RICERCA ITALIANA     

Methodology for the actuation of the European Norm on Measuring Instrument Devices (MID)

Università degli Studi di Padova

Abstract

The research aims to give a complete scientific support for a rapid and effective application of the Measuring Instrument Directive (MID) within national contest. The Directive renews completely the legal metrology sector, proposing a "new approach" aiming to technical normalization and harmonization and toward a "global approach" to evaluation and conformity. Legal metrology constitutes an essential tool for markets' operations and involves a wide range of instruments and is therefore of primary socioeconomic interest. The Directive operates on the basis of these two principles:
- formulation of essential requirements (having cogent power) and of requirements for conformity evaluation;
- mutual agreement among the member States of results of conformity evaluation.

The Directive essentially proposes two types of challenges, one relative to competitiveness of the involved companies and another relative to the efficacy of its actuation among the member States, so that acting promptly at a national level seems to be essential. Because of the fact that the key point for the implementation of the Directive is the availability of procedures for functional and metrological characterization of instruments, in the present research it is suggested an activity of experimentation and development of standard procedures optimized, relatively to the available information, in terms of simplicity, execution reliability and costs, and of the relative metrological software. In particular three classes of instruments will be considered, chosen for their relevant socioeconomic impact and/or their wide diffusion: volumetric counters, weighting devices and taximeters. The optimized procedures will be formulated in a general way so to be renewable dynamically as the technological knowledge advances, in respect of the general purposes. The procedures will allow the verification of all functional and metrological significative parameter, in the operative conditions of the instrument. The optimization will result from a systematic enquiry of interfering effects, held both in modelling and experimental studies. In particular will be considered climatic effects (temperature an humidity), mechanical effects (vibration, shocks), inaccurate installation of the instrument (orientation relative to gravity), dynamical effects (sudden variation of the measurand), effects due to chemical-physical variations of the measurand (such as temperature and concentration).
The research will be conducted in close collaboration with the Comitato Centrale Metrico, with the Istituto Nazionale Galileo Ferraris, and with the Istituto di Metrologia G. Colonnetti.
This collaboration might be particularly useful also because it happens in concomitance with the institution of the Istituto Nazionale di Ricerca Metrologica, and can give a contribution to the strengthening of the whole national metrological system.
The working plan foresees a full integration among the eight proposing Research Units, considering both transversal aspects, relative to modelling and software, and specific experimental aspects, relative to the three classes of instruments considered.
The results of the research will consist basically in guides for the realization of the optimized and experimentally validated procedures, and in the relative metrological software.
On the basis of such results, information will be given, in the appropriate form of communication, to three classes of users:
- to the measurement instruments manufacturers, so that they can operate in a competitive manner;
- to the Camere di Commercio, that have the responsibility of metric controls and that need technical support in this transition phase;
- to the final users, so to ease an aware use of the instruments of their interest, with a consequent improvement in the quality of life. <<<

Principal Investigator

Francesco ANGRILLI Università degli Studi di PADOVA

Research Objectives

The Measuring Instrument Directive (MID) represents a milestone in the building process of the european common market. In fact it completely reforms, the legal metrology sector, under the spirit of the "new approach" towards the technical normalization and harmonization.
The legal metrology, as known, aims to guarantee the tutelage of parts, for example in commercial transactions, and constitutes an essential tool to warrant markets' operations. The field of instruments covered by metrology is extremely wide and of primary socioeconomic interest. It comprehends for example meters of public interest services, scales of retailers, filling machines for packed products, taximeters, instruments for analysis of exhaust gas and instruments for linear measurement (length measurement).
The "new approach" toward technical normalization and harmonization has been thought to ease the realization of the internal market and to facilitate a flexible and technologically neutral legislation, to promote innovation and competitiveness (see Council act of May 7th 1985). It belongs to a general approach for evaluation of conformity, that is based substantially on modern criteria of quality assurance (see Council act of October 28th 1999).
The MID operates accordingly with the new approach and aims to constitute an internal market of the measurement instruments subjected to legal metrological control, on the basis of two principles:
- formulation of essential requirements (having cogent power) and of requirements for conformity evaluation;
- mutual agreement among the member States of results of conformity evaluation.
This formulation involves a deep renewal process that affects, as said, classes of measurement instruments that have a relevant socioeconomic impact. Moreover, given its strongly innovative form, it could influence also the voluntary field, involving therefore virtually the whole area of manufacturing, testing and marketing of measurement instruments, which constitute a strategic sector for each nation.

The novelties introduced by the Directive essentially propose two kinds of challenges, relative to the competitiveness of the involved companies and to the efficacy of actuation within the member States.
To accept these challenges, it seems necessary to associate to the coming Directive an adequate support of public research, both in European and national sphere.
In European ambit, since the first issue of the proposal for the Directive, three research programs have been presented and financed, within the V Framework Program, aiming essentially to harmonize the application of the principles expressed from the Directive among the member States.
It seems useful to put beside these actions, that are typically international, research programs like the present proposal, aiming to promote competitiveness of companies operating in our Country, and the efficient application of the requirements foreseen by the controlling bodies in charge, operating on the national territory. In fact, on one side the companies potentially involved are prevalently PMI and they might not be able to directly sustain the necessary research activities, on the other side the National Chambers of Commerce, which recently have been put in charge of control, would be very interested in a support of this kind, as came out for example during the study day "Legal Metrology: the Chambers of commerce and the mechanical measurements research group" hold in Varenna on September 2001.

The key point for implementing the Directive is the availability of procedures for the functional and metrological characterization of the instruments involved. These procedures are rich in technical contents, and their optimization can be a key element for competitiveness for instruments manufacturers on the European market. As it will be underlined in the following, the procedures' definition touches relevant and still open scientific problems, regarding mainly the definition specific experimentation for classes of instruments envisaged by the Directive and moreover two fundamental aspects like the testing processes and the use of metrological software.
In the present research it is proposed to investigate the two general themes mentioned above, with reference to the problems enlightened by the Directive and the execution of experimental activity and of development of standard procedures optimized in reference to:
- available information;
- simplicity and reliability of execution;
- costs.
Because of the fact that the Directive, as said, involves a plurality of classes of instruments, the aim of the present research is to cover a significative part of them according with the timing of development of the project. Therefore it is proposed to consider three classes of instruments of relevant socioeconomic impact and/or having large diffusion: volumetric counters, weighting devices and taximeters.
The expected final results are essentially:
a) three guides, one for each class of instruments considered, for the realization and optimization of testing procedures, accordingly to the Directive and able to give additional information, without significative cost increase (by means of optimization);
b) metrological software for measurements results presentation accordingly to current regulations, including the expression of measurement uncertainties, and able to give a probabilistic representation of such results, useful for risk evaluation and cost analysis.

The operating scheme that would be adopted is briefly summarized in the following table.



The scheme foresees a full integration among the duties of the Research Units (RU), with an optimal use of specific knowledge.
The research will be followed in close collaboration with the Comitato Centrale Metrico (CCM), with the Istituto Elettrotecnico Nazionale Galileo Ferraris (IEN) and with the Istituto di Metrologia G. Colonnetti (IMGC), that have showed interest and willingness in cooperation. This cooperation will take place with the presence of personnel from the former bodies, with particular experience in the problems under exam, in the RU 1 and 6, and thanks to the fact that the person in charge of the RU 2 is a member of the Comitato Centrale Metrico.
This collaboration seems to be particularly useful also because it takes place together with the Istituto Nazionale of Ricerca Metrologica (National Institute for Research in Metrology, I.N.RI.M, DL January 21st 2004, n. 38) and it can give a contribution to the strengthening of the whole system of national metrology.

The results of the research will be given in the appropriate form for the three classes of users:
- to the instruments manufactures, that using the provided procedures, might not only verify the compliance of their instruments in an effective way and with minimal costs, but also obtain additional information, relative to how to improve the product, letting it be more competitive, without additional costs;
- to theChambers of commerce, that, as said, have the duty of metric controls and need technical support in this phase of transition;
- to the final users, using appropriate forms of communication of the information essential to them, so to aid a conscious fruition of the instruments of their interest, with the consequent improvement of the quality of life. <<<

First Results

Expected results:
- Technical note on the scientific-technical literature and definition of state of art
- Technical note on test design for the mathematical model validation
- Technical note on usable model
- Technical note on the design of the numerical code
- Draft of the preliminary procedures for the measurement uncertainty evaluationExpected results:
- Technical report on the study and development of the mathematical models
- Technical report on procedures for the uncertainty estimation
- Technical report on the extension of the proposed model
- Characterisation procedures for the two classes of instruments selected.
- Procedure for uncertainty evaluation.
- Preliminary version of the computing codes with proper documentation.
- Technical report about comparison procedure of test results;
- Technical report about effect on different instrumentation configurations with reference to the environmental effects;
- Technical report about results of the tests carried out.Expected results:
- Technical report on experimental procedures
- Technical report on identification procedures
- Definitive version of the supporting codes for uncertainty.
- Technical report on the validation of the codes.
- Preliminary version of codes for risk evaluation and costs analysis.
- Technical report on the application of the procedure to the first experimental data.- Technical note on model validation
- Technical note on influence parameters and global uncertainty estimation
- Technical note on developed procedures
- Report on the information diffusion policies and on the obtained feedbacks.
- Final standard procedures;
- Report concerning the final standard procedure validation and uncertainty evaluation. <<<

Timescale

24 months

National and international background

Legislation in measurement and in measuring instruments is one of the earliest in existence, because the quality of measurement results conditions for various aspects daily life of citizens in a direct or indirect manner. In all Countries with advanced development have been created therefore Metrology Institutes in charge of guaranteeing the respondance of measurement results to the international metrological regulations managed by the Bureau International des Poids et Mesures.
When, for public interest reasons, a minimal degree of accuracy of measurement is required, the measuring instrument is subjected to legislative requirements that guarantee the minimal degree of performance required, in the working conditions usually predictable.
Whithin the European Community the member States have put in force such legislation much before (1957) the creation of the Community itself. A process of harmonization of these legislations has been therefore necessary, and it has been started in 1971.
The actual legislation on measuring instruments, that comprehends the norm reference (71/316/CEE) and a series of directives of the sector has shown to be lacking from different points of view. For example the specific directives usually contain technical requirements too restrictive, and inadequate to the rapid evolution of measuring techniques. To overcome these inconveniences (see the document COM(2000) 566) the Measuring Instrument Directive (MID) has been prepared, and it is going to be definitively approved.
The Directive operates according to the "new strategy" aiming to establish an internal market of the measuring instruments subjected to legal metrological control, foreseeing:
1) the specification of essential requirements and of requirements relative to the conformity evaluation,
2) the mutual agreement amomng the member States of the results of the conformity evaluation.

The MID inaugurates a completely new view about fulfilment of essential requirements of measuring instruments on the European Market, view characterized by the following points:
- specifications expressed in functional terms, so to leave full freedom to the technical development of instruments;
- wide and articulated sphere of performance
- possibility to proove conformity also in indirect way, using a quality assurance system.
This more open and dynamic approach, explicitly aiming to remove the obstacles to the free circulation of involved products, presents two kinds of challenge:
- at European level, about the harmonization in the application of procedures;
- at national level, about the ability of companies to exploit the new approach in terms of increased competitiveness and, on the side of the Bodies in charge of control, to adopt the new approach with efficiency and efficacy.
At European level the emerging necessities of research have been promptly collected by means of financing three research projects oriented to create the background to realize the harmonization of the required verifications (projects in which Italian presence is almost null).
At a national level it seems useful to sustain with an adequate research activity, the mentioned aspects of competitiveness to gain advantage of the opportunities that open up. It must be considered, in fact , that the MID largely emphasizes and redraws the role of the manufacturer.
The necessary support to the research embraces two fundamental aspects:
- testing ;
- metrological software
To draw briefly the starting scientific basis concerning these two aspects, it can be useful to refer to two recent international events:
- the workshop "Metrology for Regulation and Trade" (2002) for the testing aspects;
- "International Conference on Advanced Mathematical and Computational Tools in Metrology" (2003)for the metrological sofware.
According to the testing, in the mentioned workshop, it has been underlined the criticality of realising a new approach to regulation. Significant news emerge connected to the critic remarks on the progressive application experience on the schemes of crediting of the laboratories, mainly associated to the ISO IEC 17025.
It is particularly relevant the experience gained in the chemical sector, in which the concept of "validated test method" is widely explored. Such concept is nevertheless of general interest and perfectly related to the theme under exam.
As a drawback it is recognized the great amount of work still to be done and in particular it clearly emerges the lack of formalization, in general terms, of the testing procedures.
In particular it will be necessary to develop procedures and tools aiding design, testing and calibration of legal measurement devices, optimizing such procedures in terms of:
- guarantee the verification of all the significative metrological parameters in all the operating conditions under which the instrument can operate. It will be taken into account also of the verification in perspective of the operative life and of the non operating environmental conditions;
- fulfil simplicity and reliability test execution criteria;
- minimization of costs
- respect of generality criteria.
Because of the wideness of commercial trades, legal metrology concerns several measurement instruments: meters for public utility services, scales of retailers, belt weighting machines, filling machines for packed products, taximeters, instruments for the analysis of exhaled, linear measuring instruments, and so on.
In the present research a significant part of the present overview will be covered, compatibly with project development timing. It is proposed therefore to analyze the following classes of instruments: volumetric meters, weighting devices and taximeters.

VOLUMETRIC METERS:

In relation to the water meters, the normative preceding the MID was based on the directive 75/33/CEE, in which were described the metrological, functional and technological characteristics which the meters had to respect. The first and periodical verifies are intended to provide the estimation of the metrological characteristics, and in particular the respect of the maximum allowable errors. When the MID will be effective, the 75/33/CEE will be banned and substituted by the water meters specific part: the attachment MI001. The substantial differences which arise from a comparison between the 75/33/CEE and the MID are: a considerable reduction of the specific requirements, which implies a shorter documentation; a shifting of the attention only on the accuracy requirements; and the fact that the conformity certification is based on the quality systems certification rather than on the metrological verify of every single product.
In this context, the experiments, executed with the task of validating a model, acquire more importance. They have to show the dependence of the metrological characteristics from the environmental condition and from the setup, in order to guarantee the nominal performance for a certain duration. The possibility that products of new conception may come out with a less restrictive normative, makes more urgent the need to define new experiment setup able to put in evidence critical working conditions which were not encountered using traditional instruments.
Many studies have been performed about water flow meters usually not used in commercial transactions, and therefore not subject to legal control. In these studies, the effects of critical disturbance grandezze has been put in evidence.
Another interesting characteristic is the possibility to have diagnostics information from the installed instrumentation. Some previous studies face the problem using the flow signal in turbine meters with diagnostics purpose. The results appear controversial and not conclusive.
Another interesting topic, likely to have attractive developments, consists in the possibility of performing the calibration on the installed meters. This has two positive effects: it is indubitably cheaper to execute the operation in situ, and the advantage of execute the calibration in the real working conditions.

Weighting meters:

The automatic weighting meters machines are very important in this research due to the large number of instruments devices and the economical importance of the related measurements.
Products packaged according to mass or volume criteria, also accordingly to the greater and greater development of the large distribution, are assuming and will assume more and more in the future, an important role. The reasons are the following:
- goods destined to a great number of final user
- goods for which the final user can get rapidly the characteristic information of the product itself

The evaluation of the quantity of the product and the evaluation of the cost is made using devices called weighting machines and/or prizing machines. They are automatic weighting instruments that put on the single articles the label indicating weight and price. It appears thus the importance of a complete and reliable metrological characterization of these machines.
The relevance of these problems appears even more actual if also the automatic gravimetric fillers in industrial field is considered. The filling machines are automatic instruments to weight the containers filled with a mass of pre-evaluated and virtually constant value, of the product in grain form. The filler are composed of one or more automatic feeding device associated with one or more weighting cells, and with the appropriate control and the unloading devices.
The development of reliable, complete procedures for metrological characterization, that might also bring technological advancement is particularly critic because of the evaluation of the thermal and mechanical effects that involve different aspects of the weighting process such as: measurand temperature, environmental temperature, thermal cycles in the instrumentation lifetime, hostile environmental conditions, vibration induced by devices/machines.


The automatic weighting machines are normally used to measure with proper accuracy the weight of food or drink containers (packs or cans) or more generally the weight of hardware elements.
The pharmaceutical and food industries are involved in a continuous process in order to improve the product's quality and the efficiency of the production process. Generally the automatic weighting system is used to weight the containers having weight variable within a large range. The most important requirement that an automatic weighting machine must have are: (1) accuracy; (2) repeatability; (3) readiness; (4) reliability and (5) stability in time. These metrological characteristics are compromised by the disturbances that may be identified mainly in the effects induced by temperature, vibrations, etc. Moreover to obtain load cells stable in time, zero drift, drift of sensitivity and creep must be limited, and these represent some key metrological properties for these kinds of instruments. All these disturbances may compromise the quality of the products and decrease the company's competitiveness.

Taximeter

The working principle of taximeter is based on counting impulse provided by a sensor (i.e Hall effect sensor) which is placed normally on the gear shaft. kilometers and speed are calculated knowing the sensor feature (pulse per round) and the vehicle features as gear and wheel radius. Measures are managed by a data processing system which calculate the tariff and displays it on a screen. The data processing system is most of the time very complex to be implemented.
It is common experience that, even through the same fare, same journey, done with time slightly different may don't have the same cost.
The cost is calculated through a threshold procedure on which the threshold is the speed v=x/t. If the speed is higher than a fixed limit the cost is proportional to the meter of the journey, if the speed is lower than the selected threshold the cost is proportional to the time duration of the journey.
Cost unit, space and time parameters usually change weekly or daily. Modern taximeter are equipped with a radio-calendar which automatically update cost-parameter with no need of manual operations.

Basing on what mentioned above it become evident that different instrumentation, with different accuracy, may calculate , under certain conditions, different cost for same journey.

It should be interesting at this point to introduce a "standard journey" to be applied in laboratory tests to operate test program required by MID. These tests will allow, for different taximeter, to determine the repeatability and accuracy of the selected instrumentation based on the same kilometric distance and time of the journey. Repeatability and accuracy will be used to verify the specific instrumentation requirements on the nominal condition defined by the producer, and to verify if the maximum error is within the expected tolerance bandwidth of time distance, and cost calculation.

Software

Finally, concerning the meteorological software, at this time are well defined validation criteria and are available example of software for particular problems.
International research activities , concerning the uncertainty evaluation, are still ongoing following different approaches.

In this research program, it is proposed the development of a software package to support test which will have to be implemented following MID. This software will identify the measurement uncertainty as requested by the present norms. Moreover the final results will be presented with their statistic dispersion. The last will provide every useful indication about the decision-making-risk and cost preview. <<<