Overview of Order Analysis and Signals Used
1. Download the LabVIEW sample VI "Order Analysis Demo.vi" from the Attachments section at the bottom of this article.
2. Perform order analysis with LabVIEW
For order analysis, the following two are required: vibration signal data and data that measures changes in rotational speed. For example, in "Sound/Vibration Signals" in the figure below, the change in intensity (or amplitude) of the sound/vibration signals is measured for 10 seconds. On the other hand, in "Speed Profile", it records the change in rotational speed for 10 seconds. The figures of "Order-Time" and "Frequency-Time" are the results of order analysis for "Sound/Vibration Signals" and "Speed Profile".
First, from the above figure, check the change in rotational speed with "Speed Profile". The rotational speed is 1000 RPM near 0-second mark and 6000 RPM near the 10-second mark. The frequency of vibration or noise of a rotating body is proportional to the rotational speed, and an order refers to a frequency of vibration components that is a multiple of the reference rotational speed. A vibration signal with the same frequency as the rotational speed is considered first order, while a vibration signal that is twice the rotational frequency will be second order. If you check "Order-Time", you can see that "Sound/Vibration Signals" contains vibration signals of the 1st, 2nd, 3rd, and 8th order. Also, if you check the "Frequency-Time", you can see that each frequency increases as the rotational speed increases. For example, when the time axis is around 10 seconds, the rotational speed is 6000 RPM, so the frequency of the vibration signal with an order of 1 is 6000 rotations/minute = 100 rotations/second = 100 Hz. Since "Sound/Vibration Signals" contains vibration signals of the 1st, 2nd, 3rd, and 8th order, the vibration signals that appear around the 10-second mark of "Frequency-Time" are 100 Hz, 200 Hz, 300Hz, and 800 Hz, respectively.
Order Analysis in DIAdem
1. Load the analysis data into DIAdem.
In order to perform order analysis with DIAdem, it is necessary to load the vibration signal data and rotational speed data. Sample data is available from "ExampleTDMS.tdms" in the Attachments section at the bottom of this article. If you delete the internal data of DIAdem and drag and drop "ExampleTDMS.tdms," the data will be loaded as shown below.
2. Perform order analysis in the time domain.
Order Analysis (Time Domain) can calculate the vibration signal intensity corresponding to the specified order. Here, the vibration intensities of orders 1 to 5 are calculated.
You can check the calculation results for the vibration intensity corresponding to orders of 1 to 5 in the figure below. Here, it can be confirmed that only signals of orders of 1, 2 and 3 can be detected.
The difference in the shapes of each signal intensity (amplitude) is because a window was applied to each signal at its specific frequency. In the sample data used for this case, the signal with 1st order has no window applied, the signal with 2nd order has a sine-type window applied, and the signal with 3rd order has a triangular window applied.
3. Perform order analysis in the frequency domain.
When performing order analysis on the frequency domain, specify the search area by rotational speed as shown in the figure below, and perform order analysis on the data of each rotational speed. In many cases, parameter settings on the Parameters
tab will automatically select the appropriate range and analysis interval from the minimum and maximum values of the RPM channel. Here, the order analysis is run from 1050 RPM to 6000 RPM in step widths of 1000 RPM.
You can see in the figure below the results of the order analysis for the vibration signals at 1050, 2050, 3050, 4050, and 5050 RPM, from the 1st order to the 10th order.
4. Perform order analysis for the bode display.
In "Order Analysis for Bode Display", you can perform order analysis using the timestamp for when the rotating body makes one revolution. In the sample data, the Pulse Rising Time channel includes the timestamp for when the rotating body makes one revolution, and it can be used by specifying it as the Pulse times
channel as shown below. Here, we have set the band width of the signals to be +/- 0.2 for each order (1-3).
In "Order Analysis for Bode Display", it takes more time to calculate as the number of calculations increase, so it is important to set the Number of intervals
like below. Here, the signal intensity is calculated and shown for 100 intervals in the time axis direction.
The plots of the signal intensities and phases of orders of 1, 2 and 3 obtained by "Order Analysis for Bode Display" can be seen in the following figure.