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1、BRITISH STANDARD BS 2842:1992 Specification for Whirling hygrometer UDC 551.508.71:536.512 BS 2842:1992 This British Standard, having been prepared under the direction of the Laboratory Apparatus Standards Policy Committee, was published under the authority of the Standards Board and comes into effe
2、ct on 15 October 1992 BSI 07-1999 First published April 1957 Second edition February 1966 Third edition October 1975 Fourth edition October 1992 The following BSI references relate to the work on this standard: Committee reference LBC/36 Draft for comment 91/56996 DC ISBN 0 580 21161 4 Committees re
3、sponsible for this British Standard The preparation of this British Standard was entrusted by the Laboratory Apparatus Standards Policy Committee (LBC/-) to Technical Committee LBC/36, upon which the following bodies were represented: Association for Science Education British Glass Manufacturers Con
4、federation British Laboratory Ware Association CLEAPSS School Science Service Department of Trade and Industry (Laboratory of the Government Chemist) Institute of Medical Laboratory Science The following bodies were also represented in the drafting of the standard, through subcommittees and panels:
5、British Medical Association Department of Health Department of Trade and Industry (National Physical Laboratory) Institute of Petroleum Medical Sterile Products Association Amendments issued since publication Amd. No.DateComments BS 2842:1992 BSI 07-1999i Contents Page Committees responsibleInside f
6、ront cover Forewordii Section 1. General 1.1Scope1 1.2Informative references1 Section 2. Thermometers 2.1Type2 2.2Temperature scale2 2.3Stabilization2 2.4Material2 2.5Range2 2.6Dimensions2 2.7Graduation and figuring2 2.8Accuracy2 2.9Expansion chamber3 2.10 Marking3 Section 3. Frame 3.1Construction o
7、f frame4 3.2Water container4 Annex A (informative) Method of use of whirling hygrometers5 Annex B (informative) Tables suitable for use with whirling hygrometers5 Annex C (informative) Errors in computed relative humidity5 Annex D (informative) Thermometric glasses approved by the National Physical
8、Laboratory7 Annex E (informative) Testing of thermometers7 Figure 1 Whirling hygrometer: example of general design4 Table 1 Dimensions for thermometer2 Table C.1 Maximum error in computed relative humidity due to thermometer error6 Table D.1 Identification stripe(s) or approved abbreviations and nor
9、mal maximum working temperature of all glasses that have been approved for the manufacture of thermometer bulbs7 List of referencesInside back cover BS 2842:1992 ii BSI 07-1999 Foreword This British Standard has been prepared under the direction of the Laboratory Apparatus Standards Policy Committee
10、, and supersedes BS 2842:1975 which is withdrawn. This British Standard is one of a series prepared at the request of the Temperature Measuring Instruments Sub-committee (since disbanded) of the Defence Materials Standardisation Committee of the Ministry of Defence. It is intended to cover the Servi
11、ce requirements for this type of hygrometer as well as the requirements of commercial users. This standard was first published in 1957, with the title Whirling hygrometer (medium size). It was revised in 1966 to permit a wider range of bulb diameters, to specify an alternative thermometer with a pla
12、in front, and to relax the dimensional requirements for the button top. Experience in using the whirling hygrometer specified in the 1966 edition showed that the figures for maximum error given in Table 2 understated the actual error values. The 1975 edition specified a larger hygrometer incorporati
13、ng a longer thermometer of improved design to overcome the inaccuracy. At the same time, the increased length was to allow a single thermometer with an extended temperature range to be used. Though more accurate, the 1975 larger model was never produced. Consumers demanded manufacture of the smaller
14、 1966 medium size model. In response to this demand the present standard reinstates the medium size model, but with realistic revised error figures. Thermometers with a Fahrenheit scale have not been included in this revision. In order to avoid confusion between the various revisions of this specifi
15、cation, the thermometers now specified are to be marked to indicate the year of issue of this British Standard. For the information of users a method of using the hygrometer is given in Annex A. The whirling hygrometer is used, in conjunction with appropriate relative humidity tables (see Annex B),
16、for the determination of the temperature and relative humidity of the air. Annex C indicates, for each hygrometer, the size of errors in relative humidity arising from thermometer errors. Figure 1 illustrates the general design of the hygrometer, but the details shown are not to be taken as being re
17、quirements of this British Standard except as indicated in the text. When wet-bulb and dry-bulb measurements of humidity of a higher precision are required, an aspirated hygrometer conforming to BS 5248:1990 should be used. NOTEFor accurate determination of humidity, hygrometers of the whirling or a
18、spirated type are not recommended for use in isolation from other, more direct means of measurement. Product certification. Users of this British Standard are advised to consider the desirability of third party certification of product conformity with this British Standard based on testing and conti
19、nuing product surveillance, which may be coupled with assessment of a suppliers quality systems against the appropriate Part of BS 5750. Enquiries as to the availability of third party certification schemes are forwarded by BSI to the Association of Certification Bodies. If a third party certificati
20、on scheme does not already exist, users should consider approaching an appropriate body from the list of Association members. BS 2842:1992 BSI 07-1999iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their co
21、rrect application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 8, an inside back cover and a back cover. This standard has been updated (see copy
22、right date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. iv blank BS 2842:1992 BSI 07-19991 Section 1. General 1.1 Scope This British Standard specifies requirements for thermometers suitable for use in whirling (sling) hygrometer
23、s, together with sufficient details of the other parts of the instrument to ensure that the thermometers are interchangeable in the frames. 1.2 Informative references This British Standard refers to other publications that provide information or guidance. Editions of these publications current at th
24、e time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions. BS 2842:1992 2 BSI 07-1999 Section 2. Thermometers 2.1 Types The thermometers shall be of the mercury-in-glass, gas-filled, solid-stem type, with a lens magnifying front and a b
25、utton top. They shall be graduated for complete immersion, i.e. to give correct readings when wholely immersed in the medium whose temperature is being measured. NOTEIt is recommended that there be a slight neck, to allow a closely fitting cylindrical absorbent sleeve of suitable type to be fitted s
26、ecurely to the bulb. 2.2 Temperature scale The thermometers shall be graduated in degrees Celsius, as defined in the International Temperature Scale of 1990 1. 2.3 Stabilization The thermometers shall be stabilized before graduation using a process such that the accuracy of the finished thermometer
27、is within the limits specified in clause 2.8. 2.4 Material The stem or capillary tube shall be of thermometric glass appropriate for the temperature range with an enamel back. The bulb shall be made of a thermometric glass approved by the National Physical Laboratory (see Annex D). NOTETo reduce the
28、 likelihood of fracture due to mechanical or thermal shock, all the glass should be annealed following any high temperature treatment during manufacture. 2.5 Range The nominal ranges of the thermometers shall be 15 C to + 40 C 5 C to + 50 C + 10 C to + 65 C. 2.6 Dimensions The thermometers shall con
29、form to the dimensions given in Table 1. Table 1 Dimensions for thermometers 2.7 Graduation and figuring 2.7.1 Scale lines The thermometers shall be graduated at each 0.5 C, with a longer line at each 1 C. The lines at each 5 C shall be extended further. The scale lines shall be fully numbered at ea
30、ch 5 C. The shorter scale lines shall extend towards the magnified image of the mercury column formed by the lens front, so that the thermometer is easily readable. All scale lines and figures shall be legibly etched or otherwise durably marked. The thickness of the lines shall not exceed 0.2 mm. 2.
31、7.2 Figuring The figures shall be upright when a thermometer is held in a horizontal position and viewed from the front with the bulb to the left, and shall be placed symmetrically below the lines to which they refer. 2.8 Accuracy The reading of a thermometer shall not be in error by more than 0.3 C
32、, at any point on the scale when the thermometer is completely immersed. Dimensions in millimetres Overall length164 to 168 Scale length80 to 108 Bulb length15 to 22 Bulb diameter (max.)5.5 Stem diameter (max.)5.5 Distance from bottom of bulb to lowest scale line (min.) 38 Button top diameter6 to 8
33、Button top thickness (min.)1.5 BS 2842:1992 BSI 07-19993 2.9 Expansion chamber The thermometers shall be so constructed as to withstand a temperature of 20 C above the maximum temperature on the thermometer scale without damage. To enable the thermometers to withstand this temperature an expansion c
34、hamber, which shall be pear-shaped with a hemispherical top, shall be visible in the frame. This chamber shall not be obscured by any part of the thermometer clamping assembly. There shall be at least 5 mm of unchanged capillary tube above the highest scale line. 2.10 Marking Each thermometer shall
35、be permanently and legibly marked with the following. a) The official symbol “C”, or an abbreviation of the name Celsius such as “C”. b) The identification of the bulb glass, e.g. by coloured stripe or stripes on the bulb or an approved abbreviation on the stem (see Annex D). c) An identification nu
36、mber, e.g. a batch number. d) The makers and/or vendors name or readily identifiable mark. e) If required, the purchasers name or mark. f) The number and date of this British Standard, i.e. BS 2842:19921). 1) Marking BS 2842:1992 on or in relation to a product represents a manufacturers declaration
37、of conformity, i.e. a claim by or on behalf of the manufacturer that the product meets the requirements of the standard. The accuracy of the claim is solely the claimants responsibility. Such a declaration is not to be confused with third party certification of conformity, which may also be desirabl
38、e. BS 2842:1992 4 BSI 07-1999 Section 3. Frame 3.1 Construction of frame The frame of the hygrometer shall be of robust construction, manufactured from material of a type known to be stable within the temperature range of the thermometer. The design shall be such as to accept thermometers of stem di
39、ameter 5.5 mm and button top diameter 8 mm. The instrument shall be capable of being rotated at about 180 r/min when held in the hand and shall allow free passage of air past the two thermometer bulbs. The thermometers shall be held securely side by side with the whole length of the scales clearly v
40、isible. Means shall be provided to prevent the thermometers from rotating in the frame, and to enable the frame to be opened to permit replacement of the thermometers. NOTEAn example of the general design of a whirling hygrometer is shown in Figure 1. 3.2 Water container The frame shall incorporate
41、a water container, designed so that water cannot leak from it during use, in such a position that a short length of sleeve (see A.1) dipping into it can be fitted to the wet bulb thermometer. At least 5 mm of sleeve below the bulb of the thermometer shall be exposed to the stream of air. Figure 1 Wh
42、irling hygrometer: example of general design BS 2842:1992 BSI 07-19995 Annex A (informative) Method of use of whirling hygrometers A.1 Apparatus The whirling hygrometer consists of two mercury-in-glass thermometers mounted side by side in a frame which is provided with a handle and spindle so that t
43、he frame and thermometers can be rotated at approximately 180 r/min about a horizontal axis. The bulb of one of the thermometers is covered by a closely fitting cylindrical sleeve, the end of which dips into a small water container attached to the end of the frame. When the frame is rotated the ther
44、mometer bulbs pass through the air at a rate dependent on the speed of rotation. Provided the air velocity is sufficiently great, the wet bulb thermometer cools down to a constant (wet bulb) temperature due to the evaporation of water from the wet sleeve. Rotation for 30 s to 40 s is sufficient. Fro
45、m the readings of the wet bulb and dry bulb thermometers the relative humidity, dew point or vapour pressure of the water in the air can be obtained from hygrometric tables for whirling (sling) or aspirated hygrometers (see Annex B). A.2 Precautions The following precautions are recommended. a) The
46、sleeve should be of a suitable width to fit tightly over the wet bulb and should be long enough to reach the bottom of the distilled water reservoir. The sleeve should not be of so tight a fit in the tube or hole of the water container that water is prevented from passing up the sleeve. Before it is
47、 fitted to the thermometer the sleeve should be made water absorbent. This can be achieved by boiling for about 10 min in water to which a little detergent has been added, and then thoroughly rinsing in distilled or de-ionized water. b) When handling the sleeve, care should be taken to prevent conta
48、mination by dirt or grease from the hands. c) Only distilled or de-ionized water conforming to Grade 3 of BS 3978:1987 should be used for filling the water container. d) The hygrometer should always be rotated in front and to windward of the observer. Observations should be taken in the shade in suc
49、h a location as to minimize the effect of thermal radiation on the thermometers during the period of rotation and while they are being read. e) In still air conditions it is advisable to walk forwards while whirling the hygrometer since the observer may set up local variations in humidity. f) Care should be taken that when the instrument is being read, the observers hands are kept away from the bulb; the observer should also take care not to breathe on the instrument. g) It is particularly important that the wet bulb temperature be read f
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