Technical atmosphere
Physical unit | |
---|---|
Unit name | Technical atmosphere |
Unit symbol | |
Physical quantity (s) | pressure |
Formula symbol | |
dimension | |
system | Technical measurement system |
In SI units | |
Derived from | Meters of water column |
See also: Pascal , Physical Atmosphere |
The technical atmosphere is a non- SI -conforming unit of pressure . Since January 1, 1978, it is no longer permitted in Germany for specifying the pressure. The unit symbol is at .
etymology
The word atmosphere is derived from ancient Greek ἀτμός atmós , German 'steam' , 'haze', 'breath' and σφαῖρα sphaira , German 'ball' ( Latinized sphära ). In the present context it refers to the gaseous envelope above the earth's surface . The pressure unit is based on the size of the normal pressure exerted by this shell, but deviates by around 3% from the physical atmosphere in order to connect to the unit of force, the kilopond .
definition
The technical atmosphere was originally defined as the magnitude of the pressure of ten meters of water column :
Since this variable depends on temperature, acceleration due to gravity and water purity, it was then standardized with the SI pressure unit Pascal :
For example, a pressure of exactly 1 at is created if the density of the pressure-generating liquid is exactly 1 g / cm 3 , the acceleration due to gravity is exactly the same as the standard fall acceleration 9.80665 m / s 2 and the height is exactly 10 m.
Designations
In contrast to the units of the international system of units (SI), it was customary in the technical atmosphere to indicate in the unit symbol what type of pressure specification it was in each case. An index a, ü or u was then added to the unit symbol:
- ata: absolute pressure in at, counted from pressure in a vacuum
- atü: overpressure in at, counted from the pressure of the surrounding air
- atu: negative pressure in at, counted from the pressure of the surrounding air
atü
The old unit atmospheres (for " At mosphären- Ü overpressure") was found for. B. on the tire pressure inflators at gas stations. Since the car tire can only carry the vehicle if the tire has a higher pressure in relation to the ambient pressure (≈ 1 at), tire pressure inflation devices have measured the pressure difference to the ambient pressure accordingly.
Individual evidence
- ^ Paul Dobrinski, Gunter Krakau, Anselm Vogel: Physics for engineers . Springer, 2003, ISBN 3-519-46501-9 , pp. 690 ( limited preview in Google Book search).
- ↑ DIN 1301, Part 3: Units - Conversion of non-SI units , 2018