1、BRITISH STANDARD CONFIRMED AUGUST 1997 BS 5248:1990 Incorporating Amendment No. 1 Specification for Aspirated hygrometerBS5248:1990 This British Standard, having been prepared under the directionof the Laboratory Apparatus Standards Policy Committee, was published underthe authority of the BoardofBS
2、I and comes into effect on 31 May 1990 BSI 08-1999 First published October 1975 First revision May 1990 The following BSI references relate to the work on this standard: Committee reference LBC/4 Draft for comment 88/56009 DC ISBN 0 580 18060 3 Committees responsible for this British Standard The pr
3、eparation of this British Standard was entrusted by the Laboratory Apparatus Standards Policy Committee (LBC/-) to Technical Committee LBC/4, upon which the following bodies were represented: British Laboratory Ware Association British Medical Association Department of Health Department of Trade and
4、 Industry (National Physical Laboratory) Institute of Petroleum Medical Sterile Products Association Scientific Glassware Association Amendments issued since publication Amd. No. Date of issue Comments 7383 January 1993 Indicated by a sideline in the marginBS5248:1990 BSI 08-1999 i Contents Page Com
5、mittees responsible Inside front cover Foreword ii Section 1. General 1 Scope 1 Section 2. Thermometers 2 Types 2 3 Range 2 4 Temperature scale 2 5 Material 2 6 Annealing 2 7 Stabilization 2 8 Construction 2 9 Graduation and figuring 4 10 Accuracy 4 11 Marking 4 Section 3. Frame 12 General 5 13 Radi
6、ation shields 5 14 Aspirating motor 5 15 Thermometer locating holes 5 16 Ventilation rate 6 17 Carrying case and accessories 6 18 Marking of carrying case and frame 6 Appendix A Method of use of aspirated hygrometer 7 Appendix B Tables suitable for use with aspirated hygrometers 7 Appendix C Errors
7、in computed relative humidity due to thermometer errors 8 Appendix D Thermometric glasses approved by the National Physical Laboratory 8 Appendix E Testing of thermometers 9 Figure 1 Thermometer with fitted cap and collar 3 Figure 2 General arrangement of aspirated hydrometer assembly 5 Table 1 Dime
8、nsions for thermometer 2 Table 2 Maximum error in computed relative humidity due to thermometer error 8 Table 3 Indication stripe(s) or approved abbreviations and normal maximum working temperature of all glasses that have been approved for the manufacture of thermometer bulbs 9 Publications referre
9、d to Inside back coverBS5248:1990 ii BSI 08-1999 Foreword This British Standard has been prepared under the direction of the Laboratory Apparatus Standards Policy Committee and supersedes BS 5248:1975 which is withdrawn. This British Standard was first published in 1975 as a result of a growing dema
10、nd for a type of wet and dry bulb hygrometer which was more accurate than the whirling hygrometer specified in BS2842. The accuracy of the measurement of humidity using a whirling hygrometer is limited by the rapid rise in the wet bulb thermometer temperature when the rotation of the instrument is s
11、topped in order to read the thermometer. Additional errors arise when the instrument is not fitted with radiation shields and the presence of the observer may also affect the humidity of the air. These sources of error are eliminated or reduced by the use of an aspirated hygrometer. The electrically
12、 aspirated instrument is recommended to obtain the highest reproducibility of readings. This revision introduces changes to bring the standard up to date and in particular to modify the information on available glasses and arrangements for calibration and testing. For the information of users a meth
13、od of using the aspirated hygrometer is given inAppendix A. Tables suitable for use with aspirated hygrometers are listed in Appendix B, andAppendix C gives the maximum errors in the computed relative humidity due to thermometer errors. Appendix D lists thermometric glasses approved by the National
14、Physical Laboratory andAppendix E gives details of the testing of British Standard thermometers. Product certification. Users of this British Standard are advised to consider the desirability of third party certification of product conformity with this BritishStandard based on testing and continuing
15、 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 will be forwarded by BSI to the Association of Certification Bodies. If a third party certification scheme
16、does not already exist, users should consider approaching an appropriate body from the list of Association members. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a B
17、ritish 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 and ii, pages1 to 10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendmen
18、ts incorporated. This will be indicated in the amendment table on the inside front cover.BS5248:1990 BSI 08-1999 1 Section 1. General 1 Scope This British Standard specifies requirements for mercury-in-glass thermometers suitable for use in an electrically or mechanically aspirated wet and dry bulb
19、hygrometer together with the essential construction and performance requirements for the frame. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover.BS5248:1990 2 BSI 08-1999 Section 2. Thermometers 2 Types The thermometers shall be of the mercury-in-gl
20、ass gas-filled, solid-stem or enclosed-scale types, graduated for complete immersion (graduated to give a correct reading when the whole of the thermometer is immersed in the medium the temperature of which is to be measured), and fitted with caps and collars. NOTEGenerally the thermometers fitted t
21、o the hygrometer are of the solid-stem type. However, it is desirable to use the enclosed-scale type for the measurement of low relative humidities, i.e. for large wet bulb depression of about10 C to15 C, because the heat conduction down the stem to the wet bulb is less. 3 Range The nominal scale ra
22、nges for the thermometers shall be as follows: 0 C to55 C; 15 C to +40 C; 35 C to+20 C. For a 0 C to 50 C thermometer the scale shall be extended by two divisions below 0 C. NOTEThe scale, if required, may also be extended by six divisions, i.e. 3 C, above55 C, to accommodate its use in the environm
23、ent testing of electronic components (see BS 2011-2.1Db). 4 Temperature scale The thermometers shall be graduated in degrees Celsius, as defined in the International Temperature Scale of1990 1) . 5 Material The stem or capillary tube shall be of thermometric glass appropriate to the temperature rang
24、e with an enamel back. The bulb shall be made of a thermometric glass approved by the National Physical Laboratory (seeAppendix D). 6 Annealing Stress in the glass shall be reduced to a level sufficient to minimize the possibility of fracture due to mechanical or thermal shock. 7 Stabilization The t
25、hermometers shall be stabilized before graduation using a process such that the accuracy of the finished thermometer is within the limits specified in clause10. 8 Construction 8.1 Neck There shall be a slight neck in the stem, at a point14 2mm of unchanged capillary tube above the thermometer bulb,
26、to allow a closely fitting cylindrical absorbent cotton sleeve of suitable type to be fitted securely round the bulb (seeFigure 1). 8.2 Collar A cylindrical non-ferrous metal collar and a flanged cylindrical non-ferrous metal cap shall be securely fixed with waterproof adhesive coaxially to the stem
27、 of the thermometer as shown inFigure 1. 8.3 Expansion chamber The thermometer shall be so constructed as to withstand a temperature of70 C without damage. To enable the thermometer to withstand this temperature a pear-shaped expansion chamber with a hemispherical top, shall be provided towards the
28、top of the stem. This chamber shall not be obscured by the cylindrical cap. There shall be at least10mm of unchanged capillary tube above the highest scale line. 8.4 Dimensions The thermometer (whether solid-stem or enclosed-scale) shall be in accordance withTable 1 andFigure 1. Compliance with the
29、provisions for the diameter of bulb and stem shall be tested by means of appropriate ring gauges. Table 1 Dimensions for thermometer 1) The International Temperature Scale of 1990, HMSO 1991. Length Diameter mm mm Bulb 19 4 4 0.5 Stem between bulb and neck 14 2 Stem above neck Collar 16 2 9.5 0.1 Bo
30、dy of cap 18 2 9.5 0.1 Flange of cap 1 0.2 11 0.3 Thermometer, overall 280 8 Minimum nominal scale 145 From top of tap to top of collar 210 2 Maximum from top of cap to lower limit of nominal scale 206 5 +0 0.5 6 +1 0.5BS5248:1990 BSI 08-1999 3 Figure 1 Thermometer with fitted cap and collarBS5248:1
31、990 4 BSI 08-1999 9 Graduation and figuring 9.1 Scale lines The thermometer (whether solid-stem or enclosed-scale) shall be graduated at each0.5 C, with a longer line at each1 C. The lines shall be fully numbered at each5 C. All scale lines shall be clearly etched or otherwise durably marked, shall
32、not exceed a thickness of0.15mm and shall be suitably placed in relation to the enamel back. 9.2 Figuring The figures shall be upright when the thermometer is held vertically and viewed from the front and shall be placed so that they would be intersected by the lines to which they refer if these lin
33、es were extended. All negative figures shall have a minus sign placed above them. 9.3 Datum line An enclosed-scale thermometer shall bear a permanently marked datum line, of thickness comparable with that of the scale lines and placed on the sheath on a level with a main scale line, so that any disp
34、lacement of the scale can be easily noticed. 10 Accuracy The accuracy of the thermometers shall be as follows. a) Permissible error at a point 1) At points below 0 C: 0.3 C. 2) At 0 C and points above: 0.2 C. b) Permissible change in error over any interval of10 C 1) For an interval below0 C: 0.25 C
35、. 2) For an interval above 0 C: 0.1 C. 11 Marking Each thermometer shall be permanently and legibly marked with the following. a) The symbol C or an abbreviation of the name Celsius, e.g. C. b) The identification of the bulb glass, e.g. by a coloured stripe or stripes on the bulb or an approved abbr
36、eviation on the stem (seeAppendix D). c) An identification number. d) The makers and/or vendors name or readily identifiable trade mark. e) If required, the owners name or trade mark. f) The number of this British Standard, i.eBS5248 2) . 2) Marking BS5248 on or in relation to a product represents a
37、 manufacturers declaration 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 therefore solely the responsibility of the person making the claim. Such a declaration is not to be confused with third par
38、ty certification of conformity, which may also be desirable.BS5248:1990 BSI 08-1999 5 Section 3. Frame 12 General The frame shall be of robust construction designed to accommodate two similar thermometers of a type in accordance withclause2, held securely side by side, and provided with means of dra
39、wing air over the bulbs at the required rate (seeFigure 2). The electric or clockwork motor and the aspirating fan assembly shall be readily removable from the frame. 13 Radiation shields The thermometer bulbs shall be protected from external radiation by double-walled shields which form the air int
40、ake and extend at least5mm above the top of the bulb and at least10mm below the bottom of the bulb. The air shall pass between the walls of the shields as well as past the thermometer bulbs. The shields shall be non-corrodible, highly polished inside and outside and thermally insulated from each oth
41、er and from the frame. The shields shall be readily removable for access to the thermometer bulbs. 14 Aspirating motor NOTEIt is intended that the references in14.1 and14.3 to BS3456-101 should be replaced by reference to BSEN61010-1, when that standard is published. BS EN 61010-1 will include safet
42、y requirements for various types of laboratory equipment. 14.1 The motor shall be suitable for operation in environmental temperatures of 35 C to+57 C. When tested with the most unfavourable voltage (asdetermined by the testing authority) between0.94and1.06 times the rated voltage, at50 C for10min,
43、the temperature rise of the windings and other parts of the equipment shall not exceed the values given inTable3 of BS3456-101:1978. 14.2 Electric motors shall create no interference in the radio and television frequency bands and shall comply with BS800. 14.3 Electric motors and associated electric
44、al parts shall comply with clauses8, 15, 16, 19, 21, 22, 25, 27 and29 of BS3456-101:1978. 14.4 Mains-operated electric motors shall be provided with a cable of a minimum length of3m. 15 Thermometer locating holes The thermometer locating holes in the top mounding plate and in the portion above the r
45、adiation shields shall be coaxial. Means shall be provided to retain the thermometers in place after removal of the motor and also to prevent them from rotating during aspiration. Figure 2 General arrangement of aspiratedhygrometer assemblyBS5248:1990 6 BSI 08-1999 16 Ventilation rate 16.1 Electric
46、motor The speed of the air flowing past the thermometer bulbs shall be between 4.5m/s and9m/s. 16.2 Clockwork motor The speed of the air flowing past the thermometer bulbs shall be between 3m/s and9m/s, maintained for at least7 min in one full winding. 17 Carrying case and accessories The aspirated
47、hygrometer shall be supplied in a carrying case with compartments containing the following accessories: a) 1m length of sleeve; b) a supply of cotton thread; c) 1 water applicator; d) 1 suspension rod; e) 6 spare O-rings. Provision shall be made in the carrying case for the thermometers to be housed
48、 separately from the instrument in securely held protective cases during transit. 18 Marking of carrying case and frame A label shall be affixed to both the frame and the carrying case, bearing the following inscriptions: a) makers and/or vendors name or readily identifiable trade mark; b) owners na
49、me or trade mark (if required); c) identification number; d) rated supply voltage (if applicable); e) the number of this British Standard, i.e.BS5248 3) . 3) Marking BS 5248 on or in relation to a product represents a manufacturers declaration 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 therefore solely the responsibility of the person making the claim. Such a declaration is
