Infra-Red Lock-in Thermography A. Reichold M. Lefebvre 20 June 2000 Detect features or defects in a material from heat wave interference effects on the surface Potentially useful for ATLAS Inner Detector, but also for the NAPL in general A prototype experimental setup was constructed and successfully operated •Principle of operation •Theory excerpts •Experimantal setup •Data acquisition and analysis •Analysis results •IR Camera calibration setup •Prospects M. Phys project students Alex Ivison and Steven Mould
Transcript
Infra-Red Lock-in Thermography A. Reichold M. Lefebvre 20 June 2000Detect features or defects in a material from heat wave interference
effects on the surface
Potentially useful for ATLAS Inner Detector, but also for the NAPL in general
A prototype experimental setup was constructed and successfully operated
•Principle of operation
•Theory excerpts
•Experimantal setup
•Data acquisition and analysis
•Analysis results
•IR Camera calibration setup
•Prospects
M. Phys project students Alex Ivison and Steven Mould
20 June 2000 A. Reichold, M. Lefebvre
Principle of Operation
IR ca
mera
heat
measures surface temperature
s/2mconstant diffusion
J/kgKcapacity heat specific
3kg/mdensity
W/mKty conductivi thermal
p
p
c
c
•a periodic heat flux is incident on the surface of interest
•the surface temperature is measured and local variations in the phase and/or amplitude are sought
20 June 2000 A. Reichold, M. Lefebvre
Theory excerpts
TαT
Tρcq Jq
TλJ
2equation diffusion get the then we0cρλ that assuming
3J/mdensity heat theispwhereonconservatienergy local states
3W/mequation flowheat theis
p
Consider the simplest case where the object is an infinite plate of thickness l along x, and with the steady state boundary conditions
t TxT
Jπ/4ωtcosJ0xJ A
ll
We also assume heat transport via thermal conduction in the plate, that is no convection and no radiation. The problem is then, for the static case,
tx,T find lα,λ,,T,J,Jω,Given lA
20 June 2000 A. Reichold, M. Lefebvre
Theory excerpts (continued)We find that the oscillatory part of the solution is proportional to
ηx2kωtcose ηkxωtcose x2kkx ll
where we recognise the forward and backward damped waves, where
2
k 2k cos
sintan l
e
But to study the amplitude and phase of the x=0 surface temperature, it is more convenient to seek a solution of the form
sinh
sinω0,xn taand
cosδcoshδ
cosδcoshδδ2ω0,xg where
λJ
21
A ,cos, xtxg l
A study of the transient solution reveals a longest component lifetime to which we can associate a natural frequency of the object
~
2 ~
4define which wefrom
2
2
l
20 June 2000 A. Reichold, M. Lefebvre
Theory excerpts (continued)
At low frequency, the temperature spectrum follows the heat input. It acquires a /4 phase lag at high frequency
The amplitude decrease with frequency, as the surface temperature falls behind the heat input. The rate of change of the amplitude is maximum at the natural frequency
20 June 2000 A. Reichold, M. Lefebvre
Experimental Setup
HV30A 60VPowerTen
PCComputerBoards
PCJenoptik
Varioscan software
glass
Bakelite object with “defects”
IR Camera Jenoptik Varioscan 3011-ST
9 X 200W bulbs for a usable 1500W
DAQ control Labview
1 2
3 4
2.07mm)(
1.10mm)(
9.64mm)(
hole2
hole1
plate
l
l
l
20 June 2000 A. Reichold, M. Lefebvre
Data Acquisition and AnalysisM. Phys. Project Students: Alex Ivison and Steven Mould
DAQ under Labview control •sinusoidal heat source (frequency and amplitude)
•IR camera trigger (number and relative phase)
•T-probes (light array, glass, object)
Data taken: sets of 4 pictures for periods between 15 and 500s
Data analysis: extract amplitude and phase from each set of 4 pictures
Compare with the theory for the infinite plates case with the following nominal quantities for bakelite
/scm 0072.0
J/gK 1.5c
W/mK 1.4λ
g/cm 1.3ρ
2
obtain which weFrom
p
C20 @
C20 @3
The results are in qualitative agreement… clearly the experimental conditions are not infinite plates with constant temperature at the back!
2.07mm)(
1.10mm)(
9.64mm)(
hole2
hole1
plate
l
l
l
20 June 2000 A. Reichold, M. Lefebvre
IR Camera calibration setup
Need to obtain the relation between the camera ADC and the object temperature
An isothermal box was designed and built
An inner 1.5cm thick Al box surrounded by 15cm of isulation material, with one port for the camera (with shutter) and two ports for heating/cooling (with plugs).
Blackbody suspended in the box, in the camera field of view. Under construction. Special paint ordered.
T probes on the box inner face and on the blackbody.
20 June 2000 A. Reichold, M. Lefebvre
IR Camera calibration setup (continued)
Views of the isothermal box
20 June 2000 A. Reichold, M. Lefebvre
ProspectsVery promising.
Next steps...
•try with other materials (eg ATLAS ID carbon fibre)
•improve experimental setup
redesign the light array (more power?)
build proper support for light array, glass, object
control interference from ambient conditions (cooling?)
allow for higher frequencies
•finite difference analysis?
•Continue C++ analysis code development (within ROOT?)
•fully commission the isothermal box for IR camera calibration
