(For Private Circulation Only)

SR.NOPROPERTIES ORIFICE PLATE VENTURI ROTAMETER PITOT TUBE MAG. FLOWMETER VORTEX MASS FLOWMETER ULTRASONIC

1 Working

As the flowing fluid passes through

the orifice plate, the restricted cross

section are causes an increase in

velocity & decrease in pressure.

The pressure difference before &

after the orifice plate is used to

calculte the f,ow velocity.

Similar to pitot tubes but with

multiple openings, averaging Pitot

tubes take flow profile into

consideration to provide better

overall accuracy in pipe flows.

Operates on Faraday's low of

Electromagnetic

Induction.Conducting material

passes through the magnetic field

produces avolatge perpendicular to

magnetic field & velocity of fluids.

E=BLV where E = EMF, B=

Magnetic Field, L = Length of

Conductor, V= Velocity of

Conductor . Therefore

E=4.B.L.Q/Pie d²

1.An obstruction (Bluff body or

strut) located in the flow stream.

Low-low : Fluid flow around

obstruction.

High-Flow: Alternating vortices are

formed.(No. of vortices formed are

proportional to fluid velocity.

2.These vibrations senses by

piezoelectric crystals which convert

it into elctric pulses.

3.Vortex meter can not measure

zero since it works on fluid velocity

principle.It required some flow to

work.

Coriolis mass flowmeters measure

the force resulting from the

acceleration caused by mass moving

towards ( oe away from) a center

rotation..This effect can be

experienced when ridinga merry-go-

round,where moving toward the

center will cause aperson to have to "

lean into" the rotation so as to

maintain balance. As related to

flowmeters, the effect can be

demonstrated by flowing water in

aloop of flexible hose that is "swung"

back & forth in front of the body with

both hands.Becasue the water is

flowing toward & away from the

hands oppsite forces are generated

and cause the hose to twist.

Doppler Type : 1. Under no flow

condition, the frenquencies of the

ultrasonic beams and its reflrction

are the same.

2.With the flow in the pipe

difference between the frequencies

of the Ultrasonic beam and its

reflection increses propotional to

flow velocity.

Transit Time : 1.Transit time

ultrasonic flowmeter alternately

transmit ultrasonic energy into the

fluid in the direction and against the

direction of flow.

2.The time difference between

ultrasonic energy moving upstream

to downstream in the fluid is used

to determine the fluid velocity.

3.Undergo flow condition time for

ultrasonic energy to travel upstream

& downstream are same. 4.With

flow in pipe time for ultrasonic

energy to travel upstream will be

greater than the downstream time.

2 Flowrate Medium High Flow Low Flow rate Wide range of flowsElectric conductivity greater than 5

mS/cm.

Measurement with flow velocities

( Re < 4000) not possible.

1.Measures the acceleration caused

by vibration by moving fluids towards

centers. 2.Amount of twist is

proportional to the massflowrate of

fluid passing through tubes.

3 Pressure Drop ChangesPermanent Pressure drop & good

recovery.Constant Pressure drop Negligible pressure drop

Confirm allowable pressure drop

loss while selecting meter size.

4 Application Suitable for most of gases & liquidsNot handles viscous slurries only

solids fluids.Handle almost corrosive services

Utility services where accuracy is

not necessary.

1.Conductive liquids such as

water,acids, caustic and slurriesMuch higher for gases/vapors.

2.Custody transfer application.

5 Characteristics Predictable Accurate over long range. Accurate over small or short range Wide range flows & pipe sizes.Bi-directional flow and large size

available.

Accuracy degraded during low range

flow application.

6 Rangeability 3.5:1 3.5 : 1 10:01 3:01 10:1, 30:1 10:01 20:01

7 Accuracy 2% ~ 4% of full scale 1% of Full scale 2% ±0.5 % to ±1.5 % ±0.5% typically 1% of measurement 0.2 typically 2% typically

1.Low Cost1.Low differential

press.compensation.

1.Relatively low in cost. 2.Can

handles wide variety of corrosives.

1.Available from 1/2 to 150 inches

of pipe size.1.Large pipe sizes & capacities.

1.Low installtion cost & calibration

not required.

1.Direct mass flow measurement of

any liquid flow.1.Wide flow range.

2.Available in wide range of sizes &

construction.

2. Can be used for slurries & dirty

fluids.

3.Especially suited for low flow

metereing. 4.Linear output2.Long term measurement stability.

2.Can handles slurries & greasy

materials

2.Good accuracy of fluids can be as

good as ±0.75% of rate for gases &

±1% of rate for liquids. 3.Wide

range ( 1/2 " to 12" : 18" on request.

2.Wide rangeability.3.Can be used for highly corrosive

fluids.

3.No moving parts 3.Can be welded into pipe lines.

5.Can be easily equipped with

magnetic,electronic,induction or

mercury switch alarms, or

transmitting devices.

3. Can be placed in service under

pressure.

3.Very small erros in flow

measurement.Measurement in both

directions. 4.No pressure drop. 5.No

obstruction in pipe.

4.Wide temp. range (-200 to

400°C).

5.Can be used for steam, gases or

liquids.

3.Because of the mass flow is

measured,hence the measurement is

not affected by fluid-density ,

viscosity, pressurechanges.

4.Immune to liquid chemistry and

physics property.

6.Glass tube version capable of

measuring low flow rates. 7.

Can be installed immediately

downstream of control valve.

4.Negligible permanent pressure

drop.

5.Minimum lengths of straight

piping runs.

6.Good Linearity over widerange.

7.Unaffeceted by fluid properties

such as density,viscosity &

temperature.

6.Linearity is independent of

density, viscosity & pressure.

FLOW INSTRUMENTATION DESIGN GUIDE

Advantages8

SR.NOPROPERTIES ORIFICE PLATE VENTURI ROTAMETER PITOT TUBE MAG. FLOWMETER VORTEX MASS FLOWMETER ULTRASONIC

FLOW INSTRUMENTATION DESIGN GUIDE

1.Square root relationship. 1.high Cost. 1.must be mounted vertically.1.Not applicable for dirty & sticky

services.1.Relatively high cost.

1.Not suitable for dirty arabrasice

fluid as well as for high viscous

liquids.

1.Pressure drop may be high. 1. Susceptible to noise.

2.Low accuracy. 2. Square root v/s flow relationship.

2.Relatively low temperature

limitations.

3.Limited to small pipe sizes and

capacities unless put in bypass. 2.Operating data still limited.

2.Fluid measured must be atleast

slightly conductive.Not Suitable for

gas service.

2.Measurement with low flow

velocities ( Re < 4000) not

possible.Vortex frequency remains

constant & independent of press.,

temp, density in the range of Re>

20,000 that is utilized for measuring

volume flow.

2.cannot measure gas flow with low

pipeline pressure.

2.Straight run upstream piping is

required.

3.Accuracy affected by density &

flow profile.3. Big & heavy in larger pipe size.

4.May be used only with relatively

clean fluids.

3.Pitot tube doesn't work very well

at low velocities because at low

velocity differential press. Is very

low.

3.Complex elctronic circuitary

neede.

3.Confirm allowable pressure drop

loss while selecting meter size.

3.Can be costly & should be taken

into consideration.

3.Integral

linners(Rubber,Cement,Glass etc.)

must be intimately bonded to pipe

material.

4.Viscosity affects the flowmeters.

4.If support not required then tube

strengths calculation & resonance

frequency vibration for all services

including liquids to be checked.

4.Temperature limit may be depend

on insulation materials (usually less

than 200°C)

4.Vortex meter is used for steam

water , light hydrocarbons and any

gases where large turndown is

required.

10Straight Run

Requirement

1.For Reliable measurement fluid

must enter the primary element free

of Turbulence.This can be achieved

by providing suitable lengths of

straight pipe ( Refer Annexure -A).

1.For Reliable measurement fluid

must enter the primary element free

of Turbulence.This can be achieved

by providing suitable lengths of

straight pipe ( Refer Annexure -A).

Really not required. No Straight Run Requirements.

Long staright lengths necessary

depending on the type of fitting

upstreams.

No straight meter run requirement.Straight Run requirement to be

maintained.

1.Liner material - hard Rubber,PTFE

etc.

When flow is obstructed it creates

vortices across shredder bar which

in turn creates vibrations flow.

Dopper Equation: Vf=K*Df where

K = Constant; Vf= Velocity of fluids

where ultrasonic energy is

reflected; Df=Diff. between

transmitted & reflected frequencies.

2.Electrode material -SS

316,Hestalloy c, titanium,Platinum

etc.

Transmit Time Equation:

Vp=K(Tu-Td)/Tu*Td Where Vp=

Average Velocity ib=n fluid

path,K=Constant;Tu=Upstream

Transit Time, Td= Downstream

transit time.grounding : Done by Rings on

eithrside or Times grounding by

electrode in order to go around

spurious voltages.

General

Requirements11

Disadvantages9

Plates : Orifice Tappings

Pitot Tubes

Magnetic Flowmeter Vortex Flowmeter

Transit-Time Doppler Type

FIELD INSTRUMENTATION DESIGN GUIDE

Venturi Meter

Orifice Plate Assembly

Ultrasonic Flowmeter

Mass Flowmeter

Rotameter

Sl.No. Sensor Rangeability1 Accuracy2 Dynamics (s) Advantages Disadvantages Applications / Remarks

-low cost -high pressure loss

-extensive industrial practice -plugging with slurries

-lower pressure loss than orifice -high cost

-slurries do not plug -line under 15 cm

-good for slurry service -higher cost than orifice plate

-intermediate pressure loss -limited pipe sizes

4 elbow meter 3:1 5-10% of full span - -low pressure loss -very poor accuracy

-low pressure loss

-poor performance with dirty or sticky

fluids

-large pipe diameters - straight run requirement

-wide rangeability

-linear output

-bidirectional flow & large size available

-No straight meter run required

-high reangeability -high pressure drop

-good accuracy -damaged by flow surge or solids

-wide rangeability -high cost

-good accuracy -strainer needed, especially for slurries

-wide rangeability

-insensitive to variations in

density, temperature, pressure, and

viscosity

11 Target flowmeter - Typically 2% -

-for high viscous flow such as

tars,asphalt etc -

-wide rangeability

-no straight meter run required

13

Ultrasonic

Flowmeters Typically 2%

These flowmeters are growing exponentially in popularity, mainly due to their effectiveness in use for measuring natural

gasses. They are non-intrusive and have no pressure drop. It is essential that they operate on clean fluids.

Flow Instruments Comparision Sheet

These twisting meters measure mass flow as opposed to volumetric flow. They are known for their accuracy but their size is

limiting. They carry an initial high cost, but a low maintenance cost. They are used for clean liquids and gases flowing at

medium to high velocity, in pipes six inches and under.

A higher-cost flowmeter, used mainly for water applications. They are limited to conductive fluids. They operate on a voltage

generator.

These are used as an alternative to differential pressure flowmeters. They operate best with clean, low-viscosity, medium to

high speed fluids.

orifice 3.5:1 2-4% of full span -

venturi 3.5:1 1% of full span -

flow nozzle 3.5:1 2% full span -

annubar 3:1 0.5-1.5% of full span -

-

Magnetic flowmeter 10:1 0.5% typically -

-temperature limit may depend on

insulation material (usually less than

200°C)

rotameter 10:1 2% -

positive displacement 10:1 or greater

0.5% of

measurement -

turbine 20:1

0.25% of

measurement -

-expensive

Coriolis mass

flomwmete 20:1 0.2% typically - -

vortex shedding 10:1 1% of measurement -

1

2

12

5

6

7

8

9

10

3

Sr No. Instrument Clean Liquid

Dirty Liquid Slurry Viscous

Liquid

Corrosive / Errosive Liquid

Clean Gas

Dirty Gas Steam Viscosity

EffectFull Bore Size

AvailabilityType of

MeasurementAccuracy

( % )Typical

Rangeability

Reynolds Nos. or other limitations

Sensitivity to Installation

effects

Straight Piping Requirements Typical ancillary Equipments Other Considerations Preferred Meter

Orientation Initial Cost Installation Cost maintenance Cost

Operation Cost

Performance Stability Standard or Recommended Practise.

1Concentric Orifice Plate (Square edge)

G L X X L G L G High > 1" >25mm

Square root

Volumetric

± 2 to ± 4 of full scale

( 0.5% to 3% )3:1 to 5:1 >10,000 High 10D to 40D- Up

2D to 6D DownDrain, Vent Blow -off &

S/D Valves

Pressure and/or Temp. Compensation May be required

Pressure Tap orientation Depends on the Pipe orientation & Fluid Being Metered

Low to High

Medium to High

Medium to High

Medium to High

Performance affected by Edge & Tap Wear

* AGA3* ANSI/API 2530 * ANSI/ASME MFC 3M* ISO 5167 ASME Fluid Meters

2 Segmental Wedge G G G G G G G G Low > 1/2">15 mm

Square root

Volumetric

± 0.5 to ± 2 of full scale(0.5% to 5%)

3:1 to 5:1 > 500 Low5D to 10D - Up2D to 5D - Down

None with Remote Seal Version

Same as Orifice Plate

No Limitations on Remote Seal Elements

High Low Low Low to Medium GOOD -

3 Venturi Tube G G L X L G G G High > 2" >50 mm

Square root Volumetric

± 1of full scale(0.5% to 1.5%) 3:1 to 5:1 >10,000 Low

Upsteram Runs shorter than Orifice Plate by Factor 2-9 times

Same as orifice plate,air purge & vent cleanners on Dirty liquids

Same as Orifice Plate

Same as Orifice Plate

Medium to High Medium Low Low GOOD

* AGA3* ANSI/API 2530 * ANSI/ASME MFC 3M* ISO 5167 ASME Fluid Meters

4 Flow Nozzle G L X X L G L G High > 2" >50 mm

Square root Volumetric

± 1 to ± 2 of full scale(1% to 2%)

3:1 to 5:1 > 75,000 Mod Same as Orifice plate Same as Orifice plate Same as

Orifice plateSame as Orifice plate

Medium to High Medium Low Medium GOOD

* AGA3* ANSI/API 2530 * ANSI/ASME MFC 3M* ISO 5167 ASME Fluid Meters

5 V-cone G L L L L G L G1 to 16"( 25mm to 400 mm)

Square root

Volumetric0.5% to 2% 3:1 to 5:1 > 4000 Low 5 to 10D - Up Same as Orifice plate Same as

Orifice plate - Medium Medium to High Medium Medium GOOD -

6 Target G G G G L G G L Medium > 1/2 " > 15 mm

Square root

Volumetric

± 1 to ± 2 of full scale(0.5% to 5%)

3:1 to 20:1 > 1000 High Same as Orifice plate -

Viscosity Affetcs performace below critical Rd

Zero May need adjustment in vertical installtion

Low to High Low Medium to

High Medium

Performance affected by Wear of Target

-

7 Variable Area G L X L L G L L Medium < 3" < 75mm

Linear Volumetric

± 1 to ± 10of full scale

(0.5% to 5%)10:01

Fluids under 3 Cp

None None - -

Cn only beinstalled Vertical pipe with Flow up

Low to Medium Low Low Medium GOOD -

8 Magnetic G G G G G X X X None > 1/16" > 1mm

Linear Volumetric

±0.5 of rate(0.2 to 2%)

30:1 to 100:1 None Low 5 to 10D - Up

3D - Down

Block valve may be required to Isolate Meter for Servicing

AC Design may give better Performance ON some Slurries

Electrodees must be in Horizonatal plane.Flow should be Upwards in vertical installation.

Medium to High

Low to Medium

Low to Medium Low GOOD ISO 6817

9 Vortex G L X X L G L G1/2" to 12"15 to 300mm

Linear Volumetric

± 1 of rate(0.5% to 1.5%)

10:1 to 20:1 > 20,000 High

Same as Orifice plate with 0.70 Beta

Block valve may be required to Isolate Meter for Servicing

Indicates Zero Flow below cut-off

- Medium Low to Medium

Low to Medium Medium GOOD ANSI / ASME MFC 6M

10 Turbine G L X L L G L G > 1/4" > 6 mm

Linear Volumetric

± 0.25% of rate (0.1% to 1%)

10:1 to 50:1

Fluids under 10 CST

High Similar to Orifice Plate

Strainers, Filters, Air Eliminators, steam taps may be required

Viscosity can affects Performance

Some design must be oriented as Calibrated

Low to High

Medium to High

Medium to High Medium

Performance affected by wear of bearing & other parameters

* AGA7* API 2534* ISO 2715 ASME Fluid meter* API Manual for Petroleum Measurement Standards

11 Ultrasonic - Doppler Type X G G L G X X X None > 1/2 "

> 15 mm

Linear Mass Volumetric

± 5 of full scale (1% to 5%) > 10:1

Fluids Must Have Suspensoids

High Similar to Orifice Plate -

May have problems on concentrated slurries

Transducers must bein horizontal plane

Low to High

Low to Medium Low Low GOOD -

12 Ultrasonic - Transit Time G X X L G G X L None > 1/2 "

> 15 mm

Linear Mass Volumetric

± 1 to ± 5 of full scale(1% to 5%)

> 10:1Fluids must be clean

High Similar to Orifice Plate -

May have problems on Dirty Fluids

Transducers must bein horizontal plane

Low to High

Low to Medium Low Low GOOD ANSI / ASME MFC - YY

L = LIMITED APPLICATION

FLOWMETER SELECTION GUIDETERMINOLOGY G = GOOD X = NOT RECOMMENDED

Sr No. Instrument Clean Liquid

Dirty Liquid Slurry Viscous

Liquid

Corrosive / Errosive Liquid

Clean Gas

Dirty Gas Steam Viscosity

EffectFull Bore Size

AvailabilityType of

MeasurementAccuracy

( % )Typical

Rangeability

Reynolds Nos. or other limitations

Sensitivity to Installation

effects

Straight Piping Requirements Typical ancillary Equipments Other Considerations Preferred Meter

Orientation Initial Cost Installation Cost maintenance Cost

Operation Cost

Performance Stability Standard or Recommended Practise.

L = LIMITED APPLICATION

FLOWMETER SELECTION GUIDETERMINOLOGY G = GOOD X = NOT RECOMMENDED

13 Coriolis Type G G G G L L L X None < 6"< 150 mm

Linear Mass Volumetric

± 0.4 of rate(0.15% to 2%)

40:1 to 100:1 None None None Special supports may be

required for meters

Entrained air may cause problem

Specific orientations vary with meter designs

High Low to Medium Low Low to High GOOD

*ANSI / ASME MFC-11M California weights & standards

14 Thermal Dispersion X X X X X G L G < 3" <75 mm

LogirithmicMass 1% to 5% Upto

100:1 None Mod to High 10 to 20D - UP -

May need to provide comensation for wide TEMP. ranges

Some types require same orientation as in calibration

Low to High

Low to Medium Low Low to

Medium

Performance affeccted by severe Build up on sensor for immersion types

-

Displacer LT Float type

The difference in pressures between to points in a vessel

depends on the fluids between these two points. If the

difference in densities between the fluids is significant,

which is certainly true for a vapor and liquid and can be

true for two different liquids, the difference in pressure can

be used to determine the interface level between the

fluids. Usually, a seal liquid is used in the two connecting

pipes (legs) to prevent plugging at the sensing points.

Perhaps the most frequently used device for the

measurement of level is a differential pressure transmitter.

Using DP for level is really an inferential measurement. A

DP is used to transmit the head pressure that the

diaphragm senses due to the height of the material in the

vessel multiplied by a density variable.

2.Displacers work on the Archimedes

Principle, when a body is immersed in a

fluid it loses weight equal to that of the

fluid displaced.

The float of material that is lighter than

the fluid follows the movement of the

liquid level. The position of the float,

perhaps attached to a rod, can be

determined to measure the level.

1.By Archimedes principle, a body immersed in a liquid is buoyed by a

force equal to the weight of the liquid displaced by the body. ( Thus, a body

that is more dense than the liquid can be placed in the vessel, and the amount of

liquid displaced by the body, measured by the weight of the body when in the

liquid, can be used to determine the level. )

1.Ultrasonic transmitters work on the principle of

sending a sound wave from a peizo electric

transducer to the contents of the vessel. The

device measures the length of time it takes for the

reflected sound wave to return to the transducer. A

successful measurement depends on reflection

from the process material in a straight line back to

the transducer.

Also 2.Time of Flight Technilogy.

3. Short ultrasonic impulses emitted from

transducer. 4.Bursts are created from electrical

energy applied to piezo electric crystal inside the

transducer. 5.The

transducer creates sound wave ( mechanical

energy).

6.With longer measuring ranges a lower frequency

and higher amplitude are needed to produce sound

waves that can travel further.

7.The longer the measuring range the larger the

transducer nust be

Radar Technology is a time flight measurement

1. Microwave energy is transmitted by the radar.

2.The Mircowave energy is reflected off the product surface.

3.The Radar Sensor receives the microwave energy.

4.The time from transmitting to receving the microwave

energy is measured. 5.

The time is converted to a distance measurement and then

eventuallly a level Radar Wavelength =

Speed of Light / Frequency

Ultrasonic LT

2 Arrangement

DP Cell

Level Instruments Design Guide

Working1

Guided Wave Radar level measurement

1.Time of Flight , 2.Top Mounted 3.Solids &

liquids applications. 4.Contact Management.

5.GWR is virtually unaffected by

Temperature,Pressure &

vacuum,Conductivity,Dielectric

constant,Specific Gravity,Vapor steam or Dust

air movement, Build ups & Foam.

Principle of Operation:

Radar LT Guided Wave Radar LTSl.No. CharacteristicsDisplacement type

λλλλ = c / f

Frequency 6.3 GHz

wavelength 5 = 47.5 mm

Frequency 26 GHz

wavelength 5 = 11.5 mm

•A microwave pulse (2 GHz) is guided

along a cable or rod in a 20” diameter or

inside a coaxial system.

•The pulse is then reflected from the solid

or liquid, back to the head of the unit.

•The travel time of the pulse is measured

and then converted to distance.

Displacer LT Float typeUltrasonic LTDP Cell

Level Instruments Design Guide

Radar LT Guided Wave Radar LTSl.No. CharacteristicsDisplacement type

3 Accuracy Typical accuray ± 5~ 10 mm.1. Typical Accuracy for High Frequency(26Ghz " K " Band) - ± 3~ 5 mm. 2.Typical Accuracy for Low Frequency ( 6.3 Ghz - "C" Band-

± 10 mm.

1.the transducer does not come into

contact with the process material

2.No Moving Parts in this level

measurement techniques.

2.There are certain measurements such as total level in

separator vessels that due to wide variations in material

composition of the upper phase DP is the only viable if

not ideal option.

3.a single top of vessel entry makes

leaks less probable than fully wetted

techniques

2.radar can be highly accurate, is immune to

most vapours / physical characteristics of the

measured media, other than, in some cases,

dielectric constant.

1.D/P transmitters are subject to errors due to changes in liquid density.

Density variations are caused by temperature changes or change of

product.

1.It’s primary disadvantage is cost.

2.The pressure ratings on radar antenna are

limited and these devices cannot measure

interfaces.

2.These variations must always be compensated for if

accurate measurements are to be made.

3.DP’s are mainly intended for clean liquids and require

two vessel penetrations. One is near the bottom of the

vessel where leak paths are the cause of the majority of

problems. D/P’s should not be used with liquids that

solidify as their concentrations increase. An example is

paper pulp stock.

3.Pulse radar has difficulty making accurate

measurement when the media is in close

proximity to the antenna because the time

difference between send and return signals is

too fast to measure accurately.

5 Application Refer Annexure - 1 Refer Annexure - 1 Refer Annexure - 1 Refer Annexure - 1 Refer Annexure - 1 Refer Annexure - 1

6 Practical Limitation

Fluid density must be stable if readings are to be

accurate. If liquid density is subject to change a second

d/p transmitter is required to measure density and then

used to compensate for any changes. To accommodate

the measurement of light slurries, differential pressure

transmitters are available with extended diaphragms that

fit flush to the side of the vessel. However, if the d/p

transmitter diaphragm becomes coated, it may require

recalibration, which can be impractical and will add to the

"cost of ownership". Frequently, the measuring device is

only one consideration in the total installation of the job.

Although a D/P transmitter is often less expensive than

other types of level sensors, there is usually considerable

additional hardware and labour required to make a

practical installation. The implementation of a stable, low-

pressure leg and 3 / 5 valve manifolds will add

considerable cost to the installation.

Successful measurement depends on

the transmitter being mounted in the

correct position so that the internal

structure of the vessel will not interfere

with the signal path. To ignore

obstructions in the vessel, tank mapping

has been developed. Tank mapping lets

the operator take a "sonic snapshot" of

an empty vessel. The transducer

transmits a sound burst and the echo is

recorded as a signature of the tank. Any

obstructions in the vessel will send an

echo and create a profile. Later on, this

signature or profile is locked into the

ultrasonic unit’s memory so it will not

respond to echoes created by these

obstructions.

In the case of hydrocarbons, an accurate water

bottoms measurement must be made for precise

inventory control. Typically, another technology, such

as RF Admittance is used to make the interface

measurement between water and hydrocarbons. Some

installations, such as floating roof tanks, require the

installation of a stillpipe. Inconsistencies on the internal

surface of the stillpipe can cause erroneous echoes,

these can have an adverse effect on the accuracy of

some vendor's equipment.

Interface Measurement

1.The primary benefit of DP’s is that it can be externally

installed or retrofitted to an existing vessel. It can also be

isolated safely from the process using block valves for

maintenance and testing.

1.This non-contact technology produces highly

accurate measurements in storage tanks and

some process vessels. Radar is an excellent,

but fairly expensive technology (£1k to £5k per

measurement) for continuous level

measurements.

There are various influences that affect

the return signal. Things such as

powders, heavy vapors, surface

turbulence, foam and even ambient

noise can affect the returning signal.

Temperature can also be a limiting factor

in many process applications. Ultrasonic

devices will not operate on vacuum or

high pressure applications.

1. Displacers and floats should only be used for relatively non-viscous, clean

fluids and provide optimal performance in switch applications and over for short

spans. 2 .Spans of up to 12m are possible, but they

become prohibitively expensive.

3.Cost of installation for displacers is high and many refineries are now replacing

them due to the inaccuracies experienced under process density changes

especially on interface duties.

4. High quality float switches still provide reliable and repeatable performance.

Even with todays array of level technologies, if a 100% process seal is required

under fail conditions for a Cryogenic application the only technique available,

other than nucleonic, is a magnetically coupled float switch

Advantages

2.the process fluid measured must maintain its density if repeatability is required,

this is particularly true of displacers

This is especially problematic in interface measurements, where both liquids

increase or decrease density, while the signal is proportional to the density

difference. Because the displacer is emersed in the process fluid it will be

vulnerable to particulate deposition. This will change the displacer mass and the

effective displacement causing a calibration shift.

Disadvantages5

4

1.Both floats and displacers work well with clean liquids and are accurate and

adaptable to wide variations in fluid densities

Displacers are affected by changes in product density since the displacement of

the body (its weight loss) is equal to the weight of the fluid displaced. eg. If the

specific gravity changes, then the weight of the displaced material changes, thus

changing the calibration.

High frequency shorter wavelength

narrower beam angle more

focused signal ability to measure

smaller vesselswith more flexible

mounting

Low frequency longer wavelength

wider beam angle less focused

signal ability to measure smaller

vessels with difficult application

variables.

3 Accuracy

2 Arrangement

Level Instruments Design Guide

Working1

1.Nucleonic level controls are used for point and continuous measurements, typically

where most other technologies are unsuccessful. 2.The

radioisotopes used for level measurement emit energy at a fairly constant rate but in

random bursts. Gamma radiation, the source generally used for nucleonic level

gauging is similar to microwaves or even light (these are also electromagnetic

radiation, but of lower energy and longer wavelength). The short wavelength and higher

energy of gamma radiation penetrates the vessel wall and process media.

3.A detector on the other side of the vessel measures the radiation field strength and

infers the level in the vessel. Different radioisotopes are used, based on the penetrating

power needed to "see" the process within the vessel. With single point gauges the

radiation provides a simple on/off switching function, whereas with continuous level

measurement the percentage of transmission decreases as the level increases.

The theory of operation for an RF Admittance level transmitter is

similar to that of Capacitance transmitters, but with two important

circuit additions. The oscillator buffer and chopper drive circuits

permit separate measurement of resistance and capacitance. Since

the resistance and capacitance of any coating are of equal

magnitude (by physical laws), the error generated by a coating can

be measured and subtracted from the total output. The result is an

accurate measurement regardless of the amount of coating on the

probe.

Nuclear LT Capacitance LT RF AdmittanceSl.No. Characteristics

A capacitance probe can be immersed in the liquid of the tank,

and the capacitance between the probe and the vessel wall

depends on the level. By measuring the capacitance of the

liquid, the level of the tank can be .As the level rise’s and

material begins to cover the sensing element the capacitance

within the circuit between the probe and the media (conductive

applications) or the probe and the vessel wall (insulating

applications) increases. This causes a bridge misbalance, the

signal is demodulated (rectified), amplified and the output is

increased.

Capacitance Type

RF Ad mittance Type

Level Instruments Design Guide

Nuclear LT Capacitance LT RF AdmittanceSl.No. Characteristics

1.As no penetration of the vessel is needed there are a number of situations that cause

nucleonic transmitters to be considered over other technologies.

2.These applications generally involve high temperatures / pressures or where toxic or

corrosive materials are within the vessel. Placing the source and / or detector in wells

within the vessel can reduce source sizes.

3.An extension of this is to use a moving source within the vessel; this facilitates the

unique ability to combine density profiling with accurate tracking of a moving interface.

5 Application

6 Practical Limitation

From a psychological standpoint, the radiation symbol found on these controls is

frequently the cause of unfounded concern with uninitiated plant personnel. Plant

Management is usually required to ensure that appropriate education is given to any

staff likely to be involved with this measurement technology. Source size regulations

can often be met in difficult applications by placing the source and / or detector in wells

within the vessel if necessary.

Most users’ realise the limitations of Capacitance level

measurement, such as the large errors caused by coatings. This

has led to a decrease in the number of these systems in

operation. Other technologies such as FMCW radar and in

particular RF Admittance have now gained acceptance due to

high levels of reliability and accuracy.

Admittance technology and nucleonic measurement provide the

only practical methods for level measurement in coating

applications. For insulating materials with changing dielectric

constants, the measurement can only be made reliably if the

material being measured is homogeneous. A reference sensor is

added to monitor the dielectric constant and then compensate the

calibration based on this information. Smart RF transmitters are

available providing superior levels of stability and accuracy as well

as remote communication. Knowledge of the approximate electrical

character of the process material is key to optimum system

selection and performance.

In other words

Advantages

Disadvantages5

4

RF Admittance is next generation capacitance as such it is by far

the most versatile technology for continuous level measurement. It

can handle a wide range of process conditions anywhere from

cryogenics to approximately 850 o C and from vacuum to 10,000

psi pressure. Aside from the electronic circuit technology, sensing

element design is very important to handle these process

conditions. There are no moving parts to wear, plug, or jam. As with

capacitance systems there is only a single tank penetration, usually

at the top of the tank, above the actual process level.

RF admittance is intrusive. Insulating granular measurements

require special considerations, such as the moisture range and

location of the sensing element to minimize errors caused by probe

movement.

It would appear that nucleonic gauges provide a truly universal "fit and forget" level

measurement technology. Although when the "cost of ownership" is calculated nuclear

level measurement is often more expensive than conventional systems. Hidden costs

include initial licensing and periodic surveying. These services are usually provided by

external authorities or by the equipment supplier, assuming they have appropriately

qualified staff. If no longer required, the nucleonic gauge must be disposed of through

appropriately licensed, external organizations, which again can be a costly exercise.

Capacitance techniques are capable of operation at extremes of

temperature and pressure. They work well for materials that

won’t leave a coating. Usually only a single tank penetration is

required.

Capacitance systems are intrusive. Have problems with varying

dielectric materials and those media’s, that coat the sensing

element. Thus users are normally limited to water-like media.

Even acids and caustics that don’t appear to coat the sensing

element are so conductive that the thin film they leave can

cause serious errors in measurement.

Single Seated Double Seated 3-Way valve Angle Valve Cage guided Butterfly valve Ball Valve Eccentric spherical plug valve

1. Minimum leakage in close position.1.Higher leakage rate than Singale

seated valve

1.Three pipeline connections provide

general converging (flow mixing0 or

diverging(flow-splitting) services.

1.For high pressure

services

1.Leakage rate is like

as Single seat.

1. For High capacity and low

pressure drop services.

1.Suitable for erosive and viscous fluids

or slurries containing entrained solids or

fiber

1.Usually less costly than conventional

globe valves and adaptable to ordinary

control requirements.

2.Require large actuator force,particulrly

large sizes.

2.Required less actuato forces due to

balancing feature of plug.

2.Usually single port type

only.

2.Balanced Plud design

permits operation with

smaller actuators.

2.Conventional discs provide

throttling control for up to 60°disc

rotation.

2.V-Notch produces an equal % flow

characteristicn,and used for control of

above fluids and application where very

high rangeability is required.

3.Most common body atype & simple in

Construction

3.Noise attenuation or

anti-cavitation type trim

available.

3.Typical wafer body design , a lug

wafer design and flanged design.

3.Low torque requirements can permit

ball valves to be used inQuick manual or

automatic operation.

4.Full Ball : 1.A complete sphere as the

flow controlling member.

2.Rotary shaft design and include aflow

passage.

3.Trunion mounted with a Single piece

ball & shaft to reduce torque

requirements & last motion.

V-Port Ball Valve:1. V -Port ball valve

utilizes a partial sphere that has a V-

shaped notch in it. 2.Notch permits wide

range of service & produces an equal %

flow charcteristics. 3.Straight forward

flow design produces very little pressure

drop & the valve is suited to the control

of erosion & viscous fluids.

4.V-port ball reduces the clogging when

it comes in contact with seal which

produces shearing effect.

Applicable Codes

2BEST SUITED

CONTROLLinear and Equal %

Exhibits approximately equal % flow

characterics.

Quick opening,Linear ; offer full flow with

minimum turbulence and can balance or

throttle fluids.Best suited for On-off .

Linear flow characteristics through 90° of

disk rotation.

3DESIGN

INFORMATION

Valve shall be designed to meet the

design pressure and temperature.

Interchangeability o ftrim permits

choice of several flow characteristics

or noise attenuation or anti-cavitation

components.

1.Actuator selection demands careful

consideration,particularly for

construction with unbalanced valve

plug.

1.High performance butterfly valve

should be sized to control within 15

to 75 range of disk opening.

1.Efiicient throttling

1.Reduced unbalance permits

operation of valves with smaller

actuators than those necessary of

single ported valves.

1.Low cost and Maintenance.

2.High Capacity1.Low cost. 2.High Capacity. 1.Erosion resistance.

2.Accurate flow control2.Higher capacity than the Single

ported valves.3.Good flow control. 3.Low leakage and maintenance

3.Available in Multiple ports

3.Many double seated bodies

reverse, so the plug can be installed

either push-down-to -open or push-

down-to-close.

4.Low pressure drop. 4.Tight sealing with low torque.

1.High Pressure drop1.Will not provide same "Shut-off "

as the Single Seated do.1.High torque required for control. 1.Poor throttling characteristics.

2.More expensive than other valve 2.Prone to Caviation at lower flows. 2.Prone to Cavitation.

1.Throttling service/flow regulation

1.Throttling service/flow regulation

but not generally recommended

because of their maintenance cost

and leakage.

1. Can be used for throttling mid-

travel position control either

converging or diverging fluids.

1.Fully open/closed at throttling

services & on-off valve.1.Fully open/closed, limited -throttling

2.Frequent operation

2.Frequent operation. 3.Minimal

fluid trapping inline. 4.Big

lines(Liquid service upto 96").

2.Higher temperature fluids.

ADVANTAGES

Rotary Valves

1

SR.NO PropertiesGlobe Body Valves

WORKING

Control Valve Comparision Sheet for Reference

DISADVANTAGES5

RECOMMENDED

USED6

4

Single Seated Double Seated 3-Way valve Angle Valve Cage guided Butterfly valve Ball Valve Eccentric spherical plug valve

Rotary ValvesSR.NO Properties

Globe Body Valves

Control Valve Comparision Sheet for Reference

1.Liquids,vapors,gases,corrosive

sustances,slurries

1.Typically used in refineries on

highly viscous fluids (

dirt,contaminants, or process

deposits on trim) concern

1.Coking service.

2.Solids carried in

supsension. 3.Severe

flashing services.

4.Cavitaion services.

5.High pressure drops.

1.Lquid,gases ,slurries,liquids with

suspended solids.

1.Most liquids, high temperatures,

slurries.

2.Specified for application stringent shut-

off requirements.

2.Often used for on-off or low

pressure throttling device.

8CONNECTION

RATING(Typical upto ANSI 2500) As per Piping Specifications.(H-103)

Standard end connections

(Flanged,screwed,butt weld etc.)Can

be specified to mate with piping

design specs.

As per Piping

Specifications.(H-103)

As per Piping

Specifications.(H-103)

Std. Raised faced piping

flanges.Typical ANSI 600.

As per Piping Specifications.(H-

103).Typical upto ANSI 900. As per Piping Specifications.(H-103)

9 MATERAIL As per Piping Specifications.(H-103) As per Piping Specifications.(H-103)Variations include trim materials

selected for high temperature service.

As per Piping

Specifications.(H-103)

As per Piping

Specifications.(H-103) As per Piping Specifications.(H-103) As per Piping Specifications.(H-103)

10 PACKING

PTFE( Polytetrafluro ethylene widely

used because of its inert and has low co-

efficient of friction. Can be applied to

400°F.

11 SEAT LEAKAGE

Metal-to- Metal saeting surfaces pr soft

seating with PTFE.Tight shut-off

achievable.

Metal-to-Metal seating usually

provides only Class II shut-off

capability,although Class III

capability is also possible.

Tight-off can be achieved. Tight shut-off achievable.

13 SIZING

The shear Safety factor should be a

minimum 150% at the specied Shut-

off pressure drop condition.

14 Flow Capacity Moderate High High

12

TRIM

CHARACTER-

ISTICS

7 APPLICATION

Equal% is suitable for pressure control application, or on application where highly varying pressure drop can be expected and pressure drop at the control valve is relatively small against the system pressure drop.

Quick Opening:Provides a maximum change in flowrate at lower valve tarvel with fairly linear relationship and lesser flow increase as the plug further opens.(Normally not used for throttling)

Linear: Provides equal increase in CV for equal increment in stem travel.

Linear one often specified for liquid level control and application requiring constant gain (Pressure drop is Constant)

Equal %:Provides equal% increase in CV for equal increament of stem travel.This characteristic provides throttling control valve at valve close position and rapidly increaasing capacity as the plug is near the open position.

Wire Number(Gauge) (Inches) (MM) (Inches) (MM) (MM2)

1 0.3 7.62 0.289 7,348 42.429

2 0.276 7.01 0.258 6,543 33.592

3 0.252 6.401 0.229 5,827 26.694

4 0.232 5.893 0.204 5,189 21.155

5 0.212 5.385 0.182 4,621 16.763

6 0.192 4.877 0.162 4,115 13.267

7 0.176 4.47 0.144 3,665 10.52

8 0.16 4.064 0.128 3,264 8.346

9 0.144 3.658 0.114 2,906 6.605

10 0.128 3.251 0.102 2,588 5.268

11 0.116 2.946 0.091 2,304 4.154

12 0.104 2.642 0.081 2,052 3.3

13 0.092 2.337 0.072 1,829 2.63

14 0.08 2.032 0.064 1,628 2.086

15 0.072 1.829 0.057 1,450 1.651

16 0.064 1.626 0.051 1,291 1.306

17 0.056 1.422 0.045 1,150 1.038

18 0.048 1.219 0.04 1,024 0.817

19 0.04 1.016 0.036 0,9119 0.65

20 0.036 0.9144 0.032 0,8128 0.515

21 0.032 0.8128 0.028 0,7239 0.407

22 0.028 0.7112 0.025 0,6426 0.321

23 0.024 0.6096 0.023 0,5740 0.255

24 0.022 0.55.88 0.02 0,5106 0.204

25 0.02 0.508 0.018 0,4547 0.159

26 0.018 0.4572 0.016 0,4038 0.125

27 0.0164 0.4166 0.014 0,3606 0.101

28 0.0148 0.3759 0.013 0,3200 0.08

29 0.0136 0.3454 0.011 0,2870 0.066

30 0.0124 0.315 0.01 0,2540 0.049

31 0.0116 0.2946 0.009 0,2261 0.041

32 0.0108 0.2743 0.008 0,2032 0.032

33 0.01 0.254 0.007 0,1803 0.024

34 0.0092 0.2337 0.0063 0,1601 0.02

35 0.0084 0.2138 0.0056 0,1422 0.015

36 0.0076 0.193 0.005 0,1270 0.012

37 0.0068 0.1727 0.0044 0,1143 0.009

38 0.006 0.1524 0.004 0,1016 0.008

39 0.0052 0.1321 0.0035 0,0889 0.006

40 0.0048 0.121 0.0031 0,0787 0.005

S.W.G. American Wire Gauges (AWG) MetricWIRE CONVERSION CHART

American Wire Gauge Diameter Diameter Cross Sectional Area

(AWG) (inches) (mm) (mm2)

1 0 0.46 11.68 107.16

2 0 0.4096 10.4 84.97

3 0 0.3648 9.27 67.4

4 0 0.3249 8.25 53.46

5 1 0.2893 7.35 42.39

6 2 0.2576 6.54 33.61

7 3 0.2294 5.83 26.65

8 4 0.2043 5.19 21.14

9 5 0.1819 4.62 16.76

10 6 0.162 4.11 13.29

11 7 0.1443 3.67 10.55

12 8 0.1285 3.26 8.36

13 9 0.1144 2.91 6.63

14 10 0.1019 2.59 5.26

15 11 0.0907 2.3 4.17

16 12 0.0808 2.05 3.31

17 13 0.072 1.83 2.63

18 14 0.0641 1.63 2.08

19 15 0.0571 1.45 1.65

20 16 0.0508 1.29 1.31

21 17 0.0453 1.15 1.04

22 18 0.0403 1.02 0.82

23 19 0.0359 0.91 0.65

24 20 0.032 0.81 0.52

25 21 0.0285 0.72 0.41

26 22 0.0254 0.65 0.33

27 23 0.0226 0.57 0.26

28 24 0.0201 0.51 0.2

29 25 0.0179 0.45 0.16

30 26 0.0159 0.4 0.13

Sl.No. Remarks