![Alcohol-In-Glass Taylor Thermometer](https://upload.wikimedia.org/wikipedia/commons/1/11/Alcohol-In-Glass_Taylor_Thermometer.jpg)
A thermometer is a device that
measures temperature or a
temperature gradient
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degree ...
(the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a
mercury-in-glass thermometer
The mercury-in-glass or mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam (1714). It consists of a bulb containing mercury attached to a glass tube of narrow diameter; the volume of mercury in the tube is much le ...
or the pyrometric sensor in an
infrared thermometer
An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation sometimes called black-body radiation emitted by the object being measured. They are sometimes called laser thermometers as a laser is use ...
) in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer or the digital readout on an infrared model). Thermometers are widely used in technology and industry to monitor processes, in
meteorology
Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...
, in medicine, and in scientific research.
History
![1024 Pyrometer-8445](https://upload.wikimedia.org/wikipedia/commons/2/2a/1024_Pyrometer-8445.jpg)
While an individual thermometer is able to measure degrees of hotness, the readings on two thermometers cannot be compared unless they conform to an agreed scale. Today there is an absolute
thermodynamic temperature
Thermodynamic temperature is a quantity defined in thermodynamics as distinct from kinetic theory or statistical mechanics.
Historically, thermodynamic temperature was defined by Kelvin in terms of a macroscopic relation between thermodynamic wor ...
scale. Internationally agreed temperature scales are designed to approximate this closely, based on fixed points and interpolating thermometers. The most recent official temperature scale is the
International Temperature Scale of 1990
The International Temperature Scale of 1990 (ITS-90) is an equipment calibration standard specified by the International Committee of Weights and Measures (CIPM) for making measurements on the Kelvin and Celsius temperature scales. It is an appro ...
. It extends from to approximately .
Early developments
![Termometri cinquantigradi inv 85 IF 46774](https://upload.wikimedia.org/wikipedia/commons/f/f9/Termometri_cinquantigradi_inv_85_IF_46774.jpg)
Various authors have credited the invention of the thermometer to
Hero of Alexandria
Hero of Alexandria (; grc-gre, Ἥρων ὁ Ἀλεξανδρεύς, ''Heron ho Alexandreus'', also known as Heron of Alexandria ; 60 AD) was a Greece, Greek mathematician and engineer who was active in his native city of Alexandria, Roman Egy ...
. The thermometer was
not a single invention, however, but a development.
Hero of Alexandria
Hero of Alexandria (; grc-gre, Ἥρων ὁ Ἀλεξανδρεύς, ''Heron ho Alexandreus'', also known as Heron of Alexandria ; 60 AD) was a Greece, Greek mathematician and engineer who was active in his native city of Alexandria, Roman Egy ...
(10–70 AD) knew of the principle that certain substances, notably air, expand and contract and described a demonstration in which a closed tube partially filled with air had its end in a container of water. The expansion and contraction of the air caused the position of the water/air interface to move along the tube.
Such a mechanism was later used to show the hotness and coldness of the air with a tube in which the water level is controlled by the expansion and contraction of the gas. These devices were developed by several European scientists in the 16th and 17th centuries, notably
Galileo Galilei
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
[R.S. Doak (2005) Galileo: astronomer and physicist p36] and
Santorio Santorio
Santorio Santori (29 March, 1561 – 25 February, 1636) also called Santorio Santorio, Santorio de' Sanctoriis, or Sanctorius of Padua and various combinations of these names, was an Italian physiologist, physician, and professor, who introduc ...
.
As a result, devices were shown to produce this effect reliably, and the term ''thermoscope'' was adopted because it reflected the changes in
sensible heat
Sensible heat is heat exchanged by a body or thermodynamic system in which the exchange of heat changes the temperature of the body or system, and some macroscopic variables of the body or system, but leaves unchanged certain other macroscopic vari ...
(the modern concept of temperature was yet to arise).
[ The difference between a ]thermoscope
A thermoscope is a device that shows changes in temperature. A typical design is a tube in which a liquid rises and falls as the temperature changes. The modern thermometer gradually evolved from it with the addition of a scale in the early 17th c ...
and a thermometer is that the latter has a scale. Though Galileo is often said to be the inventor of the thermometer, there is no surviving document that he actually produced any such instrument.
The first clear diagram of a thermoscope was published in 1617 by Giuseppe Biancani
Giuseppe Biancani, SJ (Latin: Josephus Blancanus) (1566–1624) was an Italian Jesuit astronomer, mathematician, and selenographer, after whom the crater Blancanus on the Moon is named. He was a native of Bologna.
Works
His ''Aristotelis ...
(1566 – 1624); the first showing a scale and thus constituting a thermometer was by Santorio Santorio
Santorio Santori (29 March, 1561 – 25 February, 1636) also called Santorio Santorio, Santorio de' Sanctoriis, or Sanctorius of Padua and various combinations of these names, was an Italian physiologist, physician, and professor, who introduc ...
in 1625. This was a vertical tube, closed by a bulb of air at the top, with the lower end opening into a vessel of water. The water level in the tube is controlled by the expansion and contraction of the air, so it is what we would now call an air thermometer.
The word thermometer (in its French form) first appeared in 1624 in ''La Récréation Mathématique'' by Jean Leurechon
Jean Leurechon (c. 1591 – 17 January 1670) was a French Jesuit priest, astronomer, and mathematician, known for inventing the pigeonhole principle and naming the thermometer.
Life
Leurechon was born in Bar-le-Duc where his father, also named J ...
, who describes one with a scale of 8 degrees.[R.P. Benedict (1984) Fundamentals of Temperature, Pressure, and Flow Measurements, 3rd ed, page 4] The word comes from the Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
words θερμός, ''thermos'', meaning "hot" and μέτρον, ''metron'', meaning "measure".
The above instruments suffered from the disadvantage that they were also barometer
A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis ...
s, i.e. sensitive to air pressure. In 1629, Joseph Solomon Delmedigo
Joseph Solomon Delmedigo (or Del Medigo), also known as Yashar Mi-Qandia ( he, יש"ר מקנדיא) (16 June 1591 – 16 October 1655), was a rabbi, author, physician, mathematician, and music theorist.
Born in Candia, Crete, a descendant of ...
, a student of Galileo and Santorio in Padua, published what is apparently the first description and illustration of a sealed liquid-in-glass thermometer. It is described as having a bulb at the bottom of a sealed tube partially filled with brandy. The tube had a numbered scale. Delmedigo did not claim to have invented this instrument. Nor did he name anyone else as its inventor. In about 1654, Ferdinando II de' Medici, Grand Duke of Tuscany
Ferdinando II de' Medici (14 July 1610 – 23 May 1670) was grand duke of Tuscany from 1621 to 1670. He was the eldest son of Cosimo II de' Medici and Maria Maddalena of Austria. He was remembered by his contemporaries as a man of culture and ...
(1610–1670) did produce such an instrument, the first modern-style thermometer, dependent on the expansion of a liquid and independent of air pressure. Many other scientists experimented with various liquids and designs of thermometer.
However, each inventor and each thermometer was unique — there was no standard scale. Early attempts at standardization added a single reference point such as the freezing point of water. The use of two references for graduating the thermometer is said to have been introduced by Joachim Dalence in 1668 although Christiaan Huygens
Christiaan Huygens, Lord of Zeelhem, ( , , ; also spelled Huyghens; la, Hugenius; 14 April 1629 – 8 July 1695) was a Dutch mathematician, physicist, engineer, astronomer, and inventor, who is regarded as one of the greatest scientists of ...
(1629–1695) in 1665 had already suggested the use of graduations based on the melting
Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which incre ...
and boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envir ...
s of water as standards and, in 1694, Carlo Renaldini (1615–1698) proposed using them as fixed points along a universal scale. In 1701, Isaac Newton
Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a "natural philosopher"), widely recognised as one of the grea ...
(1642–1726/27) proposed a scale of 12 degrees between the melting point of ice and body temperature
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
.
Era of precision thermometry
In 1714, scientist and inventor Daniel Gabriel Fahrenheit
Daniel Gabriel Fahrenheit FRS (; ; 24 May 1686 – 16 September 1736) was a physicist, inventor, and scientific instrument maker. Born in Poland to a family of German extraction, he later moved to the Dutch Republic at age 15, where he spent ...
invented a reliable thermometer, using mercury instead of alcohol and water mixtures. In 1724, he proposed a temperature scale
Scale of temperature is a methodology of calibrating the physical quantity temperature in metrology. Empirical scales measure temperature in relation to convenient and stable parameters, such as the freezing and boiling point of water. Absolute ...
which now (slightly adjusted) bears his name. In 1742, Anders Celsius
Anders Celsius (; 27 November 170125 April 1744) was a Swedish astronomer, physicist and mathematician. He was professor of astronomy at Uppsala University from 1730 to 1744, but traveled from 1732 to 1735 visiting notable observatories in Germa ...
(1701–1744) proposed a scale with zero at the boiling point and 100 degrees at the freezing point of water, though the scale which now bears his name has them the other way around. French entomologist René Antoine Ferchault de Réaumur
René Antoine Ferchault de Réaumur (; 28 February 1683, La Rochelle – 17 October 1757, Saint-Julien-du-Terroux) was a French entomologist and writer who contributed to many different fields, especially the study of insects. He introduced t ...
invented an alcohol thermometer and, temperature scale
Scale of temperature is a methodology of calibrating the physical quantity temperature in metrology. Empirical scales measure temperature in relation to convenient and stable parameters, such as the freezing and boiling point of water. Absolute ...
in 1730, that ultimately proved to be less reliable than Fahrenheit's mercury thermometer.
The first physician to use thermometer measurements in clinical practice was Herman Boerhaave
Herman Boerhaave (, 31 December 1668 – 23 September 1738Underwood, E. Ashworth. "Boerhaave After Three Hundred Years." ''The British Medical Journal'' 4, no. 5634 (1968): 820–25. https://www.jstor.org/stable/20395297.) was a Dutch botanist, ...
(1668–1738). In 1866, Sir Thomas Clifford Allbutt
Sir Thomas Clifford Allbutt (20 July 183622 February 1925) was an English physician best known for his role as president of the British Medical Association 1920, for inventing the clinical thermometer, and for supporting Sir William Osler in fou ...
(1836–1925) invented a clinical thermometer
A medical thermometer (also called clinical thermometer) is a device which is used for measuring human or animal body temperature. The tip of the thermometer is inserted into the mouth under the tongue (''oral'' or ''sub-lingual temperature''), ...
that produced a body temperature reading in five minutes as opposed to twenty.[Sir Thomas Clifford Allbutt](_blank)
''Encyclopædia Britannica
The (Latin for "British Encyclopædia") is a general knowledge English-language encyclopaedia. It is published by Encyclopædia Britannica, Inc.; the company has existed since the 18th century, although it has changed ownership various time ...
'' In 1999, Dr. Francesco Pompei Francesco "Frank" Pompei is the founder and chief executive officer of Exergen Corporation. Pompei earned BS and MS mechanical engineering degrees from the Massachusetts Institute of Technology.“Virtual Classroom ensures cost savings, waste reduct ...
of the Exergen Corporation introduced the world's first temporal artery thermometer, a non-invasive temperature sensor
A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon.
In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
which scans the forehead in about two seconds and provides a medically accurate body temperature.
Registering
Traditional thermometers were all non-registering thermometers. That is, the thermometer did not hold the temperature reading after it was moved to a place with a different temperature. Determining the temperature of a pot of hot liquid required the user to leave the thermometer in the hot liquid until after reading it. If the non-registering thermometer was removed from the hot liquid, then the temperature indicated on the thermometer would immediately begin changing to reflect the temperature of its new conditions (in this case, the air temperature). Registering thermometers are designed to hold the temperature indefinitely, so that the thermometer can be removed and read at a later time or in a more convenient place. Mechanical registering thermometers hold either the highest or lowest temperature recorded until manually re-set, e.g., by shaking down a mercury-in-glass thermometer, or until an even more extreme temperature is experienced. Electronic registering thermometers may be designed to remember the highest or lowest temperature, or to remember whatever temperature was present at a specified point in time.
Thermometers increasingly use electronic means to provide a digital display or input to a computer.
Physical principles of thermometry
Thermometers may be described as empirical or absolute. Absolute thermometers are calibrated numerically by the thermodynamic absolute temperature scale. Empirical thermometers are not in general necessarily in exact agreement with absolute thermometers as to their numerical scale readings, but to qualify as thermometers at all they must agree with absolute thermometers and with each other in the following way: given any two bodies isolated in their separate respective thermodynamic equilibrium states, all thermometers agree as to which of the two has the higher temperature, or that the two have equal temperatures. For any two empirical thermometers, this does not require that the relation between their numerical scale readings be linear, but it does require that relation to be strictly monotonic. This is a fundamental character of temperature and thermometers.[Truesdell, C.A. (1980). ''The Tragicomical History of Thermodynamics, 1822-1854'', Springer, New York, .]
As it is customarily stated in textbooks, taken alone, the so-called "zeroth law of thermodynamics
The zeroth law of thermodynamics is one of the four principal laws of thermodynamics. It provides an independent definition of temperature without reference to entropy, which is defined in the second law. The law was established by Ralph H. Fowl ...
" fails to deliver this information, but the statement of the zeroth law of thermodynamics by James Serrin
James Burton Serrin (1 November 1926, Chicago, Illinois – 23 August 2012, Minneapolis, Minnesota) was an American mathematician, and a professor at University of Minnesota.
Life
He received his doctorate from Indiana University in 1951 under t ...
in 1977, though rather mathematically abstract, is more informative for thermometry: "Zeroth Law – There exists a topological line which serves as a coordinate manifold of material behaviour. The points of the manifold are called 'hotness levels', and is called the 'universal hotness manifold'." To this information there needs to be added a sense of greater hotness; this sense can be had, independently of calorimetry
In chemistry and thermodynamics, calorimetry () is the science or act of measuring changes in ''state variables'' of a body for the purpose of deriving the heat transfer associated with changes of its state due, for example, to chemical reacti ...
, of thermodynamics
Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of the ...
, and of properties of particular materials, from Wien's displacement law
Wien's displacement law states that the black-body radiation curve for different temperatures will peak at different wavelengths that are inversely proportional to the temperature. The shift of that peak is a direct consequence of the Planck r ...
of thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is ...
: the temperature of a bath of thermal radiation is proportional, by a universal constant, to the frequency of the maximum of its frequency spectrum
The power spectrum S_(f) of a time series x(t) describes the distribution of power into frequency components composing that signal. According to Fourier analysis, any physical signal can be decomposed into a number of discrete frequencies, ...
; this frequency is always positive, but can have values that tend to zero. Another way of identifying hotter as opposed to colder conditions is supplied by Planck's principle, that when a process of isochoric adiabatic work is the sole means of change of internal energy of a closed system, the final state of the system is never colder than the initial state; except for phase changes with latent heat, it is hotter than the initial state.
There are several principles on which empirical thermometers are built, as listed in the section of this article entitled "Primary and secondary thermometers". Several such principles are essentially based on the constitutive relation between the state of a suitably selected particular material and its temperature. Only some materials are suitable for this purpose, and they may be considered as "thermometric materials". Radiometric thermometry, in contrast, can be only slightly dependent on the constitutive relations of materials. In a sense then, radiometric thermometry might be thought of as "universal". This is because it rests mainly on a universality character of thermodynamic equilibrium, that it has the universal property of producing blackbody
A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body ...
radiation.
Thermometric materials
There are various kinds of empirical thermometer based on material properties.
Many empirical thermometers rely on the constitutive relation between pressure, volume and temperature of their thermometric material. For example, mercury expands when heated.
If it is used for its relation between pressure and volume and temperature, a thermometric material must have three properties:
(1) Its heating and cooling must be rapid. That is to say, when a quantity of heat enters or leaves a body of the material, the material must expand or contract to its final volume or reach its final pressure and must reach its final temperature with practically no delay; some of the heat that enters can be considered to change the volume of the body at constant temperature, and is called the latent heat of expansion at constant temperature; and the rest of it can be considered to change the temperature of the body at constant volume, and is called the specific heat at constant volume. Some materials do not have this property, and take some time to distribute the heat between temperature and volume change.[Truesdell, C., Bharatha, S. (1977). ''The Concepts and Logic of Classical Thermodynamics as a Theory of Heat Engines. Rigorously Constructed upon the Foundation Laid by S. Carnot and F. Reech'', Springer, New York, , page 20.]
(2) Its heating and cooling must be reversible. That is to say, the material must be able to be heated and cooled indefinitely often by the same increment and decrement of heat, and still return to its original pressure, volume and temperature every time. Some plastics do not have this property;[Ziegler, H., (1983). ''An Introduction to Thermomechanics'', North-Holland, Amsterdam, .]
(3) Its heating and cooling must be monotonic. That is to say, throughout the range of temperatures for which it is intended to work,
:(a) at a given fixed pressure,
::either (i) the volume increases when the temperature increases, or else (ii) the volume decreases when the temperature increases;
::but not (i) for some temperatures and (ii) for others; or
:(b) at a given fixed volume,
::either (i) the pressure increases when the temperature increases, or else (ii) the pressure decreases when the temperature increases;
::but not (i) for some temperatures and (ii) for others.
At temperatures around about 4 °C, water does not have the property (3), and is said to behave anomalously in this respect; thus water cannot be used as a material for this kind of thermometry for temperature ranges near 4 °C.[Truesdell, C., Bharatha, S. (1977). ''The Concepts and Logic of Classical Thermodynamics as a Theory of Heat Engines. Rigorously Constructed upon the Foundation Laid by S. Carnot and F. Reech'', Springer, New York, , pages 9-10, 15-18, 36-37.]
Gases, on the other hand, all have the properties (1), (2), and (3)(a)(α) and (3)(b)(α). Consequently, they are suitable thermometric materials, and that is why they were important in the development of thermometry.
Constant volume thermometry
According to Preston (1894/1904), Regnault found constant pressure air thermometers unsatisfactory, because they needed troublesome corrections. He therefore built a constant volume air thermometer. Constant volume thermometers do not provide a way to avoid the problem of anomalous behaviour like that of water at approximately 4 °C.
Radiometric thermometry
Planck's law
In physics, Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature , when there is no net flow of matter or energy between the body and its environment.
At ...
very accurately quantitatively describes the power spectral density of electromagnetic radiation, inside a rigid walled cavity in a body made of material that is completely opaque and poorly reflective, when it has reached thermodynamic equilibrium, as a function of absolute thermodynamic temperature alone. A small enough hole in the wall of the cavity emits near enough blackbody radiation of which the spectral radiance In radiometry, spectral radiance or specific intensity is the radiance of a surface per unit frequency or wavelength, depending on whether the Spectral radiometric quantity, spectrum is taken as a function of frequency or of wavelength. The Internat ...
can be precisely measured. The walls of the cavity, provided they are completely opaque and poorly reflective, can be of any material indifferently. This provides a well-reproducible absolute thermometer over a very wide range of temperatures, able to measure the absolute temperature of a body inside the cavity.
Primary and secondary thermometers
A thermometer is called primary or secondary based on how the raw physical quantity it measures is mapped to a temperature. As summarized by Kauppinen et al., "For primary thermometers the measured property of matter is known so well that temperature can be calculated without any unknown quantities. Examples of these are thermometers based on the equation of state of a gas, on the velocity
Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity is a ...
of sound in a gas, on the thermal noise
A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
or current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
of an electrical resistor, and on the angular anisotropy
Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...
of gamma ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
emission of certain radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
nuclei in a magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
."
In contrast, "Secondary thermometers are most widely used because of their convenience. Also, they are often much more sensitive than primary ones. For secondary thermometers knowledge of the measured property is not sufficient to allow direct calculation of temperature. They have to be calibrated against a primary thermometer at least at one temperature or at a number of fixed temperatures. Such fixed points, for example, triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at which the subli ...
s and superconducting
Superconductivity is a set of physical properties observed in certain materials where Electrical resistance and conductance, electrical resistance vanishes and magnetic field, magnetic flux fields are expelled from the material. Any material e ...
transitions, occur reproducibly at the same temperature."
Calibration
Thermometers can be calibrated either by comparing them with other calibrated thermometers or by checking them against known fixed points on the temperature scale. The best known of these fixed points are the melting and boiling points of pure water. (Note that the boiling point of water varies with pressure, so this must be controlled.)
The traditional way of putting a scale on a liquid-in-glass or liquid-in-metal thermometer was in three stages:
#Immerse the sensing portion in a stirred mixture of pure ice and water at atmospheric pressure and mark the point indicated when it had come to thermal equilibrium.
#Immerse the sensing portion in a steam bath at Standard atmospheric pressure
The standard atmosphere (symbol: atm) is a unit of pressure defined as Pa. It is sometimes used as a ''reference pressure'' or ''standard pressure''. It is approximately equal to Earth's average atmospheric pressure at sea level.
History
The s ...
and again mark the point indicated.
#Divide the distance between these marks into equal portions according to the temperature scale being used.
Other fixed points used in the past are the body temperature (of a healthy adult male) which was originally used by Fahrenheit as his upper fixed point ( to be a number divisible by 12) and the lowest temperature given by a mixture of salt and ice, which was originally the definition of .[R.P. Benedict (1984) ''Fundamentals of Temperature, Pressure, and Flow Measurements'', 3rd ed, , page 5] (This is an example of a Frigorific mixture A frigorific mixture is a mixture of two or more phases in a chemical system that, so long as none of the phases are completely consumed during equilibration, reaches an equilibrium temperature that is independent of the starting temperature of t ...
.) As body temperature varies, the Fahrenheit scale was later changed to use an upper fixed point of boiling water at .
These have now been replaced by the defining points in the International Temperature Scale of 1990
The International Temperature Scale of 1990 (ITS-90) is an equipment calibration standard specified by the International Committee of Weights and Measures (CIPM) for making measurements on the Kelvin and Celsius temperature scales. It is an appro ...
, though in practice the melting point of water is more commonly used than its triple point, the latter being more difficult to manage and thus restricted to critical standard measurement. Nowadays manufacturers will often use a thermostat
A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint.
Thermostats are used in any device or system tha ...
bath or solid block where the temperature is held constant relative to a calibrated thermometer. Other thermometers to be calibrated are put into the same bath or block and allowed to come to equilibrium, then the scale marked, or any deviation from the instrument scale recorded.[R.P. Benedict (1984) ''Fundamentals of Temperature, Pressure, and Flow Measurements'', 3rd ed, , chapter 11 "Calibration of Temperature Sensors"] For many modern devices calibration will be stating some value to be used in processing an electronic signal to convert it to a temperature.
Precision, accuracy, and reproducibility
The precision or resolution of a thermometer is simply to what fraction of a degree it is possible to make a reading. For high temperature work it may only be possible to measure to the nearest 10 °C or more. Clinical thermometers and many electronic thermometers are usually readable to 0.1 °C. Special instruments can give readings to one thousandth of a degree. However, this precision does not mean the reading is true or accurate, it only means that very small changes can be observed.
A thermometer calibrated to a known fixed point is accurate (i.e. gives a true reading) at that point. The invention of the technology to measure temperature led to the creation of Scales of Temperature
Scale of temperature is a methodology of calibrating the physical quantity temperature in metrology. Empirical scales measure temperature in relation to convenient and stable parameters, such as the Freezing point, freezing and boiling point of w ...
. In between fixed calibration points, interpolation
In the mathematical field of numerical analysis, interpolation is a type of estimation, a method of constructing (finding) new data points based on the range of a discrete set of known data points.
In engineering and science, one often has a n ...
is used, usually linear.[ This may give significant differences between different types of thermometer at points far away from the fixed points. For example, the expansion of mercury in a glass thermometer is slightly different from the change in resistance of a ]platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Platinu ...
resistance thermometer, so these two will disagree slightly at around 50 °C.[T. Duncan (1973) Advanced Physics: Materials and Mechanics (John Murray, London) ] There may be other causes due to imperfections in the instrument, e.g. in a liquid-in-glass thermometer if the capillary tube
Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of, or even in opposition to, any external forces li ...
varies in diameter.[
For many purposes reproducibility is important. That is, does the same thermometer give the same reading for the same temperature (or do replacement or multiple thermometers give the same reading)? Reproducible ]temperature measurement
Temperature measurement (also known as thermometry) describes the process of measuring a current local temperature for immediate or later evaluation. Datasets consisting of repeated standardized measurements can be used to assess temperature tren ...
means that comparisons are valid in scientific experiments and industrial processes are consistent. Thus if the same type of thermometer is calibrated in the same way its readings will be valid even if it is slightly inaccurate compared to the absolute scale.
An example of a reference thermometer used to check others to industrial standards would be a platinum resistance thermometer
Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a heat-resistant ceramic or glass core but other constructio ...
with a digital display to 0.1 °C (its precision) which has been calibrated at 5 points against national standards (−18, 0, 40, 70, 100 °C) and which is certified to an accuracy of ±0.2 °C.[Peak Sensors]
Reference Thermometer
According to British Standards
British Standards (BS) are the standards produced by the BSI Group which is incorporated under a royal charter and which is formally designated as the Standards organization#National standards bodies, national standards body (NSB) for the UK. The ...
, correctly calibrated, used and maintained liquid-in-glass thermometers can achieve a measurement uncertainty of ±0.01 °C in the range 0 to 100 °C, and a larger uncertainty outside this range: ±0.05 °C up to 200 or down to −40 °C, ±0.2 °C up to 450 or down to −80 °C.[BS1041-2.1:1985 Temperature Measurement- Part 2: Expansion thermometers. Section 2.1 Guide to selection and use of liquid-in-glass thermometers]
Indirect methods of temperature measurement
;Thermal expansion
: Utilizing the property of thermal expansion
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
of various phases of matter
In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, magnetizat ...
.
: Pairs of solid metals with different expansion coefficients can be used for bi-metal mechanical thermometers. Another design using this principle is Breguet's thermometer.
: Some liquids possess relatively high expansion coefficients over a useful temperature ranges thus forming the basis for an alcohol
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
or mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
thermometer. Alternative designs using this principle are the reversing thermometer
Unlike most conventional mercury (element), mercury thermometers, a reversing thermometer is able to record a given temperature to be viewed at a later time. If the thermometer is flipped upside down, the current temperature will be shown until it ...
and Beckmann differential thermometer.
: As with liquids, gases can also be used to form a gas thermometer
A gas thermometer is a thermometer that measures temperature by the variation in volume or pressure of a gas.
Volume Thermometer
This thermometer functions by Charles's Law. Charles's Law states that when the temperature of a gas increases, so d ...
.
;Pressure
: Vapour pressure thermometer
A vapour pressure thermometer is a thermometer that uses a pressure gauge to measure the vapour pressure of a liquid.
References
Thermometers
{{thermodynamics-stub ...
;Density
: Galileo thermometer
A Galileo thermometer (or Galilean thermometer) is a thermometer made of a sealed glass cylinder containing a clear liquid and several glass vessels of varying density. The individual floats rise or fall in proportion to their respective density ...
;Thermochromism
: Some compounds exhibit thermochromism
Thermochromism is the property of substances to change color due to a change in temperature. A mood ring is an excellent example of this phenomenon, but thermochromism also has more practical uses, such as baby bottles which change to a differen ...
at distinct temperature changes. Thus by tuning the phase transition temperatures for a series of substances the temperature can be quantified in discrete increments, a form of digitization
DigitizationTech Target. (2011, April). Definition: digitization. ''WhatIs.com''. Retrieved December 15, 2021, from https://whatis.techtarget.com/definition/digitization is the process of converting information into a Digital data, digital (i ...
. This is the basis for a liquid crystal thermometer
A liquid crystal thermometer, temperature strip or plastic strip thermometer is a type of thermometer that contains heat-sensitive (thermochromic) liquid crystals in a plastic strip that change colour to indicate different temperatures.
Liquid cry ...
.
:
;Band edge thermometry (BET)
: Band edge thermometry (BET) takes advantage of the temperature-dependence of the band gap of semiconductor materials to provide very precise optical (''i.e.'' non-contact) temperature measurements. BET systems require a specialized optical system, as well as custom data analysis software.
;
: All objects above absolute zero
Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvin. The fundamental particles of nature have minimum vibration ...
emit blackbody radiation
Black-body radiation is the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment, emitted by a black body (an idealized opaque, non-reflective body). It has a specific, continuous spect ...
for which the spectra is directly proportional to the temperature. This property is the basis for a pyrometer
A pyrometer is a type of remote-sensing thermometer used to measure the temperature of distant objects. Various forms of pyrometers have historically existed. In the modern usage, it is a device that from a distance determines the temperature of ...
or infrared thermometer
An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation sometimes called black-body radiation emitted by the object being measured. They are sometimes called laser thermometers as a laser is use ...
and thermography
Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a Thermographic camera, thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are ...
. It has the advantage of remote temperature sensing; it does not require contact or even close proximity unlike most thermometers. At higher temperatures, blackbody radiation becomes visible and is described by the colour temperature
Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...
. For example a glowing heating element or an approximation of a star's surface temperature.
;Fluorescence
: Phosphor thermometry Phosphor thermometry is an optical method for surface temperature measurement. The method exploits luminescence emitted by phosphor material. Phosphors are fine white or pastel-colored inorganic powders which may be stimulated by any of a variety of ...
;Optical absorbance spectra
: Fiber optical thermometer Fiber-optical thermometers can be used in electromagnetically strongly influenced environment, in microwave fields, power plants or explosion-proof
areas and wherever measurement with electrical temperature sensors are not possible.
Structure
O ...
;Electrical resistance
: Resistance thermometer
Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a heat-resistant ceramic or glass core but other constructio ...
which use materials such as Balco alloy
Balco is a nickel-iron alloy with a thermal conductivity similar to nickel but twice the resistivity. It is used for making low cost resistance temperature sensors. It consists of 70% nickel and 30% iron.
Balco is Carpenter Technology Corporation ...
: Thermistor
A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of ''thermal'' and ''resistor''.
Thermistors are divided based on their conduction ...
: Coulomb blockade thermometer
;Electrical potential
: Thermocouples
A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the ...
are useful over a wide temperature ranges from cryogenic temperatures to over 1000°C, but typically have an error of ±0.5-1.5°C.
: Silicon bandgap temperature sensor The silicon bandgap temperature sensor is an extremely common form of temperature sensor (thermometer) used in electronic equipment. Its main advantage is that it can be included in a silicon integrated circuit at very low cost. The principle of t ...
s are commonly found packaged in integrated circuits with accompanying ADC
ADC may refer to:
Science and medicine
* ADC (gene), a human gene
* AIDS dementia complex, neurological disorder associated with HIV and AIDS
* Allyl diglycol carbonate or CR-39, a polymer
* Antibody-drug conjugate, a type of anticancer treatm ...
and interface such as I2C. Typically they are specified to work within about —50 to 150°C with accuracies in the ±0.25 to 1°C range but can be improved by binning.
;Electrical resonance
: Quartz thermometer
;Nuclear magnetic resonance
: Chemical shift
In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of ...
is temperature dependent. This property is used to calibrate the thermostat of NMR
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with a ...
probes, usually using methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
or ethylene glycol
Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
. This can potentially be problematic for internal standards which are usually assumed to have a defined chemical shift (e.g 0 ppm for TMS) but in fact exhibit a temperature dependence.
;Magnetic susceptibility
:
: Above the Curie temperature
In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Cur ...
, the magnetic susceptibility
In electromagnetism, the magnetic susceptibility (Latin: , "receptive"; denoted ) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization (magnetic moment per unit volume) to the ap ...
of a paramagnetic material exhibits an inverse temperature dependence. This phenomenon is the basis of a magnetic cryometer.
Applications
Thermometers utilize a range of physical effects to measure temperature. Temperature sensors are used in a wide variety of scientific and engineering applications, especially measurement systems. Temperature systems are primarily either electrical or mechanical, occasionally inseparable from the system which they control (as in the case of a mercury-in-glass thermometer). Thermometers are used in roadways in cold weather climates to help determine if icing conditions exist. Indoors, thermistor
A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of ''thermal'' and ''resistor''.
Thermistors are divided based on their conduction ...
s are used in climate control systems such as air conditioner
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
s, freezers, heater
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
s, refrigerator
A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...
s, and water heater
Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated t ...
s. Galileo thermometers are used to measure indoor air temperature, due to their limited measurement range.
Such liquid crystal thermometer
A liquid crystal thermometer, temperature strip or plastic strip thermometer is a type of thermometer that contains heat-sensitive (thermochromic) liquid crystals in a plastic strip that change colour to indicate different temperatures.
Liquid cry ...
s (which use thermochromic
Thermochromism is the property of substances to change color due to a change in temperature. A mood ring is an excellent example of this phenomenon, but thermochromism also has more practical uses, such as baby bottles which change to a differen ...
liquid crystals) are also used in mood ring
A mood ring is a finger ring that contains a thermochromic element, or "mood stone", that changes colors based on the temperature of the finger of the wearer. Finger temperature, as long as the ambient temperature is relatively constant, is si ...
s and used to measure the temperature of water in fish tanks.
Fiber Bragg grating
A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in th ...
temperature sensors are used in nuclear power
Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced b ...
facilities to monitor reactor core temperatures and avoid the possibility of nuclear meltdown
A nuclear meltdown (core meltdown, core melt accident, meltdown or partial core melt) is a severe nuclear reactor accident that results in core damage from overheating. The term ''nuclear meltdown'' is not officially defined by the Internation ...
s.
Nanothermometry
Nanothermometry Nanothermometry is a branch of physics and engineering exploring the use of non-invasive precise thermometers working at the nanoscale. These devices have high spatial resolution (below one micrometer Micrometer can mean:
* Micrometer (device), use ...
is an emergent research field dealing with the knowledge of temperature in the sub-micrometric scale. Conventional thermometers cannot measure the temperature of an object which is smaller than a micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
, and new methods and materials have to be used. Nanothermometry is used in such cases. Nanothermometers are classified as luminescent
Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light".
It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a cryst ...
thermometers (if they use light to measure temperature) and non-luminescent thermometers (systems where thermometric properties are not directly related to luminescence).
Cryometer
Thermometers used specifically for low temperatures.
Medical
* Ear thermometers tend to be an infrared thermometer
An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation sometimes called black-body radiation emitted by the object being measured. They are sometimes called laser thermometers as a laser is use ...
.
* Forehead thermometer is an example of a liquid crystal thermometer
A liquid crystal thermometer, temperature strip or plastic strip thermometer is a type of thermometer that contains heat-sensitive (thermochromic) liquid crystals in a plastic strip that change colour to indicate different temperatures.
Liquid cry ...
.
*Rectal
The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the le ...
and oral
The word oral may refer to:
Relating to the mouth
* Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid
**Oral administration of medicines
** Oral examination (also known as an oral exam or oral ...
thermometers have typically been mercury but have since largely been superseded by NTC thermistors with a digital readout.
Various thermometric techniques have been used throughout history such as the Galileo thermometer
A Galileo thermometer (or Galilean thermometer) is a thermometer made of a sealed glass cylinder containing a clear liquid and several glass vessels of varying density. The individual floats rise or fall in proportion to their respective density ...
to thermal imaging.[
]Medical thermometer
A medical thermometer (also called clinical thermometer) is a device which is used for measuring human or animal body temperature. The tip of the thermometer is inserted into the mouth under the tongue (''oral'' or ''sub-lingual temperature''), u ...
s such as mercury-in-glass thermometers, infrared thermometers, pill thermometers, and liquid crystal thermometer
A liquid crystal thermometer, temperature strip or plastic strip thermometer is a type of thermometer that contains heat-sensitive (thermochromic) liquid crystals in a plastic strip that change colour to indicate different temperatures.
Liquid cry ...
s are used in health care
Health care or healthcare is the improvement of health via the prevention, diagnosis, treatment, amelioration or cure of disease, illness, injury, and other physical and mental impairments in people. Health care is delivered by health profe ...
settings to determine if individuals have a fever
Fever, also referred to as pyrexia, is defined as having a body temperature, temperature above the human body temperature, normal range due to an increase in the body's temperature Human body temperature#Fever, set point. There is not a single ...
or are hypothermic
Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe h ...
.
Food and food safety
Thermometers are important in food safety
Food safety (or food hygiene) is used as a scientific method/discipline describing handling, preparation, and storage of food in ways that prevent food-borne illness. The occurrence of two or more cases of a similar illness resulting from t ...
, where food at temperatures within can be prone to potentially harmful levels of bacterial growth after several hours which could lead to foodborne illness
Foodborne illness (also foodborne disease and food poisoning) is any illness resulting from the spoilage of contaminated food by pathogenic bacteria, viruses, or parasites that contaminate food,
as well as prions (the agents of mad cow disease) ...
. This includes monitoring refrigeration temperatures and maintaining temperatures in foods being served under heat lamps or hot water baths.
Cooking thermometers are important for determining if a food is properly cooked. In particular meat thermometer
A meat thermometer with a dial. Notice the markings for each type of meat
A meat thermometer or cooking thermometer is a thermometer used to measure the internal temperature of meat, especially roasts and steaks, and other cooked foods. The de ...
s are used to aid in cooking meat to a safe internal temperature while preventing over cooking. They are commonly found using either a bimetallic coil, or a thermocouple or thermistor with a digital readout.
Candy thermometer
A candy thermometer, also known as a sugar thermometer or jam thermometer, is a cooking thermometer used to measure the temperature and therefore the ''stage'' of a cooking sugar solution. (See candy making for a description of sugar stages.) The ...
s are used to aid in achieving a specific water content in a sugar solution based on its boiling temperature.
Environmental
* Indoor-outdoor thermometer
*Heat meter
A heat meter attached to a heat exchanger in a District heating substation in a residential neighborhood. Right in white-blue: the calculator; in the center in bronze: the ultrasonic flow meter
A heat meter or energy meter is a device which mea ...
uses a thermometer to measure rate of heat flow The rate of heat flow is the amount of heat that is transferred per unit of time in some material, usually measured in watt (joules per second). Heat is the flow of thermal energy driven by thermal non-equilibrium, so that 'heat flow' ...
.
*Thermostats
A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint.
Thermostats are used in any device or system tha ...
have used bimetallic strips but digital thermistors have since become popular.
Alcohol thermometer
The alcohol thermometer or spirit thermometer is an alternative to the mercury-in-glass thermometer and has similar functions. Unlike the mercury-in-glass thermometer, the contents of an alcohol thermometer are less toxic and will evaporate qui ...
s, infrared thermometer
An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation sometimes called black-body radiation emitted by the object being measured. They are sometimes called laser thermometers as a laser is use ...
s, mercury-in-glass thermometers, recording thermometers, thermistor
A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of ''thermal'' and ''resistor''.
Thermistors are divided based on their conduction ...
s, and Six's thermometers are used in meteorology
Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...
and climatology
Climatology (from Greek , ''klima'', "place, zone"; and , '' -logia'') or climate science is the scientific study of Earth's climate, typically defined as weather conditions averaged over a period of at least 30 years. This modern field of stud ...
in various levels of the atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
and oceans. Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
use thermometers and hygrometer
A hair tension dial hygrometer with a nonlinear scale.
A hygrometer is an instrument used to measure the amount of water vapor in air, in soil, or in confined spaces. Humidity measurement instruments usually rely on measurements of some other qu ...
s to determine if atmospheric icing
Atmospheric icing occurs in the atmosphere when water droplets suspended in air freezing, freeze on objects they come in contact with. It is not the same as freezing rain, which is caused directly by precipitation. Icing conditions can be particul ...
conditions exist along their flight path
In the United States, airways or air routes are defined by the Federal Aviation Administration (FAA) in two ways:
"VOR Federal airways and Low/Medium Frequency (L/MF) (Colored) Federal airways"
These are designated routes which aeroplanes ...
. These measurements are used to initialize weather forecast models. Thermometers are used in roadways in cold weather climates to help determine if icing conditions exist and indoors in climate control systems.
See also
* Automated airport weather station
Airport weather stations are automated sensor suites which are designed to serve aviation and meteorological operations, weather forecasting and climatology. Automated airport weather stations have become part of the backbone of weather observi ...
* Thermodynamic instruments
A thermodynamic instrument is any device which facilitates the quantitative measurement of thermodynamic systems. In order for a thermodynamic parameter to be truly defined, a technique for its measurement must be specified. For example, the ultim ...
* Maximum-minimum thermometer
* Wet-and-dry bulb thermometer
* Mercury-in-glass thermometer
The mercury-in-glass or mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam (1714). It consists of a bulb containing mercury attached to a glass tube of narrow diameter; the volume of mercury in the tube is much le ...
* Infrared thermometer
An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation sometimes called black-body radiation emitted by the object being measured. They are sometimes called laser thermometers as a laser is use ...
* Medical thermometer
A medical thermometer (also called clinical thermometer) is a device which is used for measuring human or animal body temperature. The tip of the thermometer is inserted into the mouth under the tongue (''oral'' or ''sub-lingual temperature''), u ...
* Resistance thermometer
Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a heat-resistant ceramic or glass core but other constructio ...
References
Further reading
* Middleton, W.E.K. (1966). ''A history of the thermometer and its use in meteorology''. Baltimore: Johns Hopkins Press. Reprinted ed. 2002, .
History of the Thermometer
- Recent review on Thermometry at the Nanoscale
External links
History of Temperature and Thermometry
The Thermometer—From The Feeling To The Instrument
History Channel – Invention
– Notable Modern Inventions and Discoveries
– Thermometers – Early History, Anders Celsius, Gabriel Fahrenheit and Thomson Kelvin.
– Mercury and Alcohol.
The NIST Industrial Thermometer Calibration Laboratory
Thermometry at the Nanoscale
Review
{{Authority control
Thermometers,
Temperature
Meteorological instrumentation and equipment