The thermometer is a mechanical or electrical digital device for measuring temperatures. The term „thermometer“ comes from the Greek and means „thermós“ for warm and „metrós“ for measure. Depending on the purpose of the temperature determination different types of thermometers can be distinguished, which can also work in different ways. Many thermometers use the physical, temperature-dependent properties of certain liquids, gases or solid bodies to expand with heat or to contract accordingly in the cold, as in the known mercury column in older glass thermometers for measuring human body temperature or indoor temperature. as well as outside temperatures. With electric thermometers, the temperature is determined by the electrical conductivity of substances or bodies as a function of the temperature.

The different types of thermometers

First of all, in the various types of thermometers, so-called „touch thermometers“ and no contact are measured thermometer distinguished. The contact thermometers must be in direct contact with the object to be measured at their measuring point. As a result, they are also prone to error in some way, for example, if the contact can not be made close enough and the heat may be dissipated by the environment. Likewise, measuring errors may also occur if other higher heat sources are present in the environment, whose temperature is also partially detected in addition to the object to be measured. For example, the touch thermometers include

Expansion thermometers, for example as bimetallic thermometers or liquid thermometers,
– gas thermometer,
– thermometerolder type with mercury column,
Liquid crystal thermometer,
– heating thermostatic valves filled with wax,
– Resistance thermometers, thermocouples and more.

Thermometerss that do not need to touch the object to be measured operate with different sensors. You can record the temperature via the electromagnetic radiation of the objects. The sensors used for this purpose include, for example, infrared sensors and others. contactless thermometer are for example

– clinical thermometer with infrared measurement,
– so-called radiation thermometers for different measuring wavelengths, these are also called pyrometers,
– Raman thermometer, where the temperature is measured using fiber optic spectroscopy.

Another type of temperature measurement is possible with the Galileo thermometer. The Galileo thermometer detects the temperature of a liquid by gravity and density measurement. The different ones thermometer find a variety of different applications, such as in the private households as fever, kitchen, wine, room and air temperature or for measuring food in the kitchen of catering establishments, in all conceivable commercial production facilities in the processing and processing of raw materials or in other manufacturing processes, in soil and air measurements, for example in the observation of the weather and in many other areas more.

The invention of the thermometer

Up to the present state of development of modern temperature measurement many different development steps and physical insights were necessary. Even in ancient times, the expansion of the air was known by heat. About 200 to 300 years BC Physicists and inventors such as Heron of Alexandria and Phylon of Byzantium invented a „thermoscope“. In this case, water was heated. Depending on the increase in water temperature, the water level rose or fell in a container. This type of thermoscope has been used for many hundreds of years. In this type of temperature measurement, however, the temperature was measured by the extent of the air – similar to a barometer for the air pressure measurement. More accurate measurements could be obtained from the middle of the 17th century onwards with the production of an alcohol-filled glass thermometer Fernando II de Medici, the then Grand Duke of Toscana in Italy. The well-known Fahrenheit scale was developed in 1724 by Daniel Fahrenheit. This unit of measurement, for example, where the temperature at which frozen water melts at 32 ° F, or the average body temperature of a human being at 96 ° F, is still used in many Anglo-American countries, such as the United States, to the present day , By Anders Celsius from 1742 comes the world famous and also used in this country Celsius scale for the measurement of temperatures. The temperature measurement after Fahrenheit takes place at finer intervals compared to the measurement after Celsius. In addition to the habit of using the Fahrenheit scale, this may sometimes be a reason for reuse instead of the Celsius scale in some countries. On many thermometers for domestic use and others both scales are given in parallel. The physical fundamentals for thermometer , which measure temperatures due to thermal radiation, were created in 1859 by the German physicist Gustav Robert Kirchhoff with his definition of the law of radiation and the invention of spectroscopy.