1、BRITISH STANDARD BS2648:1955 Incorporating Amendment Issued June, 1956(PD2517) Performance requirements for Electrically-heated laboratory drying ovensBS2648:1955 This British Standard, having been approved by the Scientific Glassware and Related LaboratoryApparatus Industry Standards Committee and
2、endorsed by the Chairman of theChemical Divisional Council,was published under theauthority of the General Council on 29th December 1955 BSI 04-1999 The following BSI references relate to the work on this standard: Committee reference LBC/14 Draft for comment CT(LBC)3072. ISBN 0 580 32665 9 Co-opera
3、ting organizations The Scientific Glassware and Related Laboratory Apparatus Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Admiralty* Air Min
4、istry Association of British Chemical Manufacturers Association of Scientific Workers Board of Trade British Association for the Advancement of Science British Chemical Ware Manufacturers Association British Laboratory Ware Association* British Lampblown Scientific Glassware Manufacturers Associatio
5、n British Pharmacopoeia Commission British Scientific Instrument Research Association* Chemical Society Department of the Government Chemist* D.S.I.R. Chemical Research Laboratory Glass Manufacturers Federation Institute of Petroleum Ministry of Education Ministry of Health* Ministry of Supply* Nati
6、onal Physical Laboratory Oil Companies Materials Committee Royal Institute of Chemistry Science Masters Association Society for Analytical Chemistry* Society of Chemical Industry Society of Glass Technology Standardization of Tar Products Tests Committee The Government departments and scientific and
7、 industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: British Coal Utilization Research Association British Dairy Farmers Association Central Electricity Au
8、thority Milk Marketing Board Ministry of Agriculture, Fisheries and Food National Institute for Research in Dairying Individual manufacturers Amendments issued since publication Amd. No. Date Comments PD 2517 June 1956 Indicated by a sideline in the marginBS2648:1955 BSI 04-1999 i Contents Page Co-o
9、perating organizations Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Conditions of tests 1 4 Measurement of temperature 1 5 Manual adjustment of temperature setting 1 6 Temperature variation 1 7 Temperature fluctuation 1 8 Temperature drift 2 9 Reproducibility of oven temperature 2 10 T
10、ime of temperature recovery 2 11 Temperature overshoot 2 12 Ventilation rate 2 13 Marking 2 Appendix A Construction and use of loaded thermocouple 3 Appendix B Measurement of temperature variation 3 Appendix C Measurement of temperature fluctuation 4 Appendix D Measurement of ventilation 4BS2648:195
11、5 ii BSI 04-1999 Foreword In order to keep abreast of progress in the industries concerned, British Standards are subject to periodical review. Suggestions for improvements will be recorded and in due course brought to the notice of the committees charged with the revision of the standards to which
12、they refer. A complete list of British Standards, numbering over6000, fully indexed and with a note of the contents of each, will be found in the British Standards Yearbook, which may be purchased from BSI Sales Department. It may also be consulted in many public libraries and similar institutions.
13、This standard makes reference to the following British Standard: BS593, Laboratory thermometers. This British Standard has been prepared under the authority of the Scientific Glassware and Related Apparatus Industry Standards Committee. A representative technical committee was set up following a req
14、uest from the dairying industry that a British Standard should be prepared for laboratory ovens. The committee decided to concentrate in the first place on the performance requirements of the type of electrically-heated oven widely used for the determination of moisture by drying at or near100C. Wor
15、kers in many laboratories were invited to supply information on the performance of their ovens and to comment on tentative standards suggested by the committee. After the replies had been considered, typical ovens were submitted to a comprehensive programme of tests devised by the committee, with th
16、e co-operation of the British Scientific Instrument Research Association and the British Laboratory Ware Association. The limits specified in this standard will satisfy the requirements of most users without unduly increasing the cost of manufacture. While not desiring to exclude existing designs of
17、 oven incorporating adjustable speed fans or adjustable ventilation ports, the committee found no evidence that either of these facilities for adjustment confers an advantage in performance. It is therefore recommended that no provision for restricting the air flow or for altering the speed of the f
18、an (if present) should be made. 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 British Standard does not of itself confer immunity from legal obligations. Summary o
19、f pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to5 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 theinside front cover.BS2648:1955 BSI 04-1
20、999 1 1 Scope This British Standard specifies the performance requirements of electrically-heated laboratory ovens of the type used for the determination of moisture by drying within the temperature range95C to110C, and having external provision for manual adjustment to any desired temperature withi
21、n that range. Ovens having a wider temperature range are not excluded provided they comply with the other requirements of this standard. The standard applies to ovens with an internal space of about1to3cu. ft which are ventilated by convection, whether or not they are fitted with internal fans to as
22、sist the circulation of air; it does not apply to vacuum ovens or to forced draught ovens. 2 Definitions For the purposes of this British Standard, the following definitions shall apply: working space that portion of the internal space which is above the lowest shelf and not less than3cm from any wa
23、ll (including the roof) oven-temperature the temperature at the centre of the working space temperature variation the difference at any moment between the temperature at the centre of the working space and at any other point in the working space temperature fluctuation the short-term changes in temp
24、erature at any point in the working space temperature drift any long-term changes in oven temperature during continuous operation of the closed oven temperature overshoot any excess of actual over desired oven temperature during a heating-up period 3 Conditions of test The performance of the oven sh
25、all be tested with vents fully open and with the shelves in position, but with the oven otherwise empty 1) . Measurements shall not commence until at least two hours after the oven has been switched on. In any test to determine the rate of ventilation of an oven the door-joint and all other possible
26、 sources of leakage shall be effectively sealed. 4 Measurement of temperature The oven temperature shall be measured by means of a mercury-in-glass thermometer with the unshielded bulb as near as practicable to the centre of the working space. The oven shall be so constructed that a thermometer can
27、be conveniently inserted for this purpose. The thermometer used shall have a bulb capacity not greater than0.5ml and a maximum error not greater than0.3C, and the error over any interval of10C shall not vary by more than0.3C 2) . Temperature variation and temperature fluctuation shall be measured by
28、 means of loaded thermocouples of the type described in Appendix A. 5 Manual adjustment of temperature setting The external provision for manual adjustment of temperature shall be such that an oven temperature can be attained within0.5C of any desired temperature in the range95C to110C. 6 Temperatur
29、e variation The temperature variation, measured as described in Appendix B, shall not exceed2.5C. 7 Temperature fluctuation The temperature fluctuation, measured as described in Appendix C, shall not exceed1.0C over a period of30minutes. 1) Experience has shown that the effect of loading an oven is
30、to disturb the temperature conditions to an extent depending on the quantity and nature of the particular loading material. As it is impossible to specify a standard condition of loading which would represent the wide range of uses to which these ovens may be put, the tests have been specified for t
31、he empty oven. 2) Thermometer B110C/Total of BS593 “Laboratory thermometers” is suitable.BS2648:1955 2 BSI 04-1999 8 Temperature drift The difference between the highest and lowest oven temperature recorded during72hours of continuous operation without alteration to the thermostat setting shall not
32、exceed1.0C 3) . For this purpose the oven temperature shall be measured at least thrice daily at intervals of at least three hours. 9 Reproducibility of oven temperature The initial oven temperature shall be regained to within1.0C after the oven has been switched off, allowed to cool for at least si
33、x hours and switched on again for at least two hours, without any alteration to the thermostat setting. 10 Time of temperature recovery An oven temperature of99C shall be regained in not more than20minutes after the temperature has been reduced from an initial steady value of100C by opening the oven
34、 door fully for one minute. 11 Temperature overshoot Any temperature overshoot induced by the procedure described in Clause10 shall not result in the temperature exceeding103C, and a temperature of101C shall not be exceeded for longer than10minutes. 12 Ventilation rate The rate of ventilation shall
35、be measured with the oven in operation at a temperature exceeding that of the room by80 2 C. It shall be not less than800litres per hour, measured at the temperature and pressure obtaining in the laboratory at the time of test by either of the methods of test described in Appendix D or by any other
36、method which has been found to give equivalent results 4) . 13 Marking Each oven shall have permanently and legibly marked on it: a) An identification number. b) The manufacturers or vendors name or registered trade mark. c) The number of this British Standard, i.e.BS2648 5) . 3) The temperature lim
37、its specified in Clauses7 and8 are similar, but it should be pointed out that temperature fluctuation refers to measurements using a thermocouple at any point in the oven, whereas temperature drift refers to measurements using a mercury-in-glass thermometer at the centre of the oven; thus steadier r
38、eadings may be expected for the latter. 4) It is important that the method used should impose no appreciable restraint upon the flow of air through the oven. 5) The mark “BS2648” on the product is an indication by the manufacturer that it purports to comply with the requirements of this British Stan
39、dard. BS2648:1955 BSI 04-1999 3 Appendix A Construction and use of loaded thermocouple The loaded thermocouple shall be constructed by attaching with a minimum of solder one end of a length each of iron and of constantan 6)No.30S.W.G.(0.0124in.) insulated wire to a flat about2mm in diameter, ground
40、on a 3 / 16 -in.diameter steel ball. A circuit including the thermocouple, a cold junction and measuring device (e.g.a critically-damped galvanometer) shall be established, sufficiently sensitive to allow temperature measurement to within0.1C. The thermocouple shall be calibrated and the ball shall
41、then be cleaned and thinly but uniformly blackened by coating with a colloidal graphite preparation 7) . Except as indicated in Appendix B, the thermocouple shall not be used less than3cm from a shelf or other part of the oven. The leads may be brought out through a split rubber stopper inserted in
42、the thermometer aperture. Appendix B Measurement of temperature variation Two of the loaded thermocouples described in Appendix A shall be used differentially, the free ends of the constantan leads being joined together. The temperature differences shall be measured with one thermocouple as near as
43、possible to the centre of the working space and the other placed in turn at: a) the upper corners of the working space; b) points as near as possible to the centres of the four sides of the working space; c) points vertically above the lower corners of the working space and1cm above the lowest shelf
44、; where this shelf has more than one position the lowest shall be used for this test. In the case of horizontal cylindrical ovens the test points are defined with reference to a concentric cylinder of radius3cm less than the internal radius of the oven extending between planes parallel to, and3cm in
45、wards from, the door and back wall. The working space is the space within the segment of this cylinder lying above the lowest shelf. The positions of the four “lower corners” of the working space are unambiguous; the “upper corners” are taken to be on the cylinder defining the upper part of the work
46、ing space, at points vertically above the lower corners. The “centres of the four sides of the working space” are defined by the midpoints of the four lines formed by the intersection of a horizontal diametral plane with the boundaries of the working Space. A suitable multi-junction system composed
47、of such loaded thermocouples may be used, the temperature differences being measured with respect to a thermocouple placed as near as possible to the centre of the working space. Whichever method is used, the mean shall be taken of at least three readings at each point tested. 6) Any other suitable
48、combination of metals may be used. 7) “Dag479”, supplied by Messis. Acheson Colloids Ltd. has been found suitable. The British Standards Institution is the owner of the registered certification mark: which can bc used by manufacturers only under licence from the BSI. The presence of this mark in add
49、ition to the mark “BS2648” on a product is an assurance that the product does comply with the requirements of the standard. It indicates that the BSI has satisfied itself, by inspection and testing, that the system of production, supervision and control used by the manufacturer is such as to ensure compliance with all the requirements of the standard. Maintenance of this approved system is secured by periodical inspection and testing on behalf of the BSI. The mark must be accompanied by the name or registered trade mark or licence number of the lic
