How does a bimetal thermometer work?

The origins of some branches of science track almost impossible. How, for example, you can determine: who was the first astronomer or mathematician. Meteorology is likely to be attributed to such areas of human knowledge. The weather could not but interest man, especially in the antediluvian times, when he was much less protected from natural disasters. One of the basic characteristics of weather is temperature.

Why measure the temperature?

We are used to measuring the temperature inside and outside the dwelling, and we usually look at the thermometer outside the window before we leave the house, wondering whether to wear a scarf and gloves. An alcohol, mercury, bimetal thermometer outside the window is a familiar picture for most citizens. Practically there is more than one medical examination without measuring body temperature.

bimetal thermometer

But meteorologists are not only interested in the value of air temperature in terms of the impact on our skin.The formation of air currents, winds, which form the weather of the continents, depends on how heated up these or other layers of the atmosphere.

Temperature measurement in production is a separate topic. Such processes as cracking, polymerization, crystallization, and thousands of other chemical and physical phenomena used in plants and factories occur at precisely defined temperature and pressure. And sometimes accuracy is required in tenths of a degree. And in this case, traditional thermometers, using the effect of the expansion of bodies when heated, are quite difficult to apply. This is especially true when working in ultra-low temperatures, when most liquids lose their fluidity. And here a bimetallic thermometer - TB, as it is customary to write in abbreviated form, often comes to the rescue.

How did you learn to measure temperature?

The inventor of the thermometer is not known for certain. Some researchers attribute this merit to the great Galileo. The device for measuring temperature, created by him, used compression-expansion of air. Even the scale of the device (they called it a thermoscope) did not have.With its help, observing the movement of the boundary of the liquid pushed out by air, it was possible only to determine whether the temperature rises or falls. The accuracy of such a device left, to put it mildly, much to be desired: its work was significantly influenced by atmospheric pressure, and the boundary of water and air, both the air saturation with water vapor and the dissolution of air in water, constantly "knocked" the setting.

Later, liquids with a significant coefficient of thermal expansion began to be used as the working fluid. Thermometers have become much more accurate, the size of the structure has decreased to acceptable and this device slowly began to become widespread.

bimetal thermometer

Mercury, various alcohols and even kerosene are used as working fluids in such thermometers.

Other more modern and progressive methods of measuring temperature are methods based on electricity. It is known that all electrically conductive materials change resistance depending on temperature. The soldering of some different metals when heated (thermoelectric couple) produces an electric current.These and other physico-chemical phenomena formed the basis of means for measuring temperature.

Bimetallic products

A bimetallic thermometer, like a liquid, uses the effect of expanding bodies when heated. Only in the quality of the working fluid are used not liquids or gases, but solid objects.

Consider its principle of action. Take two plates of different materials with different coefficients of thermal expansion.

bimetallic thermometer

At a temperature of T1 the sizes of the plates will be equal. But with increasing temperature (up to T2) it is obvious that the product, which is made of a material with a large coefficient of expansion, will increase more. This is the case if both plates are on their own. But it is necessary to combine these two plates (riveting, soldering, hot pressing, etc.), as the picture changes.

bimetal thermometer

The different size of plates welded together (∆a <∆b) will force the whole structure to bend. And the bulge will appear from the side of the material with a large coefficient of expansion. Using this simple effect, a bimetallic thermometer works. The magnitude of the bend indicates the ambient temperature. In various designs, only the methods for measuring this bend differ.


What qualities distinguish a bimetallic thermometer from fellows?

- The liquid in a glass vessel itself is dangerous, especially if it is mercury, it is obvious that the bimetallic structure does not have this disadvantage.

“Also, such a system does not need thermoelectric thermometers for power supply and additional equipment, which makes it more mobile and more convenient to use.

- Expansion of liquids under the action of temperature occurs irregularly, and therefore their readings are not always correct, the bimetallic thermometer does not suffer from this disadvantage.

bimetal thermometer radial

Its design uses a plate twisted into a spiral. Due to the large length of the working fluid temperature measurement is very accurate.

WIKA products

The German company Wika is a recognized leader in the manufacture of devices for measuring temperature and pressure. The company's specialists did not accidentally pay attention to the effect of changing the geometry of bimetallic plates. It must be said that the company has achieved perfection in the manufacture of such temperature measuring instruments.Bimetallic thermometer Wika is available in both domestic versions and in special versions. The main consumers of Wika products are firms engaged in heat networks and boiler equipment.

bimetallic thermometer wika

Due to the use in the production of advanced technical solutions, careful selection of the highest quality materials, Wika products are successfully sold in more than one hundred countries of the world.

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