I. Content, Classification and Characteristics of Metrology
(1) The content of metrology
In the vast expanse of nature, all phenomena and substances have their unique ways of manifestation, and this manifestation is often accurately described and reflected through "quantity". It can be said that "quantity" is a special attribute of phenomena, objects, or substances. It enables us to distinguish different things in terms of their nature and precisely determine them in terms of quantity.
To gain a deeper understanding of this complex and diverse world and then use the knowledge they have acquired to benefit themselves, humans have no choice but to conduct detailed analysis and confirmation of various "quantities". This process includes both clarifying the nature of quantities, that is, understanding the specific meanings and characteristics represented by different quantities, and determining the quantity values, that is, accurately giving the specific numerical values of quantities. And metrology is undoubtedly one of the key means to achieve this goal.
In a broad sense, metrology is actually a complete process of qualitative analysis and quantitative confirmation of "quantities". It is committed to achieving the unity of units and ensuring the accuracy and reliability of measured values. Metrology, as a science about measurement, comprehensively covers every aspect of measurement theory and practice, regardless of the level of measurement uncertainty or the specific field in which the measurement is carried out.
To meet the diverse measurement needs of society in a cost - effective manner, it is necessary to carry out metrological management work from multiple dimensions such as legal systems, technology, and management. For a fairly long historical period, the main objects of metrology were concentrated on physical quantities. Throughout history, metrology was vividly referred to as weights and measures, mainly involving the measurement of length, volume, and mass. The instruments used at that time were relatively simple, mainly rulers, dou (a traditional Chinese unit of volume measure), and scales.
However, with the rapid development of technology, the continuous prosperity of the economy, and the sustained progress of society, the objects of measurement have gradually undergone significant changes. It is no longer limited to physical quantities but has gradually expanded to a wider range of fields such as engineering quantities, chemical quantities, physiological quantities, and even psychological quantities. Meanwhile, the content of measurement is also constantly enriched and expanded, which can generally be summarized into the following six aspects:
1. Measurement Units and Unit SystemsMeasurement units are the basic standards for measuring quantities, while unit systems are complete systems composed of a series of inter - related measurement units. Unified measurement units and scientific unit systems are the foundation for ensuring accurate and comparable measurements.
2. **Measuring instruments**: This includes measurement standards, measurement references, and working measuring instruments that realize or reproduce measurement units. The measurement reference is the highest standard in measurement, featuring extremely high accuracy and stability. The measurement standard serves as a basis for measurement within a certain scope. Working measuring instruments are tools directly used for daily measurements.
3. **Value Transmission and Traceability**: It includes various methods such as verification, calibration, testing, inspection, and detection. Value transmission is the process of gradually transmitting the measured values from the measurement standards to working measuring instruments. Traceability, on the other hand, is to link the measurement results with the measurement standards through an unbroken comparison chain with specified uncertainties, ensuring the accuracy and reliability of the measured values.
4. **Measurement of Physical Constants and Characteristics of Materials and Substances**: Accurately measuring physical constants and various characteristics of materials and substances is of great significance in fields such as scientific research and engineering technology.
5. **Measurement Uncertainty, Data Processing, and Measurement Theory and Its Methods**: Measurement uncertainty reflects the credibility of measurement results. Data processing is the process of analyzing and processing measurement data. Measurement theory and its methods provide theoretical support and operational guidelines for scientific and accurate measurements.
6. **Measurement Management**: It encompasses aspects such as measurement assurance and measurement supervision. Measurement assurance is committed to ensuring the accuracy and reliability of measurement results. Meanwhile, measurement supervision involves overseeing and managing measurement activities to guarantee that measurement work is carried out in a standardized and orderly manner.
(2) Classification of metrology
The influence of metrology permeates extensively into all fields of society. According to its role and status in society, metrology can be roughly divided into three categories: scientific metrology, engineering metrology, and legal metrology, which respectively represent the fundamental, applied, and public - welfare aspects of metrology.
1. **Scientific Metrology**: This is a fundamental, exploratory, and pioneering metrological scientific research. It usually actively adopts the latest scientific and technological achievements to precisely define and realize measurement units. In this way, it provides a solid and reliable measurement foundation for the latest scientific and technological development. Scientific metrology is like the cornerstone of the scientific and technological edifice, laying an important foundation for the progress of the entire scientific and technological field.
2. **Engineering Metrology**: Also known as industrial metrology, it mainly involves practical measurements in various engineering, industrial, and business settings. As the technological content of products continues to increase and their complexity grows day by day, in order to ensure the consistency and interchangeability of products in the context of global economic and trade, engineering metrology has become an indispensable and crucial part of the production - process control. It is like the eyes on the production line, constantly monitoring various measured values during the production process to ensure the stability and reliability of product quality.
3. **Legal Metrology**: This is a social public service that is compulsorily managed by the government or authorized institutions based on legal, technical, and administrative requirements. Its main purpose is to ensure the fairness and reliability of measurement work related to trade settlement, safety protection, medical and health care, environmental monitoring, resource control, social management, etc. As a fundamental national undertaking, metrology not only provides a solid technical foundation for the development of science and technology, the national economy, and national defense construction, but also can minimize potential disputes in many fields such as commerce, medical care, and safety, effectively safeguarding the legitimate rights and interests of consumers.
(3) Characteristics of measurement
Measurement has four prominent characteristics: accuracy, consistency, traceability, and legality.
1. **Accuracy**: It refers to the degree of agreement between the measurement result and the true value of the measured quantity. In the actual measurement process, due to the influence of various factors, a completely accurate measurement hardly exists. Therefore, when presenting a measured value, it is necessary to clearly state the uncertainty or the possible error range that meets the application purpose or actual needs. The so - called accuracy of a measured value actually means the accuracy that the measurement result shows within a certain measurement uncertainty, error limit, or allowable error range.
2. **Consistency**: It refers to the characteristic that, on the basis of a unified measurement unit, regardless of when and where the measurement is carried out, what measurement method is used, what measuring instrument is employed, and who conducts the measurement, as long as the relevant requirements are met, the measurement results should remain consistent within a given range. This means that the measurement results should have the characteristics of repeatability, reproducibility, and comparability. Just like a precise ruler, no matter who holds it, similar results can be obtained when measuring the same object.
3. **Traceability**: Any measurement result or the value of a measurement standard can be linked to a measurement reference through an unbroken comparison chain with a specified uncertainty. This characteristic enables all values of the same quantity to be traced back to the source of measurement along this comparison chain through calibration, ultimately leading to the same measurement reference (national reference or international reference). This ensures the accuracy and consistency of the values from a technical perspective.
4. **Legal compliance**: This is a characteristic of measurement in terms of legal protection. Since measurement involves all aspects of society, the accuracy and reliability of measurement values not only rely on advanced scientific and technological means but also require strong support from corresponding laws, regulations, and administrative management. Especially in areas that have a significant impact on the national economy and people's livelihood, involve public interests and sustainable development, or require special trust, the government must play a leading role in establishing a sound legal protection system for measurement.
It can be seen from this that there are obvious differences between metrology and general measurement. Measurement is merely a set of operations aimed at determining the quantity value. Generally, it does not possess and need not fully possess the above - mentioned characteristics. While metrology belongs to the category of measurement, it is more stringent in requirements than general measurement. From a narrow perspective, it can be considered that metrology is a standardized measurement that is related to the confidence level of measurement results and closely linked to measurement uncertainty.