Basic knowledge of metrology
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1. What is metrology? What is measurement? Metrology is the activity aimed at achieving unit consistency and ensuring the accuracy and reliability of measurement values; it encompasses a range of activities in science and technology, as well as in laws, regulations, and administrative management. Measurement is a set of operations carried out to determine a quantity. 2. What are the contents of measurement? The contents of metrology can generally be summarized into the following six aspects: units of measurement and measurement systems; measuring instruments, including those that serve as benchmarks for realizing units of measurement, as well as standard measuring instruments and working measuring devices; value transfer and traceability, including verification, calibration, testing, inspection, and examination; determination of physical constants and properties of materials and substances; measurement uncertainty, data processing, and measurement theory along with its methods; and metrological management, including metrological assurance and supervision. 3. How are measurements classified? What are its features? Metrology is divided into three categories: scientific metrology, engineering metrology, and legal metrology, which represent the fundamental, applied, and public welfare aspects of metrology respectively. The characteristics of measurement include accuracy, consistency, traceability, and legality. 4. How is China’s metrological regulatory framework structured? China’s metrology regulatory framework consists of three parts: 1) The Metrology Law of the People’s Republic of China; 2) Metrology administrative regulations formulated (or approved) by the State Council, as well as local metrology regulations established by the people’s governments of provinces, municipalities directly under the Central Government, and autonomous regions; 3) Metrology management methods and technical specifications formulated by the metrology administrative department of the State Council, departmental metrology management methods formulated by relevant departments of the State Council, and local metrology management methods formulated by the metrology administrative departments at or above the county level. 5. What is the basic content of the Metrology Law? The basic contents of the Metrology Law are: 1) The purpose of metrology legislation; 2) Scope of application; 3) Metric system; 4) Management of measuring instruments; 5) Metrological supervision; 6) Metrological authorization; 7) Metrological certification; 8) Resolution of metrological disputes; 9) Legal responsibilities in metrology. 6. What is calibration? What is the basis for calibration? Under specified conditions, a set of operations intended to determine the relationship between the value indicated by a measuring instrument or measuring system, or the value represented by a physical measuring tool, and the corresponding value reproduced by a standard is called calibration. Calibration is based on calibration specifications or methods, which should generally be standardized; in special cases, they can also be established independently. 7. What is calibration? What is the basis for the verification? What are the areas subject to mandatory inspection in our country? The calibration of measuring instruments refers to the procedure for determining and confirming whether such instruments meet all legal requirements; it includes inspection, labeling, and/or issuing a calibration certificate. Verification has a legal basis, and its target are measuring instruments within the scope of legal regulation. The basis for verification is the metrological verification regulations approved and published in accordance with legal procedures. According to our country’s regulations, the working measuring instruments listed in the Detailed Catalogue of Working Measuring Instruments Subject to Mandatory Verification in the People’s Republic of China, and those used in trade settlement, safety protection, medical and health care, and environmental monitoring, fall under the scope of **mandatory verification. In addition, our country also mandates mandatory verification for national social public metrological standards, as well as various highest metrological standards used by departments and enterprises (institutions). 8. What is value traceability? The property that enables the value of a measurement result or a measurement standard to be linked to a specified reference standard (usually a **metrological standard or international metrological standard**) through an unbroken chain of comparisons with defined uncertainties is known as traceability of measurement values. 9. What is a unit of measurement? A unit of measurement is a specific quantity that is defined and adopted to quantitatively express the magnitude of the same kind of quantity. 10. The composition of the legal units of measurement in our country. Legal units of measurement in the People’s Republic of China: Units of the International System of Units (SI). SI units: There are 7 base SI units. Derived SI units: There are 21 derived SI units, including auxiliary SI units with specific names. Combined forms of derived SI units: There are 20 multiple units of SI units, including decimal multiples and decimal fractions of SI units. **There are 16 non-SI units that have been selected as legal units of measurement. Units that are combinations of these units. International System of Units (SI). Quantity, Name of the unit, Unit symbol: Length – l(L); Meter – m. Mass – m; Kilogram – kg. Time – t; Second – s. Electric current – I; Ampere – A. Thermodynamic unit – T; Kelvin – K. Amount of substance – n(v); Mole – mol. Luminous intensity – I(Iv); Candela – cd
11. What are the basic usage methods of the legal units of measurement in our country? Basic usage of the legal units of measurement in our country: 1) Names of the legal units of measurement. 2) Symbols for legal units of measurement and prefixes. 3) Rules for the use of prefixes in legal units of measurement. 12. What is a measuring instrument? How is it classified? A measuring instrument (measuring device) is a device used for measurement, either alone or in conjunction with auxiliary equipment. 1) Display-type measuring instruments 2) Comparative measuring instruments 3) Integral measuring instruments 4) Accumulative measuring instruments 13. What are measurement systems and measurement equipment? A measurement system refers to a system formed by assembling a complete set of measuring instruments and related equipment for specific measurement purposes. Measurement equipment refers to a general term for measuring instruments, measurement standards, reference materials, auxiliary equipment, and the data necessary for conducting measurements. 14. What aspects are included in the control of measuring instruments? Control includes one, two, or all of the following actions regarding measuring instruments: 1) type approval, 2) calibration, 3) inspection. 15. What are the nominal range, span, and measurement range? The nominal range refers to the range of readings that can be obtained when the operating elements of a measuring instrument are set to specific positions. The range is the absolute value of the difference between the upper and lower limits of the nominal range. The measurement range (operating range) refers to the range of measured values for which the error of the measuring instrument remains within specified limits. 16. What are rated operating conditions, extreme conditions, and reference conditions? Rated operating conditions refer to the normal operating conditions of a measuring instrument, that is, the conditions under which its specified metrological characteristics remain within given limits. Extreme conditions refer to the extreme conditions that a measuring instrument can withstand without its specified metrological properties being impaired or reduced, and still be able to operate under its rated operating conditions. Reference conditions refer to the operating conditions under which a measuring instrument is used in performance tests or during calibration, verification, and double comparison, that is, the standard operating conditions. 17. What are indicated error and maximum allowable error? The indication error of a measuring instrument is the difference between the value shown by the instrument and the true value of the corresponding input quantity. The maximum allowable error of a measuring instrument refers to the error limit permitted for a given measuring instrument as specified by standards, regulations, etc. 18. What is sensitivity? The change in the response of a measuring instrument divided by the corresponding change in the stimulus is called sensitivity. The sensitivity value should be appropriate for the purpose of measurement; a higher value is not necessarily better. 19. What is resolution? The smallest difference in values that a display device can effectively distinguish is referred to as the resolution of the display device. The resolution of analog display devices is usually half the value of the scale division. For digital display devices, the resolution is one digit of the last digit. 20. What are stability and drift? Stability generally refers to the ability of a measuring instrument to maintain its metrological properties constant over time. Drift is the slow change in the metrological characteristics of a measuring instrument.
21. What are the principles for selecting measuring instruments? The selection principle is based on technical and economic considerations, ensuring that its measurement characteristics adequately meet the prescribed requirements – being sufficient without being excessive. 22. What is accuracy? Measurement accuracy refers to the degree of consistency between the measurement result and the value being measured. Measurement accuracy is a qualitative concept, generally expressed in terms of an accuracy grade, and should not be directly associated with numbers. 23. What is the repeatability of measurement? Reproducibility? Under the same measurement conditions, the consistency of the results obtained from multiple consecutive measurements of the same quantity being measured is known as the repeatability of the measurement results. Under changed measurement conditions, the consistency among the measurement results of the same quantity being measured is known as the reproducibility of the measurement results. 24. How to conduct measurement error analysis? What is the difference between error and uncertainty? Error = Measurement result – True value = (Measurement result – Population mean) + (Population mean – True value) = Random error + Systematic error. Measurement uncertainty represents the variability of the value assigned to the quantity being measured; it is related to the degree of understanding people have of that quantity, and it is an interval obtained through analysis and evaluation. Measurement error is the difference that indicates how much the measurement result deviates from the true value; it exists objectively, but it cannot be determined with accuracy. 25. What are the sources of measurement uncertainty? 1) The definition of the quantity being measured is incomplete or imperfect ； 2) The method for defining the quantity to be measured is not ideal ； 3) The samples taken are not representative enough; that is, the samples being measured cannot represent the quantity in question ； 4) Inadequate understanding of the impact of the environment on the process being measured, or imperfect measurement and control of environmental conditions ； 5) There is a human-induced bias (offset) in the readings of the simulator ； 6) The resolution or discrimination capability of the measuring instrument is insufficient ； 7) The values assigned to measurement standards and reference materials are inaccurate ； 8) The constants and other parameters used for data calculation are inaccurate ； 9) Approximations and assumptions of the measurement methods and procedures ； 10) The variation in the repeated measurements of the quantity being measured under conditions that appear to be exactly the same. 26. What is standard uncertainty? The measurement uncertainty expressed in terms of standard (partial) deviation is called the standard uncertainty. 27. What is experimental standard (bias) deviation? When N measurements are taken on the same measured quantity, and the quantity S, which characterizes the dispersion of the measurement results, is calculated using the following formula, it is referred to as the experimental standard deviation. 28. What is Type A evaluation of uncertainty? Class B assessment of uncertainty? Evaluating the standard uncertainty using statistical analysis on the observed columns is referred to as Category A evaluation of uncertainty. Evaluating the standard uncertainty using a method different from that of statistical analysis on the observed data is called Category B evaluation of uncertainty, sometimes also referred to as Category B uncertainty assessment. 29. What is the combined standard uncertainty? Expanded uncertainty? When the measurement result is obtained from the values of several other quantities, the standard uncertainty of the measurement result is equal to the square root of the sum of the squares of the variances and covariances of these other quantities; this is known as the combined standard uncertainty. The expanded uncertainty is the measurement uncertainty expressed as a multiple of the standard (bias) deviation or as the half-width of an interval indicating the confidence level. 30. How are measurement uncertainties classified? Expanded uncertainty, standard uncertainty, measurement uncertainty, Type A standard uncertainty, combined standard uncertainty, Type B standard uncertainty, U(k=2,3), Up (confidence probability)
31. What components make up the measurement control system? The measurement control system consists of two parts: 1) the metrological verification of measurement equipment ； 2) Measurement process control. 32. What is measurement recognition? Calibration verification refers to a set of operations carried out to ensure that measuring equipment meets the intended requirements for use. The confirmation process has two inputs: user metering requirements and measurement device characteristics ； The output of the determination process is the verification status of the measuring equipment. 33. What is measurement system analysis, and what is the most fundamental question when evaluating a measurement system? Measurement system analysis involves using some effective principles, methods, and tools from the field of statistical process control to understand the various factors in a measurement system that affect the variability of measurement results, thereby ensuring the quality of that measurement system. Measurement system analysis can employ numerical analysis techniques, as well as the use of graphical techniques. When evaluating a measurement system, three fundamental questions are whether it has sufficient resolution, whether it maintains statistical stability over time, whether it falls within the expected range, and whether it meets the requirements for process analysis or control. 34. What is data rounding? For a given number, its excess digits are discarded according to the requirements regarding the number of digits to be retained. Following certain rules, a number that is an integer multiple of the rounding interval (referred to as the rounded value) is chosen to replace the original number that is to be rounded. This process is known as data rounding, or also referred to as rounding a number to the nearest whole number.