Need to perform math (sum, average, inverse, etc) on frequency or order domain data in Simcenter Testlab? Use the Data Calculator feature!
This article covers how to use the Data Calculator: 1. Getting Started and Selecting Data 2. Create Formulas 3. Phase Considerations 4. Multiple Blocks 5. Repeat Blocks 6. Calculate and Display 7. Save Results
1. Getting Started and Selecting Data
In the Navigator worksheet of Simcenter Testlab, select the curves to perform the math upon. Right click on them and choose “Replace Data in Input Basket” as shown in Figure 1.
Figure 2: Highlight the data to be used in the Data Calculator and choose “Replace in Input Basket”.
If using data from two different locations, choose “Replace in Input Basket” for the first piece of data and then “Add to Input Basket” for the second.
Any type of data stored in project (frequency spectrum, FRF, autopower spectrum, order, etc) can be used in the Data Calculator. Data from a Throughput time history cannot be used. See the knowledge article “Time Signal Calculator” for how to manipulate time histories.
Then click on the “Data Calculator” in the upper left (Figure 2):
Figure 2: Click on “Data Calculator” in the upper left of the Navigator worksheet.
After clicking on “Data Calculator”, the screen should look like Figure 3:
Figure 3: After “Data Calculator” is active, there is a Data Set area for managing data and results (red), and a formula area for calculations (orange).
The calculator data set management is in the middle of the left side, and the calculator itself is in the lower left.
Click on the “Add from Input Basket” icon (third icon) in the Data Set area to make the previously selected data available for processing (Figure 4).
Figure 4: Select “Add from Input Basket” to activate the data for processing.
Notice that each data block is assigned an identification, like “F1”, “F2”, “F3”, etc.
2. Create Formulas
Highlight the first formula cell and then press the “f(x)” button as shown in Figure 5.
Figure 5: Create new calculation formula by using the f(x) button.
Look for the desired operation in the list. Some common operations:
Math: ADD, AVERAGE, DIVIDE, MULTIPLY, SUBTRACT, SUM
Reciprocal: Use the INVERSE command to invert a measurement. For example, a FRF can be converted from accelerance to dynamic stiffness.
For example, to subtract two frequency measurements, choose SUBTRACT from the list (Figure 6).
Figure 6: After highlighting the desired command, press the OK button.
Press the OK button.
Fill in the identifications of the data blocks in the resulting menu (Figure 7):
Figure 7: Fill in the identifications of the blocks (F1, F2, etc) as desired.
And press the OK button when finished.
Note that commands like SUBTRACT and ADD will use phase if present in the frequency data. For example, a two "g" acceleration signal that is 180 phase difference with another two "g" signal will result in four g’s after subtraction.
3. Phase Considerations
If the amplitude difference without phase is desired, use the command SUBTRACT_BLOCKS_AMPLITUDE instead of SUBTRACT.
Formula would look like Figure 8:
Figure 8: The SUBTRACT_BLOCKS_AMPLITUDE allows subtraction without using phase (set type to “2”).
Additional calculations can be added to the list if desired.
4. Multiple Functions
Many of the Data Calculator operations come with just a few functions (for identifying blocks) by default. It is possible to add more functions as needed as shown in Figure 9.
Figure 9: Press the “New Function” button to perform calculations on multiple data blocks.
For example, clicking on the button two times would allow three blocks of spectral data to be averaged as shown in Figure 9.
Once finished, the calculation can be performed.
5. Repeat Blocks
It is also possible to perform on operation on multiple data blocks by writing a single function.
Instead of using block numbers F1, F2, F3, etc., the block is specified as FX instead. The X acts as a variable.
In the "Repeat for..." column, a range of values to be used in the X variable are defined. For example, "1:4" would tell the FX function to perform operations on blocks F1, F2, F3, F4 as shown in Figure 10 below:
Figure 10: Multiple operations can be performed with a single function using "FX" and a "Repeat For".
The "Repeat For" column may not be visible. The Data Calculator are can be widened by dragging the border. Otherwise, use the scroll bar at the bottom.
6. Calculate and Display
Press “Calculate” to perform the math. Note the Point Id of the resulting calculated block can be set as shown in Figure 11. In this case, the result will have the label “difference”.
Figure 11: Enter the desired Point id for the result and press the Calculate button.
A new block (in this case F3) appears in the Data Set. The “Id” field is usually set to an unoccupied Id as to not overwrite any of the data being used in the calculation. In Figure 11, data blocks F1 and F2 are being subtracted and the result is placed in F3.
The results can be dragged and dropped into a display to view it as shown in Figure 12.
Figure 12: To view calculated results, drag the result into a display. The cursor turns into a four-way cursor to indicate that data can be selected to drag.
Note: The cursor becomes a four-way arrow when it is possible to drag data into a display.
Any displays created are only available while using the Data Calculator. After switching back to “Data Viewing” the previous Navigator displays are used.
7. Save Results
If the data looks OK, it can be stored into a project. The calculated results are not permanently stored unless they are specifically saved.
To permanently store the results, choose the “Save Results As…” button in the Data Set area (Figure 13):
Figure 13: Choose “Save Results As…” to store data into project.
Store the results back into the project in the section or run desired. Use the buttons in upper right to move up in the hierarchy to select a project or run.
Switch back to the default “Data Viewing” (upper left corner) of the Navigator worksheet to view and create plots.