Research On Error And Optimization Of Thermocouple Measuring Surface Temperature Rise

In the daily use of new energy vehicles,there are serious personal safety accidents such as fire and explosion,so the thermal reliability of automotive electronic and electrical components is particularly important.At present,using thermocouple to measure the temperature rise is fast and cheap,which is an important means to evaluate the thermal reliability of auto parts.However,this method has the inherent defects of large artificial error and large cold end compensation error,resulting in low test accuracy and poor reproducibility of the results.Based on the principle of temperature rise measurement by thermocouple method,this paper analyzes the source of error introduced by this method in the test,and uses the uncertainty evaluation model to carry out quantitative characterization of the introduced error source;according to the characterization results,it is concluded that the heat transfer between thermocouple and temperature measurement surface,thermocouple aging degradation and thermoelectric signal acquisition are the three most weighted error sources,and the in-depth analysis is carried out.In this paper,the thermal transfer impedance model of thermocouple and temperature measurement surface is analyzed,and the circuit analysis method is used to analyze the contact heat transfer path between the thermocouple and the temperature measurement surface.The results show that the temperature of the hot end of the thermocouple is lower than that of the temperature measurement surface in the existing scheme,which proves the correctness of the heat transfer impedance model and the effectiveness of the analysis method Based on the above model,a simple and effective optimization method is proposed to improve the heat transfer accuracy of the contact surface.The temperature error of the optimized thermocouple hot end is less than 0.5 ℃ by finite element analysis and experiment.In this paper,the thermoelectric conversion principle of thermocouple is deeply analyzed,and it is concluded that long-term high temperature and temperature cycle degrade thermocouple measurement accuracy;design and carry out experiments to explore the relationship between different thermocouple specifications(wire diameter,brand)and thermocouple measurement accuracy under long-term high temperature and temperature cycle,and summarize the general experience of thermocouple specification selection.This paper briefly introduces the processing process of thermoelectric signal conversion to digital signal,and concludes that the error weight of cold end compensation and measurement noise in the process of thermoelectric signal conversion is large;the cold end compensation error and measurement noise of existing equipment are characterized by experiments,and the sum of the errors can reach 1℃;a set of multi-channel thermoelectric signal acquisition device is designed,and its cold end compensation is verified by experiments 2℃ and 0.03℃ respectively.Finally,this paper optimizes the evaluation model of uncertainty in the industry,and uses the optimized evaluation model to evaluate the existing industry operation methods and the optimization methods proposed in this paper.It is concluded that the application of a series of optimization measures proposed in this paper can effectively reduce the measurement error by 50% in the scheme of temperature rise measurement by thermocouple method.