计量科学与技术

Research on Fiber-Optic Sensing Technology of Short-Circuit Test Current

LI Chuansheng, ZHAO Yeming, LIN Feipeng, LIANG Bo, WANG Jiafu, ZHAO Wei, SHAO Haiming

2021, 65(5): 3-7. doi: 10.12338/j.issn.2096-9015.2020.9054

Abstract(647)

HTML (398)

PDF(66)

Abstract:
A fiber-optic short-circuit current sensing method is proposed in order to solve the short-circuit test current calibration problem for the AC and DC switch electric appliance. A low-frequency simplified dynamic model of the fiber-optic current sensor was established, and the parameters of the closed-loop signal-detection system were obtained according to the time-domain and frequency-domain characteristics simulation results. The results show that the dynamic performance of the sensor can meet the requirements of tracking the measured short-circuit current. A fiber-optic current sensor calibration device was built, and the calibration results showed that the measurement accuracy of the sensor prototype was better than 0.2% in the range of 5 to 300 kA DC and 5 to 50 kA power frequency. The comparison tests of the AC short-circuit current between the fiber-optic current sensor and the common adopted Rogowski coil were performed. The results showed that for DC short-circuit currents from 6 to 100 kA, the relative error between the shunt and the fiber-optic current sensor was less than 0.3%. For the power frequency short-circuit currents from 10 to 130 kA, the relative error between the Rogowski coil and the fiber-optic current sensor does not exceed 0.2%. The research work provides a new solution for the short-circuit test current measurement.

Structure Improvement and Stability Research of Double Crystal Monochromator

GUO Siming, HOU Dongjie, WANG Eryan, SONG Ruiqiang, ZHOU Pengyue

2021, 65(5): 8-13. doi: 10.12338/j.issn.2096-9015.2020.9024

Abstract(974)

HTML (630)

PDF(94)

Abstract:
The double crystal diffraction structure based on Bragg diffraction is the core component of the monochromator commonly used in synchrotron radiation beamlines and monochromatic X-ray radiation devices. The stability of the monochromatic X-ray generated by the T-structure double crystal monochromator was investigated. In addition, inspired by the Channel-cut monochromator structure, a new double crystal monochromator structure was designed, and stability of the diffraction-generated monochromatic X-ray was tested. The experimental results show that the stability of the monochromatic X-ray flux generated by the T-structure double crystal monochromator is poor due to its structural defects, while the stability of the monochromatic X-ray flux generated by the new double crystal monochromator structure is better than 1.0%, and the energy range and dose rate of the monochromatic X-ray are significantly improved.

Measurement of Dielectric Properties of Materials in Millimeter-Wave Frequency Range

GUO Wen, XU Hao, LIANG Weijun, LIU Ke, JIA Chao, GAO Qiulai

2021, 65(5): 14-19, 45. doi: 10.12338/j.issn.2096-9015.2020.9020

Abstract(1307)

HTML (599)

PDF(164)

Abstract:
This paper systematically studied the measurement method of complex permittivity of materials in the millimeter-wave frequency range. Based on the free space-method, a two-tier calibration and the time-domain gating technology were proposed to characterize the dielectric property of materials in the broad frequency range of 75～110 GHz, and an open resonant cavity with a high-quality factor is developed based on the quasi-optical Fabry-Perot resonance principle. An inverse model of the dielectric properties of materials is developed using Gaussian beam theory, which is particularly suitable for the accurate measurement of low-loss dielectric materials. By comparing the measurement results of polyvinyl chloride (PVC) and fused quartz, the consistency of these two methods was verified. In addition, we proposed a de-embedding algorithm for multilayer materials, which can characterize the anisotropic dielectric properties for liquid crystals. The Gaussian beam theory was used to establish an inversion model for extracting the complex permittivity, which was especially suitable for the accurate measurement of low-loss materials.

Recent Advances in Single-Cell Mass Spectrometry Methods

TAN Siyuan, LI Manli, FU Boqiang, DAI Xinhua, GONG Xiaoyun

2021, 65(5): 20-29, 13. doi: 10.12338/j.issn.2096-9015.2020.9021

Abstract(2104)

HTML (489)

PDF(284)

Abstract:
The heterogeneity between individual cells is essential for the realization of various biological functions. Accurate measurement of biomolecules at the single-cell scale is beneficial to obtain microcosmic biological mechanisms that are scarcely acquired at the tissue scale. However, the measurement of biomolecules in single cells is extremely difficult due to the complex composition in individual cells, the extremely low content of substances, and the significant differences in concentration of different components. With its high sensitivity, high specificity, accurate quantitation, and structural identification capabilities, mass spectrometry technology has attracted much attention in single-cell analysis field in recent years. At present, research on single-cell mass spectrometry methods has focused on the development of ionization techniques and corresponding sample pre-treatment methods. From the perspectives of ionization techniques, there are mainly four categories: nano-electrospray ionization mass spectrometry (nanoESI-MS), laser desorption ionization mass spectrometry (LDI-MS), secondary ion mass spectrometry (SIMS) and inductively coupled plasma mass spectrometry (ICP-MS). This review summarizes the recent developments of these methods and their future trends in metrology field.

Research on Key Technologies of Ultra-Low Frequency Voltage Traceability

SHI Zhaomin, ZHANG Jiangtao, PAN Xianlin, SONG Ying

2021, 65(5): 30-35. doi: 10.12338/j.issn.2096-9015.2020.9011

Abstract(665)

HTML (437)

PDF(76)

Abstract:
To address the problem that the thermal voltage converter (TVC) is unable to achieve the AC-DC conversion of ultra-low frequency voltages, an AC-DC transfer method is proposed with using dual-heater TVC based on the square characteristics of the output thermoelectric potential of the TVC and the square sum identity characteristics of two quadrature sinusoidal signals with identical amplitude. The ultra-low frequency voltage below 10 Hz is traced to the DC voltage standard. The ultra-low frequency voltage AC-DC transfer system is developed. The standard uncertainty of AC-DC transfer results at 10 Hz does not exceed 14 µV/V. A verification experiment is developed by comparing the AC-DC transfer results that from dual-heater TVC and planar multijunction thermal converter (PMJTC). The AC-DC transfer results obtained by the two different methods are consistent and the inconsistency is within the uncertainty range.

Traceability of 0:45 Colorimetric Values for Standard Whiteboards

SUN Ruoduan, WANG Kai, MA Yu, DAI Caihong

2021, 65(5): 36-39, 66. doi: 10.12338/j.issn.2096-9015.2020.9003

Abstract(693)

HTML (213)

PDF(79)

Abstract:
This paper combines the physical definitions of 0:d diffuse reflectance ratio and 0:45 diffuse reflectance factor and proposes a conversion formula between them according to the difference of geometric conditions in the diffuse reflectance model. Furthermore, a method is proposed to calculate the 0:45 diffuse reflectance factor from the 0:d diffuse reflectance ratio and the relative radiance factor of a standard whiteboard to obtain the 0:45 chromaticity and whiteness values of a standard whiteboard, which is successfully traced to the chromaticity primary reference and transferred to the comparison results of BIPM.CCPR-K5.

Novel Nanomaterials-Based Fluorescent Assay for Rapid Detection of Glutathione

PENG Tao, JIAO Xueshima, ZHENG Pimiao, LIANG Zhanwei, XIONG Jincheng, DAI Xinhua

2021, 65(5): 40-45. doi: 10.12338/j.issn.2096-9015.2020.9026

Abstract(979)

HTML (871)

PDF(61)

Abstract:
The level of glutathione (GSH) in serum has been correlated with the occurrence of various diseases. In this paper, a fluorescence method that can measure GSH levels rapidly and sensitively was successfully established. In this method, manganese dioxide-coated silica nanoparticles (SiO₂@MnO₂) were synthesized simply and rapidly under ultrasonic conditions using silica nanoparticles as carriers and stabilizers, and fluorescent gold nanoclusters (Arg/ATT/AuNCs) with high fluorescence quantum yields were synthesized using arginine and thymine as ligands. The experimental results showed that the strong reduction of GSH could decompose MnO₂ to release Mn(II) to burst the fluorescence of Arg/ATT/AuNCs, so a fluorescence method based on SiO₂@MnO₂ and Arg/ATT/AuNCs was established to measure GSH in serum. Under optimal conditions, the linear range of the method for quantitative measurement of GSH was from 2.5 to 20 nmol/L with a minimum detection limit of 1.23 nmol/L, which was better than similar methods that have been reported. The relative extended uncertainties of the method were 8.6%, 12.4%, and 18.8% (k = 2) for low, medium, and high GSH concentrations, respectively, with accuracies ranging from 87.0% to 105.6%, which meet the requirements of GSH determination and provide a new technique for sensitive and accurate measurement of GSH in serum.

Temperature Coefficient Measurement of LED Filament Standard Lamp

ZHAO Weiqiang, YAN Jingyun, LIU Hui, SU Ying

2021, 65(5): 46-49. doi: 10.12338/j.issn.2096-9015.2020.9043

Abstract(727)

HTML (374)

PDF(43)

Abstract:
National Institute of Metrology (NIM) has independently developed LED filament standard lamp. Temperature is the main factor affecting the measurement value of LED filament lamps, and the accurate measurement of the temperature coefficient is required to study and analyze the characteristics of LED filament lamps. This paper introduces the definition and measurement principle of LED temperature coefficient, as well as NIM’s facility to implement the measurement. Experimental measurements of LED filament lamps are performed to analyze the relationship between lamp voltage, total luminous flux value and reference point temperature. The linear expressions of the total luminous flux value versus the reference point temperature and the lamp voltage versus the reference point temperature are fitted using the least squares method, and the temperature coefficients of the luminosity value and the lamp voltage are calculated sequentially. The experimental data show that the developed LED filament lamp has a photometric temperature coefficient of 0.17%/°C and a voltage temperature coefficient of −0.025 V/°C.

Temperature Measurement of Pd-C and Ru-C Cells at NIM

LU Xiaofeng, ZHANG Tingting, DONG Wei, TANG Xiaojie, YUAN Zundong, WANG Tiejun

2021, 65(5): 50-54. doi: 10.12338/j.issn.2096-9015.2020.9034

Abstract(689)

HTML (282)

PDF(61)

Abstract:
The results of the research on two new eutectic fixed point cells, Palladium-Carbon (Pd-C) and Ruthenium-Carbon (Ru-C), conducted by the National Institute of Metrology (NIM) after participating in an international joint study on high-temperature fixed point cells thermodynamic temperatures are reported. Two types of crucibles were designed for Pd-C (1492 °C) and Ru-C (1953 °C), which can be used to calibrate radiation thermometers and high-temperature thermocouples. The International Temperature Scale of 1990 values (T₉₀) of Pd-C and Ru-C are measured extrapolated from a primary standard thermometer, and the thermodynamic temperature (T) is obtained using a precision photoelectric pyrometer LP4 measurement, where LP4 is interpolated and indexed by Co-C (1324 °C), Pt-C (1738 °C) and Re-C (2474 °C) with thermodynamic temperature values. The experimental results show that the differences between T and T₉₀ of Pd-C and Ru-C are 0.25 K and 0.29 K, respectively; the uncertainties of T and T₉₀ of Pd-C are 0.32 K and 0.45 K, and those of Ru-C are 0.49 K and 0.50 K. The results not only promote the application of calibration for high-temperature fixed points, but also establish an important basis for transferring thermodynamic temperature.

Exploration of Calibration Methods for Ocean NTC Thermistor Thermometers

LI Ting, WANG Hongjun, SUN Jianping, HAO Xiaopeng, WANG Chengke, YU Jiao

2021, 65(5): 55-61. doi: 10.12338/j.issn.2096-9015.2020.9027

Abstract(1177)

HTML (529)

PDF(109)

Abstract:
To meet the demand for high-precision measurement of ocean temperatures, the long-term stability of domestic Negative Temperature Coefficient (NTC) thermistor elements for ocean temperature measurement was investigated by using the national temperature reference of water triple point and gallium melting point. The calibration method for NTC thermistor thermometers was explored by introducing the thermostatic bath with the isothermal heat pipe technique and adopting the “instantaneous comparison method”. The results showed that the domestic NTC thermistor elements can have a half-year stability better than 1 mK, but long-term evaluation is still necessary. The conventional packaging processes can easily decrease the stability of NTC thermistors, and multiple thermal cycles are an effective way to improve the stability. The number and distribution of calibration points have a great influence on the calibration. But there are high-performance thermometers with little calibration deviation, hardly affected by the distribution of selected points. The analysis of these thermometers can help establish NTC thermistor evaluation standards and shed light on the development of the field of ocean temperature measurement.

Ultra-Stable Laser Technology and its Realization in Strontium Optical Lattice Clock

LI Ye, LIN Yige, WANG Qiang, YANG Tao, SUN Zhen, LU Bingkun, FANG Zhanjun

2021, 65(5): 62-66. doi: 10.12338/j.issn.2096-9015.2020.9018

Abstract(1452)

HTML (431)

PDF(150)

Abstract:
National Institute of Metrology (NIM) has realized the ultra-stable laser systems of hundred Hz, Hz and sub Hz magnitudes in 2008, 2011, and 2018. This paper focuses on the methods and conditions for the realization of ultra-stable lasers of various indices, discusses the reference cavity, fast feedback locking technique, and precision control technique to suppress the influence of external environment on the length of the reference cavity, and obtain 10⁻¹⁵ or higher frequency stability of the ultra-stable laser. Experimentally, an external cavity diode laser (ECDL) is locked to the 30-cm-long high-finesse ULE reference cavity, and the frequency stability of 3×10⁻¹⁶is achieved.

Application of FTIR in the Research on Gas Reference Materials

WANG Defa, ZHOU Fengran, YE Jing, ZHANG Tiqiang, ZENG Wu, HAN Qiao

2021, 65(5): 67-76. doi: 10.12338/j.issn.2096-9015.2020.9041

Abstract(1207)

HTML (857)

PDF(134)

Abstract:
Gas reference materials are widely used in gas measurement and play an important role in achieving traceability of measurement results to the SI units. The measurement of gas composition is indispensable in the development of gas reference materials. Besides chromatography and mass spectrometry, spectroscopy is also widely used. Fourier Transform infrared spectroscopy (FTIR) is a spectrum measurement technology that can be used for purity analysis of raw gases and accurate measurement of characteristic components and interference components of gas reference materials. This paper introduces the applications of FTIR in the measurement of impurities in several kinds of raw gases, and some applications in the property value measurement and international comparison of gas reference materials. The results show that FTIR is more suitable for the measurement of active components and simultaneous measurement of multiple components. The operation of the measurement process is relatively simple and does not require complex optimization and control of the chromatographic column or chromatographic parameters as in GC or GCMS. FTIR is also suitable for the measurement of stable gases. For example, it can obtain high repeatability and accuracy in the measurement of greenhouse gases. This paper points out that the accurate measurement results are related to the calibration method used, and relatively accurate measurement results can be obtained by using single-point exact-match calibration or two-point calibration, with an alternating measurement sequence “reference-sample-reference”.

Mass Spectrometry Matrix Effect Study for the Trace Analysis of Chloramphenicol Residues in Honey

TIAN Tian, LIU Shuyu, ZHANG Yan, ZHOU Xia, JIAO Hui, LI Xiuqin

2021, 65(5): 77-82, 100. doi: 10.12338/j.issn.2096-9015.2020.9037

Abstract(704)

HTML (298)

PDF(47)

Abstract:
Organic isotope dilution mass spectrometry (IDMS) is a potential reference method for the accurate measurement of trace components in complex matrix samples. However, the analytical conditions, isotope dilution reagents, matrix effects (MEs), and other factors can also affect the results. In this paper, jujube and wattle honey were used as the study samples to compare the MEs in the trace measurement of chloramphenicol residues in honey under different extraction methods, so as to investigate the influence of MEs on the results, the compensation and elimination methods of MEs.

Development of Verification Equipment for Phoropters

LI Fei, LIU Wenli, HONG Baoyu, ZHANG Jiyan

2021, 65(5): 83-88. doi: 10.12338/j.issn.2096-9015.2020.9048

Abstract(1014)

HTML (419)

PDF(65)

Abstract:
To solve the verification of the phoropters, optoelectronic equipment for measuring spherical vertex power, cylinder vertex power, axis position, and the center error of refractor heads based on the self-collimation sharpness method was developed. The equipment uses a grating length sensor to achieve precision measurement of concave reflector displacement, an angle encoder to measure the angular of the cross-line reticle, a CCD to achieve image acquisition, and a computer to achieve analysis and measurement. In this paper, the factors affecting the measurement accuracy and range are analyzed, the optical system of the comprehensive optometer and the key objective lens is designed, the photoelectric parameters are given, and the equipment is traceable to the national primary standard of vertex power. Theoretical analysis and experimental results indicate that the expanded uncertainly for phoropters can reach (0.03~0.08) m^-1(k=2), which meets the verification demand for the phoropters.

An Initial Exploration of Survivorship Bias in Verification of Build-up Force Standard Machines

ZHANG Wei, ZHANG Zhimin, LI Nan

2021, 65(5): 89-92. doi: 10.12338/j.issn.2096-9015.2020.9049

Abstract(951)

HTML (423)

PDF(68)

Abstract:
The paper introduces the characteristics and verification of build-up force standard machines (BMs). Differences between verification and actual working conditions for BMs were analyzed. To deal with the inconsistency under different conditions, a new concept, Verification Survivorship Bias (VSB), was proposed for the first time. An experimental method for BM VSB was developed. The new concept can be used to explore BM characteristics and explain some problems discovered. This work can shed light on manufacturing, verification, use, and evaluation of BMs.

Study on Saturation Magnetization Behavior of Sintered NdFeB

HOU Ruifen, ZHANG Zhigao, XU Zhiyi, DONG Hui, YAN Lizhong, YANG Tian, YANG Yiwei

2021, 65(5): 93-95, 35. doi: 10.12338/j.issn.2096-9015.2020.9012

Abstract(1509)

HTML (332)

PDF(121)

Abstract:
To clarify the relationship between the minimum saturation magnetization field strength required for sintered NdFeB magnets and their intrinsic coercivity or saturation polarization in the initial state of magnetic neutrality and magnetized history, three different grades of sintered NdFeB magnets were selected in different initial states. The magnetic dipole moments and the demagnetization curves were measured after magnetizing under different magnetic field strengths. The results show that for sintered NdFeB magnets, only a magnetization field of H_s=2J_s/μ₀ is required to saturate the magnets in the state of magnetic neutrality. For magnets with magnetized history, a magnetization field of H_s=3J_s/μ₀ is required to realize saturation magnetization.

Research and Design of NTP-Based Time Synchronization System for Parking Lot

YUAN Xiaodi, SONG Wenxia, ZHANG Yue

2021, 65(5): 96-100. doi: 10.12338/j.issn.2096-9015.2020.9057

Abstract(747)

HTML (368)

PDF(60)

Abstract:
To solve problems of time synchronization and monitoring of parking lot, an NTP-based time synchronization system for the parking lot was designed to synchronize and trace the time of the parking lot to UTC (NIM), and the filtering algorithm of NTP was optimized to reduce the impact caused by network link asymmetry, and the average time deviation after synchronization is reduced by 2.62 ms. The system runs on μC/OS real-time operating system, adopts NTP to synchronize time to time standard in near real-time through 4G wireless transmission, then transmits the synchronized time to the parking lot timing and charging system through bus or Ethernet, and uploads the time deviation to the monitoring platform at the same time, which effectively solves the time synchronization problem of parking lot timing and charging system.

Bayesian Uncertainty Evaluation for Accelerometer Calibration

HU Hongbo, LIU Aidong, ZUO Aibin, YANG Lifeng

2021, 65(5): 101-107, 61. doi: 10.12338/j.issn.2096-9015.2020.9051

Abstract(1016)

HTML (431)

PDF(111)

Abstract:
In this paper, Bayesian statistics is applied for the uncertainty evaluation of accelerometer calibration results. The process of analyzing measurement uncertainty based on GUM, GUM S1, and Bayesian statistics for linear measurement models is first presented to illustrate the differences in the analysis of the three methods. Combined with the vibration and shock calibration accelerometer data in actual work, the Bayesian statistics and GUM series methods with different prior distributions were used to analyze and compare the results. For the estimation of the reference value and its uncertainty for the key comparison in the field of shock acceleration, two different statistical models were developed using the Bayesian unpooled method and numerical method, on which the reference values and the corresponding uncertainties were calculated in combination with the Markov chain Monte Carlo method (MCMC) comparison, and the results were compared with those of the general method. The advantages and disadvantages of Bayesian statistics for uncertainty assessment are illustrated by the consistency and variability of the results obtained by the different methods.

Research on Chi-Square Statistics in Data Analysis of Inter-laboratory Comparison

HANG Chenzhe, XU Dinghua, YUAN Zundong

2021, 65(5): 108-114. doi: 10.12338/j.issn.2096-9015.2020.9042

Abstract(938)

HTML (407)

PDF(108)

Abstract:
The chi-square statistics, which can be used in the consistency test of comparison results and the estimation of reference value uncertainty, is a key statistical tool in data analysis of inter-laboratory comparison. In this study, under the condition that the comparison results obey Gaussian distribution with a common mean, a chi-square statistic containing generalized linear estimation is proposed, and the properties and distribution of the statistic are investigated. The statistic enables consistency testing and uncertainty estimation of general linear reference value estimates, and provides a statistical tool for a wider range of linear reference value estimates, which can be used for comparison data analysis or multi-laboratory fixed value measurements. As an example, against the limitation of using the traditional chi-square test for the arithmetic means based on the same uncertainty claimed by each laboratory, this method gives the chi-square statistic for the arithmetic mean under any combination of uncertainties, providing a new statistical analysis method for the extended application of this common linear reference value estimation.

Measurement Uncertainty Evaluation Method for Task-Oriented Coordinate Measuring Machines

WEI Hengzheng, WANG Weinong, PEI Limei, GUO Siyi, CUI Jianqiu, ZHENG Qingguo, GAO Tongling

2021, 65(5): 115-119, 54. doi: 10.12338/j.issn.2096-9015.2020.9053

Abstract(830)

HTML (242)

PDF(98)

Abstract:
To solve the problem of analyzing and synthesizing multiple uncertainty sources of coordinate measuring machines (CMMs), the 21-item geometric motion error separation method of CMMs based on spherical column and Monte Carlo simulation algorithm is used to realize the task-oriented measurement uncertainty evaluation of CMMs, and the traceability service system of CMMs based on “Internet+” is established. The provincial and municipal metrology institutes act as traceability network nodes to assist in data collection, including error parameters, environmental parameters, and instrument parameters. When the user needs to perform task-specific measurements, the measurement strategy is sent to the National Institute of Metrology and the results are fed back to the user via the network. This traceability network reduces the length of the traceability chain to a certain extent and realizes the flattening of measurement.

Uncertainty Analysis of Center-of-Mass Measurement Methods for the Mass Standard

ZHONG Ruilin, WU Di, WANG Jian, CAI Changqing, CHEN Hanghang, HU Manhong, JIAO Kai, DING Jing’an

2021, 65(5): 120-123, 131. doi: 10.12338/j.issn.2096-9015.2020.9016

Abstract(1072)

HTML (505)

PDF(81)

Abstract:
Highly accurate mass measurements require correction of mass differences introduced by the difference in center-of-mass height between the measured weight and the reference weight and therefore require measurement of the center-of-mass height of the mass standard. The center-of-mass height can be obtained by placing the mass standard in different positions on the weighing bridge with different orientations and calculating the change in the indicated value of the mass measurement instrument. In this paper, the uncertainty assessment of the 2 center-of-mass height measurement methods is studied, the source of each uncertainty is analyzed, the uncertainty evaluation method is given and discussed in conjunction with examples.

The Evaluation Method and Application Research of Measurement Uncertainty

JIN Haoyuan, LIU Jun

2021, 65(5): 124-131. doi: 10.12338/j.issn.2096-9015.2020.9002

Abstract(3703)

HTML (2339)

PDF(1226)

Abstract:
In this paper, the development history of measurement uncertainty, the current research status at home and abroad, and the possible future development directions are mainly introduced. The seven main evaluation algorithms are introduced and summarized, and the current situation of the application of measurement uncertainty in different fields is investigated and summarized. Finally, the applicable scenarios of different evaluation algorithms are summarized, and the possible future development directions of measurement uncertainty are discussed.

Analyses of Status Quo and Strategies of China’s Metrological Technical Assistance

ZHU Xiumei, GAO Wei, LI Mengwan, CAI Juan, YAN Liuying

2021, 65(5): 132-137. doi: 10.12338/j.issn.2096-9015.2020.9031

Abstract(544)

HTML (405)

PDF(108)

Abstract:
First this paper briefly introduces the metrological technical assistance implemented by some developed countries and international metrology organizations and reviews the metrological technical assistance carried out by National Institute of Metrology, China from 2015～2020. Then SWOT method is applied to analyze the internal strengths and weaknesses and external opportunities and challenges facing China’s metrological technical assistance, which leads to preliminary researches on the development strategies in this regard. Last practical suggestions are proposed with a view to providing a reference for better implementing China's metrological technical assistance.

2021 Vol. 65, No. 5

DynamicMORE+

ScienceMORE+