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I. Concept of metrology Metrology is the activity aimed at achieving unit consistency and accurate, reliable measurement values. All activities such as science and technology, legal systems, and management that aim to achieve uniformity in measurement units and accurate and reliable measurements fall within the scope of metrology. In ancient times, measurement was referred to as weights and measures, and this practice has a history of several thousand years. Its original meaning was the measurement of length, volume, and mass, with the main instruments being rulers, measuring bowls, and scales. In human activities such as production, daily life, trade, and scientific research, hundreds of millions of measurements are carried out every day. Humans use measurement tools to understand the world. For example, in ancient times, people measured time, distance, area, volume, and weight in order to plan agricultural activities, hunt within designated areas, and exchange food and valuable items. The methods used were relying on their sense organs and natural phenomena to determine the duration of time and the size of objects. To enable the results of such measurements to have social value, it is necessary to ensure that the measurement tools and methods are accurate and reliable, as well as to guarantee consistency in the measurement results across society; this complex process is known as metrology. The scope of modern metrology has far exceeded simple measurements of length, weight, and volume. With the development of social productivity and advancements in science and technology, the range of measurements is constantly expanding, the accuracy of measurements is improving, and measurement tools as well as measurement techniques are continually evolving. After the 1960s, the application of technologies such as microelectronics, quantum mechanics, polymer synthesis, bioengineering, and ocean engineering, along with the modernization of production and the expansion of international trade, led to the gradual development of metrology into an emerging interdisciplinary field—metrology. II. Characteristics of metrology Metrology has the following basic characteristics: accuracy, consistency, traceability, and legality. 1. Precision is the main characteristic of measurement. Measurement not only requires specifying the value of the quantity being measured, but also its error range (uncertainty), that is, its precision. Accuracy refers to the degree of closeness between the measurement result and the true value being measured. A result that has only a magnitude but no precision is not a measurement result. The so-called unification of measurement values also refers to unification within a certain range of precision. 2. Consistency: It refers to the fact that, regardless of the time or place, the instrument used, the method employed, or the person carrying out the work, as long as it is done in accordance with the relevant metrological requirements, the measurement results obtained should be consistent within the specified error range. Otherwise, it will lose its social significance; the consistency of measurement applies both internationally and domestically. 3. Traceability: Traceability is the property that enables the value of a measurement result or a measurement standard to be linked to a specified reference standard, usually one that is associated with a **measurement standard or an international measurement standard, through an unbroken chain of comparisons with defined uncertainties. It is the technical foundation of “precision” and “consistency”. Since any precision and consistency are relative, tracing the origin can bring metrology into relative alignment with people’s understanding, thereby ensuring the basic integrity of metrology’s \"precision\" and \"consistency\". In daily practical work, since the objectives to be achieved and the required conditions vary, the requirements for measurement results also differ. For a **, all measurement values should be traced back to the **benchmark (or standard); on a global scale, they should be traced back to international benchmarks (or standards), otherwise it will lead to confusion in measurement values. 4. Legality: For the accurate consistency of measurement values, not only certain technical capabilities and methods are required, but also relevant laws and regulations to provide support. This is determined by the social nature of measurement; especially when it comes to matters related to the national economy and people’s livelihoods, measurements that have a direct impact on people’s lives must be guaranteed by legal frameworks. Otherwise, value transfer will not achieve consistency, and it will be difficult to fulfill the role of measurement. In short, metrology is measurement that ensures the accuracy and uniformity of quantities; it originates from measurement, but is stricter than ordinary measurement. III. The Role of Metrology in the National Economy As social productivity increases, the market economy continues to develop, and science and technology advance, the scope and concepts of metrology have also changed accordingly. While early forms of measurement were limited to the concepts of weights and measures and confined to the realm of commercial trade, modern measurement has penetrated into all areas of the national economy. Whether it is in industrial and agricultural production, national defense construction, scientific experiments, domestic and international trade, or people’s daily lives, measurement is indispensable. It has become an important foundation and tool for scientific research, economic management, and social governance. The level of measurement has become one of the important indicators for measuring the degree of technological, economic, and social development of a **. Measurement has duality in terms of disciplines. From a scientific and technological perspective, it belongs to the natural sciences; while understood in terms of concepts from economics, management, and sociology, it falls within the category of social sciences. Therefore, metrology has a dual nature in both natural sciences and social sciences. This property objectively determines its important position and role in the national economy. 1. Metrology and people’s lives: Metrology is closely related to people’s lives, as the production and exchange of goods are characteristics of contemporary society. The accuracy of measuring instruments used in daily transactions, whether household electricity meters, water meters, and gas meters are of proper quality, and whether public transportation schedules are accurate – all these factors are directly related to people’s vital interests. Food is an essential item for people's lives, as it is directly related to their survival and health. Additives, colors, flavorings, preservatives, and other substances used in the food production process must all be tested and measured; otherwise, they can lead to adverse effects that harm people's health. Therefore, measurement and testing are indispensable throughout the production, storage, and processing of food and food products. For the freezing and preservation of agricultural and sideline products, as well as meat, eggs, and vegetables, it is necessary to control the freezing temperature, and this can only be ensured through measurement and testing. In the field of healthcare, the role of metrology and testing becomes even more important. Modern medicine relies on quantitative testing for the prevention, diagnosis, and treatment of diseases, such as measuring body temperature, blood pressure, performing electrocardiograms and electroencephalograms, using magnetic resonance imaging for diagnosis, and conducting various laboratory tests. Inaccurate measurement and testing data can also lead to serious consequences. With the development of modern technology, the level of measurement and testing is continuously improving, and new types of high-precision medical diagnostic and treatment instruments will keep emerging. 2. Metrology and industrial and agricultural production: The role and significance of metrology in industrial and agricultural production are evident; it serves as the technical foundation for scientific production. From the selection of raw materials to the controlled feeding of materials, from the monitoring of the production process to the inspection of product quality, measurement is essential in every step. High-quality raw materials, advanced processing equipment, and modern measurement and testing methods are the three pillars of modern production. The reason why products manufactured by advanced production lines abroad have high quality and excellent standards is largely due to the full utilization of online measurement and monitoring technologies. Agricultural production, especially modern agricultural production, also must be guaranteed by measurement. To practice scientific farming, it is necessary to measure parameters such as soil pH, salt content, moisture, organic matter, as well as the levels of nitrogen, phosphorus, and potassium, along with temperature. Processes such as seed selection using saline solutions, germination at appropriate temperatures, and centrifugal dehydration all rely on precise measurement. In field management, it is necessary to have an appropriate planting density as well as to practice intercropping and relay cropping, which requires measuring factors such as the light intensity available for the plants’ photosynthesis. It has been proven that both scientific production and the development and application of new technologies rely on metrological testing. 3. Metrology and Defense Science: Metrology plays a very important role in defense development. Defense-related advanced systems are complex and involve many fields of science and technology; they present high technical challenges, which requires that the metrological parameters have high precision, wide ranges, and broad frequency bands. Therefore, metrology is even more crucial in the field of advanced defense technologies. For advanced defense technology systems, the working environment is quite special; effective measurement and testing often need to be carried out on-site, and this presents significant challenges. For example, during transportation, launch, operation, and recovery, aircraft have to withstand a series of harsh conditions such as vibrations, shocks, high temperatures, low temperatures, and intense radiation. The development of nuclear weapons such as atomic bombs and hydrogen bombs, as well as experiments to test their explosive power, impose special requirements on metrology. During the Gulf War in 1991, accurate measurement and testing were crucial technical guarantees for the Patriot missiles to successfully intercept Scud missiles. In national defense construction, metrology and testing constitute an extremely important technical foundation, playing a significant role in providing technical support; they offer reliable basis for commanders to make judgments and decisions. 4. Metrology and Trade: Metrology plays a very important role in trade. From the simple exchange of goods in history to today’s sophisticated international trade, metrology is essential at every stage. In transactions between different ** and various ethnic groups, there must be certified, standardized measuring instruments to ensure the fairness and legitimacy of such transactions. In accordance with international practices and the terms of the contract, the quantity of goods is generally determined based on the measurement results after they are brought ashore, and this serves as the basis for settlement. In the past, when exporting crude oil, our country lacked accurate and reliable measurement methods. To avoid claims and fines, it was common to overload the shipments, resulting in a great deal of crude oil being wasted; in some cases, shipowners even filed claims on the grounds of excess weight. If we raise the measurement accuracy to a level close to international standards, we can avoid unnecessary economic losses and enhance our country’s reputation in the field of metrology on the international stage. Metrology is the main technical guarantee for ensuring product quality and enhancing the competitiveness of goods in the market. It is also one of the important tools for international trade measurement. The level of measurement has become an important indicator for measuring the degree of progress in **scientific, economic, and social development. Following the signing of the WTO agreements, as China’s foreign trade continues to expand, the requirements for measurement accuracy will also become increasingly stringent. 5. Metrology and Science and Technology: Science and technology are an important foundation for human survival and development; without them, there would be no modern humanity. Metrology itself is a part of science and technology. The emergence of scientific and technological achievements in recent years, such as atomic colliders, deep-sea exploration robots, Earth resource satellites and satellite tracking and control technologies, the Shenzhou experimental spacecraft in aerospace engineering, and the successful development of hydrogen-storing nanocarbon tubes, demonstrates the advanced level of modern scientific and technological development in our country. The emergence of these advanced achievements marks a new stage in the development of measurement technology in our country, as well as pushing its level into a new phase. Contemporary technological innovation relies on requirements for measurement standards and testing techniques; especially in fields such as electronic materials, high-precision manufacturing, and optomechanical systems, there are extremely high demands for accuracy. Meanwhile, the emergence of new technologies and achievements drives the development of measurement technologies. Over the past 50 years, metrology agencies have gone through changes, evolving from **Metrology Bureaus**, to **Technical Supervision Bureaus**, and then to **Quality and Technical Supervision Bureaus**. With each of these changes, metrological activities have been gradually strengthened and developed; the scope of metrology has expanded, and the importance and role of metrological work have grown even further. Especially in recent years, metrological work has taken serving the \"two fundamental transformations\" as its guiding principle, closely integrating with the important tasks of economic construction and social development; it addresses the new challenges that arise under a market economy system, thereby providing reliable technical support for economic construction and social progress. IV. Measurement Principles and Methods 1. Overview Measurement is a set of operations aimed at determining a quantitative value. It is an essential means for humans to understand and transform the objective world; it involves obtaining quantitative information from objective entities in order to achieve a numerical representation of certain properties of materials or objects. It is a process in which known quantities of the same type are used to directly or indirectly compare with the unknown quantity to be measured, ultimately yielding a ratio of the measured value to the unit of measurement. Due to the imperfections in the entire measurement process and the inevitability of measurement errors, the measurement results are usually merely estimates of the true value of what is being measured. Therefore, when presenting such results, it is necessary to indicate whether they represent displayed values or averages; whether corrections have been applied or not; how the uncertainty was determined; and what the confidence level and degrees of freedom are. 2. Measurement methods ① Direct measurement method: In the direct measurement method, the value displayed by the measuring instrument is the value of what is being measured; for example, using an electronic scale to determine the weight of goods. If the unknown quantity to be determined is Y and the observed value is X, then the mathematical model is expressed as Y=X. ②Indirect measurement method: The indirect measurement method involves determining the value of the quantity being measured by measuring other quantities that have a functional relationship with it; for example, average speed is calculated by measuring the distance traveled and the time taken to cover that distance. Expressed in mathematical terms as ③ combined measurement method. The combined measurement method is only applicable to quantities that can be added together, such as gauge blocks, capacitors, resistors, etc.; it is difficult to apply this method to quantities that cannot be added together, such as temperature, hardness, roughness, color, sound level, etc. Combined measurement involves combining m quantities to be determined into n groups (n > m) in different ways, measuring each of the n combinations separately, and then using least squares method to determine the value of each quantity to be determined. ④Comparative measurement: In a broad sense, any measurement is a comparative measurement. However, the comparative measurement referred to here is a method in which, using techniques such as substitution, exchange, differential, or zero-point methods, the quantity to be measured is compared with known quantities of the same type that have the same or similar values, using measuring instruments or devices, and then a value is assigned to the quantity to be measured. In addition, there are also classifications based on measurement accuracy, such as equal-accuracy measurement and unequal-accuracy measurement. There are also classifications based on the state of the object being measured, such as static measurement, dynamic measurement, transient measurement, as well as online measurement in industrial settings, contact measurement, and non-contact measurement. 3. Measurement principle: The measurement principle is the scientific basis of measurement. For example, laser interference is used to measure length, the piezoelectric effect of crystals is used to measure dynamic forces and accelerations, the pyroelectric effect is used to measure temperature, the Josephson effect is used as a substitute for standard batteries, the photopiezoelectric effect is used to measure illuminance, and the radar Doppler effect is used to measure velocity, while the laser Doppler effect is used to measure impacts, among other things. Source: Digital display instruments http://yunrun.com.cn/product/