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Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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The Measurement Chain
Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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Early Methods of Vibration “Measurements”
Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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Classification of Motion Transducers
• Absolute or relative transducers• Active (self-generating) or passive transducers
Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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Mechanical Lever
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Piezo-electric Accelerometer
Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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Types of Accelerometers
Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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Mass-Spring Transducers (Seismic)
P Sk k k
P Pf (t) k (y(t) x(t)) P PF ( ) k (Y( ) X( ))
Mx(t) k(y(t) x(t)) c(y(t) x(t)) 2M X( ) (k i c)(Y( ) X( ))
2k i c
X( ) Y( )M k i c
Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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Mass-Spring Transducers (Seismic)
P P
P 2
2
P 2
F ( ) k (Y( ) X( ))
k i ck (1 )Y( )
M k i c
Mk Y( )
M k i c
P PF ( ) k (Y( ) X( ))
2k i c
X( ) Y( )M k i c
Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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Mass-Spring Transducers (Seismic)
2
2n
P P 2
2nn
D
F ( ) k Y( )
1 i 2
H
2PP 2 2
n2
nn
A
k 1F ( ) Y( )
1 i 2
H
P Sn
k k kM M
2PP 2
P S2
nn
A
k 1F ( ) M Y( )
k k1 i 2
H
c
c cc 2 Mk
Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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Mass-Spring Transducers (Seismic)
2
2n
D 2
2nn
H ( )
1 i 2
A 2
2nn
1H ( )
1 i 2
Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group
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Useful Frequency Range
1a a
1f
R C
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Sensitivity and Frequency Range
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Special Accelerometers
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Choosing an Accelerometer
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Transverse Sensitivity
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The “Mass Loading” Effect
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Properties
• Linearity
• Phase distortion• Effect of temperature
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Environmental Effects
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Handle the Accelerometer Carefully
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The Calibration Chart
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Calibration
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Calibration using “Back-to-Back” method
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Preamplifier
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Choice of Preamplifier
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Single-ended or Floating Input
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Ground Loop Problem and Solution
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Preamplifiers On and Inside Accelerometers
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Charge Amplifier
OUTf
qV
C
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Typical ICP Sensing System
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ICP / Charge Mode
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Piezoresistieve accelerometer
R LK
R L
Brug van Wheatstone
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Capacitieve accelerometer
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Velocity Pickup
d d dxe n n
dt dx dt
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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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Acceleration Mounting - Fixed
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Acceleration Mounting - Handheld
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Choosing the Mounting Position
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Choosing the Transducer