Gunadarma University - Active –...

Active – ThermographyPrinciples

Pulse Thermography

Steap Heating Thermography

Lock-In Thermography

Pulse-Phase Thermography

Derivative technics

Active – Thermography

Principles

Pulse Thermography




Derivative technics

Reflexion

object

IR Sensor

ThermalanalysisThermalanalysis

voidMetallic part

voidvoidMetallic partMetallic part

Active – Thermography

Principles

Pulse Thermography




Derivative technics

Basically, PT consists of briefly heatingthe specimen and then recordingits temperature decay curve.

16,5

16,7

16,9

17,1

17,3

17,5

17,7

0 5 10 15 20 25 30 35 40N° échantillon

Poids (g)

avec colle

sans colle

fausses alarmes

Piece(plastic lid)

IR camera

Infrared cameras - ElectroPhysics3-14µm - 320*240 pixelsPyroelectric BST Uncooled FPAobjective : 50 mm - 3-5µmdistance lid - camera : 50 cm

Halogen Lamp

halogene Lamp1000 WDistance Lid - Lampe : 12cm

Acquisition system

Air

Glue

Thermal front

20

40

60

80

100

120

Niveau de gris

2 s ; zone avec colle

2 s ; zone sans colle









0

2

4

6

8

10

12

14

16

18

20

0 10000 20000 30000 40000 50000 60000 70000 80000 90000Temps d'attente en ms

Contraste de différence

Temps de chauffe = 2 secondes





9

( )( )

{ }

( )

{ }

,,, ,

: ; :

y Sx A

Ng y tNg x tC A S t

Card x A Card y S

A zone avec colle B zone avec colle

∈∈= −∈ ∈

∑∑

0

2

4

6

8

10

12

14

16

0 10000 20000 30000 40000 50000 60000 70000 80000 90000Temps d'attente en ms

Contraste de différence

Jour 1 17:20:00

Jour 1 19:30:00

Jour 2 09:25:00

Jour 2 17:39:00

Heating time = 5s

� Differences between the mean contrastand the best contrast for each trial lessthan 3,8%� Differences for the best contrast for various « waiting time » beforeacquisition: 500ms

10

Thermal imagesWithout glue

With glue spots

�� Thermal prints can identify presence of glue

70

90

110

130

150

170

190

210

230

13 33 53 73 93 113 133 153 173 193Position

Niveau de gris

12

Raw (unprocessed) thermal image

40

60

80

100

120

140

160

180

200

7 27 47 67 87 107 127 147 167 187Position

Niveau de gris

Mean image subtracted

Unprocessed thermal images

Examples

Processed images

Without glueWith glue

14

[ ]répartition suivant les valeurs 0,255

de proportion i

i

h

p

∈

Original image histogram Thresheld image histogram M=4

[ ]répartition selon les niveaux de gris ,

1, ,de proportion

j

j

z

j M q∈

Multithresolding algorithm (Tsai)

mask m×n

Pixel of interest{ } { }voisins 0,5. voisins

Card jaunes Card

site conservé

>⇒

X. Maldague


Pulse Thermography




Derivative technics

The sample is continuously heated, at low power. Variations of surface temperature with time are related to specimen features as in pulse thermography. This technique of step heating (SH) is sometimes referred to as time-resolved infrared radiometry or TRIR.



Pulse Thermography




Derivative technics

Lock-in principle: The principle oflock-in thermographyconsists of introducing periodicallymodulated heat into an object and

monitoring only the periodic surface temperature modulation phase-referred to the modulated heat supply. Hence, if thesurface temperature is measured via an

infrared (IR) thermocamera, lock-inthermography means that the information ofeach pixel of the image is processed as if it

were fed into a Lock in amplifier.

Background theory:T

TTaT

c ∂∂=∆=∆

ρλ

Solution (of the form):( ) ( ) ( )( ) fwithetT

tTzTtzTti ..2

.,.. πωω ==

=

Excitation: tωsin.0Ε=Ε

For one dimension: t

tzT

z

tzTa

∂∂=

∂∂ ),(),(

2

2

)(.),(

2

2

zTa

iz

tzT ω=∂

∂

ikzeTzT 0)( =Which solution is: k?

)(..)(2 zTa

izTkω=−

aikω−=2

2)1(2 −=− iitricka

ik2

).1(ω−=

)2

cos(.),(

...),(

2.

0

2.

2.

0

za

teTtzT

or

eeeTtzT

az

tiaiz

az

ωωω

ωωω

−=

=

−

−−

Thermal diffusion length (initial amplitude divided b y « e »)ω

µ a2=

Thermal wave propagation speed

Thermal wave wavelength

First method: Synchronize the camera (not easy/linkto the camera frame rate) with the excitation source and acquired four points (every T/4) per period andper pixel.

( ) ( )224

213 SSSSA −+−=

24

13

SS

SSarctg

−−=ϕ

Second method (most used now):acquire the signal and process it in the Fourier domain

Benefits of Lockin Thermography

1. Non contactOn large structureOn small objects down to 1mm

2. Full fieldComplex structures

3. Easy to useReal componentsSine loadRandom loading

4. Fast to set upblack paint on metal. No paint on composites

5. Wide spectral rangeup to 20kHz

6. Energy measurementPlastic and dissipated energy

NDT Lockin Thermography• SET UP

LampsAmplifier

Function generator

PC

Camera

Trig out (rear)

Analogue input (rear)

Output (front panel)

Lockin (rear)

USB or camlink

USB or Camlink

specimen

Example : Stress analysis fracture mechanics

Load Frequency 10 Hz.

The lines in data graph show time history of the image’s in the B&W image.

Note that camera is calibrated in absolute temperature, and shows small amplitude temperature swings of 100 mK and 45mK.

Thermal image movie (Colors)

Thermal image (B&W)

xx

Map of amplitude in °CThermal image

Frame rate : 140Hz Full-frame

Frame accumulation: 1000 frames

Processing Time : 7 seconds

Lockin Frequency : 10 Hz

Map of phase in degrees

Map of amplitude in MPaLocal value of stress region 1 (MPa)

Library of material (Coefficient of thermoelasticity)

Coefficient of thermo-elasticity allows to transform temperature change in MPa

Km = α/(ρ.Cp)

α = linear expansion (K-1)

ρ = density (Kg/m3)

Cp= specific heat J/kg/K

Frame rate : 140Hz Full-frame

Frame accumulation: 1000 frames

Processing Time : 7 seconds

Acquisition : every 30s

Lockin Frequency : 20 Hz

Thermal profile T=30sT=1min00sT=1min30sT=2min00sT=2min30sT=3min00sT=3min30sT=4min00sT=4min30sT=5min00sT=5min00sT=5min30sT=6min00sT=6min30sT=7min00sT=7min30sT=8min00sT=8min30sT=9min00sT=9min30sT=10min00sT=10min30sT=11min00sT=11min30sT=12min00sT=12min30sT=13min00s

Crack propagation

Lockin Thermography test

Click on the film to see film:• Frequency 0.1Hz• Recording: 1 period

Results - LIT

Average image during the test

Phase image

Magnitude image


Pulse Thermography




Derivative technics

NDT Phase Pulse Thermography• SET UP

LampsAmplifier

Function generator

PC

Camera

Trig out (rear)

Analogue input (rear)

Output (front panel)

Recorder trigger in on LPT

USB or camlink

USB or Camlink

specimen

Phase Pulse Thermography test

Click on the film to see film:• Frequency 0.1Hz• Recording: 1 period

Result - PPT

Steel plate thickness

Phase imageMagnitude image

Frequency : 0.020 Frequency : 0.023 Frequency : 0.025 Frequency : 0.028 Frequency : 0.031 Frequency : 0.033 Frequency : 0.036 Frequency : 0.039 Frequency : 0.041 Frequency : 0.044 Frequency : 0.047 Frequency : 0.049 Frequency : 0.052 Frequency : 0.055 Frequency : 0.057 Frequency : 0.060 Frequency : 0.063 Frequency : 0.065 Frequency : 0.068 Frequency : 0.071Frequency : 0.073 Frequency : 0.076 Frequency : 0.079 Frequency : 0.081 Frequency : 0.084 Frequency : 0.087

Result analysis - PPT

Phase image frequency=0.03Hz

Shunt detection in Solar cells

Solar cell during the test

Standard thermal image shows the test facilities for shunt detection. The set up of the complete system lasts 15 minutes.The test consists of applying a voltage to the solar cells. In case of shunt the current goes directly from the grid line to the base and heats up locally the solar cell. Lock in Thermography allows detecting the heating up by detecting of the periodic heating.

The equivalent circuit of local photocurrent generation near a strong ohmic shunt in a solar cell.

Function generator

Data acquisition

Excitation was set at the following values: Frequency 1 Hz. The voltage is 2.5V +/-2.5V and the shape of the signal was square.

Double click on the images to see motion.

The lines in data graph show time history of the image’s in the B&W image.

Note that camera is calibrated in absolute temperature, and shows small amplitude temperature swings from 100 mK to 25mK in real time. The yellow line doesn’t not show any change of temperature due to limitation of the real time thermal resolution of the camera (20mK).

Thermal image movie (Colours)

Thermal image (B&W) Timing graph of areas of interest 1, 2, 3 and 4

Solar cell quality control

Map of amplitude at 1 Hz

Map of phase at 1Hz

Map of amplitude at 10 Hz

Map of phase at 10Hz

At higher frequency one can detect accurately the defect on the surface.

VIbrothermography (VT)

Detector technology road map

1998 2000 2002 2004 20061998 2000 2002 2004 2006

30 µm25µm

20µm

320 x 256

30µm

InSb - HgCdTe

15µm

640 x 512

15µm

InSb

640 x 512

20µm

InSb

640 x 512

25µm

InSb

640 x 512

15µm

HgCdTe

2nd generation

3nd generation

AltairThermography

JADE family320x256

InSb & MCT

Altair LIStress and NDT

EMERALD 640x512Insb 25µm

1998 2000 2006

EMERALD 640x512Insb 20µmMCT 15µmQWIP

Silver family320 x 256640x512

InSb 30µm & 15 µm

Titanium family320 x 256640x512

InSb et MCT 30µm & 15 µm

Electronics, Electricity and microelectronics.

Mechanics

Plastic industry

Automotive industry

Aeronautics

Medical diagnosis

Biology

Habitat industry, architectural surfaces and material evaluation, road inspection

Food industry:

predictive maintenance in the newspaper industry petroleum facility

Chemistry industry : inspection of tank and vessels.

Arts : paintings, cultural heritage conservation, frescoes.

Textile, paper industry, pharmacetics, wood industry , cosmetics

Areas of active thermography

Depth information, size information?

Integration (finite elements) of the Heat equation for simplified models (already verycumbersome) and comparison.

Supposed to know a lot of information related to the thermal behavior of the samples(thermal conductivity, convection coefficient, emissivity), materials supposed to behomogenous……..

Classification : learning from samples and decision

Two technics have been used

Gaussian based classification (density probality function)

Neural networks approach.

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