Mechanische trillingen

1
Mechanische trillingen

• LES 4 TRILLINGSOPNEMERS

Patrick Guillaume E-mail patrick.guillaume_at_vub.
ac.be Tel. [phone]
2
The Measurement Chain
3
Displacement, Velocity or Acceleration?
4
Conversion from Displacement to Acceleration
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Conversion from Acceleration to Displacement
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Vibration Parameters
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Units of Vibration Signals
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Early Methods of Vibration Measurements
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Classification of Motion Transducers

• Absolute or relative transducers
• Active (self-generating) or passive transducers

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Piezo-electric Accelerometer
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Types of Accelerometers
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Mass-Spring Transducers (Seismic)
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Mass-Spring Transducers (Seismic)
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Mass-Spring Transducers (Seismic)
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Mass-Spring Transducers (Seismic)
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Sensitivity and Frequency Range
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Useful Frequency Range
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Special Accelerometers
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Choosing an Accelerometer
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Properties

• Linearity
• Dynamic range
• Effect of temperature

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Transverse Sensitivity
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The Mass Loading Effect
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The Mass Loading Effect

• MDOF
• Geen invloed in een knooppunt van een
  trillingsmode
• Grootste invloed in de buikpunten van een
  trillingsmode

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Environmental Effects
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Avoiding Errors due to Sensor Resonance
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Choosing the Mounting Position
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Acceleration Mounting - Fixed
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Acceleration Mounting - Handheld
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The Calibration Chart
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Handle the Accelerometer Carefully
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Calibration

• In the field
• Sensitivity check
• Total system check

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Calibration

• In the lab (e.g., the Back-to-Back method)
• Frequency response measurement

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Choice of Preamplifier
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Preamplifier
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Influence of Cables
Lange kabels ?? CKABEL stijgt ?? ZL daalt
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Preamplifiers On and Inside Accelerometers
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ICP / Charge Mode
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Typical ICP Sensing System
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Single-ended or Floating Input
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Floating Mode
E.g., Common Mode Rejection Ratio of 60 dB ??
? 0.001
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Single-ended Mode
Common Mode Rejection Ratio of 0 dB ?? ? 1
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Ground Loop Problem and Solution
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Piezoresistieve accelerometer
Brug van Wheatstone
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Capacitieve accelerometer
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Velocity Pickup
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Eddy Current Proximity Probes
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Eddy Current
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Calibration Curve

• Mechanical run-out
• Electrical run-out
• Cross-coupling

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Operational Range of Vibration Transducers
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Absolute verplaatsingsopnemers (assen)
Contactsonde
Gecombineerde sonde
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Choosing the Transducer
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Scanning Laser Vibrometer
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Scanning Laser Vibrometer
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Laser Vibrometry
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Laser Vibrometry