17540119 basic instrumentation

8/8/2019 17540119 Basic Instrumentation

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Contents

Definition of instrumentation &Process Control

P&IDs & Instrument symbolsProcess MeasurementnTransducer (Temperature-Pressure-

Flow-Level)nTransmitting and Switching Elements


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Definition of Instrumentation & Process

Instrumentation:n A collection of instruments for the purpose

of observation, measurement, protection orcontrol.

Process Controln Regulation or manipulation of variable

influencing the process to achieve desirequantity/quality in an efficient manner


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P&ID and Instrument

P&ID stands for Piping & InstrumentationDiagram

n Definition:diagram where it will show the

process piping and instrumentationconnections with Process tanks and vessels,reactors, exchangers, etc. in order toproduce particular product or perform

specific task.n The P&IDs contains detail connections for

the instrumentations where defined bygraphical symbols and identification letters.


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Instrumentation

Example of instrument Identificationn FIC4003 (Flow indication and Control)

n FI4002 (Flow Indication)

n FT4003 (Flow Transmitter)

n FV4003 (Flow Control Valve)

n PIC4002 (Pressure Indication and Control)

n

PV4002 (Pressure Control Valve)n PDSL1234 (Pressure Differential Switch Low)


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Control Loops

FT-1

FV-1

FIC

1SV

PV

MV

FE-1

FY

1Vent

AFC

FSL1

IA

i


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I. Temperature

Definition:n It is the Degree of Coldness or

hotness or in other word related tothe kinetic energy of molecules.

nTemperature generated by heatenergy.

n Heat energy has unit of BTU(Brithish Thermal Unit) or Calorie


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Temperature (Cont.)

Units:n Fahrenheit (F), Centigrade (Celsius)

C, Kelvin K, Ranklin RF= 5/9 x C + 32

C= 9/5 (F-32)

K= 273.15 + C

R= 459.7 +F


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Temperature (Cont.)

F C K R

-459.7

32

212

-273.15

0

100

0

273.15

373.15

0

459.7

671.7

WaterFreezing

WaterBoiling

Absolutezero


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Temperature

nThermocouple: Consists of twodissimilar metals joined at one endand other end connected to meter.When joined end (Hot junction)heated, voltage will be produced at


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Temperature


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Temperature

Resistance Temperature Detector (RTD)n Heat Sensitive element prepared with

carefully made electric resistance.n Used material: Platinum, Nickel, Iron, Salver

w In our plant most of RTDs used are Pt100

platinum resistance= 100 ohm at 0 degree C

n As tem erature rises resistance increases.


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Temperature

Thermostor:n Very small Solid thermo-electric

devise made of solid semiconductorof various metal oxides.

nThe electric resistance of thermostordecrease with an increase in


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II. Pressure

Definition:n Defined as the normal force per unit

area acting on surface of an object.n P=F/A

Units:n

Pa, psi, inches of mercury, inches ofwater, BAR, atm, Kg/cm2


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Pressure (Cont.)

Scale of measurement:n Gauge Pressure Scale

n Absolute Pressure Scalen Vacuum Pressure Scale

Pg= Pa - Atmospheric Pressure


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Pressure (Cont.)

vacuum

Gage pre.Range

BarometricAtm.Range

Zero gauge

Zero (Absolute)

Abs.Pressure


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Pressure (Measurement)

Manometers:n Used for the direct measurement of

pressure and vacuum.n U-Tube Manometer

wA glass of U- tube shape, partially filledwith liquid.

wThe zero is connected to the scale whenboth ends of the U-glass opened toatmosphere.


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P1 P2

U-Tube Manometer


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n U-Tube Manometer (Cont.)wWhen applied pressure at one end of the

tube, difference in level will occur:

wP2-P1=


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n Well Manometer (Single Leg):wUsed for low pressure application with

higher accuracy from the U-Manometer.

wP2-P1=

P2

zero line

A2

A1


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n

w

w

P1

P2

zero line

A1


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Pressure Elementn Mechanical devices changed its shape

when pressure is appliednThe pressure elements sometimes

called elastic deformation pressureelement

n

Each type has its range of operationressure.


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Pressure Transducersn Elastic deformation element joined to

electrical device.n Changes in resistance, inductance, or

capacitance


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Strain Gauge:n Fine wire in form of grid.

n

When the grid distorted, resistance ofthe wire will change according to:

R=K. L/A

K : Resistively of the metal

L : Length of wire

A : Cross sectional Area


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Grid Wire

Ceramic ora er backin

Leadwires

Strain Gage


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Strain Gage (Cont.)n As Strain Gage is distorted by the

elastic deformation length will

increase and area will reduced.n Resistance will increase accordingly.


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Inductance Typen Consists of Coil, Movable Magnet

core, and elastic deformationelement.

n AC current pass through coil.

n As the pressure varies the elastic

deformation, the magnet core willmove through the coil.

nThis will chan e the inductance.


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Movable Iron Core

CoilNon Conductive Tube


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Capacitance Typen Consists of two conductive plates,

dielectric, and diaphragm.n As the pressure increases diaphragm

will move the plate changing thecapacitance.



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Flow (Measurement)

Flow rate and flow quantity ofmaterials is made primarily for

determining the proportions ofmaterials introduced to theprocess.

Method of measurements:n Head Elements

n Area Elements

n Quantity Velocity Elements


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Flow (Measurement)

The following properties areimportant for the flow

measurement:n Pressure: Force applied on Area

n Density : Weight divided by volume

n Viscosity : Resistance to flow

n Velocity : Speed of the fluid. Itdetermine the behavior of the fluid.


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Flow (Measurement)

Flow Types:n When the average velocity is slow,

the flow is called laminar, i.e fastestlayers at the center and the slowestat the edges

n When the average velocity increases,

the flow is called turbulent.nThe measurement of laminar,

turbulent flow is as per Reynolds


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Flow (Measurement)

Most Flow are design to work inturbulent flow

Units of Flow:n lb/Hr, Kg/Hr, T/Hr: mass flow

n cfm, M3/H, KNM3/Hr: Volumetric Flow


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Flow Measurement

Head Flow Elementsn When the liquid flows through a

restriction, the energy convertedkinetic energy.

nThe pressure will drop and velocity

C: constant


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Flow Measurement

Head Flow Elementsn Orifice Plate: the loss in the pressure is

more that other type of flow measurement.

wThe selection of orifice plate based on ratio ofbore diameter to (d) to inside pipe diameter (D).

w

w

n

n

n


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Flow Measurement

n Venturi tube: expensive and the most

accurate type

w

Upstream Tap Downstream Tap


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Flow Measurement

n

w

w

w

Upstream Tap Downstream Tap


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Flow Measurement

Variable Area Flow Metern Rotameter: consists of tapered, vertical

glass consists of float.

n Flow will carry the float from bottom to topthrough variable area glass.

A: cross sectional area of the glassg: gravitational acceleration

constant


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Variable Area Flow Meter

In

Out

Float


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Flow Measurement

Quantity Flow Measurementn Positive displacement

wMeasure the total quantity of the flow

w separate the liquid into discrete volumes

wTotal of these volumes in time period willgive the total flow amount

n Mass Flow meter:wmeasurement of the weight per unit time.

wContinuous measurement of density


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Level

There is two ways of measuringleveln

Direct level measurementwby varying liquid will get the level

n Indirect level measurementwby using a variables which changes with

the liquid level changes.


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Level Measurement

Floatn special material designed to follow

the level or the interface level of atank

nThe specialty is the density of thefloat shall be always touching thedesired measurement level.

n As the level increases/decreases, floatwill follow and causing a connectingta e to chan e its len th.


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Level Measurement

Displacern Archimedes Principle: a body wholly or

partially immersed in a fluid is buoyed up by

a force equal to the weight of the fluiddisplaced.

n The level is measured by detecting thebuoyancy force of an immersed displacer

n The major difference between float anddisplacer is that displacer is partially ortotally immersed, while float is always


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Displacer

Flexible

Float


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Level Measurement

Differential pressuren P/

n P/(g.n

LT


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Instrument Signal Types

All measurement elements aresent to DCS/ESD/PLC Either for

alarming, interlocking orcontrolling.

Measurement Instrumentation

consists of two partsn Measurement elements (Transducer)-

Covered in the previous sections

nTransmitting elements

n Switchin elements


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Transmitting Elementsn Transmitting element will convert theTransducer signals into either electronic or

pneumatic signalsn Transmitting elements are commonly used

for indication and controln Electronic transmitter will send 4 ~ 20 mA

w 4mA : min. range

w 20mA: max. rangen Pneumatic transmitter will convert the

transducer signal into 3~15 psiw


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Switching Elementsn Switching elements will convert the

transducer signal into a switchingcontact

nThe contacts are used commonly inalarming and interlocking processes


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Conclusion

Definition of instrumentation &Process Control

P&IDs & Instrument symbolsProcess MeasurementnTransducer (Temperature-Pressure-

Flow-Level)nTransmitting and Switching Elements


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??QUESTIONS??


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17540119 basic instrumentation

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