true altitude at field elevation.
The main difference between altimeter and cabin altimeter is the place where they take their pressure: Altimeter takes the pressure from static ports, while cabin altimeter takes it's pressure from the cabin.
No, that wafers do not move independent of the hole part. When pressure is adjusted, the whole base of the altimeter, including wafers, turn. Thus it changes the setting of the altitude. While the whole base is turning, the barometric pressure dial turns accordingly to show the correct pressure reading you are adjusting it to.
The altimeter works by measuring minute changes in barometric pressure. Barometric pressure decreases as altitude increases, and altimeters are able to detect this change and use it to determine altitude. Barometric pressure is also effected by weather conditions, and so pilots must frequently adjusting the altimeter setting in order to compensate. Some new cessna 172's are being equipped with Garmin GPS cockpits which also get altitude information from GPS receivers, but these aircraft are also equipped with a standard altimeter in the interest of redundancy.
Radar altimeter gets altitude information by bouncing a radio wave off the surface of the Earth and determines the aircrafts altitude by measuring the length of time it takes for the signal to return. Barometric altimeters get altitude information by measuring the barometric air pressure outside the aircraft. Barometric pressure decreases as altitude increases. Radar altimeters will give altitude above ground level while barometric altimeters give altitude above sea level.
The altimeter is basically a specialized pressure gauge. It measures the pressure of the column of air above it. As the altitude varies, the air column height varies, which registers on the altimeter. Since the air pressure also varies with changes in the barometric pressure, altimeters must have an adjustment to compensate for changes in local barometric pressure.
In order to answer your question, first I will briefly explain how an altimeter works. An altimeter senses current atmospheric pressure, and converts it into an altitude reading. The lower the pressure, the higher altitude it will show. In aviation, the pilot needs to select the correct altimeter setting before takeoff and during flight in order to get a correct reading. This is required because the pressure at sea level changes based on weather conditions. For example, if I parked my aircraft at an airport, then came back the next morning, my altimeter would give me a different reading than before because the weather conditions changed slightly overnight. I would then have to change the altimeter to the current local altimeter setting. The local altimeter setting is defined as the atmospheric pressure at Mean Sea Level (MSL) in inches of mercury. Once the altimeter has the pressure at sea level, it can give an accurate reading of the current altitude. Air Traffic Control keeps pilots updated on the local altimeter settings as they fly. The other way to calibrate an altimeter, this only works on the ground, is to turn the pressure selector until the altimeter show the elevation of the airport you are currently at. At this point, the pressure shown is the local altimeter setting.
Typically, enroute aircraft cruise at or above FL180, in which the barometric pressure (or altimeter) setting is standardly 2992. However, if aircraft are below FL180, ATC must issue the nearest accurately reported altimeter setting from an airport every few miles.
Altimeter 2992 means that the air pressure is 29.92 in. HG. 29.92 in. HG. With this information, you would calibrate your altimeter to 29.92.
An altimeter determines the height by the difference in air pressure. The higher you go the thinner the air becomes (lower air pressure). A skydiver will zero his altimeter on the ground, and as the skydiver increases altitude the altimeter can determine the distance traveled by determining the difference in air pressure.
An altimeter (altitude meter) tells the pilots how high the aircraft is flying. There are 2 types of altimeters commonly used in aircraft: pressure altimeters and radar altimeters.
When the barometric pressure is greater than 31.00 inches Hg., issue the altimeter setting and: 1. En Route/Arrivals. Advise pilots to remain set on altimeter 31.00 until reaching final approach segment. 2. Departures. Advise pilots to set altimeter 31.00 prior to reaching any mandatory/crossing altitude or 1,500 feet AGL, whichever is lower. PHRASEOLOGY-ALTIMETER, THREE ONE TWO FIVE, SET THREE ONE ZERO ZERO UNTIL REACHING THE FINAL APPROACH FIX.orALTIMETER, THREE ONE ONE ZERO, SET THREE ONE ZERO ZERO PRIOR TO REACHING ONE THOUSAND THREE HUNDRED.
air pressure