Pressure Measurements

Submitted by:MOHD ATIF

B.TECH(I.N.)

III YEAR

10231022

CONTENTS

INTRODUCTION

UNITS OF PRESSURE

CLASSIFICATION OF PRESSURE MEASUREMENT

INTRODUCTION

Pressure means force per unit area, exerted by a fluid on the surface of the container.

P=F/AF - FORCE (in Newton)

A - AREA (in meter²)

Pressure is of two types-

STATIC PRESSUREDYNAMIC PRESSURE

WHERE,

F

Pressure is of two types-

1- STATIC PRESSURE2- DYNAMIC PRESSURE

STATIC PRESSURE- when the force in a system under pressure is constant or static (i.e. unvarying), the pressure is said to be static pressure.

DYNAMIC PRESSURE- If the force is varying, on the other hand, the pressure is said to be dynamic pressure.

UNITS OF PRESSURE

1 atm = 14.7 Psi at sea level = 101.3 Kilo Pascal = 760 mm of Hg = 10.3 m of water = 1013 mili bar 1 Pascal = 1N/m2

1 Bar = 100 Pascal

MECHANICAL ELECTROMECHANICAL

STATIC DYNAMIC(Force Summing Devices)

MANOMETER

U-TUBE

WELL TYPE

INCLINED

DIAPHRAM BELLOWS BOURDON-TUBE

CLASSIFICATION OF PRESSURE MEASUREMENT

FLAT CORRUGATED CAPSULE

C-TYPE HELICAL TYPE

SPIRAL TYPE

ELECTROMECHANICAL

POTENTIOMETER

PHOTOELECTRIC TYPE

CAPACITIVE PIEZOELECTRIC TYPE

INDUCTIVE

Wet Meters (Manometers)

U-tube Manometer

This manometer consist of U-shaped tube in this manometric fluid is filled.

Water and mercury are used as a manometric fluid.

Advantage of using these fluid is that mass density of these fluid can be obtained easily and they do not stick to the tube.

Since, P = ρgh h = (P₁ - P₂)/ρg P₁ - P₂ = ρgh

Where, ρ - mass density of fluid g - gravity P₁ - unknown pressure P₂ - atmospheric pressure

The well type manometer is widely used because of inconvenience; the reading of only a single leg is required in it.It consist of a very large-diameter vessel (well) connected on one side to a very small-sized tube.Thus the zero level moves very little when pressure is applied.

Inclined Tube Manometer

Force Summing Devices

The force summing devices are those which converts the applied pressure into displacements by primary transducers while generated displacements may be measured by secondary transducers.The commonly used force summing devices are-

1- DIAPHRAGM

2- BALLOWS

3- BOURDON TUBE

Diaphragm

Diaphragm are widely used for pressure (gauge pressure), particularly in very low ranges. They can detect a pressure differential even in the range of 0 to 4mm.The diaphragm can be in the form of Flat, Corrugated and Capsules the choice depends on the strength and amount of deflection required.

Diaphragm Gauge

BELLOWSA bellows gauge contains an

elastic element that is a convoluted unit that expands and contracts axially with change in pressure.The pressure to be measured can be applied to the outside or inside of the bellows however, in practice, most bellows measuring devices have the pressure applied to the outside of the bellows.

BOURDON TUBE

An elastic transducer , that is bourdon tube which is fixed and open at one end to receive the pressure which is to be measured. The other end of the bourdon tube is free and closed.The bourdon tube is in a bent form to look like a circular arc.All the various form of bourdon tube have the common feature that they are constructed the tube of non circular cross-section