International Journal of Chemical and Pharmaceutical Engineering

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Accuracy in fourdimensions

Coriolis Mass Flowmeter

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2007

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Temperature variations must be measuredand compensated in order to ensure accu-rate density measurement. For the fluidtemperature this is quite usual. What isnew with ABB's CoriolisMaster is that themeter's housing temperature is also measu-red and considered accordingly. Thisallows for compensation of even consider-able temperature variations, e.g. resultingfrom exposure to direct sunlight during theday and considerable cold at night. Withthis an accuracy of 0.001 kg/l is achieved.An example is the density measurement of

ethanol water mixtures in distilleries orchemical plants. The measuring instru-ments are installed outdoors and are,hence, exposed to direct sunlight causingan ambient temperature of up to +50 °C,whereas, at night, the temperature may falldown to -20 or even -40 °C, depending onthe climatic zone. CoriolisMaster with itshigh-precision density measurement op-tion continuously measures the housingtemperature at different points and com-pensates these influences using special con-verter algorithms.

Practical, even with airand gas content

Besides the already described advantagesregarding the meter accuracy, another im-portant point which is essential for theuser is the question how the meter willcope with suboptimal conditions like airbubbles or gas content. The basic Coriolisoperating principle implies that the metertube vibrations are transmitted to the measured fluid. This is considerably moredifficult if the fluid contains air or gas.These gas portions do not necessarily follow the tube vibrations. In fact, theymay attenuate the vibrations and can,hence, cause considerable measuringerrors or even impede proper meter opera-tion. Two measures can be taken to avoidthis effect. On the one hand, you can use aningenious converter technology, and on the other hand you can optimise the tubedesign. CoriolisMaster benefits from bothsolutions. Its advanced DSP technologyprovides for a high-speed control loop that controls the vibration energising cur-rent and, thus, the energy input. Thisavoids potential attenuation right from thebeginning. Secondly, an elaborate filterprovides for optimal signal processing and online plausibility checking. The most important factor in addition tothese electronic measures, however, is thedesign of the meter tubes. The special S design provides for optimal transmissionof the vibrations to the fluid and for astrong differential signal. Moreover, thetube design ensures that local effects resulting from gas bubbles only have littleimpact on the tube vibration and, thus,only slightly affect the measuring accuracy.Test measurements have shown that evenfor a viscous fluid with an air content of 50 % (like gummi bear jelly) and largely

Accuracy in four dimensions Exact mass flow, density, concentration and temperature measurement using a single device Frank Frenzel

CoriolisMaster flowmeters feature an outstanding accuracy, not only for the measured variable (mass flow or volume flow) but also regarding density and temperature measurement. The essential factor for achieving this accuracy is the appropriate meter tube geometry. The special double S design provides the best possible vibration properties and, thus, allows for especially thick tube walls, which are hardly affected even by external vibrations or a homogene-ously distributed air or gas content.

INSTRUMENTATION, CONTROL AND AUTOMATION

The intuitive 3-key operation panel and a clear text dis-play without incomprehensible codes does away withthe need to read the instruction manual in many cases

The special S design pro-vides for optimal trans-mission of the vibrationsto the fluid and for astrong differential signal.As a result, the Coriolis-Master can even handleapplications with high airor gas content.

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homogeneously distributed gas bubbles a very high filling accuracy of approxi-mately half a percent could be achieved.With a reduced air content the result iseven better. In contrast, the reproducibilityamounts to around 0.1 %. As a result, thesensitivity to disturbances is negligible.

Goodbye use restrictions

Things have changed: contrary to the for-mer trend to design a specific tube geo-metry for each measuring task, state-of-the-art solutions are often just the oppositeway around. The disadvantages were justtoo obvious. In the past, meters with a highreproducibility but limited accuracy wererequired for process monitoring, whereasaccounting or filling measurements calledfor devices with optimal accuracy. Bothtasks were accomplished using devices ofdifferent designs and installation lengths

which could not be exchanged with eachother. As a result, the companies either hadto use, keep on stock and provide trainingfor twice the number of meters they ac-tually needed, or they had to decide for themore accurate but also more expensivedesign, even though they did not needthese sophisticated device features inmany cases. ABB's universal approach isdifferent. A device with the potential forhigh-accuracy applications is available indifferent accuracy classes, ranging from 0.4to 0.1 %. The only difference between theindividual classes results from differentcalibration requirements. Devices withminor accuracy can be calibrated usingreference mass flowmeters, whereas

meters with an accuracy of 0.1 % requireexpensive high-precision scales and consi-derable calibration efforts. These additio-nal costs can be saved if less accuratemeters are sufficient, and the customer willbenefit from this price advantage. The

flowmeter converter is another example ofthe high flexibility offered. In the past, anyconverter replacement, e.g. when chan-ging over from Hart to Profibus, eithernecessitated a recalibration or the custo-mer parameters had to be set again. Today,a plugon Fram chip provides for data storage, reducing the time requirementsfor replacing the electronics to only a fewseconds. The special strength of Coriolis massflowmeters is their variety of measuringvalues. Besides the mass and volume flow, they can measure the density with0.001 kg/l and with a reproducibility of0.0001 kg/l. In a practical example thismeans you can exactly measure a knife

point of sugar (1g) inapproximately one liter ofcoffee. Even a tenth of thisquantity would be detectedby the meter. A typicalapplication which benefitsfrom the advantages of thismulti-variable flowmeter isthe phosphoric acid fillingprocess for Coca Cola. Acidwater mixtures of differentconcentration are deliveredfor different truck loads. Inthe past, phosphoric acid ina 98 % concentration wasfilled in the truck tank and

then the corresponding water quantity wasadded. Nowadays, the water is added in online mode, i.e. a Coriolis Master controls the exact concentration to 1g/l(reproducibility 0.1g/l) through densitymeasurement.The truck is no longer filled up to its totalcapacity (approximately 30 t) minus 10 kg,but to its full capacity, without the risk tooverload the truck in breach of the roadtraffic regulations or the need to spendmuch effort on reloading the truck.In other applications, e.g. the density measurement of a methanol water mixture,the devices are used as pure density metersto replace other methods like radiometricor optical density measurement. As thedisposal of radioactive water or thecleaning of lenses is no longer required, themeasurement is possible at reduced costsand with less bureaucracy and maintenan-ce requirements.

Conclusion

ABB's Coriolis flowmeter technologyoffers a combination of high accuracy,practice orientation and application flexi-bility. Due to its numerous measuringvalues, a single meter replaces severalmeasuring points with density meters andtemperature sensors and can fully benefitfrom its versatility in both demanding andstandard applications. What is moreimportant: due to their state-of-the-arttechnology ABB´s Coriolis flowmeters areso easy to install and operate – just like awalk in the park.

Test measurements show that the CoriolisMaster reliably measures even pastyhigh-viscosity fluids with high gas content.

Different accuracy classes allow for using a

universal meter with identicalinstallation length for all

applications.

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ABB is a leader in power and automation technologies that enable utility and industry customers to improve performance while lowering environmental impact. The ABB Group of companies operates in around 100 countries and employs about 111,000 people.

www.abb.com/instrumentation

The Company‘s policy is one of continuousproduct improvement and the right is reserved to modify

the information contained herein without notice.

Printed in Germany (10.2007)

© ABB 2007

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