first time humanity is faced with the problem of measuring the pressure in the construction of fountains in Florence.Fortunately for builders in the city of resident physicist Torricelli, who suffered a problem from the construction site in his lab, replacing the water with mercury to a more compact experience.
history has left evidence of how the opening of the Italian physicist helped the builders, but the fact that mankind has received proof of the existence of atmospheric pressure, is indisputable.
baton picked up a great Torricelli Blaise Pascal, who was able to measure the atmospheric pressure and to prove empirically that it depends on the altitude.Thus, the first pressure unit were expressed Hg height measured in inches and elbows.It is only natural that modern pressure units named after the two scientists.
To measure the pressure applied various instruments.The most simple - a liquid manometer.It is said that his invention had a hand in Leonardo da Vinci, but also for that of his brilliant guess there was no use in his lifetime.
only from the time of Pascal for pressure began to use a U-shaped tube filled with mercury.Subsequently, mercury was replaced with a vacuum oil.
With equal pressure at both ends of the tube the liquid level is the same, when pressure is applied to one end of the tube there is the height difference.
P * (1) -P * (2) = gph, where g - acceleration of a freely falling body, P - the density of the liquid, h - height difference of liquid levels in the gauge.
Despite the fact that liquid manometers have high sensitivity, their field of application is quite limited because of their bulk, inconvenience in exploitation and comparatively small measuring range of 20 kPa to 140 kPa.
With the development of technology is growing in popularity began to take Bourdon tube pressure gauges, otherwise they are called deformation.Inside this gauge is C-shaped tube made of brass with a gear mechanism.When pressure is applied to the free end of the tube is straightened, and the gear train moves the arrow that indicates the amount of pressure on the graduated scale of the instrument.The more complex form of the tube, the tool has a smaller error.
Mechanical gauges used to measure the pressure of 40 kPa to 100MPa.They are characterized by the deterioration of the measurement accuracy during continuous operation.This is due to the residual strain operating element.
To measure the pulsating pressure of up to 8 x 10 3 GPa using piezoelectric pressure gauges.
Historically, that the pressure units are not related to each other a multiple of, it seems that there is total chaos.The general formula for measuring the pressure as follows: P = F / S where P - pressure, F - force, S - area.In the SI system the force is measured in Newtons, the area in square meters - hence the dimension of the pressure unit is n / m ^ 2, and it is called Pascal.But in practice it is often used also the atmosphere, the bars, the Torah, mm Hg, mm water column, kg / cm ^ 2.
try to clarify this issue.Units of atmospheric pressure - it mmHg or torr;as you know, taken as the standard atmospheric pressure is 760 mm Hg - this value is called the atmosphere;bar is approximately equal to one atmosphere - it's an old unit of the GHS;there are still technical atmosphere, which equals one kg / cm ^ 2 - all of these values are used as a non-SI unit of measurement of the gas pressure;mm water column is used in hydraulics and is 13.6 torus.It should be noted that in physics pascal and derivatives thereof are recognized as single system pressure unit.
