1、BS EN ISO6145-7:2010ICS 71.040.40NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDGas analysis Preparation ofcalibration gasmixtures usingdynamic volumetricmethodsPart 7: Thermal mass-flow controllersThis British Standardwas published under theauthority of the St
2、andardsPolicy and StrategyCommittee on 30 April2009 BSI 2011ISBN 978 0 580 72205 930 June 2011 This corrigendum renumbers BS ISO 6145-7:2009as BS EN ISO 6145-7:2010BS EN ISO 6145-7:2010National forewordThis British Standard is the UK implementation of EN ISO 6145-7:2010. It is identical to ISO 6145-
3、7:2009. It supersedes BS ISO 6145-7:2009which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee PTI/15, Natural gas and gas analysis.A list of organizations represented on this committee can be obtained onrequest to its secretary.This publication does not purpo
4、rt to include all the necessary provisionsof a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunityfrom legal obligations.Amendments/corrigenda issued since publicationDate Comments EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN
5、ISO 6145-7 December 2010 ICS 71.040.40 English Version Gas analysis - Preparation of calibration gas mixtures using dynamic volumetric methods - Part 7: Thermal mass-flow controllers (ISO 6145-7:2009) Analyse des gaz - Prparation des mlanges de gaz pour talonnage laide de mthodes volumtriques dynami
6、ques - Partie 7: Rgulateurs thermiques de dbit massique (ISO 6145-7:2009) Gasanalyse - Herstellung von Kalibriergasgemischen mit Hilfe von dynamisch-volumetrischen Verfahren - Teil 7: Thermische Massendurchflussregler (ISO 6145-7:2009) This European Standard was approved by CEN on 11 December 2010.
7、CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate 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 a
8、pplication to the CEN-CENELEC Management Centre or to any CEN member. This European Standard 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-CENELEC
9、 Management Centre has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, N
10、etherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2010 CEN All rights of exploitat
11、ion in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN ISO 6145-7:2010: EForeword The text of ISO 6145-7:2009 has been prepared by Technical Committee ISO/TC 158 “Analysis of gases” of the International Organization for Standardization (ISO) and has been taken over
12、 as EN ISO 6145-7:2010. 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 June 2011, and conflicting national standards shall be withdrawn at the latest by June 2011. Attention is drawn to the possi
13、bility 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. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries ar
14、e bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Sp
15、ain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of ISO 6145-7:2009 has been approved by CEN as a EN ISO 6145-7:2010 without any modification. BS EN ISO 6145-7:2010EN ISO 6145-7:2010 (E)iiiContents Page Foreword iv 1 Scope . 1 2 Normative references . 1 3 Terms and defini
16、tions. 1 4 Principle. 2 5 Set-up. 2 5.1 General. 2 5.2 Thermal mass-flow controller using a constant current supply 2 5.3 Thermal mass-flow controller under constant temperature control . 3 6 Preparation of gas mixtures 4 6.1 Description of the experimental procedure .4 6.2 Area of validity 6 6.3 Op
17、erating conditions 6 7 Calculations. 7 7.1 Volume fraction. 7 7.2 Sources of uncertainty. 7 7.3 Uncertainty of measurement . 8 Annex A (informative) Pre-mixed gases for preparation of mixtures of high dilution 9 Annex B (informative) Practical hints. 10 Annex C (informative) Calculation of uncertain
18、ties 12 Bibliography . 15 ISO 2011BS EN ISO 6145-7:2010EN ISO 6145-7:2010 (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
19、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
20、 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 2. The main task of technical committees is to prepare International Standards.
21、 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
22、document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 6145-7 was prepared by Technical Committee ISO/TC 158, Analysis of gases. This second edition cancels and replaces the first edition (ISO 6145-7:2001). In preparation of
23、 the first edition, it was assumed that each thermal mass-flow controller (TMC) would be configured for use at its optimum performance, and the uncertainty in the method was estimated on that basis. In this edition, therefore, extra precautionary text has been added to make it clear that the method
24、shall not be employed, for example, to make a 10:1 binary mixture by using two thermal mass-flow controllers of identical range with one operated at its maximum, say, of 1 000 ml/min and the other at 100 ml/min. In the first edition, this necessary provision was only stated briefly in an informative
25、 annex; it has now been expanded and stated more explicitly in a normative part. Another major update is separation of the original Clause 3 into two clauses, one of which (Clause 4) defines the principle while the other (Clause 5) presents additional explanation to the user. The latter of these cla
26、uses now includes the necessary requirements. By introducing two new and relevant bibliographic references, the understanding of Annex B has been improved. Finally, some typing errors have been corrected. ISO 6145 consists of the following parts, under the general title Gas analysis Preparation of c
27、alibration gas mixtures using dynamic volumetric methods: Part 1: Methods of calibration Part 2: Volumetric pumps 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: Saturat
28、ion method Part 10: Permeation method Part 11: Electrochemical generation ISO 6145-3, entitled Periodic injections into a flowing gas stream, has been withdrawn. ISO 2011BS EN ISO 6145-7:2010EN ISO 6145-7:2010 (E)BS EN ISO 6145-7:2010INTERNATIONAL STANDARD 1Gas analysis Preparation of calibration ga
29、s mixtures using dynamic volumetric methods Part 7: Thermal mass-flow controllers 1 Scope This part of ISO 6145 is one of a series of International Standards dealing with dynamic volumetric methods used for the preparation of calibration gas mixtures. This part specifies a method for continuous prod
30、uction of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by use of commercially available thermal mass-flow controllers. If this method is employed for the preparation of calibration gas mixtures, the optimum performance is as follows: the relative
31、 expanded uncertainty of measurement, U, obtained by multiplying the combined standard uncertainty by a coverage factor k = 2, is not greater than 2 %. If pre-mixed gases are used instead of pure gases, mole fractions below 106can be obtained. The measurement of mass flow is not absolute and the flo
32、w controller requires independent calibration. The merits of the method are that a large quantity of the gas mixture can be prepared on a continuous basis and that multicomponent mixtures can be prepared as readily as binary mixtures if the appropriate number of thermal mass-flow controllers is util
33、ized. NOTE Gas-blending systems based upon thermal mass-flow controllers, some including the facility of computerization and automatic control, are commercially available. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated refe
34、rences, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 6143, Gas analysis Comparison methods for determining and checking the composition of calibration gas mixtures ISO 6145-1:2003, Gas analysis Preparati
35、on of calibration gas mixtures using dynamic volumetric methods Part 1: Methods of calibration 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 2011EN ISO 6145-7:2010 (E)2 4 Principle Continuous produc
36、tion of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by the use of commercially available thermal mass-flow controllers is described. By adjusting the set-points on the flow controllers to pre-determined values, it is possible to change the compo
37、sition of the gas mixture rapidly and in a continuously variable manner. By selecting appropriate combinations of thermal mass-flow controllers and with the use of pure gases, the volume fraction of the component of interest in the complementary gas can be varied by a factor of 1 000. 5 Set-up 5.1 G
38、eneral To prepare the gas mixture, each gaseous component is passed at a known, controlled flow rate, and at constant pressure, from a calibrated thermal mass-flow controller. Use accurate flowmeters in measuring the relevant flows in order to reach an acceptable measure of uncertainty regardless of
39、 the setting of the mass-flow controller (see also ISO 6145-1:2003, Table 1). A thermal mass-flow controller consists of a measuring unit for mass flow and a proportioning valve which is controlled by an electronic unit (see also References 1 and 2). 5.2 Thermal mass-flow controller using a constant
40、 current supply The flowing gas is passed through a heater connected to a constant current supply and the temperature is sensed upstream and downstream from the heater. Figure 1 shows the principle of a thermal mass-flow controller: heater, temperature sensors and associated circuitry. The two tempe
41、rature sensors, one upstream and one downstream from the heater form two arms of a Wheatstone bridge circuit, which is balanced to give a zero reading when there is no gas flow. When there is a gas flow through the system, a temperature difference, T, is established between the two sensors such that
42、 the heat flux, , is given by: pm cTq= (1) where cpis the heat capacity per unit mass, or molar heat capacity, of the gas at constant pressure; qmis the mass flow rate. ISO 2011BS EN ISO 6145-7:2010EN ISO 6145-7:2010 (E)3Key 1 temperature sensor 1 2 temperature sensor 2 3 heater 4 gas supply 5 curre
43、nt supply 6 Wheatstone bridge 7 differential amplifier 8 signal readout Figure 1 Principle of a thermal mass-flow controller with constant current supply The difference in temperature between sensors results in a potential difference across the Wheatstone bridge circuit and thus a signal. The signal
44、 is compared with an adjustable reference voltage in a differential amplifier. The resulting output signal is in turn used for operating a control valve to regulate the flow of gas. 5.3 Thermal mass-flow controller under constant temperature control In this system (see Figure 2), the gas passes thro
45、ugh three heaters in sequence, each of which is connected to an arm of a self-regulating Wheatstone bridge. Instead of the difference in temperature being measured, the input to each heater is such that the temperature distribution along the flow path is maintained uniform. The Wheatstone bridge cur
46、rent is proportional to the heat loss and therefore proportional also to the mass flow of the gas. The output signal is again used to operate a solenoid valve to control the mass flow rate. ISO 2011BS EN ISO 6145-7:2010EN ISO 6145-7:2010 (E)BS EN ISO 6145-7:20104 Key 1 heater 1 2 heater 2 3 heater 3
47、 4 gas supply 5 current supply 6 Wheatstone bridge 7 differential amplifier 8 signal readout Figure 2 Thermal mass-flow controller under constant temperature control In the preparation of multicomponent mixtures, it is in general necessary to use one mass-flow controller for each component. Dual-cha
48、nnel controllers are available and may be used in the preparation of binary mixtures or, for example, in the preparation of mixtures of a given gas in air. 6 Preparation of gas mixtures 6.1 Description of the experimental procedure A schematic diagram of the arrangement used for the preparation of b
49、inary mixtures is shown in Figure 3. The pressure and temperature at the time of the calibration shall be recorded. Depending on the gases to be mixed and the fact that they are not ideal, the volume fraction can be somewhat influenced by the ambient pressure and temperature. The pressure and temperature at the time of calibration of the analyser should be as near as possible to those prevalent at the time the thermal mass-flow controllers were checked by the comparison method given in ISO 6143 (see 7.3). Concentra
