## Mechanical vibration and shock measurements |

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Page 151

A narrow

diagnostic and experimental work. This is especially the case with vibration

problems associated with rotating machines such as gearboxes where a fine

to modulation which occur at constant frequency intervals. The Heterodyne

Analyzer shown in Fig. 6. 61 facilitates

bandwidths between 3, 1 6 ...

A narrow

**constant bandwidth**analysis may often be required in development,diagnostic and experimental work. This is especially the case with vibration

problems associated with rotating machines such as gearboxes where a fine

**constant bandwidth**is needed to identify multiple harmonics and sidebands dueto modulation which occur at constant frequency intervals. The Heterodyne

Analyzer shown in Fig. 6. 61 facilitates

**constant bandwidth**analysis withbandwidths between 3, 1 6 ...

Page 168

Also, the filter characteristic is the same for all lines and is thus

) must first be collected before it can be transformed, whereas with digital filtering

each sample is processed fully before the next one arrives, and the time signal

does not need to be stored. 7.1.4. Choice of Bandwidth, Frequency Scale and

Amplitude Scale In general it is found that analysis time is governed by

expressions of the type ...

Also, the filter characteristic is the same for all lines and is thus

**constant****bandwidth**. Another major difference is that a complete time record (of /V samples) must first be collected before it can be transformed, whereas with digital filtering

each sample is processed fully before the next one arrives, and the time signal

does not need to be stored. 7.1.4. Choice of Bandwidth, Frequency Scale and

Amplitude Scale In general it is found that analysis time is governed by

expressions of the type ...

Page 169

a) Discrete frequency signals dB CHOICE OF BANDWIDTH B<fh/3 (typical) b)

Stationary random signals (& Impulsive) Frequency B = Bandwidth of filter

characteristic Harmonic spacing Br= Bandwidth of resonance peak B<Br/3 (

typical) Frequency Fig. 7. 8. Choice of filter bandwidth scale would often be most

appropriate. Sometimes it is necessary for practical reasons to choose

the spectrum, ...

a) Discrete frequency signals dB CHOICE OF BANDWIDTH B<fh/3 (typical) b)

Stationary random signals (& Impulsive) Frequency B = Bandwidth of filter

characteristic Harmonic spacing Br= Bandwidth of resonance peak B<Br/3 (

typical) Frequency Fig. 7. 8. Choice of filter bandwidth scale would often be most

appropriate. Sometimes it is necessary for practical reasons to choose

**constant****bandwidth**in order to achieve a sufficiently small percentage bandwidth in part ofthe spectrum, ...

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### Contents

INTRODUCTION | 13 |

CHARACTERISTICS OF VIBRATION AND SHOCK | 20 |

RESPONSE OF MECHANICAL SYSTEMS | 40 |

14 other sections not shown

### Common terms and phrases

acceleration accelerometer Acoustic Emission Amplifier amplitude application averaging axis balancing band bandwidth cable calibration characteristics charge amplifier constant bandwidth curve damping decibel degree-of-freedom system digital filter displacement dynamic range effect electronic element Engineering equation equipment example excitation factor fatigue force frequency analysis frequency components frequency range frequency response frequency spectrum harmonic high frequency impulse instruments integration Level Recorder limit linear load machine mass maximum mechanical impedance Mechanical vibration method modes monitoring motion mounted noise non-linear normally obtained octave output parameters peak piezoelectric plane portable preamplifier quency random signals random vibrations real-time resonant frequency rotating rotor S-N curve sensitivity Shock and Vibration shock pulse shock spectrum shown sinusoidal sound level meters spectra speed structure techniques tion transducer transient typical unbalance values velocity vibration and shock vibration isolation vibration level vibration measurements Vibration Meter vibration signals vibration test visco-elastic