Research On The Compensation Of Dynamic Characteristics Of Thermocouple And Its Real-time Processing Method

In fields such as industry,military,and aerospace,precise measurement of dynamic temperatures with high temperature and fast rate of change is required.Currently,measurement methods for such temperature signals are limited.Although contact-type temperature sensors are simple,reliable,and low-cost,accurate temperature measurement requires sufficient contact with the measured medium and reaching thermal equilibrium,which results in temperature measurement delay.To meet the dynamic testing requirements,its response speed must be improved through dynamic compensation.This paper selected the most widely used thermocouple in temperature measurement instruments as the research object and tested its dynamic performance.The dynamic characteristics compensation of the thermocouple and its real-time processing methods were studied,including the following aspects:(1)A dynamic response test system for thermocouples based on a high-temperature furnace was constructed.The system can control the constant temperature zone in the furnace within the range of 400-1500℃ through a temperature controller.The thermocouple was rapidly inserted into the furnace by the sensing quick-insertion device to achieve near-step response excitation of the thermocouple.The influence of the exposed length of the junction of a 0.38 mm diameter alumina sheath thermocouple on its dynamic characteristics was discussed.The dynamic performance indicators of the homemade thermocouple were tested at different furnace temperatures,and the results showed that the furnace temperature is positively correlated with the thermocouple’s passband and negatively correlated with its time constant.(1)A dynamic response test system for thermocouples based on a high-temperature furnace has been built.The thermocouple is rapidly inserted into the furnace at 400～1500℃ with the help of a sensor fast feeding device to achieve near-step response excitation of the thermocouple.The effect of the exposed length of the coupling junction on the dynamic characteristics of the corundum-sheathed thermocouple with a wire diameter of 0.38 mm was investigated.The results show that the furnace temperature is positively correlated with the passband of the thermocouple and negatively correlated with the time constant.(2)For the problem of large dynamic errors in the actual testing of thermocouples,the feasibility of the thermocouple dynamic compensation method based on an intelligent optimization algorithm is verified by using software simulation.It is also demonstrated through several independent experiments that the convergence speed and stability of the Gray Wolf Optimization(GWO)algorithm are better than those of the other three intelligent optimization algorithms.The passband of the thermocouple simulation model is expanded from 317 Hz to25k Hz after compensation,and the time constant is reduced from 0.5ms to less than 0.06 ms.This method can broaden the passband of the homemade thermocouple from 0.0582 Hz to1.66 Hz,a broadening of about 28.5 times.(3)To address issues such as inconsistent temperature rise and fall processes of thermocouples,a thermocouple dynamic compensation method based on NARX neural network was proposed.By training the neural network with slow and fast response thermocouple experimental data as input and output,it was experimentally proven that the fitting accuracy of NARX was far higher than that of BP neural network.The trained neural network model can make the response speed of the slow-response thermocouple consistent with that of the fast-response thermocouple.The time constant of the slow-response thermocouple was increased from 2.3-4.06 s to 1.15-2.23 s.(4)To meet the real-time temperature measurement requirements of the measurement and control system,a thermocouple real-time acquisition compensation system was designed based on the ZYNQ platform.The system has a sampling frequency of 39k～1MHz,and the collected data can be compensated and displayed in real-time on the upper computer panel.A dynamic compensation module was designed in the logic part of the ZYNQ,and through simulation and on-board testing,this design scheme was proven to be capable of completing real-time acquisition and compensation processing tasks.