1 §6 applications of fiber optic sensors strain sensors and temperature sensors strain sensors and...
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§6 Applications of fiber optic sensors§6 Applications of fiber optic sensors
Strain sensors and temperature Strain sensors and temperature sensorssensors
Acoustic sensors, displacement sensorsAcoustic sensors, displacement sensors Electric current sensorsElectric current sensors Rotation sensorsRotation sensors Chemical sensorsChemical sensors Sensors for mechanical and civil Sensors for mechanical and civil
structuresstructures
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Three application examples using Three application examples using FBG sensors FBG sensors
Sensing mechanismSensing mechanism
Bragg resonance wavelength: Bragg resonance wavelength: BB=2n=2n BB=0.78x10=0.78x10-6-6BB. 1. 1 1pm 1pm BB=6.7x10=6.7x10-6 -6 BBT. 1°C T. 1°C 10pm 10pm
Bragggrating
fibercore
fibercladdingI
input spectrum
measurandinduced
shift
ITransmitted signal
I
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Wavelength detection using passive optical filtersWavelength detection using passive optical filters ( (Melle et alMelle et al) )
broadbandsource
I
I
input spectrum
gratingsensor
coupler
strain-induced shift
lllllllllll
I/Iref
edgefilter
photodetectorIIref
Output
decreasingstrain
increasing strain
wavelength
Outp
ut
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Wavelength detection using tunable optical filters(Wavelength detection using tunable optical filters(Kersey et aKersey et al)l)
Well suited for WDMWell suited for WDM Resolution demonstrated: Resolution demonstrated: 11 and and 0.2°C 0.2°C Types of TOFs: Fabry-Perot filters, FBG- based filters Types of TOFs: Fabry-Perot filters, FBG- based filters
Broadbandsource
output
couplerlllllllllllllllllllllllllllllllll
1
FiberFabry-Perot
Photodetector
.....2 N
VFP
scanningwaveform
VFP
Output
. . .
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Application 1:Application 1: Internal strain monitoring of Internal strain monitoring of structural materialsstructural materials
Schematic of the test specimen showing the location of the FBG Schematic of the test specimen showing the location of the FBG sensors and loading setupsensors and loading setup
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Result of strain measurement at position 3 (Result of strain measurement at position 3 ( ) ) strain measured by grating, (o) strain measured strain measured by grating, (o) strain measured for a strain gauge attached at the surfacefor a strain gauge attached at the surface
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
0 5 10 15 20 25 30 35 40
Applied load (kN)
Str
ain
()
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Result of strain measurement at position 1 (Result of strain measurement at position 1 ( ) strain measured by grating, (o) ) strain measured by grating, (o) strain measured for a strain gauge attached at the surfacestrain measured for a strain gauge attached at the surface
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25 30 35 40
Applied load (kN)
Str
ain
()
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Structure under investigation with FBG sensors
FBGsensing unit
U
xy
SignalConditioner
Hot wire
Square Cylinder
d = 6 mm
x/d = 2.0
FBG sensor
FBG sensor
DataAcquisition
System
y/d = 1.5
FBGsensing unit
U
U x
y
x
y
Configuration ofwake generator
d
d
Optical Interrogation System
Wind Tunnel
Computer Data Acquisition System
Application 2: Measurement of flow-induced vibration
Experimental setup
THE HONG KONG POLYTECHNIC UNIVERSITY香港理工大學
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a) Strain measured from FBGb) Displacement measured from vibrometerc) Wind velocity measured from hot-wire
10 20 30 40 500
10
20
30
40
50
Xrm
s(
m)
( b )
Ur
0
10
20
30
40
50
Yrm
s(
m)
( a )
= 0 = 15 = 30 = 45
Dependence of the vibration amplitude of the square cylinder on Ur: (a) Yrms, (b) Xrms.
Results
THE HONG KONG POLYTECHNIC UNIVERSITY香港理工大學
See: Zhou Y, Wang ZJ, So RMC, Xu SJ, and Jin W, JOURNAL OF FLUID MECHANICS 443: 197-229 SEP 25 2001
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Application 3: Investigation on Structural Fatigue Problems of the KCR Vehicles
• Fiber Bragg Gratings Interrogator is used to monitor the strain and stress in the bodyshell of the KCRC compartments in order to identify the possible fatigue problems that may affect the life expectancy.
SG1FBG1
SG2
SG3
Strain gauge (SG)Optical sensor (FBG)
SG4FBG2
SG5FBG3
THE HONG KONG POLYTECHNIC UNIVERSITY香港理工大學
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Results of static and dynamic load test of the FBG sensors
• The results from FBG sensors agree well with the electrical strain gauges.
-800
-600
-400
-200
0
200
400
600
800
2.5 3 3.5 4 4.5 5 5.5
Pressure Transducer Output (V)
Mic
ro-S
trai
n
FBG1
FBG2
FBG3
THE HONG KONG POLYTECHNIC UNIVERSITY香港理工大學
See: W. Jin et al., “Structural strain and temperature measurements using FBG sensors,” Chapter in book: Guided wave optical components and devices, B. P. Pal (Eds), Elsevier,Burlington, USA, pp.389-400. 2005