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Chapter 29 ZOOM ANALYSIS Zoom analysis provides the means to separate quickly machine-train components, such as gear sets, from a complex vibration signature. The technique lets the user select a specific range of vibration frequencies, which the real-time analyzer converts to a high-resolution, narrowband signature. This capability is unique to real-time ana- lyzers and is not available in general-purpose, single-channel vibration analyzers. Real-time zoom analysis can be performed with no data gaps up to a range of 10 kHz with most microprocessor-based,real-time analyzers. However, the center frequency plus one-half of the selected frequency span cannot exceed 10 kHz. Above this range, pseudo-real-time processing occurs, which means that data required to perform the zoom transform are acquired until the extended recorded memory of the analyzer is full. When this occurs, the acquired data are processed before additional data are gathered. However, this may result in data gaps that can adversely affect the accuracy of the zoomed spectra. The gaps will be proportional to the time required to perform the zoom transform for each channel, which in some cases can be between 5 and 10 sec. When using the zoom mode, the extended recorder memory should be set to the max- imum available to obtain the best zoom accuracy and resolution. Reducing the num- ber of active channels and lines of resolution also increases the speed and minimizes the data gaps. FREQUENCYSPAN The frequency span parameter allows the user to select the frequency span for spec- trum (FFT-based) and octave (digital filter-based) acquisition and analysis. For spec- trum analysis, the frequency span can be set to any frequency notch from 1 Hz to 100 265
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Chapter 29 ZOOM ANALYSIS
Zoom analysis provides the means to separate quickly machine-train components, such as gear sets, from a complex vibration signature. The technique lets the user select a specific range of vibration frequencies, which the real-time analyzer converts to a high-resolution, narrowband signature. This capability is unique to real-time ana- lyzers and is not available in general-purpose, single-channel vibration analyzers.
Real-time zoom analysis can be performed with no data gaps up to a range of 10 kHz with most microprocessor-based, real-time analyzers. However, the center frequency plus one-half of the selected frequency span cannot exceed 10 kHz.
Above this range, pseudo-real-time processing occurs, which means that data required to perform the zoom transform are acquired until the extended recorded memory of the analyzer is full. When this occurs, the acquired data are processed before additional data are gathered. However, this may result in data gaps that can adversely affect the accuracy of the zoomed spectra. The gaps will be proportional to the time required to perform the zoom transform for each channel, which in some cases can be between 5 and 10 sec.
When using the zoom mode, the extended recorder memory should be set to the max- imum available to obtain the best zoom accuracy and resolution. Reducing the num- ber of active channels and lines of resolution also increases the speed and minimizes the data gaps.
FREQUENCYSPAN
The frequency span parameter allows the user to select the frequency span for spec- trum (FFT-based) and octave (digital filter-based) acquisition and analysis. For spec- trum analysis, the frequency span can be set to any frequency notch from 1 Hz to 100
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266 Vibration Fundamentals
kHz (usually limited to two-channel operation only) or 1 Hz to 40 kHz (for three- to eight-channel operation). In real-time zoom mode, the frequency span can be set to any frequency notch from 5 Hz to 10 kHz, as long as the new frequency span is in the range of zoom capabilities.
CENTER FREQUENCY
The center frequency setting is used to set the center frequency for zoom mode opera- tion. The center frequency can be set to any value in the range up to 100 kHz - (Fre- quency spad2) for two-channel operation or 40 kHz - (Frequency spad2) for three- to eight-channel operation.
