BS-ISO-6145-5-2001.pdf
BRITISH STANDARD BS ISO 6145-5:2001 Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 5: Capillary calibration devices ICS 71.040.40 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 6145-5:2001 This British Standard, having been prepared under the direction of the Sector Committee for Materials and Chemicals, was published under the authority of the Standards Committee and comes into effect on 15 August 2001 © BSI 08-2001 ISBN 0 580 37910 8 National foreword This British Standard reproduces verbatim ISO 6145-5:2001 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee PTI/15, Natural gas and gas analysis, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, page ii to v, a blank page, pages 1 to 10, an inside back cover and a back cover. The BSI copyright date displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. DateComments Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI INTERNATIONAL STANDARD ISO 6145-5 First edition 2001-04-01 Reference number ISO 6145-5:2001(E) Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 5: Capillary calibration devices Analyse des gaz Préparation des mélanges de gaz pour étalonnage à l'aide de méthodes volumétriques dynamiques Partie 5: Dispositifs d'étalonnage par capillaires Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-5:2001(E) ii Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-5:2001(E) diii ContentsPage 1Scope .1 2Normative references .1 3Singular or multiple capillary combinations 1 4Multiple capillary devices using gas dividers 5 Annex ANumerical example .8 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-5:2001(E) iv Foreword ISO (the International Organization for Standardization) is a worldwide federation 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 committee. 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 accordance with the rules given in the ISO/IEC Directives, Part 3. 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. Attention is drawn to the possibility that some of the elements of this part of ISO 6145 may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. International Standard ISO 6145-5 was prepared by Technical Committee ISO/TC 158,Analysis of gases. ISO 6145 consists of the following parts, under the general titleGas analysis Preparation of calibration gas mixtures using dynamic volumetric methods: Part 1: Methods of calibration Part 2: Volumetric pumps Part 4: Continuous injection method Part 5: Capillary calibration devices Part 6: Critical orifices Part 7: Thermal mass-flow controllers Part 9: Saturation method Part 10: Permeation method Diffusion will be the subject of a future part 8 to ISO 6145. Part 3 to ISO 6145, entitledPeriodic injections into a flowing stream, has been withdrawn. Annex A of this part of ISO 6145 is for information only. Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-5:2001(E) v Introduction This part of ISO 6145 is one of a series of International Standards dealing with the various dynamic volumetric techniques used for the preparation of calibration gas mixtures. Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI INTERNATIONAL STANDARDISO 6145-5:2001(E) 1 Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 5: Capillary calibration devices 1Scope This part of ISO 6145 specifies a technique for the continuous production of calibration gas mixtures from pure gases or gas mixtures using capillary devices in single or multiple combinations (gas dividers). Single capillary systems can be used to provide gas mixtures where the minor component is in the range of volume fractions fromto. The relative repeatability of this technique is approximately. This application is used in industrial gas mixing panels for the production of specific gas atmospheres. Gas dividers can be used to divide gas mixtures prepared from gases or gas mixtures into controlled proportions by volume. These devices are capable of dilutions in the range of volume fractions from 0,1 to 0,9 of the primary gas with a relative repeatability of better than. Traceability of the gas mixtures produced by a gas divider can be achieved by comparison of a mixture at the higher and lower end of the range with gas mixtures related to national or international gas standards. An example is given in annex A. 2Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of ISO 6145. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this part of ISO 6145 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 6143,Gas analysis Comparison methods for determining and checking the composition of calibration gas mixtures. ISO 6145-1:1986,Gas analysis Preparation of calibration gas mixtures Dynamic volumetric methods Part 1: Methods of calibration. 3Singular or multiple capillary combinations 3.1Principle A constant flow of gas from a capillary tube under conditions of constant pressure drop is added to a controlled flow of complementary gas. The complementary gas may be derived from another capillary tube. 1080,5 2 % 0,5 % Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-5:2001(E) 2 3.2Apparatus 3.2.1Two-capillary system, as shown in Figure 1 and consisting of the following. 3.2.1.1Capillaries, each capillary is supplied with gas from a cylinder fitted with a two-stage pressure regulator, gas filter and a fine adjustment valve. The appropriate capillaries shall be selected to give the required flows of gases A and B into the mixing manifold. These capillaries shall be calibrated using the method described in ISO 6145-1:1986, clause 3. The gas flow from one capillary is passed into a soap-film meter and readings are taken of the differential pressures required to provide a range of flows. A calibration curve is constructed by plotting pressure differences () against flow rates. The gradient of this line will be the individual calibration factorfor the specified gas see equation (2). The results of this calibration will allow a capillary to be selected such that the required flow can be obtained by adjusting the pressure drop across the capillary. Key 1Gas A 2Two-stage pressure regulator 3Fine adjustment valve 4Pressure differential manometer 5Capillary 6Mixing manifold 7Complementary gas 8Gas mixture Figure 1 Two-capillary blending system p1 p2 K Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-5:2001(E) 3 3.2.1.2Two-stage pressure regulator, equipped with fine adjustment valves. 3.2.1.3Differential manometer, capable of measuring the pressure drop across the capillary. 3.2.1.4Gas manifold, fed by the flow from each capillary where mixing occurs to produce the calibration gas mixture at the outlet. 3.2.1.5Gas filters, to filter the component gases, so as to prevent blockage of the capillaries. 3.2.1.6Thermostatic controller (optional), to maintain the temperature of the capillaries constant. Variations in temperature can cause a significant change in the viscosity of the component gas passing through the capillary. For high accuracy, it is necessary to provide thermostatic control of the capillaries. With thermostatic control of a water- jacket to, the volume fraction of the final mixture will not vary by more than. 3.3Procedure Open the gas supply cylinders and adjust the two-stage pressure regulators to approximatelygauge outlet pressure. Open the fine adjustment valves to give the pressure drop across the capillaries required for the desired flows. 3.4Calculations 3.4.1Capillary flow rate The volume flow rateof a gas A emerging from a capillary can be approximately expressed as: (1) where is the radius of the capillary tube; is the inlet pressure to the capillary; is the outlet pressure of the capillary; is the dynamic viscosity of the gas at the temperature of usage; is the length of the capillary tube. For a given capillary this expression can be simplified: (2) whereis an individual factor for gas A. ±1 C ±2 % 200 kPa qA qA= r4(p1 p2) 8L r p1 p2 L qA= KA(p1 p2) KA Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-5:2001(E) 4 3.4.2Volume fraction The volume fraction of component A,is defined by the equation (3) where is the volume flow rate of gas A; is the volume flow rate of gas B. 3.4.3Uncertainty Variations in pressure differentialwill be affected by changes in atmospheric pressure acting on the outlet of the mixing manifold. In a binary system, both gases will be similarly affected and the combined error in the system will be compensated. There will be an error associated with the calibration measurement using the method defined in ISO 6145-1:1986, clause 3. Referring to equation (2): (4) whereis equal to (). The relative combined standard uncertaintyofis: (5) where is the standard uncertainty ofaccording to the calibration of the capillary; is the standard uncertainty of the pressure differentialdue to its variability. For the example of a binary mixture the uncertainty of the composition can be expressed in the form of the relative uncertainty of the volume fraction of component A, as in equation (3): (6) i.e. (7) The reported expanded uncertainty of measurementis stated as the standard uncertainty of measurement multiplied by the coverage factorcalculated for a normal distribution to give a coverage probability of approximately. The accuracy of the mixture produced at any moment is principally affected by the constancy of the flow rates of each component. These can be estimated by observations of the variation in the pressure differential manometers applied across each capillary. A A= qA qA+ qB qA qB p(= p1 p2) qA= KAp pp1 p2 ucqA uc(qA) qA = s? u(KA) KA ?2 + ? u(p) p ?2 u(KA)K u(p)p A= qA qA+ qB U (A) A = 2qB qA+ qB s? u(qA) qA ?2 + ? u(qB) qB ?2 U (A) k =2 95 % Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-5:2001(E) 5 4Multiple capillary devices using gas dividers 4.1Gas dividers Commercially available units called gas dividers which contain combinations of similar capillaries can be used to further dilute calibration gas mixtures with complementary gas, thus generating further calibration standards. The gas mixtures generated by these units are frequently used to assess the performance of analytical instrumentation. This instrumentation may be employed in cases where a requirement of traceability is mandatory. In such cases, it is necessary that these units be calibrated by a method traceable to national or international standards. An approved method is to select two generated gas mixtures atandof a given range and carry out a comparison check with these gas standards at similar volume fractions. The agreement between the two results will confirm the accuracy of the gas divider and provide traceability to the other gas mixtures in that range. An example of this technique is given in annex A. 4.2Principle 4.2.1A gas divider contains a combination of capillary tubes of exactly the same lengths and diameters. Provided there is not a large difference in viscosity of the gases employed and the pressure across the capillaries is constant, each tube will possess the same resistance to flow. 4.2.2The flow rates of a component gas and a dilution gas are controlled by the capillary tubes and blended to generate the gas which is divided. The volume fraction of the generated gas is determined from the flow rates of component and dilution gas. In the example illustrated in Figure 2, the gas divider has 10 capillaries. Key 1Dilution gas 2Pressure regulator 3Capillary 4Division-switching valve 5Generated gas 6Component gas, volume fraction, 7Exhaust gas Figure 2 Calibration gas generator using gas divider 75 % 0 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:04 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-5:2001(E) 6 By se
