Modeling of Intrinsic Thermal Feedback in Resistance Temperature Devices

Abstract

The purpose of work is a research of intrinsic thermal feedback in the temperature detector namely resistance temperature device by computer-aided engineering. The model is created based on the electrothermal analogy that is on similarity of the mathematical equations of the description of thermal and electric processes. On the one hand, it allowed for considering thermal processes as electric, but on the other hand at the same time to include in the electric processes in the connection circuit of thermal elements in the thermo measuring equipment. The known computer Micro-Cap program is chosen as a simulation environment, it is developed by Spectrum Software, which makes it possible to measure to a precision of tenth of a percent in both the static and dynamic modes. The significant advantage of the program is the possibility to apply idealized components with arbitrarily set values of the main parameters that previously was not possible to do physical simulation by the method of electrothermal analogy using real electrical components, such as resistors, condensers, etc. Practical conclusions on creation of thermometric devices and use of results in adjacent areas are made by results of modeling. In particular, it was found that there is a positive thermal feedback by feeding the thermal element from current power supply or in case of resistance series resistor in a bridge of bigger resistance than at the thermal element; the positive thermal feedback is watched. There is a negative feedback in case of a supply of the thermal element from a voltage source or small on resistance, serial resistors to the thermal element. There are conditions under which the feedback was not reflected. The dependence of overheating of a sensing element on value of survey current is investigated. It is established that the dependence has nonlinear character, and there is a sharp increase of thermal overload up to melting of a sensitive element. It is also established that to decrease in intrinsic thermal feedback in thermal elements of resistance it is necessary to reduce value of survey current and to reduce thermal resistance “a sensitive element - surroundings”.