## 1 Introduction  
Thermocouple sensor is widely used in dynamic temperature measurement in harsh environment because of its simple structure, low cost, and strong robustness. The temperature measurement principle of the thermocouple is based on the heat balance, that is, the thermocouple must contact the object to be measured and achieve the heat balance. The existence of the heat transfer process causes the thermocouple to have thermal inertia, which affects the dynamic performance of the thermocouple. The time constant is the most important dynamic parameter and reflects the response speed of temperature sensor. It refers to the time for the system's step response to reach 63.2% of its final temperature value. Before applying the thermocouple to dynamic temperature measurement, its time constant should be measured first. The time constant of the thermocouple is not only related to the material and structure of the sensor itself, but also to the object to be measured and the heat transfer mode. At present, there are many kinds of measurement methods and devices of time constant, such as constant temperature water/oil tank, hot wind tunnel, shock tube, laser, and so on. Stable temperature fields in water flow and airflow environments are generated by constant temperature water/oil tank and hot wind tunnel respectively. The thermocouple is inserted into the stable flow field rapidly, and the thermocouple is excited by step temperature. The time constant is obtained by the thermocouple response. [PERSON] and [PERSON]. [1; 2] measured the response time and delay time of the thermocouple by constant temperature water/oil tank, and the dynamic error was corrected. [PERSON]. [3] developed a hot wind tunnel with the temperature range from 1000 \({}^{\circ}\)C to 1700 \({}^{\circ}\)C, and the step response of the thermocouple was obtained. Shock tube is used to generate step pressure, which is usually used for dynamic calibration of pressure sensors. After breaking the film, the gas in the high pressure chamber compresses the gas in the low pressure chamber to produce the shock wave. The step pressure is generated on the pressure sensor by the shock wave and used to excite the pressure sensor. At the same time, due to the gas compression, there is also a temperature step behind the shock wave, which can be used to excite the thermocouple. [PERSON] et al. [4; 5] modified the shock tube and constructed a new dynamic calibration system for the thermocouple, which can generate a stable temperature excitation lasting for a long time. [PERSON] et al. [6] heated the thermocouple to a certain temperature by laser, then turned off the laser, and the thermocouple was excited by a negative temperature step. [PERSON] and [PERSON] et al. [7; 8; 9; 10; 11] used high-power laser to generate a rapid temperature rise on the thermocouple surface and obtained the time constant. In addition, there are other methods for dynamic excitation and calibration of thermocouple [12; 13; 14; 15]. In the measurement methods and systems for time constant, how to produce stable temperature field and step excitation is the main research content when the system is established. In the above measurement methods, the measurement systems under water flow and air flow environments were constructed for different heat transfer environments. The constant temperature water/oil tank can provide uniform and stable temperature field, but the temperature is low. Hot wind tunnels and shock tubes can produce higher air temperature, but the temperature field is less uniform. In some industrial production, various types of kilns are widely used, such as roller kilns in metallurgical industry, kilns in ceramic industry and cement rotary kilns in construction industry. The measurement of dynamic temperature in kilns is of great significance for product process control and energy consumption reduction. At present, thermocouple sensors are commonly used to measure the temperature, and the response speed directly affects the accuracy of dynamic temperature measurement in furnace.