1、 Reference number ISO 6144:2003(E) ISO 2003INTERNATIONAL STANDARD ISO 6144 Second edition 2003-02-01 Gas analysis Preparation of calibration gas mixtures Static volumetric method Analyse des gaz Prparation des mlanges de gaz pour talonnage Mthode volumtrique statique ISO 6144:2003(E) PDF disclaimer
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6、uester. 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 Published in Switzerland ii ISO 2003 All rights reservedISO 6144:2003(E) ISO 2003 All rights reserved iiiContents Page Foreword iv 1 Scope1 2 Normative
7、references1 3 Terms and definitions .1 4 Principle .2 5 Apparatus.2 6 Procedure for preparing the calibration gas mixture 4 7 Calculation of the volume fraction of the calibration component in the gas mixture7 8 Determination of the uncertainty in the concentration of the calibration component in th
8、e gas mixture 9 Annex A (informative) Example of an apparatus suitable for the preparation of calibration gas mixtures by the static volumetric method12 Annex B (informative) Example of determination of the volume of metering syringes 15 Annex C (informative) Example of the determination of the unce
9、rtainty in the concentration of a calibration gas mixture prepared by the static volumetric method.17 Annex D (informative) Example of the determination of the stability, as a function of time, of prepared calibration gas mixtures 22 Bibliography29 ISO 6144:2003(E) iv ISO 2003 All rights reservedFor
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12、 electrotechnical standardization. International Standards are drafted in accordance 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 t
13、o 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 document may be the subject of patent rights. ISO shall not be held responsible for
14、 identifying any or all such patent rights. ISO 6144 was prepared by Technical Committee ISO/TC 158, Analysis of gases. This second edition cancels and replaces the first edition (ISO 6144:1981), which has been technically revised. INTERNATIONAL STANDARD ISO 6144:2003(E) ISO 2003 All rights reserved
15、 1Gas analysis Preparation of calibration gas mixtures Static volumetric method 1 Scope This International Standard specifies a method for the preparation of calibration gas mixtures by a static volumetric method and provides a procedure for calculating the volumetric composition of the mixture. It
16、can be used either with binary gas mixtures (containing one calibration component in a complementary gas, which is usually nitrogen or air 1, 2 ) or with mixtures containing more than one component in the complementary gas. This International Standard also specifies how the expanded uncertainty in t
17、he volume fraction of each calibration component in the mixture is determined by a rigorous evaluation of all the measurement uncertainties involved, including those associated with the apparatus used for the preparation of the gas mixture and those associated with the experimental procedure itself.
18、 NOTE 1 This International Standard is generally applicable to the preparation of calibration gas mixtures containing calibration components in the concentration range 10 10 9(10 ppb parts per billion) to 50 10 6(50 ppm parts per million) by volume. However, gas mixtures may be prepared at larger or
19、 smaller volume fractions, provided that the components used in the static dilution process are selected appropriately. NOTE 2 A relative expanded uncertainty of not greater than 1 % at a level of confidence of 95 % may be achievable at these concentrations, provided that: the purities of the parent
20、 gases have been determined by analysis and any significant impurities and the uncertainties in their measured concentrations have been taken into account; no significant adsorption effects or chemical reactions occur between the gaseous constituents and the internal surfaces of the apparatus, and t
21、here are no reactions between any of the gaseous components, i.e. between the calibration component and complementary gas or between the calibration components themselves; all the relevant apparatus used in the preparation of a calibration gas mixture have been calibrated with assigned measurement u
22、ncertainties which are appropriate to calculating the final expanded uncertainty for the calibration gas mixture prepared. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undat
23、ed references, the latest edition of the referenced document (including any amendments) applies. ISO 7504, Gas analysis Vocabulary 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 7504 apply. ISO 6144:2003(E) 2 ISO 2003 All rights reserved4 Principle
24、A calibration gas mixture consists of one of more calibration components in a complementary (diluent) gas, mixed in a suitable gas-mixing chamber. These calibration components are generally pure gases taken from cylinders, or from pure, volatile liquids that are allowed to evaporate into the gas-mix
25、ing chamber. The gas mixture is prepared using syringes to inject: either known volumes of gaseous calibration components (each at a pressure of about 1 10 5Pa); or known masses or volumes of liquid calibration components; These are injected into a volume of complementary gas contained in the mixing
26、 chamber (which is also at a pressure of about 1 10 5Pa). Further complementary gas is then added to increase the overall pressure of the gas mixture to an accurately measured value above ambient atmospheric pressure. This final (above- atmospheric) pressure is required so that the calibration gas m
27、ixture will subsequently flow out of the mixing chamber and can be used to calibrate a gas analyser, which is usually operated at ambient pressure. At each stage in the preparation procedure, the mixture is homogenized, usually by means of a suitable stirring device, and then left to equilibrate to
28、ambient atmospheric temperature. The volume fraction of each calibration component in the calibration gas mixture is determined by calculation of the ratio of the volume of the calibration component to the total volume of the mixture. 5 Apparatus 5.1 Gas-mixing chamber, consisting of the components
29、specified in 5.1.1 to 5.1.8. NOTE An example of a suitable gas-mixing chamber is described in Annex A. 5.1.1 Vessel, comprising the gas-mixing chamber itself, of sufficient internal volume to deliver the amount of calibration gas mixture required for any subsequent instrumental calibrations, manufac
30、tured of a suitable material that is inert to all the component gases, and designed both to be evacuable and to withstand the required above-atmospheric operating pressures. It shall also have vacuum/high-pressure flanges to allow access to the components that are mounted within the mixing chamber.
31、NOTE 1 Vessels with internal volumes of 0,1 m 3to 0,5 m 3 , capable of operating up to pressures of about 2 10 5Pa (2 bar) and of maintaining a vacuum of better than 0,1 10 2Pa (0,1 mbar), have been found to be suitable (see Annex A). NOTE 2 Mixing chambers manufactured from borosilicate glass or st
32、ainless steel have been found to be suitable for the commonly used gaseous species (e.g. gas mixtures which contain SO 2 , NO, NO 2 , CO and C 6 H 6as the calibration components). However, care shall be taken in selecting the materials of the mixing chamber, and of the other components which come in
33、to contact with the gas mixtures, so that they do not affect the mixtures stability adversely particularly when more reactive gas mixtures are to be prepared. 5.1.2 Vacuum pump, capable of evacuating the mixing chamber and its associated components to a low pressure, and including a suitable vacuum
34、shut-off valve. This low pressure shall be defined either so that any gaseous contamination resulting from the residual low pressure has no effect on the accuracy of the concentration of the gas mixture prepared, or so that a quantitative correction for the effect of this residual low pressure may b
35、e made to the concentration of the mixture. NOTE The residual gas pressure is generally due mainly to nitrogen from residual air. However, care must be taken to ensure that other gases that may react with the constituents of the gas mixture are not present at significant concentrations in this resid
36、ual gas (e.g. traces of water vapour when acid gases are being used as calibration components, or traces of oxygen in the case when nitric oxide calibration mixtures are being prepared). 5.1.3 Gas line, used for the injection of the complementary gas, and including appropriate metering and shut-off
37、valves. ISO 6144:2003(E) ISO 2003 All rights reserved 35.1.4 Pressure, vacuum and temperature gauges, used to monitor these parameters inside the mixing vessel. 5.1.5 Septum, enabling a gas or liquid of known volume or mass to be injected into the mixing chamber from a metering syringe (5.2). 5.1.6
38、Motor-driven gas-mixing device, e.g. a fan, enabling the gaseous components in the gas-mixing chamber to be homogenized, and designed to provide satisfactory mixing of all the gaseous components to a given degree of homogeneity within a specified time. Experimental tests shall be carried out to demo
39、nstrate that the mixing device is able to achieve the required homogeneity within the specified time. 5.1.7 Pressure relief valve, used to ensure that the maximum internal safe working pressure specified for the mixing vessel and its associated components is not exceeded. 5.1.8 Outlet-gas sampling l
40、ine, enabling the gas mixture prepared to be used for calibration purposes, and having a device for equalizing the internal pressure of the gas mixture in the mixing chamber with atmospheric pressure so as to enable the gas mixture to be determined at ambient pressure for calibration purposes. 5.2 C
41、alibrated metering syringe, which can be used to inject, by means of a piston, a known volume of gas or liquid through a needle. The syringe shall have gastight seals to ensure that no significant leakage of the gas or liquid takes place. NOTE 1 Glass syringes having polytetrafluoroethene (PTFE) bus
42、hings as seals, and with internal volumes of 10 ml, 5 ml, 1 ml, 0,5 ml and 0,1 ml, have been found to be suitable when used with mixing chambers of volumes which are in practical use, and when used to prepare gas mixtures for the calibration of ambient-air analysers. NOTE 2 It is recommended that th
43、e internal volume of the syringe be measured experimentally with a maximum relative uncertainty of 1 % (at a level of confidence of 95 %). In addition, the syringe should have a maximum leak rate of 10 10 2Pa (10 mbar) per hour after evacuation to 5 Pa (5 10 2mbar), in order that it has satisfactory
44、 leaktightness. 5.3 Apparatus for filling the metering syringe, consisting of the components specified in 5.3.1 to 5.3.9. NOTE An example of a suitable set-up for filling the syringe is described in Annex A. 5.3.1 Evacuable gas reservoir, capable of containing gas at above-atmospheric pressure so as
45、 to enable the metering syringe to be filled to that pressure, its internal surfaces being made of a material that does not react with any of the calibration components. NOTE A gas reservoir with an internal volume of about 100 ml, capable of operating up to a pressure of 1,4 10 5Pa (1,4 bar) and of
46、 maintaining a vacuum of better than 0,1 10 2Pa (0,1 mbar), has been found suitable. 5.3.2 High-pressure gas cylinder, containing the selected pure gas component (or a pre-mixture containing a higher concentration of gas mixture). 5.3.3 Pressure regulator, used to enable the pressure of gas in the r
47、eservoir to be adjusted to a pre- defined pressure above that of the ambient atmosphere. 5.3.4 Septum, constructed of appropriate material, enabling the needle of the metering syringe to be introduced into the gas reservoir. 5.3.5 Vacuum pump, enabling the gas reservoir and its associated components
48、 to be evacuated to below the required vacuum. NOTE It is important to ensure that any gaseous component which may be hazardous, and which is exhausted by the vacuum pump to the atmosphere, is vented in a safe way. 5.3.6 Pressure gauge, used to monitor the pressure of the gas in the reservoir during
49、 the various stages of the preparation procedure. ISO 6144:2003(E) 4 ISO 2003 All rights reserved5.3.7 Gas shut-off valves, used to isolate the gas cylinder from the reservoir, and the gas reservoir from the vacuum pump. 5.3.8 Pressure-relief valve, capable of relieving a gas pressure selected to protect the apparatus (typically 1,4 10 5Pa). It should be vented to a safe location. 5.3.9 Suitable vessel, for use when the metering syringe is to be filled with a volatile liquid rather than a ga
