Understanding the Concept Metrology
Metrology may be divided into three different branches: Scientific Metrology, Technical Metrology and Legal Metrology.
Scientific metrology deals with the realization of measurement standards for individual measurable quantities and the development of new methods of measurement.
Technical metrology is occupied with the measurement of individual measurable quantities, the development of measurement instruments and measurement techniques.
Legal metrology is the part of metrology that is governed by regulations in order to ensure the accuracy and uniformity of measurements, especially when there is a possible conflict of interest, or when inaccurate measurement results may have damaging consequences for the individual or for society.
The Law on metrology (Official Gazette no. 11/94) regulates the field of metrology in the Republic of Croatia. The enforcement as well as the supervision of enforcement lies within the responsibility of the State Office for Standardization and Metrology (DZNM).
The fundamental objective of metrology is to ensure traceability as an essential precondition for the comparison of measurement results. The tasks of legal metrology are carried out by calibration of measurement standards and by testing the accuracy of measuring instruments. The testing of the accuracy of measuring instruments consists of the following procedures:
type-examination, verification, and assessment of conformity of measuring instruments to specific metrological requirements and declarations.
Type-Examination of Measuring Instrument
Type-examination of measuring instruments is regulated by the Regulation on the performance of type-examination of measuring instruments (Official Gazette no. 93/96). The manufacturer or the distributor of the measuring instrument is obligated to lodge an application for type examination with the State Office for Standardization and Metrology (DZNM), prior to placing the measuring instrument on the market.
If the examined type of measuring instrument meets the relevant metrological requirements, the State Office for Standardization and Metrology issues for this type of measuring instrument a pattern approval. Based on the pattern approval the measuring instrument may be manufactured, distributed or used in the field of legal metrology. An approved instrument, complying with the requirements applicable to it, gets a due approval mark (e.g. Non-automatic weighing machines, accuracy class III) carry the approval identity mark HR M-3-x, where x stands for a yearly running number.
Measuring instruments carrying type approval identity marks may be manufactured, imported or placed on the market as well as used in the field of legal metrology.
Accuracy Testing if Measuring Instrument
All measuring instruments, which are used in the field of legal metrology, are subject to mandatory metrology control. The fields of operation in which metrology control of measuring instruments is mandatory are determined by the Ordinance on the category of measuring instruments subject to metrology control.
Measuring control is non-mandatory for measuring instruments used for the purpose of technology process control, scientific and development research, the process of education, for exhibition purposes or for private use only. In order to establish the accuracy of measurement of such a measuring instrument its owner may apply for assessment of conformity to be carried out in order to test for conformity with the manufacturer’s declaration, a relevant standard or with the applicable metrological requirements.
Initial Verification and Re-verification of Measuring Instruments
All instruments used in the field of legal metrology have to be marked with a valid verification label or verification seal. Appropriate testing of each individual measuring instrument has to be performed, before they are brought into use. If the measuring instrument complies with the requirements referred to in the pattern approval, the verification seal is stamped or affixed on the instrument as a sticker (label), thus indicating the reliability of the measuring instrument.
Initial verification is carried out under the responsibility of the manufacturer or distributor of the measuring instrument or the authorized foreign firm representative when the measuring instrument is placed on the market from the consignment stock.
The validity of the verification is limited to a certain period of time. The reverification periods are stipulated by Ordinance on the determination of intervals for reverification of standards and measuring instruments (Official Gazette no. 50/96).
Weights of classes E1, E2, F1, F2, M1, M2, M3 as well as non-automatic weighing machines meeting accuracy class I, II and III and maximum weight up to 9000 kg have to be submitted for reverification every two years. Water meters intended for the metering of cold water with volumetric flow rate up to 10 m3/h every five years, gas meters every eight to sixteen years, electricity meters every four to 16 years, etc.
The owner of the measuring instrument has to pay attention that reverification of the measuring instrument is always carried out in time. The means of carrying out reverification are provided by the Sectors for metrology control, located in Rijeka, Zagreb, Split and Osijek, the temporary measuring instruments verification centers, the accredited metrology laboratories, the certified metrology laboratories or at the installation site of the measuring instruments.
The Sectors for metrology control in close co-operation with the market inspection organizes periodical verification of measuring instruments in larger municipal centers. By verifying the measuring instrument at a temporary verification center, the customers save themselves considerable time and expenses.
The measuring instrument has to be cleaned and made ready for testing. Those measuring instruments, which have been repaired by a service technician whose metrology laboratory has been certified, are verified by the authorized staff members, in the premises of the Sector for metrology control.
The application for the verification of these measuring instruments in a certified metrology laboratory has to be lodged by the service technician. Accredited metrology laboratories perform verification tasks under the same conditions as the Sectors for metrology control for those categories of measuring instruments they have been authorized for by the State Office for Standardization and Metrology. For build in measuring instruments the application for verification has to be submitted by the owner.
Verification of this kind of measuring instruments is performed on-site by authorized staff members of the Sector for metrology control. This also applies to highly sensitive measuring instruments as for example analytical weighing instruments.
The owner of measuring instruments has to provide auxiliary work force and measuring equipment for testing. The fees and expenses in the verification procedure have been fixed by the Ordinance concerning the amount of fees and modes of payment intended to cover the expenses for type examination of measuring instruments, the testing of standards, reference material samples and measuring instruments (Official Gazette no. 49/92).
Verification of measuring instruments in the premises of the Sectors of metrology control is performed every day. In order to save time it is recommended to make an appointment in advance.
Conformity Assessment of Measuring Instruments
Accredited and certified metrology laboratories carry out conformity assessment of measuring instruments. For some measuring instruments the laboratories of the Department for metrology control carry out assessment of conformity.
Conformity assessment of measuring instruments is not provided under the law. The owner of the measuring instrument applying for conformity assessment has to specify in its application the documents in relation to which he would like to have the conformity of the measuring instrument checked (manufacturer’s declaration, standard, metrological requirement, etc.).
In case the measuring instrument meets subject requirements it will be equipped with the following label.
For the issuance of the declaration of conformity a supplementary request has to be filed. The owner as evidence of his approved quality assurance system requires subject declaration.