altimeter

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altimeter

(ăltĭm`ĭtər, ăl`tĭmē'tər), device for measuring altitude. The most common type is an aneroid barometerbarometer
, instrument for measuring atmospheric pressure. It was invented in 1643 by the Italian scientist Evangelista Torricelli, who used a column of water in a tube 34 ft (10.4 m) long.
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 calibrated to show the drop in atmospheric pressure in terms of linear elevation as an airplane, balloon, or mountain climber rises. It shows height above sea level, but not above such land features as hills, mountains, and valleys. The radio altimeter, or terrain-clearance indicator, is an absolute altimeter; it indicates the actual altitude over water or over terrain, however uneven. It operates by first sending either continuous or pulse radio signals from a transmitter in an aircraft to the earth's surface. A receiver in the aircraft then picks up the reflection of the signals from the surface. The time it takes for the signals to travel to the earth and back is converted automatically into absolute altitude that can then be read from a calibrated indicator. The radio altimeter is used in the automatic landing systems of aerospace vehicles; systems developed from radio altimeters can automatically control military aircraft flying at high speeds and low altitudes.
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altimeter

[al′tim·əd·ər]
(engineering)
An instrument which determines the altitude of an object with respect to a fixed level, such as sea level; there are two common types: the aneroid altimeter and the radio altimeter.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

altimeter

altimeter
Altimeter indicator dial.
altimeter
Construction of a simple altimeter.
An instrument to indicate the height of an aircraft above a predetermined datum, normally sea level. Specifically, an instrument similar to an aneroid barometer that utilizes the change of atmospheric pressure with altitude to indicate the approximate elevation above a given point or plane used as a reference. A simple pressure altimeter is an airtight metal case, the interior of which is kept at atmospheric pressure by a tube connecting it to the static tube of the ASI (airspeed indicator). Inside the instrument case, a partially evacuated aneroid capsule is secured at the center of one of its faces to a base rigidly fixed to the casing. A leaf spring prevents the collapse of the capsule. The capsule expands as aircraft gains height. The expansion of the capsule is converted into height through a system of gears. A pressure altimeter suffers from barometric, temperature, instrument, and lag errors. Radio or radar altimeters indicate heights above ground level.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved

altimeter

an instrument that indicates height above sea level, esp one based on an aneroid barometer and fitted to an aircraft
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Some autopilot altitude preselect systems, including models from S-TEC, BendixKing and Sperry, rely on the encoding altimeter for a baro source input.
Given the inevitable lag for processing time, reaction time, radar sweeps, etc., I'd probably set my altimeter to indicate about 3230feet when the controller reported seeing 3200 feet.
Some of these works focus on autonomous orbit determination based on either optical imagery or altimeter data or inter-satellite range data.
The cutaway drawing on the opposite page might help refresh our understanding of how changes in air pressure and temperature can affect an altimeter. Basically, the altimeter senses pressure, and displays a lower altitude when experiencing higher pressure and, conversely, a high altitude in low-pressure environments.
Avionics systems supplier FreeFlight Systems said today that its newest radar altimeter display, the RAD-40, has been granted TSO certification in the US.
Earlier yesterday the coroner ordered the MoD's barrister, Oliver Sanders, to get Capt Wright's altimeter, which indicates altitude, tested to see if it works or not.
The error is believed to have been caused by multiple factors including a malfunctioning altimeter showing different data for the pilot and the copilot, an erroneous assumption by the pilot and the failure of maintenance staff to give the pilot proper guidance.
Using the ICS, he also announced three indications of climb on the radar altimeter, vertical-speed indicator, and barometric altimeter.
This article describes a frequency modulated single-antenna radio altimeter The entire structure includes a transmitter/receiver network with a single antenna for operation in both a continuous wave (CW) mode and an interrupted continuous wave (ICW) mode to provide a highly accurate altitude indication.
Robin Tudor, business services manager at Liverpool John Lennon Airport, said: ``There was a discrepancy between the altimeter readings but the problem rectified itself.
We also had new radio altimeters to accurately set the pressure altimeters and, thus, greatly improve the ability to make low-altitude attacks on shipping.