Research On Time Constant Testing Technology Of Laser Excited Thermocouple Temperature Sensor

With the rapid development of temperature sensor technology,the research of temperature testing has shifted from the steady-state temperature field to the transient temperature field,especially the research on the precise testing of transient high temperature has become a hot topic nowadays.As one of the commonly used temperature sensors,thermocouples are widely used in high temperature test environment because of their large temperature measurement range and high temperature upper limit.However,the existence of its hysteresis often leads to the delay of temperature measurement,which eventually leads to the inaccuracy of temperature measurement.Therefore,it is of great significance to carry out the research on the thermocouple time constant test method and the precise test of time constant in view of the strict requirements of temperature test for thermocouple sensor in the harsh environment such as high temperature,high difficulty and single transient.In order to solve the key problem in the process of thermocouple time constant testing,that is,how to obtain an ideal step temperature excitation signal,this paper proposes to use the positive and negative step signal excitation method based on laser heating to achieve the study about the test of the thermocouple time constant.And the time constant test experiment is completed in the constructed thermocouple time constant test system.The time constant test system is mainly composed of a heating energy source-a high-power semiconductor laser,a conjugate non-aberration large ellipsoidal mirror,an infrared detector,and a feedback control module.When the positive step signal excitation method is used to test the thermocouple time constant,the fuzzy PID feedback control module in the system controls the output power of the laser according to the thermocouple surface temperature signal received by the infrared detector,so that the thermocouple can obtain the expected equilibrium temperature excitation in a short time.When the negative step signal excitation method is used to test thethermocouple time constant,the laser is used to heat the thermocouple junction with a certain output power under a stable environment.When the thermocouple reaches the thermal dynamic equilibrium,the laser heating source should be cut off immediately,so that the thermocouple generates a negative step form of dynamic temperature measurement process.In view of the above two time constant test methods,this paper first simulates the transient heat transfer process of laser heating thermocouple nodes based on the ANSYS finite element simulation software platform.And the simulation results are analyzed and calculated theoretically.Secondly,the superiority of fuzzy PID feedback control technology is proved by the thermocouple time constant test system.At the same time,the time constant test experiment of thermocouple under the two methods is completed,and the advantages and disadvantages of the two methods are compared,and the method of combining the two methods is proposed.Finally,the influence of different test temperature on the time constant of fast response thermocouple is explored,and the fitting curve and function are given.