Multifunctional Signal Generator for Calibration System of Jet Engine Exhaust Gas Temperature Measurement

Abstract

One of the most important systems of an aircraft jet engine is exhaust gas temperature measurement system that ensure right function of the engine. Temperature of the gas flowing from the engine turbine is quite high. There is one way, how to measure high temperature and it is by thermocouple. So the main aim of the paper is to describe creation and correct function analysis of a thermocouple simulator. Thermocouple generates very low voltage depending on a temperature that ranges from units micro-volts to several tens of millivolts. Generating of such low voltage using simulator is not easy, because this voltage may move at levels of noise. Voltage generation is performed by digital-analogue converter, which is controlled by a microcontroller via SPI bus. The generated voltage is further reduced to a level corresponding to the voltage output of the thermocouple. Several calibration waveforms are performed belonging to appropriate thermocouple type for multifunctional use. Only positive temperatures are generated, because exhaust gas temperature measurement system is aimed at high temperatures. The power supply circuit offers two options. It is supply from accumulator for its portability or from the laboratory power supply. Surface mounted devices are selected in terms of module miniaturization. The newest device base is chosen for modern design of the module. The temperature waveform is generated by the way of polynomial approximation with correction. Dependence of real generated voltage on the voltage, which is defined by appropriate thermocouple type standard and errors evaluation, is used as a proof of proper function.