溫度測量

A medical/clinical thermometer showing the temperature of 38.7 °C（101.7 °F）

溫度測量 (亦即測溫術) 是一個描述測量此時此地 溫度 以立即或稍後估計的過程。由重複標準化測量組成的數據集可被用於評估溫度趨勢。

歷史

参见：溫度計、溫度、溫度標準、測溫器和高溫計

Attempts at standardized temperature measurement prior to the 17th century were crude at best. For instance in 170 AD, physician Claudius Galenus mixed equal portions of ice and boiling water to create a "neutral" temperature standard. The modern scientific field has its origins in the works by Florentine scientists in the 1600s including Galileo constructing devices able to measure relative change in temperature, but subject also to confounding with atmospheric pressure changes. These early devices were called thermoscopes. The first sealed thermometer was constructed in 1654 by the Grand Duke of Toscani, Ferdinand II. The development of today's thermometers and temperature scales began in the early 18th century, when Gabriel Fahrenheit produced a mercury thermometer and scale, both developed by Ole Christensen Rømer. Fahrenheit's scale is still in use, alongside the Celsius and Kelvin scales.

技術

Many methods have been developed for measuring temperature. Most of these rely on measuring some physical property of a working material that varies with temperature. One of the most common devices for measuring temperature is the glass thermometer. This consists of a glass tube filled with mercury or some other liquid, which acts as the working fluid. Temperature increase causes the fluid to expand, so the temperature can be determined by measuring the volume of the fluid. Such thermometers are usually calibrated so that one can read the temperature simply by observing the level of the fluid in the thermometer. Another type of thermometer that is not really used much in practice, but is important from a theoretical standpoint, is the gas thermometer.

Other important devices for measuring temperature include:

• Thermocouples
• Thermistors
• Resistance temperature detector (RTD)
• Pyrometer
• Langmuir probes (for electron temperature of a plasma)
• Infrared thermometer
• Other thermometers

One must be careful when measuring temperature to ensure that the measuring instrument (thermometer, thermocouple, etc.) is really the same temperature as the material that is being measured. Under some conditions heat from the measuring instrument can cause a temperature gradient, so the measured temperature is different from the actual temperature of the system. In such a case the measured temperature will vary not only with the temperature of the system, but also with the heat transfer properties of the system.

What thermal comfort humans, animals and plants experience is related to more than temperature shown on a glass thermometer. Relative humidity levels in ambient air can induce more or less evaporative cooling. Measurement of the wet-bulb temperature normalizes this humidity effect. Mean radiant temperature also can affect thermal comfort. The wind chill factor makes the weather feel colder under windy conditions than calm conditions even though a glass thermometer shows the same temperature. Airflow increases the rate of heat transfer from or to the body, resulting in a larger change in body temperature for the same ambient temperature.

The theoretical basis for thermometers is the zeroth law of thermodynamics which postulates that if you have three bodies, A, B and C, if A and B are at the same temperature, and B and C are at the same temperature then A and C are at the same temperature. B, of course, is the thermometer.

The practical basis of thermometry is the existence of triple point cells. Triple points are conditions of pressure, volume and temperature such that three phases are simultaneously present, for example solid, vapor and liquid. For a single component there are no degrees of freedom at a triple point and any change in the three variables results in one or more of the phases vanishing from the cell. Therefore, triple point cells can be used as universal references for temperature and pressure (see Gibbs phase rule).

Under some conditions it becomes possible to measure temperature by a direct use of the Planck's law of black-body radiation. For example, the cosmic microwave background temperature has been measured from the spectrum of photons observed by satellite observations such as the WMAP. In the study of the quark–gluon plasma through heavy-ion collisions, single particle spectra sometimes serve as a thermometer.

非侵入性測溫術

During recent decades, many thermometric techniques have been developed. The most promising and widespread non-invasive thermometric techniques in a biotech context are based on the analysis of magnetic resonance images, computerized tomography images and echotomography. These techniques allow monitoring temperature within tissues without introducing a sensing element. In the field of reactive flows (e.g., combustion, plasmas), laser induced fluorescence (LIF), CARS, and laser absorption spectroscopy have been exploited to measure temperature inside engines, gas-turbines, shock-tubes, synthesis reactors etc. The capability of such optical-based techniques include rapid measurement (down to nanosecond timescales), notwithstanding the ability to not perturb the subject of measurement (e.g., the flame, shock-heated gases).

Surface air temperature

主条目：Air temperature

关于temperature measurements made by instruments，请见「Instrumental temperature record」。

关于temperature changes relevant to historical climate change over Earth's geologic past (distinguished from recent climate change)，请见「Temperature record」。

The temperature of the air near the surface of the Earth is measured at meteorological observatories and weather stations, usually using thermometers placed in a shelter such as a Stevenson screen, a standardized well-ventilated white-painted instrument shelter. The thermometers should be positioned 1.25–2 m above the ground. Details of this setup are defined by the World Meteorological Organization (WMO).

A true daily mean could be obtained from a continuously-recording thermograph. Commonly it is approximated by the mean of discrete readings (e.g. 24 hourly readings, four 6-hourly readings, etc.) or by the mean of the daily minimum and maximum readings (though the latter can result in mean temperatures up to 1 °C cooler or warmer than the true mean, depending on the time of observation).

The world's average surface air temperature is about 14 °C.

標準

美國機械工程師學會(American Society of Mechanical Engineers (ASME)) 在溫度測量上制定出了兩種不同且獨特的標準,B40.200和PTC 19.3.。 B40.200 為雙金屬驅動(bimetallic-actuated)、填充系統(filled-system)、玻璃液體(liquid-in-glass)溫度計提供指。 It also provides guidelines for thermowells. PTC 19.3 provides guidelines for temperature measurement related to Performance Test Codes with particular emphasis on basic sources of measurement errors and techniques for coping with them.

美國機械工程師學會(ASME)之標準

• B40.200-2008: 溫度計, 直接讀取和遠端讀取。
• PTC 19.3-1974(R2004): Performance test code for temperature measurement.

參見

• 溫度與壓力測量技術時間線
• 溫度單位換算
• 色溫
• 普朗克單位制
• 溫度資料收集器
• 衛星溫度測量

外部連結

• Callendar, Hugh Longbourne. Thermoelectricity. Encyclopædia Britannica 26 (第11版). London: 814–821. 1911.  Another contemporaneous survey of related material.
• Callendar, Hugh Longbourne. Thermometry. Encyclopædia Britannica 26 (第11版). London: 821–836. 1911.  A detailed contemporaneous survey of thermometric theory and thermometer design.
• A comparison of different measurement technologies Agilent Technologies, Inc. Practical Temperature Measurements (PDF). [2018-11-19]. （原始内容 (PDF)存档于2017-11-16）. [We] explore the more common temperature monitoring techniques and introduce procedures for improving their accuracy.