AVERAGE TOTAL HEMISPHERIC EMISSIVITY MEASUREMENT IN THE LWIR SPECTRUM FOR ADHESIVE TAPES USED IN THE THERMOGRAPHY TAPE TEST

Abstract

Thermographers often use comparative methods to estimate surface
emissivity. Among the most used is the tape method. In this method a known
emissivity tape in the LWIR (Long Wavelength Infrared) spectrum is placed
on the surface to be inspected. After thermal equilibrium, the temperature of
the tape and the surface under inspection must be the same. In this case, the
temperature observed on the tape is the reference temperature. The emissivity
of the surface must then be changed until the reference temperature is
reached. It is common practice to admit the value of the emissivity of the
adhesive tape as 0.95, there are few studies that present these data with
metrological rigor, which leads to doubts about the emissivity of the
commercial tapes. In this work, experiments were performed on Tekbond,
Double A, 3M 101, Rapix, Altape, adhesive tapes for temperatures of 50, 55,
60, 65 and 70ºC. An experimental apparatus was developed through which it
was possible to estimate surface reflection, transmission and atmospheric
emission for one and two layers of tapes, in order to make emissivity
measurements possible. Through the data it was possible to statistically
estimate the LWIR average total hemispheric emissivity as well as the
acceptance range to 95% certainty, being therefore equal to ε=0.94±0.03. It
is possible to arm, therefore, that the value of 0.95, usually used as emissivity
of the adhesive tape, is extremely reasonable because it is 0.01 of the average
value of the Gaussian distribution calculated by this work.