jesse yoder - worldflowresearch.com

A nyone who observesthe flowmeter mar-ket today can seevery quickly that thedemand for some

types of flowmeters is growing fasterthan the demand for other types. Forexample, the use of Coriolis and ultra-sonic flowmeters is increasing at amuch faster rate than the use of posi-tive displacement or variable-areameters. The reason for this trend is duein large part to the advent of newertechnologies, including advancementsin computer processing capability.

Published articles have proposed adistinction between the growing tech-nologies and the flat or decliningtechnologies by classifying them into

two categories — new-technologyflowmeters and traditional-technolo-gy flowmeters. This article restatesthe distinction between new-technol-ogy and traditional-technologyflowmeters. It then explains the para-digm case method for flowmeterselection, as it applies to new-technol-ogy flowmeters.

New-Technology FlowmetersMost new-technology flowmeters

came into industrial use in the 1960sand 1970s, while differential pressureflowmeters (traditional technology)were used in the early 1900s. Eachnew-technology flowmeter is basedon a different physical principle andconstitutes a unique approach to

flow measurement. New-technology flowmeters have

the following characteristics:1. They were developed after 1950.2. They incorporate technological

advances that overcome problemsinherent in earlier flowmeters.

3. They attract more developmentattention from major flowmetersuppliers than traditional-tech-nology meters.

4. They perform at a higher levelthan traditional-technology meters.

Included in this category areCoriolis, magnetic, ultrasonic, vortex,and multivariable differential pres-sure (DP) meters. All of these flowme-ters have been introduced since 1950.Magnetic flowmeters first came onto

By Jesse Yoder

38 January 2004 Flow Control

Paradigm CaseApplications for ‘New-Technology’Flowmeters

www.FlowControlNetwork.com January 2004 39

the market in 1952, while Tokimec(then Tokyo Keiki) introduced ultra-sonic meters in Japan in 1963. Eastechbrought out vortex meters in 1969,and Yokogawa developed its vortexmeter at about the same time. MicroMotion introduced Coriolis flowme-ters in 1977. Bristol Babcock broughtmultivariable DP flowmeters onto themarket in 1992.

Flowmeters that incorporate oldertechnologies are “traditional-technol-ogy” flowmeters. These include singlevariable DP, positive displacement,turbine, open channel, thermal, andvariable-area flowmeters. As a group,these flowmeters have been in uselonger than new-technology meters.Generally speaking, they have highermaintenance requirements than new-technology flowmeters. And eventhough suppliers continue to intro-duce new traditional-technologyflowmeters, they are not typically thefocus of new product development.

The history of turbine flowmetersgoes back to the mid-1800s, while DPmeters came into use in the early1900s. Many of the problems inherentin DP flow measurement have to dowith the primary elements usedtogether with a DP transmitter. Forexample, orifice plates can beknocked out of position by impuritiesin the flowstream, and they are sub-

ject to wear. Positive displacementand turbine meters have moving partsthat are subject to wear. The accuracylevels of open channel, thermal, andvariable area flowmeters are substan-tially lower than that of new-technol-ogy flowmeters.

Coriolis Flowmeters Coriolis flowmeters are made up of

one or more vibrating tubes, usuallybent. The fluid to be measured travelsthrough the vibrating tubes. The fluidaccelerates as it approaches the pointof maximum vibration and deceler-ates as it leaves this point. As a result,the tubes take on a twisting motion.The amount of twisting motion isdirectly proportional to mass flow.Position detectors are used to sensethe positions of the vibrating tubes.Most Coriolis flowmeter tubes arebent, and many different designs areavailable. However, some suppliershave also introduced straight-tubeCoriolis meters.

Straight-tube flowmeters operateon the same principle as bent-tubemeters. Fluid inertia causes the fluidin the first half of the meter to acceler-ate, while the fluid decelerates in thesecond half of the meter. The inertia ofthe fluid generates a Coriolis forcethat slightly distorts the measuringtube. The amount of this distortion is

proportional to mass flow. Sensors areused to detect the amount of distor-tion. Temperature is constantly meas-ured because the oscillatory proper-ties of the tube vary with temperature.This makes it possible to make anynecessary adjustments in the meas-urement.

It is often said that Coriolis flowme-ters measure mass flow “directly,”unlike other flowmeters that calculatemass flow by using an inferred densi-ty value. Multiplying the cross-sec-tional area of a pipe by the fluid’saverage velocity yields volumetricflow (Q). Mass flow is obtained bymultiplying volumetric flow (Q) byfluid density. Some multivariableflowmeters measure the temperatureand pressure of the fluid and usethese values to infer the density of thefluid. It is then possible to calculatemass flow.

Coriolis meters can be used tomeasure flow of both liquids andgases. While these meters are highlyaccurate, they are limited in terms ofthe pipe sizes they can efficiently beused on. Over 90 percent of Coriolisflowmeters are used in pipe sizes oftwo inches or less. While they can beused in pipes up to and including sixinches in diameter, the meters becomeexpensive and unwieldy in the largerpipe sizes.


While a number of different methods of flowmeter selec-tion have been devised, the most effective approach

incorporates a step-by-step method that begins by matchingthe applications involved with the paradigm case applica-tions for various flowmeters. The selection process shouldalso apply application, performance, cost, and supplier crite-ria in order to select a flowmeter. A statement of the para-digm case method follows.

1. Every flowmeter is based on a principle that draws a cor-relation between flow and some specified set of conditions.This principle determines the paradigm case application forthis particular type of flowmeter. The first step is to selectthose types of flowmeters whose paradigm case applicationsare most like your own.

2. Make a list of application criteria that relate to the flowmeasurement you wish to make. These conditions mayinclude fluid type (liquid, gas, steam slurry), measurementtype (volumetric or mass), pipe size, process temperature andpressure, fluid condition (clean or dirty), fluid density, flowprofile considerations, fluid viscosity, range, Reynolds numberconstraints, and other. From the type of flowmeters selected inStep One, select those that meet these application criteria.

3. Make a list of performance criteria that apply to theflowmeter you wish to select. These include accuracy, reliability,range, repeatability, and others. From the flowmeters selected inStep Two, select those that meet your performance criteria.

4. Make a list a list of cost criteria that apply to yourflowmeter selection. These include purchase price, installa-tion cost, cost of ownership, maintenance cost, and others.From the flowmeters selected in Step Three, choose those thatmeet your cost criteria.

5. Make a list of supplier criteria that govern your selectionof a flowmeter supplier. These include flowmeter type, serv-ice requirements, company location, training, responsive-ness, internal requirements, and others. From the flowmetertypes selected in Step Four, select the suppliers of thoseflowmeters who meet your supplier criteria.

6. For the final step, review the flowmeters selected in StepFour and the suppliers selected in Step Five. Review theapplication, performance, and cost conditions for theflowmeter types that remain, and select the one that bestmeets these conditions. Now, select the best supplier for thistype of flowmeter from the suppliers specified in Step Five.You now have selected the best supplier for the flowmetertype that best meets your criteria.

It is possible that an application may fit the paradigm casefor more than one flowmeter type. In this case, steps twothrough four are especially important in determining whichtype of meter to use. In some cases, however, new-technolo-gy flowmeters are complementary rather than competing.For example, Coriolis flowmeters work best in pipe sizes oftwo inches and less, while ultrasonic flowmeters typicallywork best in pipe sizes of six inches and up. This is especial-ly true for natural gas applications. So pipe size can some-times dictate whether to use a Coriolis or ultrasonic flowme-ter. And if an application involves hydrocarbons, gas, orsteam, magnetic flowmeters should not be selected.

Reliability and accuracy are the two highest rated perform-ance criteria by flowmeter users. Coriolis meters have thehighest accuracy, followed by ultrasonic and magnetic meters.While Coriolis flowmeters typically have a higher purchaseprice, many users are now distinguishing between initial costand cost of ownership. A flowmeter that offers reduced main-tenance costs may be a better value than one with a lower pur-chase price that requires significant maintenance.

In many cases, users may choose to replace like with likewhen selecting a flowmeter to buy. They may do this for sev-eral reasons. Some users build up a stockpile of parts. It canbe expensive to train staff on the use of a new flowmeter. Andselecting a different flowmeter type may mean changing sup-pliers. Differential pressure flowmeters have a large installedbase, and will continue to maintain significant market shareover the next few years.

Multivariable flowmeters are an important growing trendin the flowmeter market. Multivariable flowmeters areflowmeters that measure more than one process variable. Forexample, multivariable flowmeters may measure tempera-ture and/or pressure in addition to flow. Both multivariablemagnetic and vortex flowmeters have been developed, andmore types are likely in the future.

Multivariable transmitters are one way for suppliers of DPflowmeters to hold onto market share in the face of the grow-ing trend towards new-technology flowmeters. Users canreplace a DP transmitter with a multivariable transmitter,while leaving the primary element in place. Multivariable DPtransmitters also measure more than one process variable, butmay not measure flow. For example, some multivariable trans-mitters measure pressure (DP and/or P) and temperature, andoutput the results to a flow computer for the flow calculation.Other DP transmitters contain the computer power onboard tomake a volumetric and/or mass flow calculation.

Multivariable flowmeters are considered to be new-tech-nology flowmeters. However, magnetic and vortex metersare already new-technology flowmeters, so this mainlyapplies to multivariable DP flowmeters. A multivariable DPflowmeter is a multivariable DP transmitter that has theonboard capability of computing flowrate and is attached toa primary element. A DP transmitter that is not attached to aprimary element is simply a transmitter and is not yet aflowmeter. Some companies are offering a multivariabletransmitter connected to a primary element such as an orificeplate or an Annubar. This is an important new trend in theflowmeter market.


Coriolis flowmeters have a relative-ly high initial cost, although bothMicro Motion and Endress & Hauserhave introduced Coriolis meters withprices in the $3,000 range. While theselower-cost meters do not have thesame accuracy level as the higher-priced meters, they represent animportant breakthrough in terms ofprice. The higher cost of Coriolisflowmeters is offset by normally lowmaintenance costs. These meters canbe used to measure the flow of somefluids with varying densities that can-not be measured by other flowmeters.

Paradigm Case Application:Coriolis Flowmeters

The paradigm case application forCoriolis flowmeters is with clean liq-uids and gases flowing fast enough tooperate the meter and flowing throughpipes of two inches or less in diameter.

While three, four, and even six-inchmeters are available, conditions are notideal for meters of these sizes due tothe required size of the meter. Some

low-pressure gases do not have suffi-cient density to operate the meter.

Coriolis meters have the advantagethat they can be used to measure dif-

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Type of Paradigm Case Conditions CommentFlowmeterCoriolis Clean liquids and gases flowing Measure mass

sufficiently fast through pipes flow directly; sometwo inches or less in diameter. provide density

measurement Magnetic Conductive liquids flowing through Do not work with

full pipes that do not contain gas or steammaterials that could damage theliner or coat the electrodes.

Ultrasonic: Clean, swirl-free liquids and gases High accuracy mayTransit Time of known profile require the use of

a multipath meterVortex Clean, low viscosity, swirl-free, Work for liquids,

medium to high-speed fluids. gas, and steam

Table 1. The principles of operation for new-technology and DP flowmeters.

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ferent types of fluids, including fluidsthat have different density values.They can be used to measure the flowof dirty liquids and slurries. However,it is advisable to measure these fluidsat relatively low flowrates to reducethe possibility of meter wear.

Magnetic Flowmeters Magnetic flowmeters use Faraday’s

Law of Electromagnetic Induction.This principle states that a voltage isgenerated in a conductive mediumwhen it passes through a magneticfield. This voltage is directly propor-tional to the velocity of the conductivemedium, the density of the magneticfield, and the length of the conductor.These three values are multipliedtogether in Faraday’s Law, along witha constant, to yield the magnitude ofthe voltage.

Magnetic flowmeters use coils thatare generally mounted outside of a

pipe, although some models have thecoils mounted inside the pipe wall. Ascurrent passes through these coils, amagnetic filed is generated inside thepipe. As conductive fluid passesthrough the pipe, a voltage is generat-ed and detected by electrodes that aremounted on either side of the pipe.The flowmeter uses this voltage valueto calculate flowrate.

Magnetic flowmeters can be sued tomeasure the flow of conductive liq-uids and slurries, including blackliquor and paper pulp slurries. Theirmain limitation is that they cannot beused to measure hydrocarbons, whichare nonconductive. As a result, theyare not widely used in the petroleumindustry. Magmeters, as they are oftencalled, create little to no pressuredrop, and are highly accurate. Whiletheir initial purchase price is relativelyhigh, most magmeters are pricedlower than equivalent Coriolis meters.


Flowmeter Type Technology Coriolis Fluid is passed through a vibrating tube; this

causes the tube to twist. Mass flow is proportionalto the amount of twisting by the tube

Magnetic Creates a magnetic field within a pipe, typically using electrical coils. As electrically conductive fluid moves through the pipe, it generates a voltage. Flowrate is proportional to amount of voltage, which is detected by electrodes

Ultrasonic: Single Measures the time it takes for an ultrasonic pulsePath Transit Time or wave to travel from one side of a pipe to the

other. This time is proportional to flowrate.Ultrasonic: Multipath Uses multiple ultrasonic paths to calculate Transit Time flowrate; typical paths are two to six.Ultrasonic: Doppler Calculates flowrate based on the shift in

frequency observed when ultrasonic waves bounce off particles in the flowstream

Vortex A bluff body is placed in a flowstream; as flow passes this bluff body, vortices are generated.The flowmeter counts the number of vortices, and flowrate is proportional to the frequency of vortices generated.

Table 2. A summary of paradigm caseapplications for different types of new-technology flowmeters.

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Paradigm Case Application:Magnetic Flowmeters

The paradigm case application formagnetic flowmeters is for conductiveliquid flowing through a full pipe thatdoes not contain materials that dam-age the liner or coat the electrodes.The most important limitation onmagnetic flowmeters is that they donot work with nonconductive fluids.Since gases and steams are noncon-ductive, magmeters cannot be used tomeasure them. The pipe has to be fullof liquid, since magmeters computeflowrate based on velocity times area.Liner damage and electrode coatingcan affect the accuracy of magneticflowmeters.

Ultrasonic Flowmeters Tokyo Keiki (now Tokimec) first

introduced ultrasonic flowmeters forindustrial use in Japan in 1963. Transittime and Doppler are the two maintypes of ultrasonic flowmeter. Transittime meters have both a sendingtransducer and a receiving transduc-er. The sending transducer sends anultrasonic signal from one side of apipe to the other. A signal is then sent

in the reverse direction. When anultrasonic signal travels with the flow,it travels faster than when it travelsagainst the flow. The flowmeter meas-ures both transit times. The differencebetween the two transit times (acrossthe pipe and back again) is propor-tional to flowrate. Transit timeflowmeters are mainly used for cleanliquids.

Like transit time flowmeters,Doppler meters send an ultrasonicsignal across a pipe. However, the sig-nal is reflected off moving particles inthe flowstream, instead of being sentto a receiver on the other side. Themoving particles are traveling at thesame speed as the flow. As the signalpasses through the stream, its fre-quency shifts in proportion to theaverage velocity of the fluid. A receiv-er detects the reflected signal andmeasures its frequency. The meter cal-culates flow by comparing the gener-ated and detected frequencies.


Flowmeter Type Technology DP-Orifice Plate A flat metal plate with an opening in it; a DP

transmitter measures pressure drop and calculates flow rate

DP-Venturi Tube A flow tube with a tapered inlet and a divergingexit; a DP transmitter measures pressure dropand calculates flowrate

DP-Pitot Tube An L-shaped tube inserted into a flowstream thatmeasures impact and static pressure; the opening of the L-shaped tube faces directly intothe flowstream. The difference between impactand static pressure is proportional to flowrate.

DP-Averaging A Pitot Tube having multiple ports to measure Pitot Tube impact and static pressure at different points.

Flowrate is calculated by DP transmitter based onaverage of difference in pressure readings at different points.

DP Flow Nozzle A flow tube with a smooth entry and sharp exit;flowrate is calculated based on differencebetween upstream and downstream pressure


Doppler ultrasonic flowmeters requirethe presence of impurities in the flow-stream so the signal can bounce offthem. Hence, they are used with dirtyliquids and slurries.

Ultrasonic flowmeters are used tomeasure the flow of both liquids andgases. In June 1998, the American GasAssociation (AGA) published AGA-9,a report that laid out criteria for theuse of ultrasonic flowmeters for cus-tody transfer of natural gas. The pub-lication of this report gave a majorboost to the ultrasonic flowmeter mar-ket in the oil production and trans-portation industry. Only multipathmeters are approved for custodytransfer use.

Multipath ultrasonic flowmetersuse more than one pair of sending andreceiving transducers to determineflowrate. Most multipath flowmetersuse four to six different paths or ultra-sonic signals to determine flowrate,although dual-path meters can also beconsidered multipath. The transduc-ers alternate sending and receiving asignal over the same path length.Flowrate is determined by averagingthe values given by the differentpaths, yielding greater accuracy thansingle-path meters.

Paradigm Case Application:Ultrasonic Flowmeters

The paradigm case application fortransit time ultrasonic flowmeters isclean, swirl-free liquids and gases of aknown profile. If high accuracy isrequired, it may be necessary to use amultipath flowmeter. Having cleanfluid is the most important constrainton ultrasonic flowmeters, althoughtransit time meters today can handlesome impurities. A single-path ultra-sonic meter bases its flowrate calcula-tion on a single path through the pipe,making it susceptible to aberrations inflow profile. Multipath meters usemultiple paths to make the flowratecalculation, and hence are more accu-rate. Ultrasonic flowmeters can han-dle both liquids and gases, and theycan be affected by swirl.


Company DescriptionMax Machinery Inc. focuses its entire line of

positive displacement flowmeters on difficultflow measurement applications. Where else

can you find a meter with a 2,000 to 1 operating range, an ability tomeasure down to 1 cc/min that will accurately measure intermittentflows, and can withstand temperatures to 550 F and pressures to7,500 psi? On top of these impressive capabilities, throw in the abilityto measure liquids with high or changing viscosities and you can onlybe talking about a Max meter. Max welcomes the chance to tackle youmost difficult applications.

Corporate Capabilities

ProductSummary

Max Machinery’sflowmeters offerstandard operatingpressures of 1,000psi and are com-plimented by

3,000 psi and 7,500 psi-ratedmeters for hydraulic testing,

dispensing of viscous fluids,and other high-pressure applications (shown here).Max’s family of piston, gearand helix meters covers theentire range of flows, viscosities, and pressures;from 1 cc/min to 1,400 gpm,from 0.2 cps to 1,000,000 cps,and from 1/2 psi to 7,500 psi.

Type of Applications They Excel In DisadvantagesFlowmeter Differential Clean liquids, steams, and gases Pressure drop;Pressure with low to medium accuracy Orifice plates

subject to wear Positive Low flows and viscous flows Moving parts Displacement subject to wear Turbine Steady, high speed flows Bearings subject

to wear; Limited ability to handle impurities

Open Channel Rivers, streams, partially filled Medium accuracylarge pipes

Thermal Very low flows Low to medium accuracy

Variable Area Visual flow indication Low accuracy; Many without transmitters

This table is excerpted from The World Market for Flowmeters report published by Flow Research, Inc. in February 2003.

Table 3. Applications in which traditional-technology flowmeters excel.


Ultrasonic flowmeters are availablein both clamp-on and inline models.The paradigm case application forultrasonic flowmeters requires takingboth pipe characteristics and fluidcharacteristics into account.

Vortex Flowmeters Vortex flowmeters make use of a

principle called the von Karman effect.According to this principle, the pres-ence of an obstruction in the flow-stream causes the fluid to generatealternating vortices. In a vortex meter,this obstruction is called a bluff body. Itconsists of a piece of material with abroad, flat front that is mounted atright angles to the surface of the flow-stream. Flow velocity is proportionalto the frequency of the vortices.Flowrate is determined by multiplyingflow velocity times the area of the pipe.

In some cases, straightening vanesor a specified length of straight pipeupstream are required to eliminateswirl and distorted flow patterns.Under low-flow conditions, vorticesare formed irregularly, so low-flowconditions present a problem for vor-tex meters. Vortex meter accuracy isfrom medium to high, depending onmanufacturer and model. Vortexmeters are among the most versatileof meters and can be used to measureliquid, gas, and steam flows.

Paradigm Case Application:Vortex Flowmeters

Paradigm case applications for vor-tex flowmeters are clean, low-viscosi-ty, swirl-free fluids flowing at medi-um-to-high speed. Ideal conditionsinclude medium-to-high flow,because the formation of vortices isirregular at low flowrates. The stream

should be swirl-free, since swirls caninterfere with the accuracy of thereading. Any erosion, corrosion, ordeposits that change the shape of thefluff body can shift flowmeter calibra-tion, so ideal conditions include cleanliquids. Vortex meters also work bestwith low-viscosity fluids, since vortexformation in high-viscosity fluidsmay be undependable.

Dr. Jesse Yoder ispresident of FlowResearch and a regu-lar contributor to FlowControl magazine. Dr.Yoder has been aleading analyst in theprocess control industry since 1986.He has written over 40 market studiesand is currently completing a 12-vol-ume series of studies on the worldwideflowmeter market. Included in thisseries is The World Market forFlowmeters, which covers all flow-related technologies on the markettoday. Flow Research (www.flowre-search.com) offers a quarterly updateservice called the WorldflowMonitoring Service. You can contactDr. Yoder by phone at 781 245-3200 orby e-mail at [email protected].


The most effective selection

approach incorporates a step-by-step

method that begins by matching the

applications with the paradigm case

for various flowmeters.

FC

The flowmeter images featured in thisarticle were provide by Endress + Hauser,Fuji Electric, McCrometer, and SparlingInstruments.

jesse yoder - worldflowresearch.com

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