1、BRITISH STANDARD BS4309:1968 Methods of Measuring the performance of laboratory electric resistance furnacesBS4309:1968 This BritishStandard, having been approved by the LaboratoryApparatus IndustryStandards Committeeand endorsed bytheChairman of the ChemicalDivisional Council, waspublished under th
2、e authorityof the General Councilon 25October1968 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference LBC/19 Draft for comment D65/4302 ISBN 0 580 00143 1 Co-operating organizations The Laboratory Apparatus Industry Standards Committee, under whose super
3、vision this BritishStandard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Agricultural Research Council Association for Science Education Association of Scientific Workers Board of Trade British Chemical Ware Manufact
4、urers Association British Laboratory Ware Association* British Lampblown Scientific Glassware Manufacturers Association British Pharmacopia Commission British Scientific Instrument Research Association* Chemical Industries Association Glass Manufacturers Federation* Institute of Petroleum Ministry o
5、f Defence, Air Force Department Ministry of Health Ministry of Technology, Laboratory of the Government Chemist* National Physical Laboratory (Ministry of Technology) Pharmaceutical Society of Great Britain Royal Institute of Chemistry Scientific Instrument Manufacturers Association* Society for Ana
6、lytical Chemistry Society of Chemical Industry Society of Glass Technology Standardization of Tar Products Test Committee The Government departments and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the co
7、mmittee entrusted with the preparation of this BritishStandard: British Coke Research Association British Electrical and Allied Manufacturers Association Ministry of Technology, National Engineering Laboratory Amendments issued since publication Amd. No. Date CommentsBS4309:1968 BSI 12-1999 i Conten
8、ts Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Test conditions 2 4 Temperature measuring equipment for tests 2 5 Temperature distribution and variation 2 6 Temperature fluctuation 2 7 Thermal loss 2 8 Case temperature 2 9 Adjacent surface temperature 3B
9、S4309:1968 ii BSI 12-1999 Foreword This standard makes reference to the following BritishStandard: BS1041, Code for temperature measurement Part4: Thermocouples. Arising out of a suggestion from the British Scientific Instrument Research Association, the Laboratory Apparatus Industry Standards Commi
10、ttee authorized the preparation of a BritishStandard for methods of describing and measuring the performance characteristics of laboratory furnaces, and in the first place of electric resistance furnaces. The representative technical committee constituted for the purpose was thus not asked to specif
11、y appropriate performance requirements for furnaces, as had been done in the standards for various types of laboratory ovens 1) . The reason for this different approach was the opinion that the wide range of electric furnaces and of their uses would make unprofitable any attempt to lay down requirem
12、ents in numerical terms for the various performance characteristics. Nevertheless, it was felt that a list of definitions relating to performance and a statement of general principles of measurement would provide a basis on which specifications of performance could be drawn up to the mutual advantag
13、e of manufacturer and purchaser. In all standards of performance for ovens and furnaces not designed for heat treatment of specific loads, the problem of whether to test the equipment with a charge or empty has to be resolved. Since the type of load can have a very marked effect on certain character
14、istics such as the distribution of temperature in the furnace, no one load can be regarded as a representative working load. It was therefore decided to recommend that furnaces whose performance is specified by reference to the standard should be tested empty. Test results on this basis will enable
15、fair comparisons to be made; the user should bear in mind that the load will probably affect some aspects of the performance of the furnace. If precise temperature values are important the temperature distribution in the load itself should be measured. A British Standard does not purport to include
16、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 of pages This document comprises a front cover, an inside front cover, pagesi an
17、dii, pages1 to3 and a back cover. 1) BS2648, “Performance requirements for electrically heated laboratory drying ovens”, BS3421, “Performance of electrically heated sterilizing ovens” and BS3718, “Laboratory humidity ovens (non-injection type)”.BS4309:1968 BSI 12-1999 1 This standard has been update
18、d (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. 1 Scope This BritishStandard defines the important performance characteristics of general purpose laboratory electric resistance furnaces of box or tube form (the
19、 latter for use either horizontally or vertically) with exposed or concealed heating elements, and recommends appropriate methods of measuring these characteristics. The standard is intended to apply to furnaces with rating up to about8kW and maximum temperature not exceeding1600 C. The tests are pr
20、imarily intended for the following: 1) Furnaces with atmospheres of air (they may, however, be applied to furnaces with other atmospheres, e.g.reducing atmospheres, where appropriate). 2) Furnaces with static atmospheres or mechanical re-circulation. 3) Furnaces fitted with control devices, either a
21、s supplied or fitted for the purpose of the tests only (see Clause3). NOTEIt should be understood that this BritishStandard does not specify any type of furnace as to its performance or safety; or in any other way. It would thus be meaningless to state that a furnace “complies with the requirements
22、of BS4309”, and such a form of words should not be used. 2 Definitions For the purposes of this BritishStandard the following definitions apply: 2.1 working space the space within which the stated performance of the furnace is achieved 2.2 furnace temperature the temperature at the centre of the wor
23、king space or at some other defined point in the working space 2.3 furnace temperature (indicated) the temperature indicated by a suitable device installed by the manufacturer or in accordance with his instructions 2.4 maximum temperature the highest temperature at which the furnace is designed to o
24、perate without unduly shortening its useful life NOTEThe criterion by which a useful furnace life is defined depends to a large extent on the nature of the employment of the furnace. For instance, a greater rate of deterioration of the heating elements or insulation at maximum temperature may be tol
25、erated for experimental work than for a long-term heat treatment process. For this reason the length of time for which a furnace can be operated at maximum temperature is not defined in this standard. Furnace manufacturers should be prepared to state whether the quoted maximum temperature relates to
26、 short or to long periods of operation. 2.5 steady-state period the period, during operation of the furnace from ambient temperature in specified ambient and voltage conditions, which commences when the mean power consumption has reached the minimum necessary to maintain a given mean furnace tempera
27、ture 2.6 average maximum temperature the arithmetic mean of the successive maximum furnace temperatures occurring in a specified number of temperature cycles during a steady-state period 2.7 average minimum temperature the arithmetic mean of the successive minimum furnace temperatures occurring in a
28、 specified number of temperature cycles during a steady-state period 2.8 mean temperature the arithmetic mean of the average maximum temperature and the average minimum temperature determined over the same specified number of temperature cycles 2.9 temperature variation the difference between the me
29、an temperatures at any two points in the working space, determined over the same specified number of temperature cycles 2.10 temperature fluctuation the difference between average maximum and average minimum temperatures at any one point NOTETemperature fluctuation indicates the short-term changes i
30、n temperature caused by the operation of the controller. The magnitude of fluctuation is usually attributed mainly to the characteristics of the controller, whilst the frequency is also dependent on the thermal capacity of the furnace. 2.11 temperature drift change in furnace temperature over a long
31、 period of time during a steady-state periodBS4309:1968 2 BSI 12-1999 2.12 heating-up time the time from switching on the cold furnace to the time when a specified indicated furnace temperature is first attained 2.13 stabilization time the time measured from the end of the heating-up period to the b
32、eginning of the steady-state period 2.14 rating or Maximum power consumption the maximum power requirements under any operating condition. The voltage at which the power consumption is calculated, or measured, must be stated 2.15 thermal loss rate of loss of heat during a steady-state period 3 Test
33、conditions Tests to determine the values of the characteristics covered by the foregoing definitions are carried out with the furnace empty and preferably with the control system with which it is to be used, because some of the characteristics to be measured are dependent more on the controller than
34、 on the furnace. When the specification or test result is quoted for a furnace not supplied with control equipment, the control equipment used in obtaining the data on that particular furnace should be identified either by manufacturers designation or by precise specification. The voltage of the ele
35、ctricity supply must be that for which the furnace is designed and it should be kept reasonably constant throughout the tests, as should ambient conditions. 4 Temperature measuring equipment for tests The temperature measurements should be made by means of a suitable thermocouple, or thermocouples,
36、and measuring system. (Forguidance on the use of thermocouples seeBS1041-4 2) .) The choice of a bare or a sheathed thermocouple for the temperature distribution, variation and fluctuation tests depends on the type of furnace and the nature of the test. Both types are used but where possible the use
37、 of a stationary thin-walled, narrow-bore tube, through which the thermocouple is drawn, is recommended. 5 Temperature distribution and variation The measurements required to determine temperature variation are made at a number of specified points in the working space; these points will usually lie
38、along the line of the axis of the furnace or along the centre line of the floor or will be distributed about the working space, whichever is the more appropriate to the normal mode of use of the furnace. Precautions must be taken to ensure that temperature drift which might occur during the measurem
39、ent period does not introduce error; for example the differential method using two thermocouples connected in series may be used, or the measured temperatures may be corrected for drift by reference to the simultaneously determined mean indicated furnace temperature. The temperature distribution is
40、obtained by calculating the mean temperature at each of the specified points during a steady-state period. These mean values are then plotted in the form of a curve or a set of curves or a chart, from which temperature variation may be determined, if necessary by interpolation. 6 Temperature fluctua
41、tion The temperature fluctuation is conveniently determined from the measurements made for calculation of temperature distribution. 7 Thermal loss The mean power consumption during a steady-state period may be taken as a measure of thermal loss and may be determined either with an integrating power
42、meter or by timing the operations of the controller if this is of the on/off type. Measurements should be made over a sufficient period of time to ensure that a true average is obtained. 8 Case temperature Where the case temperature is important, for example where anything in actual contact with the
43、 furnace is likely to be damaged by excessive temperature, or where the operator is likely to receive burns by touching the furnace case, the temperature at specified points should be measured by a suitable thermocouple placed in contact with the case, when the furnace is operating under steady-stat
44、e conditions at the manufacturers recommended maximum temperature. 2) BS1041, “Code for temperature measurement”. Part4, “Thermocouples”.BS4309:1968 BSI 12-1999 3 9 Adjacent surface temperature The purpose of this test is to check that the heat loss from the furnace is not excessive, thereby causing
45、 damage to adjacent surfaces by overheating. The surface usually affected is the supporting surface. Astandard surface, e.g.a matt black surface on a material which has a high conductivity, should be used in the test. The standard surface can be set flush with the adjacent surface to be tested in a
46、sheet of soft wood with a thermocouple fitted to the conducting material in order to measure the surface temperature. All measurements should be taken when the furnace is operating under steady-state conditions at the manufacturers recommended maximum temperature.BS4309:1968 BSI 389 Chiswick High Ro
47、ad London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revisions BritishStandards are updated by amendment or
48、revision. Users of BritishStandards should make sure that they possess the latest amendments or editions. It is the constant aim of BSI to improve the quality of our products and services. We would be grateful if anyone finding an inaccuracy or ambiguity while using this BritishStandard would inform
49、 the Secretary of the technical committee responsible, the identity of which can be found on the inside front cover. Tel:02089969000. Fax:02089967400. BSI offers members an individual updating service called PLUS which ensures that subscribers automatically receive the latest editions of standards. Buying standards Orders for all BSI, international and foreign standards publications should be addressed to Customer Services. Tel:02089969001. Fax:02089967001. In response to orders for international standards, it is BSI policy to supply the BSI implementation of those tha
