Thermal impedance modeling of a temperature dependent resistance

As a new application of thermal impedance modeling the thermal behavior of a glow plug is examined. The self-heating device is basically a temperature dependent resistance, which is directly exposed to the highly dynamic combustion process. Therefore it can be used as a sensor in the combustion chamber for diagnosis reasons. In order to deduce the temperature changes in the gas chamber the dynamic heat transfer of the device, called thermal impedance, has to be modeled. The thermal impedance of the device is determined by its inside structure, mounting and surrounding environmental conditions. In this paper initially the substantial underlying physical processes are shown and a new approach for modelling the thermal behaviour is presented. The model differentiates between varied excitations (thermal and/or electrical) as well as it considers the parallel heat transfers caused by different heat sinks.