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M.Sc-I (Electronics)DOES – PC (UOP)
Manometer
Manometers are devices in which one or more columns of a liquid are used to determine the pressure difference between two points.
U Tube Manometer:
U- Tube Manometer:• A manometer is comprised
of a bulb containing a gas and a U-shaped tube.
• The U-shaped tube is partially filled with mercury. The weight of the mercury puts pressure on the gas.
• If the U-tube is OPEN there is also air pressure acting on the gas.
• The gas molecules put pressure on the mercury.
PHg
Closed Manometers:
• There is a balance between the weight of the mercury on the left (PHg) and the pressure of the gas on the right (Pgas).
• The difference between the heights of the mercury on each side of the tube is a measure of the pressure of the gas.
Pgas = Dh
vacuum
PHg
Open Manometers:• When gas pressure is greater than
atmospheric pressure, the mercury is pushed toward the open end.
• The balance is between the gas on the right, and the air plus mercury on the left.
Pair + PHg = Pgas
• The weight of the mercury is measured as the height difference:
PHg = Dh
So Pgas = Pair + Dh
Pair
PHg
Open Manometers:
• When gas pressure is less than atmospheric pressure, the mercury is pushed toward the gas reservoir.
• The balance is between the air on the left and the gas plus mercury on the right:
Pair = Pgas + PHg
• The weight of the mercury is measured as the height difference:
PHg = DhSo Pair = Pgas + Dh
Or Pgas = Pair- Dh
PHgPair
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