A dynamic model of electric resistor’s warming and its verification by micro-thermocouples
Czech University of Life Sciences in Prague, Faculty of Engineering, Department of Electrical Engineering and Automation, Kamýcká 129, CZ165 21 Prague, Czech Republic
The object of research is a resistor, a real electronic component, loaded by constant or impulse power. As a first approximation, resistor follows 1st order dynamic system, i.e. heating of the hottest spot on its surface is exponential to the power increase. The validity of this model is confirmed by measurements in a constant power loading regime. In an impulse power loading, it is only valid when the pulse duration approaches time constant of the resistor. The aim of this article is to show more credible model warming of the resistor, which is valid even for the case of pulse duration (ms) much shorter than the time constant of the resistor. The model can reveal an overload which does not lead to destruction of the resistor. Dynamic model of the resistor is based on its construction. Typically, an insulating ceramic rod is coated with a resistive layer connected with outlet wires on both sides, all being coated with insulating lacquer layer. The resistive layer is a source of heat flow. Formulation of the model comes from general power balance in a form of three differential equations and it is solved using Scilab. The input variable is the impulse power and the outputs are temperature changes in the ceramic rod, the resistive layer and the lacquer layer, compared to the ambient temperature. The simulation allows to determine solutions for various parameters including very short power pulses, which are confirmed experimentally.