1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58straight open tanksICS 17.120.20Hydrometry Calibration of current-meters in BRITISH STANDARDBS ISO
2、3455:2007BS ISO 3455:2007This British Standard was published under the authority of the Standards Policy and Strategy Committee on 29 June 2007 BSI 2007ISBN 978 0 580 52948 1Amendments issued since publicationAmd. No. Date CommentsThis publication does not purport to include all the necessary provis
3、ions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.National forewordThis British Standard was published by BSI. It is the UK implementation of ISO 3455:2007. It supersedes BS 3680-8C:1980 which is wit
4、hdrawn. The UK participation in its preparation was entrusted by Technical Committee CPI/113, Hydrometry, to Subcommittee CPI/113/5, Measuring instruments and equipment.A list of organizations represented on this committee can be obtained on request to its secretary.Reference numberISO 3455:2007(E)I
5、NTERNATIONAL STANDARD ISO3455Second edition2007-06-01Hydrometry Calibration of current-meters in straight open tanks Hydromtrie talonnage des moulinets en bassins dcouverts rectilignes BS ISO 3455:2007ii iiiContents Page Foreword iv 1 Scope . 1 2 Normative reference . 1 3 Terms and definitions. 1 4
6、Principle of calibration . 1 5 Design criteria for calibration stations. 1 5.1 Dimensions of rating (calibration) tank 1 5.2 Rating carriage (trolley) 3 5.3 Measuring equipment. 4 5.4 Other requirements. 5 6 Computerized data acquisition and processing system 6 6.1 Data acquisition 6 6.2 Data proces
7、sing 6 7 Calibration procedure. 7 7.1 Calibration of rotating-element current-meters. 7 7.2 Calibration of electromagnetic meters . 13 BS ISO 3455:2007iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The
8、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 and non-gover
9、nmental, 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, Part 2. Th
10、e 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 casting a vote
11、. 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 3455 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 5, Instruments
12、, equipment and data management. This second edition cancels and replaces the first edition (ISO 3455:1976), which has been technically revised. BS ISO 3455:20071Hydrometry Calibration of current-meters in straight open tanks 1 Scope This International Standard specifies the procedure of calibration
13、 of current-meters of rotating-element type as well as stationary-sensor type (electromagnetic type) in straight open tanks. It also specifies the types of tank, rating carriage and equipment to be used and the method of presenting the results. The procedure does not take into account any possible d
14、ifference existing between the behaviour of a current-meter moving in motionless water and that of a fixed current-meter in turbulent flow. 2 Normative reference The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited ap
15、plies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 772, Hydrometric determinations Vocabulary and symbols ISO 2537, Hydrometry Rotating-element current-meters 3 Terms and definitions For the purposes of this document, the terms and de
16、finitions given in ISO 772 apply. 4 Principle of calibration Calibration of a current-meter means experimental determination of the relationship between liquid velocity and either the rate of revolution of the rotating element or the velocity directly indicated by the current-meter. For this purpose
17、, the current-meter is mounted on a towing carriage and drawn through still water contained in a straight tank of a uniform cross section at a number of steady speeds of the towing carriage. Simultaneous measurements of the speed of the towing carriage and the rate of revolution of the rotating elem
18、ent or the velocity indicated by the current-meter are made. In the case of rotating-element current-meters, the two parameters are related by one or more equations, the limits of validity of which are stated. In the case of stationary-sensor type current-meters, the velocity indicated by its displa
19、y unit is compared with the corresponding carriage speed to know the error in measurement. 5 Design criteria for calibration stations 5.1 Dimensions of rating (calibration) tank 5.1.1 General The dimensions of the tank and the number and relative position of current-meters in the tank cross section
20、shall be chosen so that the test results are not affected. BS ISO 3455:20072 5.1.2 Length The length of a rating tank can be considered as comprising accelerating, stabilizing, measuring and braking sections. The length of the accelerating and braking sections depends on the design of the carriage,
21、the maximum acceleration and deceleration achievable at maximum payload and the maximum speed at which the payload is to be towed along the tank. Safety requirements of the carriage need to be taken into account while working out the length of the braking section. The length of the measuring section
22、 shall be such that the calibration error, which is composed of inaccuracies in the measurement of time, distance covered and rate of revolution, does not exceed the desired tolerance at any velocity. The required length will, therefore, depend on the type of current-meter being calibrated, type of
23、carriage and the way the signals are produced and transmitted. For example, if measured times both for distance covered by the carriage and for the revolutions counted are accurate to 0,01 s in order to limit the error in time measurement to 0,1 % at the 95 % confidence level, the duration of the te
24、st shall be at least 10 s at maximum speed. If the maximum speed is 6 m/s, the measuring section of the tank would be 60 m long. The total length of the tank would be about 100 m of which about 20 m would be for acceleration and stabilizing and 20 m for braking. 5.1.3 Depth and width The depth of th
25、e tank can have an influence on the test results which cannot be regarded as negligible, more particularly when the towing speed coincides with the velocity of propagation of the surface wave. The dependence of this critical velocity, vc, on tank depth is given by the Equation (1): cvgd= (1) where g
26、 is the acceleration due to gravity; d is the depth of water. The wave crest produced by the current-meter and its means of suspension, which moves forward with the instrument, causes an increase in the height of the wetted cross section and thus, in accordance with the continuity equation, a reduct
27、ion of the relative velocity. This phenomenon, known as the Epper effect, may cause an error in calibration within a narrow band in the velocity range from 0,5 vcto 1,5 vc. The magnitude of the Epper effect depends on the size of the current-meter(s) and suspension equipment, relative to the cross-s
28、ectional area of the tank. It may be little more than the uncertainty of a single calibration point. It is a systematic and not a random error. It may be negligible when a very small current-meter is being calibrated. The depth of the tank shall therefore be chosen to suit the size and the maximum v
29、elocity limits of the current-meters to be calibrated. Care shall be taken to ensure that either the calibration velocities in higher range are attained before the interference or that they exceed it sufficiently for the critical zone to be bridged without extrapolation. The width of the tank is of
30、importance because the Epper effect is more pronounced in a narrower tank. The width also limits the number of instruments that can be calibrated simultaneously and has an effect on the stilling characteristics (time taken for the water to become reasonably still). For example, when a field type cur
31、rent-meter on rod suspension is being calibrated in a tank 1,83 m wide in which the depth of water is 1,83 m, the Epper effect is greater at a speed of about 4 m/s ( 9,81 1,83 ) and amounts to 0,3 %. The size of the effect dies away on either side of the critical velocity, but is detectable at veloc
32、ities between 3 m/s and 5 m/s. BS ISO 3455:200735.2 Rating carriage (trolley) 5.2.1 General During calibration, the current-meter is suspended from the carriage and immersed in the water at specified depth and the carriage travels along the length of the tank at known and accurate speeds in the meas
33、uring section. 5.2.2 Carriage track system The carriage may run on two parallel rails which must be accurately aligned with both the length of the tank and the surface of the water in the tank. It is essential that the rails are straight and that the rails and the wheels of the carriage are free of
34、irregularities, otherwise the carriage will move with irregular motion and cause vibration which may be transmitted to the current-meter(s) and disturb the rating. The material and hardness of the rails and the driving wheels should be chosen so that there shall not be undue wear and tear of the whe
35、els. In the case of rubber tire wheels, provision shall be made to lift the wheels above the rail surface when not in use for a long time. Another track system may have toothed belts, mounted on both sides of the tank, driven by the guiding rollers and used for transportation of the carriage. If thi
36、s system is adopted, it shall be ensured that there is no slippage or sag of the belt and in case the slippage or sag occurs, it shall be possible to remove it manually. The belts shall be strong enough to withstand the load of the carriage they have to transport during calibration and the climatic
37、conditions prevailing at the rating laboratory. 5.2.3 Types of rating carriages The following types of rating carriages are in common usage. a) The towed carriage which is moved along the track by a cable driven from a constant speed motor standing apart from the moving carriage. The towed carriage
38、may be lighter in construction with the consequent advantage of high acceleration and quick braking, but the elasticity of the towing cable can cause irregularities in the running of the carriage thereby affecting the accuracy of current-meter calibration. b) The self-propelled carriage which is mov
39、ed along the track by internally mounted electric motor(s). The power to the carriage may be fed by a trailing wire track system or by an overhead conductor system or other systems specially designed for the purpose. The self-propelled carriage will be heavier in construction as it has to carry the
40、driving motors. This results in greater inertia of the carriage and assists in smoothing out the running irregularities of the carriage. The weight of the rating carriage can substantially be reduced by using light but rugged material for its construction. The lightweight carriage can achieve a high
41、 rate of acceleration/deceleration resulting in relatively smaller length of tank. 5.2.4 Carriage operation The carriage shall travel smoothly and at constant speed in the measuring section of the rating tank ensuring that oscillatory motion is not transmitted to the current-meters under calibration
42、. The carriage shall remain stable during acceleration, deceleration and braking. There shall not be any forward/backward or sideways rocking, or slippage during peak acceleration/deceleration and during normal operation at any speed in specified range. The carriage shall have smooth operational cap
43、ability in both forward and reverse directions. An interlock shall be provided in the system to ensure that the direction of start up is correct. BS ISO 3455:20074 During calibration, the measuring equipment, sensors and other instruments shall not be affected by noise and spurious signals induced b
44、y the mains power supply or carriage drive and control system or otherwise by electrical equipment installed in the rating tank building and vicinity. Normal braking of the carriage shall be accomplished by dynamic braking through the drive system. In addition to normal braking, an alternate brake s
45、ystem shall also be provided on the carriage which would automatically activate during an emergency. 5.2.5 Carriage control The carriage may be manned or unmanned. In the case of a manned carriage, an operator on-board controls various functions of the carriage. The unmanned carriage is operated rem
46、otely without any operator on board. An on-board programmable controller unit controls various functions of the carriage, i.e., speed, acceleration, deceleration, braking, etc. The controller exchanges control signals with the supervisory computer, installed in a control room through suitable digita
47、l communication system. 5.3 Measuring equipment 5.3.1 General The calibration of a current-meter calls for the simultaneous measurement of the following three parameters: a) distance covered by the carriage; b) time; and c) number of signals (pulses) delivered by the current-meter. The towing speed
48、is calculated from the simultaneous measurement of distance and time and, in case of rotating-element current-meter, the rate of current-meter revolutions (rotations) is obtained by the simultaneous measurement of the number of signals (pulses) and the time. For acquisition of calibration data, a st
49、rip chart recorder or magnetic tape or a computerized data acquisition system as described in 6.1 may be used. 5.3.2 Distance measurement Different methods are available for measurement of distance to the specified measurement uncertainty (see 5.3.5). Two of the most common methods are as follows: a) the establishment of light barriers (markers) at regular intervals along the length of the tank which actuate mechanical or optical pulse transmitters fitted to the carriage; b) the use of measuring wheels with mechanical or photoelectric pul
