What type of barometer is used to measure altitude

Banfield, Edwin. Barometers: Aneroid and Barographs. Trowbridge, Wiltshire, England: Baros Books, Brombacher, W. Mercury Barometers and Manometers. Washington, DC: U. Department of Commerce, National Bureau of Standards, The Illustrated Science and Invention Encyclopedia. Westport, CT: H. The seal on the open end is removed, which causes a portion of the mercury to flow out of the tube forming a near-vacuum at the closed end of the tube.

It is a near-vacuum because of the mercury vapor present in that portion of the tube. The remaining mercury in the tube represents the balance between the atmospheric pressure pushing on the surface of the mercury in the cistern, the weight of the mercury, and the vacuum in the tube. This is the absolute atmospheric pressure measured in units corresponding to the height of mercury above the surface of the mercury in the cistern.

A common pressure unit for barometric pressure is millimeters of mercury mmHg or inches of mercury inHg. Mercury manometers were one of the first barometers to be used and were instrumental in the discovery of principles governing the atmosphere. The accuracy of mercury barometers depends on the accuracy of the height measurement, density and vapor pressure of the mercury used.

Mercury barometers are impractical for many industrial applications and their use has diminished over time due to their size, cost, delicate nature, and toxicity of mercury. An aneroid barometer is made without the use of mercury or any other fluid. The chamber is sealed with most of the air pumped out of it. The difference in pressure between the inside of the chamber a near-vacuum and the outside causes it to expand or contract, depending on the change in atmospheric pressure.

Mechanical linkages transfer this movement to a calibrated dial that shows the atmospheric pressure. Aneroid barometers range in price and accuracy based on the manufacturer and quality.

Aneroid barometers are typically used aboard ships and sailing vessels for the purpose of monitoring the weather, in homes for the same purpose, or as a novel decoration. A digital barometer uses a micro-electromechanical MEMs sensor to measure pressure. Pressure sensing MEMs are typically tiny integrated circuits IC , which combine electronic and mechanical elements to sense pressure. The most common MEMs pressure sensors are either capacitive or piezoresistive. Capacitive sensors sandwich conducting layers between a diaphragm to form a capacitor.

The mercury sits in a circular, shallow dish surrounding the tube. The mercury in the tube will adjust itself to match the atmospheric pressure above the dish. As the pressure increases, it forces the mercury up the tube. The tube is marked with a series of measurements that track the number of atmospheres or bars.

Observer s can tell what the air pressure is by looking at where the mercury stops in the barometer. In , the French scientist Lucien Vidi invented the aneroid barometer. An aneroid barometer has a sealed metal chamber that expand s and contract s, depending on the atmospheric pressure around it.

Mechanical tools measure how much the chamber expands or contracts. These measurements are align ed with atmospheres or bars. The aneroid barometer has a circular display that indicate s the present number of atmospheres, much like a clock. One hand moves clockwise or counterclockwise to point to the current number of atmospheres. The terms stormy, rain, change, fair, and dry are often written above the numbers on the dial face to make it easier for people to interpret the weather.

Aneroid barometers slowly replaced mercury barometers because they were easier to use, cheaper to buy, and easier to transport since they had no liquid that could spill.

Some aneroid barometers use a mechanical tool to track the changes in atmospheric pressure over a period of time. These aneroid barometers are called barographs. Barograph s are barometers connected to needles that make marks on a roll of adjacent graph paper. The barograph records the number of atmospheres on the vertical axis and units of time on the horizontal. The spikes in the graph show when air pressure was high or low, and how long those pressure systems lasted.

A severe storm, for instance, would appear as a deep, wide dip on a barograph. Many digital barometers display both current barometric readings and previous 1-, 3-, 6-, and hour readings in a bar chart format, much like a barograph. They also account for other atmospheric readings such as wind and humidity to make accurate weather forecasts. This data is archive d and stored on the barometer and can also be downloaded onto a computer for further analysis.

Digital barometers are used by meteorologists and other scientists who want up-to-date atmospheric readings when conducting experiments in the lab or out in the field. This type of digital barometer uses atmospheric pressure data to make accurate elevation readings. App s like PressureNet automatically collect barometric measurements from each of its users, creating a vast network of atmospheric data. This data network makes it easier and faster to map out storms as they develop, especially in areas with few weather station s.

A barometer measures atmospheric pressure. Air Force. Evangelista Torricelli. GPS receiver. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

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