Research On Dynamic Calibration Technology Of Contact Temperature Sensor

Dynamic measurement technology is widely used in industry,agriculture,national defense and other fields.Compared with static measurement,dynamic measurement has the characteristics of space-time,randomness,correlation and dynamic,which puts forward high requirements for the dynamic performance of the test system.Temperature is one of the basic physical quantities.The temperature measurement in engineering is of great significance for evaluating the system performance and guiding the system design.The various dynamic temperatures,such as vehicle engine gas temperature,rocket and missile gas jet temperature and ammunition detonation temperature and so on,not only change quickly,but also the test environment is usually harsh,which puts forward higher requirements for the applicability of the test system.Non-contact temperature measurement method has a fast response speed,but its application is limited by the limitations of temperature measurement principle,complex structure and high price.Contact temperature measurement method,such as thermocouple,thermal resistance,fiber temperature sensor,etc.,is widely used in dynamic temperature measurement in harsh environments due to simple structure,low cost and robustness.Since contact temperature sensor needs to exchange heat with the object to be measured and achieve thermal balance,its response speed is limited by the thermal inertia.When its dynamic characteristics cannot meet the requirements of dynamic test,dynamic errors will occur.Therefore,the dynamic calibration of the sensor and the understanding of its dynamic characteristics are of great significance for in-situ test,sensor design and error correction.Aiming at the problem of dynamic calibration of thermocouple sensor,two dynamic calibration methods based on pulse excitation and step excitation were studied in this paper.The dynamic calibration systems based on laser and high temperature furnace were constructed respectively,and the dynamic calibration experiments were carried out.The main research contents and work are as follows:(1)For the dynamic calibration of the thermocouple,the dynamic calibration criterion of narrow pulse excitation and the error of step dynamic calibration were analyzed.The method that the pulse excitation of the thermocouple is generated by a laser was studied,and the thermal effect and heat transfer process of solid metal heated by laser were studied.The simulation analysis was carried out by using thermal analysis software ANSYS.The step excitation dynamic calibration system based on high temperature furnace was studied.A data processing method for step excitation and response signals was proposed,and the accurate time constant can be obtained when the rise time of ramp excitation and the thermocouple time constant are approximate.(2)The thermocouple dynamic calibration system based on high power laser was built,which mainly includes three parts: pulse laser control,laser beam homogenization and sensor dynamic calibration.In order to develop the repeatability and accuracy of the calibration experiment,the imaging laser beam homogenization system was constructed by microlens array.Firstly,the beam homogenization principle of microlens array was studied,and the influence of some parameters on the homogenization effect was simulated by using optical simulation software ZEMAX.Secondly,in order to measure and evaluate the homogenization effect,wedge prisms were used to attenuate the power of high power laser.In the calibration system,the excitation temperature of the thermocouple surface was measured by the infrared thermometer with fast response speed,and the dynamic calibration experiments were carried out by the system.(3)In order to analyze the dynamic characteristics of the calibrated sensor,its dynamic mathematical model should be established.Based on the analysis of system identification theory and modeling methods,the dynamic mathematical model of the thermocouple was established by recursive least squares method,and a method for analyzing the model uncertainty in frequency domain was proposed.In order to verify the model,the dynamic calibration experiments of the thermocouple were carried out under different laser powers,and the thermocouple response signals and model response signals were compared and analyzed.(4)The thermocouple dynamic calibration system based on high temperature furnace was built,and the heat transfer environment in the furnace was analyzed.In order to generate step excitation on the calibrated thermocouple,the fast feed device was used to realize the fast insertion,speed and position control of the thermocouple in the high temperature furnace.The time constants of a K-type thermocouple was measured at different high temperature furnace temperatures by the calibration system.Repeated experiments were carried out at the same temperature.The time constant of the sensor at the same temperature was obtained,and the uncertainty was evaluated.(5)For system identification of two-thermocouple sensor and dynamic temperature measurement,the blind system identification method based on cross-relation(CR)algorithm was studied.The thermocouple dynamic calibration system based on high temperature furnace was applied to make the two-thermocouple sensor move back and forth in the furnace by using the fast feed device,and the sensor was excited by periodic change temperature.The blind system identification method based on CR algorithm was used to estimate the time constants.In order to optimize the cost function in CR algorithm,the particle swarm optimization(PSO)algorithm was proposed to optimize in solution spaces,and the precision and anti-noise performance of the method were simulated and analyzed.The measurement results were corrected and the input temperature signal was reconstructed by using the model and the response signals of two thermocouples.