Tag Archives: load factor

1072–1083 M. Linda, G. Künzel and M. Hromasová
A dynamic model of electric resistor’s warming and its verification by micro-thermocouples
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A dynamic model of electric resistor’s warming and its verification by micro-thermocouples

M. Linda, G. Künzel and M. Hromasová*

Czech University of Life Sciences in Prague, Faculty of Engineering, Department of Electrical Engineering and Automation, Kamýcká 129, CZ165 21 Prague, Czech Republic
*Correspondence: hromasova@tf.czu.cz

Abstract:

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.

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768–778 M. Hromasová and M. Linda
Analysis of rapid temperature changes
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Analysis of rapid temperature changes

M. Hromasová* and M. Linda

Czech University of Life Sciences in Prague, Faculty of Engineering, Department of Electrical Engineering and Automation, Kamycka 129, CZ165 21 Praha – Suchdol, Czech Republic
*Correspondence: hromasova@tf.czu.cz

Abstract:

 The analysis of rapid temperature changes in the dynamic system is described in the paper. Temperature changes are in range of tens of milliseconds. The sensor we used has a significant influence on the dynamic system. In these cases we need to use thermocouples that have appropriate transfer characteristics and can be manufactured with a low time constant. The time constant directly corresponds with weight and size of the sensor. The quality factor is usually in a range between 0.98 and 0.995. Information about the temperature course is particularly important in the field of dynamic systems, e.g. agricultural machines where the switching components are overloaded by pulse switching of technology systems. For the object analysis we use the thermocouples with diameter 0.012 mm with non-encapsulated finish and 0.12 mm with suppression of interference impact and comparative temperature fluctuation. For the analysis of dynamic temperature changes we conduct a measurement with a load factor change, which is the mean value of power change, expressed as ratio of the pulse duration to the delay between pulses, this way we will affect the measurement conditions. As a solution we use measurement methods for a steady state, an impulse test and a method of local measurement of temperature. Compared to a real principle of a component we do not increase temperature of the environment during experiments. The results of measurement can be applied for design and implementation of switching systems for electronic circuits with signal modulation and power load.

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