Presentation(pressure devices).pptx

PRESSURE

MEASURMENT

DEVICES

GROUP MEMBERS:

WASEEM AHMED (K-15ME-19)-GL

MUHAMMAD SHEERAZ (K-15ME-01)-AGL

RASHEED AHMED (K-15ME-17)

ZAIN-UL-AABDIN (K-15ME-18)

BILAL CHUHAN (K-15ME-20)

CONTENTS:

INTRODUCTION

PRESSURE MEASURMENTS TERMS

PRESSURE SOURCES

PRESSURE MEASUREMENT DEVICES

INTRODUCTION

Pressure is the force exerted per unit area.

Pressure is the action of one force against another force. Pressure is force applied to, or distributed over, a surface. The pressure P of a force F distributed over an area A is defined as P = F/A.

TOTAL VACUUM - 0 PSIA

PRESSURE

ABSOLUTE

GAUGE

COMPOUND

BAROMETRIC RANGE

ATMOSPHERIC PRESSURE

NOM. 14.7 PSIA

PRESSURE MEASURMENT TERMS

Absolute Pressure

Measured above total vacuum or zero absolute. Zero absolute represents total lack of pressure.

Atmospheric Pressure

The pressure exerted by the earth’s atmosphere. Atmospheric pressure at sea level is 14.696 psia. The value of atmospheric pressure decreases with increasing altitude.

Barometric Pressure

Same as atmospheric pressure.

Gauge Pressure

The pressure above atmospheric pressure. Represents positive difference between measured pressure and existing atmospheric pressure. Can be converted to absolute by adding actual atmospheric pressure value.

PRESSURE SOURCES

• STATIC PRESSURE

Due to weight of the molecules “pressing down”

PRESSURE SOURCES

• Dynamic Pressure

Relative movement when a body is moving through air.

PRESSURE MEASUREMENT DEVICES

MECHANICAL DEVICES

1. Bourdon Tube

2. Helix and spiral tubes

3. Spring and Bellows

4. Diaphragm

5. Manometer

6. Single and Double Inverted Bell

PRESSURE MEASUREMENT DEVICES

• ELECTRICAL DEVICES

1. Strain gauge

2. Piezoelectric

PRESSURE MEASUREMENT DEVICES(MECHANICAL)1. BOURDON TUBE

The Bourdon tube is a hollow tube with an elliptical cross section. When a pressure

difference exists between the inside and outside, the tube tends to straighten out and the

end moves. The movement is usually coupled to a needle on a dial to make a complete

gauge. It can also be connected to a secondary device such as an air nozzle to control air

pressure or to a suitable transducer to convert it into an electric signal. This type can be

used for measuring pressure difference.

2. HELIX AND SPIRAL TUBES

• With one end sealed, pressure causes the tube to straighten out.

• Helical suitable up to 500000 kPa

• Spiral suitable up to 28000 kPa

3. SPRING AND BELLOWS

• Expandable element

• Free end responds to pressure

• Spring used to oppose force

• Linkage connects end to pointer for indication

• Primarily for ON / OFF control

• Provides clean contacts for electrical circuits

• Responds to pneumatic or hydraulic pressure changes

4. DIAPHRAGM

• Pressure applied to actuator

- Diaphragm, bellows or piston type

• Piston used for hydraulic fluids at high pressure

• Not used for air or water as accuracy is limited

• Sensor measurement dependent on deflection of diaphragm

• Flexible disc

• Flat or with concentric corrugations

• Sheet metal with high tolerance dimensions

5. MANOMETER

• Simplest form is U-shaped, liquid filled tube

• Reference and measured pressure applied to ends of tube

• Difference in pressure causes difference in liquid level

between sides.

6. SINGLE AND DOUBLE INVERTED BELL

• Measures pressure difference between sides of bell shaped compartment

• The bell instrument is used where very low pressures are to be measured, typically 0 - 250 Pa

• To reference to surrounding conditions

Gauge pressure measured

Lower compartment vented to outside

PRESSURE MEASUREMENT DEVICES(ELECTRICAL)

1. Strain gauge

• Metal wire or semiconductor chip

• Change in resistance as metal is deformed by pressure

• Temperature sensitive

• Temperature compensation required

• Often use Wheatstone bridge

2. PIEZO-ELECTRIC

• Crystals elastically deformed when force applied

• Measure rate of change of deformation

• Electrical output proportional to applied acceleration