment.
You are correct, 1st oder may not be a dominant order if it's well balanced.