What Is an Air Thermometer?

Air thermometer is an instrument invented by Galileo based on the thermal expansion and contraction of gas. Also known as "Galileo thermometer" refers to a tool for measuring temperature developed based on the principle of thermal expansion and contraction of materials, which has been improved several times to become a commonly used temperature measuring device today.

As early as 250 BC, Philo of Bizatium described experiments that heated the air to expand it. By 100 AD, Hellen of Alexandria once again described the same experiment. These indicate that humans have long recognized that air has thermal expansion

In 1632, French physicist Rey first improved Galileo's air thermometer. He turned the device of Galileo upside down, pouring water into the glass bubble, and leaving the air in the glass tube, still using the height of the water column in the glass tube to indicate the temperature level. Because this improvement made water a temperature-measuring substance, it actually became the first liquid thermometer. The disadvantage is that the upward nozzle is not closed, and the water will continuously evaporate, which affects the accuracy of the measurement. Scientists are studying the relative size of glass bubbles and glass tubes to reduce this evaporation, so that the liquid can rise and fall throughout the length of the glass tube over the course of a year. Although from the perspective of today, such efforts are not in the right direction, but from the perspective of the whole process of thermometer development, such efforts are valuable and will inevitably appear. Without the various improvements that were made in every aspect, there would not be the perfection today.

In 1657, members of the Simanto Academy of Sciences in Florence proposed the idea of sealing pipes and suggested that alcohol be used instead of water as a temperature measurement substance, so that the earliest thermometers entered a more practical stage.

In the 18th century, Leoomer in France had strongly opposed the use of mercury as a temperature measurement substance in view of the small expansion coefficient of mercury. He is committed to making an alcohol thermometer that is both convenient and accurate. But because his thermometer results are not good, and different thermometers are not consistent,

Thermometer rotating thermometer

The rotary thermometer is made of a rolled bimetal. The bimetal is fixed at one end and connected to a pointer at the other end. Due to the different degree of expansion of the two metal sheets, the bimetal sheet curls differently at different temperatures, and the pointer then points to different positions on the dial. The temperature can be known from the reading on the dial.

Thermometer semiconductor thermometer

The resistance change of a semiconductor is different from that of a metal. When the temperature increases, the resistance decreases, and the change range is larger. Therefore, a small amount of temperature change can also cause a significant change in the resistance. The manufactured thermometer has a higher precision and is often called a temperature sensor.

Thermocouple Thermometer

A thermocouple thermometer consists of a sensitive voltmeter connected to two different metals. At different temperatures, metal contacts will produce different potential differences between the two ends of the metal. The potential difference is so small that it requires a sensitive voltmeter to measure it. From the reading of the voltmeter, you can know what the temperature is.

Thermometer optical pyrometer

If the temperature of an object is high enough to emit a large amount of visible light, the temperature can be determined by measuring the amount of its thermal radiation. This type of thermometer is an optical thermometer. This thermometer is mainly made of a telescope with a red filter and a set of circuits with a small bulb, an ammeter and a variable resistor. Before use, establish the relationship between the temperature corresponding to the different brightness of the filament and the reading on the galvanometer. When using, align the telescope with the object to be measured and adjust the resistance so that the brightness of the bulb is the same as the object to be measured. At this time, the temperature of the object to be measured can be read from the galvanometer.

LCD thermometer

Liquid crystals made with different formulations have different phase transition temperatures. When the phase transition occurs, the optical properties of the liquid crystal also change, making the liquid crystal appear discolored. If liquid crystals with different phase transition temperatures are coated on a piece of paper, the temperature can be known from the change in the color of the liquid crystal. The advantage of this thermometer is that it is easy to read, but the disadvantage is insufficient accuracy. It is often used in ornamental fish tanks to indicate the water temperature.

Digital thermometer

Digital thermometer uses a temperature sensor to convert (temperature) into a digital signal, and then displays the temperature in digital form through a display (such as LCD, digital tube, LED matrix, etc.). It can quickly and accurately measure the highest value of human body temperature. Compared with mercury thermometers, it has the advantages of convenient reading of numbers, short measurement time, high measurement accuracy, memorization, and prompt sounds. Especially, digital thermometers do not contain mercury and are harmless to the human body and the surrounding environment. They are especially suitable for hospitals and families.

Mercury thermometer

The spilled mercury must be immediately collected with a dropper and a brush to collect information on the digital thermometer display, and covered with water (preferably with glycerin), and then sprinkle sulfur powder on the contaminated area. When there is no liquid (usually about a week), Can be cleaned.

There is no estimate of the reading of this thermometer. Or the last digit of the reading is the exact value, so there is no need to estimate the number after the graduation value. ^[3]