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.<\/p>\n
This International Standard is applicable to configurations 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.<\/p>\n
This International Standard 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 Earth’s magnetic field.<\/p>\n
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| 3<\/td>\n | TitlePage – Measurement of total discharge in open channels\ufffd\u2014 Electromagnetic method using a full… <\/td>\n<\/tr>\n | ||||||
| 5<\/td>\n | TableofContent – Contents Page <\/td>\n<\/tr>\n | ||||||
| 6<\/td>\n | Foreword – Foreword <\/td>\n<\/tr>\n | ||||||
| 7<\/td>\n | Scope – 1\ufffd\ufffd\ufffd Scope NormativeReference – 2\ufffd\ufffd\ufffd Normative references Clause1 – 4\ufffd\ufffd\ufffd Principles of operation and practice UntitledSubclause2 – 4.1\ufffd\ufffd\ufffd This is a velocity-area method of discharge determination. The electr… <\/td>\n<\/tr>\n | ||||||
| 8<\/td>\n | UntitledSubclause2 – 4.2\ufffd\ufffd\ufffd The principle is widely applied to flow meters in circular pipes runn… UntitledSubclause2 – 4.3\ufffd\ufffd\ufffd Bevir’s formula for the potential generated between electrodes placed… <\/td>\n<\/tr>\n | ||||||
| 9<\/td>\n | UntitledSubclause2 – 4.4\ufffd\ufffd\ufffd In this simple case, if the water depth is UntitledSubclause2 – 4.5\ufffd\ufffd\ufffd However, there is a sensitivity to non-uniform velocity distribution … UntitledSubclause2 – 4.6\ufffd\ufffd\ufffd With most channels, the material comprising the bed and sides will ha… <\/td>\n<\/tr>\n | ||||||
| 10<\/td>\n | UntitledSubclause2 – 4.7\ufffd\ufffd\ufffd A layer of silt settling on the bed (or the protective layer describe… UntitledSubclause2 – 4.8\ufffd\ufffd\ufffd The value of induced voltage in a practical application is generally … UntitledSubclause2 – 4.9\ufffd\ufffd\ufffd Since the coil current is alternating, the possibility exists of elec… <\/td>\n<\/tr>\n | ||||||
| 11<\/td>\n | UntitledSubclause2 – 4.10\ufffd\ufffd\ufffd From Clause1 – 5\ufffd\ufffd\ufffd Applications UntitledSubclause2 – 5.1\ufffd\ufffd\ufffd The electromagnetic gauge is particularly suited to the measurement o… UntitledSubclause2 – 5.2\ufffd\ufffd\ufffd Different versions of the electromagnetic gauge are suitable for meas… UntitledSubclause2 – 5.3\ufffd\ufffd\ufffd The advantages of the method include the following: <\/td>\n<\/tr>\n | ||||||
| 12<\/td>\n | UntitledSubclause2 – 5.4\ufffd\ufffd\ufffd There are however some disadvantages associated with the method, such as Clause1 – 6\ufffd\ufffd\ufffd Selection of site UntitledSubclause2 – 6.1\ufffd\ufffd\ufffd A site survey should be carried out if necessary as outlined in UntitledSubclause2 – 6.2\ufffd\ufffd\ufffd Owing to the high power consumption of the coil, equipment intended t… UntitledSubclause2 – 6.3\ufffd\ufffd\ufffd The site shall afford adequate on-bank working space for handling the… UntitledSubclause2 – 6.4\ufffd\ufffd\ufffd The site characteristics shall be such that the calibration of the st… UntitledSubclause2 – 6.5\ufffd\ufffd\ufffd Sites shall be selected where there is no spatial variation in water … Clause1 – 7\ufffd\ufffd\ufffd Design and construction Subclause2 – 7.1\ufffd\ufffd\ufffd General <\/td>\n<\/tr>\n | ||||||
| 14<\/td>\n | Subclause2 – 7.2\ufffd\ufffd\ufffd System equipment Subclause3 – 7.2.1\ufffd\ufffd\ufffd Coil UntitledSubclause4 – 7.2.1.1\ufffd\ufffd\ufffd The sensitivity of the equipment to the flow is improved by incre… <\/td>\n<\/tr>\n | ||||||
| 15<\/td>\n | UntitledSubclause4 – 7.2.1.2\ufffd\ufffd\ufffd Any electrical leakage between the coil and the water in the chan… UntitledSubclause4 – 7.2.1.3\ufffd\ufffd\ufffd The coil shall be installed in ducting (normally of about UntitledSubclause4 – 7.2.1.4\ufffd\ufffd\ufffd For convenience, the coil may be wound with a multi-core cable an… UntitledSubclause4 – 7.2.1.5\ufffd\ufffd\ufffd In cases where installation is in potentially explosive atmospher… UntitledSubclause4 – 7.2.1.6\ufffd\ufffd\ufffd The frequency at which the magnetic field is reversed shall be lo… UntitledSubclause4 – 7.2.1.7\ufffd\ufffd\ufffd A typical coil design is described in Subclause3 – 7.2.2\ufffd\ufffd\ufffd Electrodes UntitledSubclause4 – 7.2.2.1\ufffd\ufffd\ufffd It is recommended that the electrodes be made from stainless stee… UntitledSubclause4 – 7.2.2.2\ufffd\ufffd\ufffd In channels containing foul water which is liable to putrify, the… UntitledSubclause4 – 7.2.2.3\ufffd\ufffd\ufffd In the event of a lightning strike in the vicinity of the gauge, … UntitledSubclause4 – 7.2.2.4\ufffd\ufffd\ufffd The inductive or capacitive coupling between the signal cable and… UntitledSubclause4 – 7.2.2.5\ufffd\ufffd\ufffd In open channels, the electrodes may be supported in guides mount… <\/td>\n<\/tr>\n | ||||||
| 16<\/td>\n | Subclause3 – 7.2.3\ufffd\ufffd\ufffd Insulating membrane UntitledSubclause4 – 7.2.3.1\ufffd\ufffd\ufffd An insulating membrane shall be used which is strong enough to wi… UntitledSubclause4 – 7.2.3.2\ufffd\ufffd\ufffd The membrane shall be mechanically anchored and sealed at the lea… UntitledSubclause4 – 7.2.3.3\ufffd\ufffd\ufffd In practice, the membrane may be covered by a variety of material… <\/td>\n<\/tr>\n | ||||||
| 17<\/td>\n | UntitledSubclause4 – 7.2.3.4\ufffd\ufffd\ufffd The membrane shall not be punctured, except along the edges for a… UntitledSubclause4 – 7.2.3.5\ufffd\ufffd\ufffd In a concrete channel the upstream leading edge and sides of the … UntitledSubclause4 – 7.2.3.6\ufffd\ufffd\ufffd It is recommended that the length of the lining be no less than 1… UntitledSubclause4 – 7.2.3.7\ufffd\ufffd\ufffd In closed conduits a special preformed section may be inserted in… Subclause3 – 7.2.4\ufffd\ufffd\ufffd Instrumentation unit UntitledSubclause4 – 7.2.4.1\ufffd\ufffd\ufffd The instrumentation shall consist of: UntitledSubclause4 – 7.2.4.2\ufffd\ufffd\ufffd To obtain meaningful determinations of flow, measurements shall b… Subclause3 – 7.2.5\ufffd\ufffd\ufffd Water level measurement Subclause2 – 7.3\ufffd\ufffd\ufffd Measurement of coil current and electrode voltage <\/td>\n<\/tr>\n | ||||||
| 18<\/td>\n | Subclause2 – 7.4\ufffd\ufffd\ufffd Signal processing UntitledSubclause3 – 7.4.1\ufffd\ufffd\ufffd The equipment shall measure the difference in electrical potential … UntitledSubclause3 – 7.4.2\ufffd\ufffd\ufffd The electrical interference is regarded as random and so will in th… UntitledSubclause3 – 7.4.3\ufffd\ufffd\ufffd When making comparison for calibration purposes, the averaging peri… Subclause2 – 7.5\ufffd\ufffd\ufffd Power supply failure Clause1 – 8\ufffd\ufffd\ufffd Uncertainties in flow measurement Subclause2 – 8.1\ufffd\ufffd\ufffd Calibration graph Subclause2 – 8.2\ufffd\ufffd\ufffd Single determination of discharge UntitledSubclause3 – 8.2.1\ufffd\ufffd\ufffd The uncertainty in a single determination of discharge may be calcu… <\/td>\n<\/tr>\n | ||||||
| 19<\/td>\n | UntitledSubclause3 – 8.2.2\ufffd\ufffd\ufffd The component uncertainties are the following: Clause1 – 9\ufffd\ufffd\ufffd Gauge calibration and verification UntitledSubclause2 – 9.1\ufffd\ufffd\ufffd Provided always that the design of an electromagnetic gauge is such t… UntitledSubclause2 – 9.2\ufffd\ufffd\ufffd The measurand\/determinand relationship may take more than one form, d… UntitledSubclause2 – 9.3\ufffd\ufffd\ufffd Once the general form of a relation is established, the optimum value… UntitledSubclause2 – 9.4\ufffd\ufffd\ufffd A series of calibration determinations should be such as to have suff… UntitledSubclause2 – 9.5\ufffd\ufffd\ufffd The independent determinations of flow should be made with very great… UntitledSubclause2 – 9.6\ufffd\ufffd\ufffd Care shall be taken to ensure that the act of check gauging does not … UntitledSubclause2 – 9.7\ufffd\ufffd\ufffd Annex\ufffdD UntitledSubclause2 – 9.8\ufffd\ufffd\ufffd Once a sufficiently numerous and range-representative calibration sam… UntitledSubclause2 – 9.9\ufffd\ufffd\ufffd Following the satisfactory completion of gauge calibration, it would … <\/td>\n<\/tr>\n | ||||||
| 20<\/td>\n | AnnexInformative – Site survey for electrical interference <\/td>\n<\/tr>\n | ||||||
| 21<\/td>\n | AnnexInformative – Design aspects of the electromagnetic coil <\/td>\n<\/tr>\n | ||||||
| 22<\/td>\n | AnnexInformative – Numerical example of the calculation of uncertainty <\/td>\n<\/tr>\n | ||||||
| 23<\/td>\n | AnnexNormative – Gauge calibration procedure UntitledClause1 – D.1\ufffd\ufffd\ufffd A series of calibration check gaugings should be carried out to establis… UntitledClause1 – D.2\ufffd\ufffd\ufffd All current meter gauging for calibration purposes should be undertaken … UntitledClause1 – D.3\ufffd\ufffd\ufffd Multi-point gauging should be adopted as the norm for calibration gaugin… UntitledClause1 – D.4\ufffd\ufffd\ufffd In the course of a calibration gauging steps should be taken at the outs… <\/td>\n<\/tr>\n | ||||||
| 24<\/td>\n | UntitledClause1 – D.5\ufffd\ufffd\ufffd The procedure for undertaking both formal calibration and verification g… UntitledClause1 – D.6\ufffd\ufffd\ufffd As a matter of policy, calibration gauging at any given site should not … UntitledClause1 – D.7\ufffd\ufffd\ufffd Individual gaugings should be most carefully vetted before being accepte… UntitledClause1 – D.8\ufffd\ufffd\ufffd The minimum target calibration gauging data set should have the followin… UntitledClause1 – D.9\ufffd\ufffd\ufffd Once a set of calibration data has been obtained, the data should be sub… <\/td>\n<\/tr>\n | ||||||
| 25<\/td>\n | Bibliography – Bibliography <\/td>\n<\/tr>\n<\/table>\n","protected":false},"excerpt":{"rendered":" Measurement of total discharge in open channels. Electromagnetic method using a full-channel-width coil<\/b><\/p>\n |