Want to interface a Polytec laser vibrometers with a Simcenter Testlab and Simcenter SCADAS data acquisition system? This article covers how to interface with different Polytec products shown in Figure 1.
Figure 1: Polytec Laser Vibrometer products.
This article is not intended to be a complete guide to using a Polytec (www.polytec.com) laser vibrometer products. It only explains how to interface Polytec laser vibrometers with Simcenter Testlab software and Simcenter SCADAS hardware.
Contents include: 1. Single Point Laser Vibrometer 2. Rotational Laser Vibrometer 3. Scanning Laser Vibration via Universal File
1. Single Point Laser Vibrometer
The Polytec VibroGo single point laser vibrometer measures vibration at a single point or location. An analog voltage proportional to the vibration can be output from the laser and digitized using Simcenter SCADAS hardware.
The vibration data can be acquired from the laser in real time along with other analog channels (accelerometers, etc) with Simcenter SCADAS hardware.
1.1 Hardware Setup
The VibroGo laser vibrometer consists of the parts shown in Figure 2:
Figure 2: Polytec VibroGo laser vibrometer has a built-in touch screen (picture on left) for set up and an analog output (picture on right side, middle BNC) with vibration data.
The laser vibrometer measurement setup can be done entirely with the built-in touchscreen. On the back of the unit is a BNC connector that outputs an analog voltage that is proportional to the dynamic vibration being measured. This analog output is the center BNC connector. It is to be connected to a Simcenter SCADAS input channel.
1.2 Measurement Setup via Touchscreen
On the home screen of the touchscreen, there are three key settings as shown in Figure 3.
Figure 3: Home screen of built-in touchscreen of single point laser vibrometer.
The three key settings:
Output Format Quantity: Select from Acceleration, Velocity, or Displacement. A laser vibrometer directly measures velocity. Velocity will be used in this example.
Velocity Range: Set the range based on the expected level of the vibration measurement. It should be set high enough (with some overhead) to avoid overloads when measuring the vibration. It should not be set so high that the measurement resolution suffers.
Sensitivity: Based on the range, the sensitivity value is calculated. This value relates the analog voltage output to the vibration velocity. For example, the value might be “25 mm/s/V” which means that one volt of output is equal to 25 mm/s of vibration velocity.
1.3 Simcenter Testlab and SCADAS Settings
After connecting the output of the laser vibrometer to an input channel on a Simcenter SCADAS, the following information needs to be entered in the channel setup of Simcenter Testlab (Figure 4):
Figure 4: Channel settings in Simcenter Testlab software for single point laser vibrometer.
The following needs to be entered in Simcenter Testlab:
Conditioning: Set mode to Voltage and not ICP.
Coupling: Select AC coupling if only dynamic vibration is to be measured. Set DC coupling if the absolute overall velocity is to be measured in addition to the dynamic vibration. More information in the knowledge article: AC versus DC Coupling - What's the difference?
Measured Quantity: Set the measured quantity field to “Velocity”
Sensitivity: If the laser sensitivity is set to “25 mm/s/V”, the Simcenter Testlab sensitivity should be “40 mV/(mm/s)”. The sensitivity value from the laser vibrometer needs to be inverted and multiplied by 1000. The factor of 1000 converts from volts to millivolts.
1.4 Acceleration, Velocity, and Displacement Comparisons
In Simcenter Testlab, frequency data can be transformed between acceleration, velocity, and displacement by right clicking on the Y-axis of any display and choose “Processing” (Figure 5).
Figure 5: In Simcenter Testlab, convert frequency based data between acceleration, velocity, and displacement. Right click on the Y-axis and choose “Processing” and select “Integrate/Differentiate” operations.
Using this feature accelerometer data can be compared to laser vibrometer data in a FrontBack display as shown in Figure 6.
Figure 6: Overlay of accelerometer data and laser vibrometer Frequency Response Function (FRF) data.
A Polytec RLV-5000 Rotational Laser Vibrometer measures torsional vibration on rotating shafts. It can measure rpm in both negative and positive directions and does not require an encoder device. It uses a dual laser head pointed at the rotating shaft.
The torsional vibration data can be acquired from the laser in real time along with other analog channels with Simcenter SCADAS hardware.
2.1 Hardware Setup
A Polytec RLV-5000 Rotational Laser Vibrometer consists of the following components (Figure 7):
Figure 7: A Polytec RLV-5000 Rotational Laser Vibrometer uses two laser beams aimed at rotating shaft to measure rpm and torsional fluctuations.
The main components are:
Dual Laser Head: Two laser beams pointed at the rotating shaft are used to measure rpm and angular velocity. Two different spacings (7.5 millimeters and 24 millimeters) are used. The shorter spacing is typically used on higher rotational speed applications while the wider spacing is used for lower rotational speed applications.
Touchscreen: The complete measurement can be setup from the touchscreen panel on the conditioning box.
BNC Outputs: There three different BNC outputs on the conditioning box that can be connected to input channels on Simcenter SCADAS hardware.
The three outputs available from the Polytec RLV-5000 Rotational Laser Vibrometer are shown in Figure 8:
Figure 8: The three outputs of a Polytec RLV-5000 are angular velocity fluctuations from top BNC output, angular displacement from middle BNC output, and overall rpm from bottom BNC output.
There are three BNC analog outputs that can be connected to the Simcenter SCADAS hardware:
Angular Velocity (Top BNC): The fluctuating component of the angular speed is output in (typically) degree/seconds. The output is labelled as Δω.
Angular Displacement (Middle BNC): The fluctuating component of the angular displacement is output in (typically) degrees. The output is labelled as Δφ.
Overall RPM (Bottom BNC): The overall rotational speed is output in units of RPM. For example, the overall RPM might be 1000 rpm while the fluctuations in the rotational speed are available on the other two output channels. Overall RPM is not used for torsional vibration analysis.
2.2 RLV-5000 and Simcenter Testlab Settings
The “Δω” output (Top BNC): On the RLV-5000, a 100 degree/second per volt sensitivity corresponds to 10 mV/degree/second sensitivity in Simcenter Testlab software (Figure 9):
Figure 9: A 100 degree/second per volt the setup screen of the Polytec RLV-5000 corresponds to a 10 mV/degree/second sensitivity in Simcenter Testlab.
The conditioning mode should be set to “Voltage” and coupling set to “DC”.
For “Δφ” output (Middle BNC): On the RLV-5000, a 1 degree per volt sensitivity corresponds to 1000 mV/degree sensitivity in Simcenter Testlab software (Figure 10):
Figure 10: A one degree per volt the setup screen of the Polytec RLV-5000 corresponds to a 1000 mV/degree sensitivity in Simcenter Testlab.
The sensitivity can be altered via the touchscreen controls on the Polytec RLV-5000.
For RPM Output (Bottom BNC), the sensitivity is entered in units of mV/rpm as shown in Figure 11.
Figure 11: Simcenter Testlab settings for a 7.5 mm laser head.
Depending on the spacing between the two lasers in the head of the RLV-5000, a different sensitivity should be used:
7.5 mm beam spacing is 2000 RPM/Volt: Enter 0.5 mV/rpm as sensitivity in Channel Setup of Siemens. This is the 2000 RPM/Volt inverted and multiplied by 1000.
24 mm beam spacing is 1000 RPM/Volt: Enter 1 mV/rpm as sensitivity in Channel Setup of Siemens. This is the 1000 RPM/Volt inverted and multiplied by 1000.
The conditioning mode should be set to “Voltage” and coupling set to “DC”.
A scanning laser vibrometer acquires data multiple locations on a test object:
Multiple Frequency Response Functions (FRFs) at multiple locations.
Geometry co-ordinates of each measurement location.
With a scanning laser vibrometer, the data is not acquired in real-time with SCADAS hardware.
Instead, the FRFs and geometry are all measured with Polytec PSV software and a scanning laser vibrometer. The geometry and measurement data is exported to universal file (*.unv or *.uff) from Polytec PSV software. The universal file is then imported into Simcenter Testlab for analysis (example: modal curvefitting).
3.1 Component Check
It is easiest to import FRF and geometry data from the scanning laser measurement file (*.svd) if there is no component name.
In the Polytec PSV software, check if a component exists as shown in Figure 13:
Figure 13: Choose “View -> Project Viewer” in the Polytec PSV software from the main menu to check if a component name exists in the SVD file.
To remove the component name in the Polytec PSV software, right click on component name (left side of screen) and choose “Edit” (Figure 14):
Figure 14: Right click on the component name on the left side of screen and choose “Edit”.
Remove the name entirely (do not even leave a space) as shown in Figure 15:
Figure 15: Remove the component name entirely, do not leave even a space.
In the dialog box, press OK when finished.
3.2 Universal File Export
From the main menu, choose “File -> Export -> Universal File” as shown in Figure 16.
Figure 16: Export the geometry and FRFs to a universal file by selecting “Export -> Universal file” in the Polytec PSV software.
Choose “Universal Files (*.unv)”, enter a name, and press “Save” (Figure 17):
Figure 17: Select a directory and choose “Save as Type: Universal Files (*.unv) and press the Save button.
Select the options shown in Figure 18:
Figure 18: Best options for universal file export.
In the options menu, select:
“H1 Acceleration / Force” and “Coherence” data. This is the minimum necessary to perform a modal analysis.
“Display Objects (Nodes and Elements)”
Choose “Export in Binary Format”. This is the most compact data format.
Press “OK” when finished.
A universal file will be generated in the selected directory with a *.unv extension.
3.3 Universal File Import in Simcenter Testlab Classic
Start Simcenter Testlab Classic. Open a project file (*.lms) to transfer the laser vibrometer universal file data.
Go to the Navigator tab. In the data tree, navigate under “My computer” to the Universal file.
Highlight all the FRF data to be imported. Holding down shift and selecting the first and last FRF to select all FRFs. Then right click on the data and choose “Copy” as shown in Figure 19.
Figure 19: Select all FRF data and choose “Copy”.
Next highlight the area of the current Testlab project where the FRF data is to be stored. Right click and choose “Paste” as shown in Figure 20.
Figure 20: Highlight the area of the current Testlab project where the FRF data is to be stored. Right click and choose “Paste”
All the FRF data is now stored in the Simcenter Testlab project. Next the geometry must also be imported.
Turn on Geometry under “Tools -> Add-ins” (16 tokens). Go to the “Geometry” workbook.
In the geometry workbook, in the tree on the left hand side, drill under “My computer” into the universal file. Highlight the geometry as shown in Figure 21:
Figure 21: In the Geometry workbook, highlight the geometry in the universal file, then click on the “Import Geometry” button.
With the universal file geometry highlighted, click on the “Import Geometry” button. The universal file geometry will copied into the Simcenter Testlab Classic project (*.lms) file.
Be sure to save the project (File -> Save) after importing the FRF measurements and geometry.
With both the FRFs and geometry imported, modal curvefitting can be performed and mode shapes calculated as shown in Figure 22 below:
Figure 22: Mode shapes from modal curvefitting of scanning laser vibrometer data.
3.4 Universal File Import in Simcenter Testlab Neo
Open a Simcenter Testlab Neo project file (*.lms) to store the laser vibrometer universal file data.
In the “Desktop” tab, drill into the current Simcenter Testlab project in the data selection tree on the left side of the screen. Under one of the sections, right click and create a “New folder” for storing the FRF data as shown in Figure 23:
Figure 23: Right click on a section in the current project and create “New Folder”.
Then select the FRFs in the universal file to be imported. Drill under the computer name to the directory that contains the universal file.
Highlight the file in the data tree. Hold down shift, select the first FRF and the last FRF in the list, right click and choose “Copy” as shown in Figure 24.
Figure 24: While holding down the shift key, select the first FRF and the last FRF in the universal file, right click and choose “Copy”.
Then right click on the newly created folder in the current Testlab project and select “Paste” as shown in Figure 25 below:
Figure 25: Right click on the newly create folder in the project and choose “Paste”.
The FRFs are imported into the Simcenter Testlab Neo project. Press “File -> Save”.
Next import the geometry from the universal file. Under “File -> Add-ins” turn on “Geometry Creation". It requires 16 tokens as shown in Figure 26:
Figure 26: Turn on “Geometry Creation” under “File -> Add-ins”.
In the Geometry task, go to the “Import” task (bottom left of screen) as shown in Figure 27:
Figure 27: Go to the “Import” task in the “Geometry” tab, highlight the Universal file geometry, and select the “Import” button from the Home ribbon.
Press the “Import” button in the Home ribbon. Choose “Create New Geometry” and give a name if desired. After pressing “OK” a copy of the universal file geometry will be made in the current Simcenter Testlab Neo project.
Save the project (File -> Save)! Now perform modal curvefitting to extract the modes! (Figure 28).
