Coating evaluation methodology for low-temperature thermographic application

Non-contact temperature measurement by infrared camera systems is commonly used to detect the temperature distribution on a surface of measured objects. The paper presents an evaluation methodology for coatings in order to be used as reference for non-contact temperature measurement by infrared camera systems. The conditions of measurements using infrared camera systems, such as surface emissivity of the analyzed material, distance of between the object and the measurement system, atmospheric transmissivity and others, affect the accuracy of temperature measurement. Incorrect measurement parameters cause deviations in measured temperature. In order to reduce the emissivity effect, the analyzed surface can be modified by applying a reference coating, featuring not only high emissivity value but also other functional properties. The coating properties such as spectral and band transmissivity, spectral and band emissivity and temperature and time stability of coating photo-thermal properties serve for basic assessment of coating to be used as suitable reference for thermographic applications. Moreover, a satisfactory coating deposition process should be ensured. The methodology introduces proper methods how to analyze the coating properties and also evaluation criteria according to which the coating can be designated as reference thermographic coating. Application of the methodology is shown on one example of the coating; therefore the measured properties such as effective emissivity, thermal conductivity, or thickness of the coating sample are discussed in relation to its usage as the reference thermographic coating for infrared camera systems operating in the spectral range of 7.5 to 13 m and measured surface temperature up to 120 °C.