You are here: NI Home > Support > Product Reference > Manuals > Sound and Vibration Measurement Suite 7.0 Help

Owning Palette: Frequency-Domain Measurements Express VIs

Installed With: Sound and Vibration Measurement Suite

Performs common noise measurements when expecting a stationary, stochastic signal on the input channel. These common measurements include spectrum-based computations of the noise power, noise level, and maximum noise spur within the specified frequency range. Because the frequency range of interest can include low frequencies, you can use this step to measure and remove the DC component of the signal before performing additional computations.

Dialog Box Options

Block Diagram Inputs

Block Diagram Outputs

Dialog Box Options

Parameter	Description
View	Specifies the display that appears in the Signals graph.
Signals	Displays the input signals, AC signals, and frequency spectra. Select the data you want to view from the View pull-down menu. Use the Zoom button to zoom in and out of the display.
Autoscale	Automatically adjusts the scales of the graph to display the data.
Noise measurements	Displays the selected noise measurements in a table. Total noise power, noise density level, maximum spur, and SNR (signal-to-noise ratio) are computed on the AC signal if you place a checkmark in the Remove DC checkbox on the Noise measurements tab. These measurements are computed on the input signal if you remove the checkmark from the Remove DC checkbox. You can replace the Signals graph with a larger Noise Measurements table by selecting Results Table from the View pull-down menu. You can transpose the column and row information by clicking the Transpose button in the bottom right corner of the Noise measurements table. Transpose—Transposes the column and row information in the results table.
Input/Output	Contains the following options: Input signal—Configures the measurement for a single channel or N channels. Changing this selection changes the data types of the input signals and computed measurements. Export signals—Contains the following option: Export spectra—Exports the resulting spectra.
FFT Configuration	Contains the following options: Window—Specifies the window to apply to the input signal. Contains the following options: None Hanning (default) Hamming Blackman-Harris Exact Blackman Blackman Flat Top 4 Term B-Harris 7 Term B-Harris Low Sidelobe Scaling—Specifies the scaling parameters. Contains the following options: Spectrum type—Specifies whether the converted spectrum has units of magnitude or power (magnitude^2). Peak conversion—Specifies the peak scaling of the converted spectrum. You can select RMS (default), Peak, or Peak to Peak. Magnitude scale—Specifies whether the converted spectrum is expressed in a linear scale or in decibels. Spectral density—Specifies whether the input signal is converted using spectral density.
Noise measurements	Specifies noise measurement options. Noise evaluation—Specifies the analysis that is returned and exported. Contains the following options: AC and DC—Specifies whether the AC and DC components of the input signal are computed. Total noise power—Specifies whether the total noise power is returned and exported. Noise density level—Specifies whether the noise density level is returned and exported. Maximum spur—Specifies whether the frequency and amplitude of the maximum spur are returned and exported. SNR—Specifies whether the signal-to-noise ratio (SNR) is returned and exported. Remove DC—Specifies whether to remove the DC component from the time-domain signal before computing the noise measurements. Full-scale level (EU rms)—Specifies the full-scale level of the device under test in root-mean-square (rms) engineering units for the noise measurement. This option is used for the SNR (signal-to-noise ratio) measurement. The default is 2. Noise bandwidth—Specifies the frequency range of the measurement. Noise outside the specified bandwidth is ignored. Start frequency (Hz) and Stop frequency (Hz) are coerced to the nearest spectral bin. Contains the following options: Start frequency (Hz)—Specifies the start frequency of the measurement. This option is coerced to the nearest spectral bin. The default is 20. You also can use the vertical, green cursors on the Spectra graph to change the value of Start frequency (Hz) and Stop frequency (Hz). Stop frequency (Hz)—Specifies the stop frequency of the measurement. This option is coerced to the nearest spectral bin. The default is 20k. You also can use the vertical, green cursors on the Spectra graph to change the value of Start frequency (Hz) and Stop frequency (Hz).

Block Diagram Inputs

Parameter	Description
input signal	Specifies the input signal for the measurement.
error in	Describes error conditions that occur before this Express VI runs. The default is no error. If an error occurred before this VI or function runs, the VI or function passes the error in value to error out. If an error occurs while this VI or function runs, it runs normally and sets its own error status in error out. Use the Simple Error Handler or General Error Handler VIs to display the description of the error code. Use error in and error out to check errors and to specify execution order by wiring error out from one node to error in of the next node.

Block Diagram Outputs

Parameter	Description
spectrum	Returns the computed spectrum. This input appears only if you place a checkmark in the Export spectra checkbox.
spectrum info	Returns information about the spectrum needed by the Spectrum Extended Measurements VIs and the Waterfall Display VIs. Do not modify the spectrum info values. This output appears only if you place a checkmark in the Export spectra checkbox.
AC level	Returns the AC level of the input signal.
DC level	Returns the DC level of the input signal.
noise measurements	Returns the noise measurement data. total noise power—Returns the total noise power of the input or AC signal in the specified frequency range. average noise level—Returns the average noise level of the input or AC signal in the specified frequency range. SNR—Returns the measured signal to noise ratio (SNR) defined as the ratio of the root-mean-square (RMS) energy of the fundamental tone to the RMS energy of the noise in the specified frequency range.
maximum spur	Returns the frequency and value, in root-mean-square (RMS) engineering units, for the maximum noise spur in the specified Noise bandwidth. This indicator appears only if you place a checkmark in the Maximum spur checkbox. frequency—Returns the frequency of the maximum noise spur. value—Returns the value of the maximum noise spur.
unit label	Returns the unit label specified by the Scaling section on the FFT Configuration tab.
error out	Contains error information. This output provides standard error out functionality.