Abstract
Thermocouples are widely used as temperature sensors and most commonly made of two different metallic electrodes which are in contact at the measuring junction. In this work we present an approach to embed thermocouples in the painted surface of machine components, facilitating measurement directly at the point of interest for certain applications. The utilized spray process allows a cost-effective and fast fabrication method. In order to be competitive with available sensors, the spray-processed sensor ideally has to provide an output voltage in the same range as commercial ones and should withstand temperatures up to 200 °C while providing reliable adhesion to the surface at the same time. To meet these requirements, a material screening was performed including commercial as well as custom-fabricated paints. In particular, different commercial paints based on silver were combined with a carbon black polyamide-imide paint to form thermocouples which were then characterized regarding adhesion, noise and sensitivity (Seebeck coefficient). Furthermore, custom-fabricated paints based on iron and silver in a polymer binder were evaluated and compared to a commercial type J thermocouple (iron-constantan thermocouple). The paper reports on identified suitable material combinations and the associated sensor performances.
Highlights
Measuring temperature is a challenging task and of interest in many application fields
Thermocouples are widely used as temperature sensors and most commonly made of two different metallic electrodes which are in contact at the measuring junction
Custom-fabricated paints based on iron and silver in a polymer binder were evaluated and compared to a commercial type J thermocouple
Summary
Measuring temperature is a challenging task and of interest in many application fields. In environments where deformations and high pressures are present, thermocouples are among the most suitable temperature sensors as, compared to thermistors, the temperature/pressure cross-sensitivity becomes significant at much higher pressure levels [8, 9]. Besides their robustness, thermocouples are available for a wide temper ature range from −270 up to 2760 °C [10]. Due to the adhesive layer and the polymer substrate (which is typically in the thickness range of 100 μm) the measured temperature can deviate or the measurement response delayed To overcome these drawbacks, thermocouples can be fabricated directly onto the surface of interest. The following section gives an overview of the prep aration of the insulation and the conducting paints which are divided into commercial (silver inks) and customfabricated paints (based on carbon black, iron or silver as conductive material)
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