Some unique features of Simcenter Testlab Neo Impact Acquisition include:
Smart Hit Selection: Individual impact hits are not only screened for overloads and double hits, but selecting hits that yield the highest coherence is another criterion that can be used.
Multiple Hammers: Hammers which excite low and high frequency ranges can be used together to yield FRFs that cover a wider combined frequency range.
Campaigns: Measurements to be acquired can be planned in advance and executed automatically. This is helpful for both modal analysis and virtual point transformation measurements.
The menus and procedures in this article are based on Simcenter Testlab Revision 2506 and higher.
Article contents: 1. Minimal Equipment Required 2. Getting Started 3. Instrumentation 3.1 Channels 3.2 Geometry Creation 3.3 Geometry Setup 4. Hammer Setup 4.1 Trigger Level 4.2 Impact Settings 5. Campaign Setup 6. Measure 6.1 Measuring and Saving Data 6.2 Excluding hits and Smart Hit Selection 6.3 Autoranging 6.4 Impact Sounds 7. Measuring Without a Campaign 8. Task Layouts
1. Minimal Equipment Required
Measuring a structural Frequency Response Function (FRF) requires at least two distinct transducers: one to measure the force applied to the test object, another to measure the test object’s response to the input force.
In a modal impact test, the input force is typically delivered by a modal impact hammer. Meanwhile, the resulting output response from the test object is typically captured using an accelerometer (as illustrated in Figure 2).
Connect the SCADAS to the measurement PC. Make sure the SCADAS is turned ON. Connect hammer and accelerometers to SCADAS. Suspend the test object as desired and plan the test campaign of points to be measured.
To begin, first navigate to the Simcenter Testlab icon on the computer and find the folder titled “Testlab Neo Structures Acquisition” and then open the program “Impact Acquisition” (Figure 3).
Figure 3: Click on the “Simcenter Testlab 2506” desktop icon, then open “Testlab Neo Structures Acquisition” and click on the “Impact Acquisition” executable.
It is also possible to simply search for “Impact Acquisition” in the Windows search menu to find the executable.
After starting “Impact Acquisition”, select the “Blank Project” template to open a new file (Figure 4).
Figure 4: Opening a new project in Simcenter Testlab Neo Impact Acquisition.
If the “Show hardware selection configuration” flag is on, the software will prompt for the SCADAS frontend to be selected (Figure 5):
Figure 5: Be sure “Connect to frontend” is selected, choose the SCADAS and press “OK”.
In the task menu, select “Channel Setup” to begin configuring the channels (Figure 6).
Figure 6: Open the “Channels” task in the “Instrumentation” group to begin setting up channels.
Note that the example splash screen has some tasks hidden for easier viewing. The task menu opened for the first time may look more complicated and include more tasks.
The flow of impact acquisition is like the original impact testing in Simcenter Testlab. It begins by setting up the channels, linking a geometry (if using), choosing the hammer, setting impact measurement settings, and then measuring the data. The tabs at the bottom of the screen follow this flow (Figure 7).
Figure 7: The tabs at the bottom of Impact Acquisition are used to perform a modal impact test when followed from left to right.
First the hammer and accelerometer information will be entered in the “Instrumentation” tab.
3. Instrumentation
To setup the transducers (hammer and accelerometers) to be used in the test, go to “Instrumentation” tab.
3.1 Channels
In the “Instrumentation” tab, choose “Channels” (if not already in “Channels” from the splash screen). An Excel-like table appears with multiple columns and rows. Each row corresponds to one input channel on the SCADAS frontend (Figure 8):
Figure 8: Transducer information (accelerometers and hammer) are entered in the “Channels” tab of “Instrumentation”.
In the channel table, start by turning on channels that will be used during measurement. This can be done in the “On/Off” column (orange box) shown in Figure 9.
Figure 9. Explanation of each column for setting up the transducers in the channel setup task.
Additional settings in the “Channels” tab include:
On/Off (light orange/yellow): Choose which channels are active for acquisition.
Reference (light green): Indicate which channel has modal impact hammer (can have multiple impact hammers)
Conditioning (purple): As shown in the blue box, select the type of signal conditioning for the sensor of each channel. Common IEPE accelerometers should be set to “ICP”. Other accelerometers will either be Voltage AC or Voltage DC.
Point and Point Direction (light and dark blue): Enter the name of the measurement location (Point) and Direction. Anything written in the Point and Point directions fields can be overwritten. For example, when using a campaign (covered further in the article), or after assigning a geometry, or during hammer setup. These can be seen in the navy box. For the mode shape to animate properly, the measurement direction for each channel must be set properly.
Sample rate (black): Sample rate of the data. Sample rates can be assigned to three groups: high, low, slow. The highest frequency (bandwidth) of the measurement is half the sample rate.
Measured Quantity (red): In the measured quantity column (yellow box in figure 4), select the type of quantity for each channel. For hammers this should be force, and for accelerometers, acceleration should be selected.
Sensitivity (dark orange): Under the Sensitivity column, input the sensitives for each accelerometer listed on the data sheets, or calibrate to find these values using the calibration task. Learn more about how to calibrate sensors here.
An example of setting directions for the hammer and a triaxial accelerometer is shown in Figure 10 below.
Figure 10: Example of how to setup a coordinate system for a test object and set the appropriate directions in the channel setup.
A triaxial accelerometer will have three channels with each channel measuring in either the positive or negative orientation for directions X, Y, and Z. A hammer in this example, may have a -Z orientation since its impacting down in the negative Z direction. Set these in the “Direction” column in the Channel list.
In order to create an animated mode shape of the results, a geometry can also be created and used for the measurements.
3.2 Geometry Creation
If a animated mode shape is desired, a geometry can be either created in the “Geometry” task or imported. Go to “File -> Add-ins -> Geometry” to add the “Geometry” task. Create or import the geometry here and then click back on the “Instrumentation” and “Geometry Lookup” subtask (Figure 11).
Figure 11: Create or import geometry in the “Geometry” task.
It is also possible to use finite element meshes and CAD models to create geometries.
3.3 Geometry Lookup
In the “Geometry Lookup” task located under the “Instrumentation” task, accelerometers and hammers can be assigned to locations on the imported geometry.
To assign an accelerometer channel to a location, either manually type in the point ID into the “Point” column or use the geometry wireframe to select a node. Nodes may not automatically default to on, so to show the nodes, right click in the geometry display and selecting “Deformed Model -> Nodes -> Markers”.
Select a node on the geometry, highlight the row that corresponds to that accelerometer location, and then select the “Assign to channel” button located in the ribbon (Figure 12).
Figure 12: Assign the accelerometer(s) a location by clicking on the geometry nodes and then selecting “Assign to channel”.
Figure 13 shows an example of a triaxial accelerometer set up using the assign to channel method. The accelerometer has the correct name listed under Point.
Figure 13: An example of a triaxial Accelerometer with a new Point ID listed after using the “Assign to channel” feature.
After assigning the point names, the next step is to setup the hammer.
4. Hammer Setup
To begin setting up a hammer, navigate to the “Hammer Setup” subtask located under the “Impact” tab as shown in Figure 14.
Figure 14: “Hammer setup” is a subtask in the “Impact” task.
In the upper left of the “Hammer Setup” task, the hammer channel can be selected in the pulldown menu next to “Reference channel” (Figure 15).
Figure 15: Select the hammer channel using the pulldown menu next to “Reference Channel” in the upper left of the “Hammer Setup” task.
The hammer channel is selected in the “Reference Channel” pulldown. Channels that are marked as reference and have the unit of “Force” will be available for selection. If no channels have these settings, the pulldown will be empty.
Additional settings can be found by clicking “More” to the right of the pulldown. These offer the ability to label additional information about the hammer such as tip type, and extender mass. These do not affect any final calculations and are for documentation purposes.
4.1 Trigger Level
Press “Start” in the lower left so the trigger level can be set by measuring a few hits as shown in Figure 16.
Figure 16. Determine the trigger level by acquiring a few hits (Press Start and then Stop). In the “Scope hammer” window use “Add Single Cursor -> Y (front) to determine the trigger level. Manually enter the level in the “Trigger Level” field.
Press the “Start” button in the bottom left corner and take some practice hammer hits on the structure to determine a trigger level. Click the stop button in the bottom left corner to stop the hammer acquisition. The trigger level can be input under the hammer settings along with the appropriate unit.
A trigger level can be found visually by adding a single y-axis cursor. Right click on the scope hammer graph and click “Add single cursor -> Y (front)”. Align the cursor so that it goes through every practice impact. Make sure the level is high enough above the noise.
If done correctly, the hammer should only register an impact after a hit has been performed on the test article, and not from small movements such as moving the hammer around or lightly tapping on it.
4.2 Impact Settings
Further settings for the acquisition setup, such as frequency resolution and corresponding frame length can be adjusted in the “Impact Settings” pane on the right side of the screen as seen in Figure 17.
Figure 17. The “Impact Settings” menu is used to set the frequency resolution, windows, and FRF Estimation method.
Some other key settings found in the “Impact Settings” menu:
Sampling Rate/Maximum Frequency: The sampling rate for the impact acquisition is not set in the “Impact Settings” menu. The sampling rate is a channel property that can be found in the Instrumentation/Channels tab. The “Maximum Frequency” can be set lower that the sampling rate which causes the data to be downsampled. In 2606 and higher, the Maximum Frequency will automatically be set to half the Sampling Rate.
History Size: This is the amount of time that is continuously shown of the impact hammer in the top graph of “Hammer Setup” used in determining the trigger level.
FRF Estimation Method: Choices include H1, H2, and Hv. These are different methods that account for noise on the FRF measurement.
Windows: In impact testing, usually force-exponential windows are used. Ideally, the exponential decay of the response window can be set to 100% if the response decays within the measurement time. The reference window cab be set to 10% to avoid any extraneous noise on the hammer input.
One of the new features of Simcenter Testlab Impact acquisition is the ability to use multiple hammers to excite different frequency bands. This is an optional feature that can be setup during normal hammer setup. Read more about multiple hammer setups here.
5. Campaign Setup
New to Simcenter Testlab Neo Impact Acquisition is configuring a test around a campaign. A campaign:
Allows a user to select ahead of time all the locations to be measured.
The software will automatically increment between the different locations as defined in the campaign.
In this article, a roving accelerometer case is shown, but it is also possible to rove the hammer excitation as well.
To setup a campaign, go to the “Campaign Setup” task (Figure 18), and swap the impact mode in the campaign settings task to “Roving Responses”. This will unlock an additional window towards the bottom of the campaign task called “Response Layouts”.
Figure 18: Setting up a campaign: turning on roving response mode to move the accelerometers during testing. In response layouts, change “Add 1” to “Add 3” to do three roves/moves of the accelerometers.
Under the response layouts, type a number into the add box, to add the number of times the accelerometers will move. In this example, with two accelerometers and six possible positions, the accelerometers will move three times, so “3” would be entered.
Simcenter Testlab Neo will also need to know where the hammer is planned on being hit:
For a roving hammer test, add multiple locations for the hammer.
For roving accelerometers, only one hammer location is required.
To add a hammer impact location, click the “Add Excitation DOF” icon (Figure 19) and click on a yellow node on the geometry.
Figure 19: Creating an impact location by selecting the “Add Excitation” icon and clicking on a node on the geometry.
Nodes may need to be turned on if they are not on by default. This can be done by right clicking in the geometry display and selecting “Deformed Model -> Nodes -> Markers”.
Press the OK button when finished, and a list of hammer excitations and response layouts should populate. To choose the locations for the accelerometers, points and directions need to be manually entered and cannot be picked from the geometry.
To make it easier to enter the point names, and locations, the values can be typed, copied and pasted from Microsoft Excel (Figure 20).
Figure 20: An example of roving accelerometer point names and directions, in a layout that will position the accelerometers during the test.
If the same locations are being used, the excel sheet can be saved or a template can be made in Simcenter Testlab Neo that saves the accelerometer positions for quicker set up.
An important setting to complete in the campaign setup is the minimum number of impacts per hammer. This will decide how many impacts are required before Simcenter Testlab moves on to the next set of measurements. This can be set in the processing settings (Figure 21).
Figure 21: Setting the minimum number of impacts required before a measurement is considered “complete”.
If a minimum number of impacts is set to “3” for example, Simcenter Testlab Neo will not consider the measurement complete until three hits are saved. If a hit is rejected, it will not count towards the minimum impacts required.
With the transducer information entered, the hammer setup, and the measurement campaign planned, measurements can be taken.
6.1 Measuring and Saving Data
Go to the “Measure” task. The geometry display will show where the software expects an excitation location and where the response locations are. In Figure 22, the blue accelerometers are exaggerated in size for clarity. Press the “Start” button in the lower left corner to begin taking impacts.
Figure 22: Measurements being performed at the first response layout.
Simcenter Testlab Neo will show live feedback of the total average for all the hits (green) versus the instantaneous average for the previous hit (red). Colors of graphs can be changed if desired.
After finishing hits at a certain accelerometer location, the software can either be set to auto increment, or it can be manually incremented by clicking the “Increment” button located in the lower left of Measure screen.
A specific accelerometer layout can also be selected at any time by selecting a response layout manually in the “Excitation” window (Figure 23).
Figure 23: Changing response layouts quickly by selecting them in the excitation window of the “Measurement” task.
Once all measurements are complete and all roves have been achieved, click the “Save” button in the bottom ribbon (Figure 24).
Figure 24: Saving the FRF data to the project in a Campaign.
If the “Save” button is not pressed, no FRFs are stored in the project.
Impact data is stored in two different folders in the project:
The individual impact hits are stored in a Run.
The calculated FRFs are stored separately in the Campaign.
If a user wants to include or exclude new hits, the save campaign button will need to be clicked again to save the new FRF results.
If for some reason the FRFs were not saved (for example if user forgot to press save), it is possible to recalculate the FRFs from the time data:
Make sure the project and section that were used to acquired the time data impacts is active.
In the "Desktop" tab, navigate to the run that contains the data. Right click on "Archived Settings" in the run and choose "Load Archived Settings".
Go back to the "Measure" tab in the "Impact" task. The previously acquired hits should be present.
The next section will cover how to exclude or include hits.
6.2 Excluding Hits and Smart Hit Selection
Each hit will appear in the measurements task. If it is included in the average, a green check mark will appear. If it is not included, a red x will appear next to it.
A measurement may be automatically rejected if it is either a double hit or if it is an overload (Figure 25).
Figure 25: Two rejected hammer hits: one excluded for an overload, and one excluded for a double hit.
Excluding double hits and overloads in the measurement setup will prevent these hits from ever being saved, and double hits and overloads will not appear as measurements in the measurement window.
To check double hit settings, go to the “Campaign” subtask under the “Impact” task and select “Measurement Advanced” settings (Figure 26).
Figure 26: Turning on double impact and overload rejection for the measurement.
If only “Auto reject with overload” and “Auto reject with double impact” are turned on, they will appear in the measurements window, but will have a red box with an ‘x’ next to them if they are an overload or double hit. If exclude for measurement is turned on, no double impacts will appear in the measurement window and they will not be saved.
Measurements can be excluded or included manually by clicking the check mark or x. It will automatically update the response in green in the display window, so users can see how adding measurements will affect the final coherence and FRF (Figure 27).
Figure 27: The effect of including or excluding a hit on the overall coherence and frequency response function (FRF) shown in green.
In the latest version of Simcenter Testlab Neo, smart hit selection is automatically defaulted on and will select the best hits based on default parameters.
For the highest quality measurements, it is best to optimize the voltage range of the input channels to the signals being measured. This is done in the “Ranging” tab of the “Instrumentation” task (Figure 28):
Figure 28: The range of input channels can be optimized in the “Ranging” tab of the “Instrumentation” task.
Press the “Range” button, take some impact measurements, and press “Stop”. New ranges will be shown next to the old ranges. Press “Apply” to accept the new ranges.
More information on setting appropriate ranges for data acquisition in the knowledge articles:
If enabled, Impact Acquisition has audio cues that indicate if the system is waiting for a impact, measuring, overloads, etc. The sounds used can be turned on and off or changed in the “Home” ribbon in the “Audio Feedback” section (Figure 29):
Figure 29: In the Home ribbon, click on “Setup” in the Audio Feedback section to change the sounds used in Impact Acquisition.
Enjoy substituting different sounds!
7. Measuring without a Campaign
Measuring without using a campaign is possible in the Simcenter Testlab Impact Acquisition. It is not necessary to plan multiple accelerometer moves in advance:
The hammer name and hit location MUST be entered before any other hammer settings or test hits are taken. Otherwise, arming the system will cause the software to provide the hammer with a default name and location. To do this, manually type a name and the location on the geometry that the hammer will be hitting at in the Point and Point Direction fields. This can also be done in the “Geometry Lookup” task to see physical geometry locations.
Set accelerometer point names and directions. If desired, go to the “Geometry Lookup” task and assign channels a direction and location on the geometry by clicking a node and pressing the “Assign to channel" button (figure 23).
Set up the hammer and choose appropriate hammer settings.
Go directly to the “Measure” task and take a measurement (skip “Campaign Setup”). Click the save campaign results button after each measurement.
After saving, go back to geometry lookup or manually type in the new locations of the accelerometers or use the “Assign to channel” button.
8. Task Layout
A task layout can be created that contains only the key steps for doing a modal impact measurement. This makes switching between steps quicker and more efficient.
First go to the task menu by clicking the task menu button (Figure 30):
Figure 30. Task Menu button location.
This will bring up the tasks that are currently viewable in the software. Click the cog wheel (Figure 31) to begin editing the tasks.
Figure 31:. Task menu layout. Click the cog wheel to edit the settings.
Unneeded tasks can be hidden by clicking the eye icon in the box of each task. In the bottom right corner, create a specific group of tasks by typing a name into the box, and clicking and dragging tasks in the order desired (Figure 32).
Figure 32: Creating a custom layout called “Roving Accel”. It includes three tasks: Geometry Lookup, Hammer Setup, and Measure.
Then click save. In the example below the task group is called “Roving Accel” (Figure 33):
Figure 33: New task group called "Roving Accel" contains "Geometry Lookup", "Hammer Setup", and "Measure".
Now Simcenter Testlab Neo will only display the tasks desired and will remove any extraneous tasks from the menu, making swapping between displays much quicker.
