Mechanische trillingen

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Mechanische trillingen

• LES 5 BASISMEETTOESTELLEN

Patrick Guillaume E-mail patrick.guillaume_at_vub.
ac.be Tel. [phone]
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Frequency Spectrum or Overall Level
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Types of Signals
Periodic
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Which Time Signal Parameters Do We Use?
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Signal Parameters for a Harmonic Signal
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Periodic Signals (Deterministic)
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Signal Parameters for a Random Signal
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Why Make a Frequency Analysis?
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Hand-held Instrumentation
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Filters
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The Detector/Averager
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Averaging Time
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Frequency Spectrum or Overall Level
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Selecting Bandwidth
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Bandwidth of Filters
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Constant Bandwidth Filtering
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Constant Percentage Bandwidth Filters
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Response of Band-pass Filter
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Uncertainty Principle of Spectral Analysis
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Parallel Filter Spectrum Analyzer
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Spectrum Analyzer with Tunable Filter
frequency (time)
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Spectrum Analyzer with Mixer
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Phase Measurement - Keyphasor
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Phase Measurement
V
?
H
?
360
180
0
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FFT Spectrum Analyzer
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FFT
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Aliasing
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Leakage
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Leakage
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Leakage
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Rectangular Window (with MatLab)
gtgt t0.50512-1/512 gtgt xsin(2pi16t) gtgt
plot(20512-1,abs(fft(x)),'o')
gtgt t0.50512-1/512 gtgt xsin(2pi17.5t) gtgt
plot(20512-1,abs(fft(x)),'o')
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Windowing
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Hanning Window (with MatLab)
gtgt t0.50512-1/512 gtgt xsin(2pi17.5t) gtgt
plot(t,x.hanning(512)) gtgt plot(20512-1,abs(f
ft(x.hanning(512))),'o')
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Hanning Window (with MatLab)
gtgt t0.50512-1/512 gtgt xsin(2pi16t) gtgt
plot(t,x.hanning(512)) gtgt plot(20512-1,abs(ff
t(x.hanning(512))),'o')
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Overlap
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Real Time Processing

• No overlap
• With 30 overlap

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Frequency Averaging (Power Spectrum)
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Time Averaging
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Zoom FFT
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Zoom FFT
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Zoom FFT
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Cepstrum
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Cepstrum