Learn about Polytec’s latest laser vibrometer, specifically designed for remote, long range vibration and deflection measurements on bridges, buildings, towers, industrial plant, high voltage insulators or indeed any surface that is inaccessible or hard to reach. The system features a very high optical sensitivity, which means that it can also be used on surfaces at distances that would otherwise require surface treatment for vibrometry measurement. The webinar will share examples showing how the RSV-150 saves time and effort when monitoring the health of structures, including the measurement of resonant frequencies and deflections of bridges subjected to traffic loading. Find out how the laser Doppler approach compares with the alternative contacting and remote sensing methods.

1. Structural Health Monitoring of Bridges
Buildings and Industrial Plant with New
Ultra-Long-Range Vibrometer

2. RSV-150 – The Optical Alternative
Optical measurement of
displacement and velocity
No transducers to attach
Fast repositioning to different locations
Point and shoot
No targets need to be attached or surface prep
Stand-off distance to > 100 m
even higher with retro-reflective targets
Works on all materials and target temperatures
High spatial resolution / localization <10mm
Voltage output: compatible with all data acquisition systems
3/6/2012 #2

3. Compared to Accelerometers
Velocity and displacement instead of
acceleration
Relative measurement instead of absolute
direct DC displacement can be measured
Absolute directional sensing
in direction of the laser beam, no crosstalk
No temperature sensitivity
Laser spot is the sensor – not fixed to structure
3/6/2012 #3

4. What is Laser Doppler
Vibrometry (LDV)?
Laser Doppler Vibrometry is a non-contact, "point and shoot"
technology that directly measures the vibration of a test object
using the Doppler effect.
For car moving at velocity V,
Analogy: Acoustic Doppler Effect the observer hears the
frequency fD = c/(λ -V/f).
λ
Sound emitted from
c
stationary car has
frequency f = c/λ v
c: velocity of the sound wave Emitted Observed
frequency f frequency fD
λ: emitted wavelength
For a vibrometer: Δ fD α V
f: emitted frequency
Δ fD = 2V/λ

5. The Heterodyne Interferometer
Measurement Beam
f0
f0 ± f D Bragg cell
Reflected Beam He-Ne Laser
<1mw (633nm)
x(t)
v(t) f0 + 40 MHz
Photo-detector
Frequency Modulated
signal
40 MHz ± fD
Δ fD = 2V/λ

6. Signal Demodulation
Photo-detector system
Controller Example
FM Doppler signal
Voltage ~
Velocity
AM electrical signal FFT Spectrum
Voltage ~
Displacement

7. RSV-150: Features
Long Range Capabilities due to
High power, but eye-safe & visible laser (class 2)
Long Range lens
Easy operation due to:
Quick setup:
No need for access to measurement surfaces
Point, focus, measure
Green target laser with good visibility day & night
Coaxial video camera shows measurement location
even in bright sunlight
Signal level indicator to maximize laser return signal
Optional zoom scope for wider field of view 3/6/2012 #8

8. The RSV-150 System
3/6/2012 #9

9. RSV-150 Setup
Optics
Position using tripod
Focus using camera, laser and bargraph
Electronics (Controller)
Adjust ranges and output filters
16 ranges displacement
< 0.1 µm to > 1 m
8 ranges velocity
< 1 µm/s to > 1 m/s
bandwidth: 0Hz – 25 kHz
Various high- and low-pass filters
3/6/2012 # 10

10. RSV-150 Sensor Head
Comprises
Laser sources for targeting and
measurement
Inline camera
Long range optics long range optics scope (option)
Pan/tilt fine adjustment
better than10mm @ 100m
for targeting on fine structures
eg stay cables
Spray water resistant (IP63)
Weight < 9 kg
fine adjustment
3/6/2012 # 11

11. RSV-150: The System
RSV-150 Sensor Head
Properties
Spray water resistant (IP63)
Manual focusing lens
laser focus = camera focus
focal length approx 1000 mm
(equiv. 35mm)
View though internal
Green laser for targeting camera
Mechanical adapter for
compensation sensor
compensates for strong ambient vibration of the
sensor or tripod
view through zoom
scope
3/6/2012 # 12

12. RSV-150: The System
RSV-150 Controller
Decoding
decodes high frequency signals for sensor head
Output (BNC)
displacement and velocity (+/- 10V)
video (PAL, Composite)
optical signal level (RSSI)
Power supply
100...240VAC (50/60Hz )
12-24 V DC
approx. 60W
RSV-E-150 Controller
USB 1.1 for remote control
3/6/2012 # 13

13. Applications
Applications
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14. Applications
Condition Monitoring
Piping vibration problems
Safe and convenient distances
high temperatures
explosion hazard
nuclear radiation
Easy localization by manual “probing” of the pipe length
Easy assessment of machinery vibration severity level
according to ISO 10816-3 for trending
with standard data loggers
Suitable for mining environments
Insensitivity to target surface
Hot targets
Magnetic fields (transformers)
High voltage
3/6/2012 # 15

15. Applications
Structural Dynamics
Eigenfrequency Assessment
bridges, stay cables
suitable for high voltage
insulators, power poles and
cables
Displacement/Deflection
bridges under defined testing loads
Validation of Finite Element Models
Dynamic behavior assessment for update of FE
models
3/6/2012 # 16

16. Troubleshooting
Perfect solution when:
Fast response is necessary
Contact transducers cannot be mounted
Access is limited, dangerous or
impossible
Location of problem is unknown
Manual “scanning” can be performed
3/6/2012 # 17

17. Applications
Applications Tested
Structural Dynamics
TV Tower (Eigenfrequency)
Drilling Rig (Troubleshooting)
Steel Railroad Bridge (Displacement)
Cable Stay Bridges (Tension of stay cables)
Bridge bearing integrity (Differential displacement)
Condition Monitoring
Conveyor belt (bearing condition)
High voltage power cables and supports
(Eigenfrequency)
3/6/2012 # 18

18. Applications: Structural Dynamics
TV Tower
Distance 300m
Long time average
3/6/2012 # 19

19. Coal Mine: Conveyor Belt
Distance 8m
meas. point encrusted
and rusty
Target: bearing
monitoring
red: damaged
green: good reference
3/6/2012 # 20

20. Applications: Condition Monitoring
Power Lines
Distance up to 100m
Frequency measurement
for condition monitoring
Eigenfrequency
measurement for
resonance tuning
Excitation: Ambient (wind,
current)
3/6/2012 # 21

21. Applications: Structural Dynamics
Müngsten Bridge
Height 108m
Steel framework -train bridge
Distance > 140m
Excitation: train
displacement of the
bridge during slow
train pass-by
3/6/2012 # 22

22. Application: Structural Dynamics
Concrete Bridge
Highway bridge
Target
Eigenfrequency
Displacements
2 1
4 3
3/6/2012 # 23

23. Application: Structural Dynamics
Concrete bridge 1
Eigenfrequency
5 averages
0.031Hz frequency
resolution
3/6/2012 # 24

24. Application: Structural Dynamics
Concrete Bridge 1
Displacement
time history during green target
laser spot
traffic excitation
3/6/2012 # 25

25. Application: Structural Dynamics
Concrete Bridge
Displacement
time history during
traffic excitation
measured on pier
3
3
Photo
pier displacement (in µm)
View through internal camera
3/6/2012 # 26

26. Application: Structural Health Monitoring (SHM)
NPL Foot Bridge
Built in the mid 1960s,
Test bed for many different
structural monitoring techniques
15 tonnes, 5 meters high, 20
meters long concrete bridge
Courtesy: Elena Barton, NPL, GB
3/6/2012 # 27

27. Application: Structural Health Monitoring (SHM)
Foot Bridge: Modelling and Monitoring
Modeling: 3D Laser Scan
Monitoring sensors
Acoustic Emission
Digital Image Correlation
Digital Leveling
Electro level Beam Sensors
Fiber Bragg Gratings
Resistance Strain Gages
Time-Domain Reflectometry
Distributed Crack Sensor Finite element analysis model
Vibrating Wire Strain Gages of the bridge to further
understand and predict the
Video Gauge Technique
structural health
Wireless Accelerometer and Magnetic
InductionSensors
Courtesy: Elena Barton, NPL, GB
Laser Doppler Vibrometer
3/6/2012 # 28

28. Application: Structural Health Monitoring
Foot Bridge: Results
Velocity Output
Direct
Displacement
Output
Max Peak to Peak Displacement 0.534mm
3/6/2012 # 29

29. LDV Measurement Advantages
• Observed LDV and Accelerometer
Data Compares Very Well
• Very easy to extract:
• FRF - Frequency Response
Function
• Time History
• It is easy to then relate this
information to any modelling
# 30

30. Arts Tower Sheffield University
Special Thanks to Prof. Brownjohn, Sheffield University
At 255 feet (78 m) tall it is the second
tallest building in Sheffield, England
Has an active condition monitoring
system in operation
# 31

31. Vibrometer Measurement Result Arts Tower
Time Response Velocity Output
0.53Hz
FFT
Displacement (Velocity Integrated)
# 32

32. Vibrometer Measurement Result Arts Tower
Above: Results from
Arts Tower monitoring
system:
e then n directions
Polytec Vibrometer
Results are Consistent
with Accelerometer-
based Condition
Monitoring System
33

33. Humber Bridge
The Humber Bridge is a suspension
bridge with the north tower sited on the
high water line and the south tower
founded in shallow water 500m from
the shore.
# 34

34. Measurement Targets
Primary weight-bearing cables
Smaller suspension cables
Deck
# 35

35. Measurement 1- Main Cable Velocity at Clamp
Thanks to Prof. Brownjohn, Sheffield University
Quick Setup 0.29Hz
Good Signal Levels 2.46Hz
Results are plausible
No one has measured before
3.87Hz
Target difficult to reach
Main cables need more study
# 36

36. Measurement 2 - Cable Duct
Some good clean data with
Realistic results up to 4 to 5Hz
For Humber Bridge, there would
be no other way to measure
response of main cables, and the
response looks realistic.
4.34Hz
# 37

37. Measurement 3 – Hanger 6
For the hangers, the harmonics validate
the measurements showing the capability
for mass measurement on
stay cables/hangers of bridges .
# 38

38. Conclusion
Long stand-off distance
Safe, fast and convenient operation
Quick setup
No sensor mounting = time saving
Easy Troubleshooting
Monitor many locations from one sensor position
Time-saving localization of vibration sources
Flexibility
Works on all surfaces
Works with all data collectors 3/6/2012 # 39

39. RSV-150: Summary Structural Dynamics
Conclusion
High stand-off distance
assess many measurement points from one
location
Quick setup
no sensor mounting = time saving
High resolution
delivers reliable data for model validation
3/6/2012 # 40

40. Engineering Services and Rental Program
Advanced non-contact vibration measurements available for every budget
Measurements using Polytec’s latest, non-contact measurement technology
Application engineers to operate the measurement system to its fullest potential
Rental of any of Polytec‘s products
Convenience of testing at the customer’s facility or in a Polytec lab
Complete measurement data for further processing
Short-notice, critical measurements
Occasional measurements
Extended evaluation prior to purchase
Budget Flexibility