Active thermography for non-destructive control applications
|Configuration of a NDT system based on active thermography|
The objective of conventional thermography is to measure the surface temperature. The thermography system detects the temperature-dependent infrared thermal radiation emitted by a body. Using the so-called passive thermography, informations about a given surface can be obtained without contact. Currently, with high resolution thermography systems, it is possible to detect temperature differences of 10 mK.
Automatic process control
With an infrared camera, many processes can be observed and controlled which involve changes in temperature or heat flux. This may be an exothermic process that reveals heat during generation, or samples that must or may not reach a certain temperature. Such a process can be, for example, the functional control of a seat heating system for applications in the automotive industry. With the edevis QTvis image processing system, such automatic testing and evaluation is an easy and cost-effective task.
The methods of active thermal measurement are based on the evaluation of a previously excited heat flow in the test component and its disturbance by the hidden defects. The heat flow is generated by a heat pulse or by sinusoidal modulation. The test is performed with a thermography chamber and is followed by a mathematical analysis of the measured sequence, in order to extract the necessary informations for a reliable defect detection.
Lock-In Thermography is a method to significantly increase the signal-to-noise ratio for active thermography applications. The heat flow is thus analyzed, and the delay interval of the heat flow is displayed, thus revealing important material properties or defects.
Excitation methods for active thermograpy
The thermography methods listed below are well established in the non-destructive control of materials:
- OTvis - Optical Lock-In Thermography: heat flux analysis based on optical heating.
- PTvis - Pulsed (Phase) Thermography: a test method based on fast heat flux.
- LTvis - Laser Induced Thermography: a test method based on fast heat flux.
- ITvis - Induction Thermography.
- UTvis - Ultrasound Lock-In Thermography: a test method based on mechanical dissipation effects.