Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group © Brüel&Kjær The Measurement Chain.

Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group

© Brüel&Kjær

The Measurement Chain


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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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Mechanical Lever


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Piezo-electric Accelerometer


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Types of Accelerometers


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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


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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


© Brüel&Kjær


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


© Brüel&Kjær


2

2n

D 2

2nn

H ( )

1 i 2

A 2

2nn

1H ( )

1 i 2


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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


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Scanning Laser Vibrometer

Vrije Universiteit Brussel - Mechanical Engineering - Acoustics & Vibration Research Group © Brüel&Kjær The Measurement Chain.

Documents

calibration chart slide

measurement chain slide

mass loading effect

passive transducers

backtoback method