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Classification of pressure gauges. their construction and application
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Pressure Measurement Devices
Classification of Pressure Measuring Devices
Pressuremeasurement
Atmospheric Pressure/
BarometersManometers Pressure Gauges
Classification of Barometers
Barometers
Mercury Aneroid
In 1643, Evangelista Torricelli invented the barometer
Torricelli’s barometer used a glass column suspended in a bowl of mercury. The pressure of the air molecules pushed the mercury up into the glass tube.
The weight of the mercury in the tube was equal to the weight of the air pressing down on the mercury in the dish.
As atmospheric pressure increases…
The mercury in the tube rises.
The Mercury Barometer
Good: Bad:
•Simple to construct
•Highly accurate
•Glass tube is fragile
•Mercury is very toxic!
The Aneroid Barometer
•No fragile tubes!
•No toxic chemicals!
•No batteries!
•Never needs winding!
An aneroid barometer uses a cell which has had most of the air removed.
As the air pressure around the cell increases, it presses on the cell, which causes the needle to move.
Television weather forecasters usually give barometric pressure in inches of mercury. However, meteorologists measure atmospheric pressure in millibars.
MILLIBARS
Classification of Pressure Measuring Devices
Pressuremeasurement
Atmospheric Pressure/
BarometersManometers Pressure Gauges
√
Classification of ManometersManometers
Simple Manometers
Piezometers
U- Tube Manometers
Single Column
Manometers
Vertical Inclined
Differential Manometers
0p h p 1Ap h
•Piezometer is simple and accurate
•Piezometer is only suitable if the pressure in the container is greater than atmospheric pressure
•Fluid in the container in which the pressure is measured must be a liquid rather than gas
Piezometer tube.
Simple U-tube manometer.
1 2 0Ap h h
2 1Ap h h
Single column manometers
Vertical Single manometerThe volume that move from x-x to z-z datum= the volume that rise in right tube above x-x datum
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V1=V2
Inclined single column manometers
Single column manometers
This type of manometers is useful for the measurement of small pressure and is more sensitive than the vertical tube type
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1122
222211
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Classification of Manometers
Manometers
Simple Manometers Differential Manometers
Two Piezometer
Inverted U-Tube
U-Tube Differntial
Micro-Manometer
Two Piezometer manometers
ghhgPhgP
PP
datumAt
liquidBBAA
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1 2Inverted U-tube Differential manometers
Differential manometers
ghhgPhgP
PP
datumAt
liquidBBAA
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1 2Inverted U-tube Differential manometers
Differential manometers
Micro manometers
Classification of Pressure Gauges
Pressuremeasurement
Atmospheric Pressure/
BarometersManometers Pressure Gauges
Bourden Tube
Diaphram Bellows Deadwei
ght
Bellows
Made of Bronze, S.S., BeCu, Monel etc..The movement is proportional to number of convolutionsSensitivity is proportional to sizeIn general a bellows can detect a slightly lower pressure than a
diaphragmThe range is from 0-5 mmHg to 0-2000 psiAccuracy in the range of 1% span
Bellows
Bourdon Tube
Bourdon Tubes
• (a) C-type tube.• (b) Spiral tube. • (c) Helical tube
Bourdon Tubes
Diaphragm
• A diaphragm usually is designed so that the deflection-versus-pressure characteristics are as linear as possible over a specified pressure range, and with a minimum of hysteresis and minimum shift in the zero point.
(a) flat diaphragm; (b) corrugated diaphragm
Diaphragm
Dead Weight Pressure Gauges
