CORESTA Guide N 10 March 2011

Transcription

1 CORESTA Guide N 10 March 2011 A User Guideline fr the Measurement f Diameter f Cigarettes and Filter Rds Sub-Grup Physical Test Methds

2 1 Review and Histry Issue Date Reasn 1.0 July 2009 Original issue. 1.1 August 2009 Added measuring principles diagrams 1.2 Octber 2009 With cmments frm PTM Sub-Grup 1.3 March 2010 With cmments frm PTM Sub-Grup 1.4 March 2011 With cmments frm the CORESTA SC 1.5 March 2011 With cmments frm the CORESTA Bard 2

3 2 Cntents 1 Review and Histry Cntents Intrductin Purpse Outline The Diameter measurement prcess Intrductin Definitins Prperties Mst widely used systems Laser CCD Vide camera Factrs affecting the measured Diameter Surces f errr that are cmmn t laser, CCD and camera systems Surces f errr that are specific t laser systems Surces f errr that are specific t CCD systems Surces f errr that are specific t camera systems Cnfirming crrect instrument functin Intrductin Methds f checking and assuring instrument functin Care and maintenance f Diameter calibratin standards Intrductin Essential prperties f calibratin standards Recmmendatins fr the management f standards Prcedure fr calibratin f instruments Checking the validity f measurements The calibratin prcess The purpse f calibratin checking Precautins when checking calibratin A recmmended prcess fr checking calibratin Calibratin Checking instrument perfrmance Measuring repeatability Measuring instrument-t-instrument variability Making Diameter measurements Glssary and abbreviatins References

4 3 Intrductin 3.1 Purpse The Diameter f cigarettes and filter rds has a direct effect n the pressure drp and the ventilatin and therefre n the smking perfrmance f the assembled cigarette. Furthermre differences in the Diameter f tbacc rd and f filter rd might cause assembling prblems. The Diameter f the final prduct will als influence the packing. The Diameter is a principal measure fr the quality cntrl f cigarette manufacture. This guideline is intended as a reference fr manufacturers f cigarettes and filter rds as t the best practice fr the measurement f Diameter, s as t cnsistently btain the mst accurate and mst reliable measurements despite the many external influences that can affect the measured value. 3.2 Outline Wrk dne within the ISO/TC126/WG2, frm 2005 t 2008, quantified the envirnmental influences n the measured Diameter and additinal wrk carried ut since has highlighted a number f ther ptential causes fr variatin in the measured Diameter f a filter rd r cigarette sample. In rder t maintain the validity f Diameter measurements, attentin needs t be given t all f the factrs that impact their accuracy. This can nly be dne by understanding the nature and magnitude f the influences and hw they might be minimised and cntrlled. 4 The Diameter measurement prcess 4.1 Intrductin Diameter measurement brings tgether several factrs, including samples, instruments, calibratin standards and varius prcedures and techniques. Each f these factrs must be ptimised if it is nt t disturb r crrupt the measurement prcess. Hence, it is imprtant t understand the effect that external influences might have n each f these factrs and the influence f each factr n the verall prcess. Where ptimisatin is nt practicable r pssible, allwance needs t be made fr ptential errrs incurred. 4

5 4.2 Definitins D(α) α - A cigarette r a filter rd crss-sectin is a cnvex surface. The Diameter D f a cigarette r f a filter rd is defined as the mean f the apparent Diameters measured n a full rtatin f the rd. D The Perimeter P is the Diameter multiplied by π. 2 0 P D D( ) d 4.3 Prperties - It can be demnstrated that the perimeter f a cnvex curve is equal t the mean f the apparent Diameters multiplied by π. In ther wrds the mean f the apparent Diameters f a cigarette r filter rd is equal t its perimeter divided by π and is independent f its shape as lng it remains cnvex. - This methd requires that the sample is rtated thrugh an integer multiple f 180º t avid the shape f the sample biasing the result. - The abve Diameter definitin is based n an infinite number f Diameter scans. Any practical instrument makes a finite number f Diameter scans, which affects the accuracy f the measurement. A theretical study undertaken by the Wrking Grup (WG2) shwed that 36 individual scans perfrmed n a full rtatin at cnstant angular interval f an elliptical shape whse relative vality is less than 40%, prvided 1 µm accuracy n the Diameter and 1 pint accuracy n the relative vality determinatin. An experimental study using a laser device shwed that 64 individual scans perfrmed n a full rtatin at a cnstant angular speed f a test piece whse vality is less than 30%, prvided a difference lwer than 1 µm n the mean Diameter and 0.2 pint n the relative vality determinatin cmpared with a determinatin based n 1024 individual scans. On the basis f these studies it is recmmended t carry ut a minimum f 64 scans n a full rtatin, r 32 scans n a half rtatin, at cnstant angular interval f the test piece. - The abve Diameter definitin is based n a cnstant angular rtatin speed and nt a cnstant peripherical rtatin speed. It has been demnstrated that in the case f a cnstant peripherical rtatin speed an errr n the Diameter f val test pieces is made. Fr example n an val rd having 30 % f vality and 8 mm f Diameter this errr n the measured Diameter will be 0.1 mm. 5

6 4.4 Mst widely used systems Laser The laser beam emitted by a semicnductr laser is cast n and reflected frm an ctagnal mirrr and a reflectin mirrr. The diffused laser beam is then parallelized by a cllimatr lens and thrwn upn the bject t be measured. The beam mves in the scan path at a cnstant speed and parallel t itself. After scanning the bject the laser beam is cnverged by a receiver lens t a receiver element. An edge detectin device generates a pulse when the beam reaches the bject and anther ne when it leaves the bject. The elapsed time between the 2 pulses is prprtinal t the size f the bject. 6 Rd 3 5 = Time measurement Figure 1 Diagram f a laser gauging system Key 1 Laser emitter 2 Octagnal mirrr 3 Reflectin mirrr 4 Cllimatr lens 5 Receiver lens 6 Receiver element CCD (Charge-Cupled Device) The light beam emitted by a LED is parallelized by a cllimatr lens and thrwn upn the bject t be measured. After scanning the bject the beam is cnverged by a cnverging lens and parallelized n a CCD array. The size f the shadw prjected n the CCD array is prprtinal t the size f the bject = Distance measurement 6 Figure 2 Diagram f a CCD gauging system 6

7 Key 1 CCD array 2 Cnverging lens 3 Test piece 4 Cllimatr lens 5 LED 6 Parallelized light beam 7 Receiving lens Vide camera The bject is rtated in the field f view f a digital vide camera. An apprpriate device is used t maintain the rd perpendicular t the scan path and t rtate the rd alng its lngitudinal axis. The bject is imaged n t the digital imaging sensr within the camera. The digital images are scanned and captured by a digital image prcessing system with image prcessing sftware. The size f the bject in the image is determined by reference t similar images captured frm a series f calibratin standards. Figure 3 Diagram f a vide camera and digital image prcessing system Key 1 Sample illuminatin 2 Vide camera 3 Sample and rtatin device 4 Digital imaging device 5 Digital image prcessing hardware 6 Digital image prcessing sftware 4.5 Factrs affecting the measured Diameter The measured Diameter is affected by the fllwing factrs: ambient cnditins at the time f measurement sample temperature and misture cntent at the time f measurement temperature f standards and ambient cnditins at the time f calibratin temperature f standards and ambient cnditins at the time f calibratin checks 7

8 In additin, any errrs within the instrument that affect the measurement and any errrs in the marked value f the calibratin standard (e.g. damage r cntaminatin) will als have an effect n the measured value. Finally, when expressing and interpreting measurement results, it is necessary t have a knwledge f the capability and uncertainty f the measurement prcess. This will ensure that valid inferences are drawn frm the results Surces f errr that are cmmn t laser, CCD and camera systems Sample rd nt perpendicular t beam The errr magnitude is: Where 1 D 1 cs θ D θ is the actual Diameter; is the angle f tilt by cmparisn with the perpendicular t the scan path. D Incrrect measurement psitin alng sample rd length Sample surface rughness Aberratins due t pr ptics Sample rd rtatin is nt a multiple f 180 Angular rtatin speed nt cnstant Angular interval between tw successive scans nt cnstant Acquisitin rate nt cnstant Number f scans per rtatin nt high enugh Dirt in system can cause incrrect edge interpretatin Selectin f test pieces that have raised seams (bad r irregular seam verlap) Incrrect placing f the test piece in the measurement area f the system Use f test piece with ill-defined edge characteristics such as nn-wrapped acetate filter plugs Trembling r scillatin f the sample rd Surces f errr that are specific t laser systems Cllimated beam may nt be exactly parallel Instability f the lateral beam speed Very narrw beam width can result in high sensitivity t measurement psitin alng rd Very narrw beam width can result in errrs due t detectin f small artefacts (fibres) n surface f test piece Surces f errr that are specific t CCD systems Cllimated beam may nt be exactly parallel Very narrw measurement width can result in high sensitivity t measurement psitin alng rd Very wide measurement width can result in lw sensitivity t measurement psitin alng rd Abslute reslutin nt apprpriate fr measurement reslutin 8

9 4.5.4 Surces f errr that are specific t camera systems Variatins in sample range Shadws due t pr lighting Calibratin based n a prduct s Diameter, clur, brightness r cntrast that is different frm the measured prduct Clur variatins f the prduct due t pr lighting Clur changes f the prduct frm ne measurement area t anther Distance variatin between the ptics and the prduct Very narrw measurement width can result in high sensitivity t measurement psitin alng rd Very wide measurement width can result in lw sensitivity t measurement psitin alng rd Sensr reslutin nt apprpriate fr measurement reslutin 5 Cnfirming crrect instrument functin 5.1 Intrductin Checks fr Diameter instrument functin are trying t assure all instrument cmpnents and systems are set up and perating crrectly. They are separate frm any measures f instrument perfrmance and are a necessary pre-cnditin fr all f the fllwing checks and validatins. 5.2 Methds f checking and assuring instrument functin The first step in assuring crrect functin shuld be a prgramme f regular preventative maintenance. Instrument manufacturers prvide infrmatin and guidance n instrument maintenance and ffer prgrammes f planned maintenance. These shuld include attentin n a regular basis (e.g. say daily, weekly and annually). Differences between instruments f different manufacture mean that there will necessarily be sme differences in their planned maintenance prgrammes. Hwever, rutine daily and weekly tasks shuld include: Checks n instrument supplies Check that all air and vacuum levels are set crrectly (if any) Blw dwn air set filter bttles t remve cllected misture (if any) Checks f wear parts and cnsumables Prtective filters shuld be changed in gd time (if any) Checks f the fixture fr rtating the test piece Checks fr build up f cntaminatin within the instrument Remve all tbacc fall ut and clean ut tbacc traps Clean lenses if necessary A test measurement run t cnfirm crrect peratin fllwing any maintenance r adjustment Planned maintenance shuld be supplemented by regular functinal checks t prvide early warning f faults. Many instruments have a self diagnstic mde r a system f built-in diagnstics that may be used fr this purpse. Alternatively, critical bservatin f key instrument functins under nrmal perating cnditins f use can shw up develping faults. Such bservatin can usefully be carried ut as part f a test measurement run fllwing rutine preventative maintenance. 9

10 6 Care and maintenance f Diameter calibratin standards 6.1 Intrductin This is a key area since the ultimate accuracy f any measurements will be directly affected by the accuracy f the Diameter standards used t make the instrument calibratin. 6.2 Essential prperties f calibratin standards Calibratin standards are used t calibrate measuring instruments fr the determinatin f the Diameter (r circumference) f cigarettes and filter rds. The reference calibratin standard shuld be a cylindrical rd made f a rigid, stable material (accrding t the instrument manufacturer s recmmendatins) with a grund surface finish f abut 0.5 µm average rughness and with a knwn and repeatable value f the Diameter. The wrking calibratin standard shuld be calibrated against a traceable reference standard under standard labratry cnditins f 22 C ± 2 C. The thermal expansin cefficient f the material shuld be knwn. The wrking calibratin standard shuld be checked fr shape prperties (vality, cnstancy ) by measuring the Diameters f a minimum f three crss-sectins, situated near the middle and tw ends respectively. The calibratin standards shuld be certificated with their measured value quted t a minimum accuracy f the Diameter f mm abslute and have a unique identificatin. Standards must have the fllwing prperties: They are stable and chemically inert They have repeatable values with a lw uncertainty f the calibrated value All calibratin standards shuld be prvided with a certificate that: Insures the traceability Recrds the value(s) and unique identificatin f the standard Gives infrmatin abut the cnditins f calibratin and the uncertainty f the assigned value Defines the methd and validity f the calibratin, quting any limits r restrictins t the use f the standard 6.3 Recmmendatins fr the management f standards Diameter calibratin standards, being made f metal fr example, are susceptible t damage by careless handling. Dust r il particles may cntaminate the surface. Calibratin standards shuld therefre be stred and handled with care t avid damage and cntaminatin. The validity f Diameter measurements can be imprved if a suitable regime is used fr the management f Diameter calibratin standards. In particular: Stre and handle standards carefully and apprpriately Carry ut a visual check n a regular basis. In particular check fr: Damage (blemishes, chips, cracks) Cntaminatin (rust, dust). 10

11 Maintain a master set f Diameter standards t allw fr simple crss checking f standards. The set shuld cver the range f Diameter values f interest a range f 5 t 9 mm is suggested Intrduce a dcumented prgramme f checking fr calibratin standards against the reference set, including: - Any standard suspected f damage r cntaminatin Any new standard befre it is released fr use All standards at regular, fixed intervals Any standard fund t be damaged, cntaminated r ut f value shuld be withdrawn frm service until it can be replaced r cleaned and recalibrated Recalibrate standards regularly. The interval chsen shuld reflect the type f duty t which the standards are put - heavily used standards will require recalibratin mre frequently than lightly used nes. Set a maximum interval fr recalibratin. Maintain the reference standard set within its validity perid recalibrate it at least every 2 years 6.4 Prcedure fr calibratin f instruments The calibratin and perfrmance testing f instruments fr the determinatin f the Diameter f cigarettes and filter rds shuld be cnducted in accrdance with instrument manufacturer s instructins. The standards shuld be maintained clean. During calibratin, the standards shuld be psitined perpendicular t the scan path t prevent frm calibratin errrs (see sectin 4.5.1). 7 Checking the validity f measurements This prcess cmprises the fllwing stages: - The calibratin prcess Calibratin checking Calibratin Calibratin check fllwing calibratin Checking Instrument perfrmance 7.1 The calibratin prcess The purpse f calibratin checking Calibratin checking is an essential part f the verall calibratin prcess and is made t cnfirm whether the instrument is measuring within the required limits f accuracy. A calibratin check shuld be carried ut at regular intervals and frequently enugh t detect changes in instrument calibratin due t the knwn influences. These influences include: - The effects f measurement system drift The effects f changes in ambient cnditins As a minimum, it is recmmended that a calibratin check is carried ut every manufacturing perid r shift and at least nce per day. 11

12 If a calibratin check shws that an instrument is measuring utside the required limits then it shuld be recalibrated Precautins when checking calibratin A calibratin check f an instrument can be made by measuring a calibratin standard in the instrument. The measured value f the standard will indicate hw clsely the instrument is measuring t the true value. A decisin can then be made as t whether t recalibrate the instrument r nt. When carrying ut calibratin checking it is necessary t take precautin that the measured value is nt crrupted and s avid unnecessary r crrupt recalibratin. In particular: - The standard shuld be in thermal equilibrium with the measurement envirnment. Always include a check fr nn-linearity within the measurement device. Nte: This can be mst easily achieved by checking with tw different values f calibratin standard, ne at r near the calibratin pint and ne at abut half this value. Any nn-linearity indicates pssible prblem with the unit r with ne r bth f the standards. Cnfirm the errr using additinal calibratin standard(s) and rectify it befre prceeding. Ensure that the instrument is stable befre checking Nte: Allw sufficient warm-up and settling time after switching n see the recmmendatins f the instrument manufacturer A recmmended prcess fr checking calibratin T carry ut a calibratin check, prceed as fllws: - Referring t the manufacture s instructins, place the instrument int the crrect mde t check the calibratin Insert the calibratin piece int the instrument measurement head Observe the measured value and nte the value Cmpare the measured value with the assigned value f the standard if the measured value differs frm the assigned value by mre than the allwable limit, then the instrument shuld be recalibrated. Nte: The allwable limits shuld be set by reference t the uncertainty f the measurement and the capability f the prcess. This is mst easily determined by regular use f a Shewhart Chart t plt the measured values fr the calibratin standards. [3] [4]. Fr additinal infrmatin n setting limits f uncertainty, please see sectin 7.2 If the measured value is within the allwable limit then the instrument des nt require recalibratin Calibratin The prcess fr calibratin is given in ISO Reference shuld als be made t the instrument manufacturer s instructins. The essential pints fr calibratin are given here fr cnvenience: - Only calibrate if there is a gd cause: - The calibratin check is ut f limits After majr wrk r disturbance t the instrument Nte: Refer t Shewhart chart. Unnecessary calibratin can lead t a wrsening f the measurement variability and hence f the manufacturing prcess that is being cntrlled 12

13 Always ensure that the value f the calibratin standard is larger than the largest value f sample Diameter that is t be measured. Where the range f values f the sample Diameter is nt knwn in advance, calibrate as clse as pssible t the full scale range f the instrument. This will ensure the best pssible accuracy acrss the cmplete range f the instrument. Observe the same precautins against bias and envirnmental effects as fr calibratin checking Nte: The easiest way t achieve this is t make the calibratin immediately fllwing a calibratin check this will use the standard in its previusly equilibrated state and will require the minimum amunt f handling f the standard. Carry ut a calibratin check after calibrating t cnfirm that n errr has been made and that the instrument is nw measuring within the allwable limits. Nte: always check with at least tw standards f different values t ensure crrect calibratin. 7.2 Checking instrument perfrmance This is a means f assessing the dynamic measurement perfrmance f a measuring instrument. It is nt necessary t carry ut this step fr rutine calibratin and calibratin checking but it shuld be carried ut peridically and particularly after any significant service wrk r repairs t the instrument. The purpse f this check is t cnfirm: - That the instrument is functining and perating crrectly The instrument is adjusted crrectly fr the prduct being measured and is capable f measuring the prduct crrectly The measurement capability f the instrument, in particular it may be used t assess the measurement: - Repeatability Instrument-t-Instrument variability Nte: These figures allw an assessment f the allwable limits fr calibratin checking. An instrument cannt be mre accurate r precise than its uncertainty f measurement Measuring repeatability Repeatability is defined as: The maximum difference t be expected between repeat measurements f a sample, made n ne instrument, by ne peratr and within a shrt perid f time. Repeatability is nrmally tested by measuring a series f samples twice in quick successin in ne instrument withut any re-calibratin f the instrument. The samples used shuld be stable and shuld clsely represent the actual samples nrmally measured n the instrument (i.e. f similar Diameter). Depending upn the type f instrument being tested, suitable samples are: - Cured filter rds Artificial cigarettes Actual cigarettes Calibratin standards Precautins shuld be taken t avid sample degradatin and hence t avid the Diameter changing frm measurement t measurement. Dependant upn the type f sample, these include: - 13

14 Minimising the amunt f handling f the samples Prviding a cushin in the sample cllectin bin t minimise damage as the samples are drpped thrugh the instrument Aviding significant misture lss frm cigarettes T btain a truly representative figure, the repeatability test shuld be carried ut in the same lcatin in which the instrument is nrmally used. This figure will then include any envirnmental effects that are present. Nte: Befre carrying ut any testing f repeatability r instrument-t-instrument variability, users shuld ensure that the instruments cncerned have been prperly calibrated and the calibratin checked, as described in sectin Measuring instrument-t-instrument variability Tests f instrument-t-instrument variability are a means f assessing the maximum difference t be expected between the measured values f a sample when measured n tw different instruments. It can be influenced by many different factrs, including the instrument repeatability, differences between the calibratin standards used t calibrate each instrument and lcal differences in peratr prcedure and technique. Instrument-t-instrument variability testing is carried ut in a similar way t repeatability testing, except that the tw measurements are made n different instruments and may be carried ut ver an extended perid f time. In additin, there may be several measurement runs, each n a different instrument. This allws testing acrss a ppulatin f instruments within an rganisatin and allws cmparisn between any ne instrument and the mean f all the instruments. This can be used t determine any biases between the instruments. Samples fr instrument-t-instrument variability testing can be the same as thse fr repeatability testing. Hwever, cigarettes are nt nrmally rbust enugh t be used and samples are generally cnfined t filter rds r artificial cigarettes Nte: - The actual instrument-t-instrument variability cannt be better than the repeatability f the individual instruments and will als include any differences between the calibratin standards used t calibrate each instrument. These values will depend upn lcal cnditins and hence the limits tabulated abve are fr guidance nly and d nt imply definitive limits. 8 Making Diameter measurements The exact prcedure fr measuring the Diameter f samples will depend nt nly n the type f sample t be measured but als n the type f instrument used. There are a number f pints, hwever, that need t be checked fr all Diameter measurements: The instrument used shuld be suitable fr the type f prduct t be measured. Generally, the measuring psitin shuld be adjusted. Fr multi-segment filter-rds it is recmmended t set the measuring psitin n a segment that is t be assembled t the tbacc rd f the manufactured cigarette. Samples shuld be handled carefully and as little as pssible t avid damage and changes f sample misture and temperature. Calibratin checks shuld be made frequently enugh t avid errrs in measurement due t Diameter calibratin changes with ambient cnditins. 14

15 9 Glssary and abbreviatins C Degrees Celsius RH ISO ISO TC 126 CCD CORESTA CRM Artificial Cigarette Shewhart Chart Relative humidity Internatinal Organizatin fr Standardizatin ISO technical cmmittee fr standardisatin f terminlgy and test methds fr unmanufactured tbacc, all types f tbacc prducts, materials used fr manufacturing tbacc prducts and tbacc smke including envirnmental tbacc smke aspects Charge-Cupled Device Cperatin Centre fr Scientific Research Relative t Tbacc CORESTA Recmmended Methd A test piece with the similar physical prperties t a cigarette but cnstructed s that its primary physical parameters (i.e. weight, length, circumference, pressure drp and ventilatin) are bth stable and repeatable. There are generally tw types f such a device: - 1. Articles made frm plastics r light metals with the apprpriate dimensins and primary physical parameter t match thse fund in real cigarettes 2. Cigarettes in which the tbacc clumn has been replaced with a piece f filter rd material f suitable Diameter. Generally, articles f the secnd type are preferred since they mre clsely mimic the prperties f actual cigarettes. A statistical tl in the frm f a cntrl chart intended t assess the nature f variatin in a prcess 10 References [1] Internatinal standard ISO 2971 Cigarettes and filter rds Determinatin f nminal Diameter Methd using a nn cntact ptical measuring apparatus (Third Editin 1998/08/01) [2] CORESTA Guide N 4, Nvember 2008 A User Guideline fr the Measurement f Pressure Drp f Cigarettes and cigarette Filter Rds. [3] Evaluating the Measurement Prcess Wheeler & Lyday. SPC Press, Inc. (1989) [4] Understanding Statistical Prcess Cntrl Wheeler & Chambers. SPC Press, Inc. (1992) 15