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?
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? Contact us!
LMS Test.Lab processing links:
LMS Test.Lab acquisition tips:
General Knowledge articles: