Temperature and heat flux errors in thin film thermometry

Abstract

Thin platinum resistance thermometers (herein called thin film sensors) are often used in applications where rapid measurements of surface temperature are required. These gauges are typically vapour-deposited onto a non-conducting substrate surface and electrically connected with small wires through access holes to the surface. The time response of the gauge is measured in milliseconds and surface temperature data obtained with this gauge are often combined with a pseudo-inverse heat conduction algorithm to provide information about the surface heat flux. However, the thermal mass of the connecting wires, though small in absolute terms, is large compared to that of the thin film, and the capacitive effect of this mass gives rise to distortions in the temperature field in the area of the gauge, resulting in a small error in the sensed temperature. This temperature error, when used in the inversion for heat flux, also results in an error. In this article, a detailed model of a particular thin film gauge is used to compute the response of the sensor to supposed heating conditions. The response of the sensor and the undisturbed surface temperature are compared to estimate the temperature error. The effect of thermal contact resistance in the model is investigated. Finally, the error in the computed heat flux is determined. A simple technique based on superposition is applied to reduce the error in the estimated heat flux.