Steady Analysis On Test Signal Transmission Under The Changing Temperature Environment

The identification and analysis of signal characteristics are constrained by the ever-changing, random and fuzzy characteristics of signal. At present, researches on signal analysis are mainly concentrated on subsequent signal processing methods. However, similarly tests of vehicles engine, many kinds of interfering factors are inevitable in the process of signal transimission, and especially the ambient temperature is uncertain. The important effect on signal characteristic from external uncertain factors is still lack of system and deep investigations. Therefore, systematical studies on the test signal variability resulting from changing ambient temperature have not only important theoretical significance, but also practical value.With respect to test signal transmission affected by interfering factors, a further study into the change of signal characteristic caused by varied ambient temperature has been made in the paper. The main contents are summarized as follows.(1) The heat diffusion equations for singal transmission cable are derived and established, and the thermoelectric couple model for whole cable is analyzed. Taking the coxial cable as main rearch subject, the heat diffusion equations are obtained for different structure and materials considering the forms of heat transfer in vehicle test system. By applying characteristic of transmission signal, the thesis constructs thermoelectric couple model to analyze the heat transfer characteristic of cable in environment of natural convection, fully heat conduction and forced convection. FEM is applied to calculate heat transfer characteristic of cable. The results show that the refinement form of heat transfer for cable helps to improve the accuracy of analysis. Moreover, the temperature of cable increases rapidly especially in space of fully heat conduction and forced convection. Correspongdingly, characteristics of cable materials changes in a short period, which has a huge impact on signal transmission.(2) A novel method for extracting the transmsission parameters of signal cable is proposed. Based on Maxwell's equations, the Hlemholtz equation with temperature variable is derived. It determines electromagnetic behavior changing with temperature in process of signal transmission. Combined with signal transmission circuit and singal integrity, a method for calculating transmission parameters is described. Contrary to other methods, the proposed method is of less calculation and can also be verified using classical energy method. The behaviors of parameters are pointed out. RLCG parameters change with ambient temperature and the most prominence is of resistance changes in proportion to increasing temperature. Considering different signal frequencies, the parameters change more obviously with respect to the higher frequency. The method is also effective for extracting self and mutual parameters of multiconductors. The results demonstrate that the signal frequency is significant for mutual parameters which exacerbate the crosstalk signal between wires. Temperature and frequency characteristics of parameters become to be the key parameters foundation for change of signal response.(3) Based on signal transmission theory, finite difference, Kirchhoff's law and FDTD, the study builds two gradient temperature models. The changes of signal response are also described. Two models are separately of temperature and time for discrete variables in modelâ… and of time and space for discrete variables in modelâ…¡. The results indicate that signal responses are directly related with conductor temperature. As the conductor temperature rises, transmission parameters are constantly changing, and the amplitude of output signal is in response to gradual attenuation. In low-frequency range, the amount of signal amplitude attenuation is greater with lower frequency. Crosstalk phenomena come to existence when multiconductor structure is applied for signal transmission, and in this case output signal is difficult to replicate the character of intial signal.(4) A sensitivity analysis method is put forward according to the change of signal response caused from ambient temperature and signal frequency, and the corresponding multi-variables sensitivity equations are constructed. By adopting the direct method, a second transformation for temperature, frequency, and RLCG parameters has been out to obtain parameter vector and the sensitivity expression are also derived. The results demonstrate that the absolute value of signal changed quality increases with the rise of temperature and lower frequency, and signal attenuation is of positive trends. The study also shows that resistance R has major influence on change of signal response contrary to other LCG parameters.(5) A test platform is constructed to implement the signal transmission in changing temperature environment by designing and processing components, and corresponding tests are also completed. The experimental results reflect that the power spectrum peak and the average time-domain amplitude of signal are gradually lowered with increasing temperature. The different ambient temperature has changed the characteristics of original signal. And the experimental analysis also verifies the validity of the results of simulation models successfully.In conclusion, taking the ambient temperature as the main disturbance factor, the change of test signal in transmission process, is systematically studied in the thesis. The study obtains a series of theoretical and experimental results for impoving the precision of test signals.