Chapter 3 Pressure measurement - Process Safety

Chapter 3 Pressure measurement - Process Safety

1. PRESSURE
MEASUREMENT
Pressure-Measuring Devices
Criteria For Selecting A Suitable
Pressure-measuring Instrument

2. OBJECTIVES
After you study this chapter, you should be
able to
1.Explain the pressure measurement.
2.Describe the importance of pressure
measurement.
3.Explain the basic operation, list the
advantages and disadvantages of each
pressure measurement device.

3. Introduction
Slightly change in atmospheric pressure
affect organism.
P vs T, P vs V mole/ mass. Purpose of
other variable measurement such as ……
Absolute pressure vsgauge pressure
Distillation column operated by
manipulating pressure and temperature.

4. Static Pressure and Dynamic
Pressure
Static Pressure
Fluid is not moving
Not be pumped through pipe or flow
channel.
Dynamic Pressure
Fluid is in motion
Pressure of water: inside and outside
nozzle.

5. Pressure-Measuring Devices
U-Tube Manometer
Bourdon Tube Sensor
Bellows-Type Sensor
Strain Gauge Sensor

6. U-Manometer

7. Bourdon Tube Sensor

8. Bourdon Tube Sensor

9. Bellows-Type Sensor

10. Diaphragms Sensor

11. Bourdon, Bellow and Diaphragm
Sensor
Bourdon, Bellow and Diaphragm ~
displacement is proportional with pressure.
Used elastic material
Displacement is convert to electrical signal
~ required secondary element

12. Strain Gauge Sensor

13. Strain Gauge Sensor

14. Basic Operation
Fluid –Force –Diaphragm Displacement
(detected by strain gauge sensor) –
resistance change (detected by
Wheatstone bridge).

15. Criteria For Selecting A Suitable
Pressure-Measuring Instrument
Operating Range
Sensing Element

16. Operating Range
The pressure ranges roughly fall into the following
categories:-
Extra low range: below 6.35 mm of water column
gauge (eg. 5 –6 mm H
2O)
Low range: from vacuum to atmospheric in mm or
inches column. Vacuum ranges can be only from
atmospheric pressure down to full vacuum (-1barg).
Medium range: 10 –hundreds bar, kg/cm, or lb/in2.
High range: thousands of bar, kg/cm, or lb/in2.

17. Sensing Element
The sensor can be divided into the following categories.
Extra low range: inclined manometer at the local area
~ no long-distance transmission.
Low range: slack diaphragm and low range
differential pressure.
Medium range: Bourdon tubes made from NiSpan C,
beryllium copper, and SS 316 chemical attack. C
type is commonly used. Spiral and helical elements
provide greater physical movement.
High range: Thick wall of helical Bourdon tube SS316
is commonly used. 10,000 units and above of
pressure –stain gauge and vibrating-microstructure
type

18. Minute paper ……

19. To be continued….