1、CEN EN*24185 93 3404589 0307847 657 BRITISH STANDARD A Measurement of fluid flow in closed conduits Weighing method The European Standard EN 24185 : 1993 has the status of a British Standard Mesure de debit des liquides dans les conduites fermes - Mthode par pese urchflumessung von Flssigkeiten in g
2、eschlossenen Leitungen -Wgeverfahren UDC 532.575531.753 BS EN 24185 : 1993 IS0 4188 : 1980 : CEN EN*24L85 93 = 3404.589 0107848 593 I I I Confirmed t -. BS 6199: Part 1 : 1981 IS0 41 85 - 1980 UDC 532.542 : 532575 : 531.753 Methods of Measurement of liquid flow in closed conduits using weighing and
3、volumetric methods Part I. Weighing method IS0 title: Measurement of liquid flow in closed conduits -Weighing method Mthodes de mesure de dbit des liquides dans des conduites fermes par pese et mesure du volume Partie 1. Pese Memethoden fr F lssigkeitsstrmungen in geschlossenen Kanlen unter Anwendun
4、g von Waagen und volumetrischen Methoden Teil 1. Wiegemethoden Brit ish Stand a rds I nstitu t i on CEN EN+*24185 93 = 3404587 OL07847 42T W 1. BS6199 : Part 1 : 1981 Contents Page National foreword Inside front cover Cooperating organizations Back cover Method 1. General 1 2. Principle 2 3. Apparat
5、us 7 4. Procedure 10 5. Calculation of flow-rate 10 6. Calculation of the overall uncertainty of the measurement of the flow-rate 10 Annexes A. Corrections on the measurement of filling time 16 6. Density of pure water 18 C. Definition of terms and procedures used in error analysis 19 O. Students t-
6、distribution 21 Table 1. Values of Students t 21 National foreword This British Standard has been prepared under the direction of the Industrial-process Measurement and Control Standards Committee and is identical with IS0 4185 Measurement of liquid flow in closed conduits -Weighing method including
7、 Technicai mgendum 1-.l published in 1980 bv the International Organization for Standardization (ISO). in 1993 the European Committee for Standuczation (CEN) accepted IS0 4186 : 1980 as European Standard EN 24185 : 1993. As a consequence of implementing the European Standard this British Standard is
8、 renumbered as BS EN 24185 and any reference to BS 6199 : Part 1 : 1981 should be read as a reference to BS EN 24185. Terminology and conventions. The text of the international standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certai
9、n conventions are not identical with those used in British Standards; attention is especially drawn to the following. Wherever the words International Standard appear, referr- ing to this standard, they should be read as British Standard. The comma has been used throughout as a decimal marker. In Br
10、itish Standards it is current practice to use a full point on the baseline as the decimal marker. :$qe A Figures 1A. Diagram of an installation for calibration by weighing (static method, supply by a constant level head tank) measure by weighing (used for an hydraulic machine test; static method, su
11、pply by a con- stant level head tank 1C. Diagram of an installation for calibration by weighing (static method, direct pumping 1 D. Diagram of an installation for calibration by weighing (dynamic method, supply by a con- stant level head tank) 2. Examples of diverter design 3. Operational law of div
12、erter 4. 5. 6. 7. 16. Diagram of an installation for flow-rate supply) Time metering for a diverter the operation law of which is identical in both directions Example of error distribution in calibration of weighing machine Typical graph used in evaluation of (ER I, for a diverter system Plotting of
13、 results of diverter timer actuator as given in A.1.2 Page 3 4 5 6 8 8 9 11 13 17 Crossref erences IS0 4006 - 1977 I nternationd siandard Corresponding British Standard BS 5857 : 1980 Glossary of terms and symbols for measurement of fluid flow in closed conduits (Identical) BS 5844 : 1980 Methods of
14、 measurement of fluid flow: esti- mation of uncertainty of a flow- rate measurement (Identical) IS0 5168 - 1978 OIML Recommendations Nos. 1, 2,3, 20, 28 and 33, which r/ are referred to in 3.4, are international recommendations of the International Organization of Legal Metrology (OIML). In complyin
15、g with this British Standard, implementation of these recommendations is not mandatory. Copies of OIML Recommendations may be purchased from the following address. The Director International Bureau of Legal Metrology 11 rue Turgot 75009 Paris France CEN EN*24L85 93 m 3404589 OL07850 L4L m EUROPEAN S
16、TANDARD EUROPISCHE NORM NORME EUROPENNE EN 24185 June 1993 UDC 532.575:531.753 Descriptors: Flow measurement, liquid flow, pipe flow, measuring instruments, flowmeters, calibratllig, weight measurement, error analysis English version Measurement of fluid flow in closed conduits - Weighing method (IS
17、0 4185 : 1980) Mesure de dbit des liquides dans conduites fermes - Mthode par pese (IS0 4185 : 1980) Durchfiu3messung von Flssiieiten in geschiossenen Leitungen - Wgeverfahren (Is0 4185 : 1980) This European Standard was approved by Cm on 1993-06-18. CEN members are bound to comply with the CEN/CENE
18、LEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any C
19、EN member. The European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN m
20、embers are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europi
21、sches Komitee fr Normung Central Secretariat: Tue de Stassart 36, B-1050, Brussels 8 1993 Copyright reserved to CEN members Ref. No. EN 24185 : 1993 E CEN ENnx2418.5 73 3404589 0107851 O88 Page 2 EN 24186 : 1993 Foreword In 1991, IS0 4185 : 1980 Measurement offludjbw in closed canu the result was po
22、sitive. This European Standard shali be given the status of a national standard, either by publication of an identical text or by endomment, at the latest by December 1993, and conflicting national stan* shall be withdrawn at the latest by December 1993. According to the CEN/CENELEX Internai Regulat
23、ions, the following countries are bound to implement this European Sandad Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portuga, Spain, Sweden, Switzerland and the United Kingdom. NOTE. The European references to internatid pub
24、lications are given in annex ZA (normativle). + CEN EN*24185 93 m 3404587 0107852 T14 m BS6199 : Part 1 : 1981 British Standard Methods of Measurement of liquid flow in closed conduits using weighing and volumetric methods Part 1. Weighing method 1 General OIML, Recommendations Nos. 1, 2, 3, 20, 28,
25、 33. 1.1 Scope and field of application 1.3 Definitions This International Standard specifies a method of liquid flow- rate measurement in closed conduits by measuring the mass of liquid delivered into a weighing tank in a known time interval. It Only terms which are used in a special sense or the m
26、eaning of which merits restatement are defined below. deals in particular with the measuring apparatus, the pro- cedure, the method for calculating the flow-rate and the uncer- tainties associated with the measurement. l .3.1 static weighing : The method in which the net mass of liquid collected is
27、deduced from tare and gross weighings made respectively before and after the liquid has been diverted for a measured time interval into the weighing tank. 1.3.2 dynamic weighing : The method in which the net mas of liquid collected is deduced from weighings made while fluid flow is being delivered i
28、nto the weighing tank. (A diverter is not required with this method.) 1.3.3 diverter : A device which diverts the flow either to the weighing tank or to its by-pass without changing the flow-rate during the measurement interval. The method described may be applied to any liquid provided that its vap
29、our pressure is such that any escape of liquid from the weighing tank by vaporization is not sufficient to affect the required measurement accuracy. Closed weighing tanks and their application to the flow measurement of liquids of high vapour pressure are not considered in this International Stan- d
30、ard. This International Standard does not cover the cases of cor- rosive or toxic liquids. Theoretically, there is no limit to the application of this method which is used generally in fixed laboratory installations only. However, for economic reasons, usual hydraulic laboratories using this method
31、can produce flow-rates of 1.5 m3/s or less. Owing to its high potential accuracy, this method is often used as a primary method for calibration of other methods or devices for mass flow-rate measurement or volume flow-rate measure- ment provided that the density of the liquid is known accurately. It
32、 must be ensured that the pipeline is running full with no air or vapour pockets present in the measuring section. 1.2 References 1.3.4 flow stabilizer : A structure forming part of the measuring system, ensuring a stable flow-rate in the conduit being supplied with liquid; for example, a constant l
33、evel head tank, the level of liquid in which is controlled by a weir of suffi- cient length. 1.3.5 buoyancy correction : The correction to be made to the readings of a weighing machine to take account of the dif- ference between the upward thrust exerted by the atmosphere, on the liquid being weighe
34、d and on the reference weights used during the calibration of the weighing machine. IS0 4006, Measurement of fluid flow in closed conduits - Vocabulary and symbols. IS0 5168, Measurement of fluid flow - Estimation of uncer- tainty of a flow-rate measurement. 1.4 Units The units used in this Internat
35、ional Standard are the SI units, metre, kilogram, and second; the degree Celsius is used for convenience instead of the kelvin. 1 3 I BS6199 : Part 1 : 1981 1.5 Notation Symbol CEN ENx524385 93 m 3404589 0307853 950 1 Designation Mass flow-rate Volume flow-rate Mass Volume Time Density of liquid Den
36、sity of air Density of standard weights Estimated standard deviation Standard deviation of variable x Uncertainty of measurement Systematic uncertainty Percentage systematic uncertainty Random uncertainty Percentage random uncertainty Dimension MT- L3T- M L3 T ML-3 ML-3 ML-3 SI Units kgls m3/S kg m3
37、 kgld kgid kglm3 S 1.6 Certification If the installations for flow-rate measurement by the weighing method are used for purposes of legal metrology, they should be certified and registered by the national metrology service. Such installations are then subject to periodical inspection at stated inter
38、vals. If a national metrology servicedoes not exist, a certified record of the basic measurement sandards (weight and timel, and error analysis in accordance with this Inter- national Standard and IS0 5168, shall also constitute certifica- tion for legal metrology purposes. 2 Principie 2.1 Statement
39、 of the principle 2.1.1 Static weighing The principle of the flow-rate measurement method by static weighing (for schematic diagrams of typical installations, see figures 1A. 1B. 1C) is : - residual liquid; to determine the initial mass of the tank plus any - to divert the flow into the weighing tan
40、k (until it is con- sidered to contain a sufficient quantity to attain the desired accuracy) by operation of the diverter. which actuates a timer to measure the filling time; - collected in it. to determine the final mass of the tank plus the liquid The flow-rate is then derived from the mass collec
41、ted, the collection time and other data as discussed in clause 5 and annex A. 2 CEN ENxx24L85 93 D 3404589 0107654 697 D BS6199 : Part 1 : 1981 Constant level head tank Flow control valve li Device under calibration Overflow Diverte- ?/ Figure 1A - Diagram of an installation for calibration by weigh
42、ing (static method, supply by a constant level head tank) 3 Constant levei head tank Figure 16 - Diagram of an installation for flow-rate measure by weighing (used for an hydraulic machine test; static method, supply by a constant level head tank) 4 Flow control Pump BS6199 : Part 1 : 1981 Sump Figu
43、re 1C - Diagram of an installation for calibration by weighing (static method, direct pumping suppiyJ 5 I 4 CEN EN*24185 73 = 3404587 0107657 5Tb = BS6199 : Part 1 : 1981 Constant levei head tank Flow control valve 2 Device under CdibratM A Weighing Figure 10 - Diagram of an installation for calibra
44、tion by weighing (dynamic method, supply by a constant level head tank) f- i 6 I CEN EN*+2L1585 93 m 3404589 OLO7B58 432 = BS 6199 : Part 1 : 1981 2.1.2 Dynamic weighing The principle of the flow-rate measurement method by dynamic weighing (see figure 10 for a schematic diagram of a typical installa
45、tion1 is : - initial mass, when the timer is then started; - collected liquid is reached. to let the liquid collect in the tank to a Predetermined to stop the timer when a predetermined final mass of The flow-rate is then derived from the mass collected, the collection time and other data as discuss
46、ed in clause 5 and annex A. 2.1.3 flow-rate Comparison of instantaneous and mean It should, however, be emphasized that only the mean value of flow-rate for the filling is given by the weighing method. Instantaneous values of flow-rate as obtained on another instrument or meter in the flow circuit c
47、an be compared with the mean rate only if the flow is maintained stable during the measurement interval by a flow-stabilizing system, or if the instantaneous values are properly time-averaged during the whole filling period. 2.2 Accuracy of the method 2.2.1 measurement Overall uncertainty on the wei
48、ghing The weighing method gives an absolute measurement of flow which in principle requires only mass and time measurements. Provided that the precautions listed in 2.2.2 are taken, this method may be considered as one of the most accurate of all flow-rate measuring methods, and for this reason it i
49、s often used as a calibration method. When the installation is carefully constructed, maintained and used, an uncertainty of I 0,l % (with 95 96 confidence limits for the random part of that uncer- tainty) can be achieved. 2.2.2 Requirements for accurate measurements The weighing method gives an accurate measurement of flow rate provided that : a) there is no leak in the flow circuit and there is no unmetered leakage flow across the diverter; b) there is no accumulation (or depletion) of liquid in
