INFO BOLETÍN INFORMATIVO DEL SISTEMA INTERAMERICANO DE METROLOGÍA - OEA INFORMATIVE BULLETIN OF THE INTERAMERICAN METROLOGY SYSTEM - OAS

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1 I INFO IM Enero 2008 / January 2008 BOLETÍN INFORMATIVO DEL SISTEMA INTERAMERICANO DE METROLOGÍA - OEA INFORMATIVE BULLETIN OF THE INTERAMERICAN METROLOGY SYSTEM - OAS N Ó D E L O S ES T AD O S A IM CI M A Z N A G R E R I C A N O SISTEMA INTERAMERICANO DE METROLOGÍA O S

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3 INFOSIM ÍNDICE CONTENTS Introducción / Introduction Humberto Brandi Metrología legal en la Argentina Héctor Laiz Evaluation of stability in ethanol in water certified reference material measurement uncertainty under transport and storage conditions Vanderléa de Souza, Janaina Marques R. Caixeiro, Raquel D. C. Cunha, Laura A. N. Valente, Renata M. H. Borges, Rafael A. L. da Silva Control of prepackages Eberhard Seiler...15 Del software de los instrumentos de medición sujetos a aprobación de modelo Autenticarlo o validarlo? C. Cajica Gómez Comparison of methods for the weighing test in calibration of high capacity non-automatic weighing intsruments Luis O. Becerra, Eduardo González, Félix Pezet, José Revuelta M. José Revuelta R. Sylvia Maeda NOTI-SIM...26

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5 INTRODUCCIÓN INTRODUCTION Whenever a conflict of interests arises due to differences between fair and unfair measures, legal metrology comes into place in order to solve controversies and to contribute to the harmonization of the parties involved in the measurement. Legal metrology helps to defend the citizens' interests by means of verifying the necessary measurements to acquire the basic goods, fuel, energy, and preserve the life, health and safety of the persons, and the environment as well. These are the reasons with we have decided to devote this issue of INFOSIM, the SIM Bulletin, to legal metrology. This issue includes papers related to: activities developed to apply and update some elements through the Instituto Nacional de Tecnología Industrial -INTI- as the authority responsible for legal metrology in Argentina; the procedure to control of the stability characteristics of reference materials required for testing ethanol contents in the breath of vehicle drivers in Brazil; some easy actions to determine the contents in prepackaged products out of the sight of the consumer, to verify the statements in the labels in economies where no control of net contents of prepackaged products is in place; precise the difference between authentication and validation of software used in measuring instruments under model approval; and, a comparative study of a number of calibration methods of large scales. As an already necessary section, NOTISIM section provides information about SIM activities. We deeply appreciate the institutes that could contribute in providing the material for this issue, and also to those who responded our call but could not deliver information this time. The original language of the paper has been respected. Those papers which had been previously been published somewhere else, have the corresponding permission granted by the first publishers. We thank specially IMEKO Secretariat for it. We expect that this issue of INFOSIM promote the full development of legal metrology in the SIM region, as a means to obtain fair measurements to protect the interests of our societies, which we are part of and we serve to. Humberto Brandi President of SIM 5

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7 METROLOGÍA LEGAL EN LA ARGENTINA Héctor Laiz Instituto Nacional de Tecnología Industrial (INTI), Argentina RESUMEN Este trabajo presenta la evolución reciente de la Metrología Legal en la Argentina, donde los cambios operados fortalecieron la intervención del Instituto Nacional de Metrología (INTI) en el ámbito regulado. Se presentan las acciones emprendidas para llevar los controles de los instrumentos reglamentados a todo el territorio y para incorporar al ámbito regulado los instrumentos con impacto para la sociedad y el Estado. Se muestran cuales son los desafíos tecnológicos a enfrentar. 1. INTRODUCCIÓN A la hora de analizar el diseño de un sistema nacional de control de las mediciones en ámbitos críticos, como el comercio, la salud o el ambiente, surgen recurrentemente interrogantes polémicos: - cuál debe ser el grado de intervención del Estado? - la supervisión estatal debe estar en manos de un organismo administrativo o tecnológico? - debe aceptarse la autodeclaración del fabricante como base de las aprobaciones? - la metrología legal es una actividad técnicamente menor o demanda investigación científica en metrología? - cuál debe ser el rol del Instituto Nacional de Metrología? La evolución reciente de la Metrología Legal en la Argentina, aporta un ejemplo de abordaje a estas cuestiones, en especial para países de un grado de desarrollo intermedio. 2. MARCO LEGAL La Metrología está regulada en la Argentina por la Ley del año Hasta el año 2003 esta Ley estaba reglamentada por dos Decretos, el 1157/72 y el 829/94. En el primero se asignaba la responsabilidad de ejecución de la Metrología a dos organismos: el INTI, en cuanto a la metrología científica e industrial, es decir el mantenimiento y diseminación de los Patrones Nacionales de Medida y la Secretaría de Comercio de la Nación en cuanto a las actividades concernientes a la reglamentación de Instrumentos, aprobación de modelo y verificaciones. El posterior Decreto 829 de 1994, estableció que las aprobaciones de modelo y las verificaciones primitivas podían aprobarse por declaración jurada del fabricante. En el año 2003, el Presidente de la Nación emitió el Decreto 788 que modificó esta distribución de funciones, asignando al INTI, además de sus históricas tareas de metrología científica e industria, la ejecución de todas las tareas técnicas necesarias en Metrología Legal. La Tabla I resume la división actual de funciones entre el INTI y la Secretaría de Comercio de la Nación. 3.EVOLUCIÓN DEL SISTEMA 2.1. Situación en el 2003 Tal como se expuso en el punto anterior, la intervención directa del INTI en metrología legal se inicia al fines del El sistema, en ese momento, presentaba los siguientes problemas: - pocos instrumentos reglamentados - instrumentos aprobados con serias deficiencias técnicas, como consecuencias del sistema de aprobación basada en la declaración del fabricante. - casi nula supervisión de instrumentos en uso (verificaciones periódicas y vigilancias de uso), como consecuencia de los escasos recursos técnicos del organismo a cargo hasta ese momento. Cambios operados Al iniciar las actividades del INTI en el área se definieron tres objetivos: a. extender la verificación periódica de instrumentos reglamentados a todo el territorio nacional. b. establecer un sistema de aprobación de modelos con la rigurosidad técnica necesaria c. modernizar los reglamentos existentes y elaborar los reglamentos faltantes y demandados por la sociedad o el Estado 7

8 4. DESPLIEGUE DE LAS VERIFICACIONES Tal como se señaló, se iniciaron las actividades en el 2004 partiendo de una situación prácticamente inexistente de verificaciones periódicas. La estrategia adoptada se adaptó a las particularidades de cada sector. Como ejemplos, tomaremos los casos de balanzas de alta capacidad, surtidores de combustibles líquidos y tanques de almacenamiento. 4.1 Verificación de Balanzas Se incorporaron dos camiones y las pesas necesarias para equipar 4 camiones calibradores. Adicionalmente, se incorporaron al sistema operadores privados, que actúan bajo la supervisión del INTI. Su cantidad y requisitos pueden verse en [1]. Estos prestadores actúan siempre con la presencia de verificadores del INTI. En al año 2006 se realizó la verificación periódica de 3150 balanzas de alta capacidad, y se inhabilitaron otras 240 en vigilancias de uso. La Fig. 1 muestra la verificación de una balanza en un establecimiento minero en la Provincia del Salta a 4200 m sobre el nivel del mar. Fig. 2 Sistema diseñado en INTI para verificar surtidores de combustibles líquidos. 4.3 Verificación de tanques La calibración de tanques de almacenamiento representa un caso paradigmático. A pesar de tener sus mediciones un alto impacto en la determinación de las exportaciones argentinas, no se encontraban dentro del ámbito de la metrología legal. La Fig. 3 muestra a técnicos del INTI realizando estas calibraciones. En el año 2006, se calibraron 337 de estos tanques. Fig. 1 - Un camión calibrador del INTI verificando una balanza de pesar camiones en una mina de ácido bórico en la Provincia de Salta, a 4200 m sobre el nivel del mar. 4.2 Verificación de Surtidores En cuanto a la verificación de surtidores de combustibles líquidos, las verificaciones se iniciaron en el 2005, con 10 equipos propios distribuidos por todo el país. La Fig. 2 muestras los equipos desarrollados para esta tarea. En el 2006 se verificaron manqueras de expendio. La complejidad creciente de los sistemas de fraude electrónico motiva la constante capacitación de los verificadores. Fig. 3 - Calibración de tanques de almacenamiento de líquidos 5. ENSAYOS DE APROBACIÓN DE MODELO La efectiva realización de los ensayos de aprobación de modelo conlleva dos desafíos: la actualización tecnológica para adaptarse a las innovaciones en el diseño de los instrumentos, y la optimización de la capacidad de respuesta del laboratorio para evitar tiempos de esperas inadmisibles. Si bien el INTI contaba ya con experiencia en los ensayos involucrados, el nuevo requisito de obligatoriedad produjo un incremento de la demanda que obliga a un permanente replanteo de la organización del trabajo y al análisis de las inversiones necesarias. Como parte de las inversiones y desarrollos efectuados vinculados con las aprobaciones de modelo de 8

9 metrología legal se destacan una nueva cámara de ensayos climáticos de gran volumen, el desarrollo de la escala primaria de fuerza y la construcción de una cámara semianecoica para compatibilidad electromagnética de 19 m x12 m x 10 m (ver Fig. 4). - caudalímetros de oleoductos - humedímetros de granos - medidores de emisiones vehiculares - sistemas de pesaje en cinta El reglamento de tanques de almacenamiento, ya aprobado puede consultarse en [2]. El resto de los reglamentos propuestos pueden consultarse en [3]. 7. DESAFÍOS TECNOLÓGICOS Fig. 4 - Construcción de la cámara semianecoica de 19m x 12 m x 10 m para ensayos de compatibilidad electromagnética 6. ASPECTOS REGLAMENTARIOS El ámbito reglamentado no incluía, en el 2003, instrumentos de alto impacto social, como los medidores de servicios públicos (eléctricos, gas, agua) o los surtidores de gas natural vehicular, combustible utilizado por el 40% del parque automotor. Por otro lado, alguno de los reglamentos vigentes necesitaban urgente modernización, por ejemplo, el reglamento de balanzas databa de 1980 y el de surtidores de combustibles líquidos de Para revertir el atraso reglamentario se creó un equipo de expertos específicamente con este objetivo. Se elaboraron las propuestas de reglamentos de: - tanques de almacenamiento - medidores de energía eléctrica - medidores de gas domiciliario - medidores de agua domiciliaria - medidores de pulsos telefónicos - medidores de gas de alto caudal - esfigmomanómetros - medidores de gas natural vehicular - alcoholímetros Se modernizaron, o se encuentran en proceso de modernización los reglamentos de: - balanzas de pesaje no automático - surtidores de combustibles líquidos Actualmente se encuentran en proceso de elaboración los reglamentos de: - celdas de carga Las mediciones en el ámbito regulado presenta crecientes desafíos tecnológicos, básicamente por dos motivos: la necesidad de abracar nuevas áreas, como las mediciones ambientales y la propia evolución de los instrumentos de medición que incorporan nuevas tecnologías. Entre estos desafíos, que motivan el desarrollo de nuevas líneas de trabajo en el INTI, podemos destacar: Seguridad en el software Seguridad de la información Telemedición Compatibilidad electromagnética Medición de gas en grandes caudales Medición de energía eléctrica en alta tensión Contenido de contaminantes (por ejemplo, PCB, pilas y baterías) Composición de comodities 8. CONCLUSIONES La baja presencia del Estado en el ámbito regulado de la Metrología sumada al sistema de autodeclaración del fabricante resultó, en el caso argentino, en notables perjuicios para la protección del consumidor y para el interés fiscal. La intervención directa del Instituto Nacional de Metrología resulta clave para la óptima supervisión del sistema, dada la creciente complejidad técnica necesaria. La evolución de la tecnología de medición, motiva necesidades de investigación que hacen necesaria la cooperación regional entre los Institutos de deben proveer las soluciones a estos desafíos. REFERENCIAS [1] Listado de reparadores de balanzas auditados por el INTI. [2] Reglamento sobre Tanques Fijos de Almacenamiento, [3] Nuevos reglamentos en elaboración, 9

10 EVALUATION OF STABILITY OF ETHANOL IN WATER CERTIFIED REFERENCE MATERIAL: MEASUREMENT UNCERTAINTY UNDER TRANSPORT AND STORAGE CONDITIONS Vanderléa de Souza, Janaína Marques R. Caixeiro, Raquel D. C. Cunha, Laura A. N Valente, Renata M. H. Borges, Rafael A. L. da Silva 1 INMETRO, Directorate of Scientific and Industrial Metrology, Chemical Metrology Division, Duque de Caxias, Brazil 2 INMETRO, General Coordination of Accreditation, Rio de Janeiro, Brazil jmrodrigues@inmetro.gov.br ABSTRACT This study simulated the transport and storage conditions of ethanol in water certified reference material (CRM) produced by the Chemical Metrology Division of Inmetro DQUIM with the purpose to estimate the measurement uncertainty related to stability. The short-term stability study was performed on five different concentrations in terms of g ethanol/100g solution (%) of the ethanol in water CRM: %, %, %, % and %, at the temperatures of 4 ºC and 60 ºC. On the other hand, the long-term stability study was developed on four different concentrations: %, %, % and %. In this paper will be shown data from the long- term stability study concerning 20 weeks. The method used complies with ISO GUIDE 35, BCR-Guideline for Feasibility Studies and ISO GUIDE 34. According to the statistical parameters used in both studies the stability of the ethanol in water CRM was confirmed for all concentrations studied. Keywords: certified reference material, stability, ethanol in water, uncertainty. 1. INTRODUCTION Stability and homogeneity are key characteristics in the certification of reference materials, as they impact the validity of the certified values and their uncertainties. Hence, in the certification process, the reference materials shall be submitted to stability and homogeneity tests [1]. ISO GUIDE 35 [2] establishes that the certification of a reference material requires a detailed study of all sources of uncertainty that affect the certified value. Among these sources are the uncertainties of characterization, homogeneity, transport and storage. The Ethanol in Water certified reference material (CRM) is produced by the Chemical Metrology Division of Inmetro - DQUIM to test breath alcohol analyzers used to determine the content of alcohol (ethanol) present in the expired air of vehicle drivers. The uncertainty concerning the storage and transport of a CRM is estimated based on a stability study of long-term and short-term, respectively [2]. In the case of ethanol in water solutions the estimation of the uncertainty related to stability is extremely important as ethanol is volatile and the impact of its volatility in regarding to storage and transport conditions is crucial for quality assurance of the material. The short-term stability study was performed in five different concentrations in g ethanol/100g solution (%) of the ethanol in water CRM: 0,0509%, 0,0890%, 0,1145%, 0,3820% and 0,4960%. The follow-up of the short-term stability was performed at the temperatures of 4ºC and 60ºC. The long-term stability study was developed in four different concentrations: 0,0509%, 0,0890%, 0,1145% and 0,4960%. In this paper it is shown data from the long-term stability study concerning 20 weeks. However, this studies continue under development at DQUIM/ DIMCI/INMETRO. All the procedures used in this study are complied with ISO GUIDE 35, ISO GUIDE 34 and the BCR document- Guideline for Feasibility Studies [2-5]. * This paper was originally presented at the IMEKO XVIII World Congress, Rio de Janeiro, Brazil, September

11 2. PURPOSE The aim of this work is to demonstrate the estimation of uncertainty related to the transport (short-term stabilility study) and storage (longterm stability study) of the ethanol in water certified reference material in five different concentrations. The short-term stability study was to assess the influence of temperature on the stability of the five different concentrations of the ethanol in water CRM, by submitting them to temperatures above and below room temperature, simulating extreme conditions. The long-term stability study consisted of following up quantitatively, for a period of 20 weeks to estimate the impact of the storage on the concentration of ethanol at room temperature. To the room temperature is been considered the range from (20 0,3) C to (25 0,3) C. 3. METHODS During the stability studies the ethanol in water solutions were considered as reference materials (RM's) under a certification process. For both stability studies each RM was prepared in a 5 L bottle subsequently subdivided into nine 500 ml bottles. In short-term stability study were prepared two different groups as follows: three bottles were considered as reference samples and, after being weighed, were stored at 4 ºC (reference temperature). The other six bottles were weighed and stored in an stove at 60 ºC. Each two days, two bottles were removed from the stove and left in the laboratory at room temperature for two hours. Immediately after, they were weighed and stored at the reference temperature (4 ºC). At the end of eight days, when all bottles had already been submitted to the reference temperature, the group was exposed to the laboratory room temperature (from (20 0,3) C to (25 0,3) C), and weighed and analyzed by gas chromatography. In long-term stability study, the monitoring of each analyte concentration in the RM was performed in two different cycles in time. The first cycle began one week after the preparation of the calibration curve and the samples. was performed, the respective time-zero analyses (the first analyses before initiating the cycles) were also performed. The internal standard solution was added to the calibration solutions and new calibration solutions and a new internal standard solution were prepared. In the second cycle the analyses were performed once a month during a period of five months (20 weeks). All material was stored and protected against light at the temperature range from (20 0,3) C to (25 0,3) C. The analysis was performed by gas chromatography with flame ionization detector (GC/FID), on-column injector (65ºC, rate : 16ºC/min, 125ºC (3min)), and the quantification was performed by the addition of 1-propanol as internal standard. The column used was a DB- FFAP of 60m (1,00m of phase thickness 0,53mm of external diameter). The temperature program was: 65ºC (10min), rate of 15ºC/min up to 120ºC (6min), column flow rate 5,65mL/min. The injection volume was 1L. The detector was kept at 220ºC. The calibration curves were made with gravimetrically prepared standards by using two curves, with 8 points each, in the concentration range of 0,035% to 0,105% and in the concentration range of 0,085% to 0,58%, respectively. The method also included checking the homogeneity within each bottle, as two aliquots were analyzed for each bottle, each one of them in duplicate. The statistical criteria adopted for assessing the stability and uncertainty in both studies were based on linear regression and residue analysis in conjunction with analysis of variance (ANOVA). Two criteria shall be simultaneously met in order to determine the stability of the material: a p-level greater than 0,05 and an angular coefficient (B) near to zero [2]. To the short-term study two more criteria were evaluated: the maximum percent differences acceptable for sample mass of each bottle before and after the study temperature (60oC) and the ethanol concentration of each bottle submitted to study temperature (600C) against ethanol concentration of bottles submitted to reference temperature (4oC). These two parameters are presented at Table 1. The analyses were performed once a week, during a period of four weeks. In the same week the preparation of calibration curves and samples 11

12 Table 1: Parameters and maximum percent differences for the short-term stability study Parameter Sample mass before and after the study temperature (60 C) Analyte concentration after study temperature against analyte concentration at reference temperature Maximum Percent difference (%) Figure 1: Ratio between the ethanol concentration for each bottle submitted to 60 ºC and the ethanol concentration for the bottles submitted only to the temperature of 4 ºC (reference), for each RM concentration. Figure 2 shows, for each bottle in each RM concentration, the mass percent difference of each o bottle before and after the study temperature (60 C). 4. RESULTS According to the number of days in the stove the ethanol concentrations obtained for each bottle in short-term stability study after them being submitted to the reference temperature are shown in the Table 2. Table 2: Ethanol concentration (g ethanol/100 g solution) after bottles were submitted to the temperature of 4ºC M ass Difference (%) 0,10 0,08 0,06 0,04 0,02 0,00 [1] [2] [3] [4] [5] Figure 1 shows, for each RM concentration, the ratio between the ethanol concentration found in each bottle submitted to the temperature of 60 C and the bottles considered as reference samples, submitted only to the temperature of 4 C. Ratio concentration Number of days in stove Concentration ,02 1,01 1,00 [1] [1] [2] [2] [3] [3] [4] [4] [5] [5] [1] [2] [3] [4] [5] -0, Bottles Figure 2: Mass Percent Difference after reference temperature for each bottle in each RM concentration. In long-term stability study, the results obtained for the [A], [B], [C] and [D] ethanol concentrations during the 20 weeks are displayed in Table 3. Table 3. Ethanol concentrations (g ethanol/100 g solution) obtained during the period of study. Ethanol Period of Study (weeks) [A] [B] [C] [D] Figures 3 and 4 show the variation of the RM concentrations [A] and [B], [C] and [D] during the period of study. 0, Days in Stove 12

13 [E tha no l] (% ) 0,11 conc A conc B 0,10 0,09 0,08 0,07 0,06 0,05 Table 4 and Table 5 show respectively to the short and long-term stability study, the uncertainty related to the transport and storage to each CRM concentration, the angular coefficient of the curve, the p-level and standard deviation (STD) in relation to time. Table 4:- Uncertainty for each concentration of CRM, obtained by statistical treatment (linear regression) 0, Time (weeks) Figure 3: RM concentrations [A] and [B], obtained during the period of study. Concentration Angular Coefficient (B) p-level (p) Uncertainty * STD [1] E E-06 [2] 5.293E E-05 [3] [4] [5] 1.822E E E E ,60 0,55 0,50 0,45 0,40 conc C conc D * The uncertainty is expressed in g ethanol/100g solution. Table 5: Statistical results obtained by linear regression for the respective ethanol concentrations. ) [Ethanol] (% 0,35 0,30 0,25 0,20 0,15 0,10 0, Time (weeks) Concentratio n Angular Coefficient (B) p-level (p) Uncertainty * STD [A] 2.370E E-06 [B] 5.353E E-05 [C] 4.978E E-05 [D] 1.913E * The uncertainty is expressed in g ethanol/100g solution. Figure 4: RM concentrations [C] and [D], obtained during the period of study. ISO GUIDE 34 [3] establishes that the uncertainty inherent to a CRM shall be calculated on the basis of the combination of all sources involved in the certification process, i.e., the combination of the uncertainties taken from the characterization, the homogeneity, the storage and the transport, being the two latter the object under estimation in this study. The uncertainties related to storage and transport, long-term and short-term studies, respectively, were calculated through an spreadsheet, that provide the following parameters: the standard deviation of ethanol concentration in relation to the time of study, the angular coefficient of the curve related to the variation of ethanol concentration with the time and p-level. The uncertainty related to the transport and storage (short and long term stability study) for each CRM ethanol concentration is calculated by the product of standard deviation and the time of study as show in Equation 1. To the short-term stability study the long-term stability study U Stability where: =STD* t U Stability = Uncertainty Stability STD= Standard Deviation t= time t = 7 days and to t = 20weeks. (1) 13

14 5. DISCUSSION In short-term stability study, the ratio between the ethanol concentrations found for each bottle at 60 ºC and the bottles submitted only to the temperature of 4 ºC (reference samples) was approximately 1, showing that no significant variation of concentration occurred when submitting the CRM to this range of temperature. In relation to the study to evaluate the mass difference of the bottles before and after they had o been submitted to the study temperature (60 C) it can be seen that there was no lost of mass evidencing the stability of ethanol solutions for all concentrations. As the study evidenced the CRM stability in the temperature range of 4 C to 60 C for 7 days, the uncertainty obtained is deemed to be the uncertainty inherent to the transport of CRM, since during the transport a material may be submitted to variable conditions and the range of temperature studied simulates extreme conditions. In relation to long-term stability study, the Figures 3 and 4 show that for all ethanol concentrations no significant difference was detected during the period of study (20 weeks). The calculations performed demonstrated that the variation of each concentration, in each week, compared to time zero (t=0) is not greater than 1.0%, indicating a satisfactory concordance of data and evidencing the stability of the material. The results of this study made possible the estimative of the impact of the CRM storage on the ethanol concentration, and also the subsequent determination of the uncertainty taken from the CRM storage during the period of study. This uncertainty can be seen at the Table CONCLUSION The short-term stability study characterized for all concentrations studied the stability of the ethanol in water CRM in the range of temperature from 4 ºC to 60 ºC at the period of 7 days, providing an estimation, for each concentration, of the uncertainty inherent to the transport of this material. The long-term stability study of the ethanol in water RM demonstrated the stability of the CRM along the 20 weeks period of study (5 months). Hence, this period corresponds to the period of storage shown in the CRM certificate. This study also facilitated the estimation of the uncertainty of the ethanol in water CRM storage, in regard to the certified values of ethanol concentration. It is important to mention that the long-term stability study of ethanol in water CRM is under development at DQUIM/ DIMCI/ INMETRO with the objective to reach the total time of 13 months. 7. REFERENCES [1] PAUWELS, J.; LAMBERTY A.; SCHIMMEL, H.; Homogeneity testing of reference materials, Accred. Qual. Assur (3) 51-55, [2] ISO GUIDE 35:2006 Reference materials General and statistical principles for certification. [3] ISO GUIDE 34:2000 General requirements for the competence of material producers. [4] BCR Guidelines for feasibility studies on Certified Reference Materials, The statistical parameters used in both stability studies are those obtained from linear regression and residues analysis. These parameters, expressed by the angular coefficient (B) and the p-level (p), indicate if a material is or not stable. A material is deemed to be stable when the following criteria are simultaneously met: B 0 and p > 0,05. At the Tables 4 and 5 can be seen that these two criteria were met, confirming the stability of the ethanol in water CRM for all concentrations studied. These results meet the criteria established in ISO GUIDE 35, ISO GUIDE 34 and BCR Guidelines for Feasibility Studies, evidencing the certification of the RM for the period of study. 14

15 CONTROL OF PREPACKAGES Eberhard Seiler Chairman of OIML s Permanent Working Group on Developing Countries eberhardseiler@msn.com Remark Dear reader, As chairman of the Permanent Working Group for Developing Countries of the International Organization of Legal Metrology (OIML) I take this opportunity to draw your attention to a special Discussion Forum as part of OIML s web site. This Forum was created to facilitate the cooperation, the exchange of information and ideas especially among Developing Countries. There you will find my proposal for the control of prepackages as printed here. If you carry out checks of prepackages already it is perhaps not necessary to read the following. If you are not yet active in this field, you will find some arguments and ideas why and how to start even with very limited resources. Why checking prepackages? Checking the net content of prepackages is one important and continuous task of legal metrology services. These controls are carried out in Germany for more than 30 years and the verification authorities aim at checking the producers once a year. More than checks are carried out every year. Although the offences against the relevant regulations decreased during the years the mean value of offences is still around 5%. The European Union established filling requirements which producers of prepackages must comply with. If they do so they can put an e on their packages which allows them to put their products on the European market. The legal metrology authorities of the packer`s country are responsible for the supervision. Despite all these regulations and checks the loss for the consumer in Europe due to under filling sums up to many million Euro per year. It is almost certain that losses in countries without any control of the net content are even higher and should be a challenge for the legal metrology services. What can be done? What can be done if there are no legal requirements for prepackages in force? Does it mean that nothing can be done? I don t share this opinion. Checks can be carried out without regulations in force but of course without legal consequences. The OIML Recommendation 87 Net content in packages can be used for the checks. The results obtained will reflect the market situation. They should be used as arguments in discussions with the responsible ministry for drafting the necessary national regulations. But what can be done if there is no equipment? Of course, this will be a handicap but here is my proposal for a first survey with simple and cheap measuring instruments: Since many prepackages are filled by volume the checks require standard graduated glass flasks (R 43) or graduated glass cylinders. If they are not among the measuring instruments of the legal metrology service they can be purchased for a small amount of money. If there is no specialized shop for such measuring instruments they may be available at shops for hospital equipment. It is recommended to set priorities for the checks to be carried out. Products which are needed for the daily life and which are fairly expensive should be chosen such as edible oil or milk products. Results obtained in Germany show significantly higher offences for these products than the mean of 5%, namely 13.5% respectively 10.8% in One disadvantage of this proposal is the destructive nature of the check, you must open the container and pore out the liquid. Usually, you have to pay for the product. If money is not available you can try to argue with your local producers to see their quality management systems and their measures to guarantee the correct filling. Perhaps you can check their products in their premises on their account. Even if that should not be possible you can do something. Since we are all consumers we have to buy prepackages. Why not using prepackages for private consumption for the first survey? If you measure before you use the food stuff and if you measure whenever you use the next item you will get information about the degree of filling of this special item and whether you get the mean value of the declared quantity after a sufficient long period of time. Another possibility to start activities is the check of empty containers which can be easily collected and used for this purpose. The containers should carry an information about their nominal volume. There is an OIML Recommendation R 96 Measuring container bottles specifying the necessary requirements. Make the experiment and determine the maximum volume of containers! I am sure you will find some which are smaller than indicated. Final remarks: 1. As shown above checks can be carried out even with very little resources. I hope the proposals will encourage you to start activities. If you have comments or questions don t hesitate to contact the Forum (under OIML s home page: you will find Developing Countries and Discussion Forum. In case you need a pass word contact one of the given reference persons). 2. It would be of interest to learn about your experience. Please let us know your results which you can publish on OIML s website. 15

16 DEL SOFTWARE DE LOS INSTRUMENTOS DE MEDICIÓN SUJETOS A APROBACIÓN DE MODELO AUTENTICARLO O VALIDARLO? C. Cajica Gómez Centro Nacional de Metrología ccajica@cenam.mx Un instrumento de medición de operación automática, entendiéndose por ello a un instrumento de medición que incluye instrumentación electrónica basada en un circuito integrado denominado microprocesador o un microcontrolador para facilitar tanto su manejo como la obtención de los resultados de sus mediciones, tendrá características metrológicas tan buenas como su programación lo permita, incluso los modelos matemáticos programados en los circuitos integrados podrían corregir la falta de linealidad en la operación de los mecanismos, transductores y sensores; realizar corrección por histéresis o señalizar la condiciones de saturación, entre otros. Actualmente la legislación mexicana exige que los instrumentos para medir que se encuentren sujetos a normas mexicanas obligatorias (NOM) y que sirvan de base o se utilicen para una transacción comercial para determinar el precio de un producto o servicio, deben contar con aprobación de modelo o prototipo, artículo 10 de la Ley Federal Sobre Metrología y Normalización. La aprobación de modelo es el procedimiento por el cual se asegura que un instrumento de medición satisface las características metrológicas, especificaciones técnicas y de seguridad establecidas en las normas antes referidas. En México, los instrumentos de medición cuya verificación inicial, periódica o extraordinaria es obligatoria, así como las normas obligatorias que los regulan son los siguientes: Instrumentos Norma Oficial Mexicana que los regulan Instrumentos para pesar de bajo, mediano y alto alcance de medición Sistemas para medición y despacho de gasolina y otros combustibles líquidos Medidores para gas natural o L. P. con capacidad máxima de 16 m3/h con caída de presión máxima de 200 Pa (20,40 mm de columna de agua) Relojes registradores de tiempo NOM-010-SCFI-1994 Instrumentos de medición-instrumentos para pesar de funcionamiento no automático-requisitos técnicos y metrológicos NOM-005-SCFI-2005 Instrumentos de medición-sistema para medición y despacho de gasolina y otros combustibles líquidos-especificaciones, métodos de prueba y de verificación NOM-014-SCFI-1997 Medidores de desplazamiento positivo tipo diafragma para gas natural o L. P. Con capacidad máxima de 16 m3/h con caída de presión máxima de 200 Pa (20,40 mm de columna de agua) NOM-048-SCFI-1997 Instrumentos de medición-relojes registradores de tiempo-alimentados con diferentes fuentes de energía Entrada en Vigor Taxímetros NOM-007-SCFI-2003 Instrumentos de medición-taxímetros El avance tecnológico actual ha permitido que todos los instrumentos de medición sujetos a normas obligatorias incluyan instrumentación electrónica basada en microcontrolador o microprocesador, permitiendo con ello que los instrumentos sean programables y realicen las mediciones sin la intervención de una persona, operando de forma automática. Los fabricantes de instrumentos de medición que incluyen estas nuevas tecnologías, realizan la programación de los microcontroladores o microprocesadores conformando un software que es colocado dentro del propio circuito integrado, este software que reside en los circuitos integrados es conocido como Firmware. La actualización del software que reside en los circuitos integrado de los instrumentos de medición es una actividad periódica que realizan los fabricantes, dada la naturaleza intrínseca de este tipo de software de poder mejorarlo o adicionarlo con nuevas funcionalidades. Por lo anterior se puede entender de manera lógica que el comportamiento metrológico de cualquier instrumento de medición podrá estar limitado por el software que lo opere, y un punto importante a considerar es que este software guardará la equidad en las transacciones comerciales como la ética profesional del fabricante lo permita. Así, considerando la situación que se presenta para los instrumentos de medición de operación automática, su verificación inicial, periódica y extraordinaria debería de incluir un procedimiento de revisión del software que permitiera comprobar íntegramente la forma en que los resultados de las mediciones realizadas y el establecimiento de precios para el caso de transacciones comerciales, son calculados y mostrados. Actualmente ninguna norma oficial mexicana lo incluye. 16

17 Los esfuerzos hasta ahora para realizar de alguna manera algún tipo de verificación de software solo han llegado a establecer un proceso de autenticación y solo por una norma oficial mexicana: la NOM-005-SCFI "Instrumentos de medición-sistema para medición y despacho de gasolina y otros combustibles líquidos-especificaciones, métodos de prueba y de verificación". La autenticación en esta norma está basada en una técnica de reducción criptográfica, lo que permite conocer en efecto, si el origen de este software es efectivamente el del fabricante. No obstante, la operación del mismo no es factible de conocer y solo el fabricante sabe como opera y como controla el instrumento de medición, con ello la autoridad que aprueba el modelo o prototipo del instrumento realiza un acto de fe sobre la ética profesional del fabricante respecto a la equidad en la transacción comercial en la que interviene el instrumento de medición. La limitación de la autenticación puede compensarse agregando esquemas de revisión de cada versión de software de cada fabricante a nivel de los códigos de operación del mismo, lo que implicaría conocer el archivo del programa fuente en el lenguaje que entienden los circuitos integrados, comprobando todo subprograma, función, procedimiento, subrutina, control de eventos, y manejo de interrupciones para lo que fuera programado el microprocesador o el microcontrolador correspondiente, este procedimiento conformaría una validación cuyo dictamen de verificación daría la certeza de lo que realmente realiza la programación del instrumento de medición y con ello la garantía de la equidad en las transacciones comerciales en las que participa. Existen fuertes dificultades técnicas para realizar una validación de software en los términos antes descritos, pues tanto el abanico de opciones y posibilidades tecnológicas para programar circuitos integrados como la disposición de tecnologías de las diferentes marcas de los propios circuitos son muy grandes; implicaría la necesidad de contar con varios especialistas en la materia para realizar las verificaciones, aunado a que la revisión de un programa de cómputo podría requerir mucho tiempo. La participación del fabricante en esta revisión sería indispensable así como la utilización de normas nacionales o internacionales relacionadas con la verificación de software; por otra parte el fabricante tendría la necesidad de mostrar a la autoridad el Know How de su tecnología, lo que implicaría manejar esquemas de protección industrial y manejo de información confidencial seguros. Los resultados que se esperarían con el establecimiento de un procedimiento de validación de software bien valen la pena, la autoridad cumpliría cabalmente con la responsabilidad de guardar la protección al consumidor asegurando la relación precio cantidad en las transacciones comerciales en las que los instrumentos de medición de operación automática participan, aunado al reforzamiento y mejor cobertura de los esquemas de evaluación de la conformidad en el procedimiento de la aprobación de modelo o prototipo. Las siguientes dos figuras esquematizan los dos procesos de verificación de software citados. 17

18 COMPARISON OF METHODS FOR THE WEIGHING TEST IN CALIBRATION OF HIGH CAPACITY NON-AUTOMATIC WEIGHING INSTRUMENTS* Luis O. Becerra, Eduardo González, Félix Pezet, José Revuelta M, José Revuelta R, Sylvia 2 Maeda 1 CENAM, Querétaro, México, lbecerra@cenam.mx; egonzale@cenam.mx, fpezet@cenam.mx 2 Básculas Revuelta Maza, S.A. de C.V., Torreón, México, jrm@revuelta.com.mx, jrevuelta@revuelta.com.mx, smaeda@revuelta.com.mx Abstract: This paper presents the results obtained from the comparison of different techniques for the weighing tests for the calibration of high capacity weighing instruments, in order to evaluate their use as a function of the amount of available weights and the required uncertainty of the instrument in their normal use. Keywords: Mass, Weighing instruments, substitution weights. 1. INTRODUCTION In calibration of high capacity non-automatic weighing instruments a common problem is the amount of available mass standards (or weights) additionally to the difficult of handling and transporting large weights. This work presents the uncertainty comparison of different procedures for the weighing tests in calibration of a truck scale. The main difference of these procedures is based on the amount of standard weight used. There is not any standard, guideline or recommendation in Mexico or at international level about the required uncertainty for the calibration of those instruments; therefore it is a choice of the user which is the suitable uncertainty for the calibration of his own weighing instrument. The calibration tests were done following the guidelines of EA-10/18 [1]. 2. PURPOSE The purpose of this study is to estimate the uncertainty of different calibration methods for high capacity non-automatic weighing instruments as a function of the amount of mass standards used and the characteristics of the weighing instruments such as repeatability and sensitivity. All tests were done in two phases: Adjusted instrument Instrument misadjusted intentionally on its characteristic response (linearity) but not the eccentric load indication neither the repeatability. It was decided to make the test methods for the adjusted instrument and repeat them for the same instrument misadjusted intentionally in order to evaluate the sensitivity of the test methods for the evaluation of the characteristic response of the high capacity non-automatic weighing instruments. The weighing test methods evaluated were: i. Mass standards ii. Substitution loads iii. Combinatorial Technique 3. WEIGHING INSTRUMENT TESTED AND MASS STANDARDS The truck scale tested is located in Rancho Monte Carlo in Torreón Coahuila, Mexico. The scale tested has the following characteristics (see fig. 1): Brand: Revuelta Model: RCC-1880-VR Serial number: C.780R Range: kg Type: Truck scale Resolution: 10 kg Accuracy Class: OIML Medium III [2] Load receptor Dimensions: 18 m x 3 m Points of support: 8 For the calibration were used eighty mass standards with the following characteristics, Nominal value: kg 2 Accuracy class: OIML M 1 3 Density: kg/m * This paper was originally presented at the IMEKO XVIII World Congress, Rio de Janeiro, Brazil, September It is reproduced with permission. 2 The Mexican Standard NOM-038-SCFI-2000 [5] allows the construction of weights of large nominal value made of steel box filled with metallic material. 18

19 eccentric loading is calculated from the following formula, I ecci I i I 1 res (1) where, I i is the indication of the weighing instrument when a the load is placed at the end i of the load receptor I 1 is the indication of the weighing instrument when a the load is placed at the centre of the load receptor is the correction due to the resolution of res the scale with zero as mean value. Fig. 1. Truck scale tested. 4.2 Repeatability test The repeatability test was done using a vehicle with load (approx kg) and the same vehicle with tow (approx kg). For this test each load was placed three times at the centre of the load receptor. From the three indications for each load I the j standard deviation for the load j is calculated using formulas (2) and (3). The repeatability of the scale is calculated with formula (4), which considers the contribution of the resolution. Fig. 2. Mass standards used. 4. TESTS The tests were done for the adjusted and misadjusted weighing instrument. The calibration tests performed were the following: Eccentric loading test Repeatability test Weighing test The differences among test methods are focused in the weighing tests which were done with different amount of mass standards and substitution weights and the number of measurements done. 4.1 Eccentric loading test The eccentric loading test was done using a vehicle with load (approx kg). The vehicle was placed in three positions along the load receptor of the scale, at the center of the load receptor and at the ends of the load receptor of the truck scale. The load was placed within the point of support of the scale in order to avoid a malfunction or damage of the instrument. The effect of the s I s j Scale n 2 I I ji j 1 (2) n 1 I s j i1 n 1 n I ji i1 2 2 I d j 12 (3) (4) where, n is the number of repetitions, three for this exercise Iji Is the repetition i of the indication with the load j on the load receptor d is the resolution of the scale 4.3 Weighing test For the weighing test, three methods were applied Weighing test with mass standards The weighing test was done with eighty mass standards of kg placed one by one in the load receptor. The results of this exercise were taken as reference values in order to evaluate the others weighing test methods. 19

20 4.3.2 Weighing test using substitution loads For this exercise, there were used m = kg in mass standards (16 pieces of kg each), and loaded vehicles in order to have loads close to the following values, Q kg 1 Q kg 2 Q kg 3 Q kg 4 The weighing sequence was the following, i. m ii. Q 1 iii. Q + m 1 iv. Q 2 v. Q + m 2 vi. Q 3 vii. Q + m 3 viii. Q 4 ix. Q + m Weighing test applying the combinatorial technique [4] This exercise was done using m = kg as mass standards, and four loaded vehicles with the following approximate mass values, R kg 1 R kg 2 R kg 3 R kg 4 n The goal of this method is to have the 2 combinations of loads. For this exercise and taking 5 individual loads (taking the mass standards as one of them) there were 32 combinations of load. 5. ERRORS OF INDICATION 5.1 Rounding error of the indication In order to reduce the uncertainty due to the resolution of the scale, there were applying small extra weights in steps of d T = d/10, for this exercise d T =1 kg. The corrected indication due to the rounding error (I ) is calculated by the following formula, L I d (5) I 2 L nd T where, I is the indication of the scale n are the number of small extra weights placed in the load receptor d is the value of the small extra weights T 5.2 Buoyancy correction Even when the calibration of the scale was done in conventional mass, all indications of the scale were corrected by the buoyancy effect by the following formula, acal m B m 1, 2 (6) c m where, mc is the conventional mass of the mass standard placed in the load receptor acal is the air density during the calibration m is the density of the mass standard or the substitution weight 5.3 Inverse of the sensitivity of the weighing instrument The inverse of the sensitivity of the scale was evaluated for the weighing test in order to correct the mass difference (given in indications of the scale) between the mass standard (or known mass) and the unknown mass or load. The impact to the uncertainty due to this factor is directly proportional to difference between the indication of the load and the indication of the mass standard. The inverse of the sensitivity is evaluated several times for the weighing test using the following formula, (7) S x m 1 mc 1, 2 1 acal I I Re p S 1 x Ecc Re p Round m where, I x+m is the indication of the weighing instrument when a load x and the mass standard are on the load receptor I x Ecc Re p S 1 Round Re p is the indication of the weighing instrument when the load x is on the load receptor is the correction due to the eccentric load of the scale with zero as mean value. is the correction due to the repeatability of the scale with zero as mean value. is the correction due to the rounding error of the indication with zero as mean value. is the correction due to the repeatability (or dispersion) of the sensitivity evaluations. This correction has zero as mean value. 20