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7/30/2019 Group 4 Reporting

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GROUP 4


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PRINCIPLESOF

ANEROID

BAROMETER


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Aneroid barometeris an

instrument

measuring atmospheric pressure

invented by French scientist Lucien

Vidie. It is constructed on the

following principles:


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Parts of an Aneroid Barometer


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Principles of Mercurial Barometer


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A mercury barometer has a

glass tube with a height of at

least 84 cm, closed at one

end, with an open mercury-filled reservoir at the base.

Invented by Evangelista

Toricilli

The weight of the mercury

creates a vacuum in the top

of the tube. Mercury in the

tube adjusts until the weightof the mercury column

balances the atmospheric

force exerted on the

reservoir.


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High atmospheric pressure places more forceon the reservoir, forcing mercury higher in thecolumn.

Low pressure allows the mercury to drop to a

lower level in the column by lowering theforce placed on the reservoir.

Since higher temperature at the instrument

will reduce the density of the mercury, thescale for reading the height of the mercury isadjusted to compensate for this effect.


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DISTINGUISHTHEATMOSPHERIC

PRESSUREREADINGOF ANEROIDBAROMETERANDTEMPERATURE

READING.


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To read your barometer, first tap the

glass lightly, but firmly, to ensure that

the linkage mechanism is not sticking.

The hectopascal is the international

meteorological unit of pressure. One

hectopascal is exactly equal to onemillibar, the unit of pressure mainly

used for barometer scales before

1986.


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The other hand that is found on

most instruments is the 'setpointer' (usually brass). This can

be turned by means of the knob

at the centre of the glass so that itcovers the reading pointer. In this

way you can tell, next time you

check your barometer, whether

the pressure is now lower or

higher and by how much.


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STATE THE FUNCTIONS OF

HYGROMETER AND EXPLAINTHEIR BASIC PRINCIPLES


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Hygrometer

Instrument used in finding the Dew - point

temperature .

It is always accompanied by a table which

shows the difference in dew point between

the dry-bulb temperature and the wet-bulb

temperature


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Example :

Dry bulb temperature (t) = 20.8C

Wet bulb temperature (t) = 19.4CCalculations:

you get t-t = 1.4 and t=19.4. In the table, you

can find:

Dew point temperature = 19.0 for t-t-1.0 and t-19.5(the

nearest value for 19.4)

Dew point temperature = 18.8 for t-t= 1.5 and t = 19.5.

then make the interpolation to get the dew-point

temperature for t-t = 1.4 and t = 19.5


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19.0+ (18.8-19.0)(1.4-1.0)/(1.5-1.0) = 18.8

Finally , make the interpolation to get the dew

point temperature for t-t = 1.4 and t = 19.4assuming the variance of t is approximately

the same with 18.8 0.1 = 19.7C

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