Why is the height measured with pressure

The Air pressure is this Weight the Column of airwhich are based on a unit area of ​​the ground to outer limit the the atmosphere works. The pressure is from the Dimensions the air under the action of Gravity exercised. The air pressure in the lower air layers of the atmosphere decreases rapidly with increasing altitude and reaches the 500 hPa threshold over Central Europe about 5,500 m above sea level (sea level) and with further increasing altitude the pressure decrease slows down more and more.
The air pressure is worldwide in hPa (Hectopascals = millibars). In Great Britain the air pressure is also in mmHg (mm of mercury column [750 mmHg = 29.53 inches = 1000 mbar = 1 bar)).
Absolute / relative air pressure

The relative air pressure is the value of the locally measured absolute air pressure (effective air pressure) Sea level is calculated back. As a result he has as a for the whole country Reference value valid for the weather condition and the weather development. So z. B. a absolute air pressure of 961 hPa on a height about 600 m above sea level one relative air pressure of 1021 hPa on Sea level. This z. B. Hamburg, Munich, Stuttgart or Cologne always with 1013 hPa or 760 mmHg. The absolute or relative air pressure is in hPa (Hectopascals = millibars) or in Great Britain the air pressure is also in mmHg (mm mercury column [750 mmHg = 29.53 inch = 1000 mbar = 1 bar)).

Baro donors
With the Baro donors will the absolute air pressure the atmosphere at the respective Location measured. The device is suitable for outdoor and indoor use. A tempered, piezoceramic Absolute pressure sensor used, which is characterized by thermal and mechanical stability. The electrical connection is made via an 8-pin terminal strip and a special cable gland with an air pressure compensation function.
Barometer in the environmental measuring range
Source: Adolf Thies GmbH & Co. KG
The baro giver is for him commitment in the Environmental measurement range designed because it depends on high accuracy, quick response, long-term stability and reliability.
The Readings weden as electrical voltage values issued.
A digital baro sender has a Analog output to determine the atmospheric air pressure. An aneroid box with an inductive displacement transducer serves as the sensor. The sensor signal is electronically amplified and digitally displayed on an LED display. For connection to electronic registration and Control devices a current output is available.
Baro donors for data logger systems
Source: Adolf Thies GmbH & Co. KG
With a barometer will the Air pressure in the the atmosphere measured. Nowadays it is in HectoPascal (hPa) specified. But on many scales you can still find the information in Millimeters of mercury ( mm Hg) or millibar (mbar). In order to be able to compare the air pressure values, the display value is always related to at different locations Sea level called. The actual air pressure is not measured, but corrected for the difference between sea level and the measuring location. The air pressure increases 8 meters each around approx. 1 hPa from.
Barometer types
  • Liquid barometer (mercury and weather glass [Goethe barometer])
  • Can barometer and tube barometer
  • Storm glass barometer
With the invention of the Mercury barometer in 1643 by Evangelista Torricelli began the Air pressure measurement. This is a vertical pipe, that with mercury filled and at the top hermetically sealed is. The bottom end is in a Storage jar submerged, which also contains mercury. The liquid flows due to the Dead weight downward. This creates a picture at the upper end vacuum. The Column of liquid stops at a certain height because the air pressure counteracts the column of liquid. Mercury reaches one under normal conditions height of 760 mm. After the inventor became the unit Torr called> 1 torr = 1 mm Hg - approx. 133.32 Pa.


Source: D. Tusche Glashütte Görlitz
A Weatherglass (Goethe barometer) has been used as a Measuring device For Air pressure fluctuations used. The Goethe barometer is the oldest barometer in the world. When the Moors founded Cordoba in Spain in 711, they carried such barometers with them. You were the leading scientists in the world at the time. It wasn't invented until 1643 Toricelli, a student of Galileo Galileo, the more accurate Mercury barometer, which works according to the same principle of the application of pressure on a liquid.
It consists of a with distilled water, that with Food coloring is colored, filled, closed at the top Glass container from the one from the bottom one thin pipe (beak) goes up sideways. The air pressure acting on the thin opening of the spout is compared with the air pressure inside the closed bottle. When the outside air pressure drops, one comes in Low pressure area (bad weather), the internal pressure outweighs the external pressure and the fluid rises in the thin beak. If the external air pressure rises, it comes in High pressure area (Fine weather), then the water sinks in the beak.
These display can but inaccurate be because the Changes in water level also from the Ambient temperature being affected. For this reason, a place of installation or suspension should be chosen that is not in the vicinity of radiators, stoves, cold surfaces and direct sunlight.
Nowadays the weather glass is "only" one Fashion item.





Canned and Tube barometer consist of one evacuated or with Gas-filled metal containers or. tube. The Pointer deflection is through the Bulging or. Curvature behavior implemented.

The Can barometer consists of one evacuated canthat is attached to the bottom of a case with a screw. The air pressure moves a corrugated lid up and down. The lid is compressed when the air pressure rises and expands again when the air pressure falls. This movement is transmitted to a curved spring by a small pin in the middle of the top.

The Tube barometer was founded in 1849 by Eugène Bourdon (Bourdon spring) patented. The principle of action is based on the fact that a curved tube has a larger surface on its outside than on the inside. As a result, there is a stronger force on the outside, depending on the air pressure. The tube bends more and more as the air pressure increases. The movement of the two tube ends turns a toothed sector, which transmits its rotational movement to a pointer.





Source: Friends of old weather instruments
Storm glass (barometer)
The Storm glass(-Barometer) actually not a "real" barometer, because the liquid (Copper sulphate or camphor alcohol solution) does not react directly to the air pressure. The storm glass will since 1750 on Sailing ships for the Storm warning used. To date, there is no precise explanation for how it works.
Source: E. S. Soerensen / Stig Larsen
The storm glass consists of a hermetically sealed glass tube with a saturated, colorless one Copper sulfate or Camphor alcohol solution. When the weather changes, crystals grow in this solution, the size and shape of which indicate the weather.

For the functionality is there various explanations.

  • At a open glass can the Crystal growth caused by falling air pressure, which heralds a storm front. The lower the air pressure, the lower the amount of foreign matter that can be dissolved in a liquid without it becoming oversaturated. The reduced air pressure leads to a temporary supersaturation of the solution, and crystals form temporarily.
  • Since the storm glass is mainly with a hermetically sealed glass tube is used, the air pressure cannot influence the crystal formation or the change or dissolution of the crystals. It is believed that the size of the crystals in the glass depends on the occurrence electromagnetic longitudinal waves (Sferics - small electromagnetic impulses that arise during thunderstorms) are influenced. The storm glass shows sferics and thus the elevator of a low pressure area (bad weather).
The storm glass should be a Weather forecast Allow for a period of approx. 24 to 36 hours.
Fern-like crystals form
Fern-like crystals disappear
Star crystals float down
Crystals all over the liquid
The fern-like crystals are highest on the windward side (windward side).