(1) Metrology can be classified into the following three categories based on its field:
1. Legal Metrology
Legal metrology is carried out to ensure public safety, national economic and social development. It is enforced by the government or authorized entities according to legal, technical, and administrative needs. This includes explicit regulations and specific requirements for measurement units, measuring instruments (especially measurement standards and benchmarks), measurement methods, and the professional skills of measurement personnel. Legal metrology mainly involves mandatory measurements in areas with interests or special circumstances, such as safety protection, healthcare, environmental monitoring, and trade settlement. For example, it includes the metrology of weighing instruments, pressure gauges, electric meters, water meters, gas meters, and blood pressure monitors.
2. Scientific Metrology
Scientific metrology mainly refers to fundamental, exploratory, and advanced scientific research in metrology, such as studies on measurement units and systems, measurement standards and benchmarks, physical constants, measurement errors, measurement uncertainty, and data processing. Scientific metrology is typically a primary task of metrology research institutions, particularly national metrology research organizations.
3. Industrial Metrology
Industrial metrology, also known as engineering metrology, refers to applied metrology in various engineering and industrial enterprises. This includes measurements related to energy and raw material consumption, monitoring of process flows, and testing of product quality and performance. Industrial metrology is widely applicable and commonly practiced across various industries.
(2) According to metrology, it can be divided into the following ten categories:
1. Geometric Measurement
Geometric measurement, commonly referred to as length measurement, is one of the earliest developed fields of metrology. In summary, it involves the geometric dimensions, shapes, and positions of objects, which are the “three major elements” of geometric measurement. The basic parameters of geometric measurement are length and angle, along with derived parameters such as straightness, surface roughness, roundness, cylindricalness, slope, taper, involute, and spiral. It also includes calibration of universal measuring tools, optical instrument calibration, and measurement of special parts in production. The basic unit of geometric measurement is the “meter”, symbolized as “m”, which is one of the seven base units of the International System of Units.
Common measuring instruments used in geometric measurement include: gauge blocks, angle blocks, rulers, micrometers, calipers, dial indicators, depth gauges, flatness gauges, levels, measuring microscopes, projectors, roundness gauges, surface profile gauges, gear measurement instruments, length measuring instruments, and coordinate measuring machines.
2. Temperature Measurement
Temperature measurement refers to measuring the degree of hotness or coldness of an object using the thermal effects of various substances. It includes ultra-low temperature, low temperature, medium temperature, high temperature, ultra-high temperature, and heat. The unit of temperature measurement is Kelvin, symbolized as “K”.
Common measuring instruments used in temperature measurement include: mercury thermometers, thermocouples, semiconductor point thermometers, clinical thermometers, dynamic circle instruments, temperature indicating and regulating instruments, temperature monitoring instruments, automatic temperature recorders, drying ovens, constant temperature and humidity chambers, incubators, and high and low temperature test chambers.
3. Mechanical Measurement
Mechanical measurement includes measurements of mass, volume, density, pressure, vacuum, force, torque, hardness, impact, speed, flow, vibration, and acceleration. Common measuring instruments used in mechanical measurement include: weights, balances, belt scales, weighing instruments, standard hardness blocks, hardness testers, tensile testers, force gauges, load cells, material testing machines, fatigue testing machines, torque meters, torque wrenches, torque wrench calibration devices, torsion testing machines, dynamometers, accelerometers, speed sensors, pressure gauges, blood pressure monitors, pressure meters, pressure transmitters, fuel dispensers, densitometers, flow meters, water meters, gas meters, radar speed meters, speed meters, and tachometers.
4. Electromagnetic Measurement
Electromagnetic measurement involves measuring various electromagnetic physical quantities using various electromagnetic standards and instruments based on electromagnetic principles. It includes current, electromotive force, resistance, inductance, capacitance, magnetic field strength, and magnetic flux. Common measuring instruments used in electromagnetic measurement include: standard batteries, standard voltage sources, standard current sources, resistors, capacitors, transformers, resistance boxes, ammeters, voltmeters, wattmeters, megohmmeters, fluxmeters, electric energy meters, electric energy meter calibration devices, DC potentiometers, DC bridges, AC bridges, and multimeters.
5. Radio Measurement
Radio measurement refers to measuring all electrical characteristics within the frequency range used by radio technology, from ultra-low frequency to microwave. This includes high-frequency voltage, power, phase, pulse, impedance, noise, and distortion. Common measuring instruments used in radio measurement include: signal generators, modulation analyzers, audio analyzers, distortion measurement instruments, oscilloscopes, function generators, electroencephalographs, electrocardiographs, sweep frequency analyzers, and cardiac monitoring devices.
6. Time and Frequency Measurement
Time and frequency measurement are fundamental parameters describing the development and changes of various objective phenomena in time and space. Time and frequency are two different aspects of periodic phenomena and are mathematically reciprocal to each other, sharing the same reference. The unit of measurement is seconds—”s”. Common measuring instruments used in time and frequency measurement include: frequency synthesizers, quartz crystal oscillators, frequency counters, general electronic counters, stopwatches, time interval generators, electronic timers, and telephone timing billing devices.
7. Ionizing Radiation Measurement
Also known as radioactive measurement, ionizing radiation measurement refers to measuring radiation that can directly or indirectly cause ionization (X-rays, γ-rays, X-ray radiation, radium, and neutron radiation from uranium and thorium elements). Ionizing radiation measurement is divided into intensity measurement and dose measurement. It is widely used in healthcare (such as isotopes and liver scans that require accurate dose diagnosis), environmental monitoring, nuclear power generation, exploration, flaw detection, oil pipeline decontamination, and agricultural breeding applications. Common measuring instruments used in ionizing radiation measurement include: working γ-ray radiation sources, medical CT scanners, radiation processing dose meters, X-ray flaw detectors, X-ray protective instruments, dose pens, γ-radiation protective instruments, medical diagnostic X-ray sources, solid working dose meters, chemical working dose meters, and X-ray meters.
8. Optical Measurement
Optical measurement mainly involves measuring light intensity, luminous flux, brightness, illuminance, chromaticity, radiance, sensitivity, and laser. Optical measurement is widely applied, especially in modern building construction, which requires measuring light intensity to meet specified illuminance standards. In spectroscopy, measuring light intensity in spectra is essential. Additionally, the sensitivity of film and photographic paper, the refractive index of optical glass, dyeing, pigments, movies, and television all require accurate light intensity, chromaticity, and color temperature measurements. In national defense, accurate measurements of lasers, ultraviolet light, and infrared light are crucial for missile guidance and special photography. The basic unit of optical measurement is the candela, symbolized as “cd”. Common measuring instruments used in optical measurement include: illuminance meters, brightness meters, standard color plates, color difference meters, spectrophotometers, medical laser sources, focal meters, Abbe refractometers, corneal contact lenses, pupillometry devices, phoropters, standard lenses, spectrometers, gloss meters, and automobile headlight testers.
9. Acoustic Measurement
Acoustic measurement specifically studies the generation, transmission, reception, and influence characteristics of sound waves in materials. Sound intensity, sound pressure, and sound power are three important basic parameters in acoustic measurement, with sound pressure being the most widely used. Acoustic measurement is involved in communication, broadcasting, film, television, building construction, healthcare, navigation, coastal defense, language, music, agriculture, and various scientific fields. Common measuring instruments used in acoustic measurement include: microphones, sound level meters, ultrasonic flaw detectors, ultrasonic thickness gauges, medical ultrasound sources, ultrasonic power sources, audiometers, and hearing aids.
10. Chemical Measurement