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Progress in On-Aircraft Application of Thermography
Dr. Steven ShepardThermal Wave Imaging, Inc.
www.thermalwave.com
Thermography System Evolution
1997
2006
1992 2011
2001
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Anatomy of a Thermography System
Detector
Excitation
Processing
Application Requirements
Physics
Inspection
NDT System
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Today…
• Frame rate: 30 – kHz• Array size: 64x64 – 1k x 1K• NETD 20-2000 mK• Cooled / uncooled• Cost: $2K - $250K
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Many Excitation Choices
500 W 1500 W 4800 J [watt-sec]
250 W600 W / m210 W / in2
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Best Solution?
FlashClose proximityNon-contactFOV: ~ 1 sq ft
ProjectionLong range (45’)Non-contactFOV: ~ 6 sq ft
Hot airClose proximityNon-contactFOV: ~ 2 sq ft
VibroClose proximityContactFOV: large
ScanningClose proximityNon-contactFOV: large stripe
All of these approaches detect the impact damage successfully, but they vary in sensitivity, cost, working distance, coverage area and inspection time.
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On-Aircraft Inspection Requirements
• Performance • Area coverage • Size / weight• Ease-of-use• Cost• Cost• Cost
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On-Aircraft Inspection Requirements
• Performance – Demonstrated for many applications– Some applications require laboratory scale systems
• Area coverage – Inherent feature of thermography
• Size / weight• Ease-of-use• Cost• Cost• Cost
Critical issues
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Optical Excitation
• Noncontact• Well-suited to area excitation• Pulse heating (xenon flash lamp)
– Precise high energy pulse facilitates high performance– Size, weight, cost issues
• Step Heating (halogen lamp)– Low cost– High power when applied over longer duration– Some applications may be inaccessible
Conventional Optical Heating IR NDT
reflector
IR camera
lamptarget
emitted IR
light
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Conventional Optical Heating IR NDT
reflector
IR camera
lamptarget
emitted IR
Visible + IR
reflected IR
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Spectral Filtering of Lamp Output
reflector
IR camera
halogen lamp (visible + IR)
IR filter target
emitted IR
visible
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Halogen Lamp Spectral Distribution
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Integtrate Planck Equation
Integrating Planck Equation over visible range (4-7 um):
temperature efficiency 3000 K 8.1% 3200 K 10.5% 4000 K 20.8% 5000 K 31.6% A typical 1500 W halogen lamp puts out ~ 150 W of visible light!
typical
Halogen lamps are inefficient generators of visible light!
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Spectral Distribution and Efficiency
visiblevisible + IR
filter
visible + NIR visible
INPUT OUTPUT
Solving Planck Equation for visible range (4-7 um):
temperature efficiency 3000 K 8.1% 3200 K 10.5% 4000 K 20.8% 5000 K 31.6% A typical 1500 W halogen lamp puts out ~ 150 W of visible light!
typical
Ref: Carl Zeiss
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Where Does Blocked Energy Go?
• Heat applied to one side of the filter passes through to the outer surface• This is the same heat conduction mechanism thermography is based on • Long wave IR (5-12 um) is emitted from the outer surface• Time constant for passage through filter is similar to inspection time scale• By blocking NIR, the filter creates a LWIR source.
visiblevisible + NIR visible + LWIRvisible +NIR
time
visiblevisible + NIR
filter
t0 t1 t2
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Uniformity, Efficiency and Lamp Geometry
Reflective optics can achieve excellent uniformity for a point source.
Point source
Parabolic reflector
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Uniformity, Efficiency and Lamp Geometry
• Actual lamps are not point sources, and may not be at exact focus of reflector. Collimation and uniformity suffer as source becomes larger.
• With a line source, a simple reflector illuminates a stripe. Diverging components may not hit the target.
• Can improve line source area uniformity with multiple lamps and reflectors in a reflective cavity, but system becomes larger.
Parabolic reflector
Line source
Diverging
Collimated
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Conventional Step Heating IR NDT System
• Poor efficiency– IR component of lamp output is blocked by filter.
Net efficiency is approx. 10%
• Non-uniform heating of target– Linear lamp array with reflecting enclosure required for
uniform heating of 2D area. Much of the output of a single linear tube does not hit the target
• Reflection artifacts– Light passing through raises filter temperature– Black paint may be required for reflective surfaces
• Transient reflection artifacts– Elevated temperature in reflector heats filter wall– Heat conduction through filter results in delayed
temperature increase on outer filter wall
• Slow onset and decay of heating– Processing methods are based on rectangular step
reflector
IR camera
Halogen lamp (visible + NIR)
IR filter target
emitted IR
visible
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Lamp and Focusing Reflector
Lamp
Focusing Reflector
• High intensity lamp, e.g. halogen
• Source element to allow focusing
• Reflector surface optimized for visible and IR wavelengths
Focal Point
Visible and IR beam
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Direct Visible and IR Onto Surface
Reflector
Lamp
Focusing Reflector
Focal Point
Visible and IR beam
Target
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Reflector Motion
Reflector rotates between open and closed positions
Beam directed away from target
Closed position
Target
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“Paint” Beam Onto Surface
Beam forward direction Beam off-axis
Target
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VoyageIR PROTM
Patents Pending
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VoyageIR PROTM
• Precise and efficient excitation• Compact, lightweight• 12” x 9” field of view• Uncooled microbolometer camera • Low cost (~ 40 K$)• TSR signal processing
Integrated touch screen control Large area inspection using MOSAIQ® software
Single case transport
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Applications: Moisture Ingress
+
++
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Drill Down Validation of Image Result
A320 Rudder
TSRRaw
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Drill Down Validation of Image Result
A320 Rudder
water
water
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Patch Identification: Raw IR Result
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TSR result
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Overlay Result Onto Aircraft
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Overlay Result Onto Aircraft
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Applications: Polymer FOD
Raw IR (video)
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Raw IR Result
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TSR Result
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TSR Result
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11.9”
0.5
” 1”
1” 0.75” 0.5”
0.25”
7.2”
poly insert
Hole 1 Hole 2
A B C D
1
2
0.12”
Lab flash system – cooled camera
VoyageIR Pro with uncooled camera
Boeing 7X7 Al Doubler Disbond Inspection
Raw IR result TSR result
Boeing disbond cal std
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Boeing 7X7 Al Doubler Disbond Inspection
TSR result
Boeing disbond cal std
UT
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ProjectIRTM
• Far-field thermography– Working distance 5 – 50 ft
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Summary
• VoyageIR Pro
– Unique approach to excitation removes
– Artifact reduction
– Advanced signal processing
– Apply to wide range of applications
– Drill-down confirmation of result
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