Ambient Weather Fischer 1486-22-B Manual do utilizador - Página 3

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4. Barometer Operation

Barometer Mechanism Case

Barometer calibration set screw

4.1 How the aneroid barometer works

An aneroid barometer uses a small, flexible metal box called an aneroid cell. This aneroid capsule

(cell) is made from an alloy of beryllium and copper. The evacuated capsule is prevented from

collapsing by a strong spring. Small changes in external air pressure cause the cell to expand or

contract. This expansion and contraction drives mechanical levers such that the tiny movements of the

capsule are amplified and displayed on the face of the aneroid barometer. This model includes a

manually set gold needle which is used to mark the current measurement so a change can be seen. It

was invented by Blaise Pascal.

4.2 Reading the barometer

The ability if the barometer to indicate changes in barometric pressure makes it a useful instrument in

weather forecasting.

The weather forecast or pressure tendency is based on the rate of change of barometric pressure. In

general, when the pressure increases, the weather improves (sunny to partly cloudy) and when the

pressure decreases, the weather degrades (cloudy to rain).

The weather forecast is an estimation or generalization of weather changes in the next 24 to 48 hours,

and varies from location to location. The tendency is simply a tool for projecting weather conditions

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