1、 ISO 2014 Gas analysis Preparation of calibration gas mixtures using dynamic methods Part 2: Piston pumps Analyse des gaz Prparation des mlanges de gaz pour talonnage laide de mthodes volumtriques dynamiques Partie 2: Pompes piston INTERNATIONAL STANDARD ISO 6145-2 Second edition 2014-08-15 Referenc
2、e number ISO 6145-2:2014(E) ISO 6145-2:2014(E)ii ISO 2014 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2014 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including ph
3、otocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested 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
4、 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ISO 6145-2:2014(E) ISO 2014 All rights reserved iii Contents Page Foreword iv 1 Scope . 1 2 Normative references 1 3 T erms and definitions . 2 4 Symbols 2 5 Principle and equipment . 3 5.1 Principle 3 5.2 Equipment . 3 6 Calibr
5、ation gas mixture preparation . 5 6.1 Safety issues 5 6.2 Mixture feasibility 6 6.3 Preparation system and setting-up of mixture composition 7 6.4 Input pressure control 7 6.5 Temperature control 7 6.6 Homogenization . 7 6.7 Stability 8 6.8 Output pressure and flow pulsation . 8 6.9 Composition of t
6、he parent gases . 8 7 Calculation of volume fractions and associated uncertainty evaluation .9 7.1 Calculation method A 9 7.2 Calculation method B .10 8 Gas mixtur e c omposition v erification .12 Annex A (normative) Amount-of-substance fractions 13 Annex B (informative) Uncertainty evaluation of th
7、e gas mixture composition .15 Annex C (informative) Gas mixtur e v erification 21 Annex D (informative) Numerical example 25 Bibliography .30 ISO 6145-2:2014(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies
8、). 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 no
9、n-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. The procedures used to develop this document and those intended for its further maintenance are descr
10、ibed in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives Attention is drawn to the
11、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. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO li
12、st of patent declarations received. www.iso.org/patents Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement. For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as
13、information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information The committee responsible for this document is ISO/TC 158, Analysis of gases. This second edition cancels and replaces the first edition (ISO 61
14、45-2:2001), which has been technically revised. The main objective of this revision is to extend the first edition for calculating the composition in volume and amountofsubstance fractions from the displacement volumes of piston pumps. Appropriate measurement functions and guidance on uncertainty ev
15、aluation are given for the mixing of real gases at unequal operational conditions of the piston pumps. ISO 6145 consists of the following parts, under the general title Gas analysis Preparation of calibration gas mixtures using dynamic methods: Part 1: Methods of calibration Part 2: Volumetric pumps
16、 Part 4: Continuous syringe injection method Part 5: Capillary calibration 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 ISO 6145-3, entitled Periodic injection
17、s into a flowing gas stream, has been withdrawn.iv ISO 2014 All rights reserved INTERNATIONAL ST ANDARD ISO 6145-2:2014(E) Gas analysis Preparation of calibration gas mixtures using dynamic methods Part 2: Piston pumps 1 Scope ISO 6145 comprises a series of International Standards dealing with vario
18、us dynamic methods used for the preparation of calibration gas mixtures. This part of ISO 6145 describes a method and preparation system using piston pumps. The mixture composition and its associated uncertainty are based on calibration of the piston pumps by dimensional measurements. The calibratio
19、n gas mixtures prepared using this method consist of two or more components, prepared from pure gases or other gas mixtures using gas-mixing pumps. Such gas-mixing pumps contain at least two piston pumps, each driven with a defined ratio of strokes, and appropriate accessories for gas feeding and mi
20、xture homogenization. This part of ISO 6145 is applicable only to mixtures of gaseous or totally vaporized components including corrosive gases, as long as these components neither react with each other nor with the wetted surfaces of the mixing pump. The use of gas mixtures as parent gases is cover
21、ed as well. Multi-component gas mixtures and multi-step dilution procedures are included in this International Standard as they are considered to be special cases of the preparation of two-component mixtures. This part of ISO 6145 describes a method of preparing calibration gas mixtures whose compos
22、ition is expressed in volume fractions. The necessary equations and associated uncertainty evaluation to express the gas composition in amountofsubstance fractions are given in Annex A. With this method, provided that sufficient quality assurance and control measures are taken, calibration gas mixtu
23、res can be prepared with a relative expanded uncertainty of 0,5 % (coverage factor k = 2) in the volume fraction. Numerical examples showing that under specified conditions smaller uncertainties are attainable are given in Annexes B through D. Using this method, dilution ratios of 1:10 000 can be ac
24、hieved in discrete increments. Lower fractions (down to 1 10 8 ) can be achieved by multi-stage dilution or by the use of gas mixtures as input gases. Final mixture flow rates of 5 l/h to 500 l/h can be realized depending on the equipment used. 2 Normative references The following documents, in whol
25、e or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 7504, Gas analysis Vocabulary ISO 1
26、4912, Gas analysis Conversion of gas mixture composition data ISO/IEC Guide 98-3, Uncertainty of measurement Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) ISO/IEC Guide 99, International vocabulary of metrology Basic and general concepts and associated terms (VIM) ISO 2014
27、 All rights reserved 1 ISO 6145-2:2014(E) 3 T erms an d definiti ons For the purposes of this document, terms and definitions given in ISO/IEC Guide 99, ISO/IEC Guide 98-3, ISO 14912, ISO 7504, and the following apply. 3.1 operational conditions pressure and temperature in the piston pumps at which
28、the gas mixture is prepared 3.2 parent gas pure gas or gas mixture used for preparation of a gas mixture 3.3 piston pump gas forwarding system comprising cylinder, piston, steering plate, and eccentric driving disk mounted on a common plate 3.4 reduction gear ratio quotient of the number of strokes
29、and the maximum number of strokes of the piston pump that can be set in distinct steps by the switch gear 3.5 reference conditions pressure and temperature to which volume fractions refer 3.6 stroke volume forwarding geometric displacement volume per stroke of a piston pump 4 Symbols Symbol Quantity
30、 Unit B second virial coefficient (virial equationofstate in pressure) Pa 1 i index of a component k,l index of a piston pump; index of a parent gas L gear ratio N number of strokes (in a given period of time) N max maximum number of strokes (in a given period of time) n amountofsubstance mol n mix
31、total amountofsubstance of a mixture mol p pressure Pa R ideal gas constant J mol 1K 1 T temperature K u standard uncertainty V gas volume m 32 ISO 2014 All rights reserved ISO 6145-2:2014(E) Symbol Quantity Unit V geo stroke volume m 3 x amountofsubstance fraction (of a component in a parent gas) 1
32、 y amountofsubstance fraction (of a component in the prepared gas mixture) 1 Z compressibility 1 volume fraction (of a component in the prepared gas mixture) 1 volume fraction (of a component in a parent gas) 1 5 Principle and equipment 5.1 Principle The principle of the dynamic preparation method d
33、escribed in this part of ISO 6145 is based on the displacement volume of piston pumps forwarding defined gas portions that are continuously merged and homogenized for obtaining the required gas mixture. For pure gases, the volume fraction of component i in the prepared gas mixture is approximately e
34、qual to the volume of component i divided by total volume of all components, as given by Formula (1): i ig eoi kg eo k k NV NV , ,(1) where idenotes the volume fraction of component i at the operational conditions of the piston pumps. These conditions may differ from the conditions at which the cali
35、bration gas mixture thus prepared is going to be used. The calculation of volume fractions is described in Clause 7, in two variants. Method A requires the prepared gas mixture to be used at the operational conditions (7.1), whereas method B covers the expression of the volume fractions at reference
36、 conditions (7.2). Depending on the situation, one of these methods shall be used in applications where volume fractions are needed. In applications, where amountofsubstance fractions are needed, these shall be calculated directly from the displacement volumes. The necessary expressions and associat
37、ed uncertainty evaluation are given in Annex A. 5.2 Equipment Calibration gas mixtures with defined composition are prepared using gas-mixing pumps containing two or more piston pumps, pneumatically separated from each other. A common motor drives the piston pumps via separate gear trains and indivi
38、dual switch gears. The number of strokes of the individual piston pumps is defined by preset reduction gear ratios. The gas portions forwarded by each of the piston pumps are quantified by the stroke volume V geo,kand by their individual number of strokes N k(see Figure 1). ISO 2014 All rights reser
39、ved 3 ISO 6145-2:2014(E) Key d diameter of cylinder h height of piston stroke Figure 1 Principle of a piston pump To achieve the required calibration gas mixture, separately forwarded gas portions are merged and homogenized. Since the stroke volume V geo,kis constant, different gas compositions are
40、prepared only by variation of the number of strokes N k . The use of both quantities is sufficient for the calculation of mixture composition when using pure gases. The stroke volume of piston pump k is calculated from the diameter of its cylinder and the height of its piston stroke Vd h geok kk (2)
41、 The forwarded gas volume is usually given as a whole number times the stroke volume. The number of strokes can be chosen in order to achieve the desired mixing ratio. The gear ratio L krelates the stroke number to the maximum number of strokes NL N kk (3) An example of realization of the described
42、method is shown in Figure 2 for a gas-mixing pump comprising two piston pumps 1 and 2 of the same size. Both piston pumps are driven by a common electrical motor, key 8, via defined gear trains with switch gears key 2 and key 4, respectively. Gases 1 and 2 are fed to the piston pumps via gas inlets
43、figure footnotes a and b, respectively. Bubbling vessels (key 5) at the gas inlets are used to control the input pressure to the piston pumps and to adjust a small excess gas flow which is vented at ambient pressure. The temperature of each piston pump can be measured with temperature sensors T 1and
44、 T 2that shall be integrated into the body of the piston pumps. The gases forwarded by the piston pumps are merged and homogenized in mixing vessel (key 6). The final gas mixture is provided at gas outlet (key 7) to the intended application. Details of the implementation of temperature control of pi
45、ston pumps and parent gases attaining reduced uncertainties is given in Annex B.4 ISO 2014 All rights reserved ISO 6145-2:2014(E) 8 1 2 + Gas 2 Gas 2 Gas 1 Gas 1 2 p 1 T 2 T 1 p 7 a b 1 4 2 3 5 5 6 Key p 1 pressure, piston pump 1 4 switch gears 2 p 2 pressure, piston pump 2 5 bubbling vessel T 1 tem
46、perature sensor, piston pump 1 6 mixing vessel T 2 temperature sensor, piston pump 2 7 gas outlet for gas mixture 1 piston pump 1 8 drive motor 2 switch gears 1 a Gas inlet for gas 1. 3 piston pump 2 b Gas inlet for gas 2. NOTE Piston pumps 1 and 2 as shown in Figure 1. Figure 2 Example of realizati
47、on for the dynamic preparation of two-component calibration gas mixtures 6 Calibration gas mixture preparation 6.1 Safety issues The possibility of dangerous reactions, such as explosions (e.g. mixtures containing flammable gases and oxygen) or strongly exothermic polymerisations (e.g. hydrogen cyan
48、ide) and decompositions (e.g. acetylene), shall be excluded for safety reasons. If there is the possibility of formation of hazardous gas mixtures, all appropriate safety precautions shall be applied. Information on dangerous reactions and dangerous combinations that shall be excluded for safety rea
49、sons is provided in dangerous goods regulations and in gas supplier handbooks. 1 Safe discharge of toxic or flammable gases and gas mixtures shall be ensured. Contact with ignition sources shall be avoided, if merging of the parent gases can form flammable mixtures. Shortterm concentration peaks can occur when the composition is changed. ISO 2014 All rights reserved 5 ISO 6145-2:2014(E) Precautions shall be taken during feeding the parent gases
