Heat flow thermography: Illustration of the measuring principle and possible arrangements of stimulation, component and camera: Left incident light measuring, right transmitted light measuring on the weld of a two-sheet joint. Red color shades represent higher temperatures, blue color shades lower temperatures.

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t Stimulation Sources for Heat Flux Thermography

Halogen lamps

Induc- tion

Flash- lamps

Heat flow thermography requires a local stimulation of the specimen. The stimulation takes place periodically (for lock-in thermography), either as a delta or square pulse or staggered. Thermosensorik adapts and develops different stimulation techniques for this purpose, and integrates them into their infrared test systems. The following pages contain a brief introduction of the most common stimulation sources.

Laser

LED arrays

Hot/cold air

Ultra sound

Stimulation Sources for Heat Flux Thermography

2010 Thermosensorik GmbH, Erlangen, Germany

Flash-lamps "Classic" pulse thermography stimulation via high-power flash introduces a large amount of energy (up to 6000 J per flash head) within a few milliseconds. The simple and safe handling represents one of the key advantages. Also suitable for large surface areas and materials with rapid heat conduction.

a) Laboratory version (left in figure):

standard flash head ring flash Energy max. 6000 J max. 3000 J Flash frequency 1 / 4.4 s Power connection 110-230 V / 50-60 Hz Accessories lamps, reflectors, filters

b) Industry version (right in figure):

Energy 5000 J Flash frequency 1 / 3.5 s fatigue endurable Power connection 380 V / 50 Hz, 32 A Accessories lamps, reflectors, filters, robot mounting Halogen lamps The simplest type of heating. It is suitable for stimulation periods from a few seconds to several days with outputs in the kilowatt range, and is used especially for specimens with slow heat conduction and in lock-in operation.

Typical specifications: single lamps Power consumption 500 – 1000 W / lamp @ 230 V

Light output 37.000 – 350.000 cd axial

Modulation frequency sensible up to max. 1 Hz

Accessories reflectors, filters, robot mounting Typical specifications: halogen lamp array

Power consumption 4 x 650 W or 8 x 650 W

Description compact housing with air cooling and heat protective glass

Ultrasound Ultrasound stimulation selectively heats material defects such as cracks and delaminations while fault-free, homogenous material remains largely unchanged. In contrast to most of the other stimulation methods, however, ultrasound stimulation is not contactless. Typical output 1 kW – 4 kW 500 W Frequency range fixed frequency

20 kHz 10 – 40 kHz tunable

Coupling via sonotrode Accessories sonotrodes, pneumatic clamping unit,

table for NDT Induction This stimulation is especially suitable for defects on or close to the surface in electrically conducting materials. Here, too, the defect itself, e.g. a crack, is heated the most. Thermal diffusion thus allows even the detection of faults which are smaller than the resolution capacity of the IR camera system. The required output depends on the size, electrical conductivity and thermal capacity of the specimen. Output levels 5 kW or 10 kW 1 – 2 kW

Working frequency 150 – 350 kHz 1 – 30 kHz tunable Modulation frequency max. 40 – 80 Hz

(depending on the output)

> 200 Hz

Accessories inductors, cooler in 19" rack design Hot/cold air The stimulation type that makes the most sense when testing for consistency, e.g. with cooling ducts. Apart from "single" heating, periodic stimulation for lock-in measurements (e.g. for determining wall thickness) can be implemented. Heating hose supply 230 V / 50 Hz,

compressed air approx. 2 bar Achievable air temperature approx. 250°C

2010 Thermosensorik GmbH, Erlangen, Germany

LED array Because of their narrow-band light spectrum, LED arrays can be well adapted to the material properties. Typical application: Homogenous illumination for defect detection on solar cells.

Typical specifications Light output / area e.g. 600 W/m2 @ 850 nm or 940 nm

on 20 cm x 20 cm with 6 arrays

Power consumption 120 W / array

Max. modulation frequency 2 kHz

Laser The method of choice for locally and temporally precise stimulation of high power densities. Furthermore, the laser - at a suitable wave length – is, just like the LED array, a "cold" stimulation source, which does not cause any interference with the infrared images.

Typical specifications Wavelength 910 nm Light output 200 W cw Power consumption approx. 600 W Accessories fiber-optic coupling, scanner

Electrical stimulation The method of choice for detecting defects in electrical circuits. Here, too, the defect itself is heated through the locally increased current flow. Thermal diffusion allows even the most minute flaws to be detected; these can be localized up to approx. 3 µm using microscope lenses and to 1 µm with solid-state immersion lenses. Mechanical stimulation Plastic but also elastic deformation is always accompanied by a temperature change. Mechanical stimulation is known by the term 'Thermal Tension Analysis'. Because the signal amplitudes that occur are low, this method is usually carried out as a lock-in measurement.

Thermosensorik GmbH Am Weichselgarten 7 91058 Erlangen Germany Tel.: +49 9131 691-400 Fax: +49 9131 691-419 info@thermosensorik.com www.thermosensorik.com

2010 Thermosensorik GmbH, Erlangen, Germany

Stimulation Sources for Heat Flux Thermography