Pressure Measurement Devices

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

11

2

1

112

1122

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2211

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small very is A

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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

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PP

datumAt

liquidBBAA

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x- x

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1 2Inverted U-tube Differential manometers

Differential manometers

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datumAt

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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