Hey, guys, this is Germán or at least the interpretation of my glow! By using a thermal imaging camera, you are able to see the infrared radiation or thermal radiation that I’m emitting. To put it simply, you can see my temperature. This is one of the most advanced forms of temperature measurement and this article will cover how we got to it from one of the most simple thermometers, the bimetallic thermometer.

On the video, you can see me emitting radiation because everything that has a temperature above 0 Degrees Kelvin {-273.15 Degrees Celcius} glows. However, the frequencies are so high that they are not within our visible spectrum. You need a camera like we are using right now to see this radiation and actually know my temperature.

So how did we get here from bimetallic thermometers?

## The beginnings of temperature measurement

How did we know if something was hot, or if it was getting hotter or cooler before advanced temperature measurement solutions? Expert Japanese swordsmiths were able to tell the exact temperature of a blade just by looking at the glow of the blade. This same technique was used in glass and pottery production for centuries all over the world.

The Italians, Galileo, and Santori were the first to try to measure the changes in temperature, but Daniel Gabriel Fahrenheit was the first one to offer a precision thermometer.

## What is a thermometer?

A thermometer is composed of two parts: a temperature sensor and a temperature scale. The Fahrenheit thermometer uses a glass mercury bulb as a sensor. Fahrenheit observed that the increase in temperature by 1 degree will increase the volume of mercury by a known value.

This is how the Fahrenheit scale came to be with 32 degrees as water melting point and 212 as its boiling point, with 180 steps between the melting and boiling points. This was the first standard scale used in temperature measurement. The most common temperature scales are Celsius [˚C] and Kelvin [˚K]

The industry still uses mercury thermometers, but there are two big limitations:

• First is that mercury thermometers are usually made from glass, that is a fragile material and sensors break quite easily,
• Second, it cannot be used in a lot of industrial applications since mercury has a limit of 356.73 °C that is the boiling point of Mercury.

## The bimetallic thermometer and the beginnings of process automation

A bimetallic thermometer’s temperature sensor consists of two metal strips bonded together and coiled like the shell of a Snail. One of the metals expand more quickly than the other if exposed to heat, and this difference makes the coil expand or contract. You can measure temperature by translating this rotation into a polar scale.

Bimetallic thermometers are really inexpensive sensors and are still used in various applications, but they have a low accuracy [2 degrees˚C / ˚K]. Bimetallic thermometers also have to be changed regularly since they are made of moving components.

If you would like to learn about all the other types of temperature sensors that have been invented since then, check out this article.

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