1、BRITISH STANDARD BS 1041-2.1: 1985 Temperature measurement Part 2: Expansion thermometers Section 2.1 Guide to selection and use of liquid-in-glass thermometersBS1041-2.1:1985 This British Standard, having been prepared under the directionof the Laboratory Apparatus Standards Committee,was published
2、 underthe authority of the BoardofBSI and comes into effect on 31 July 1985 BSI 01-2000 BS 1041 first published January1943 First published as BS 1041-2.1 January 1969 First revision July 1985 The following BSI references relate to the work on this standard: Committee reference LBC/4 Draft for comme
3、nt 84/52217 DC ISBN 0 580 14500 X Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Laboratory Apparatus Standards Committee (LBC/-) to Technical Committee LBC/4 upon which the following bodies were represented: British Laboratory Ware Ass
4、ociation British Lampblown Scientific Glassware Manufacturers Association Ltd. British Medical Association Department of Health and Social Security Department of Trade and Industry (National Physical Laboratory) Institute of Petroleum Ministry of Defence Amendments issued since publication Amd. No.
5、Date of issue CommentsBS1041-2.1:1985 BSI 01-2000 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle of temperature measurement by liquid expansion 1 3 Materials 1 4 Construction and marking 4 5 Thermometer selection 6 6 Calibration 8 7 Conditions of use 10 8
6、 Maintenance 14 9 Working standard liquid-in-glass thermometers 16 Appendix A Calibration services 18 Appendix B The International Practical Temperature Scale of 1968 (IPTS-68) 18 Appendix C Procedure for ice point measurements 18 Figure 1 Emergent liquid column correction for partial immersion meas
7、urements 12 Figure 2 Error in reading a thermometer due to parallax 14 Table 1 Thermometric glasses approved by the National Physical Laboratory 2 Table 2 NPL measurement uncertainties of total immersion thermometers 7 Table 3 NPL measurement uncertainties of partial immersion thermometers 7 Table 4
8、 Values of k, the apparent cubic thermal expansion coefficient of thermometric liquids in glass 12 Publications referred to Inside back coverBS1041-2.1:1985 ii BSI 01-2000 Foreword This revision of this Section ofBS1041 has been prepared under the direction of the Laboratory Apparatus Standards Comm
9、ittee. It supersedes the 1969 edition ofBS1041-2.1, which is withdrawn. Previous editions (published in 1943 and1969) classified and reviewed liquid-in-glass thermometers under four main groups, broadly defined by their applications in meteorology, industry and the laboratory. In this revision, howe
10、ver, those classifications are discontinued since their meaning or relevance is considered obscure or out-dated and, in some cases, too specialized for a document intended to give guidance of a general nature. Paradoxically, the current diffusion of standardization and increasing demand for traceabi
11、lity 1)in measurement call for a degree of specialization weighted towards the use and maintenance of generally high quality thermometers, conveniently designated as “working standards”. Accordingly, this revision is intended to provide an essentially practical guide to the selection and use of ther
12、mometers wherever standardization, calibration and traceability are of concern and interest. Revisions ofBS1041-3 toBS1041-5andBS1041-7are in preparation. For the purposes of this Section ofBS1041, the terminology and conventions ofISO386 “Liquid-in-glass laboratory thermometers Principles of design
13、, construction and use” 2)have been adopted. Throughout this Section ofBS1041, the symbol “ C” is used to denote actual temperature, and the words “degree(s) Celsius” to denote temperature intervals. A British Standard does not purport to include all the necessary provisions of a contract. Users of
14、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 to 18, an inside back cover and a back
15、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. 1) Traceability is an accepted term and is, for the purposes of this Section ofBS1041, defined as the ability of a measurement
16、 result to be related to the current International Practical Temperature Scale through an unbroken chain of comparisons. 2) Published by the International Organization for Standardization (ISO).BS1041-2.1:1985 BSI 01-2000 1 1 Scope This Section ofBS1041 gives guidance on the selection and use of: a)
17、 hermetically-sealed glass thermometers in which a thick-walled capillary stem is fused to a reservoir or bulb containing a thermometric liquid and the temperature scale is engraved or permanently marked on the stem; NOTEThermometers of this type are commonly known as “solid-stem thermometers”. b) e
18、nclosed-scale liquid-in-glass thermometers, in which a comparatively thin-walled capillary together with a separate strip bearing the scale is enclosed in a hermetically-sealed glass sheath. Collectively, they span a temperature range from200 C to1050 C and are in some cases capable of measurement u
19、ncertainties of 0.005degrees Celsius (see5.2). Generally, but not without exception, they fall within the scope of the following British Standards: NOTE 1In this Section ofBS1041, temperatures below0 C are indicated with a minus sign; temperatures above0 C have no sign. NOTE 2The titles of the publi
20、cations referred to in this Section ofBS1041 are listed on the inside back cover. 2 Principle of temperature measurement by liquid expansion The apparent differential expansion of a liquid, in glass, provides a conveniently measurable parameter (length) to indicate a temperature along the scale asso
21、ciated with a capillary stem. This expansivity, defined in terms of the apparent cubic thermal expansion coefficient of the thermometric liquid concerned k (in C 1 ), is given by the following equation: where V is the liquid volume; is the rate of change of volume with temperature. Therefore, the sc
22、ale length, L, equivalent to a temperature interval t for a given capillary and liquid volume is given by the equation: where a is the cross-sectional area of the capillary. If k and a are constant, then L is, to first order accuracy, linearly dependent on temperature. Tapering or non-uniformity in
23、the bore and errors in marking and dividing in the graduation process lead to inherent errors in the reading of a thermometer and hence to the need for calibration of the complete instrument. Other potentially serious sources of error arise from both short-term and long-term glass instabilities, the
24、 characteristic behaviour of the liquid filling, conditions of immersion, pressure and anomalous effects, parallax and poor maintenance. All of these aspects of liquid-in-glass thermometry are normal and are discussed in this guide. 3 Materials 3.1 Glasses 3.1.1 General. Thermometric glasses are fus
25、ed mixtures of inorganic oxides, in which the major constituent is silica, but whose characteristic properties can be altered significantly by the addition of other constituents in various concentrations. Of the important physical and chemical properties, the following are those of overriding import
26、ance in the development of the three major approved glass types (see3.1.2 to3.1.4) which are used in the manufacture of thermometers: a) the softening point which limits the working temperature range; b) resistance to devitrification; c) the ability to be clearly etched or engraved and to be welded
27、to an opaque enamel backing; d) freedom from physical imperfections; e) thermal stability. 3.1.2 Normal glass. Of the three glasses, so-called normal glass is most common. It is a soda-lime glass, also containing zinc oxide and alumina and used extensively to make both bulb and stem for continuous u
28、se from200 C up to350 C, and for short-term use from200 C up to400 C. NOTEThe term “normal” arises from an early practice of glass technologists, namely that of setting out the limits of composition of durable commercial glasses by molecular formulae. The existence of a compound whose molecular rati
29、o of silica-lime-soda was 6:1:1 was investigated, and samples were found to be comparatively most resistant to corrosion. This nominal composition came to be known as “normal”. BS 593 BS 692 BS 791 BS 1365 BS 1704 BS 1900 BS 5074 BS 2000-0:Addendum 1 k 1dV Vdt - = dV dt - L Vtk a - =BS1041-2.1:1985
30、2 BSI 01-2000 3.1.3 Borosilicate glass. Borosilicate glasses contain soda, boric oxide and alumina; they offer considerably improved thermal stability over normal glass, and an extended working range from200 C up to450 C and500 C for long- and short-term exposures, respectively. Where high stability
31、 and precision are of primary interest, borosilicate thermometers are used to advantage in place of normal glass thermometers. Both the bulb and stem are made from the same glass since it does not fuse satisfactorily with alternative thermometric glasses. 3.1.4 Combustion glass. Combustion glass is
32、borosilicate glass containing higher proportions of boric oxide and alumina than in normal borosilicate glass (see3.1.3). Thermometers made throughout from this glass can be used up to600 C. 3.1.5 Approval. The thermometric glasses in3.1.2 to3.1.4 have been the subject of approval tests by national
33、standardizing laboratories and they are registered and recognized internationally by a scheme of coloured lines running the length of the bulb glass or by an engraved inscription (seeTable 1). Sometimes the coloured lines may be very fine and difficult to detect; if the thermometer is held verticall
34、y with the bulb resting on a white surface, the line is usually made visible against the reflected white background. Combustion-type glasses do not satisfactorily fuse to the coloured enamel glasses used for identification purposes and are therefore recognized instead by a coded inscription engraved
35、 on the thermometer stem. It should be emphasized that only approved glasses appropriate to the required range of temperature are suitable for thermometer manufacture and usage. 3.1.6 Lead glass. In the temperature range from200 C up to 300 C an alternative glass containing lead, which imparts a cha
36、racteristic brilliance and clarity to the stem, may be used in conjunction with a normal glass bulb. Table 1 Thermometric glasses approved by the National Physical Laboratory Glass Identification stripe(s) or approved abbreviation Normal maximum working temperature C Normal glass, made by Whitefriar
37、s Glass Ltd. Single blue stripe 350 Normal glass, Dial, made by Plowden and Thompson Ltd. Double blue stripe 350 Normal glass, Schott-N16, made by Jenaer Glaswerk Schott and Genossen, Mainz Single red stripe 350 Normal glass, 7560, made by Corning Glass Co. CN 350 Corning borosilicate glass, made by
38、 Corning Glass Co. CB 450 Thermometric glass, Schott-2954, made by Single black stripe 460 Jenaer Glaswerk Schott and Genossen, Mainz Borosilicate glass, made by Whitefriars Glass Ltd. Single white stripe 460 Corning glass, 1720, made by Corning Glass Co. C1720 600 Schott-Supremax R8409, made by Jen
39、aer Glaswerk SPX 8409 600 Schott and Genossen, Mainz NOTE 1The 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 given during manufacture, and a well-made the
40、rmometer of normal glass may be quite satisfactory for many purposes at temperatures as high as400 C. On the other hand, for the best accuracy, the use of one of the borosilicate glasses may be preferred for temperatures lower than350 C. In general, the lower the maximum temperature of use when comp
41、ared with the approved temperature of the glass, the better will be the “stability of zero” of the thermometer (see6.8). NOTE 2The list of manufacturers included in this table is complete at the time of publication, but may not remain exhaustive. Reference should be made to the National Physical Lab
42、oratory.BS1041-2.1:1985 BSI 01-2000 3 3.1.7 Silica 3) . Thermometers made from fused silica offer the highest stability for use from200 C up to600 C. Additionally, fused silica thermometers can be used up to1050 C and are more resistant to mechanical and thermal shocks than other thermometric glasse
43、s (see also3.2.4). 3.2 Liquid fillings 3.2.1 Mercury. Mercury continues to be the most popular filling fluid because: a) it is easily obtained in a pure form; b) it remains liquid between its freezing point,38.84 C, and its boiling point,356.66 C; c) its surface tension is high (not giving rise to d
44、rainage problems); d) it is readily detectable in glass; e) its thermal expansion coefficient is very uniform. Although it boils at approximately356 C under100kPa 4)pressure, its useful range can be extended to600 C by sealing the thermometer at a high pressure of gas, usually nitrogen, to suppress
45、evaporation. At600 C, the internal gas pressure is2MPa. 3.2.2 Mercury-thallium. Mercury alloyed with8.7% thallium, by mass, forms a eutectic retaining essentially the same characteristics as mercury, notably stability, while extending the useful working range to55 C from38.84 C. 3.2.3 Organic liquid
46、s. Some organic liquids enable the thermometer range to be extended downwards. Pure ethanol and toluene have freezing points of112 C and95 C, respectively, while technical grade pentane can be used down to as lowas200 C. Such liquids, having thermal expansion coefficients some six or seven times tha
47、t of mercury, offer considerable improvement in terms of sensitivity, but some major disadvantages lead to the construction of thermometers having much larger capillary bores and bulbs than mercury-filled thermometers. The expansivity is less regular, being greater at some temperatures than at other
48、s. Furthermore, the organic liquids have a low surface tension making them unsuitable for accurate thermometry because they wet the walls of the capillary which cannot, therefore, be as fine as for mercury thermometers. They are also highly volatile even at room temperature; as a result, partial dis
49、tillation of the liquid and separation of the liquid column can also occur quite readily. It follows that extra care and maintenance in the use of organic liquid thermometers is required (see8.3.4). 3.2.4 Gallium. This element is used as the filling liquid in high temperature silica thermometers. In spite of its freezing point being at29.78 C, it readily supercools and remains liquid within the common range of ambient temperatures. Its great advantage in thermometry derives from its boili
