In this measurement column, we will address and answer frequently asked questions received by our customer support center.
We are providing an overview of the contents.
This time, we'll be using the DS-3000 series real-time Sound and Vibration Analysis System software DS-0320.
This document outlines the procedure for performing offline FFT analysis on recorded data.
DS-0320 and Record File Viewer screen
Figure 1 shows the screen of the real-time Sound and Vibration Analysis System software DS-0320, and Figure 2 shows the Record screen.
This shows the File Viewer screen.
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Figure 1: Screenshot of the DS-0320 real-time Sound and Vibration Analysis System software.
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Figure 2: Record File Viewer screen
Procedure for opening a record file and performing offline FFT analysis
From the DS-0320's file menu (Figure 1 ①), select "Open Offline Analysis Data" to access the record data.
Open the file (Figure 3). Select "FFT (Offline)" as the mode.
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Figure 3 File menu ⇒ Open offline analysis data dialog
You can set the FFT analysis conditions in the input/output settings. You can also display the necessary graphs and adjust the analysis settings and data.
We will also configure the data display settings.
If the record data contains multiple recording results (records), launch the Record File Viewer (Figure 1 ②) and select the record to be analyzed using the display record switching (Figure 2 ⑤). Also, if you want to analyze only a portion of the time range of the record data rather than the entire data, refer to Figure 2 ⑥ “Table
Specify the analysis range using options such as "Register the indicated range as the analysis range" or "Analysis range" in Figure 2, section ⑦.
Press the first button on the DS-0320 (Figure 1 ③), then press the START button to access the record data.
Analysis is performed sequentially from the beginning of the entire dataset or the specified analysis range, and the analysis is completed at the end of the range.
Analysis will stop.
How to adjust the calculation speed of offline analysis
The DS-0320 does not have a function to set the calculation speed for offline analysis, but overlap
Increasing the quantity increases the amount of computation required for FFT analysis, thus slowing down the calculation speed.
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The overlap amount is determined by comparing the time-domain waveform used in the FFT calculation performed immediately before with the waveform used in the current calculation.
This setting determines what percentage of the time-domain waveform used in the FFT calculation is overlapped. The larger the overlap amount, the more...
The overlap between the previous and current time-axis waveforms is large, and the amount of shift in the range from which the time-axis waveform is cropped is small.
Therefore, the processing speed will be slower.
The overlap amount can be configured in the "Input/Output Settings Menu ⇒ Sample Condition Settings".
Open the window and set the "Overlap Amount" to your desired value.
Set it to an arbitrary value (Figure 4). Set it to a value of about 90% or 95% and check the calculation speed and expect
Please adjust the settings to achieve the desired calculation speed before performing the FFT analysis. The waveform to be observed is...
When this message appears, stop it with the STOP button and save the data, etc.
The maximum value that can be set to the burlap amount is 99%.
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Figure 4 Configuration Window ⇒ Input/Output Settings ⇒ Sample Condition Settings
The relationship between an arbitrary overlap amount and the amount of time-domain waveform shift per FFT operation is as follows:
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- Number of lines [points] = Number of sample points [points] ÷ 2.56
- Frequency resolution [Hz] = Frequency range [Hz] ÷ Number of lines [points]
- FFT time length [seconds] = 1 ÷ frequency resolution [Hz]
- Displacement amount [seconds] = FFT time length [seconds] × (100 - arbitrary overlap amount) ÷ 100
For a frequency range of 20 kHz and 2048 sample points, the number of lines is 800, and the frequency resolution is
The frequency is 25 Hz, and the FFT time length is 40 ms. The amount of shift per FFT operation is arbitrary, and the overlap amount is arbitrary.
When the value is 90%, it will be 4 ms, and when it is 95%, it will be 2 ms.
Method for checking the time-domain waveform, spectrum, etc., after each FFT operation.
If you want to stop the calculation after each FFT operation, use the averaging function.
Open the configuration window via “Input/Output Settings Menu ⇒ Averaging Processing Settings”, and then set the average
Set the averaging process setting to "Power SP Additive Averaging", the averaging condition to "Number of times", and the number of averaging processes to "1".
Set it to (Figure 5).
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Figure 5 Configuration window ⇒ Input/Output settings ⇒ Averaging settings
Turn the AVG button ON, press the first button on the DS-0320 (Figure 1 ③), and then press the START button.
Pressing this button will perform the FFT calculation only once and then stop. With the AVG button still ON,
Each time you press the START button, the time axis shifts by an amount determined by the overlap amount (a value of your choice).
The waveform progresses, and the FFT calculation result is displayed.
Procedure for averaging analysis (averaging process)
The procedure for average analysis is almost the same as for online FFT analysis.
The overlap amount (Figure 4) is usually set to around 66.7% or 75%. Averaging processing settings (Figure
5) Please revert to the original settings. Set the averaging processing condition to "time", and the average processing time to analysis.
Set the time to a duration longer than the specified range. Note that the maximum value that can be set for the average processing time is 999.9 seconds.
Specify the analysis range you want to average in the Record File Viewer, turn on the AVG button, press the first move button on the DS-0320 (Figure 1 ③), and then press the START button to start the averaging analysis.
It will happen.
summary
This time, we will discuss FFT offline analysis on the DS-3000 series and adjusting the calculation speed of the offline analysis.
We introduced methods such as stopping the calculation after each FFT operation.
For instructions on how to use the DS-3000 series Record File Viewer, please refer to the measurement column from two posts ago.
Please refer to
(Excerpt from the email newsletter issued on March 18, 2020)
