Abstract:The 26th General Conference on Weights and Measures (CGPM) approved the redefinition of the International System of Units (SI) using fundamental constants. The temperature unit “Kelvin (K)” will be redefined using Boltzmann constant (k). Accurate measurement of Boltzmann constant is the key to redefining Kelvin and reproducing thermodynamic temperature. In this paper, four kinds of primary thermometers used for measuring Boltzmann constant are introduced in detail, namely acoustic gas thermometery (AGT), dielectric-constant gas thermometery (DCGT), Johnson noise thermometery (JNT) and Doppler broadening thermometery (DBT). The working principle, main parameters and practical application of the four primary thermometers are expounded, and their contributions to the revision of Boltzmann constant value is explained. Finally, the future development direction of the primary temperature measurement method is summarized and prospected, which provides research support for the reproduction and transfer of thermodynamic temperature.

Abstract:The measurement of water vapor in gas is very important for many industrial production and scientific research fields. With the more stringent test requirements of gas moisture content, the analysis and measurement methods are also required to be more sensitive. At present, the instrument methods for measuring nmol / mol trace water include tunable diode laser absorption spectroscopy, optical cavity ring down spectroscopy and atmospheric pressure ion mass spectrometry. In addition, the measurement techniques of sensors reaching this trace level include quartz crystal microbalance method, cold mirror dew point method, resistance capacitance method and electrolytic method. These approaches are reviewed. The advantages and disadvantages of these methods as well as the future development trends are discussed. It is pointed out that the measurement accuracy of trace moisture content can be improved to a certain extent by overcoming the interference factors in the measurement process. It is beneficial to promote the development of accurate measurement technology of trace water content.

Abstract:In order to improve the detection accuracy of cooperative target ball used for the precision assembly of large-scale devices by laser tracker in complex scenes, an efficient cooperative target ball detection method based on deep learning is researched. Firstly, the image features of the cooperative target are analyzed. Then, by using the improved YOLOv2 model, an improved method based on attention mechanism is proposed aiming to the cooperative target characteristics of multi-scale and large proportion of small targets. In order to improve the anti-interference ability of the network model in complex background, a method of data enhancement is also proposed. The test result shows that the proposed improved YOLOv2 network based on attention mechanism and data enhancement has strong anti-interference ability against complex background and significantly improves the detection accuracy of cooperative target ball. The detection accuracy on the cooperative target test set has reached 92.25%, which meets the target detection accuracy requirements of laser tracker in the large equipment precision assembly.

Abstract:As one of the important ways to realize the "meter" benchmark, the accuracy of laser wavelength is of great significance in the fields of metrological calibration, precision measurement and spectral detection. However, at present, the wavelength reference based on the absorption spectrum of reference materials can only be used for the metrological calibration of single wavelength, and the calibration methods for the wavelength of broadband light source are limited. This paper mainly researches on broadband continuous tuning laser wavelength calibration technology. Using the characteristics of wide spectrum, optical frequency traceable to atomic frequency standard and high stability of femtosecond laser frequency comb, the continuous optical wavelength of broadband tunable light source during tuning output is measured. Finally, the measurement of instantaneous value of the tunable laser in the tuning output process under the bandwidth of 1 nm is realized. Meanwhile, the frequency modulation nonlinearity of tunable laser in 121 GHz bandwidth is evaluated by using the measurement results.

Abstract:In order to meet the demodulation requirements of dynamic pressure better, a diaphragm-type optical fiber dynamic pressure sensor based on Fabry-Perot (F-P) interference principle is studied. The influence of multiple reflective surfaces on the spectrum of the F-P cavity is theoretically analyzed, and a method is proposed to obtain a single F-P cavity. The outer surface of the sensor diaphragm is roughened by mechanical grinding, which effectively solves the complex spectrum problem caused by multiple reflective surfaces. Static pressure and dynamic pressure calibration tests are carried out on the sensor, and the results show that the sensor performs well. The static pressure measurement error of the sensor in the range of 0-200 kPa (gauge pressure) is not more than 0.5 %FS, and the amplitude sensitivity relative error of the sensor does not exceed ±10% within the range of 20~2500 Hz.

Abstract:Aiming at the problem of high-speed water impacts formed during the water drawing of amphibious aircraft water tanks, the high-speed water impact load characteristics was studied. Firstly, a water impact experiment method based on adjusting the air pressure in the cavity is proposed. By adjusting the air pressure in the water storage container to change the water impact speed, the high-speed water flow impact experimental research is carried out. Then, based on ABAQUS CEL numerical simulation method, the initial velocity of water flow is preset, and the finite element model of high-speed water flow impact is established. The effects of water velocity and the distance between the end of water pipe and flat plate on the impact pressure was analyzed. The results show that the numerical simulation results are not much different from the experimental results, which verifies the accuracy of the model. The higher the water velocity is, the greater the impact pressure on the plate becomes, and the greater the distance between the end of the water pipe and the plate is, the smaller the impact pressure on the plate becomes.

Abstract:Electroactive polymer (EAP) has a wide range of applications in real life. As one of its typical applications, the dielectric EAP cylindrical actuators are affected in output lateral deflection force and lateral bending angle by the tensile area ratio of dielectric EAP film, the number of winding layers of dielectric EAP film and the coating area ratio of flexible electrode, which needs to be further studied to determine the law of action. In view of the influence of these factors on the lateral performance of the output of dielectric EAP cylindrical actuator, a test device was designed and manufactured, and a large number of test data were measured through the control variable test. The action law of the influencing factors was preliminarily obtained by analyzing and processing the test data. The results showed that the output lateral deflection force and lateral bending angle of the dielectric EAP cylindrical actuator are all affected by the tensile area ratio of the dielectric EAP film, the number of winding layers of the dielectric EAP film and the coating area ratio of the flexible electrode. These factors have different effects on the output lateral performance.

Abstract:Length measurement, one of the key generic and basic technologies of geometric measurement, has important applications in scientific research, high-end equipment manufacturing and space exploration. The dual optical comb absolute distance measurement technology makes the best of the characteristics of the optical frequency comb in time domain ultra-short pulse and frequency domain high-resolution. Further it achieves absolute distance measurement with high measurement rate. Until now, the problems of limited measurement range and low measurement accuracy ail the community of double optical comb ranging. To relieve it, this work presents a novel technological solution, which combines the double optical comb ranging and phase ranging. The double optical comb ranging technology is adopted to realize the high-precision measurement of the length within the non-fuzzy range. The phase ranging technology is used to measure and indicate the integer multiple of the non-fuzzy range, which is an effective complement to the high-precision measurement of double optical comb ranging. An experimental system is built to verify the feasibility of the proposed technological solution, and the results show that the measurement error is less than ±5 μm within the measurement range of 0~70 m.

Abstract:Aiming at the problems that the thrust range of medium and high power electric thrusters for satellites is large and the existing thrust measurement devices have incomplete measurement range and poor anti-interference ability, the research of multi-range three-filament torsional pendulum thrust measurement device has been carried out. The physical model of the thrust measurement device was established, the mathematical relationship between the thrust force and the deflection displacement was studied, and the design of the multi-range three-filament torsional pendulum thrust measurement device was realized. The measurement device was calibrated using standard weights and custom weights, and the measurement errors at each range were determined by calibration experiments. The uncertainty assessment of the device was carried out by considering the uncertainty influencing factors comprehensively and designing relevant experiments. The experimental results showed that the uncertainty of the multi-range three-filament torsional pendulum thrust measurement device was 0.030 mN (k=2) for a small thrust of 98 mN, 0.068 mN (k=2) for a medium thrust of 490 mN, and 0.092 mN (k=2) for a large thrust of 980 mN in the same experimental environment. The multi-range torsional pendulum thrust measurement device uses the measurement method of changing gears to achieve thrust measurement in the range of 9.8~1029 mN with high measurement accuracy and strong anti-interference capability, which solves the problem that it is difficult to guarantee the full range accuracyin the process of wide range thrust measurement, and provides technical support for the thrust measurement of medium and high power electric thrusters.

Abstract:Instrument landing signal generator is special testing equipment for the airborne equipment of instrument landing system. At present, there is no publicly published national and industrial technical standards for verification and calibration of instrument landing signal generator in China. By analyzing the principle of instrument landing system, and starting from the working characteristics of instrument landing signal generator, this paper analyzes the signal characteristics of localizer, glide path beacon and marker beacon, gives the measurement characteristics, and presents the calibration method of each measurement characteristic based on direct measurement method of spectrum analyzer. The uncertainty of measurement introduced by spectrum analyzer is analyzed, and the extended uncertainty is evaluated by GUM method. The results show that the calibration method presented in this paper can meet the calibration requirements of the key parameters of the instrument landing signal generator, and the calibration with spectrum analyzer meets the traceability requirements of the measurement characteristics of instrument landing signal generator.

Abstract:In order to study the correlation of vibration characteristics of RV-40E reducer and analyze the characteristic frequency of vibration signals, the RV reducer was tested at constant speed, increasing speed and decreasing speed by using the comprehensive test platform of precision reducer, and the vibration signals at different speeds were collected. Through data processing with MATLAB, the frequency domain analysis and autocorrelation analysis of vibration signals at each speed are carried out. It is found that the autocorrelation of RV reducer increases with the increase of rotating speed. The autocorrelation does not have periodicity in the process of deceleration and acceleration. The meshing frequency of the primary and secondary drives has a great influence on the operation of the reducer. This study can provide an effective means for fault diagnosis of RV Reducer.

Abstract:In view of the fact that the current metrology work lags behind industrial development and is divorced from industrial demand, starting from the basic theory, historical evolution and application practice of metrology, this paper analyze the connotation of metrology and the relationship between metrology and measurement, and discusses the existing problems in concept, technology and management of metrology in combination with current metrology system architecture and actual work. Focusing on the elements of measurement system such as measurement requirements, measurement process, measurement standards and measurement result, it puts forward the entry point of integrated development of metrology and industry, and provides a reference for giving full play to the role of metrology under the background of strong quality and digital power.