Abstract:In order to achieve accurate temperature measurement in high?temperature environments, a measurement method based on femtosecond fiber Bragg gratings (FBG) is proposed, utilizing the outstanding thermal stability of FBG fabricated by femtosecond lasers. A FBG central wavelength?temperature model was established based on the dependence of thermal optical coefficient and thermal expansion coefficient on temperature. Since there is no analytical expression for the model, the temperature?central wavelength working curve is fitted by using the single point specific solution of central wavelength?temperature and quartic polynomial. Based on this working curve and pre annealing (1 000 ℃, 20 h) FBG, temperature measurement experiments were conducted from room temperature to 900 ℃, and the results showed that the maximum measurement deviation was less than ±2 ℃. This method only needs to calibrate a single point central wavelength?temperature to achieve accurate temperature measurement over a wide temperature range. It is simple and effective, and has important research and application value in the fields such as aerospace, nuclear power metallurgy, etc.

Abstract:Aiming at the problem of circuit fault diagnosis in high?precision resonant dewpoint measurement system, this paper proposes a circuit fault diagnosis model based on improved sparrow search algorithm (ISSA) to optimize the parameters of intelligent classifier. The support vector machine (SVM) suitable for small samples and nonlinear problems is selected as the intelligent classifier. In order to solve the problems of slow convergence speed and being easy to fall into local optima of sparrow search algorithm, an improved optimization algorithm is proposed and used to optimize the parameters of SVM, and the ISSA?SVM fault diagnosis model is constructed for resonant circuit fault diagnosis. The experimental results show that the fault diagnosis accuracy rate can reach 88.9 % on the established circuit, and the ISSA?SVM classifier can be used as a high precision resonant dewpoint sensor circuit fault diagnosis method.

Abstract:Acoustic pyrometers still have such problems as insufficient probe temperature tolerance, poor temperature measurement stability, and susceptibility to the impact of airflow velocity. In order to improve the temperature measurement reliability of acoustic pyrometer, this paper establishes a corresponding airflow temperature field and sound propagation model in Virtual.Lab. The optimal topological parameters to reduce sound pressure level attenuation were analyzed and studied by changing the topological structure such as the acoustic probe distribution diameter, orientation, and tilt angle of an existing set of acoustic pyrometers, and experimental comparison was carried out. Finally, it was found that the topology structure with a diameter of 15 cm and an inclination angle of 30 degrees between the acoustic probe and the horizontal plane had the smallest comprehensive sound pressure level reduction value in the airflow temperature field environment with temperature from normal atmospheric temperature to 900 ℃ and Mach number from 0 to 0.3. The topology structure with a diameter of 20 cm and an inclination angle of 15 degrees took the second place. In conclusion, both topology structures reduce the standard deviation of data by more than 17% compared to existing topology structure, which improve the performance of acoustic source signal reception, therefore, improving the reliability of acoustic pyrometer temperature measurement in the airflow temperature field environment of temperature from normal to 900 ℃ and Mach number from 0 to 0.3.

Abstract:To reduce the impact of temperature drift on sensor measurement results in high temperature and low humidity environments, a humidity sensor based on quartz crystal microbalance (QCM) was developed by using a quartz crystal with a fundamental frequency of 4 MHz as a substrate and depositing graphene oxide (GO) on the substrate using a drop?on?demand method. The temperature drift phenomenon of AT?cut quartz crystal wafers and graphene oxide materials in high temperature environments is significant, resulting in frequency output drift of the sensor. Therefore, a deep?learning method was used to correct the temperature drift. The adaptability of the back propagation (BP) neural network correction model to the QCM humidity sensor was tested under different absolute humidity conditions. The experimental results show that the correction model obtained through deep learning can effectively improve the sensitivity, stability, and response speed of the QCM humidity sensor. It is of great significance for studying the frequency correction technology of QCM humidity sensors under temperature and humidity coupling conditions.

Abstract:Aircraft wings usually use I?beams as support structures. However, due to changes of the geometric parameters of the I?beams, theoretical calculations will be affected, and the choice of beam theory will directly affect the calculation results. At present, the existing deflection calculation of I?beams is mainly based on the Euler Bernoulli beam theory, without fully considering the shear deformation during beam bending. Therefore, this article proposes a calculation method for I?beams considering shear effects based on the Timoshenko beam theory, which is used to calculate I?beams affected by concentrated forces. By characterizing the effect of shear deformation on beam deformation, the law of action of shear deformation on the beam was obtained, and the deformation mechanism of shear deformation in the beam was explained. Research has shown that when the I?shaped cantilever beam is within a certain range near the fixed end and the span to height ratio of the beam is less than 5, the influence of shear deformation should be considered in the calculation. The theoretical results of internal force calculation obtained by this method are basically consistent with the results of simulation and electrical measurement method, and can be applied to practical engineering calculation.

Abstract:To address the computational complexity of accurately calculating molecular absorption spectra in high?temperature environments and meet the demand for theoretical absorption spectrum calculations in broad?spectrum measurement fields, this study developed a precise and fast calculation model for molecular absorption spectra based on the High?Temperature molecular spectroscopic absorption parameters database (HITEMP). The model was implemented using Python language, employing a line?by?line calculation approach combined with simplification of line shape functions, line wing truncation criteria, and optimization of spectral line databases. The Hartmann?Tran line shape function was used as the standard absorption spectrum line shape, and partially?Correlated quadratic?Speed?Dependent Hard?Collision Profile (pCqSDHC) was developed for relevant second?order velocity?dependent hard?collision functions. By incorporating the Complex Probability Function (CPF) and simplifying the model, the line shape functions were calculated accurately and rapidly, resulting in a 20?fold increase in computational speed compared to theoretical models. The line wing truncation criteria were determined based on the spectral calculation residual at the level of 10-5 and involved the truncation of fixed wavenumbers combined with equal multiple truncations of spectral line half widths. Spectral data for each temperature gradient of 100 K were selected using a threshold line intensity of 10-25?cm-1/(mol?cm-2) and integrated to create an optimized database. The absorption spectra of water molecules were calculated within the range of 6 500 ~ 8 000 cm-1 and compared with the simulation results from "SpectraPlot.com", a molecular gas integrated spectral modeling website. The calculation error of the line?by?line model was at the level of 10-7, while the optimized model achieved a calculation error at the level of 10-5, with an average speed improvement of 25 times. This model enables efficient and accurate calculation of theoretical absorption spectra for absorption spectral measurements and provides a theoretical foundation for measuring studies based on wide?tunable and supercontinuum laser absorption spectra in complex environments.

Abstract:Aiming at the narrow spectral range and wide pulse width of domestic mid?infrared laser sources, research on mid?infrared femtosecond laser technology based on difference frequency generation (DFG) was carried out. The mid?infrared femtosecond laser generated based on DFG has the advantages of a wide spectral range and narrow pulse width. The influence of different nonlinear crystals on the generated mid?infrared laser in DFG was studied. On this basis, a mid?infrared laser generation system based on DFG using a PPLN crystal was conducted. Further, this system used grating pairs to compress the pulse width to achieve femtosecond laser output. Finally, a mid?infrared femtosecond laser with a tunable wavelength range of 2.9 ~ 4.7 μm was observed, and the highest average output light power of 10.46 mW was obtained at a central wavelength of 3.2 μm. The research results provide a reference for the application of mid?infrared laser spectroscopy measurement technology in atmospheric monitoring, combustion field component detection, etc.

Abstract:In order to solve the shortcomings of Fabry?Perot (F?P) interferometer frequency?locking method in terms of response speed, anti?interference ability and long?term stability, a differential frequency?locking scheme of F?P interferometer is proposed. Dual?frequency laser with frequency difference is coupled into F?P resonator. When the laser frequency difference is small enough, the signal curves of two light intensities will cross. Taking the difference between two light intensity signals as the controlled variable, a monotone zero crossing function is constructed near the crossing point, which is used as the feedback of the closed?loop control system to realize dynamic differential frequency locking control. Based on the scheme, a set of F?P interferometer micro?displacement measurement device was built and experimental verification was performed. The results show that the device could realize micro?displacement measurement in the range of 0 ~ 300 nm, and the displacement measurement resolution reached 23 pm, which verified the effectiveness of the F?P interferometer differential frequency?locking scheme, and provided an important reference for the development of micro?displacement measurement.

Abstract:At present, there is still a lack of effective methods and devices for the calibration of humidity parameters under high temperature and pressure in China, especially for the calibration of relative humidity or water vapor content under conditions of temperature above 100 ℃, and for the calibration of dew point temperature above 100 ℃. To address this issue, a high?pressure moisture generator based on the principle of single temperature and single pressure method has been developed. The generator consists of a saturation system, an air circuit system, a constant temperature system, and a control system. The saturation system completes water vapor saturation at the set temperature and pressure; The air circuit system and constant temperature system achieve gas transmission under different pressure and temperature conditions; The control system achieves precise control of overall temperature and pressure. The standard moisture with a volume fraction of 0.5% to 15% (corresponding to a dew point temperature range of -2.8 to 110 ℃) can be ultimately produced, with an absolute pressure range from 0.1 to 1 MPa, and an expanded uncertainty from 0.50 to 0.52 ℃ (k = 2) for dew point temperature. The high?pressure moisture generator has the advantages of short stability time, high accuracy, convenient operation, and strong practicality. It can be used as a calibration humidity source under high?temperature and high?pressure conditions, and has important technical application value.

Abstract:The traditional method for calibrating strobe using simulation testers requires visual judgment by operators, resulting in poor repeatability of test results and large uncertainty in the evaluation results. A laboratory calibration method for helicopter rotor cone strobe, a specialized aviation testing equipment, was studied. This method uses the pulse frequency method to establish a calibration device in the form of photoelectric conversion to calibrate technical parameters such as the flashing frequency of the strobe. The experimental results show that while the accuracy has been significantly improved, and the uncertainty is smaller. Compared with the traditional method, this method is simple and fast to operate, and universal standard equipment can meet the calibration requirements. The traceability of measurement values is more reliable and easier, and it also meets the requirements of metrology regulations, and has certain popularization and application value.

Abstract:In order to study the vibration state of AT?cut quartz crystal resonators under different temperature environments, the vibration displacement distribution of quartz crystals along the x direction at different temperatures was analyzed using the finite element simulation software COMSOL Multiphysics 6.0. The vibration displacement of parasitic modes was visually observed and the energy ratio and quality factor of electrode region at different temperatures were calculated. The quality factor and temperature frequency effect of AT?cut quartz crystal at different temperatures were measured experimentally. The simulation results show that the typical energy trapping effect always exists on the surface of AT?cut quartz crystal with the change of temperature, and the coupling between modes is not aggravated. The experimental results show that the variation trend of AT?cut quartz crystal frequency with temperature is consistent with the theory, and the experimental data and the quality factor calculated by simulation have no obvious change with temperature. The research results show that AT?cut quartz crystal has good thermal stability and can be used as the sensitive element of Quartz Crystal Microbalance (QCM) sensor in high temperature environment, which has guiding significance for the selection of sensitive devices in high temperature environment.

Abstract:The high?temperature eutectic point（HTEP）crucible is made of graphite material with low structural strength, so it is prone to fracture after reproducing test, causing HTEP crucible damage. Durability of crucibles has become one of the main obstacles for HTEP to enter the next generation of temperature scale. In order to solve this problem, in this article, the stress situation of the crucible is analyzed based on ANSYS, and the theoretical positions of the main stress points of the crucible are clarified. Then, combined with the actual fracture situation of various HTEPs, the reasons for the fracture of different types of eutectic point crucibles are analyzed. Two improvement plans for HTEP crucibles are proposed: improved Hybrid structure and flow?guide?cover structure. Finally, some new high?temperature eutectic/peritectic points are made by using an improved structure crucible, and no damage issues are found after reproducing test, which has preliminarily verified the effectiveness of the improvement.

Abstract:The oretical analysis is conducted on the typical fault problem of abnormal voltage output during the use of a certain type of single axis pendulum accelerometer. The fault tree comprehensive analysis method is used to track and analyze layers by layers, expressing the internal relationship between abnormal output voltage faults and intuitively pointing out the logical relationship between unit faults and overall faults, We have effectively summarized and summarized the problem of abnormal output voltage faults of single axis pendulum accelerometers encountered in engineering applications. Then, the cause of the fault was accurately and meticulously located, and the D4 diode positive electrode gold wire fracture in the oscillator circuit was proposed as the root cause of the accelerometer fault. The circuit gold wire fracture mechanism analysis method was incorporated, and the accuracy of this fault analysis was verified through experimental testing and improvement measures, which to some extent improved the reliability of the accelerometer. The research results can provide a certain reference for the reliable use of accelerometers.

Abstract:Aiming at the problem of large measurement errors in input resistance, the physical mechanism and practical reasons were analyzed. Several main factors affecting the uncertainty of input resistance measurement were discussed, including standard voltage, measurement voltage, standard resistance value and error, and so on. The main measures to reduce the uncertainty of input resistance measurement were given, that is, the closer the value of standard resistance and input resistance, the better, and the two should be in the same order of magnitude, moreover, the difference between two different excitation voltages should be as large as possible. The evaluation results of input resistance measurement uncertainty are provided through an example, and both the correctness and feasibility of the process are proved.

Abstract:The calibration of total station distance measurement accuracy needs to be carried out on a standard baseline field, and it is of great significance to judge the reliability of the measurement results of the total station due to the uncontrollable field environment and the drastic fluctuation of meteorological conditions. In order to solve the problems of nonlinearity and strong correlation of inputs of the total station distance measurement uncertainty evaluation model, this paper firstly adopts the adaptive Monte Carlo method to evaluate the uncertainty, and then compares the uncertainty evaluation results with those of the GUM. When the ranging distance is 1 176 m, the uncertainty evaluation results of the adaptive Monte Carlo method is 2.2 mm, and the GUM is 2.6 mm. The results show that the measurement results of both uncertainty assessment methods are within reasonable expectations, and the uncertainty confidence interval of the adaptive Monte Carlo method is narrower. The adaptive Monte Carlo method combines the advantages of a large number of data samples and adaptive optimization of the simulation times, which not only provides a more comprehensive assessment of the uncertainty components introduced by various error sources in the process of total station distance measurement, but also saves 70% of samples compared with the Monte Carlo method, while guaranteeing the accuracy of the uncertainty assessment results of the total station distance measurement.