How does a thermometer work?

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Comment fonctionne un thermomètre ?

The thermometer is an instrument used to measure temperature. There are different types that work thanks to the dilation and the pressure of the bodies, whether they are liquid, solid or gaseous, even thanks to the electronic variations noted. Depending on your needs, such as the measurement of temperature ranges or the nature of the materials to be studied, your profession or the application of your thermometer, this operating principle may vary. Indeed, you will need two kinds of measuring device if you want to take body temperature a sick person or an industrial oven. Whether your use is domestic or professional, you will find on the market three types of thermometer with different functions : the electronic thermometer, the liquid thermometer (mercury, alcohol or rapeseed) and the Galileo thermometer. The temperature taking specialists of explains to you how do these thermometers work.

Operation of the digital electronic thermometer 📲

The electronic thermometer is probably the most common thermometer in the world. Childishly easy to use thanks to their probe and tips coupled with an LCD screen, they allow fast and accurate temperature measurement. Some digital thermometers are also non-contact (the infrared thermometers) and offer remote measurement. Their application is often professional, for example there are many medical thermometers or kitchen that are electronic; forehead thermometers, ear thermometers, thermometers with probe (outer, retractable, wired or removable) or with case. Some high-performance devices used in particular in meteorology or in the scientific field also offer a recorder allowing you to compare complete data ranges, different units of measurement, monitoring and reading of data via an application, etc.

But let's see together more precisely how an electronic/digital thermometer works.

The electronic thermometer is made up of 3 main elements. The sensor, the computer and the display.

It is the sensor that will measure the temperature and convert it into a signal measurable by the computer. For RTD probes (Pt100, Pt1000) and NTC and PTC thermistors the resistance of the sensor changes according to the temperature.

The computer therefore comes to measure the resistance of the sensor to deduce a temperature in degrees Celsius or degrees Fahrenheit.

The display then recovers this temperature information via an electrical signal and displays it in a manner understandable to humans.

If your thermometer no longer transmits this data, it may be faulty or even broken, do not hesitate to consult our article My thermometer is broken: what should I do?

📝 Note 📝
As you will have understood, there are a multitude of digital thermometers, to know how to use your thermometer correctly do not hesitate to contact your supplier or refer to the user manuals. Indeed, if most electronic thermometers work the same way, they have a different use. 

How the alcohol thermometer works 🌡

The alcohol thermometer (which has the same effect as gallium or rapeseed oil) replaces the mercury thermometer known for its toxicity, which our grandparents' generation already used to measure body temperature or assess the ambient temperature of a room or refrigerator. the how the alcohol thermometer works is simple: a glass tube held on a base graduated by degrees Celsius, is filled with alcohol and nitrogen. When the temperature rises, the alcohol expands, takes up more space and rises. When the temperature drops, the alcohol shrinks, takes up less space and sinks. Nitrogen exerts a very slight pressure on the alcohol to maintain it. It is an accurate thermometer, be careful however not to put it in direct sunlight if you want to measure the outside temperature, as the temperature reading could be altered.

Operation of the Galileo thermometer ⚗️

The Galilean thermometer has now become more of a household thermometer, sometimes even considered a decorative item. You may be familiar with this elongated vessel containing glass bulbs filled with a colored liquid that move up and down. But then how does this thermometer work who hypnotizes us?

It is necessary to know that these glass bulbs do not contain any liquids… Each of them has its own properties which, depending on the temperature, modify the density of the liquid and the buoyancy increases or decreases. Each glass bulb having an assigned temperature, it is easy to determine the temperature. Galileo's thermometer is neither accurate nor fast, the measurement experts at Thermomè recommend that you use it for decoration only. 😉

Your professional thermometer

For learn more about the thermometer, you can consult our Guide complet on thermometers in which you will also find information such as our classification of thermometers by reliability, calibration or price ranges of thermometers for example. 

Depending on your activity and therefore the thermometers you will need on a daily basis, their use will not be the same. To choose your professional thermometer, you must ask yourself the question “what is a thermometer used for?” she defines the perfect instrument for you. To go further, take directly an appointment with an advisor to choose your professional thermometer.