Presentation about pressure devices, hope it will help you.

2. PRESSURE
MEASURMENT
DEVICES

3. 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)

4. CONTENTS:
 INTRODUCTION
 PRESSURE MEASURMENTS TERMS
 PRESSURE SOURCES
 PRESSURE MEASUREMENT DEVICES

5. 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

6. 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.

7. PRESSURE SOURCES
• STATIC PRESSURE
Due to weight of the molecules “pressing down”

8. PRESSURE SOURCES
• Dynamic Pressure
Relative movement when a body is moving through air.

9. 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

10. PRESSURE MEASUREMENT DEVICES
• ELECTRICAL DEVICES
1. Strain gauge
2. Piezoelectric

11. 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.

12. 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

13. 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

14. 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

15. 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.

16. 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

17. 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

18. 2. PIEZO-ELECTRIC
• Crystals elastically deformed when force applied
• Measure rate of change of deformation
• Electrical output proportional to applied acceleration