1、BRITISH STANDARDBS EN ISO 748:2007Hydrometry Measurement of liquid flow in open channels using current-meters or floatsThe European Standard EN ISO 748:2007 has the status of a British StandardICS 17.120.20g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g4
2、9g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN ISO 748:2007This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 November 2007 BSI 2007ISBN 978 0 580 54670 9National forewordThis B
3、ritish Standard is the UK implementation of EN ISO 748:2007. It supersedes BS EN ISO 748:2000 which is withdrawn.The UK participation in its preparation was entrusted by Technical Committee CPI/113, Hydrometry, to Subcommittee CPI/113/1, Velocity area methods.A list of organizations represented on t
4、his committee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.Amendments issued sinc
5、e publicationAmd. No. Date CommentsEUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMEN ISO 748October 2007ICS 17.120.20 Supersedes EN ISO 748:2000 English VersionHydrometry - Measurement of liquid flow in open channels usingcurrent-meters or floats (ISO 748:2007)Hydromtrie - Mesurage du dbit des liqui
6、des dans lescanaux dcouverts au moyen de dbitmtres ou deflotteurs (ISO 748:2007)Hydrometrie - Durchflussmessung in offenen Gerinnenmittels Fliegeschwindigkeitsmessgerten oderSchwimmern (ISO 748:2007)This European Standard was approved by CEN on 21 September 2007.CEN members are bound to comply with
7、the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre
8、 or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial ver
9、sions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spa
10、in, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brussels 2007 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Memb
11、ers.Ref. No. EN ISO 748:2007: EForeword This document (EN ISO 748:2007) has been prepared by Technical Committee ISO/TC 113 “Hydrometric determinations“ in collaboration with Technical Committee CEN/TC 318 “Hydrometry” the secretariat of which is held by BSI. This European Standard shall be given th
12、e status of a national standard, either by publication of an identical text or by endorsement, at the latest by April 2008, and conflicting national standards shall be withdrawn at the latest by April 2008. This document supersedes EN ISO 748:2000. According to the CEN/CENELEC Internal Regulations,
13、the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands,
14、Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of ISO 748:2007 has been approved by CEN as a EN ISO 748:2007 without any modification. EN ISO 748:2007Reference numberISO 748:2007(E)INTERNATIONAL STANDARD ISO748Fou
15、rth edition2007-10-15Hydrometry Measurement of liquid flow in open channels using current-meters or floats Hydromtrie Mesurage du dbit des liquides dans les canaux dcouverts au moyen de dbitmtres ou de flotteurs EN ISO 748:2007ii iiiContents Page Foreword. v 1 Scope . 1 2 Normative references . 1 3
16、Terms and definitions. 1 4 Principle of the methods of measurements. 1 5 Selection and demarcation of site 2 5.1 Selection of site 2 5.2 Demarcation of site. 3 6 Measurement of cross-sectional area 3 6.1 General. 3 6.2 Measurement of width 3 6.3 Measurement of depth 4 7 Measurement of velocity 5 7.1
17、 Measurement of velocity using current-meters. 5 7.1.1 Rotating-element current-meters 5 7.1.2 Electromagnetic current-meters . 5 7.1.3 Measurement procedure 5 7.1.4 Oblique flow 6 7.1.5 Determination of the mean velocity in a vertical . 7 7.1.6 Errors and limitations. 10 7.2 Measurement of velocity
18、 using floats. 11 7.2.1 General. 11 7.2.2 Selection of site 11 7.2.3 Measuring procedure . 11 7.2.4 Types of float. 11 7.2.5 Determination of velocity. 12 7.2.6 Main sources of error . 13 8 Computation of discharge . 13 8.1 General. 13 8.2 Graphical method . 13 8.2.1 Depth-velocity-integration . 13
19、8.2.2 Velocity-area integration method (velocity-contour method) 14 8.3 Arithmetic methods 16 8.3.1 Mean-section method. 16 8.3.2 Mid-section method 16 8.4 Independent vertical method. 17 8.5 Mean-section method Horizontal planes . 20 8.6 Determination of discharge from surface-float velocity measur
20、ements 20 8.7 Determination of discharge for variations of water level . 22 8.7.1 General. 22 8.7.2 Computation of discharge . 22 8.7.3 Computation of mean water level . 22 9 Uncertainties in flow measurement 23 9.1 General. 23 9.2 Definition of uncertainty. 23 9.3 Method of calculating the uncertai
21、nty in discharge by measurement of velocity by current-meter. 24 9.3.1 General. 24 EN ISO 748:2007iv 9.3.2 Contributory uncertainties. 24 9.3.3 Example 26 9.3.4 Combined uncertainty 26 9.4 Method of calculating the uncertainty in discharge by measurement of velocity using floats. 27 9.4.1 General .
22、27 9.4.2 Contributory uncertainties. 27 9.4.3 Combined uncertainty in discharge 28 9.4.4 Example 28 Annex A (informative) Correction for sag, pull, slope and temperature in measurement of cross-section width by tape or wire. 30 Annex B (informative) Distance measurement across the cross-section 33 A
23、nnex C (informative) Corrections for wetted length of wire when measuring depths with wire not normal to surface 36 Annex D (informative) Correction for drift . 39 Annex E (informative) Uncertainties in the velocity-area measurement. 40 Annex F (informative) Determination of mean velocity from float
24、 measurements 44 Bibliography . 46 EN ISO 748:2007vForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Eac
25、h member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the Internation
26、al Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standard
27、s adopted by the technical committees are 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. Attention is drawn to the possibility that some of the elements of this document may be the subject o
28、f patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 748 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 1, Velocity area methods. This fourth edition cancels and replaces the third edition (ISO 748:1997), which has been te
29、chnically revised. EN ISO 748:2007blank1Hydrometry Measurement of liquid flow in open channels using current-meters or floats 1 Scope This International Standard specifies methods for determining the velocity and cross-sectional area of water flowing in open channels without ice cover, and for compu
30、ting the discharge therefrom. It covers methods of employing current-meters or floats to measure the velocities. It should be noted that although, in some cases, these measurements are intended to determine the stage-discharge relation of a gauging station, this International Standard deals only wit
31、h single measurements of the discharge; the continuous recording of discharges over a period of time is covered in ISO 1100-1 and ISO 1100-2. NOTE The methods for determining the velocity and cross-sectional area of water flowing in open channels with ice cover are specified in ISO 9196. 2 Normative
32、 references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 772, Hydrometric determinations V
33、ocabulary and symbols ISO 1088, Hydrometry Velocity-area methods using current-meters Collection and processing of data for determination of uncertainties in flow measurement ISO 2537, Hydrometry Rotating-element current-meters ISO 3455, Hydrometry Calibration of current-meters in straight open tank
34、s ISO/TS 15768, Measurement of liquid velocity in open channels Design, selection and use of electromagnetic current meters 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 772 apply. 4 Principle of the methods of measurements 4.1 The principle of the
35、se methods consists of determining velocity and cross-sectional area. A measuring site is chosen conforming to the specified requirements (see Clause 5); the width, depending on its magnitude, is measured either by means of steel tape or by some other surveying method, and the depth is measured at a
36、 number of points (known as verticals) across the width, sufficient to determine the shape and area of the cross-section (see Clause 6). EN ISO 748:20072 Velocity observations using current-meters are made at each vertical preferably at the same time as measurement of depth, especially in the case o
37、f unstable beds (see 7.1.5). Velocity observations can also be made using surface floats or velocity-rods (see 7.2). 4.2 The discharge is computed either arithmetically or graphically by summing the products of the velocity and corresponding area for a series of observations in a cross-section. If u
38、nit width discharge is required, it is generally computed from the individual observations at each measurement vertical. 5 Selection and demarcation of site 5.1 Selection of site The site selected should comply as far as possible with the following requirements. a) The channel at the measuring site
39、should be straight and of uniform cross-section and slope in order to minimize abnormal velocity distribution. When the length of the channel is restricted, it is recommended for current-meter measurements that the straight length upstream should be at least twice that downstream. b) Flow directions
40、 for all points on any vertical across the width should be parallel to one another and at right angles to the measurement section. c) The bed and margins of the channels should be stable and well defined at all stages of flow in order to facilitate accurate measurement of the cross-section and ensur
41、e uniformity of conditions during and between discharge measurements. d) The curves of the distribution of velocities should be regular in the vertical and horizontal planes of measurement. e) Conditions at the section and in its vicinity should also be such as to preclude changes taking place in th
42、e velocity distribution during the period of measurement. f) Sites displaying vortices, reverse flow or dead water should be avoided. g) The measurement section should be clearly visible across its width and unobstructed by trees, aquatic growth or other obstacles. h) Measurement of flow from bridge
43、s can be a convenient and sometimes safer way of sampling width, depth and velocity. When gauging from a bridge with divide piers, each section of the channel should be measured separately. Particular care should be taken in determining the velocity distribution when bridge apertures are surcharged
44、or obstructed. i) The depth of water at the section should be sufficient at all stages to provide for the effective immersion of the current-meter or float, whichever is to be used. j) If the site is to be established as a permanent station, it should be easily accessible at all times with all neces
45、sary measurement equipment. k) The section should be sited away from pumps, sluices and outfalls, if their operation during a measurement is likely to create unsteady flow conditions. l) Sites where there is converging or diverging flow should be avoided. m) In those instances where it is necessary
46、to make measurements in the vicinity of a bridge, it is preferable that the measuring site be upstream of the bridge. However, in certain cases and where accumulation of ice, logs or debris is liable to occur, it is acceptable that the measuring site be downstream of the bridge. EN ISO 748:20073n) T
47、he measurement of flow under ice cover is dealt with in ISO 9196. For streams subject to formation of ice cover, the requirements of measurement specified in this International Standard can be used during the free water season. o) It may, under certain conditions of river flow or level, prove necess
48、ary to carry out current-meter measurements on sections other than the original chosen location. This is quite acceptable if there are no substantial unmeasured losses or gains to the river in the intervening reach and so long as all flow measurements can be related to any stage value recorded at th
49、e principal reference section. 5.2 Demarcation of site 5.2.1 If the site is to be established as a permanent station or likely to be used frequently for future measurement, it should be provided with means for demarcation of the cross-section and for determination of stage. Where the site is used only once, or infrequently, and there are no means of determining stage values on site, care should be taken to ensure that the water level and/or flow do not change significantly during the measurement period. 5.2.2 The position of each cross-section, nor
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