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Noncontact Displacement Monitoring by Lasers
Upul Attanayake, Ph.D., P.E.Assistant Professor
CAIT Workshop on International Bridge Study (IBS)June 14 – 15, 2011
Outline
Laser tracker specifications Laser tracker - accessories Reflector mounting process Field implementation - bridge deflection measurements Summary/Conclusions
Laser Tracker SpecificationsAmbient Conditions
Working temperature 0°C to 40°C (32°F to 104°F)Storage temperature -10°C to 60°C (14°F to 140°F)Relative humidity 10% to 90%, non-condensing
Absolute Interferometer (AIFM) Wavelength 633 nm / 795 nm (visible / IR - HeNe)Warm-up time, cold start 8 minWarm-up time, warm start 5 minLargest beam diameter 4 mmInterferometer distance resolution 0.32 μm (0.000013”)Interferometer distance accuracy ± 0.5 μm/m (± 0.000006”/ft)Typical lock-on working range 1.0 – 80.0 m (3.3 – 262 ft)
Measuring and Tracking PerformanceMeasuring rate 3 kHzMeasuring rate output 1 kHZTracking speed lateral > 4 m/s (13 ft/s)Tracking speed radial > 6 m/s (19 ft/s)
Laser Tracker - Accessories
0.5" Reflectoracceptance angle 500
1.5" Red-Ring Reflectoracceptance angle of 300
Laser Tracker
AT MeteoStation(Temp., humidity,
and pressure) Control Unit and Laptop Power Supply
Reflector Mounting Process
A reflector with a magnetic base
Mounting a reflector on a girder A reflector is mounted next to a potentiometer
AccessMounting a reflector using hot glue
Field Implementation -Bridge Deflection Measurements
General view of the bridge Plan view of the bridge
Reflector location on southbound span 2
Girder 3 deflection under 6 LT-BB @ L2
Distance, ft (m) % Error32.5 (19. 2) 9.865.0 (28.7) 3.097.5 (36.6) 7.7
Oct. 10-11, 2010
Field Implementation - Bridge Deflection Measurements
Bridge vibration under transient loads
0 30 60 90 120216.90
217.00
217.10
Time (sec)
Brid
ge d
eflec
tion
(in.)
Maximum deflection at the reflector = 217.09 -216.91= 0.18 in. OR 4.6 mm
90 92 94 96 98 100216.90
216.95
217.00
217.05
217.10
Time (sec)
Brid
ge d
eflec
tion
(in.)
Field Implementation - Bridge Deflection Measurements
Operational Conclusions• Laser Tracker measures deflections and translations without contact. • The technology can acquire static displacements at multiple locations and/or
dynamic displacement at a single location at a maximum rate of 3kHz.• Technology can be used during daylight or night (night time is preferred to
minimize the interference of sunlight). • Entire operation can be completed in less than two hours on a typical single span
bridge including reflector mounting. • A single operator can execute the entire measurement operation if traffic control
is provided.
Summary/Conclusions
Measurement Related Conclusions• Highly accurate measurements• Resolution of 0.0001” can be achieved very easily under field conditions• Beam divergence requires using 1.5” RR reflectors beyond 160 ft (50 m) under
normal operating conditions• 1.5” RRR could read well beyond 260 ft (80 m) distance stated in specifications• Intensity of ambient light can interfere with initial auto measurement settings
Summary/Conclusions
Thanks You !
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