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1、BRITISH STANDARD BS ISO 6145-2:2001 Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 2: Volumetric pumps ICS 71.040.40; 71.040.10 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04
2、:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO6145-2:2001 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 September 2001 BSI 08-2001
3、 ISBN 0 580 38307 5 National foreword This British Standard reproduces verbatim ISO 6145-2:2001 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
4、 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 S
5、tandards 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 St
6、andard 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 Euro
7、pean developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to v, a blank page, pages 1 to 8, an inside back cover and back cover. The BSI copyright date displayed in this document indicates when the doc
8、ument was last issued. Amendments issued since publication Amd. No. DateComments Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI INTERNATIONAL STANDARD ISO 6145-2 First edition 2001-07-01 Reference number ISO 6145-2:2001(E) ISO 2001 Gas anal
9、ysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 2: Volumetric pumps Analyse des gaz Prparation des mlanges de gaz pour talonnage laide de mthodes volumtriques dynamiques Partie 2: Pompes volumtriques Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:28 G
10、MT+00:00 2006, Uncontrolled Copy, (c) BSI ii Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-2:2001(E) iii Contents Page 1Scope . 1 2Normative references . 1 3Principle 1 4Volumetric pump . 2 5Calculations 4 Annexes APre-mixed gases
11、 for preparation of mixtures of high dilution 6 A.1Calculation of results . 6 A.2Uncertainty of volume fraction 6 BPractical hints 7 Bibliography. 8 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-2:2001(E) iv Foreword ISO (the Inte
12、rnational 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
13、 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 s
14、tandardization. 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
15、 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 6145-2 was prepar
16、ed by Technical Committee ISO/TC 158, Analysis of gases. ISO 6145 consists of the following parts, under the general title Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods: Part 1: Methods of calibration Part 2: Volumetric pumps Part 4: Continuous injection metho
17、d 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, entitled Periodic injections into a flowing gas, has been wit
18、hdrawn. Annexes A and B of this part of ISO 6145 are for information only. Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-2:2001(E) v Introduction This part of ISO 6145 is one of a series of standards dealing with various dynamic v
19、olumetric methods used for the preparation of calibration gas mixtures. Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI INTERNATIONAL
20、STANDARDISO 6145-2:2001(E) 1 Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 2: Volumetric pumps 1Scope This part of ISO 6145 specifies a method for the continuous production of calibration gas mixtures, containing two or more components, from pure gases or
21、 other gas mixtures by use of commercially available multi-piston, volumetric pumps. Pumps of this type may be employed to prepare gas mixtures in which the volume fractions of the gaseous components in the complementary gas range from upwards; the relative expanded uncertainty of measure- ment, , o
22、btained by multiplying the relative combined standard uncertainty by a coverage factor is not greater than . Lower concentrations may be obtained by cascading volumetric pumps, and the lowest volume fraction achievable by means of a two-pump cascade is . Moreover, if pre-mixed gases are used instead
23、 of pure gases, much lower concentrations can be obtained. The merits of this method are that a large quantity of the gas mixture can be prepared on a continuous basis, and that multicomponent mixtures can also be readily prepared. 2Normative references The following normative documents contain prov
24、isions 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 possi
25、- bility 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
26、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 3Principle A binary mixture of two gases, A and B, is prepared by passing each gas through
27、one of a pair of single action piston pumps, each pump of which is driven by a synchronous motor. The volume fraction, , of component A, in the gas mixture is given by: (1) in which and are the volumetric flow rates of the calibration component A and the complementary gas B respectively. 0,1 % Uk =2
28、 0,5 % 106 A A= qA/(qA+ qB) qAqB Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-2:2001(E) 2 As is the case for all of the dynamic volumetric methods described in this series of standards, and shall be provided under identical condi
29、tions of temperature and pressure. If this is not so, and in particular if volumetric pumps are used at pressures above ambient atmospheric pressure the appropriate corrections are necessary. These are made by means of the ideal gas laws, or the virial equation in the case of gases showing significa
30、nt departure from ideality. 4Volumetric pump 4.1Description The volumetric pump consists of a pair of single-stage dosing pumps with single-action pistons driven by a single synchronous motor. The drive to one of the pumps is controlled through intermediate gears while that to the other is direct. T
31、o prepare a two-component mixture of two gases A and B, the gases are to be supplied at ambient atmospheric pressure to the dosing pumps, and excess gas vented to the atmosphere through a system of bubblers. Two tubes are connected to the cylinder of each pump; the pure component, A or B, is aspirat
32、ed through one tube and the other leads to a mixing chamber. The stroke rate of the one piston may be changed by gear selection while that of the other remains constant. By this means the volume fractions of A and B in the mixture are established. Figure 1 shows a schematic diagram of the principle.
33、 Volumetric pumps of this type are commercially available and the following presents brief descriptions of three variants of the equipment: a)The capacities of the cylinders are identical; the range of flow rate ratios is 1:1 to 9:1. b)The capacity of the cylinder in which the piston drive is variab
34、le is 1/9 of that of the cylinder in which the drive is direct. In this arrangement the range of flow rate ratios is 9:1 to 99:1. c)The capacity of the cylinder in which the piston drive is variable is 1/99 of that of the cylinder in which the drive is direct. In this arrangement the range of flow r
35、ate ratios is 99:1 to 999:1. Some models are equipped with sets of gear wheels and others have integral switch gears and the ratios are selected by adjustment of dials. Pumps can be arranged as a cascade to provide a means of preparation of gas mixtures of lower concentrations. As an example, two pu
36、mps of the third type, defined in c), can be operated in series to produce a binary mixture in which the volume fraction of the calibration component is . It is also possible for two mixing systems to be combined in one pump and these systems can be switched to operate in either a parallel or a seri
37、es configuration. In the series arrangement volume fractions as low as to can be realized. 4.2Precautions and validity limits This method is applicable to the preparation of mixtures of non-reacting species, i.e. those which do not react with any material of construction of those parts of the pump,
38、and the flow paths external to the pump, with which the gaseous components come in contact. Therefore pistons of the commercially available pumps shall be constructed in either bronze or another special alloy with ceramic coating. The latter material shall be claimed by the supplier to be chemically
39、 resistant to gases such as sulphur dioxide, hydrogen sulfide, ammonia, nitrogen dioxide, hydrogen chloride, and chlorine provided that the gases are dry. The gas-conveying tubes shall be made of corrosion-resistant stainless steel, known to be inert to the gases and gas mixture used (such types of
40、stainless steel can be found in EN 10088-11). Between the pistons and cylinders of some models of the pumps a perfluorinated-polyether fluid of low volatility (vapour pressure approximately at ) is used as a sealing and lubricating fluid. In other models, particularly older models, the pump system a
41、nd gears are immersed in an oil bath and the low-vapour pressure oil which is used is of an appropriate grade (as marked on the pump). qAqB 106 106 105Pa25 C Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 04:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-2:2001(E) 3 Observe the ge
42、neral precautions common to all dynamic techniques of preparation. Particular care shall be exercised if the method is considered as a means of preparation of gaseous mixtures which contain components which form potentially explosive mixtures with air. Steps shall be taken to ensure that the apparat
43、us is safe, for example by means of in-line flame arrestors in locations appropriate to the flow paths. Although the pumps may be regarded as constant-flow devices, a calibration method is still necessary in order to confirm the ultimate gas concentration. As is the case for the other dynamic mixing
44、 methods presented in other parts of ISO 6145, it is essential to check the effectiveness of the mixing system to provide a homogeneous gas mixture; it is not satisfactory to rely upon the ratio of flow rates alone as the basis for expression of the gas composition unless the method has been validat
45、ed for the gas mixture required. This method of gas blending provides a constant flow of gas mixture of constant composition over a long period. The flow rate is limited to approximately for pumps currently available commercially. For some models however, the maximum flow rate is . Key 1Inlet for ga
46、s B 2Inlet for gas A 3Bubbler 4Drive gear for cylinder A 5Drive gear for cylinder B 6Cylinder A 7Cylinder B 8Mixing chamber 9Outlet for calibration gas mixture 10Central drive unit 11Manometer Figure 1 Schema of a volumetric pump for mixing gases 5 l/min 0,75 l/min Licensed Copy: sheffieldun sheffie
47、ldun, na, Mon Nov 27 04:21:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 6145-2:2001(E) 4 4.3Operating conditions Ensure that only suitable low-porosity and non-absorbing materials are used in the construction of the flow system external to the pumps. Also ensure that the pipe work is clean and
48、all unions secure. When using pumps with replaceable gear wheels, make sure the gears are placed on the correct shafts, otherwise the pump may be overloaded and become damaged; mark the gears appropriately. The manufacturers operating instructions shall be referenced to establish the conditions of p
49、ressure at which a pump may be run. In some models, it is necessary to restrict the differential pressure between the gas inlets. Restrict the over-pressure against ambient atmospheric pressure unless the particular model is one which is equipped with an additional forwarding piston, in which case a higher excess pressure at the outlet is permissible. Before using a pump to produce gas mixtures, operate it for to warm it up. If operation is interrupted for short periods, for example when gears are changed, a warm-up period of app