Order Waveform (Sound and Vibration Measurement Suite)
December 2007
NI Part Number:
372416A-01
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An order waveform is the time signal associated with a certain order, which is synchronous to the rotational speed. Unlike an order power spectrum, which provides information for all of the orders of a certain time block signal, an order waveform provides information only for one particular order relative to time.
Use a spectral map or order power spectrum to identify the most significant orders in a sound or vibration signal. After identifying the most significant orders, you can extract an order waveform to get detailed information for individual orders.
You can extract order waveforms to isolate specific orders from a sound or vibration signal. The following illustration shows a waveform signal and an extracted order waveform.
You can see the contribution of the fourth order to the overall waveform signal. You also can calculate the running root-mean-square (RMS) value of a certain order from the order waveform. You then can use the running RMS value to indicate the amplitude of a certain order.
One feature of order waveform extraction is the ability to play back a time signal. Playing back a time signal enables you to listen to the sound of a certain order or a combination of orders. This feature is useful for applications where a microphone acquires the signal. You can use order waveforms to perform noise analysis and to locate a noise source by comparing the noises that different orders or order combinations generate. The most common applications of this feature are in sound quality engineering. You can analyze and synthesize the sound of several orders and evaluate the subjective perception of these sounds. In automotive noise, vibration, and harshness tests, one example of sound quality engineering is the evaluation of power train components, like the engine, to obtain a more comfortable noise level for passengers.
Use the Order Waveform Express VI to compute the order waveforms of specified orders. This Express VI enables you to extract an order from a time-frequency colormap. The following front panel shows a colormap and an extracted order waveform.
In the previous front panel, the cursor in the Colormap plot indicates the order whose waveform you want to extract. The red waveform in the Order waveforms plot is the waveform of the order you specified in Colormap plot.
You also can use the OAT Extract Most Significant Order Waveforms VI to compute the order components with the highest power. You specify the number of significant orders you want to extract, and this VI returns the most significant order waveforms.