Amplitude-sensitive modulation thermography to measure moisture in building materials

Walter Wild; Konstantin A. Buescher; Herbert Wiggenhauser

doi:10.1117/12.304724

26 March 1998 Amplitude-sensitive modulation thermography to measure moisture in building materials

Walter Wild, Konstantin A. Buescher, Herbert Wiggenhauser

Proceedings Volume 3361, Thermosense XX; (1998) https://doi.org/10.1117/12.304724
Event: Aerospace/Defense Sensing and Controls, 1998, Orlando, FL, United States

Abstract

There have been reports about moisture detection in building walls by reflective IR-thermography. Typically, only limited results could be obtained because of the emission coefficient variations, leaking radiation or inhomogeneous illumination of the object. In addition, the quantitative relation between remission spectra and the moisture has often been unclear. Reflectometry uses constant excitation illumination which is recorded by the IR camera. With the use of the 'lock-in-technology' a low frequency modulated signal of an IR radiation source is coupled with the thermo camera and a frequency and phase sensitive signal from the thermal images can be derived. The advantage is, that emission coefficient dependencies are eliminated and that leaking radiation does not have any influence on the measured signal. The selective water measurement is possible, because there is an interference filter mounted in front of the radiator which has its transmission maximum at the wavelength of an absorption band of water. The area investigated is therefore illuminated under well defined circumstances and quantitative moisture measurement on the surface of building materials becomes a possibility. The illumination modulation is done with a sine wave to facilitate the calculation of the temporal intensity behavior of the amplitude signal. Subsequently, the amplitude image is used to determine the distribution and the level of moisture quantitatively. Point measurements in the laboratory were carried out on several building materials with changing moisture levels. It could be shown that this method successfully eliminates disturbing contributions to the measured signal like surface effects or leaking radiation.

Citation Download Citation

Walter Wild, Konstantin A. Buescher, and Herbert Wiggenhauser "Amplitude-sensitive modulation thermography to measure moisture in building materials", Proc. SPIE 3361, Thermosense XX, (26 March 1998); https://doi.org/10.1117/12.304724

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