1、BRITISH STANDARD CONFIRMED AUGUST 1997 BS 791:1990 Specification for Solid-stem calorimeter thermometersBS791:1990 This British Standard, having been prepared under the directionof the Laboratory Apparatus Standards Policy Committee, was published under the authority of the BoardofBSI and comes into
2、 effecton 30April1990 BSI 10-1999 First published April 1938 First revision April 1954 Third revision September 1975 Fourth revision April 1990 The following BSI references relate to the work on this standard: Committee reference LBC/4 Draft for comment 89/56007 DC ISBN 0 580 18146 4 Committees resp
3、onsible for this British Standard The preparation 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 Depa
4、rtment of Health Department of Trade and Industry (National Physical laboratory) Institute of Petroleum Medical Sterile Products Association Scientific Glassware Association Amendments issued since publication Amd. No. Date of issue CommentsBS791:1990 BSI 10-1999 i Contents Page Committees responsib
5、le Inside front cover Foreword ii 1 Scope 1 2 Type 1 3 Temperature scale 1 4 Immersion 1 5 Glass 1 6 Gas filling 1 7 Construction 1 8 Graduation and figuring 2 9 Accuracy 3 10 Marking 3 Appendix A Thermometric glasses approved by the National Physical Laboratory 4 Appendix B Testing of thermometers
6、4 Figure 1 Solid-stem calorimeter thermometer 2 Figure 2 Alternative types of graduation and figuring 3 Table 1 Dimensions 2 Table 2 Graduation 2 Table 3 Identification stripe(s) or approved abbreviations and normal maximum working temperatures of all glasses that have been approved for the manufact
7、ure of thermometer bulbs 4 Publications referred to Inside back coverBS791:1990 ii BSI 10-1999 Foreword This British Standard has been prepared under the direction of the Laboratory Apparatus Standards Policy Committee and supersedes BS791:1975 which is withdrawn. This British Standard was first pub
8、lished in1938 under the title “Bomb calorimeter thermometers” and revised in1959 and1975. BS791:1959 was adopted as the basis of ISO recommendation 651 “Solid stem calorimeter thermometers” published in1968. ISO/R651 was confirmed as ISO651 in1975. The1975 edition of BS791 was technically in agreeme
9、nt with ISO651 and also included some additional information. This revision introduces changes to bring the standard up to date and in particular changes to available glasses and arrangements for calibration and testing. Product certification. Users of this British Standard are advised to consider t
10、he desirability of third party certification of product conformity with this BritishStandard based on testing and continuing 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 certi
11、fication schemes will be forwarded by BSI to the Association of Certification Bodies. If a third party certification scheme 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 neces
12、sary provisions of a contract. Users of British Standards are responsible 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 and ii, pages1
13、 to4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS791:1990 BSI 10-1999 1 1 Scope This British Standard specifies requirements for a serie
14、s of short-range solid-stem thermometers for use in bomb calorimetry and for other purposes where an accurate measurement of a change of temperature is required. The thermometers are not provided with auxiliary scales at0 C and are therefore not suited to the absolute measurement of temperature (whi
15、ch is not normally required in calorimetry) unless they are checked against a standard thermometer immediately before use. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Type The thermometer shall be of the mercury-in-glass solid-stem type with
16、 an enamel back. 3 Temperature scale The thermometer shall be graduated in accordance with the Celsius scale as defined in the current definition of the International Practical Scale of Temperature (IPST) adopted by the General Conference of Weights and Measures (GCWM). 4 Immersion The thermometer s
17、hall be calibrated for use at total immersion,i.e.the reading is taken when the thermometer is vertical and immersed at least to the end of the liquid column in the medium, the temperature of which is required to be measured, or for use at partial immersion. NOTEThe purchaser should specify in the e
18、nquiry or order whether a partial immersion thermometer is required. On partial immersion thermometers, a line shall be etched at least halfway round the stem of the thermometer at the level to which it is intended to be immersed. 5 Glass 5.1 The stem shall be made of lead glass or other thermometri
19、c glass appropriate to the temperature range and shall have an enamel back. 5.2 The bulb shall be cylindrical and in alignment with the stem. Its external diameter shall not exceed that of the stem. It shall be made of a thermometric glass approved by the National Physical Laboratory (seeAppendix A)
20、. 5.3 The glass shall be so selected and processed that the finished thermometer shows the following characteristics. a) Stress in the glass shall be reduced to a level sufficient to minimize the possibility of fracture due to thermal or mechanical shock. b) The thermometer shall be stabilized befor
21、e graduation using a process such that the scale error and interval error of the finished thermometer are within the limits specified in clause9. c) The legibility of the reading shall not be impaired by devitrification or clouding. d) The image of the meniscus shall be distorted as little as possib
22、le by defects or impurities in the glass. 6 Gas filling Above the mercury, the thermometer shall be either vacuous or gas-filled; in the latter case, only a dry, inert gas shall be used. The indication of a gas-filled thermometer, when the meniscus is at the top of the scale, shall not change by mor
23、e than0.01 C when the temperature of the gas above the mercury is changed by30 C. NOTEIt is generally possible for this requirement to be satisfied if the internal gas pressure does not exceed50kPa when the thermometer is registering its maximum temperature. 7 Construction 7.1 Shape The thermometer
24、shall be straight and its external cross section shall be approximately circular. 7.2 Top finish The top of the thermometer shall have a rounded finish, unless otherwise specially, required. 7.3 Capillary tube The cross-sectional area of the bore shall not show variations from the average greater th
25、an5%, and the shape of the bore shall be such that, without tapping, jumping of the meniscus does not exceed one half of the graduation interval, when the temperature is rising at a uniform rate not exceeding0.05 C/min. In the case of a thermometer calibrated for use at partial immersion, the volume
26、 of mercury contained in the capillary tube between the immersion line and the lowest figured scale line shall not exceed the equivalent of2 C. NOTEThe inside of the capillary tube should be smooth. 7.4 Expansion chamber (safety chamber) The thermometer shall be so constructed as to withstand a temp
27、erature of60 C (or70 C in the case of thermometers STCal/0.01/42 and STCal/0.01/45) without damage. To enable the thermometer to withstand these temperatures, an expansion chamber, which shall be pear-shaped with a hemispherical top, shall be provided at the top of the stem. It shall be so shaped th
28、at the meniscus remains in the lower portion at temperatures up to40 C.BS791:1990 2 BSI 10-1999 7.5 Contraction chamber A contraction chamber shall be provided so that the mercury does not recede into the bulb at 0 C. It shall be elongated and as narrow as possible and shall be separated from the bu
29、lb by not less than3mm of capillary tube of uniform bore. 7.6 Enlargement of the bore No enlargement of the bore shall be so located as to produce any variation in the cross section of the capillary tube in the scale portion other than that specified in7.3. 7.7 Dimensions The thermometers shall comp
30、ly with the dimensions given inTable 1 andFigure 1. Table 1 Dimensions (seeFigure 1) 8 Graduation and figuring 8.1 The scales and graduation interval of the thermometers shall be in accordance withTable 2. 8.2 The scale lines shall be clearly etched and of uniform thickness, which in no case shall e
31、xceed0.05mm. The lines shall be at right angles to the axis of the thermometer. Table 2 Graduation 8.3 When the thermometer is held in a vertical position and viewed from the front, the left-hand ends of all the scale lines shall lie on an imaginary vertical line. When the thermometer is viewed such
32、 that the right-hand ends of the shorter lines denoting, an interval of0.01 C, align with the left-hand side of the bore, longer lines at each0.05 C shall extend across the bore towards the right. NOTEThe shorter lines should be about1mm long. mm Maximum total length 760 Maximum distance from bottom
33、 of bulb to top of contraction chamber 110 Distance from bottom of bulb to lower nominal limit of scale 280 to 300 Minimum length of main scale between nominal limits 300 Minimum distance from upper nominal limit of scale to top of thermometer 70 Maximum diameter of stem 11 External diameter of bulb
34、 not greater than that of stem Minimum length of bulb to shoulder 40 Designation Graduation interval Nominal scale range C C STCal/0.01/15 STCal/0.01/18 STCal/0.01/21 0.01 0.01 0.01 9 to 15 12 to 18 15 to 21 STCal/0.01/24 STCal/0.01/27 STCal/0.01/30 0.01 0.01 0.01 18 to 24 21 to 27 24 to 30 STCal/0.
35、01/33 STCal/0.01/36 STCal/0.01/39 0.01 0.01 0.01 27 to 33 30 to 36 33 to 39 STCal/0.01/42 STCal/0.01/45 0.01 0.01 36 to 42 39 to 45 All dimensions are in millimetres. Figure 1 Solid-stem calorimeter thermometerBS791:1990 BSI 10-1999 3 8.4 The figures shall be placed in such a way that an extension o
36、f the line to which they refer would intersect them. The figures shall be upright when the thermometer is held vertically (seeFigure 2). NOTE 1The figures may be placed either to the right or the left of the scale lines, as preferred. NOTE 2Figure 2 illustrates two different types of graduation and
37、figuring for the thermometers, but these are not intended to be obligatory. 8.5 The scale lines shall be so positioned that the enamel backing in the stem provides a background for the figures, the scale and the mercury column when the latter is seen just beyond the left-hand or right-hand ends of t
38、he short lines. 8.6 The scale of the thermometer shall be extended at each end by10divisions,i.e.0.1 C, beyond the nominal limits specified inTable 2. 8.7 The scale shall be figured at each division of0.1 C. Full figuring shall be provided at least at each division of1 C and more frequently if requi
39、red. 9 Accuracy (seeAppendix B) 9.1 Scale error The scale error, when the thermometer is under standard atmospheric pressure and when the emergent liquid column (in the case of a partial immersion thermometer) is at the prescribed temperature, shall not be greater than0.1 C. 9.2 Interval error The a
40、bsolute value of the algebraic difference between the errors at any two points on the scale which are not more than50 divisions apart shall in no case be greater than0.01 C. 9.3 Repeatability The repeatability of readings on the thermometer shall be such that the correction at any point on the scale
41、 can be determined with an accuracy of 0.002 C. 10 Marking The following inscriptions shall be permanently and legibly marked on the thermometer. a) Unit of temperature,i.e.abbreviation of the name Celsius such as C or the symbol C. b) On each thermometer graduated for use at partial immersion, the
42、immersion depth and the emergent stem temperature for which the thermometer was calibrated. c) Bulb glass identification, preferably by means of a coloured stripe or stripes, or by an approved abbreviation inscribed on the stem (seeAppendix A). d) Gas filling identification, if any,e.g.nitrogen fill
43、ed, vacuous or a suitable abbreviation. e) Identification number (manufacturers). f) Makers and/or vendors name or readily identifiable trade mark. g) Designation allotted to the thermometer,e.g.“STCal/0.01/15” (seeTable 2). h) The number of this British Standard, i.e.BS791. Figure 2 Alternative typ
44、es of graduation and figuringBS791:1990 4 BSI 10-1999 Appendix A Thermometric glasses approved by the National Physical Laboratory Table 3 gives the identification stripe(s) or approved abbreviations of all glasses that have been approved for the manufacture of thermometer bulbs. Only Jenaer Glaswer
45、k Schott and Genossen continue to supply glasses. A comprehensive list is retained, however, to assist users of existing or old thermometers in the certification of both the bulb glass and the recommended working temperature ranges. Appendix B Testing of thermometers The examination and calibration
46、of thermometers is undertaken by the National Physical Laboratory and by approved laboratories of the National Measurement Accreditation Service (NAMAS). Full details of services and fees can be obtained on application to individual laboratories. A list of NAMAS approved laboratories can be obtained
47、 from NAMAS, National Physical Laboratory, Teddington, Middlesex TW110LW (Telephone01-977-3222). Table 3 Identification stripe(s) or approved abbreviations and normal maximum working temperature of all glasses that have been approved for the manufacture of thermometer bulbs Glass Supplier Identifica
48、tion stripe(s) or approved abbreviation Normal maximum working temperature C Normal glass Schott-N16 Jenaer Glaswerk Schott and Genossen Mainz Single red stripe or N16 350 Thermometric glass Schott-2954 Jenaer Glaswerk Schott and Genossen Mainz Single black stripe 460 Schott-Supremax R8409 Jenaer Gl
49、aswerk Schott and Genossen Mainz SPX 8409 600 Normal glass Whitefriars Glass Ltd. Single blue stripe 350 Normal glass, Dial Plowden and Thompson Ltd. Double blue stripe 350 Normal glass 7560 Corning Glass Co. CN 350 Corning borosilicate glass Corning Glass Co. CB 450 Borosilicate glass Whitefriars Glass Ltd. Single white stripe 460 NOTEThe maximum temperatures given in the last column of the table are a guide to normal practice. The performance of a thermometer depends greatly on the stabilizing heat treatment which it has been g
