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1、INTERNATIONAL STANDARD IS0 8573-3 First edition 1999-06-01 Compressed air - Part 3: Test methods for measurement of humidity Air comprim - Partie 3: Mthodes dessai pour mesurer le taux dhumidit This material Is reproduced from I S 0 documenU under International Organization for Standardization (ISO)
2、 Copyright License Number IHS/ICC/I 996. Not for resale. No part of these IS0 documents may be reproduced in any form, electronic retrieval system or otherwise, except as allowed in the copyright law of the country of use, or with the prior written consent of IS0 (Case postale 56, I2 1 1 Geneva 20,
3、Switzerland, Fax + 41 22 734 IO 79), IHS or the I S 0 Licensors members. Reference number IS0 8573-3: 1999( E) STD=ISO 8573-3-ENGL 3999 = 4853903 078b557 930 M IS0 8573-3:1999(E) Contents 1 Scope 1 2 Normative references 1 3 Terms and definitions . 1 4 Units 1 5 Selection guide and available methods
4、 . 2 6 Sampling techniques . 2 7 Measurement methods 3 8 Evaluation of test results 5 9 Conversions from non-standard humidity units to standard format and vice versa . 5 1 O Uncertainty . 6 11 Expression of results 6 12 Test report 6 Annex A (informative) Example of compressed air humidity statemen
5、t . 7 Annex B (informative) Calculation of vapour pressure . 8 Annex C (informative) Preferred methods of humidity measurement . 10 Annex D (informative) Non-preferred methods of humidity measurement . 13 Bibliography 14 (Q IS0 1999 All rights reserved . Unless otherwise specified. no part of this p
6、ublication may be reproduced or utilized in any form or by any means. electronic or mechanical. including photocopying and microfilm. without permission in writing from the publisher . International Organization for Standardization Case postale 56 CH-121 1 Genve 20 Switzerland Internet isoko.ch Prin
7、ted in Switzerland ii -,-,- o IS0 STD=ISO 8573-3-ENGL 1999 q851903 078b558 877 = IS0 8573-3:1999(E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally
8、carried out through IS0 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 wo
9、rk. IS0 collaborates 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 ISOAEC Directives, Part 3. Draf International Standards adopted by the technical com
10、mittees 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. International Standard IS0 8573-3 was prepared by Technical Committee ISOKC 1 18 Compressors, pneumatic tools and pneumatic machine
11、s, Subcommittee SC 4, Quality of compressed air. IS0 8573 consists of the following parts, under the general title Compressed air - Part 1: Contaminants and quality classes - Part 2: Test methods for aerosol oil content - Part 3: Test methods for measurement of humidity - Part 4: Test methods for so
12、lid particle content - Part 5 : Test methods for oil vapour and organic solvent content - Part 6: Test methods for gaseous contaminant content - Part 7: Test methods for viable microbiological contaminant content Annexes A, B, C and D are for information only. iii STDoISO 8573-3-ENGL 1999 m q851903
13、078b559 703 IS0 8573-3: 1999( E) o IS0 Introduction This part of IS0 8573 is one in a series of International Standards (planned or published) with the aim of harmonizing air contamination measurements. It is also intended to be used for reference when stating air purity class according to IS0 8573-
14、1. iv INTERNATIONAL STANDARD o IS0 IS0 8573-3:1999(E) Compressed air - Part 3: Test methods for measurement of humidity 1 Scope This part of IS0 8573 provides guidance on selection from the available suitable methods for measurement of humidity in compressed air and specifies the limitations of the
15、various methods. It does not provide methods for measurement of water content in states other than vapour. This part of IS0 8573 specifies sampling techniques, measurement, evaluation, uncertainty considerations and reporting for the air contamination parameter humidity. It gives guidance for the co
16、nversion of humidity statements to the standard format. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this pari of IS0 8573. For dated references, subsequent amendments to, or revisions of, any of these pub
17、lications do not apply. However, parties to agreements based on this part of IS0 8573 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest editions of the normative documents referred to appl
18、ies. Members of IS0 and IEC maintain registers of currently valid International Standards. IS0 3857-1, Compressors, pneumatic tools and machines - Vocabulary - Part 7: General. IS0 5598, Fluid power systems and components - Vocabulary. IS0 7183:1986, Compressed air dryers - Specifications and testin
19、g. IS0 8573-1, Compressed air - Part 7: Contaminants and purity classes. 3 Terms and definitions For the purposes of this part of IS0 8573, the terms and definitions given in IS0 3857-1 and IS0 5598 and the specific humidity terms and definitions given in IS0 7183 apply. 4 Units For the purposes of
20、this part of IS0 8573, the following non-preferred SI units are used: 1 bar = 100 O00 Pa NOTE Bar(e) is used to indicate effective pressure above atmospheric. 1 I (litre) = 0,001 m 3 1 -,-,- - STDOIS0 8573-3-ENGL If999 q851903 078b5bL 3bIf o IS0 IS0 8573-3:1999(E) *OC a 5 Selection guide and availab
21、le methods expressed as pressure dew point c, “C -80 -60 -40 -20 O +20 +40 +60 Detection limit for water vapoui is about 0,l x 10-6to 1 x 10-6 b The methods available for measuring humidity, their grade of uncertainty and their preferred range of use are listed in Table 1. 1 ,o to 2,o 2,O to 5,O Tab
22、le 1 - Methods available for measuring humidity I Methods in order of I Uncertainty I Range for humidity level I Remarks I I I I increasing uncertainty 2,O to 5,O Method I Table t I Chemical a The uncertainy is not yet available in “C. b Volume fraction. c Pressure dew point is defined in IS0 7183.
23、- (Psychrometer I 9 0,2to l,o Il 1 I 6 Sampling techniques 6.1 General Dew point can be measured at atmospheric pressure or under actual pressure conditions. The pressure to which the dew point is referred shall be stated. It is important that the air flow is controlled within the upper and lower li
24、mits to prevent damage to the probe and to ensure that a representative measurement is made. 6.2 Probe installation 6.2.1 Full flow measurement The probe is inserted in the main air flow stream, but protected against free water and other contaminants and used within the stated lower and upper limits
25、 of flow velocity for the measurement system. 6.2.2 Partial flow measurement 6.2.2.1 Bypass The probe i s installed in a small bypass tube. In this way the flow velocity to which the probe is exposed may be controlled. 6.2.2.2 Extraction The probe is installed in a small extraction tube which conduc
26、ts an air sample from the main air flow stream into the measurement chamber, where the measurement is made under system pressure. 6.2.3 Reduced-pressure measurement The probe is installed in a chamber into which an air flow is fed from the main air stream. Before measurement, the pressure is reduced
27、 to a suitable measuring pressure (normally atmospheric). 2 -,-,- STD*ISO 8573-3-ENGL 1797 W 11851703 078b5b2 2TB o IS0 IS0 8573-311 999(E) Characteristic applications Humidity range Pressure range 6.3 Requirements on sampling and measurement conditions Atmospheric air and compressed air -80 “C to +
28、60 “C pressure dew point Atmospheric pressure 6.3.1 The measurements carried out depend on the reproducibility of the method and the experience of the patties involved in the provision of measurement facilities. Temperature range Contamination tolerance 6.3.2 Materials used for conducting the air in
29、to the sampling system shall not affect the water vapour content of the sample. See C.2 in annex C. O “C to +40 “C Good 6.3.3 The sampling system pressure shall be recorded during measurement. Characteristic applications Humidity range 6.3.4 The sampling system temperature shall be higher than the m
30、easured dew point. Atmospheric air and compressed air -20 “C to +25 “C pressure dew point 6.3.5 The measurement system shall have reached a steady state before any measurement takes place and shall be kept steady during measurement. The readings from two consecutive measurements taken with at least
31、20 min interval shall not differ by more than the accuracy of the measuring system. Temperature range Contamination tolerance 7 Measurement methods O “C to +50 “C Poor Tables 2 to 9 list a number of methods for humidity measurement, including limitations on application, measurement pressure and temp
32、erature. Descriptions of the different methods can be found in annex C. Some non-preferred methods are described in annex D. A Consideration shall be given to the measurement system integrity and the calibration requirements of the measurement equipment which shall be used as described in applicable
33、 instructions and International Standards. It shall be proven that the equipment used is capable of achieving the uncertainty required within the specified range and tolerance. Any method shall only be used within the upper or lower limits of its range of operation. Check and consider calibration re
34、cords. Table 3 - Chilled mirror (condensation) with manual thermometer reading I Pressure range 1 O bar(e) to 200 bar(e) I 3 -,-,- IS0 8573-3:1999(E) Characteristic applications Humidity range Q IS0 Atmospheric air and compressed air -80 “C to +25 “C pressure dew point Pressure range Temperature ran
35、ge O bar(e) to 20 bar(e) O “C to +50 “C Contamination tolerance Poor I Humidity range Pressure ranae Table 5 - Chemical reaction method using direct-reading (glass) tubes with hygroscopic content I Characteristic applications I Atmospheric air and compressed air I -65 “C to +35 “C pressure dew point
36、 Atmosoheric Dressure Contamination tolerance I Temperature range I O “C to +40 “C I Average Humidity range Pressure range Table 6 - Measurement with electrical sensor based on capacitance I Characteristic applications I Atmospheric air and compressed air I -80 “C to +40 “C pressure dew point O bar(
37、e) to 20 bar(e) Humidity range Pressure ranae I Temperature range I -30 “C to +50“C I -40 “C to +25 “C pressure dew point O barfel to 20 barel Contamination tolerance Average Temperature range Contamination tolerance Table 7 - Measurement with electrical sensor based on conductivity I Characteristic
38、 applications I Atmospheric air and compressed air I -30 “C to +50 “C Average Characteristic applications Humidity range Pressure range Atmospheric air and compressed air -40 “C to +25 “C pressure dew point O bar(e) to 20 bar(e) Table 8 - Measurement with electrical sensor based on resistance Temper
39、ature range Contamination tolerance O “C to +50 “C Average 4 o IS0 Characteristic applications Humidity range IS0 8573-311 999(E) Atmospheric air 5 10 to 100 % relative humidity Table 9 - Psychrometer (wet and dry bulb thermometers) Pressure range Temperature range Atmospheric pressure o “C to +1 O0
40、 “C Contamination tolerance Poor I 8 Evaluation of test results 8.1 Reference conditions Unless otherwise agreed, the reference conditions for humidity statements are: Compressed air temperature 20 “C Compressed air pressure 7 bar(e) 8.2 Recalculation for deviating pressure When necessary, the obtai
41、ned value can be referred to another pressure (reference pressure) using the absolute pressure values and partial pressures. See annex B. 8.3 Recalculation for deviating temperature Normally not required except in the case of relative humidity. 8.4 Recalculation for influence of other contaminants S
42、ome contaminants, particularly molecules which have a structure similar to water molecules, may disturb the measurements. Therefore these shall be eliminated from the sample before measurement takes place. If this is not possible, then an evaluation shall be made to determine the uncertainty caused
43、by these contaminants. 9 Conversions from non-standard humidity units to standard format and vice versa 9.1 Relative humidity The relative humidity value for a known air sample at a known temperature can be recalculated to a dew point temperature using the table in IS0 7183:1986, Annex C, which give
44、s values for saturation pressures and densities of water vapour at different temperatures. Read the saturation vapour pressure for the actual temperature and multiply this by the percentage relative humidity. In the table, read the dew point temperature corresponding to the actual partial vapour pre
45、ssure. 9.2 Dew point Dew point at atmospheric pressure (1 bar absolute) is erroneously but commonly referred to as “atmospheric dew point“. It represents an imaginary dew point and is not an acceptable term for describing the water content. 9.3 Mixing ratio (or specific humidity) Water to dry air ma
46、ss mixing ratio: use the table in IS0 71 83:1986, annex C. Water to wet air mass mixing ratio: use the table in IS0 71 833 986, annex C. 5 -,-,- - STD=ISO 8573-3-ENGL 1977 4853703 078b5b5 TO7 D IS0 8573-3:1999(E) Q IS0 10 Uncertainty NOTE Calculation of the probable uncertainty according to this cla
47、use is not always necessary. Due to the nature of physical measurements, it is impossible to measure a physical quantity without error or, in fact, to determine the true uncertainty of any one particular measurement. However, if the conditions of the measurement are sufficiently well known, it is po
48、ssible to estimate or calculate a characteristic deviation of the measured value from the true value, such that it can be asserted with a certain degree of confidence that the true error is less than the said deviation. The value of such a deviation, together with its confidence level (normally 95%)
49、, constitutes a criterion of the accuracy of the particular measurement. It is assumed that all systematic uncertainties that may occur in the measurement of the individual quantities measured and of the characteristics of the gas may be compensated for by corrections. A further assumption is that the confidence limits in uncert