1、BRITISH STANDARD BS 2842:1992 Specification for Whirling hygrometer UDC 551.508.71:536.512BS2842:1992 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 intoeffect
2、on 15October 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 respon
3、sible for this British Standard The preparation of this British Standard was entrusted by the LaboratoryApparatus Standards Policy Committee (LBC/-) to Technical Committee LBC/36, upon which the following bodies were represented: Association for Science Education British Glass Manufacturers Confeder
4、ation 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: Briti
5、sh 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. Date CommentsBS2842:1992 BSI 07-1999 i Contents Page Committees responsible Inside fron
6、t cover Foreword ii Section 1. General 1.1 Scope 1 1.2 Informative references 1 Section 2. Thermometers 2.1 Type 2 2.2 Temperature scale 2 2.3 Stabilization 2 2.4 Material 2 2.5 Range 2 2.6 Dimensions 2 2.7 Graduation and figuring 2 2.8 Accuracy 2 2.9 Expansion chamber 3 2.10 Marking 3 Section 3. Fr
7、ame 3.1 Construction of frame 4 3.2 Water container 4 Annex A (informative) Method of use of whirling hygrometers 5 Annex B (informative) Tables suitable for use with whirling hygrometers 5 Annex C (informative) Errors in computed relative humidity 5 Annex D (informative) Thermometric glasses approv
8、ed by the National Physical Laboratory 7 Annex E (informative) Testing of thermometers 7 Figure 1 Whirling hygrometer: example of general design 4 Table 1 Dimensions for thermometer 2 Table C.1 Maximum error in computed relative humidity due to thermometer error 6 Table D.1 Identification stripe(s)
9、or approved abbreviations and normal maximum working temperature of all glasses that have been approved for the manufacture of thermometer bulbs 7 List of references Inside back coverBS2842:1992 ii BSI 07-1999 Foreword This British Standard has been prepared under the direction of the Laboratory App
10、aratus Standards Policy Committee, and supersedes BS2842:1975 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. I
11、t is intended to cover the Service requirements for this type of hygrometer as well as the requirements of commercial users. This standard was first published in1957, with the title Whirling hygrometer (medium size). It was revised in1966 to permit a wider range of bulb diameters, to specify an alte
12、rnative thermometer with a plain front, and to relax the dimensional requirements for the button top. Experience in using the whirling hygrometer specified in the1966 edition showed that the figures for maximum error given inTable2 understated the actual error values. The1975 edition specified a lar
13、ger hygrometer incorporating 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, the1975 larger model was never produced. Consumers demanded m
14、anufacture of the smaller1966 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 r
15、evisions of this specification, 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 humidit
16、y tables (seeAnnex B), 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
17、 be taken as being requirements 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 BS5248:1990 should be used. NOTEFor accurate determination of humidity, hygrometers
18、of the whirling or aspirated 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
19、on testing and continuing product surveillance, which may be coupled with assessment of a suppliers quality systems against the appropriate Part of BS5750. Enquiries as to the availability of third party certification schemes are forwarded by BSI to the Association of Certification Bodies. If a thir
20、d party certification scheme does not already exist, users should consider approaching an appropriate body from the list of Association members.BS2842:1992 BSI 07-1999 iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are respon
21、sible for their correct 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, pages1to 8, an inside back cover and a back cover. This standard has been u
22、pdated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside front cover.iv blankBS2842:1992 BSI 07-1999 1 Section 1. General 1.1 Scope This British Standard specifies requirements for thermometers suitable for use in whirling (slin
23、g) hygrometers, 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
24、current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions.BS2842:1992 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 fr
25、ont and a button 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
26、be fitted securely to the bulb. 2.2 Temperature scale The thermometers shall be graduated in degrees Celsius, as defined in the International Temperature Scale of1990 1. 2.3 Stabilization The thermometers shall be stabilized before graduation using a process such that the accuracy of the finished th
27、ermometer is within the limits specified in clause2.8. 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 (seeAnnex D). NOTETo re
28、duce the 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 s
29、hall conform to the dimensions given inTable 1. Table 1 Dimensions for thermometers 2.7 Graduation and figuring 2.7.1 Scale lines The thermometers shall be graduated at each0.5 C, with a longer line at each1 C. The lines at each5 C shall be extended further. The scale lines shall be fully numbered a
30、t each5 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 exceed0.2mm. 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 than0.3 C
32、, at any point on the scale when the thermometer is completely immersed. Dimensions in millimetres Overall length 164 to 168 Scale length 80 to 108 Bulb length 15 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 diameter 6
33、 to 8 Button top thickness (min.) 1.5BS2842:1992 BSI 07-1999 3 2.9 Expansion chamber The thermometers shall be so constructed as to withstand a temperature of20 C above the maximum temperature on the thermometer scale without damage. To enable the thermometers to withstand this temperature an expans
34、ion chamber, 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 least5mm of unchanged capillary tube above the highest scale line. 2.10 Marking Each thermometer sha
35、ll 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 (seeAnnex D). c) An identification
36、 number, 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.BS2842:1992 1) . 1) Marking BS 2842:1992 on or in relation to a product represents a manufacturers declarati
37、on 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 desira
38、ble.BS2842:1992 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、ameter5.5mm and button top diameter8mm. The instrument shall be capable of being rotated at about180r/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 visible
40、. 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 inFigure 1. 3.2 Water container The frame shall incorporate a water
41、 container, designed so that water cannot leak from it during use, in such a position that a short length of sleeve (seeA.1) dipping into it can be fitted to the wet bulb thermometer. At least5mm of sleeve below the bulb of the thermometer shall be exposed to the stream of air. Figure 1 Whirling hyg
42、rometer: example ofgeneral designBS2842:1992 BSI 07-1999 5 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 the frame and
43、 thermometers can be rotated at approximately180r/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 thermometer bulbs
44、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 (wetbulb) temperature due to the evaporation of water from the wet sleeve. Rotation for30s to40s is sufficient. From the readings of t
45、he 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 (seeAnnex B). A.2 Precautions The following precautions are recommended. a) The sleeve should be of
46、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 fitted to the therm
47、ometer the sleeve should be made water absorbent. This can be achieved by boiling for about10min 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 contamination by dirt or gr
48、ease from the hands. c) Only distilled or de-ionized water conforming to Grade3 ofBS3978:1987 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 such a location as to minimi
49、ze 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 first, immediately a
