15
PRESSURE MEASUREMENT PRESENTED BY: MOHANAD FAEK NOORI

Pressure Measurements | Comprehensive search

Embed Size (px)

Citation preview

Page 1: Pressure Measurements | Comprehensive search

PRESSURE MEASUREMENT

PRESENTED BY:

MOHANADFAEK NOORI

Page 2: Pressure Measurements | Comprehensive search

PRESSURE MEASUREMENT

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

Units of pressure:standard: N/m2 (Pa-Pascal), Kpa (Kilo Pascal)1Bar=100kpa

Page 3: Pressure Measurements | Comprehensive search

Pressure Measurement

Divided into four categories :-

1.Absolute pressure – pressure at a point in a fluid relative to a vacuum (absolute zero of pressure)2.Gauge Pressure – pressure relative to local atmospheric pressure.3.Differential Pressure – difference between two unknown pressures, either of which is atmospheric pressure.4.Atmospheric pressure : Sea level standard atmospheric pressure is 101.325Kpa but it changes with altitude of earth.1 atmosphere [technical] is equal to 98.0665Kpa

Relationship between absolute and gauge pressures

Pabs=Pgauge+Patm

Page 4: Pressure Measurements | Comprehensive search

SENSING ELEMENTSThe main types of sensing elements are

•Bourdon tubes

•diaphragms

•bellows

The basic pressure sensing element can be configured as a C-shaped Bourdon tube (A); a helical Bourdon tube (B); flat diaphragm (C); a convoluted diaphragm (D); a capsule (E); or a set of bellows (F).

Page 5: Pressure Measurements | Comprehensive search

BELLOWS

• bellows sensor is an axially flexible, cylindrical enclosure with folded sides. When pressure is applied through an opening, the closed end extends axially.

• Bellows elements can measure absolute pressure, gauge pressure, vacuum, or differential pressure.

Page 6: Pressure Measurements | Comprehensive search

BOURDON TUBE

• A Bourdon gauge uses a coiled tube, which, as it expands due to pressure increase causes a rotation of an arm connected to the tube.

• bourdon are often used in harsh environments and high pressures, but can also be used for very low pressures; the response time however, is slower than the bellows or diaphragm.

 C-type bourdonpsi Range as low as 0 - 15 psi up to 0-1500

Helical bourdonRange as low as 0 - 200 psi up to 0 – 6000 psi

Spiral bourdonRange as low as 0-10 psi up to 0-100,000 psi.

Page 7: Pressure Measurements | Comprehensive search

Diaphragm

• A diaphragm is a circular-shaped convoluted membrane that is attached to the pressure fixture around the circumference . The pressure medium is on one side and the indication medium is on the other.

• Diaphragms provide fast acting and accurate pressure indication. However, the movement or stroke is not aslarge as the bellows .

Page 8: Pressure Measurements | Comprehensive search

Diaphragm

• There are two different devices that are referred to as capsule.

• The first is shown in figure . The pressure is applied to the inside of the capsule and if it is fixed only at the air inlet it can expand like a balloon. This arrangement is not much different from the diaphragm except that it expands both ways.

• The capsule consists of two circular shaped, convoluted membranes (usually stainless steel) sealed tight around the circumference. The pressure acts on the inside of the capsule and the generated stroke movement is shown by the direction of the arrow.

• The second type of capsule is like the one shown in the differential pressure transmitter (DP transmitter). The capsule in the bottom is constructed with two diaphragms forming an outer case and the interspace is filled with viscous oil. Pressure is applied to both side of the diaphragm and it will deflect towards the lower pressure.

Page 9: Pressure Measurements | Comprehensive search

We often hear about Islam, what is Islam ?

Learn through these sites about Islam and to all questions that revolve in your thoughts about this religion, and raise the level of your culture in learning religions enjoy the following sites to know everything about Islam :-

My first step in Islam :- ( http://www.1ststepsinislam.com/en/introduction.aspx )

Women in Islam :-( http://womeninislam.ws/en/introduction.aspx )

The key to understanding Islam :- http://www.thekeytoislam.com/

This is true :- http://www.thisistruth.org/

Learn about Islam will change your life , There is no money nor power nor any thing can change your life ,Islam will change your life and you will feel very happy.

We often hear about Islam, what is Islam ?

Do you have money and everything but feel dissatisfaction in your heart is not the goalof your life?!Do you want to save you from this case?Introduction to Islam through these sites and I promise you will find great pleasure

My first step in Islam :- ( http://www.1ststepsinislam.com/en/introduction.aspx )

Women in Islam :-( http://womeninislam.ws/en/introduction.aspx )

The key to understanding Islam :- http://www.thekeytoislam.com/

This is true :- http://www.thisistruth.org/

Learn about Islam will change your life , There is no money nor power nor any thing can change your life ,Islam will change your life and you will feel very happy.

Page 10: Pressure Measurements | Comprehensive search

Differential Pressure Transmitters

• Most pressure transmitters are built around the pressure capsule concept.

• They are usually capable of measuring differential pressure (that is, The difference between a high pressure input and a low pressure input) and therefore, are usually called DP transmitters or DP cells.

Page 11: Pressure Measurements | Comprehensive search

strain gauge

• The strain gauge is a device that can be affixed to the surface of an object to detect the force applied to the object. One form of the strain gauge is a metal wire of very small diameter that is attached to the surface of a device being monitored.

Page 12: Pressure Measurements | Comprehensive search

strain gauge

• When force is applied to any metallic wire its length increases due to the strain. The more is the applied force, more is the strain and more is the increase in length of the wire. If L1 is the initial length of the wire and L2 is the final length after application of the force, the strain is given as: ε =(L2-L1)/L1

• Further, as the length increases, diameter decreases.

Page 13: Pressure Measurements | Comprehensive search

capacitance

• In a capacitance-type pressure sensor, a high-frequency, high-voltage oscillator is used to charge the sensing electrode elements. In a two-plate capacitor sensor design, the movement of the diaphragm between the plates is detected as an indication of the changes in process pressure.

• Further, as the length increases, diameter decreases.

Page 14: Pressure Measurements | Comprehensive search

Impact of Operating EnvironmentAll of the sensors described in this module are widely used in control andinstrumentation systems throughout the power station

VibrationThe effect of vibration is obvious in the inconsistency of measurements,but the more dangerous result is the stress on the sensitive membranes,diaphragms and linkages that can cause the sensor to fail. Vibration cancome from many sources.

TemperatureThe temperature effects on pressure sensing will occur in two main areas:The volumetric expansion of vapour is of course temperature dependent.Depending on the system, the increased pressure exerted is usually alreadyfactored in.

Vapour ContentThe content of the gas or fluid is usually controlled and known. However,it is mentioned at this point because the purity of the substance whosepressure is being monitored is of importance - whether gaseous or fluid .especially, if the device is used as a differential pressure device inmeasuring flow of a gas or fluid.

Page 15: Pressure Measurements | Comprehensive search

We often hear about Islam, what is Islam ?

Learn through these sites about Islam and to all questions that revolve in your thoughts about this religion, and raise the level of your culture in learning religions enjoy the following sites to know everything about Islam :-

My first step in Islam :- ( http://www.1ststepsinislam.com/en/introduction.aspx )

Women in Islam :-( http://womeninislam.ws/en/introduction.aspx )

The key to understanding Islam :- http://www.thekeytoislam.com/

This is true :- http://www.thisistruth.org/

Learn about Islam will change your life , There is no money nor power nor any thing can change your life ,Islam will change your life and you will feel very happy.

We often hear about Islam, what is Islam ?

Do you have money and everything but feel dissatisfaction in your heart is not the goalof your life?!Do you want to save you from this case?Introduction to Islam through these sites and I promise you will find great pleasure

My first step in Islam :- ( http://www.1ststepsinislam.com/en/introduction.aspx )

Women in Islam :-( http://womeninislam.ws/en/introduction.aspx )

The key to understanding Islam :- http://www.thekeytoislam.com/

This is true :- http://www.thisistruth.org/

Learn about Islam will change your life , There is no money nor power nor any thing can change your life ,Islam will change your life and you will feel very happy.