Comparison of two high-end infrared thermography systems with different spectral sensitivity for thermal investigations of sensor heater elements

We discuss the measurement of temperature distributions using thermography, and its limitations due to wavelength and temperature dependent infrared-optical properties of the sample. A typical oxygen sensor has been realized by thick film technology: a platinum heater structure with integrated temperature sensor has been printed on a zirconia substrate. The variation of the temperature of the sensor with the applied heater current has been experimentally investigated by a three-wire resistance measurement and the application of two different high-resolution thermography systems. The first method is an easy and reliable direct method to obtain an average temperature value of the heater structure, whereas thermography gives the spatial distribution of the temperature. Thermography images of the sensor as-built and coated with a high-emissivity varnish are compared. Typical pitfalls in the interpretation of the thermal signature of the device under test resulting from unknown emission coefficients and semitransparency of the substrate material are discussed in detail.