INTERNATIONAL OIML D 33 DOCUMENT Edition 2019 (E) Reference standard liquids (Newtonian viscosity standard for the calibration and verification of viscometers) Liquides de référence (étalon de viscosité newtonien pour l'étalonnage et la vérification des viscosimètres) ) E ( 9 1 0 2 n ORGANISATION INTERNATIONALE o i t i d E DE MÉTROLOGIE LÉGALE 3 3 D L INTERNATIONAL ORGANIZATION M I O OF LEGAL METROLOGY OIML D 33:2019 (E) Contents Foreword ...................................................................................................................................................... 4 1 Scope and field of application ..................................................................................................... 5 2 Terms and definitions .................................................................................................................. 5 2.1 Newtonian reference liquids (RL) ..................................................................................... 5 2.2 Newtonian viscosity standard specimen (VSS) ................................................................ 5 3 Units of measurement .................................................................................................................. 5 4 Metrological requirements ......................................................................................................... 6 5 Technical requirements for reference liquids ........................................................................... 6 6 Storage .......................................................................................................................................... 7 7 Viscosity gradation of reference liquids, preparation of mixtures .......................................... 7 8 Metrological control for reference liquids ................................................................................. 8 8.1 Long-term stability ............................................................................................................ 8 8.2 Thermal stability ............................................................................................................... 8 8.3 Newtonian flow behaviour ................................................................................................ 9 9 Test method and model test report: calibration of the Newtonian viscosity standard .......... 9 9.1 Measurement of kinematic viscosity ................................................................................. 9 9.2 Calculation of the kinematic viscosity ............................................................................ 10 9.3 Measurement of density, calculation of dynamic viscosity ............................................ 10 9.4 Determination of the temperature coefficient of viscosity .............................................. 11 9.5 Measurement uncertainty ................................................................................................ 11 9.6 Calibration certificate ...................................................................................................... 12 10 References .................................................................................................................................. 13 Annex A Examples of liquids which are commonly used as reference liquids .................................... 14 Annex B Examples of mixing equations .................................................................................................. 15 Annex C Example of determination of the temperature coefficient of viscosity ................................. 16 Annex D Example for the calculation of the uncertainty of measurement for the viscosity of Newtonian viscosity standard ................................................................................................... 17 Annex E Example for the calibration certificate for viscosity reference standard ............................ 19 3 OIML D 33:2019 (E) Foreword The International Organisation of Legal Metrology (OIML) is a worldwide, intergovernmental organisation whose primary aim is to harmonise the regulations and metrological controls applied by the national metrological services, or related organisations, of its Member States. The main categories of OIML publications are: . International Recommendations (OIML R), which are model regulations that establish the metrological characteristics required of certain measuring instruments and which specify methods and equipment for checking their conformity. OIML Member States shall implement these Recommendations to the greatest possible extent; . International Documents (OIML D), which are informative in nature and which are intended to harmonise and improve work in the field of legal metrology; . International Guides (OIML G), which are also informative in nature and which are intended to give guidelines for the application of certain requirements to legal metrology; and . International Basic Publications (OIML B), which define the operating rules of the various OIML structures and systems. OIML Draft Recommendations, Documents and Guides are developed by Project Groups linked to Technical Committees or Subcommittees which comprise representatives from the Member States. Certain international and regional institutions also participate on a consultation basis. Cooperative agreements have been established between the OIML and certain institutions, such as ISO and the IEC, with the objective of avoiding contradictory requirements. Consequently, manufacturers and users of measuring instruments, test laboratories, etc. may simultaneously apply OIML publications and those of other institutions. International Recommendations, Documents, Guides and Basic Publications are published in English (E) and translated into French (F) and are subject to periodic revision. Additionally, the OIML publishes or participates in the publication of Vocabularies (OIML V) and periodically commissions legal metrology experts to write Expert Reports (OIML E). Expert Reports are intended to provide information and advice, and are written solely from the viewpoint of their author, without the involvement of a Technical Committee or Subcommittee, nor that of the CIML. Thus, they do not necessarily represent the views of the OIML. This publication – reference OIML D 33, edition 2019 (E) – was developed by Project Group 1 of OIML Technical Subcommittee TC 17/SC 5 Viscosimetry. It was approved for final publication by the International Committee of Legal Metrology at its 54th meeting in 2019 and will be submitted to the International Conference on Legal Metrology in 2020 for formal sanction. OIML Publications may be downloaded from the OIML website in the form of PDF files. Additional information on OIML Publications may be obtained from the Organisation’s headquarters: Bureau International de Métrologie Légale 11, rue Turgot – 75009 Paris – France Telephone: 33 (0)1 48 78 12 82 Fax: 33 (0)1 42 82 17 27 E-mail: [email protected] Internet: www.oiml.org 4 OIML D 33:2019 (E) Reference standard liquids (Newtonian viscosity standard for the calibration and verification of viscometers) 1 Scope and field of application This International Document specifies requirements for liquids used for the preparation and calibration of Newtonian viscosity standard specimens (reference standard liquids), according to OIML D 17 [1]. Newtonian viscosity standard specimens are used for the calibration or verification of reference standard viscometers, working standard viscometers or ordinary viscometers and other viscosity measuring devices. For viscosity measurements of Newtonian liquids, instruments calibrated or verified by means of these viscosity standard specimens are accepted in accordance with national standards of viscosity according to ISO/IEC 17025:2017 [2]. 2 Terms and definitions This Document uses the following general terms and definitions. 2.1 Newtonian reference liquids (RL) liquid in which the shear rate is proportional to the shear stress during a viscous flow Note: The ratio of the shear stress to the shear rate is the dynamic viscosity of the liquid, according to Newton’s Law of Viscosity. The kinematic viscosity is the ratio of the dynamic viscosity to the density of the liquid. 2.2 Newtonian viscosity standard specimen (VSS) Newtonian liquid sufficiently homogeneous and stable with respect to viscosity (dynamic and kinematic) which has been determined traceable to international or national measurement standards, by a metrologically valid procedure, and is documented in a calibration certificate together with the associated uncertainty, and a statement of metrological traceability 3 Units of measurement The SI unit of kinematic viscosity (ν) is m2⋅s-1. For practical use, a submultiple (mm2⋅s-1) is more convenient. The SI unit of dynamic viscosity (η) is Pa⋅s. For practical use, a submultiple (mPa⋅s) is more convenient [3]. 5 OIML D 33:2019 (E) 4 Metrological requirements The range of dynamic viscosity covered by Newtonian viscosity standard specimens ranges from about 4 × 10-1 mPa·s to 105 mPa·s at 20 °C. This corresponds to kinematic viscosities between about 4 × 10-1 mm2·s-1 and 1 × 105 mm2·s-1. Standard specimens may be calibrated and used at various temperatures (usually between –40 °C and +150 °C) and atmospheric pressure. Samples of the same RL may be qualified as reference and working VSS, depending on the class of standard viscometer used for calibration (see OIML D 17 [1]). From the viscosity values ν1 and ν2 determined