Principles of the four‐point thermographic measurement of the surface temperature and emissivity of glossy materials

Abstract

The emissivity and surface temperature of glossy materials are measured in IR thermography by covering the surface with a material with the known emissivity. The quantities can be, however, determined without using materials with the known emissivity. IR radiation is refl ected from the measured glossy surface and a thermographer detects such refl ection. This paper discusses the measurement of the surface temperature and emissivity of glossy materials which are used in external structures of the buildings -for instance, windows, light external walls or tiles. A four-point method is proposed for a more accurate determination of the surface temperature and emissivity of glossy materials. Results of successful laboratory and fi eld tests of the method are presented. Prinzipien der Vier-Punkt-Thermografi e-Messmethode für dieOberfl ächentemperatur und den Emissionsgrad glänzender Werkstoffe.

Infrared thermographic measurement of the surface temperature and emissivity of glossy materials

“…where T z is the apparent temperature of the glossy surface. In addition, assuming a constant glossy surface emissivity and temperature, T z is a linear function of T 0,b (Čmiel et al, 2016)…”

“…The plate was fitted with three water-cooled Peltier elements which can optimally heat up and/or cool down three areas in the plate. A field test of a similar method using four points of different temperatures reflected on a measured glossy surface is presented elsewhere (Čmiel et al, 2016).…”