1、November 2008DEUTSCHE NORM English price group 12No part of this standard may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 71.040.40!$Rx)“147850
2、6www.din.deDDIN EN ISO 6145-8Gas analysis Preparation of calibration gas mixtures using dynamic volumetricmethods Part 8: Diffusion method (ISO 6145-8:2005)English version of DIN EN ISO 6145-8:2008-11Gasanalyse Herstellung von Kalibriergasgemischen mit Hilfe von dynamisch-volumetrischenVerfahren Tei
3、l 8: Diffusionsverfahren (ISO 6145-8:2005)Englische Fassung DIN EN ISO 6145-8:2008-11www.beuth.deDocument comprises 25 pagesDIN EN ISO 6145-8:2008-11 2 National foreword This standard has been prepared by Technical Committee ISO/TC 158 “Analysis of gases” (Secretariat: NEN, Netherlands) and has been
4、 taken over as EN ISO 6145-8:2008 by Technical Committee CEN/SS N21 “Gaseous fuels and combustible gas” (Secretariat: CMC). The responsible German body involved in its preparation was the Normenausschuss Materialprfung (Materials Testing Standards Committee), Technical Committee NA 062-05-73 AA Gasa
5、nalyse und Gas-beschaffenheit. 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 method Part 5: Capillary calibr
6、ation devices Part 6: Critical orifices Part 7: Thermal mass-flow controllers Part 8: Diffusion method Part 9: Saturation method Part 10: Permeation method Part 11: Electrochemical generation The DIN Standards corresponding to the International Standards referred to in this document are as follows:
7、ISO 6143 DIN EN ISO 6143 ISO 6145-1 DIN EN ISO 6145-1 ISO 6145-6 DIN EN ISO 6145-6 National Annex NA (informative) Bibliography DIN EN ISO 6143, Gas analysis Comparison methods for determining and checking the composition of calibration gas mixtures DIN EN ISO 6145-1, Gas analysis Preparation of cal
8、ibration gas mixtures using dynamic volumetric methods Part 1: Methods of calibration DIN EN ISO 6145-6, Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 6: Critical orifices EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 6145-8 August 2008 ICS 71.
9、040.40 English Version Gas analysis - Preparation of calibration gas mixtures using dynamic volumetric methods - Part 8: Diffusion method (ISO 6145-8:2005) Analyse des gaz - Prparation des mlanges de gaz pour talonnage laide de mthodes volumtriques dynamiques - Partie 8: Mthode par diffusion (ISO 61
10、45-8:2005) Gasanalyse - Herstellung von Kalibriergasgemischen mit Hilfe von dynamisch-volumetrischen Verfahren - Teil 8: Diffusionsverfahren (ISO 6145-8:2005) This European Standard was approved by CEN on 30 July 2008. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which s
11、tipulate 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 CEN Management Centre or to any CEN member. This European Stand
12、ard 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 CEN Management Centre has the same status as the official versions. CEN members are the national sta
13、ndards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Ki
14、ngdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: rue de Stassart, 36 B-1050 Brussels 2008 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN ISO 6145-8:2008
15、: E2 DIN EN ISO 6145-8:2008-11 EN ISO 6145-8:2008 (E) Contents Page Foreword3 Introduction .4 1 Scope 5 2 Normative references 5 3 Principle5 4 Reagents and materials 6 5 Apparatus .7 6 Procedure .8 6.1 Preliminary checks and operating conditions8 6.2 Determination of mass loss9 7 Expression of resu
16、lts . 10 7.1 Calculation. 10 7.2 Sources of uncertainty. 11 Annex A (informative) Practical example of a diffusion cell calibrator configured for evaluating speed of response in a hygrometer 14 Annex B (informative) Example of performances of diffusion cells for toluene and trichloromethane. 17 Anne
17、x C (informative) Example of uncertainty calculations for a periodic weighing system . 19 Bibliography. 23 Foreword 3 The text of ISO 6145-8:2005 has been prepared by Technical Committee ISO/TC 158 “Analysis of gases” of the International Organization for Standardization (ISO) and has been taken ove
18、r as EN ISO 6145-8:2008 by Technical Committee CEN/SS N21 “Gaseous fuels and combustible gas” the secretariat of which is held by CMC. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by February 2009
19、, and conflicting national standards shall be withdrawn at the latest by February 2009. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights
20、. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy
21、, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of ISO 6145-8:2005 has been approved by CEN as a EN ISO 6145-8:2008 without any modification. EN ISO 6145-8:2008
22、(E) DIN EN ISO 6145-8:2008-11 Introduction This part of ISO 6145 is one of a series of International Standards that present various dynamic volumetric methods used for the preparation of calibration gas mixtures. In the lower part of the mole fraction range considered, it is difficult to prepare and
23、 maintain gas mixtures for example of certain organic or reactive components in cylinders. This dynamic method has the advantage of a practically unlimited supply of calibration component, whereby adsorption effects can be reduced or even eliminated. If the complementary gas flow is measured as a ga
24、s mass flow, the preparation of calibration gas mixtures using diffusion is a dynamic-gravimetric method which gives contents in mole fractions. Principles for the measurement of the complementary gas flow are given in ISO 6145-1. 4 DIN EN ISO 6145-8:2008-11 EN ISO 6145-8:2008 (E) 1 Scope This part
25、of ISO 6145 specifies a dynamic method using diffusion for the preparation of calibration gas mixtures containing component mole fractions ranging from 109to 103. A relative expanded uncertainty of measurement, U, obtained by multiplying the relative combined standard uncertainty by a coverage facto
26、r k = 2, of not greater than 2 % can be achieved by using this method. By keeping the path between the diffusion source and place of use as short as possible, the method can be applied for the generation of low-concentration calibration gases of organic components that are liquid at room temperature
27、, with boiling points ranging from about 40 C to 160 C. This part of ISO 6145 is applicable not only for the generation of calibration gas mixtures of a wide range of hydrocarbons at ambient and indoor air concentration levels, but also for the generation of low-concentration gas mixtures of water.
28、2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 6145-7, Gas analysis P
29、reparation of calibration gas mixtures using dynamic volumetric methods Part 7: Thermal mass-flow controllers 3 Principle The calibration component migrates by diffusion through a diffusion tube of suitable dimensions (length, diameter) into a flow of a complementary gas, i.e. the complementary gas
30、of the mixture prepared. The liquid calibration component, of a known high purity, is contained in a reservoir that acts as the source of the component vapour. The reservoir is provided with a vertically placed diffusion tube. This assembly (the diffusion cell) is placed in a temperature-controlled
31、containment that is purged at a known and constant flow rate by a high-purity complementary gas (see Figure 1). The composition of the mixture is determined from the diffusion mass flow of the calibration component and the flow rate of the complementary gas. The diffusion mass flow rate of the calib
32、ration component in principle depends on its diffusion coefficient in the complementary gas, its vapour pressure at the temperature of the containment, the dimensions of the diffusion tube. 5 EN ISO 6145-8:2008 (E) DIN EN ISO 6145-8:2008-11 Accurate determination of the mass flow rate is achieved by
33、 either continuous weighing, after mounting the tube in a suspension microbalance, or by periodic weighing. The method of determination affects the uncertainty of the (momentary) mass flow of the calibration component (see 7.2). Key 1 complementary gas inlet 2 containment 3 diffusion tube 4 liquid r
34、eservoir 5 calibration gas outlet Figure 1 Schematic of diffusion apparatus 4 Reagents and materials 4.1 Liquid substances to be used as calibration component, of the highest possible purity so as to avoid any effects on the diffusion mass flow. If possible, the nature and quantities of the impuriti
35、es should be known and allowance made for their effects. 4.2 Complementary gas, of known purity, established by appropriate analytical techniques, e.g. Fourier-transform infrared spectrometry or gas chromatography. The nature of the complementary gas shall be adapted to the substance to be used as t
36、he calibration component. For example, air shall not be used as complementary gas for the preparation by diffusion of calibration gas mixtures of oxidizable substances. 6 DIN EN ISO 6145-8:2008-11 EN ISO 6145-8:2008 (E) 5 Apparatus 5.1 Diffusion apparatus 5.1.1 Materials The materials of the diffusi
37、on apparatus shall be chosen so as to avoid effects of physical or chemical sorption or desorption on the content of the calibration component. The smaller the desired content, the greater the effect of sorption/desorption phenomena. Diffusion reservoirs and tubes, as well as temperature containment
38、s and blending apparatus, should preferably be manufactured out of borosilicate glass. Choose chemically inert, flexible tube materials for the supply of complementary gas and transport of calibration gas mixture. Pay special attention to all junctions as possible sources of leaks. 5.1.2 Complementa
39、ry gas flow configuration Before the complementary gas reaches the diffusion cell, it is essential that its temperature be controlled to that of the diffusion cell containment. In order to achieve the uncertainty stated in Clause 1, the temperature in the containment should be controlled to within 0
40、,15 K. The minimum flow rate of the complementary gas should be sufficient to remove all component vapour without saturation. The maximum allowable rate should be low enough to avoid convective transport of the calibration component vapour inside the diffusion tube. This maximum flow rate is depende
41、nt upon the geometry of the diffusion apparatus. It is recommended to keep the Reynolds number of the complementary gas flow in the diffusion cell below 100. At a temperature of 25 C, the following condition should approximately be fulfilled: 31, 6 1 0vd 0,03 m; ratio of L to diameter of diffusion t
42、ube 3; diameter: 0,001 m to 0,02 m. NOTE Units which operate on the diffusion principle are commercially available and provide calibration gas mixtures containing highly adsorptive vapours. An example of one such unit for the preparation of reference standards of humidity in volume fractions of 109a
43、nd its performance details are given in Annex A. 6 Procedure 6.1 Preliminary checks and operating conditions Before assembling or filling a diffusion cell, the purity of the substance to be used as calibration component is to be assessed using an appropriate analytical technique (e.g. Fourier-transf
44、orm infrared spectrometry or gas chromatography) so as to quantify any likely major contaminants. Periodically check the diffusion mass flow at a known, fixed temperature and complementary gas flow rate as an indication of stability of the calibration compound in the reservoir. If the diffusion mass
45、 flow drifts by more than 1 % per month, this may be an indication of the presence of impurities. In that case, the contents of the diffusion cell should be replaced. When first placing the diffusion cell in its containment, allow the system to equilibrate before performing the first weighing so as
46、to ensure constancy of the diffusion mass flow. Generally, a period of 24 h is sufficient. To change the content of the calibration gas mixture, adjust the complementary gas flow rate. Alternatively, the calibration gas mixture can be further diluted, and its contents adjusted, by application of a s
47、econdary flow of a diluent gas. Changing the temperature of the diffusion-cell containment for adjustment of the content of the calibration gas mixture is not recommended. During the period of use, maintain the diffusion cell at constant temperature in order to avoid delay due to the time needed to
48、restore equilibrium. 8 DIN EN ISO 6145-8:2008-11 EN ISO 6145-8:2008 (E) 6.2 Determination of mass loss 6.2.1 Handling the diffusion cell Ensure that all weighing is performed with extreme cleanliness and avoid direct contact of the diffusion cell with hands. Use gloves and clean pliers or tweezers.
49、If appropriate, depending on the type used, close the diffusion cell before weighing. 6.2.2 Periodic-weighing mode The temperature and relative humidity in the weighing room should be controlled and kept constant during successive readings. The cell is periodically removed from the enclosure, weighed, and returned immediately to the enclosure. In a given time interval, the diffusion cell will decrease in mass. The measurement of this change in mass will have an associated measurement uncertainty. Theref
