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A colormap is a three-dimensional display of a sound or vibration spectrum as a function of time or speed. The spectrum can be a frequency or order spectrum.

Use the Spectral Map Express VI to compute the spectral map of a sound or vibration signal. This Express VI can return the spectral map in a colormap or a waterfall graph. You can use this Express VI to create a colormap of the computer fan run-up data.

Complete the following steps to compute and display the colormap of the computer fan run-up data.

1. Press the <Ctrl-E> keys to switch to the block diagram of the Getting Started Exercise VI.
2. Place the Spectral Map Express VI on the block diagram. A configuration dialog box appears.
   
    
   
   
3. Click the OK button to save the current configuration and close the configuration dialog box. In this application, you can use the default configuration settings when you run the Spectral Map Express VI for the first time.
4. Wire the waveform signal output of the oax_Load Data (Analog Tacho, single channel) VI to the input signal input of the Spectral Map Express VI.
5. Wire the speed profile output of the Analog Tacho Processing Express VI to the speed profile input of the Spectral Map Express VI.
6. Wire the colormap output of the Spectral Map Express VI to the Colormap indicator.
   
   The block diagram should appear similar to the following block diagram.

7. Run the Getting Started Exercise VI to calculate and display the colormap of the computer fan run-up data.
8. Save this VI.

On the front panel, click the Colormap tab to view a colormap of the computer fan run-up data, as shown in the following figure.

By default, this plot displays frequency against time. Red portions of the colormap indicate areas of strong amplitudes. Notice that several red lines appear on this colormap. These red lines correspond to strong vibrations at different frequencies in the data. Notice that the strongest vibrations occur at frequencies between 150 Hz and 400 Hz. This range most likely includes several resonant frequencies from the device under test.

You also can customize a colormap to display RPM against order. An RPM-order plot displays how the vibration amplitude at different orders changes with the rotational speed. Complete the following steps to compute a colormap that displays RPM against order for the example data.

1. On the block diagram, double-click the Spectral Map Express VI to display the configuration dialog box.
2. On the Configuration page, change the Plot type to RPM-Order.
3. Zoom into the Colormap plot in the configuration dialog box. Notice that the amplitude of the seventh order is the strongest around 2,600 RPM, as shown in the following figure.

   

   
   With this Colormap plot, you also can identify orders that correspond to loud noises or strong vibrations that you observe. For example, suppose the computer fan generates loud noises between 2,800 RPM and 3,000 RPM. From the RPM-order plot, you can see that the fourth and the eighth orders contribute the most to the loud noises in this speed range.

4. Click the OK button to save the current configuration and close the configuration dialog box.
5. Run the Getting Started Exercise VI to calculate and display the colormap of the computer fan run-up data.

A colormap plot therefore provides an overview of how the intensity of a signal relates to time, speed, frequency, and order.

Previous: 2. Analyzing the Speed Profile

Next: 4. Analyzing the Order Power Spectrum

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