1、BRITISH STANDARD BS ISO 9213:2004 Measurement of total discharge in open channels Electromagnetic method using a full-channel-width coil ICS 17.120.20 BS ISO 9213:2004 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 23 March 2004 BSI 23 March
2、 2004 ISBN 0 580 45658 7 National foreword This British Standard reproduces verbatim ISO 9213:2004 and implements it as the UK national standard. It supersedes BS 3680-3H:1993 which is withdrawn. The UK participation in its preparation was entrusted by Technical Committee CPI/113, Hydrometry, to Sub
3、committee CPI/113/1, Velocity-area methods, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may be fou
4、nd in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are resp
5、onsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep
6、the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to iv, pages 1 to 19 and a back cover. The BSI copyright notice displayed in t
7、his document indicates when the document was last issued. Amendments issued since publication Amd. No. Date CommentsINTERNATIONAL STANDARD ISO 9213 Second edition 2004-04-01 Reference number ISO 9213:2004(E) OSI 2004 Measurement of total discharge in open channels Electromagnetic method using a full
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13、e 22 14 + 10 947 11 Fxa + 22 14 0 94774 9 Eam-il ocpyrithgios.ogr Web wwwi.soo.rg BSISO9213:2004OSI 1294002:3)E( ISO 4002 r llAithgs reservde iii Contents Page 1 Scope 1 2 Normative references 1 3 Terms and definitions 1 4 Principles of operation and practice 1 5 Applications . 5 6 Selection of site
14、 . 6 7 Design and construction . 6 8 Uncertainties in flow measurement . 12 9 Gauge calibration and verification . 13 Annex A (informative) Site survey for electrical interference . 14 Annex B (informative) Design aspects of the electromagnetic coil . 15 Annex C (informative) Numerical example of th
15、e calculation of uncertainty . 16 Annex D (normative) Gauge calibration procedure 17 Bibliography . 19 BSISO9213:2004ISO :3129(4002)E iv ISO 4002 All rithgs reresvde Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member b
16、odies). The work of preparing International Standards is normally carried out through ISO technical committees. Each 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 a
17、nd non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives
18、, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards 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 ca
19、sting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 9213 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 1,
20、 Velocity area methods. This second edition cancels and replaces the first edition (ISO 9213:1992), which has been technically revised. BSISO9213:2004ANRETNIITOTS LANDNADRA OSI 1294002:3)E( ISO 4002 r llAithgs reservde 1 Measurement of total discharge in open channels Electromagnetic method using a
21、full-channel-width coil 1S c o p e This International Standard specifies procedures for the establishment and operation of a gauging station, equipped with an electromagnetic flow meter, in an open channel or a closed conduit with a free water surface. This International Standard is applicable to co
22、nfigurations where an artificial magnetic field is generated through which the entire body of water flows. The induced voltage is sensed in such a way that all elements of the moving water contribute. The equipment described normally requires an electrical mains power supply. This International Stan
23、dard is not applicable to devices sampling only part of the flowing body of water (e.g. velocity meters) or to flow meters which operate by using the Earths magnetic field. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated ref
24、erences, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 748, Measurement of liquid flow in open channels Velocity-area methods ISO 772, Hydrometric determinations Vocabulary and symbols ISO 1100-2, Measure
25、ment of liquid flow in open channels Part 2: Determination of the stage-discharge relation ISO 5168: 1) , Measurement of fluid flow Evaluation of uncertainties ISO/TR 7066-1, Assessment of uncertainty in calibration and use of flow measurement devices Part 1: Linear calibration relationships 3 Terms
26、 and definitions For the purposes of this document, the terms and definitions given in ISO 772 apply. 4 Principles of operation and practice 4.1 This is a velocity-area method of discharge determination. The electromagnetic gauge operates on Faradays principle of electromagnetic induction. If a leng
27、th of conductor moves through a magnetic field, a voltage is generated between the ends of the conductor. In the electromagnetic gauge, a vertical magnetic field is generated by means of an insulated coil which is located either above or beneath the channel. The conductor is formed by the water whic
28、h moves through the magnetic field; the ends of the conductor are represented by the channel walls or riverbanks. The voltage generated is sensed by electrodes on the channel extremities and these are connected to the input of a sensitive voltage-measuring device. The faster the velocity of the wate
29、r, the greater is the voltage which is generated. 1) To be published. (Revision of ISO/TR 5168:1998) BSISO9213:2004ISO :3129(4002)E 2 ISO 4002 All rithgs reresvde 4.2 The principle is widely applied to flow meters in circular pipes running full and in this case approximate formulae may be generated
30、theoretically and refinement made by calibration through factory produced models. The open channel flow meter however does not lend itself to such treatment and hence in situ calibration is always necessary. 4.3 Bevirs formula for the potential generated between electrodes placed in a body of conduc
31、ting fluid moving in a magnetic field is given by Equation (1) and illustrated in Figure 1. (1) where is the potential between the electrodes; is the vector magnetic induction; is the vector virtual current between the electrodes; is the vector velocity function; is an element of volume. This involv
32、es integration between the electrodes over the entire space occupied by the fluid. In practice, the general case is not solvable since the spatial functions are unknown or difficult to determine. In the simple case of a rectangular horizontal channel of width , expressed in metres, with water flowin
33、g with a mean velocity , expressed in metres per second, in a uniform vertical magnetic field , expressed in amperes per metre, the induced potential , expressed in microvolts, is measured at electrodes at the sides and is calculated using Equation (2). (2) Key 1e l e c t r o d e Figure 1 Illustrati
34、on of Bevirs formula E= Bjvd E B j v d wv H E EvwH BSISO9213:2004OSI 1294002:3)E( ISO 4002 r llAithgs reservde 3 where is the magnetic permeability of the fluid. In practice, numerically, 4.4 In this simple case, if the water depth is metres, the flow , expressed in cubic metres per second, is given
35、 by the following equation: If the field is produced by an electromagnet in the form of an arrangement of coil(s), then for a given situation,is proportional to the electrical current , expressed in amperes, in the coil. Therefore where is a constant. In practice, this is an oversimplification and a
36、 more generally applicable form of the flow formula, taking account of non-uniformities, is where is a polynomial function of . Usually, a close approximation is obtained where the polynomial is a quadratic, i.e. (3) 4.5 However, there is a sensitivity to non-uniform velocity distribution in the pre
37、sence of non-uniformities in other parameters. Though the mathematical treatment is complex, for the purposes of this International Standard, it may be stated that if the vertical magnetic field is not uniform then changes to the velocity profile for given flow and depth values will produce an appar
38、ent change in the measured induced voltage. This will have the effect of producing an uncertainty in the flow value determined by the flow meter. The designer of the flow meter should strive to produce a vertical magnetic field as uniform as possible to minimize this uncertainty. A single coil above
39、 or below a channel may be sufficient if it is wide compared with the depth of water. Alternatively, better uniformity may be obtained by “saddle-shaped” coils or a pair of coils deployed above and below the channel. The design of coil systems is not covered in this International Standard although s
40、ome design considerations are given in Annex B. 4.6 With most channels, the material comprising the bed and sides will have an electrical conductivity which cannot be ignored compared with that of the water flowing in the channel (even if the material is concrete). The apparent induced potential is
41、thus reduced in the same way that voltage at the terminals of a battery is less if measured whilst a load is connected. Though attempts have been made to determine the effect and allow for it, these have generally proved unsuccessful. The recommendation is always to line the channel with an electric
42、ally insulating material which substantially removes the conduction path through the channel material (see 7.2.3). Depending on the material used for lining the channel, some form of protection is often required to prevent physical damage by debris being transported along the channel by the flowing
43、water. This protective layer is usually concrete and this itself will have a conductivity when wet which may be different from that of the water. The effect of this is much the same as a layer of silt which may settle on the bed and is described in 4.7. H =B/ E =vwH dq q=vwd=Ed/H H HI q=KEd/I K q=KE
44、f(d)/I f(d) d q= (E/I) (K 1 +K 2 d+K 3 d 2 ) BSISO9213:2004ISO :3129(4002)E 4 ISO 4002 All rithgs reresvde 4.7 A layer of silt settling on the bed (or the protective layer described in 4.6) may have an effect on the induced voltage and hence the flow calculated by the flow meter. Assuming the magnet
45、ic field is fairly uniform then the effect described in 4.5 is negligible. If the wet silt has a similar conductivity to that of the water, it will be seen as a non-moving (or slowly moving) layer of water. This is similar to a step change in velocity profile and the flow meter should be programmed
46、with an effective bed level beneath the silt (at the level of the insulating liner). If, however, the layer has a very low conductivity (packed clay for example), it will behave like an extension of the liner. In this case, the flow meter should be programmed with an effective bed position at the to
47、p of the silt. In practice the effective bed level should be taken as the level of the insulating liner. However, sometimes an offset ( ) to the depth ( ) measured from the surface to the liner should be applied. will depend on the thickness and conductive properties of the silt and will have a valu
48、e between zero and the thickness of the silt.is obtained by calibration. It is possible, due to thickness or conductivity variations, that the offset may not be constant and this is a source of uncertainty (see Clause 8). 4.8 The value of induced voltage in a practical application is generally in th
49、e range of a few tens to hundreds of microvolts. In comparison, the electrodes will be subject to various other effects which produce voltages unrelated to the flow-induced signal. These interfering voltages (or noise) will have different magnitudes and frequencies and may be far greater than the induced voltage. Table 1 gives some indication of the magnitude and frequency of sources of interference that ar
