Abstract
Active thermography is an established technique for non-destructive testing and defect localisation. For external excitation, powerful light sources are commonly used. In addition to a high optical output, a good signal shape and response characteristic as well as control ports, which allow for multiple operation modes, are important for active thermography applications. In this work, the schematics for an excitation source based on infrared LEDs is presented. It features multiple control modes for easy integration into existing measurement setups as well as sophisticated control electronics to realize a wide range of excitation patterns. The phase and amplitude stability of this prototype is investigated and compared to the performance of a modulated halogen lamp as well as a halogen lamp and mechanical chopper combination.
Highlights
Active thermography is used in many fields of applications [1]
A valuable comparison of common excitation sources for lock-in thermography is given by Ziegler et al [22]
Rise and fall time are specified to allow the use of the excitation source in transient thermography applications
Summary
Active thermography is used in many fields of applications [1]. A valuable comparison of common excitation sources for lock-in thermography is given by Ziegler et al [22] In their work, they compare halogen lamps, LEDs, and VCSELs in terms of modulation bandwidth, spectrum, and irradiance. The maximum modulation frequency as well as the dynamic range are limited by the high thermal inertia of halogen lamps In comparison, they feature low spatial resolution and often exhibit inhomogeneous excitation. The source includes a digital and analogue input to fully control the LED current and to produce arbitrary output signals This includes but is not limited to sinusoidal emission. To use the LED excitation source in a wide range of applications, including lock-in and transient measurements, different operating modes are implemented, to control the LED current and the duty cycle. Rise and fall time are specified to allow the use of the excitation source in transient thermography applications
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