ISO INTERNATIONAL STANDARD 11655 First edition 1995-06-01 Measurement of liquid flow in open channels s - Method of specifying performance of hydrometric equipment Mesurededébitdes liquides dans les canaux decouverts-Méthodede spécificationdes caracteristiques defonctionnement des appareils hydrométriques ISO Reference number ISO 11655:1995(E) ISO11655:1995(E) Contents Page 1 Scope 2 Normative references 3 Definitions Units of measurement 2 4 5 Objectives 2 6 Equipment performance 2 Overallequipmentperformance 7 3 8 Data output formats 5 9 Energy requirement 5 10 User requirements 5 Annex A Recommended checklist 6 ISO1995 Ail rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case Postale 56·CH-1211Geneve 20·Switzerland Printed in Switzerland ii oISO ISO11655:1995(E) Foreword IsO (the International Organization for Standardization) is a worldwide of preparing International Standards is normally carried out throughIsO technical committees. Each member bodyinterested in a subject for whicha technical committeehasbeen established hasthe right tobe represented onthatcommittee.International organizations,governmental and non-governmental,inliaison with IsO, alsotakepart in the work.IsO collaborates closely with the International Electrotechnical Commission (IEC)onallmatters of electrotechnical standardization. circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. ISO/TC113,Hydrometricdeterminations,Subcommittee SC5,Instru- ments,equipmentanddatamanagement. Annex A of this International Standard is for information only ili @ISO ISO11655:1995(E) Introduction ThisInternationalStandardcontainsrecommendationsforamethodof specifying the performance of equipment used for the sensing.measuring and, as appropriate,recording of physical variables related to measure- ment of liquid flow in open channels. requires the conversion of a time-related physical event or state into a numericalexpressionintermsrelativetoastandardscaleofmeasurement units. The steps in the conversion are the following: adaptation or conversion (as the individual situation requires) of the (e determination canbemade; b) if necessary,identification of a surrogate parameter and the estab lishment of the relation between changes in that parameter value and changesinthephenomenontobemeasured; c) sensing. measurement and (if appropriate) recording of the physical phenomenon or its surrogate as it varies with the passage of time; d) conversion of sampled data into numerical information. The ultimate measure of equipment performance is the evaluation of the uncertainty with whichthe equipment converts the absolute value or level of the hydrological variable into a measured quantity, relative to another arbitrary or fixed reference datum. The suitability of a piece of equipment, however, mayalso berelated to the particular method of measurement and to the measurement frequency. The nature of the uncertainty is closely related to the physical method or principle employed in the process of conversion from the natural variable to the measured quantity. Different physical systems are affected to dif- fering degrees by such factors as: - intrinsic design of the equipment; calibration methods; natural environmental factors; man-madeenvironmentalfactors; levels of care and maintenance; operator methods and skills. iv oISO ISO11655:1995(E) The user should seek to identify the three fundamental factors which may affect the uncertainty: these, which should be objectively defined from study of the method of measurement, are: a) the level of uncertainty of each individual measurement due to the principle of operation of the measurement equipment; (g