1、BS ISO12745:2008ICS 73.060.99NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDCopper, lead and zincores and concentrates Precision and biasof mass measurementtechniquesThis British Standardwas published under theauthority of the StandardsPolicy and StrategyCommit
2、tee on 32008 BSI 2008ISBN 978 0 580 63619 6Amendments/corrigenda issued since publicationDate CommentsBS ISO 12745:2008National forewordThis British Standard is the UK implementation of ISO 12745:2008.The UK participation in its preparation was entrusted to TechnicalCommittee NFE/36, Copper lead and
3、 zinc ores and concentrates.A list of organizations represented on this committee can be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisionsof a contract. Users are responsible for its correct application.Compliance with a British Standard ca
4、nnot confer immunityfrom legal obligations.0 NovemberBS ISO 12745:2008Reference numberISO 12745:2008(E)ISO 2008INTERNATIONAL STANDARD ISO12745Second edition2008-10-01Copper, lead and zinc ores and concentrates Precision and bias of mass measurement techniques Minerais et concentrs de cuivre, de plom
5、b et de zinc Justesse et erreurs systmatiques des techniques de pese BS ISO 12745:2008ISO 12745:2008(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are e
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8、roblem relating to it is found, please inform the Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT ISO 2008 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, in
9、cluding photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Publ
10、ished in Switzerland ii ISO 2008 All rights reservedBS ISO 12745:2008ISO 12745:2008(E) ISO 2008 All rights reserved iiiContents Page Foreword iv 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 1 4 General remarks 4 4.1 Draft surveys . 4 4.2 Belt scales . 5 4.3 Weighbridges 5 4.4 Hopp
11、er scales . 6 4.5 Gantry scales 6 4.6 Platform scales . 7 5 Certified weights. 7 6 Methods of operation . 8 6.1 General. 8 6.2 Draft surveys . 8 6.3 Belt scales . 12 6.4 Weighbridges 14 6.5 Hopper scales . 16 6.6 Gantry scales 18 6.7 Platform scales . 20 Annex A (informative) Tables 22 Annex B (info
12、rmative) Statistics .32 Annex C (informative) Draft surveys 41 Annex D (informative) Procedure for the testing of static scales . 44 Bibliography . 47 BS ISO 12745:2008ISO 12745:2008(E) iv ISO 2008 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide fe
13、deration of national standards bodies (ISO member bodies). 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 com
14、mittee. International organizations, governmental and 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 accord
15、ance with the rules given in the ISO/IEC Directives, 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 require
16、s approval by at least 75 % of the member bodies casting 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 12745 was prepared by Technical
17、Committee ISO/TC 183, Copper, lead, zinc and nickel ores and concentrates. This second edition cancels and replaces the first edition (ISO 12475:1996), which has been technically revised. BS ISO 12745:2008INTERNATIONAL STANDARD ISO 12745:2008(E) ISO 2008 All rights reserved 1Copper, lead and zinc or
18、es and concentrates Precision and bias of mass measurement techniques 1 Scope This International Standard provides guidelines to test for bias over a wide range of mass measurement techniques, to estimate the precision for each technique and to calculate the precision for wet mass when estimated by
19、applying one of those techniques. The guidelines are based on the application of statistical tests to verify that a mass measurement technique is unbiased, to estimate the variance as the most basic measure for its precision and to check the linearity of a static scale over its working range. Calibr
20、ation methods and performance tests for compliance with applicable regulations generate test results that can be used to quantify precision and bias for each of these mass measurement techniques and to verify linearity for static weighing devices. The guidelines apply to mass measurement techniques
21、used to estimate the wet mass for cargoes or shipments of mineral concentrate as the basis for freight and insurance charges and for preliminary payments or for final settlements between trading partners. The application of static scales requires that at least one certified weight with a mass of no
22、less than one (1) tonne be either available on location or brought in for calibration purposes, and that this certified weight be applicable to the scale in accordance with the manufacturers recommendations. A set of certified weights covering the entire working range of a weighing device simplifies
23、 the process of verifying its state of calibration, estimating its precision as a function of applied load and testing its linearity over the working range. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only th
24、e edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3534-1:2006, Statistics Vocabulary and symbols Part 1: General statistical terms and terms used in probability ISO 3534-2:2006, Statistics Vocabulary and symbols Par
25、t 2: Applied statistics ISO 5725-1:1994, Accuracy (trueness and precision) of measurement methods and results Part 1: General principle and definitions 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. NOTE 1 In authoritative textbooks on applied s
26、tatistics the use of the sigma squared (2) symbol is restricted to unknown population variances for which a measurement procedure gives an estimate only. By contrast, the symbol s2applies to variances of samples, and thus to finite sets of measurements. Standard methods on sampling of bulk materials
27、 often apply sigma-symbols (2or ) indiscriminately. BS ISO 12745:2008ISO 12745:2008(E) 2 ISO 2008 All rights reservedNOTE 2 Following are definitions for the most relevant concepts and terms in mass measurement technology. They are presented to clarify the difference between this standard method, wh
28、ich quantifies the risk of losing and the probability of gaining in commercial transactions, and other methods that deal with mass measurement techniques from the perspective of regulatory agencies. 3.1 accuracy generic term that implies closeness of agreement between an observed mass and its unknow
29、n true value NOTE Accuracy is an abstract concept that cannot be quantified, but a lack of accuracy can be measured and quantified in terms of a bias or systematic error. 3.2 bias difference between the expectation of the test result and an accepted reference value NOTE This definition is only valid
30、 if the accepted reference value is known with absolute certainty (International Units of Mass and Length). Given that most accepted reference values are known within finite confidence limits, the difference between the expectation of a test result and an accepted reference value is only a bias if t
31、he expectation of the test result falls outside the confidence limits of an accepted reference value. 1)3.3 belt scale mass measurement device that continuously integrates and records as a cumulative mass, the load on a belt while it passes the suspended scale section in a conveyor belt NOTE Belt sc
32、ales are continuous mass measurement devices that are calibrated by applying a load such as a calibrated chain on the belt above the scale section (dynamic), or a certified weight suspended from the scales frame (static), for a specified integration period, or by measuring with the belt scale a quan
33、tity of material whose mass is measured with a static scale (material-run method). 3.4 bias detection limit BDL measure for the power or sensitivity of Students t-test to detect a bias or systematic error between applied and observed loads 3.5 coefficient of variation CV measure for random variation
34、s in a mass measurement technique, numerically equal to the standard deviation as a percentage of the observed mass 3.6 confidence interval Cl interval within which a predetermined percentage of the differences between all possible measurements and their mean is expected to cluster 3.7 confidence ra
35、nge CR range within which a predetermined percentage of all possible measurements is expected to cluster NOTE In science and engineering 95 % confidence intervals and ranges are most frequently used. 1) For example, the mass of the lot is generally determined once only so that the measured value is
36、not the expectation of the test result. In this International Standard a bias is the statistically significant difference between independent estimates of the wet mass of the lot (loading versus discharge, static versus dynamic scales) and mass measurements should be traceable to National Prototype
37、Kilograms, and thus to the International Unit of Mass, through the shortest possible calibration hierarchy. BS ISO 12745:2008ISO 12745:2008(E) ISO 2008 All rights reserved 33.8 correlation coefficient r measure for the degree of association or interdependence between a set of certified weights and o
38、bserved loads 3.9 draft survey mass measurement technique that is based on converting the difference between a vessels displacement under different loads into a mass on the basis of its draft tables while taking into account the density and temperature of water and ballast, and changes in ballast an
39、d supplies NOTE Draft surveys are based on Archimedess Principle which states that a floating body displaces its own mass. The wet mass of a cargo or shipment can be measured by converting changes in draft, trim, ballast and consumable supplies into mass on the basis of the vessels draft table. 3.10
40、 precision generic term for the cumulative effect of random variations in a mass measurement technique NOTE Precision is a generic qualifier, e.g. “a high degree of precision”, “the precision is poor or low” or “the precision characteristics are excellent”, are valid statements albeit without quanti
41、tative implications. 3.11 probable bias range PBR limits within which a measured bias is expected to fall at predetermined probabilities, either for a type I risk only or for type I and II risks 3.12 relative standard deviation srmeasure for random variations in a mass measurement technique, numeric
42、ally equal to the standard deviation divided by the observed mass 3.13 standard deviation s measure for random variations in a mass measurement technique, numerically equal to the square root of the variance 3.14 static scale mass measurement device that converts into a mass a static load on a weigh
43、bridge or on a platform, inside a hopper or suspended from a gantry scale NOTE Static scales are batch mass measurement devices that are calibrated either with a single certified weight or with a set, and less frequently with a calibrated hydraulic press. Static scales may have automatic zero adjust
44、ment so that the sum of the differences between tare and gross loads can be used to generate a cumulative mass. Dual hopper scales allow a virtually continuous mass flow during loading and discharge operations without sacrificing the accuracy and precision characteristics of the static scale. 3.15 S
45、tudents t-value t ratio between the difference for the means for sets of applied and observed loads and the standard deviation for the mean difference BS ISO 12745:2008ISO 12745:2008(E) 4 ISO 2008 All rights reserved3.16 type I risk risk of rejecting the hypothesis that the means for sets of applied
46、 and observed loads are compatible when their mean difference is, in fact, statistically identical to zero 3.17 type II risk risk of accepting the hypothesis that the means for sets of applied and observed loads are compatible when their mean difference is, in fact, statistically different from zero
47、 3.18 variance s2measure for random variations in a mass measurement technique, numerically equal to the sum of squared deviations from the mean for a set of measurements divided by the number of measurements in the set minus 1 (divided by the degrees of freedom) NOTE In textbooks on applied statist
48、ics the term “mean squared deviation from the mean” is often used in reference to the variance. 4 General remarks International and national handbooks on weighing devices define uncertainties in mass measurement techniques in different ways. In some handbooks the use of the term “error” is restricte
49、d to a bias or systematic error while others refer to “maximum permissible risks”, which appears synonymous with “tolerances”, as a measure for random variations in a mass measurement technique. Unless “maximum permissible errors” or “tolerances” are, by definition, equal to 95 % or 99 % confidence intervals, neither can be converted into a variance as the most basic measure for the precision of a measurement process. However, an unbiased estimate for the variance of the wet mass of a cargo or shipment of mineral concentra
