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


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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.

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

  1. 1. Structural Health Monitoring of BridgesBuildings and Industrial Plant with NewUltra-Long-Range Vibrometer
  2. 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. 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. 4. What is Laser DopplerVibrometry (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. 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. 6. Signal DemodulationPhoto-detector system Controller Example FM Doppler signal Voltage ~ Velocity AM electrical signal FFT Spectrum Voltage ~ Displacement
  7. 7. RSV-150: FeaturesLong Range Capabilities due to High power, but eye-safe & visible laser (class 2) Long Range lensEasy 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. 8. The RSV-150 System 3/6/2012 #9
  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. 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. 11. RSV-150: The SystemRSV-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. 12. RSV-150: The SystemRSV-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. 13. ApplicationsApplications 3/6/2012 # 14
  14. 14. ApplicationsCondition 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. 15. ApplicationsStructural 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. 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. 17. ApplicationsApplications 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. 18. Applications: Structural DynamicsTV Tower Distance 300m Long time average 3/6/2012 # 19
  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. 20. Applications: Condition MonitoringPower Lines Distance up to 100m Frequency measurement for condition monitoring Eigenfrequency measurement for resonance tuning Excitation: Ambient (wind, current) 3/6/2012 # 21
  21. 21. Applications: Structural DynamicsMüngsten 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. 22. Application: Structural DynamicsConcrete Bridge Highway bridge Target Eigenfrequency Displacements 2 14 3 3/6/2012 # 23
  23. 23. Application: Structural DynamicsConcrete bridge 1 Eigenfrequency 5 averages 0.031Hz frequency resolution 3/6/2012 # 24
  24. 24. Application: Structural DynamicsConcrete Bridge 1 Displacement time history during green target laser spot traffic excitation 3/6/2012 # 25
  25. 25. Application: Structural DynamicsConcrete Bridge Displacement time history during traffic excitation measured on pier 3 3Photo pier displacement (in µm) View through internal camera 3/6/2012 # 26
  26. 26. Application: Structural Health Monitoring (SHM)NPL Foot BridgeBuilt in the mid 1960s,Test bed for many differentstructural monitoring techniques 15 tonnes, 5 meters high, 20 meters long concrete bridge Courtesy: Elena Barton, NPL, GB 3/6/2012 # 27
  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. 28. Application: Structural Health MonitoringFoot Bridge: Results Velocity Output Direct Displacement Output Max Peak to Peak Displacement 0.534mm 3/6/2012 # 29
  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. 30. Arts Tower Sheffield UniversitySpecial 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. 31. Vibrometer Measurement Result Arts Tower Time Response Velocity Output 0.53Hz FFT Displacement (Velocity Integrated) # 32
  32. 32. Vibrometer Measurement Result Arts Tower Above: Results from Arts Tower monitoring system: e then n directions Polytec VibrometerResults are Consistent with Accelerometer- based Condition Monitoring System 33
  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. 34. Measurement Targets Primary weight-bearing cables Smaller suspension cables Deck # 35
  35. 35. Measurement 1- Main Cable Velocity at Clamp Thanks to Prof. Brownjohn, Sheffield UniversityQuick Setup 0.29HzGood Signal Levels 2.46HzResults are plausibleNo one has measured before 3.87HzTarget difficult to reachMain cables need more study # 36
  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. 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. 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. 39. RSV-150: Summary Structural DynamicsConclusion 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. 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