National Instruments Order Analysis Toolset Masking

Chapter 3 Gabor Transform-Based Order Tracking

Figure 3-3(b) illustrates constant order bandwidth. The neighborhood is

considered as the region between and .

While the frequency bandwidth varies in time, the order bandwidth

k remains constant.

You can use the Gabor Order Analysis VIs to determine the frequency

bandwidth or order bandwidth automatically or in response to your input.

For example, you can automatically determine a bandwidth for the

time-frequency neighborhood based on an estimate of minimum

order-distance to nearest neighbor order-components. Normally, the

bandwidth should not exceed the distance between two nearby orders,

which is the fundamental frequency, or first order.

Masking

After you determine the coefficient positions and the bandwidth of the

selected order curves, select a subset of the initial Gabor coefficient array.

The subset of the initial Gabor coefficient array contains only the

coefficients in the neighborhood of the selected order curves. You can

generate the subset by performing a mask operation on the initial Gabor

coefficient array.

To perform the mask operation, you must construct a mask array. The mask

array is a 2D array the same size as the coefficient array. However, the mask

array contains only Boolean elements. When masking is performed, the

coefficients at value TRUE are kept unchanged, while the coefficients at

value FALSE are set to zero. The following equation represents the mask

operation.

where cm, n is the original coefficient array, is the masked coefficient

array, and maskm, n is the mask array.

You can build a mask array according to the order number you want to

analyze. In each row, elements within the bandwidth of the designated

order number are set to either TRUE or FALSE. Use the Template to Mask

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RPM

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×nk

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RPM

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kRPM

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ˆmn,

cmn, maskmn,TRUE=

0 maskmn,FALSE=





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mn,