ISO-8316-1987.pdf
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1、IS0 INTERNATIONAL STANDARD 8316 First edition 1987-10-01 - - INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXJJYHAPOAHAR OPrAHM3AL(MR fl0 CTAHflAPTM3AL(MM Measurement of liquid flow in closed conduits - Method by collection of the liquid in a volumetric
2、 tank Mesure de d4bit des liquides dans /es conduites ferm.Ges - M b) its viscosity is sufficiently low so as not to alter or delay unduly the measurement of the level in the volumetric tank; cj it is non-toxic and non-corrosive. Theoretically, there is no limit to the application of this method, bu
3、t, for practical reasons, this method of measurement is nor- mally used for flow-rates less than approximately I,5 m3/s and is used on the whole in fixed laboratory installations only. However, there is a variation of this method which uses a natural or artificial storage pond as a volumetric tank,
4、but this application is not dealt with in this International Standard. Owing to its high potential accuracy, this method is often used as a primary method for calibrating other methods or devices for volume flow-rate measurement or for mass flow-rate measurement; for the latter method or device, it
5、is necessary to know the density of the liquid accurately. If the installation for flow-rate measurement by the volumetric method is used for purposes of legal metrology, it shall be cer- tified and registered by the national metrology service. Such in- stallations are then subject to periodic inspe
6、ction at stated in- tervals. If a national metrology service does not exist, a certified record of the basic measurement standards (length, time and temperature), and error analysis in accordance with this International Standard and IS0 5158, shall also constitute certification for legal metrology p
7、urposes. Annex A forms an integral part of this International Standard. Annexes B to E, however, are given for information only. 2 References IS0 4006, Measurement of fluid flow in closed conduits - Vocabulary and symbols. IS0 4185, Measurement of liquid flow in closed conduits - Weighing method. IS
8、0 4373, Measurement of liquid frow in open channels - Water level measuring devices. IS0 5158, Measurement of fluid flow - Estimation of uncer- tainty of a flow-rate measurement. 3 Symbols and definitions 3.1 Symbols (see also IS0 4005) Table 1 Symbol e R 44 % ES qm qv t V Z e Quantity Random uncert
9、ainty, in absolute terms Random uncertainty, as a percentage Systematic uncertainty, in absolute terms Systematic uncertainty, as a percentage Mass flow-rate Volume flow-rate Filling time of the tank Discharged or measured volume Liquid level in the tank Density Dimensions * * - MT-1 L3T-1 T L3 L ML
10、-3 SI unit * - * - kg/s ma/s rz3 m kg/ma l The dimensions and units are those of the ouantities in ouestion. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/18/2007 21:32:47 MDTNo reprod
11、uction or networking permitted without license from IHS -,-,- IS0 6316 : 1667 (E) 3.2 Definitions For the purposes of this International Standard, the definitions given in IS0 4006 apply. Only terms which are used with a par- ticular meaning or the meaning of which might be usefully restated are def
12、ined below. The definitions of some of the terms concerned with error analysis are given in IS0 5168. 3.2.1 static gauging: A method by which the net volume of liquid collected is deduced from measurements of liquid levels (i.e. gaugings), made respectively before and after the liquid has been diver
13、ted for a measured time interval into the gauging tank, to determine the volume contained in the tank. 3.2.2 dynamic gauging : A method by which the net volume of liquid collected is deduced from gaugings made while liquid flow is being delivered into the gauging tank, (A diverter is not required wi
14、th this method.) 3,2.3 diverter: A device which diverts the flow either to the gauging tank or to its by-pass without changing the flow-rate during the measurement interval. 3.2.4 flow stabilizer: A device inserted into the measuring system, ensuring a stable flow-rate in the conduit being sup- plie
15、d with liquid; for example, a constant level head tank, the level of liquid in which is controlled by a weir of adequate length. 4 Principle 4,l Statement of the principle 4.1.1 Static gauging method The principle of the flow-rate measurement method by volumetric static gauging (see figure 1 for a s
16、chematic diagram of a typical installation) is - to determine the initial volume of liquid contained in the tank; - to divert the flow into the volumetric tank, until it is considered to contain a sufficient quantity to attain the desired accuracy, by operation of a diverter which actuates a timer t
17、o measure the filling time; - to determine the final volume of liquid contained in the tank, The volume contained at the initial and at the final times is obtained by reading the liquid levels in the tank and by reference to a .preliminaty calibration which gives the level-volume relationship. The f
18、low-rate is then derived from the volume of liquid col- lected and the filling time as explained in clause 7. 2 One variation of this method uses two tanks which are suc- cessively filled (see 6.3). A further variation, given in annex D, uses a valve instead of a diverter mechanism to start and stop
19、 the flow into a volumetric tank. Care shall be taken when using a valve instead of a diverter that the flow-rate does not change when the valve is operated. 4.1.2 Dynamic gauging method The principle of the flow-rate measurement method by volumetric dynamic gauging (see figure 2 for a schematic dia
20、gram of a typical installation) is - to let liquid collect in the tank to a predetermined initial level (and thus volume), at which time the timer is started; - to stop the timer when a second predetermined final level (and thus volume) is reached and then to drain the liquid collected. The flow-rat
21、e is then derived as explained in clause 7. 4.1.3 Comparison of instantaneous and mean flow-rates It should be emphasized that only the mean value of flow-rate for the filling period is given by the volumetric method. Instan- taneous values of flow-rate as obtained on another instrument or meter in
22、the flow circuit may be compared with the mean flow-rate only if the flow is kept stable during the measurement interval, by a flow-stabilizing device, or if the instantaneous values are properly time-averaged during the whole filling period. 4.2 Accuracy of the method 4.2.1 Overall uncertainty in t
23、he volumetric measurement The volumetric method gives a measurement of flow-rate which, in principle, requires only level and time measurements. After the weighing method, the static gauging method in a volumetric tank may be considered as one of the most accurate of all flow-rate measuring methods,
24、 particularly if the precau- tions given in 4.2.2 are taken. For this reason, it is often used as a standard or calibration method. When the installation is carefullv constructed, maintained and used, an uncertainty of f 0,l b) the conduit is running full at the measuring section and there is no vap
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