Thermometer

From Wikipedia, the free encyclopedia

Jump to: navigation, search
This article appears to contradict the article Timeline of temperature and pressure measurement technology. Please see discussion on the linked talk page.
It has been suggested that List of temperature sensors be merged into this article or section. (Discuss)
A common mercury thermometer

A thermometer is a device that measures temperature or temperature gradient, using a variety of different principles. The word thermometer is derived from two smaller word fragments: thermo from the Greek for heat and meter from Greek, meaning to measure. A thermometer has two important elements, the temperature sensor (e.g. the bulb on a mercury thermometer) in which some physical change occurs with temperature, plus some means of converting this physical change into a value (e.g. the scale on a mercury thermometer). Industrial thermometers commonly use electronic means to provide a digital display or input to a computer.

Thermometers can be divided into two groups according to the level of knowledge about the physical basis of the underlying thermodynamic laws and quantities. 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 of sound in a gas, on the thermal noise (see Johnson–Nyquist noise) voltage or current of an electrical resistor, and on the angular anisotropy of gamma ray emission of certain radioactive nuclei in a magnetic field.

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 points and superconducting transitions, occur reproducibly at the same temperature.

Internationally agreed temperature scales are based on fixed points and interpolating thermometers. The most recent official temperature scale is the International Temperature Scale of 1990. It extends from 0.65 K to approximately 1358 K (−272.5 °C to 1085 °C).

Contents

  • 1 Early History
  • 2 Types of thermometers
  • 3 Specialist uses of thermometers
  • 4 See also
  • 5 Notes
  • 6 References
  • 7 External links

[edit] Early History

This article needs additional references or sources for verification.
Please help to improve this article by adding reliable references. Unverifiable material may be challenged and removed.
This article has been tagged since July 2007.
Galileo thermometer

Thermometers measure temperature. The first thermometer was an air thermometer used by Avicenna in the early 11th century.[1] This was followed by the thermoscope several centuries later. Different versions of the thermoscope were invented by several inventors around the same time. The first to put a numerical scale on the thermoscopes was the Italian inventor Santorio Santorio for use in medicine in the 16th century. In 1593, Galileo Galilei invented a rudimentary water thermometer (using the contraction of air to draw water up a tube). He also discovered that liquids of lesser density than water could be suspended within it and that they would float at different heights depending on the temperature; hence Galileo's Thermoscope--Galileo's use of alcohol enclosed in glass spheres floating in a column of water in order to measure their differences in temperature. In 1714, Daniel Gabriel Fahrenheit invented the first mercury thermometer. In 1866 Sir Thomas Clifford Allbutt invented a clinical thermometer that produced a body temperature reading in five minutes as opposed to twenty.[2]

This history of the thermometer, from its invention (an achievement attributed to several scientists, including Avicenna and Galileo) through various changes and applications over the centuries, includes controversy about its invention, the story of different scales, from Fahrenheit and Anders Celsius to the now-forgotten Newton, Réaumur, Delisle, and Christin scales, and the history of the gradual scientific then popular understanding of the concept of temperature. Not until 1800 did people interested in thermometers begin to see clearly what they were measuring, and the impetus for improving thermometry came largely from study of the weather -- the liquid-in-glass thermometer became the meteorologist's instrument before that of the chemist or physicist.

[edit] Types of thermometers

Mercury-in-glass thermometer

Thermometers have been built which utilise a range of physical effects to measure temperature. Most thermometers are originally calibrated to a constant-volume gas thermometer.

[edit] Specialist uses of thermometers