For the first time, mankind has faced the problem of measuring pressure during the construction of fountains in Florence. Fortunately for the builders, the physicist Toricelli lived in the city, who transferred the problem from the construction site to his laboratory, replacing the water with mercury for a more compact experience.
History has left no evidence of how much the discovery of the Italian physicist helped builders, but the fact that humanity has received evidence of the existence of atmospheric pressure is undeniable.
The torchelli was picked up by the great Blaise Pascal, who was able to measure atmospheric pressure and prove experimentally that it directly depends on altitude. Thus, the first pressure units were expressed as the height of the mercury column, measured in elbows and inches. It is only natural that modern pressure units are named after both scientists.
Various instruments are used to measure pressure. The simplest is a liquid manometer. It is said that Leonardo da Vinci himself had a hand in his invention, but even for this ingenious conjecture, there was no use in the life of the author.
Only since the time of Pascal, a U-shaped tube filled with mercury was used to measure pressure. Subsequently, mercury was replaced by vacuum oil.
If the pressures are equal at both ends of the tube, the liquid level is the same; when pressure is applied to one of the ends of the tube, a height difference occurs.
P * (1) –P * (2) = gph, where g is the acceleration of a freely falling body, P is the liquid density, h is the difference in the heights of the liquid levels in the pressure gauge.
Despite the fact that liquid pressure gauges are highly sensitive, their scope is quite limited due to their bulkiness, inconvenience in operation and a relatively small measurement range, from 20 kPa to 140 kPa.
With the development of technology, manometers with a Bourdon tube began to gain more and more popularity, they are also called deformation ones in another way. Inside such a manometer is a C-shaped brass tube with a gear mechanism. When pressure is applied to the free end, the tube straightens, and the gear train moves the arrow, which indicates the pressure on the graduated scale of the device. The more complex the shape of the tube, the less error the tool has.
Mechanical pressure gauges are used to measure pressure from 40 kPa to 100MPa. They are characterized by a deterioration in measurement accuracy during long-term operation. This is due to permanent deformation of the working element.
Piezoelectric pressure gauges are used to measure pulsating pressure up to 8 * 10 ^ 3 GPa.
Historically, the units of pressure have not been correlated with each other multiple times, it seems that there is complete chaos. The general formula for measuring pressure is as follows: P = F / S where P is pressure, F is force, S is area. In the SI system, force is measured in Newtons, the area in square meters means that the dimension of the pressure unit will be n / m ^ 2, and it is called Pascal. But in practice, atmospheres, bars, tori, mm of mercury, mm of water, kg / cm ^ 2 are also often used.
Let's try to clarify this problem. The unit of measurement for atmospheric pressure is mm of mercury or torus; As you know, the atmospheric pressure taken as the standard is equal to 760 mm Hg - this value is called the atmosphere; the bar is approximately equal to one atmosphere - this is the old unit of the GHS system; there is also a technical atmosphere, which is equal to one kg / cm ^ 2 - all these quantities are used as off-system units for measuring gas pressure; mm of water is used in hydraulics and is equal to 13.6 tori. It should be noted that in physics, pascal and its derivatives are recognized as the only system units for measuring pressure.