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SIEMENS Process Sensors


Understanding Ultrasonic/ Non-Contact Level June 2011

04/01/2011 Siemens Industry Inc.Confidential - for Siemens authorized use only.

L. BARKER CWTRS_UU.ppt

Introduction / Contents

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ContentsUltrasonic TechnologyUltrasonic Theory & Echo RangingTroubleshooting Ultrasonic'sMounting ConsiderationsApplications



Level Measurement Technologies

UltrasonicAdvantage

Ease of installationNo contact with the processLittle or no maintenanceProven in many applicationsTypically lowest cost of non-contacting technologies



Ultrasonic Theory

Advantages of ultrasonicsValue – typically 20 to 30% less expensive than alternate non-contactingProven performance in applications where the speed of sound is predictableNon-dependant of dielectric constantRemote mounting capabilities



Level Measurement Technologies

UltrasonicDisadvantage

Poorly reflective surfacesMust “see” the levelSusceptibility to changes in air space the attenuate the speed of sound



Level Measurement – Application Chart

Measurement range

Changing vapors

Heavy dust //////

Turbulence

Interface

Slurries

Solids

Liquids 3PPPP

Ultrasonics NON-CONTACTING

Microwave Radar

NON-CONTACTING

Guided Wave Radar

CONTACTING

Capacitance CONTACTING

Differential Pressure CONTACTING

Application Variable



Level Measurement – Application Chart

Dielectric ≤ 1.4

Accuracy ≥ 2%

Variable fluid density

Variable dielectric

Pressure >60 psi

Cryogenics

Vacuum

Temperature >300°F 3PPPP

Ultrasonics NON-CONTACTING

Microwave Radar

NON-CONTACTING

Guided Wave Radar

CONTACTING

Capacitance CONTACTING

Differential Pressure CONTACTING

Application Variable


Ultrasonic Technology Questions?


SIEMENS Process Sensors


Basic Ultrasonic Theory



Ultrasonic Theory

The nature of soundSound is a series of compression waves that travel through air or many other materials

Sound waves are caused by the vibrating of some objectSound must cause another object to vibrate to be detected



Ultrasonic Theory

The nature of soundSound waves have characteristics just like any other wave

VelocityWave LengthFrequencyAmplitude



Ultrasonic Theory

The nature of soundVelocity refers to the direction and speed of soundThe speed of sound is determined by the

Medium type (gas, water, solid)Temperature of the mediumMedium stratificationVacuum



Ultrasonic Theory

Low Frequency

High Frequency

1 second

The nature of soundWavelength is a measurement of the distance from one crest to anotherFrequency refers to the vibration of pitch of a sound

Measured in Hertz (Hz)The rate at which a guitar string or loud speaker vibrates

Since the velocity of sound is approximately the same for all wavelengths, frequency is often used to better describe the effects of different wavelengths.



Ultrasonic Theory

The nature of soundThe amplitude of sound is related to sound intensity (loudness)

Amplitude is measured in dB (decibels)Sound will spread (beam angle) as it leave its source and amplitude will decrease as the square of the distance traveledAbsorption by a material –amplitude will decrease as it moves through a substance



Ultrasonic Theory

The nature of soundThe relationship of time, speed, and distance

Accurate time measurement and consistent velocity are required for distance measurement

Distance = Velocity X Time2

Velocity = 2 X DistanceTime



Ultrasonic Theory

The nature of soundThe speed of sound through air is linearly related to air temperatureAll Siemens transducers are temperature compensatedExternal temperature sensors are available for applications with rapid temperature changes

0 5 10 15 20 25 30 35 40 45 50

Degrees Celsius

380

360

340

320

300

Met

ers

per s

econ

d

Vsound in air ≈ 331.4 + 0.6Tc m/s



Ultrasonic Theory

The nature of soundThe speed of sound through gases

V is the velocity in m/secγ is the adiabatic index (the ratio of specific heats, 1.4 for air)R is the gas constant (287 J/kgK for air)T is the absolute temperature in degrees KelvinM = the molecular mass of gas (0.2895kg/mol for air)

-100 -80 -60 -40 -20 0 20 40 60 80 100

Degrees Celsius

400

300

200

100

0

Met

ers

per s

econ

d

Vsound in gas = γRTM

Air Sulphur Dioxide

Ethyl Alcohol Methyl Alcohol


Ultrasonic Theory questions?


SIEMENS Process Sensors Certified Integrators Training


Echo Ranging Theory



Echo Ranging Theory

The nature of soundBeam angle definition – Twice the angle at which off-axis transmission is 3dB less than, or half the power of, the transmission axis

Transducer

Beam Width

50%(-3dB) 50% (-3dB)

α

Axis of transmission



Echo Ranging Theory

The nature of soundThe diametrical measurement of the cone in degrees defines the half power beam angleTransducer face diameter and frequency wavelength are factors in beam angle

A1 - (D1 tan Ø)2

A2 - (D2 tan Ø)2

Energy per unit area (E/A) - 1

(Rn * tan Ø)2

Transducer

R1

R2

D2

D1

A2

A1

Ø



Echo Ranging Theory

The nature of sound10 to 1 ruleBeam angles considerations are not as relevant since the development of auto false echo suppression

A1 - (D1 tan Ø)2

A2 - (D2 tan Ø)2

Energy per unit area (E/A) - 1

(Rn * tan Ø)2

Transducer

R1

R2

D2

D1

A2

A1

Ø



Echo Ranging Theory

Transducer ringdownThe primary active component for the transducer is the piezo-electric crystal that vibrates when subjected to alternating voltageWhen voltage is removed the vibration begins to decay



Echo Ranging Theory

Transducer ringdownThe inherent nature of the crystal and the surrounding transducer mass to continue vibratingThis vibration is called “ringing”The time it takes for this ringing to stop is referred to as “ringdown”



Ultrasonic Transducers

The ultrasonic transducerKynar enclosureToroid transformerPotting compoundCorkSteel blockPiezo-electric crystalAluminum blockTemperature sensorEccofloat




The ultrasonic transducerThe primary active component for the transducer is the piezo-electric crystal that vibrates when subjected to alternating voltageWhen voltage is removed the vibration begins to decay



Ultrasonics: what is an echo profile?

Digitally generated picture of the reflected echo received by the transducer Stored by the transceiver for processing

Transmit Pulse ECHO



How it Works –Sonic Intelligence and Ultrasonic Echo Profiles

1. The Pulse

2. The Return Signal




1. The Pulse


3. Form the Profile




1. The Pulse


3. Form the Profile

4. Filtering

5. TVT




1. The Pulse


3. Form the Profile

4. Filtering

5. TVT

6. Echo Algorithms

7. Echo Selection



Echo Ranging Theory

Echo profileThe receiver must remain off during the signal transmission and ringdownSince time is relative to distance, the ringdown time is commonly referred to as the blanking distance of the transducerThe return signal cause the crystal to begin vibrating againThis signal is sent to the receiver for processing

100dB

75dB

50dB

25dB

0dB0ft 5ft 10ft 15ft 20ft 25ft

Transmit ReturnPulse Signal



Echo Ranging Theory

Echo profileTime Varying Threshold (TVT)

Time Depending Threshold (TDT)

A reference to compare echoes at different positions in timeA far echo will be weaker because sound has traveled a greater distanceAn ideal TVT would have a slope equal to the attenuation of sound

100dB

75dB

50dB

25dB


Transmit ReturnPulse Signal

Blanking Time VaryingDistance Threshold

(TVT Curve)



Echo Ranging Theory

Sonic IntelligenceEcho Lock Window

The width of the window is set by the measure response parameter Dampens false echoes outside of the windowRequires an echo outside the window to be present for five consecutive shots before it is considered a true echo

100dB

75dB

50dB

25dB


Transmit Return Echo LockPulse Signal Window


(TVT Curve)



Echo Ranging Theory

Sonic IntelligenceEcho Lock

Uses a wide transmit pulse to provide a stronger return echo to detect more distant targetsThe echo lock window locks on to the selected echo in order to ignore spurious echoes from agitator blades or from random electrical interference

100dB

75dB

50dB

25dB




(TVT Curve)



Echo Ranging Theory

Sonic IntelligenceSelecting the true material echo

Area – the measure the area of each echo

100dB

75dB

50dB

25dB




(TVT Curve)



Echo Ranging Theory


Area – the measure the area of each echoLargest – the measure of the largest height of each echo

100dB

75dB

50dB

25dB




(TVT Curve)



Echo Ranging Theory


Area – the measure the area of each echoLargest – the measure of the largest height of each echoFirst – the measure of the first significant echo

100dB

75dB

50dB

25dB




(TVT Curve)



Echo Ranging Theory

Sonic IntelligenceScoring each echo


100dB

75dB

50dB

25dB


Area

Largest

First



Echo Ranging Theory


Scores are calculated and addedThe net Confidence is the value of the chosen echo minus the value of the next most significant echoTotal

Net Confidence

Area

Largest

First



Echo Ranging Theory

Auto False Echo SuppressionTypical profile of an obstruction error

An undesired echo can be ignored by lifting the TVT curve at the position of the false echoThis can be done manually or by performing Auto False Echo Suppression

100dB

75dB

50dB

25dB


Obstruction TrueEcho


(TVT Curve)



Echo Ranging Theory

100dB

75dB

50dB

25dB



(TVT Curve)

Obstruction TrueEcho

Auto False Echo SuppressionTypical profile of an obstruction error

An undesired echo can be ignored by lifting the TVT curve at the position of the false echoThis can be done manually or by performing Auto False Echo Suppression



Process Intelligence

Signal profileTime Varying Threshold (TVT)

Process turbulentBuild-up on obstructions creates larger false echoes

Time

Amplitude




100dB

75dB

50dB

25dB


Transmit False ReturnPulse Echoes Signal

Near Time VaryingRange Threshold

(TVT Curve)


Process turbulentBuild-up on obstructions creates larger false echoes





Process turbulentBuild-up on obstructions creates larger false echoes Increases overall signalTVT is high

Lower sensitivity

AdvantageNo need to remap

100dB

75dB

50dB

25dB




(TVT Curve)




Signal profileThe receiver must remain off during the signal transmission Referred to as the near range

100dB

75dB

50dB

25dB







Process normalStrong signalTVT is high

Low sensitivity

Advantages False echoes not detectedNo mapping required

100dB

75dB

50dB

25dB




(TVT Curve)




AlgorithmsSelecting the true material echo

100dB

75dB

50dB

25dB


Transmit Return Pulse Signal


(TVT Curve)



The Anatomy of an Echo Profile

TVT – Time Varying Threshold

Confidence Marker

Echo Lock Window

Material Echo (true echo)

Noise Floor

Echo Profile(Blue line)

Indirect Echoes

Ring Down



Basic definitions – An Overview

Transmit Pulse (Produced Sound) The sound pulse that is generated by the ultrasonic transducer. Measured in decibels.

Ring DownThe time is takes for the transducer to stop vibrating after generating a pulse.

Product / Material EchoEcho received from product surface. Measured in decibels.

Noise Floor Spikes and/or general interference shown in echo profile. Generally displayed as less than

the ring down and material echo in amplitude (echo height)TVT (Time Varying Threshold)

Threshold set by the transceiver to assist in the selection of the correct echo. Shown as a red line. Any echo above this line is considered as a valid echo.



Basic definitions

A word about the Dynamic TVTAs stated on the previous slide the TVT line is set using advanced mathematical calculations. These calculations are continually updated using the information derived from the product echo and the noise floor.

As the noise floor rises the TVT line rises

As the noise floor lowers the TVT line lowers


Echo Ranging Theory questions?


SIEMENS Process Sensors Certified Integrators Training


Troubleshooting



Troubleshooting

Troubleshooting parametersEcho confidenceSignal strengthNoise level

Other important parametersCalibration Parameters Algorithm Parameter



Understanding Ultrasonics

Echo with Low Noise / High Echo Strength / High Echo Conf.Echo Confidence is an approximation of Product Echo minus NoiseThis is an example of a good application with no process or wiring issues

Noise

Echo Strength

Echo Conf.




Low Product Echo Strength / Low Echo Confidence / Low NoiseNoise level remains constant but Echo Strength and Echo Confidence go

downTypical causes: Poor aiming, foam, under-powered transducer, high dust, heavy steam, or material on face of the transducer

Noise Echo Strength

Echo Conf.




High Noise / High Echo Strength / Low Echo ConfidenceThe Echo Strength is constant but as Noise goes up the Echo Confidence goes downTypical cause is electrical or acoustical noise

Noise Echo Strength

Echo Conf



Primary readings are:Low echo conf Low echo strength Low noise


Cause: Improper aiming, presence of foam, under-powered transducer, high dust, sticky build-up on transducer face.

5:7101:5P807P806P805




Primary readings are:Low echo conf High echo strength Low noise

Cause: Over-powered transducer, or multiple echoes.

6:9731:8P807P806P805



Primary readings are: Low echo conf High echo strength High noise


VFD

P805 P807P8061:8

Cause: Electrical or Acoustical noise. Electrical source may be on transducer cable, power, or remote temperature sensor. Acoustical source may be from plant noise at the Ultrasonic Unit working frequency.

34:5560




Primary readings are:High echo conf High echo strength Low noise

Cause: Nothing. This is a good application. Time to go to the bar.

5:8591:25P807P806P805



68P 806

Troubleshooting

Signal StrentghParameter P806

Viewed in dBAn echo return is the first requirement for signal processingPoor echo strength is a result of weak echo returns and will result in poor confidence



17P 806

Troubleshooting

Signal StrentghPossible causes of a weak echo

Underpowered transducerPoor aimingHigh attenuation from extreme dust, steam or CO2

Surface may be poorly reflectiveTurbulentFoam



Troubleshooting

Echo return – troubleshootingCheck the calibration parametersCheck that the transducer face is perpendicular to the products angle of reposeRemove the transducer from the application and shoot against a solid target Temporarily install a spare transducer in the application

Use temporary wiring to eliminate wiring problems such as a faulty spice or water in conduit



Troubleshooting

Echo return – possible remediesVerify and correct the programming of the Quick Start Parameters Correct the aiming of the transducerReplace defective transducer Correct faulty wiring Replace defective wiring Use a higher powered transducerInstall a stilling well



45P 806

Troubleshooting

Summary – Troubleshooting Parameters

Signal strength - P806First requirement for signal processingTake steps to increase signal strengthRemember changing bin conditions will have an effect on signal strengthCompare to noise level to determine signal to noise ratio

23:43P 807



02:04P 807

Troubleshooting

Verify a noise problemParameter P807

Typical noise should be less than 5dB with the transducer disconnected



Troubleshooting

Determining the noise sourceStart by disconnecting the transducer from the transceiver

If the measured noise is above 5dB go to Non-Transducer Noise Sources



Troubleshooting

Non-transducer noise sourcesRemove all input and output cables from the controller individually while monitoring the noise

If the noise drops:Ensure low voltage cables are not being run adjacent to high voltage cables or near electrical noise generatorsEnsure correct wiring and proper grounding

If noise remains:Noise is either from the power source or it is being induced as EMFTry an alternative power sourceMove the controller away from the noise sourceShield the controller



Troubleshooting

Echo ConfidenceParameter P805

Signal to noise ratio is reflected in Echo ConfidenceHigh noise and/or weak echo strength will result in low confidenceThe first number is the Short Shot confidenceThe second number is the Long Shot confidence

0:18P 805



Troubleshooting



0ft 5ft 10ft 15ft 20ft 25ft

1st Echo A=8 L=20 F=20 Total=48

2nd Echo A=6 L=17 F=7 Total=30

Confidence = 48 – 30 = 18100dB

75dB

50dB

25dB

0dB



1st Echo F=25

2nd Echo F=0

Confidence = 25 – 0 = 25

Troubleshooting

Sonic IntelligenceAlgorithm parameter P820

Changing to single algorithm100dB

75dB

50dB

25dB




Troubleshooting

Sonic IntelligenceTransducer ringing

The effects of ringing or obstructions in the blanking distanceRinging is typically caused by over tightening the transducerObstruction typically from nozzle or gradingIf P820 is set for “First echo” the obstruction will be selected as the true echo

100dB

75dB

50dB

25dB


The effects of ringing



Troubleshooting

Sonic IntelligenceTransducer ringing

Extending the blanking zone, P800, the obstacle is ignored and the First Echo algorithm will select the material level as the first true echo

100dB

75dB

50dB

25dB


Extended blanking distance – P800



Troubleshooting

Sonic IntelligenceUse caution when selecting a single algorithmOccasionally a single algorithm will give a low score to a true echo and a better score to a false echo Other algorithms will push up the total score of the correct echo and push down the total score of the false echoFor a given bin condition a single algorithm will give higher echo confidence, but as bin conditions change other algorithms may be requiredGenerally using all three algorithms provides more reliable operation over time



Troubleshooting

Summary – Troubleshooting Parameters

Confidence – P805If signal strength (P806) is strongAnd noise (P807) is lowAnd the resulting confidence (P805) remains low, you have multiple echoes

0ft 5ft 10ft 15ft 20ft 25ft

1st Echo A=8 L=20 F=20 Total=48

2nd Echo A=6 L=17 F=7 Total=30

Confidence = 48 – 30 = 18100dB

75dB

50dB

25dB

0dB



Troubleshooting

New installationsMost problems are:

Wiring errorsVerify wiring against schematicsFollow proper grounding proceduresUse grounded metal conduit

Installation errorsEnsure mounting to factory specificationsProtect from noise sourcesUse grounded metal conduit

Programming errorsPerform P999 factory resetProgram Quick Start Parameters – P001 thru P007Check for proper level reading before proceeding



Troubleshooting

Old installationsWhat has changed since start-up?

Has the noise level increased?New equipment, new VFD?

Has the echo strength decreased?Transducer aiming?Foamy surface?Water in conduit?

Have the parameters changed?Has someone altered the settings?


Troubleshooting questions?


Ultrasonic Mounting Considerations



Ladder Tank support braces

Fill pipe

Mounting Considerations

Mounting location

1 2 3 4




Mounting location1. Too close to side wall –

interference from ladder rungs and support braces

1






2. Correct installation – 1/3 the distance from the side wall, no obstructions

2







3. Center of a parabolic tank –problems with secondary echoes

3

-3dB (50%)








3








4. Obstruction from fill stream

4




Mounting considerationsAll material levels should be considered when selecting mounting location

42 31




Mounting considerationsAll material levels should be considered when selecting mounting locationIf forced to mount close to side wall obstructions must be exposed before Auto False Echo Suppression can be performed

1




Mounting considerationsAll material levels should be considered when selecting mounting locationIf forced to mount close to side wall obstructions must be exposed before Auto False Echo Suppression can be performedIt is preferred to perform Auto False Echo Suppression with the vessel empty

Careful not to map the bottom of the vessel!

1




Other mounting considerationsAll material levels should be considered when selecting mounting locationIf forced to mount close to side wall obstructions must be exposed before Auto False Echo Suppression can be performedThe sound path should be perpendicular to the monitored surface




Mounting considerationsStandpipe / nozzle

Minimum standpipe diameter of 3”Standpipe height should be less than 3 times the diameterIf overall standpipe height is 6” or less, factory blanking can be usedIf height is greater than 6”increase blanking to 4” beyond the standpipe bottom

Height

Diameter





When considering height to width ratio ensure standpipe inside the vessel in included

Height

Diameter




Diameter

Height


When considering height to width ratio ensure standpipe inside the vessel in includedIdeally, standpipe nozzles should be cut at a 45° angle




Height

Diameter


When considering height to width ratio ensure standpipe inside the vessel in includedIdeally, standpipe nozzles should be cut at a 45° angleStandpipe side wall should be seamless and free of welds or burrs




Mounting considerationsStilling Well

Vessels with obstructionsFoamHighly agitated surfacesInstalled inside or outside the vesselMust be vented at top with inlet at the bottomClean liquids only




Mounting accessories – liquid applications

Bonded flanges for non-corrosive applications





Bonded flanges for non-corrosive applicationsTeflon faced flanges for corrosive applications





Bonded flanges for non-corrosive applicationsTeflon faced flanges for corrosive applicationsFlange adaptorSubmergence shield

Transducer with submergence shield, used in applications where flooding is possible

Submersible

Rigid metal conduit

Coupling

Submergence shield


SIEMENS Process Sensors Applications




Two Wire Loop Powered All in One Ultrasonic

SITRANS Probe LUTechnical specifications

ETFE or PVDF to suit chemical conditionsBlanking range – 10” (0.25m) to 40 ftAccuracy – .15% of rangeCommunications

HART standardProfibus PA option



Two Wire Loop Powered All in One Ultrasonic Unit

The new and extremely experienced SITRANS Probe LU

ApprovalsFM GeneralFM Class 1, Div. 2FM Intrinsically Safe (barrier required)



Remote Mounted Ultrasonic

Level only controllerLevel DistanceSpaceOne or three relays

Multifunctional controllerDifferentialVolume and pumped volumeOpen channel flowSix relays




Key featuresLiquids or solids to 50ft (15m)SIMATIC PDM for configuration and diagnosticsOn board Modbus RS-232 / RS-485Field installable communications

Profibus DPAllen-Bradley Remote I/ODeviceNet




Key featuresOutputs

One, three, or six relays Two mA outputs

Two transducer inputs (six relay version only)

Differential – dual point difference or dual point average Optional independent dual point measurement




Key featuresInputs

Two discrete inputsOne analog signal input (six relay model only)




Key featuresWall Cling Reduction

Set level set-point ON and level set-point offEnter a wall cling valuePump on and off levels will be a randomly selected within the Random Set-point Range

Level Set-point ON

Wall Cling Value

Level Set-point OFF

Random Set-point Range




Optional key featureTwo transducer input

Differential – dual point difference or dual point average




Optional key featureTwo transducer input

Differential – dual point difference or dual point averageIndependent dual point measurement



Applications

Typical applicationsLift stations



Applications

Typical applicationsLift stationsOCM flow



Applications

Typical applicationsLift stationsOCM flowPump control



Applications

Typical applicationsLift stationsOCM flowPump controlClean water storage



Applications

Typical applicationsLift stationsOCM flowPump controlClean water storageBulk storage



Applications

Typical applicationsLift stationsOCM flowPump controlClean water storageBulk storageThe most widely used product in the Water & Waste Water industries



Contact Information

Mike GavanSr. Application Engineer / PS2 Product PromoterWest/Midwest Region

Cell: 972-672-4664E-Mail: [email protected]

www.siemens.com/level


Thank you for your attention!

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