Checking for Mass or WeightMaking the right choice

GARVENSCheckweighing

SAFELINEMetal Detection & X-ray Inspection

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Choosing Between Weight and Mass Inspection:making an informed decision

METTLER TOLEDO offers a broad range of products toensure compliance with regulatory standards and reali-sation of internal production goals. The ProductInspection Division consisting of GARVENSCheckweighers, SAFELINE Metal Detection, and SAFE-LINE X-ray Inspection systems ensures you receive thecorrect product and technology for your application.

Gravimetric weighing technology is recognised as theonly method for checkweighing accurately and reliablywith results that can be verified and traced to a certifiedweight standard. Gravimetric checkweighers, like theGARVENS X-series™ are the gold standard ensuringpackaging compliance and operational productivity.Thousands of these systems are embedded in produc-tion lines around the world ranging from pharmaceuti-cal, to food processing, and even in industrial processessuch as metal parts manufacturing.The sole function of a gravimetric checkweigher is to bethe best at weighing; the primary functionality of the X-ray inspection system is con-taminant detection and checking for package integrity. While there has been somerecent discussion by some X-ray companies regarding the utilisation of that technol-ogy for checkweighing the fact is X-ray can estimate mass but it ccaannnnoott “weigh”!

The SAFELINE InspireX™ delivers contaminant detection in a user friendly, robustdesign. The X-ray inspection system can calculate a mass value, this tertiary capa-bility may create the following questions:

• When should I choose Mass over Weight? • Is there a place for using mass determination in the production line? • Will X-ray obsolete the traditional gravimetric checkweighers currently in use?

WWeeiigghhtt:: ('wAt) The force with whicha body is attractedtoward the earth or acelestial body bygravitation and whichis equal to the prod-uct of the mass andthe local gravitationalacceleration. (Courtesy of Merriam-Webster Online)

Mass: ('mas) The property of a bodythat is a measure of itsinertia and that is com-monly taken as a meas-ure of the amount ofmaterial it containsand causes it to haveweight in a gravitation-al field(Courtesy of Merriam-Webster Online)

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W = m x ge

SAFELINE InspireX X-ray System

GARVENS XS2 Checkweigher

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Legal or not? Checkweigher installations may require certification bylocal Weights and Measures Officials as a legal fortrade device. In most jurisdictions only gravimetriccheckweighers can comply with this requirement. Acore element to this certification is the calibration andperformance verification of the checkweigher using atraceable certified standard, also known as a testweight. Since X-ray measures item density and con-verts that value into a calculated pseudo weight, thereis no ability to trace the derived value to the certifiedtest weight standard. Your local METTLER TOLEDORepresentative can assist you in understanding thelocal Weights and Measures requirements andwhether the application requires an approved device.

Process validation? While some checkweigher installations may be legalfor trade, others are not. In either case internal qualityor maintenance procedures, regulatory or customerdriven mandates, may require the process to be vali-dated against a certified standard or test weight. Onlya gravimetric checkweigher such as a GARVENS X3can comply with this requirement.

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Know your product. Obviously the higher the value and product cost themore you will be concerned about absolute accuracyrequiring the performance of a gravimetric check-weigher.

For applications where estimated weight is a viablesolution path, it does not automatically shift the appli-cation to X-ray mass measurement. Not all productsare suitable for using an X-ray for mass determina-tion; X-ray calculates the mass by comparing eachpackage “gray scale” image to that of a known“Good” package. Deviations from that “Good” pack-age are then calculated as a change in mass. If thecalculated mass is within programmed “Accept” toler-ance zone the package remains in the productionstream, packages with images that deviate outside the“Accept” tolerance zone range are rejected.

In applications where the chemical composition of theproduct may vary from batch-to-batch or package-to-package the change in chemical composition, even ifit is minor, may cause a change in gray scale eventhough there is no change in actual weight. The X-raysystem will interpret this change in gray scale as achange in mass which results in an inaccurately cal-culated result may yield unwanted and unprofitablefalse rejects. Products which contain Calcium orChloride are prime examples where slight changes inchemical composition create inaccurate weight calcu-lations, false rejects, or false accepts.

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tion Making the right choice Weighing or Mass determination?

Believe it or not the answer is simple, use “weight” when absolute accuracyand performance is important, while you can use “mass” when a calculatedestimate is good enough.

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Halogen Elements

* Lanthanide Series

+Actinide Series

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One Size Does Not Fit AllGravimetric checkweighers are designed to optimise theweighing process for sustained accuracy and perform-ance. This includes the ensuring the results from the10,000th package are just as accurate as the 1st.Development by METTLER TOLEDO of the electro-mag-netic force restoration (EMFR) weigh cell technologyyields unprecedented gravimetric weighing accuracies athigh production rates. Unlike conventional analog weighcells used in more traditional gravimetric checkweighers,the EMFR weigh cell is not influenced by temperatureand other environmental conditions which have typicallyled to reduced long term performance. The table belowshows accuracies associated with a gravimetric check-weigher utilising EMFR weigh cell technology.

You will note there is degradation in delivered accuracyfor gravimetric checkweighing as line rates increase.“Time to weigh” is an important element in gravimetriccheckweighing, the longer the time the better the result.

Typical Gravimetric Checkweigher Accuracies

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200 ppm300 ppm

± 20 mg± 50 mg± 80 mg

220000 gg 100 ppm200 ppm300 ppm

± 100 mg± 200 mg± 300 mg

550000 gg 100 ppm200 ppm300 ppm

± 250 mg± 500 mg

± 1 g

METTLER TOLEDO EMFR Weigh Cell

METTLER TOLEDO SAFELINE manufactures the highestperformance X-ray inspection systems available.Continuing investment and development has yieldedimpressive advances in accuracy and reliability.Calculation of mass through the measurement of densityusing X-ray can achieve accuracies of 0.2% of themass at 1 sigma, while this is still does not deliver thesame accuracies of a gravimetric checkweigher it canbe suitable for some applications.

As noted earlier the abili-ty of an X-ray system toderive a calculated massvalue is largely depend-ent on the consistency ofthe product’s chemicalcomposition. Carefulconsideration of theproduct and process istherefore required prior tomaking any accuracy assumptions.

While other companies manufacture one or the other,METTLER TOLEDO manufactures both gravimetric check-weighers and X-ray inspection systems, it is our goal asa full line solution provider to deliver the right technolo-gy and solution set based on your specific applicationrequirements and business goals. Your METTLER TOLEDO Representative can help you assess the suit-ability of the product and the application to determinewhich technology is right for you.

Don’t CompromiseAll too often priorities are compromised for the sake of saving money or minimising floorspace. The resulting cost of the compromise may include additional product give-awayand the loss of greater profit recovery. While checkweighing is used to comply with fairpackaging laws, more frequently they are being employed as a process monitoring tool toenhance overall efficiency and productivity. In this second role the checkweigher may betied to the filler, a cutter, or other device providing valuable feedback to adjust delivery ratesto reduce product and profit give-away! Gravimetric checkweighers enhance “bottom line”performance. For user’s who are looking for greater precision than what the legal standardsrequire there can be no compromising when it comes to delivered performance.3

SAFELINE X-ray Side Conveyor

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Is there a place for mass determination in the production line? Absolutely, there are a number of applications where using X-ray can yield results that were previously difficult toobtain with a gravimetric checkweigher. It is important to note that in all cases the application must have accu-racy requirements which are consistent with the inspection technology employed and with items which are ofconsistent density and chemical composition. Some common examples of using X-ray for mass comparisoninclude:

Multi-compartment packages Checking for portion control in multi-compartmentpackages is an ideal application for X-ray. In the pastusers of in-line gravimetric checkweighers were forcedto check for the “gross” weight of the containerassuming that if the gross weight was correct then theindividual contents were also correct. For users thatdesired greater control meant the deployment of multi-ple checkweighers, one at each critical stop in theprocess to verify that the individual contents were cor-rectly supplied.

X-ray has the unique ability to view the package andits contents both holistically and by sub-compart-ments, checking for the correct mass of each, as wellas quality measurements such as uniformity of shape,broken or chipped contents, and accuracy of the loca-tion placement. In the world of convenience foodssuch as the tradi-tional ready meal,it’s not onlyimportant thateach item is deliv-ered to the correctportion, but that itsshape and loca-tion accuratelyresembles theimage on the package.

Broken itemsGravimetric checkweighers can only determine if theweight is correct, it can not determine if the contentsare pristine or have been damaged. A good exampleis a box of crackers, while passing over a gravimetriccheckweigher the package maybe accepted because ithad the appropriate content weight; however the samepackage when passed through the X-ray could berejected due to the image showing a broken cracker

which is an unacceptable quality condition. Beverages Conventional gravimetric checkweighers can do agood job at checkweighing containers, however tosome companies it’s just as important to ensure thatthe fill line of the container always be at the sameposition. For example bottles on a store shelf thathave the same weight may result in fill heights whichare different generally caused by inconsistencies of thecontainer. Consumers looking at the product on theshelf will have a natural reaction to buy the bottle withthe highest fill line. Further they may loose confidencein that brand and choose another which “appears” tohave a tighter control on quality. X-ray while check-ing for mass can also check for fill height rejectingproduct based onone or both crite-ria.

High package variabilityIn some applications the weight variability of thepackaging materials is greater than the “Accept /Reject” tolerances of the package contents. A goodexample is a blister pack of 12 tablets. Each tabletonly weighs 100mg however the variability of thepackaging materials is greater than 100mg. A tradi-tional gravimetriccheckweigher could notguarantee that all pack-ages would contain 12tablets, however usingX-ray the position ofeach tablet could beverified, plus a checkfor broken, deformed,or partial tablets could also be incorporated.

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Will X-ray replace the traditionalgravimetric checkweighers?

No, as presented earlier each technology has its own uniquevalue proposition which make them more complementarythan competitive. Absolute tightening of accuracies to opti-mise line performance, meet regulatory standards, and elim-inate costly product giveaway will draw users to the applica-tion of high performance gravimetric checkweighers like theGARVENS XS series. Similarly users will, to ensure productsafety, maintain delivered quality, and portion control willdeploy X-ray inspection systems like the SAFELINEInspireX™.

METTLER TOLEDO is committed to helping our customers toprotect their brand by continuing to invest heavily in bothgravimetric Checkweighing and X-ray Inspection technolo-gies to ensure that we can deliver the right solution for yourprocess in the most reliable and cost effective manner possi-ble. Combined with our expertise in Metal Detection the METTLER TOLEDO Product Inspection Division consisting ofour GARVENS and SAFELINE brands are ready to meet thereal world challenges faced by our customers both now andinto the future. Your local METTLER TOLEDO Sales andService Representatives are available to work with yourorganisation to deliver the right products and services toachieve your product inspection goals.

GARVENS XS1 Checkweigher

SAFELINE Profile Metal Detector

SAFELINE AdvanChek X-ray System

Mettler-Toledo Ltd.Product Inspection Division64 Boston RoadBeaumont LeysLeicester LE4 1AWTel: 0116 235 7070Fax: 0116 234 6719Email:pi.mtuk@mt.com

Subject to technical changes or modifications.© 03/2007 Mettler-Toledo Ltd.

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