National Instruments Order Analysis Toolset

Chapter 3 Gabor Transform-Based Order Tracking

LabVIEW Order Analysis Toolset User Manual 3-4 ni.com

processed by a Gabor transform, the index of the nth order is given by the

following equation.

where RPM is the averaged instantaneous rotational speed in the time

interval, N is the number of frequency bins, and fs is the sampling

frequency. In the LabVIEW Order Analysis Toolset, the number of

frequency bins N equals the length of the window.

Each order component in the order domain, as well as each harmonic in

the frequency domain, has a side band. Thus, in the joint time-frequency

domain, each order component contains the coefficients along the order

curve and some coefficients in the neighborhood. You must include the

coefficients in the neighborhood when selecting the order component.

Constant frequency bandwidth and constant order bandwidth are two ways

to define the bandwidth of the neighborhood for an order curve. Figure 3-3

illustrates constant frequency bandwidth and constant order bandwidth.

Figure 3-3. Constant Frequency Bandwidth and Constant Order Bandwidth

Figure 3-3(a) illustrates constant frequency bandwidth. The neighborhood

is considered as the region between and , where

∆ f is a constant frequency. The frequency of the bandwidth ∆ f remains

constant over time.

index round RPM

-------------N

----n××





500–

400–

300–

200–

100–

0–

0 5 25 30 3510 15 20 39

Time (s)

(a) Constant Frequency Bandwidth

0 5 25 30 3510 15 20 39

Time (s)

(b) Constant Order Bandwidth

Frequency (Hz)

500–

400–

300–

200–

100–

0–

Frequency (Hz)

nRPM

-------------∆

-----+nRPM

-------------∆

-----–