Barometric altimeter

Barometric altimeterBarometric altitude gauge is a measuring device which is mostly used in aviation as a pilot-navigation gauge. It is often called barometric altimeter. It is used for determining relative and absolute flight altitude.That means it determines altitude in relation to a certain reference point (for example level of the airport), or in relation to a sea level - for absolute altitude. Generally, it is a barometer-aneroid with a scale graded not for pressure but for altitude.So how does it work? It is known that atmospheric pressure drops at altitude gain. Let's say, if we know pressure at ground surface and measure it at flight altitude then we can get their difference that will indicate distance between the two points, i.e. flight altitude.Pressure values at airfield or sea levels should be acquired from ground services through radio communication, and then entered into the device manually. It is extremely important to do that right as this affects reading accuracy of the meter.Besides, atmospheric pressure at sea level changes between 950 and 1050 millibars which depends on weather conditions. Even on a stable day atmospheric pressure "floats" ±1 millibar due to air temperature. This actually corresponds to altitude change of ±8 meters. That means that the meter has to be recalibrated from time to time.So why won't pilots just use radio altimeter which works according to the principle of a radio pilot. Then they would know altitude above the current point - without any adjustments. Such device is also installed on most airplanes and, of course, its readings are very important. However, it shows true altitude which is different for all aircrafts as it depends on whether it flies over upland or depression. In this case two planes can be at the same level at such conditions.So that is why barometric altimeter is necessary. It measures relative altitude. After a takeoff all pilots enter zero altitude with isobar of 760 millimeters of mercury. This provides a common reference system for everybody. Thus all aircrafts and air controllers can properly analyze aircraft location. Altimeters are also used by mountain climbers, geologists, and tourists. They can adjust its readings when located in places with known elevation.The meter can be graded in meters or feet. It has two pointers just like in a watch. Each sector means 100 m for one pointer and 1000 m for another one.Barometric altimeter was invented by Paul Collsman in the beginning of the ...

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