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Figure 3This illustration shows the Dopplersignal penetrating the pipe and thenreflecting off the particulates in thestream. The signal phase shift ismeasured and correlated to a flowvelocity.

Selecting the Right Flowmeter—Part 2

Use pros and cons to selectfrom these unique flowmeter technologies!

By Corte SwearingenReprinted from the January 2001 edition of Chemical Engineering magazine

The Doppler Flowmeter The Transit-Time Flowmeter

The Vortex Flowmeter The Magnetic Flowmeter Final Words Table 1: A Comparison of Flowmeter Parameters References

In this article, five flow-measurement technologies are summarized: bubble,Doppler, transit-time, vortex, and magnetic.

After reviewing the basic design parameters and highlighting the pros and consassociated with each flowmeter type, process applications for each technology willbe discussed. The information is then summarized at the end of this article in atable (Table 1: A Comparison of Flowmeter Parameters), which compares thevarious attributes of these five technologies, such as accuracy, maximumpressures and temperatures, and average costs. The intention of this article is notto recommend a flowmeter for every possible application, but rather to provide thebasic knowledge needed to make an informed flowmeter selection among thesetypes for a given application.

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The Doppler Flowmeter

Anyone that has heard the pitch of a train whistle change as the train passes hasexperienced the Doppler effect, named after the 19th century Austrian scientistChristian Doppler. This effect can be used to measure the flow in a pipe.

Design Overview: The Doppler effect is the frequency shift that occurs when asound source (transmitter) is in relative motion with a receiver of that soundsource. In the case of a Doppler flowmeter, we have two sensors mounted orstrapped on the outside of a pipe. One of the sensors is the transmitter, andtransmits a high frequency (ultrasonic) signal into the pipe. This signal is reflectedoff particulate matter or entrained gas bubbles in the fluid. The reflected signal isthen picked up by the receiving signal and the frequency difference between thetransmitted and reflected signals is measured and correlated into an instantaneousflowrate or flow total (Figure 3).

The frequency is subject to twovelocity changes; one upstream andthe other downstream. Travelingupstream, the velocity of the wave is

given as (Vs - V cosθ) where Vs

equals the velocity of sound in thefluid, V equals the average fluidvelocity and θ equals the angle of theultrasonic beam to the fluid flow.Similarly, the downstream velocity isgiven as (Vs + V cosθ). The Doppler

relationship between the reflectedand transmitted frequencies can nowbe expressed as:

fr = ft[(Vs+V cosθ)/(Vs - V cosθ)]

Here, fr is the received frequency and

ft is the transmitted frequency. To

further simplify this equation, one canassume that the velocity of the fluidin the pipe is much lower than thevelocity of sound in the pipe; that is,V << Vs. With this assumption, one can write:

fr = ft[(Vs + V cosθ)/Vs + (V cosθ)]/Vs

Which reduces further to

fr = ft[1 + (2V cosθ)/Vs]

The frequency shift is given by Δf = fr-ft so that

Δf = [2(ft) cosθ/Vs]V

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Entry type:Articles and White PapersProduct Selection Guide

Topics:Energy, Fluid Handling,Food and Beverage,Industrial Process,Laboratory/Research,Natural Resources,Pharmaceutical, Waterand Wastewater,Chemical Process,Semiconductors andElectronics, Energy,Utilities, IndustrialManufacturing,Transportation, FluidHandling

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Because (2ft cosθ/Vs) is a constant, one can write the final equation as

Δf = kV

where

k = 2(ft) cosθ/Vs

This indicates that the fluid velocity in the pipe is directly proportional to thechange in frequency between the transmitted and reflected ultrasonic signals.With knowledge of the pipe size, the electronics of the flowmeter will correlate thefluid velocity into a flowrate in the engineering unit of choice. Software correctionsmay have to be made for Vs, since the sound velocity through the medium will

change with pressure and temperature fluctuations.

There are ultrasonic designs on the market that use a series of pulsed signals, asopposed to a continuous ultrasonic beam. The main advantage of the pulsedtechnology is that it can measure the vertical velocity profile within the pipe. Fluidflow will be faster along the middle of the pipe than along the pipe walls and thepulse-design allows one to obtain a better image the flow profile within the pipe.

Another sensor design that minimizes external noise uses dual-frequency Dopplertechnology to send two independent signals into the pipe at different frequencies.Since both signals are subject to the same Doppler shift, but the noise signals arerandom, the signals can be combined to calculate a flow velocity while subtractingout the noise.

Ultrasonic sensors can be used with a wide variety of pipe materials, but some willnot allow the signal to pass through. Although pipe material recommendations will

vary depending on the sensor design, you should not expect to have any problemswith carbon steel, stainless steel, PVC, and copper. However, pipes made ofconcrete, fiberglass, iron, and plastic pipes with liners, could pose transmissionproblems. One should check with the particular manufacturer to ensure that thepipe material is suitable. Some Doppler designs utilize a section of pipe with built-intransducers that make direct contact with the fluid. This design, although nolonger non-invasive, eliminates the problem of incompatible pipe materials.

The accuracy of the ultrasonic Doppler meter is typically around ±2% of full scale.Minimum concentration and particulate size required is roughly 25 PPM at 30microns. Since some meters may require slightly larger concentrations, it is a goodidea to check with the manufacturer. The vast majority of Doppler meters are usedfor liquids (roughly 88%) while the rest are used for gas (11%) and steam (1%)applications.

Advantages: The main advantage of the Doppler ultrasonic meter is its non-intrusive design. An acoustic-coupling compound is used on the surface of the pipeand the sensors are simply held in place to take a measurement or, for a morepermanent installation, they are strapped around the pipe. Some manufacturersoffer a special clamp-on probe which allows connection to smaller pipe sizes (downto 1/4-in. diameter). Other advantages include:

Easy installation and removal—no process downtime during installation

No moving parts to wear out

Zero pressure drop

No process contamination

Works well with dirty or corrosive fluids

Works with pipe sizes ranging from 1/2" to 200"

No leakage potential

Meters are available that work with laminar, turbulent, or transitional flow

characteristics

Battery powered units are available for remote or field applications

Sensors are available for pulsating flows

Advanced software and datalogging features available

Insensitive to liquid temperature, viscosity, density or pressure variations

Disadvantages: Every flowmeter has its disadvantages and the Doppler design isno exception. The main disadvantage to the technology is the fact that the liquidstream must have particulates, bubbles, or other types of solids in order to reflectthe ultrasonic signal. This means that the Doppler meter is not a good choice forDI water or very clean fluids. Although strides have been made with the Dopplertechnology so that it can work with smaller particulate sizes and smallerconcentrations, one still needs to have some particulates present (one designavoids this problem by placing a 90-deg. elbow a few pipe diameters upstream ofthe flow sensor, and sensing the turbulent swirls created by the elbow). A goodrule of thumb is to have a bare minimum of 25 PPM at roughly 30 microns in orderfor the ultrasonic signal to be reflected efficiently. Some flowmeter designs mayrequire a little more than this, so it is advisable to check the specifications of themeter one is considering.

Note that if the solids content is too high (around 50% and higher by weight), theultrasonic signal may attenuate beyond the limits of measurability. This possibilityshould also be checked with the manufacturer, referring to one's specificapplication. Another disadvantage is that the accuracy can depend on particle-size distribution and concentration and also on any relative velocity that may existbetween the particulates and the fluid. If there are not enough particulatesavailable, the repeatability will also degrade.

Finally, the only other potential problem of this technology is that it can havetrouble operating at very low flow velocities. If you suspect this may be a problemfor an application, the low-end velocity that may be obtained with a particularsensor design should be checked with the manufacturer.

Applications: Doppler meters, being non-instrusive, have a wide variety ofapplications in the water, waste water, heating, ventilation and air conditioning(HVAC),HVAC, petroleum and general process markets. Below is a list of viable



Figure 4aThis diagram of a transit-timeflowmeter shows the downstreamsignal being projected between the twotransit-time sensors.

Figure 4bThis diagram shows the upstreamsignal projection. The frequencydifference between the upstream anddownstream times is proportional tothe flow velocity.

(HVAC),HVAC, petroleum and general process markets. Below is a list of viableapplications:

Influent and effluent water flow

Clarifier monitoring

Digester feed control

Waste water

Potable water

Cooling water

Makeup water

Hot and chilled water

Custody transfer

Water injection

Crude-oil flow

Mining slurries

Acids

Caustics

Liquefied gases

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The Transit-Time Flowmeter

Design Overview: Like its Doppler cousin, transit-time meters utilize an ultrasonicpulse that is projected into and across the pipe. The design works on a slightlydifferent principle, however. The basic premise of the transit-time meter is tomeasure the time difference (or frequency shift) between the time of flight down-stream and the time of flight up-stream. This frequency shift can then becorrelated into a fluid flowrate through the pipe. To help explain one type oftransit-time design, Figure 4a shows two transducers attached to a pipe.

In this figure, V is the average fluidvelocity, Z is the distance from theupstream transducer to thedownstream transducer, and q is theangle between the ultrasonic-beamline and the horizontal fluid flow. Thetime it takes for the ultrasonic signalto go from the upstream transducerto the downstream transducer can bewritten as

tdown = Z/(Vs + V cosθ)

where Vs is the velocity of sound

through the liquid. The upstream timecan be written as (Figure 4b):

tup = Z/(Vs - V cosθ)

Because the upstream and downstream frequencies can be generated in proportionto their respective transit-times, we can say the following:

fdown = 1/tdown

and

fup = 1/tup

where fdown and fup represent the downstream and upstream frequencies

respectively. The change in frequency can then be given as

Δf = fdown - fup = 1/tdown - 1/tup

By substitution, one obtains

Δf = (Vs + V cosθ)/Z - (Vs - V cosθ)/Z = (2 cosθ/Z)V

Since (2 cosθ/Z) is just a constant, one can write the final equation as

Δf = kV

with

k = 2 cosθ/Z

This, then, is the basic relationshipused to determine flow velocity fromthe measured frequency shift. Theflow rate can then be calculated usinga Reynolds-number correction forvelocity profile and by programming inthe internal pipe diameter. TheReynolds-number correction takes intoaccount the behavior of the fluid asbeing laminar, transitional orturbulent. These calculations aremade electronically and the flowrateor flow total can then be displayed inthe engineering units of choice.Interestingly enough in thisinstrument, the frequency shift ismeasured independently of Vs. This is

an advantage, since corrections willnot have to be made for the variance of Vs because of line-pressure and



not have to be made for the variance of Vs because of line-pressure and

temperature fluctuations. Most transit-time applications involve liquids, but designsare available to handle gases, as well.

In light of the single path design discussed above, note that a single ultrasonicpulse will average the velocity profile across the transit path, and not across thepipe cross-section, where better accuracy would be obtained. Some flowmeters onthe market send several ultrasonic pulses on separate paths in order to averagethis velocity profile; these meters tend to have better accuracy than their single-pulse counterparts. Transit-time flowmeters generally exhibit accuracies of around±1% of the measured velocity. Pipe-material recommendations are the same asthose given for Doppler flowmeters.

Advantages: As pointed out, the main advantage of the transit-time meter isthat it works non-invasively with ultrapure fluids. This allows the user to maintainthe integrity of the fluid while still measuring the flow. Some of the otheradvantages are listed below.

Easy installation—transducer set clamps onto pipe

No moving parts to wear out

Zero pressure drop

Can detect zero flow

No process contamination

Works well with clean and ultrapure fluids

Works with pipe sizes ranging from 1" to 200"

No leakage potential

Meters available that work with laminar, turbulent, or transitional flow characteristics

Battery powered units available for remote or field applications

Sensors available for pulsating flows

Advanced software and datalogging features available

Insensitive to liquid temperature, viscosity, density or pressure variations

Disadvantages: Transit-time flowmeter performance can suffer from pipe-wallinterference, and accuracy and repeatability problems can result if there are anyair spaces between the fluid and the pipe wall. Concrete, fiberglass and pipes linedwith plastic can attenuate the signal enough to make the flowmeter unusable.Because these factors can vary from one design to the next, it is advisable tocheck with the manufacturer to ensure that the pipe material is appropriate.

As mentioned before, the transit-time meters will not operate on dirty, bubbly, orparticulate-laden fluids. Sometimes, the purity of a fluid may fluctuate so as toaffect the accuracy of the flow measurement. For such cases, there are hybridmeters on the market that will access the fluid conditions within the pipe andautomatically chose Doppler or transit-time operations where appropriate. Theseunits are especially useful if the unit is to be used in a wide variety of differentapplications which may range from dirty to clean fluids.

Applications: Transit-time meters have wide applicability for flow measurement ofclean or ultrapure streams. Some of these applications are listed below.

Clean water flowrate in water treatment plants

Hot or cold water in power plants, airports, universities, shopping malls, hospitals

and other commercial buildings

Pure and ultra-pure fluids in semiconductor, pharmaceutical, and the food & beverage

industries

Acids and liquefied gases in the chemical industry

Light to medium crude oils in the petroleum refining industry

Water distribution systems used in agriculture and irrigation

Cryogenic liquids

Gas-stack flow measurement in power plant scrubbers

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The Vortex Flowmeter

Design Overview: At 11 a.m. on November 7th, 1940 the Tacoma Narrowssuspension bridge in the state of Washington collapsed from wind-inducedvibrations. The torsional motion of the bridge shortly before its collapse is anindication of the power of vortex shedding. The prevailing theory on the collapseof the bridge is that the oscillations were caused by the shedding of turbulentvortices in a periodic manner. Experimental observations have in fact shown thatbroad flat obstacles (also referred to as bluff bodies) produce periodic swirlingvortices which generate high and low pressure regions directly behind the bluffbody. The rate at which these vortices shed is given by the following equation:

f = SV/L

where,f = the frequency of the vorticesL = the characteristic length of the bluff bodyV = the velocity of the flow over the bluff bodyS = Strouhal Number and is a constant for a given body shape

In the case of the Tacoma bridge, a wind speed of approximately 40 mph causedthe formation of vortices around the 8-ft.-deep, steel plate girders of the bridge.This established vortices which were shed, according to the above equation, atapproximately 1 Hz. As the structural oscillations constructively reinforced, thebridge began oscillating, building up amplitude, until it could no longer hold itself

together.

Another less tragic example of the vortex principle can be seen in the wavingmotion of a flag. The flag pole, acting as a bluff body, creates swirling vorticesbehind it that give the flag its "flapping" quality in strong winds.



Figure 5As fluid moves around thebaffles, vortices form and movedownstream. The frequency ofthe vortices is directlyproportional to the flowrate.

Figure 6This photo shows atypical vortex meter.It may be installedhorizontally orvertically in the pipe.

A practical application of vortex productioncan be found in the design of the vortexflowmeter. In this design, a bluff body orbodies is placed within the fluid stream. Justbehind the bluff body, a pressure transducer,thermistor, or ultrasonic sensor picks up thehigh and low pressure and velocityfluctuations as the vortices move past thesensor (Figure 5). These fluctuations arelinear, directly proportional to the flowrateand independent of fluid density, pressure,temperature and viscosity (within certainlimits). As given explicitly in the aboveequation, the frequency of the vortices isdirectly proportional to the velocity of thefluid. Vortex meters are very flexible and thetechnology can be used for liquid, gas and steam measurements. This, along withthe fact that they have no moving parts, makes them a very popular choice.Accuracies are typically in the ±1% range.

Generally speaking, in-line vortex meters are available in line sizes ranging from 1/2to 16". Insertion vortex meters that are installed in the top or sides of a pipe canbe used for even larger pipe sizes. This makes them versatile in a wide variety ofapplications (Figure 6).

One final remark concerns the Reynolds number limitations for these flowmeters.For vortex meters, vortices will not be shed under a Reynolds number ofapproximately 2000. From roughly 2000 to 10,000, vortices will be shed but theresulting fluctuations are non-linear in this range. Typically, a minimum Reynoldsnumber of 10,000 is required in order get optimum performance from the vortexflowmeter. This number can vary from one design to another, so it is advisable tocheck with the manufacturer.

Advantages: The advantages of a vortex meter aremany. They are summarized below:

No moving parts to wear

No routine maintenance required

Can be used for liquids, gases, and steam

Stable long term accuracy and repeatability

Lower cost of installation than traditional orifice-type

meters

Available in a wide variety of temperature ranges from

-300F to roughly 800F

Bar-like bluff design allows particulates to pass through

without getting clogged

Available for a wide variety of pipe sizes

Available in a wide variety of communication protocols

Disadvantages: There are only a couple of things towatch out for when considering a vortex meter. First,they are not a good choice for very low fluid velocities,and therefore cannot be recommended below about 0.3ft/sec. At this low flowrate, the vortices are not strongenough to be picked up accurately.

In addition to the above, be aware that a minimum length of straight-run pipe isrequired upstream and downstream of the meter for the accurate creation ofvortices within the flowmeter. Ten pipe diameters before and after the point ofinstallation are typically recommended, but the minimum length could be greater ifthere are elbows or valves nearby. This is only a disadvantage if the installationarea does not allow for this straight run of pipe.

Applications: Vortex meters have become extremely popular in recent years andare used in a variety of applications and industries. Below is a summary of some ofthe main uses of a vortex meter.

Custody transfer of natural gas metering

Flow of liquid suspensions

Higher viscosity fluids

Steam measurement

General water applications

Chilled and hot water

Water/glycol mixtures

Condensate measurement

Potable water

Ultrapure & de-ionized water

Acids

Solvents

Vortex meters are also used widely in the oil, gas, petrochemical, and pulp & paperindustries.

Go to Top

The Magnetic Flowmeter

Design Overview: The basic design principle of the magnetic flowmeter (Figure 7)is derived from Faraday's law of induction, which states that the voltagegenerated in a closed circuit is directly proportional to the amount of magnetic fluxthat intersects the circuit at right angles.

In this design, magnets are



Figure 7This illustration shows the principle ofthe manetic flowmeter. As magnetic fluxis produced upward along the Y-axis, avoltage develops across the meterelectrodes as conductive fluid movesthrough the pipe. The voltage signal isdirectly proportional to the fluid velocity.

In this design, magnets arepositioned above and below the pipeto produce a magnetic flux (B) alongthe Y-axis. Because of themovement of conductive fluid, atright angles to this magnetic fieldand at a velocity V along the Z-axis, a potential is induced into theflow stream. The instantaneousvoltage produced between theelectrodes is proportional to thefluid flow through the pipe. For thisdesign, one can rewrite Faraday'sLaw as follows:

E = kBdV

where,E = the induced voltage betweenthe sensing electrodesk = a constantB = the magnetic flux densityd = the distance betweenelectrodes (equivalent to the pipe diameter)V = the velocity of the fluid

Linear flow through a pipe can be expressed as the volumetric flowrate Q, dividedby the cross-sectional area of the pipe A; therefore one can write

V = Q/A = 4Q/πd2

Substituting this into the Faraday equation gives

E = (4k/πd)BQ

This can be solved for the volumetric flow rate Q, and leads to

Q = (πd/4k)E/B

This final equation shows that the volumetric flowrate Q is directly proportional tothe induced voltage, E, between the electrodes.

There are two main methods of producing the magnetic flux density, B, across thepipe; alternating-current (a.c.) excitation, or pulsed, direct-current (d.c.)excitation.

In order to avoid past polarization problems encountered in a d.c.-excitationdesign, some magmeters use an a.c. excitation voltage. In this design, an a.c.voltage is used to create the magnetic field which, in turn, produces a varying-voltage signal across the electrodes. This is not a problem since the amplitude ofthe voltage, E, will still be proportional to the fluid velocity.

However, the development of some induction voltages across both the transformercoils and the electrodes is undesirable. For induction voltages that are 90 degreesout of phase with the signal voltage (called quadrature voltages), a phase-sensitive filtering circuit eliminates the unwanted voltage. Induction voltages thatare in phase with the signal voltage can be eliminated with special zeroingprocedures but this usually requires the fluid flow in the pipe to be fully stoppedbefore zeroing; this may not be feasible in some applications.

Response time is quicker with a.c. excitation than with d.c. pulse-type units. Thiscan be an advantage if the process flow changes quickly or contains hardparticulate matter, like sludge, pulp-and-paper stock, mining slurries and polymers.Hard particulates impinging on the electrodes can generate signals that can bemistaken for noise as opposed to the actual flow signal. The 60-HZ sampling of theAC design will work very well in distinguishing between noise and actual flowsignals in these types of applications. Outside of these more specialized caseshowever, the d.c.-pulse design is more widely used since it eliminates many of theabove-mentioned induction-voltages altogether.

In pulsed-d.c. excitation, the electromagnet coils are energized in short pulses orbursts. The electrode voltage is then measured before and after the d.c.excitation and the voltage difference is proportional to the flowrate. Theadvantage of the d.c. pulse design is that it eliminates the induction voltagesdescribed above, as well as the need to re-zero the meter at no flow conditions.Normally, the d.c. excitation is pulsed around 10 to 15 Hz. Some companies, in aneffort to provide the advantages of the a.c. design, have increased the d.c.pulsing to 100 Hz. While this certainly allows the meter to handle more difficultflows, it may increase the amount of heat generated in the coils and can affectthe lifetime of the instrument. Some new designs claim to minimize this heatingeffect.

As a final mention, it is worth noting that somemagmeter designs have solved the problem of coating-type fluids leaving a non-conductive deposit on themeter electrodes. By embedding metal sheets in themagmeter lining, the electrodes no longer come in directcontact with the fluid, and the measured parameterbecomes capacitance instead of voltage.

Advantages: The magmeter offers some very niceadvantages. They are summarized below:

Obstructionless flow

Virtually no pressure drop

Insensitivity to viscosity, specific gravity, temperature and

pressure (within certain limitations)

Will work with laminar, turbulent, and transitional flows



Figure 8This photo shows atypical magneticflowmeter, which canbe installedhorizontally orvertically in the pipe.

Can respond well to fast changing flows (for high-

frequency d.c.—pulse and a.c.—excitation designs only)

Good accuracy (0.5 to 1%)

No moving parts

Can handle slurries and heavy particulates

Lining protectors available for harsh, chemically corrosive,

and abrasive fluids

Inline and insertion designs available to handle pipe

sizes from approximately 1/10" to 96"

Available in a wide variety of communication protocols

Disadvantages: The only main disadvantage of themagmeter is that the fluid needs to be conductive.Therefore, liquids such as hydrocarbons and de-ionizedwater are not viable applications. The minimum requiredconductivity is normally in the range of 1-5 microSiemans/cm (mS/cm) but will varyfrom design to design. One manufacturer claims a minimum conductivity of 0.008mS/cm while another recommends 20 mS/cm. Again, it is advisable to check withparticular manufacturer's requirements.

The only other item to point out is that because this technology utilizes magneticand electric fields, the pipe must normally be grounded. There are specialgrounding procedures that need to be followed for conductive piping; and forplastic pipes, special grounding rings must be used. Although this is technically nota disadvantage, it does add another step to the installation process and failure toproperly ground the pipe can result in fluctuating flow signals.

Finally, it is not recommended to use graphite gaskets when installing a magmetersince the graphite could cause an electrically conductive layer to build up on theinside wall of the meter, causing erroneous signals. In the same spirit, it almostgoes without saying that installation in an area containing stray electromagnetic orelectrostatic fields is not recommended.

Applications: The magmeter can handle a wide variety of applications. Some ofthem are listed below:

Water

A variety of industrial effluents

Paper pulp

Mining slurries

Brine

Sludge

Liquid food products

Detergents

Sewage

Corrosive acids

Solid bearing fluids

Electrolytes

Process chemicals

Problem liquids include petroleum products, crude oil, deionized water, andvegetable/animal fats.

Go to Top

Final Words

A word of caution: The technologies discussed within this article represent anoverview of what is available on the market and the values in Table 1 are averagevalues. While there are hundreds of different designs available, the purpose of thisarticle is to give the reader enough knowledge to narrow down their application toone or two flowmeter technologies. For specific issues or additional design-parameters that should be considered, the manufacturers should be apprached.

Go to Top

Table 1: A Comparison of Flowmeter Parameters

Attribute Bubble DopplerTransit-

TimeVortex Magnetic

Gases Yes Yes1 Yes1 Yes No

Steam No Yes1 Yes1 Yes No

Liquids Yes Yes Yes Yes Yes

Viscous

liquids2 Yes Yes Yes Yes Yes

Corrosiveliquids

Notrecommended

Yes Yes Yes Yes

TypicalAccuracy 2%3 2%4 0.5%4

0.75-

1.5%5 0.5-1%5

TypicalRepeatability 1%3 0.5%4 0.2%4 0.2%5 0.2%5

Maxpressure, psi Vent6 N/A7 N/A7 300 to

400600-800

Max temp.,°F

212 N/A7 N/A7 400 to500

250-300

Maxpressuredrop, psi

negligible negligible negligible15 to

20negligible



Typicalturndown

ratio8300 to 1 50 to 1 N/A9 20 to 1 20 to 1

Average

cost10 $600$2,000

to$5,000

$5,000to

$8,000

$800to

$2,000

$2,000 to$3,000

1. While specialized Doppler and transit-time meters will work for gases andsteam, they represent a small percentage of all Doppler and transit-timeapplications.

2. Upper viscosity limit will vary per manufacturer.3. % of full-scale.4. % of velocity.5. % of flowrate.6. Outlet must be vented to atmosphere7. Non-contact device.8. The turndown ratio is the ratio of maximum flow to minimum flow, also known

as rangeability.9. Transit-time technology can measure down to zero flow.

10. Cost values vary depending on process temperature and pressure, accuracy

required and approvals needed.

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References

1. Cole-Parmer, 2001-2002 catalog, Vernon Hills, Ill., 20002. Parr, E. A., "Industrial Control Handbook," 2nd ed., Butterworth-Heinemann,

England, 19953. Bernard, Ing C. J., "Handbook of Fluid Flowmetering," 1st ed., Trade &

Technical Press Limited, England, 19884. Patrick, D., and Fardo, S., "Industrial Process Control Systems," Delmar

Publishers, N.Y., 19975. Miller, R.W., "Flow Measurement Engineering Handbook," 3rd ed., McGraw-

Hill, N.Y., 19966. Swearingen, C., Choosing the Best Flowmeter, Chemical Engineering, July

1999, McGraw-Hill, N.Y., p. 627. Vidrio, D., Ten Tips to Maximize Your Magmeter Application, Flow Control,

January 2000, Witter Publishing Corp., N.J., p. 318. Lynnworth, L., Ultrasonic Flow Measurement, at Ordinary Temperatures,

Using Wetted and Clamp-On Transducers, Flow Control, February 2000,Whitter Publishing Corp., N.J., p. 28

9. Espina, P., Ultrasonic Clamp-On Flowmeters: Have They Finally Arrived?,Flow Control, January 1997, Whitter Publishing Corp., N.J., p. 13

10. Silverberg, P., High-Accuracy Flowmeters Flood the Market, ChemicalEngineering, July 1998, McGraw-Hill, N.Y., p. 39

11. Koughan, J., The Collapse of the Tacoma Narrows Bridge, Evaluation ofCompeting Theories of its Demise, and the Effects of the Disaster ofSucceeding Bridge Designs, Undergraduate Engineering Review, TheDepartment of Mechanical Engineering, The University of Texas at Austin,August 1996

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