Epson CMD-2260 (CD-ROM) Technické informace stáhnout pdf (Strana 224)

Blastware Advanced Module

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6–34 Blastware Operator Manual

velocity value and by how much must be extrapolated by examining the original signal closely.

The frequency at the peak of a complex wave is usually not a single frequency rather it is a series

of waves of different frequencies superimposed. It is intended that the frequency spectrum data be

used as a tool in conjunction with the velocity versus time waveform.

Due to the digital nature of the FFT process, some smearing or broadening of the spectrum may

occur. The algorithm used to represent the original waveform with a series of weighted sine and

cosine curves does so with discrete frequency increments. A 25.5 hertz signal, for example, may

not be represented by one frequency category alone and may therefore be represented by the next

closest frequencies, 25 and 26 hertz, with possibly some small residual leakage into neighboring

frequency categories. This is referred to as the "Picket Fence Effect".

For further reading, please see the following references.

Burrus, C.S. and Parks, T.W., DFT/FFT AND CONVOLUTION ALGORITHMS. Rice

University: John Wiley and Sons, 1985.

Lighthill, M.J., AN INTRODUCTION TO FOURIER ANALYSIS AND GENERALIZED

FUNCTIONS. Cambridge, England: Cambridge University Press, 1980.

Oppenheim, A.V. and Schafer, R.W., DIGITAL SIGNAL PROCESSING. Englewood Cliffs,

NJ: Prentice-Hall, Inc., 1975.

Rabiner, L.R. and Gold, B., THEORY AND APPLICATION OF DIGITAL SIGNAL

PROCESSING. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1975.

Brigham, E.O., THE FAST FOURIER TRANSFORM. Englewood Cliffs, NJ: Prentice-Hall,

Inc., 1974.

6.9.13 Test Wave

This command creates a sine wave based on entered amplitude and frequency parameters.

To display the Test Wave dialog box, open the Process Menu and choose the Test Wave

command.

Enter up to three amplitude and frequency components for the test wave. Select a waveform

window to display the new waveform. Name the new waveform in the last box. Press OK to

accept your settings.

6.9.14 Peak Hold

The Peak Hold command allows you to remove negative excursions from waveforms.

To display the Peak Hold dialog box, open the Process Menu and choose the Peak Hold

command.

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Epson CMD-2260 (CD-ROM) Technické informace Strana 224