level

Level 1 - LevelRMT Training - 05 /98

1

Fundamental TrainingFundamental TrainingLevel 1


2

Topics: Slide No:• Why measure level? 3 - 5• Level terminology 6 - 19• Technology selection 20 - 29• Rosemount Technology (Pressure 30 - 55

Transmitter, HTG & Hybrid System• Other Technology (Float, Capacitance, 56 - 75

Displacer, Servo, Nucleonic, Laser &

Ultrasound)• Exercise 76 - 80

ContentsContents


3

Why measure level?Why measure level?5 Common Reasons5 Common Reasons

Inventory• keep track of amount of material of material available for a process

Custody Transfer• amount of material that is bought & sold in terms of volume or weight

Effieciency• maximise storage tank capacity• preventing unnecessary expense of purchasing additional vessels

Safety• prevent spillage in open vessels• prevent overpressure conditions in closed vessels that may result in rupture

Consistent Supply• to maintain product quality in a process

» blending, pulp & paper


4

Inventory• Accuracy is primary difference

» better than 3 mm precision needed • Applications need precise measurement because of $$$$$

» Transfer of ownership» Exact quantity must be known» Product cost» Tend to be larger vessels

Process • Applications are more concerned with:

» Control of a product level within a range» Safety (prevent overflow/ pump shutoff)» Monitor inputs of components of a process» Accuracy requirements vary widely

You can have a mixture of process

and inventory applications in a

plant

Why measure level?Why measure level?Inventory vs. ProcessInventory vs. Process


5

Why measure level?Why measure level?Indication vs. ControlIndication vs. Control

Indication

• on-site level check

• operator interpret measurementIndicators

– open loop control system

– help calibrate automatic control system

Control

• closed loop systemprocess point of measure transmitter

controller control valve process


6

I/P LIC

LT

(Inflow)(Inflow)

• Level Loop Issues:– Control At Inflow or Outflow– Non-Self Regulating

Level terminologyLevel terminologyLevel Control LoopLevel Control Loop


7

I/PLIC

LT

(Outflow)(Outflow)

Level terminologyLevel terminologyLevel Control LoopLevel Control Loop


8

Interface

Level

VolumeMassDensity

Level terminologyLevel terminologyParametersParameters


9


Liquid A to air/vapor interface

Liquid A

Liquid A to B interface

Liquid B

Interface• Interface measurement finds the boundary

between two liquids stored in the same tank» each liquid has different density


10

Density• Density is a measure of the mass per volume

Example:– grams / cc– pounds / cu ft

• Specific Gravity is a ratio of the density of a fluid to the density of water, thus

density of fluid = SG

density of water

Density of fluid = density of water * SG

Density


Mass = Density / Volume


11

Volume• Volume only correlates directly to level when:

» Tank is an upright cylinder» Density is constant» Temperature is constant» There is no change in tank wall position after filling

• Volume measurements are in units such as:» gallons, liters, barrels...

• Level measurements are in units such as:» inches, feet, millimeters, centimeters, meters...

• Correlation of volume to level varies with geometry of tank and may be expressed in terms such as:» gal/inch, liters/meter, barrels/inch...

Volume



12


Volume• Vertical Cylindrical Tank

» v = r2l

• Horizontal Cylindrical» v = r2atan[l½/(2r-l)½]+h(l-r)[l(2r-l)]½

• Sphere Tank» v = l2(3r-l)/3

r

h

l

r

hl

r

l


13


Volume

• Horizontal Bullet Tank» v = r2/3 * (3r-l) + 2r2(h-2r) *atan[l½/(2r-l)½] + (h-r)[l(2r - l)]½

• Vertical Bullet Tank

» v = r2/3(3r-l) if l r

» v = r2/3(3r-l) if r l (h - r)

» v = r2(h-2r) + [(l+2r-h)2]/3 * [3r-(l+2r-h)]if (h - r) l

h

l

r

h

l

r


14


Volume• Tanks with Dished Ends

» no standard shape– use strapping tables to determine volume

10

9

7

5

3

1

Point Level Volume(inches) (gallons)

1 0 02 5 103 10 324 15 685 20 1156 25 1737 30 2308 35 3139 40 39410 100 957

A look-up table that relates level to volume for several discrete points in a tank.

Commonly used to eliminate Bulging Error.

Bulging


15

Density Changes

Steam, vapors, dust

Steam, vapors, dust

0

PSIG-14.7

High vacuum

High vacuum

Viscous or sticky fluids

Viscous or sticky fluids

Temperature extremes

Temperature extremes Agitation Agitation

Abrasive fluids

Abrasive fluids

Corrosive processes

Corrosive processes Foam Foam

...and the technologies may have to handle a number of ...and the technologies may have to handle a number of application conditions.application conditions.

Level terminologyLevel terminologyMeasurement CharacteristicsMeasurement Characteristics


16

Top-down

Bottom-up

Top-Down Measurement• Poses less potential for leakage• devices installed or removed

without emptying tanke.g., dipstick, radar gauge

Bottom-Up Measurement• Typically contacts the process fluid

e.g., pressure transmitter, weigh scale

Bottom-Up vs. Top-Down Measurement



17

• An Inferred measurement is derived from another measurement

Ex: pressure transmitter

HeadPressure = Level , Mass = Level

Density Density

Stability of variables is critical to get a good inferred measurement.

If variables are not stable, compensation needs to be made.

• A Direct measurement looks only at the desired variable

Ex: floats, dipstick


Inferred vs. Direct Measurement


18

Continuous Measurement• Constant detection of

product height

• Concerned with amount of product

• May be used to control addition of other components to the vessel

Point measurement• Has the level reached

this point?

• High or low level detection

• Often used for alarm control

• May start or stop pumps

• May open or close valves

Continuous vs. Point Measurement



19

Non-Contact Non-Contact implies that the device does not touch the fluid, but it could be invasive

Non-intrusiveNon-intrusive implies that the device may come in contact with the fluid, but does not protrude into the fluid or interfere with fluid movement

Intrusive

Non-invasive Non-invasive implies that the device does not pass the walls of the tank nor touch the process directly

Non-Contact vs. Non-Invasive vs. Non-Intrusive



20

Hydrostatic

RadarTuning ForkFloat

Capacitance

Dipstick

Sight glass

Gage Glass

Weight

Differential Pressure

Ultrasonic Gap

Displacer

Nuclear

Ultrasonic

Bubbler

Technology selectionTechnology selectionLevel Measurement TechnologiesLevel Measurement Technologies


21

Contacting Noncontacting Point Continuous Liquids Solids

BubblersCapacitanceConductivityDisplacersFloatsHTGHydrostaticLaserMagnetostrictiveNucleonicOpticalPhase DifferenceRadarResistance TapeRotation SuppressionServoTape LevelThermalUltrasonicVibrationWeighing

Technology selectionTechnology selectionClassification of Level Measurement TechnologiesClassification of Level Measurement Technologies


22

Note: Only continuous devices included

Technology selectionTechnology selectionClassification of Level Measurement TechnologiesClassification of Level Measurement Technologies


23

• Why is the level measurement needed?What are you try to measure?What are you trying to achieve?

– Indication of fluid level– Alarm set point to prevent spill over– Transfer (Sale) of product– Contol of Product Mix– Leak Detection– Interface detection

• What are the conditions within or on the vessel? Product turbulence Obstructions Mounting constraints Angle of repose for solids Temperature and pressure limits

Technology selectionTechnology selectionFactors To Consider Factors To Consider


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• What are the environmental conditions? Ambient Temperature Humidity Vibration Electro Magnetic Interference(EMI) Transient protection

• What are the product characteristics? Corrosive Viscous Dusty, Foam Variable Density Variable Dielectric constant Tendency to Coat Interfaces, gradients, suspended solids Steam or other vapors


25

Common Density/ Temperature Changes



26

Typical Dielectric/ Temperature Changes



27


• What are the instrument requirements? Performance requirements Location approvals Power requirements Output requirements Number, location, and size of taps Total costs

– Product – Installation – Maintenance


28

Environmental Factors

ProcessConditionsDevice

Technology selectionTechnology selectionPerformance Consideration Performance Consideration

Direct vs inferredMeasurement capabilitiesRangeability

Temp changesVibrationNoise

Density changestemperature changesstatic pressureagitationaerationfoamdielectric changes


29

Approximate values are shown. Pressure and temperature limits are shown independently of each other.Temperature, oF

-240 32 195 600 800-40-100 320 400 900+

Pre

ssu

re, P

SI

atm

10000+

73

1000

3626

Displacer

Nucleonic

Ultrasonic

Ultrasonic Point

Pressure/HTG

Radar

Capacitance

Pressure w/ seals

Technology selectionTechnology selectionWorking Capabilities Vary with TechnologiesWorking Capabilities Vary with Technologies


30

In open vessel a pressure transmitter mounted near the bottom of the tank will measure the pressure corresponding to the height of the fluid above it.

Open Vessel Level Measurement

XMTR

HL

Patm

Phead

Patm

What happen to Atmospheric pressure? Cancelled

Off

Phigh - Plow = Phead

Plow = Patm

Phigh = Phead + Patm

Rosemount technologiesRosemount technologiesPressure Transmitters Pressure Transmitters


31

What happens when the liquid level drop below the sensor ?

Transmitter mounted above the tap in an open vessel

XMTR

HL0%

100%

0% h

g

The 0% has to be at least at the same level as the transmitter sensor or below the tapping point..

The sensor will not be able to sense any pressure change !!



32

“Zero Suppression” is often applied to compress the range of the transmitter OR to cancel the effects of the liquid head in the pipe connecting the transmitter to a tank when the transmitter is mounted below the vessel connection.

XMTR

HL

Actual ZeroSuppressed

4mA

20mA Max. Level

Min. Level Ra

ng

e

XMTR

HL

Actual Zero Suppressed

4mA

20mA Max. Level

Min. Level

Ra

ng

e

At min. level the High side pressure is high than the low side pressure



33

“Zero Elevation” is often applied to cancel the effects of the head caused by the seal fluid in the reference leg (low side) of a transmitter measuring level in a pressurized vessel.

XMTR

Actual Zero Elevated

4mA

20mA Max. Level

Min. Level Ra

ng

e

L H At min. level the low side pressure is high than the high side pressure



34

Dry leg: no fluid in low side impulse piping, or leg

If the gas above the fluid does not condense, the piping for the low side of the transmitter will remain empty.

Closed Tank Level Measurement (Dry Leg)

XMTR

HL

Phigh = Ptop+Phead

Plow = Ptop

Ullage or Vapor

Phead

Phigh - Plow = Phead



35

Wet leg pressure is additive to pressure on low side of the transmitter.

If the gas above the liquid condenses, the piping for the low side of transmitter will slowly fill with liquid. To eliminate this potential error, the pipe is filled with a convenient reference liquid.

Closed Tank Level Measurement (Wet Leg)

XMTRHL

Phead

Ptop= Ullage

Phigh =Phead+Ptop

Phigh - Plow = Phead - Pwet leg

Pwet

Plow=Pwet leg+Ptop



36

• Bottom-mount technology: potential leakage• Often requires 2 taps• Variable density creates errors• Temperatures beyond 600 F• High vacuum applications are tricky• Highly corrosive processes limit life• Abrasive processes can damage diaphragms• Liquids Only

Limitations



37

Consists of air supply, pressure regulator, flow meter, transmitter & extended tube.

Can be used for very corrosive applications.

Tank vented.

Air is bubbled through the tube at a constant flow rate. The pressure required to maintain flow is determined by the vertical height of the liquid above the tube opening times the specific gravity.

Pin(flow=const)

Bubbler System

Pressure to maintain flow = Phead

S.Gf

H

Phead = H * S.Gf

TXR



38

Gauge Pressure Transmitter

Air Supply

Valve• Allows dp to be a top

down measurement• No process contact with

transmitter• Open or low pressure • Control of Air supply is

important for accuracy

Application of Bubbler system:



39

Reliable, Simple, Easy to Use, Well Understood, Flexible Uses:

Differential PressureTransmitter

Diaphragm Seals extend limitations due to process conditions such as:

high temperatures

corrosion

viscous materials

suspended solids

plugging

sanitary needs


Remote Seals


40

•CPI / HPIBatch reactors digestersfractionatorsdistillation column bottoms and reflux drumsseparators surge drums reservoirs intermediate storage...

•Powerdrum level dearators...

•Pulp & PaperHeadboxStock TanksChemical Storage tanksEvaporatorsLow concentration liquor tanks...

•Food and BeverageFermentorsstorage tanksaging tanks brew kettles...

And many more!

Typical Pressure Applications



41

It is basically a method for measuring mass.

A local processor handles all the real-time calculations for transmitter algorithms and equations for MASS, DENSITY, LEVEL and VOLUME.

Top transmitter PT only used on non-atmospheric tanks to compensate for ullage pressure differences.

Middle transmitter PM located at a specific distance “H” above PB to calculate liquid density (PB-PM)

Bottom transmitter PB located at the base of the tank measures static head.

RTD measures tank contents temperature for reference correlations.

Rosemount technologiesRosemount technologiesHydrostatic Tank Gauging (HTG) Hydrostatic Tank Gauging (HTG)


42


H

HBT

PB

PM

PT

Volume =

Level =

Mass =

Density =

(PB - PT) x Area

(PB - PM ) / H

Mass / Density

(PB - PT) /Density + HBT

A system approach to tank inventory

TT

Effective Level Measurement Options:


43

Top Pressure Transmitter

Middle Pressure Transmitter

Temperature Sensor

Bottom Pressure Transmitter

(1 unit per tank)

All Smart transmitters are in multi-drop mode - All Smart transmitters are in multi-drop mode - Digital signalsDigital signals only only

(can take up to 14 SAMs)

(can take up to 31 AIMs)

[Handles tank calculaton]

(obtain data from SAM & convert to std MODBUS outputs)

Smart Application Module (SAM)

HARTCommunicator

Application Interface Module (AIM)

SCADA SCADA PackagePackageRS-485 MODBUS

Communications Network



44

Multi-Parameter MeasurementsMASS: Inventory and BillingDENSITY: Quality ControlVOLUME: Inventory & BillingLEVEL: Tank Capacity

Continuous Density Measurement Improved Accuracy High Reliability Low Maintenance Diagnostic Easy Installation Non-Intrusive No Moving Parts

Advantages of HTG



45



Temperature Sensor


(1 unit per tank) (can take up to 14 SAMs)

(can take up to 31 AIMs)

[Handles tank calculaton]

(obtain data from SAM & convert to std MODBUS outputs)

Smart Application Module (SAM)

HARTCommunicator

Application Interface Module (AIM)

SCADA SCADA PackagePackageRS-485 MODBUS

Communications Network

When the Middle transmitter is removed & the Top Pressure When the Middle transmitter is removed & the Top Pressure Transmitter is replaced by a Radar Gauge, then the whole system Transmitter is replaced by a Radar Gauge, then the whole system will be known as will be known as Hybrid Inventory SystemHybrid Inventory System

Rosemount technologiesRosemount technologiesHybrid Inventory System Hybrid Inventory System

Radar Gauge


46

Rosemount technologiesRosemount technologiesHybrid Inventory System Hybrid Inventory System



Temperature Sensor


Radar Gauge

H

L

D

• LEVEL is calculated by Radar Gauge L = H - D

• VOLUME is computed by Radar Gauge Through Strapping Table

– relationship level to volume• DENSITY is computed by the system

S.G = Head Pressure / Level– Head pressure measured by

bottom pressure transmitter• MASS is computed by the system

Mass = Density X Volume• CORRECTING for Density & Volume

back to standard values is computed

Measurement Options:


47

Advantages of Hybrid System

Rosemount technologiesRosemount technologiesHybrid Inventory Systems Hybrid Inventory Systems

Highly accurate Multi-Parameter Measurements MASS: Inventory and Billing DENSITY: Quality Control VOLUME: Inventory & Billing LEVEL: Tank Capacity

Radar can be installed without removing the tank from service

Radar unit can be used with or without a stilling well Process conditions up to 375°F (190°C) and 150 psi (10 bar) Optional average temperature measurement Good for density-stratified products


48

Wavelength, Meters

10 -11

10 7

10 5

10 3

10 1

10 -5

10 -3

10 -1

10 -9

10 -7

10 -13

10 2

10 18

10 16

10 14

10 12

10 10

10 8

10 6

10 4

10 20

10 22

Frequency Cycles/second

gamma rays

x-rays

ultra violet

visible light

------ultra high freq----------

----------TV broadcasting------------------FM Radio-------------

-------low frequency------------

Radar,

3-30 GHz

Microwave oven,

2 - 10 GHz

Cellular, pager,

300-3000 MHz

Electromagnetic Spectrum Radar is an

Electromagnetic Wave

Radio Detection And Ranging

--------super high freq---------

Rosemount technologiesRosemount technologiesRadar Gauge Radar Gauge


49

• Pulse » Measures range ( distance )» Transmits a pulse and measure time until

echo is received» Accuracy depends on ability to measure time

– Radar signals travel at the speed of light.– Must measure in picoseconds ( x10-12 ) !– Cost-effective electronics do not exist to do this

accurately !

Radar Techniques



50

• FMCW: Frequency Modulated Continuous Wave

» Does NOT calculate time-of-flight

» Evaluates the phase difference between the transmitted and return signal

» Plotting these phase differences against the transmitted signal yields a result proportional to distance

Radar Techniques



51

• Non Contact, Non Intrusive

• Tolerates Wide Range of Process Conditions

» Corrosive Processes

» High Temperatures

» Changes in Vapor Space

» Variable Density

» Variable Dielectric

» Viscous or Sticky Products

• Low Maintenance

• No Special Licenses Required

• Can measure long distances

• Liquids, pastes, solids


Advantages of Radar Gauge


52

• Sensors can be completely removed from process by use of a window made out of a nonmetallic material, such as Teflon, Ryton, Ceramic

• Sensors can be removed from the process without opening the vessel

Radar Application Considerations

• Cost• May not work with processes with low dielectric constant• May not work in applications with large amounts of

turbulence• Process connections tend to be large (>4” flanges)

Radar Limitations



53

•Pulp & Paper

»High Density Storage

»Color tanks

»Bleach tanks

»Hydropulpers

»Retention tanks

»Black liquor tanks

•Pharmaceutical

»Batch reactor

»Chemical storage

•Power

»Slurries

•Chemical»Polymers»Latex»High temp»LPG tanks»Butane sphere»Batch reactors»Two-phase sludge»Cyclohexane

•Minerals»Steel Scale Holding Tanks

And More!

Possible Applications

Rosemount technologiesRosemount technologiesRadar GaugeRadar Gauge


54

Both technologies

Top down, non contact

Easy to install

Good for abrasive materials, slurries

Not affected by changing fluid properties: density, conductivity, dielectric

Radar vs. Ultrasonic Gauge

Differences:Radar

Full vacuum to several hundred psi

Wide temperature limits

Can handle steam, fog, vapors

Can handle some foams and agitation

Can be used with windows

UltrasonicVery slight vacuum to about 100 psiNarrow temp band (<200 F)Is greatly affected by changes in vapor spaceSignal is lost in foam and agitation


Similarities:


55

Gas Temp (oC) RADAR ULTRASOUNDmillion m/s m/s

Dry Air 0 299.91 331.8100 299.94 386

Water vapor 100 299.10 404.8

Carbon Dioxide 0 299.85 250.050 299.87 279.0

Ammonia 0 299.93 415.0

Acetone 0 297.64 223.0

Source: Instrument Engineer’s Handbook, Liptak

Radar vs. Ultrasonic Gauge



56

Tank

Isola

tin

g

Valv

e

Float

Drain Valves

Indicator

IndicatorExternal Still pipe to guide the float

Float

Internal Still pipe to guide the float

Float-operated gauge level-indicator, indicates liquid level in cone or flat roof unpressurised tanks.Recommended for use on tanks storing water, fuel, oil, chemicals or other liquid products where operations do not require extreme accuracy.

Other technologiesOther technologiesFloat MechanismFloat Mechanism


57

C = KEoAd

where K = dielectric constant of materialEo = permitivity of vacuum

A = Area of plates (probe)C = capacitance (pF)d = distance between plates

d

k

• A capacitance instrument measures amount of capacitance between two plates of a capacitor.

• The capacitance of a capacitor increases if a dielectric is placed between the plates

• Circuit applies high frequency signal to probe

Other technologiesOther technologiesCapacitance ProbeCapacitance Probe


58

Nonconductive Fluid

d

Conductive Fluid

NonconductiveCoating

• Process fluid is the dielectric barrier

• Tank Wall forms second plate

• The variation of dielectric is the measurement

• Process fluid is the second plate

• Insulation on probe is dielectric

• The variation of the plate size is the measurement

How Capacitance varies with process fluid?

Level is proportional to dielectric change

Level is proportional to plate area change



59

• Limitation– Change in Dielectric creates error– Coating on probe by product creates errors– With non metallic tanks or tanks without vertical

walls, addition of reference probe is required– Calibration can be difficult especially since one

cannot “bench calibrate”– Changing vapor space can affect output



60

•Pulp & PaperSewage levelLiquor tanksBulk solids

•ChemicalInterface: fatty acid/water, oil/waterCarbon blackSeparators

•Food & BeverageStorage silos

•Oil & GasWater bottomWater cut

Potential Applications



61

Angular movement is then converted to electrical or pneumatic output.

pounds

0

pounds

0Based on Buoyance Force

The displacer is buoyed up by a force proportional to the weight of the liquid it displaces

Vertical movement of the displacer is converted to angular movement by mechanical linkages

Buoyant force increases as level rise

Other technologiesOther technologiesDisplacersDisplacers


62

Liquid Level

Measurement

Interface

Measurement

Density

Measurement

Good for short span measurement



63

Benefits:• Simple, Reliable.• Good for Interface measurements.• Good for Density measurements.• Unaffected by Agitation.• Tolerates High Temperatures and pressures.• Point or Continuous .

Limitations:– Does not tolerate viscous, dirty, or sticky fluids– Variable density causes errors in level measurement– Typically used for smaller spans (cost effective)– Must be installed carefully– Intrusive & Contact



64

• Typical Applications:Oil and Water interfaceOil and Gas SeparatorsStripper Reflux Drum LevelDehydration UnitsEffluent SeparatorsAbsorption TowersCondensate Discharge AccumulatorsDensity and Interface Measurements



65

Uses a combination of a displacer and a spring balance

The servo motor strives to obtain an equilibrium between the displacer and the balance. Any change in level will cause a change in equilibrium.Advantages:

– Very precise (1 mm accuracy)– Can measure level, interface– relatively low cost

Limitations:– Intrusive– Mechanical linkages

Cable

Storage Drum

Balance Detector

Servo

Motor

Displacer

Other technologiesOther technologiesServo GaugingServo Gauging


66

Gamma rays are emitted from the source. The presence or absence of the gamma rays is measured by the detector.

Nucleonic level switches use radioisotope sources sized to provide measurable radiation at the detector when no product material is present between source and detector.

DetectorGamma

Source

Single Point System

Other technologiesOther technologiesNucleonic GaugingNucleonic Gauging


67

Nucleonic level transmitters use the same radioisotope sources, but respond to the total absorption of gamma rays as they pass from the source to detector.

The amount of radiation reaching the detector is inversely proportional to the amount of material in the vessel.

Detector

Source

Continuous System



68

– Unaffected by:• High temperatures• High Pressures• Corrosive Materials• Abrasive Materials• Viscous Materials• Agitation• Clogging/Plugging

– Point and Continuous

– Liquids and Solids

– Interface (based on H2 density)

Advantages:

– Large density changes can create errors

– Layer of coating on vessel walls create errors

– Licensing Required– Leak Checks required– Cost

Limitations:



69

•ChemicalDistillation TowerBatch ReactorStorage TanksResin Bed levelHydrocracker reactor

•Pulp & PaperDigester LevelWood Chip BinsBleach TowerConsistencyEffluent WasteSlurriesLiquor concentrates

•RefiningFractionator TowerSurge TanksCoke Drum InterfaceDesalter

•Food and BeverageHopper LevelBlending Vats

•Mining Crusher LevelStorage silosSlurries

•UtilitiesSO2 / Lime scrubber

Fly ash Slurries


Typical Applications


70

glass windowlaser device

• Function: Uses infrared light to send a focused beam towards surface. Time of travel and reflection is measured.

• Narrow, focused beam: good for applications with space restrictions.

• Non contacting: uses a window• Accuracy: +/- 1 cm• Works best in cloudy, shiny liquids or

solids• May pass through surfaces of clear, still

fluids• Cannot tolerate dust, fog, steam or vapors• High cost• Alignment is critical

Other technologiesOther technologiesLaserLaser


71

• Advantages:Non ContactNo element contaminationCan be used for liquids and solidsTolerates Many Process

Conditions:

Sound Waves

A sound pulse(9 to 160 kHz) is transmitted and reflects off the surface back to the transceiver. The true reflected echo pulse is extracted and the time interval between transmission and reception is evaluated electronically.

The higher the level the faster echo reflected

Varying Density Corrosive Processes Viscous Product Varying Dielectric Sludge Buildup

Other technologiesOther technologiesUltrasonic GaugingUltrasonic Gauging


72

• Conditions of the vapor space impact speed of signal travel and thus, the measurement

• Changes could be due to:– temperature– dust– vapor composition– stratification of the vapor

• Some units have temperature compensation

• Gas blankets can be used to provide uniform vapor space condition

Sound Waves

Application Considerations



73

• Process surface conditions can affect signal return . Surface must have ability to reflect signal.

• Heavy agitation and foam may cause signal to be absorbed

• Vortex in fluid can misdirect signal• In open, outdoor installations, wind

can blow signal off coarse• Stilling wells can be used to isolate

the surface and contain signal.

Application Considerations



74

Limitations– not suitable for vacuum service– Cannot tolerate high temperatures (>200 F)– Foam interferes with signal– Agitation may distort signal– Internal obstacles can create false echoes– Nearby equipment could generate frequencies that

will cause errors– Vapor pressure limited to 50 psi



75

•ChemicalDistillation chamberCorrosivesSlurriesLatex PVCWaxes

•Food and BeverageDearating vesselalcohol fermenterbaking batterchocolatedairy productsgrain storage

•Cryogenic systems (point level)

•Waste waterClarifierSettling tanksReservoirsFlood controlSludge levels

•Pulp & PaperBlack liquor w/ solids

•PharmaceuticalEmulsionsLotions

•MarineFuel or ballast water indicationBilge alarm


Typical Applications


76

1. Which has the best accuracy on 6 meter High Water tank?A. Hollow or glass fill float with mechanical gauge (1 inch)B. “Servo” Gauge (1 mm)C. Pressure Transmitter ±0.1% of F.S [ ]

2. An inground reservoir is 5 meters deep. Which of the following method(s) will be suitable to measure and transmit the level without having to dig a hole to reach the bottom of the reservoir or the scour main. (Answer Yes [Y] or No [N])

A. Differential Pressure [ ]B. Servo Level Gauge [ ]C. Capacitive Probe [ ]D. Nucleonic Gauging [ ]E. Ultrasonic Gauging [ ]F. Radar Gauging [ ]G. Bubbler System [ ]

ExerciseExercise


77ExerciseExercise

3. For HTG, why is a 2nd Pressure Transmitter added to tank in the middle ?

4. Which one of the following tank gauging system is based on Mass?(A) Radar(B) Nucleonic(C) Servo Balance(D) HTG [ ]

5. Which of the following statement about Radar Gauge is NOT True ?(A) Top-down mounting(B) Can handle agitated & sticky process fluid(C) Can be used on a tank with non-metallic internal surface.(D) Can handle process with deep vacuum [ ]


78

10’

5’Assuming SG is = 1.1

What is the volume?____________ft3

What is the density of this fluid?___________#/ft3

What is the mass?__________pounds

What is the pressure level reading? ________in H2O

water = 62.4 # / ft3

ExerciseExercise

6.


79

10’

5’Now, suppose the SG changes to 1.05 and the

level does not change

What is the volume?____________ft3

What is the density of this fluid?___________#/ft3

What is the mass?__________pounds

What is the pressure level reading? _______in H2O

water = 62.4 # / ft3

ExerciseExercise

7.


80ExerciseExercise

Pmeasured = 150 inH2O

s.g. = 1.5

Pin(flow=const)

What is the fluid level in the tank?

8.

level

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