Concept of Measuring Temperature: From Temper to Thermometer

 The Concept of Measuring Temperature: From Temper to Thermometer

The term "temper" was once used in the 17th century to describe the quality of steel. After the invention of the primitive form of the thermometer, the word "temperature" was coined to describe the degree of heat or coolness of a material body. At the beginning of the 17th century, the thermometer - a temperature-measuring instrument - was first developed. Although Galileo Galilei is credited with constructing the first thermometer, a Dutch scientist named Drebbel also independently created a similar instrument.

The first thermometer was simple in design. A bulb containing air was attached to a long vertical tube and inverted, then dipped into a basin of water or colored liquid. As the temperature of the bulb changed, the gas inside expanded or contracted, causing the level of the liquid column inside the vertical tube to rise or fall. A significant drawback of this instrument was its sensitivity to both temperature and atmospheric pressure variations.

Throughout the 17th and 18th centuries, advancements in thermometer design emerged. During this time, the liquid thermometer was developed. The need for two fixed reference temperatures became apparent when trying to calibrate the temperature scales. The boiling point of water and the melting point of ice provided two easily accessible references. However, other references were also explored, such as Fahrenheit's thermometer where the temperature of an ice and salt mixture was taken as 0 degrees and the temperature of the human body as 96 degrees. These two reference points resulted in the melting point of ice being assigned 32 degrees and the boiling point of water being assigned 212 degrees. On the Celsius scale, the melting point of ice was chosen as 0 degrees and the boiling point of water as 100 degrees. The Kelvin scale, which came later, took the absolute temperature of gas as 0 degrees and the freezing point of water as 273 degrees.

Initially, thermometers were used to measure atmospheric or body temperatures. With the advancement of science and technology, the need for temperature measurements over a wide range and under different atmospheric conditions with high accuracy and precision became evident. To fulfill these varied requirements, temperature sensors based on different principles were developed. These sensors can be broadly classified into the following categories:

Liquid and Gas Thermometer

Bimetallic Strip

Resistance Thermometers (RTD and Thermistors)

Thermocouple

Junction Semiconductor Sensor

Radiation Pyrometer

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