BS 7815-1995 Guide for evaluating the discharges from a charged surface《带电表面放电评定指南》.pdf

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1、BRITISH STANDARD BS 7815:1995 IEC 1087:1991 Guide for evaluating the discharges from a charged surfaceBS7815:1995 This British Standard, having been prepared under the directionof the Electrotechnical Sector Board, was published underthe authority of the Standards Board and comes into effect on 15Ju

2、ly1995 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference GEL/15 Draft announced in BSINews April 1995 ISBN 0 580 24197 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee GEL/

3、15, Insulating material, upon which the following bodies were represented: British Ceramic Research Ltd. British Industrial Ceramic Manufacturers Association Electrical and Electronic Insulation Association (BEAMA Ltd.) Electricity Association Federation of the Electronics Industry Rotating Electric

4、al Machines Association (BEAMA Ltd.) Transmission and Distribution Association (BEAMA Ltd.) Amendments issued since publication Amd. No. Date CommentsBS7815:1995 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope and object 1 2 Principle of the method

5、1 3 Test equipment 1 4 Conditioning and preliminary operations 2 5 Test procedure 2 6 Test results 2 7 Acceptance conditions 3 8 Test report 3 Figure 1 Test specimen and test electrode 3 Figure 2 Typical trace without discharges 4 Figure 3 Typical trace with discharges 4 List of references Inside ba

6、ck coverBS7815:1995 ii BSI 10-1999 National foreword This British Standard has been prepared by Technical Committee GEL/15. It is identical with IEC1087:1991 Guide for evaluating the discharges from a charged surface, published by the International Electrotechnical Commission (IEC). A British Standa

7、rd 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 of pages This document comprises a front cover, a

8、n inside front cover, pages i and ii, pages1 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.BS7815:1995 BSI 10-1999 1 1 Scope and object

9、This Technical Report is used as a guide that applies to products, materials, plastic parts of equipment, electrically-insulated metal parts of such equipment, or complete equipment. It provides a test method to determine whether a product produces discharges when its surface has been charged, for e

10、xample, by rubbing and thus be potentially the source of problems arising from electrostatic charges and discharges. 2 Principle of the method The principle of the method consists, in a first step, in charging electrically by an appropriate procedure, for instance by rubbing the external part of the

11、 product placed on a large metallic plate (where this represents an appropriate ground plane), and then, in a second step, in detecting if a discharge appears when an earthed test electrode approaches the charged area. When such a discharge appears, the electric charge transferred during the spark m

12、ay be measured by an appropriate equipment and is compared to a limiting value, characteristic of a given electrostatic problem. Examples of relevant problems and risks are ignition of flammable gases, Interference with operation of electronic equipment and damage to semiconductor devices. 3 Test eq

13、uipment The test equipment consists of three main parts: a charging device; a mobile test electrode which is driven at a given speed towards the test object; an electric equipment to measure and record the electric charge produced or transferred during the different steps of the test. 3.1 Charging d

14、evice Any charging device, based on contact and separation such as rubbing or beating, can be used. 1) The effectiveness of the charging device shall be verified in preliminary tests in that it can create a net surface charge approaching a density of at least10 5C/m 2on a highly insulating material,

15、 and an area of at least200cm 2shall be charged. The charging device shall be specified with reference to the product and it would be described in the relevant individual standard. The charging can be achieved by hand with a suitable material with an appropriate shape. A rubbing speed and pressure p

16、roviding maximum charge are used. For plane material samples the rubbing materials shall be wrapped around a metal electrode with a flat lower surface with an area of at least100cm 2and a width of at least7cm. During the rubbing period there shall be a pressure on this lower surface between400Pa and

17、600Pa. The charging device shall be electrically isolated from the operator and connected to earth by a measuring instrument. The operator shall be connected to earth by a wriststrap and hold the insulated rubbing electrode in his hand. The type of charging material shall be accurately described. Un

18、less otherwise stated in the specification, three types of materials should be used: a pure cotton fabric, wool or leather, as a conductive cloth; a material expected to produce a positive charge such as polyamide11; a material expected to produce a negative charge such as polyacrylic fabrics. In so

19、me circumstances, d.c. corona charging may be used. If tests are performed on site on a product on which there is already a charge, a charging device need not be used. 3.2 Moveable electrode Unless otherwise specified the electrode consists of a metal sphere15mm in diameter fitted on a motor driven

20、vertical rod. The device is such that the sphere can be moved down and up at a constant speed. The test equipment is shown in Figure 1. The standardized characteristics are the following: speed of the electrode: 5cm/s 1cm/s; distance between sample and sphere at furthest extent: 300mm 10mm; drive re

21、versal direction automatically switched on at a distance from the sphere to the product of1mm 0,5mm to reach the same maximum distance of300mm 10mm. 3.3 Charge meter The electric measurement circuit is shown in Figure 1. It consists mainly of a charge meter, which comprises a highly insulated and ca

22、librated10nF to100nF capacitor and a very high input resistance voltmeter, which is connected across the capacitor and has a range of1mV to10V, providing a time constant of at least120s. The output of the voltmeter shall be continuously recorded. 1) Different types of charging devices are under cons

23、ideration in order to establish their effectiveness and reproducibility.BS7815:1995 2 BSI 10-1999 4 Conditioning and preliminary operations 4.1 General remarks The test product shall be cleared from all pre-existing electrostatic charges. This can be achieved by various means: either by conditioning

24、 in a wet atmosphere(70 % r.h.) for24h minimum; or by cleaning all the surfaces with a rag wetted with alcohol or demineralized water and earthed through the operator; or by using static eliminators. The absence of static charges on all the surfaces of the product is checked by the test procedure de

25、scribed in 5.1. Consideration should be given to the fact that the act of removal of all pre-existing charges may affect the surface and its ease of charging and discharging. 4.2 Ambient conditioning Unless otherwise specified, the test product is then conditioned in an atmosphere of35% 2% r.h. at23

26、 C 1 C at minimum for24h and the test is to be performed in the same environmental conditions. However, in many circumstances a dry atmosphere of15% 2%r.h. and23 C 1 C could be more suitable. Pursuit of the test in a low humidity may enable high charge levels to be achieved, but if there is any chan

27、ce that the character of the discharge could be affected by moisture in the atmosphere or absorbed on the surface, it is desirable also to check behaviour with a higher level of humidity in this case. 4.3 Mounting of the test product After this conditioning, the test product is mounted in relation t

28、o a large metallic plate to simulate normal use conditions, and under these conditions the metallic plate should be connected to earth. In the case of a product with external electrical connection, this connection shall be earthed. If charge decay in the sample within the test time scale is suspecte

29、d, an independent measurement of the decay rate is required. 5 Test procedure 5.1 Preliminary measurements Test environment is the same as described in 4.2. When the product is ready for testing as described in4.3, the absence of remanent charges is checked by moving the electrode towards the upper

30、surface of the product. The reading of the charge meter connected to the electrode shall be less than0,1nC. The electrode is then moved up to a distance of300mm 10mm from the surface. 5.2 Sample charging In appropriate circumstances an area of at least200cm 2of the test product is then rubbed or bea

31、ten, according to 3.1 in order to create as large a charge as possible. This maximum level of charge should not decay by more than10 % in120s. This is recognized by recording the output of the charge meter connected to the movable (but now fixed) electrode. Alternatively, it can be measured by using

32、 a field meter. 5.3 Discharge measurement The movement mechanism shall be switched on as soon as possible after charging is completed. The reading of the charge meter connected to the electrode is continuously recorded during both downward and upward motion. The operations described in 5.1, 5.2 and

33、5.3 are made at other locations on the sample, according to the indications given in the specification. In appropriate circumstances three tests are to be repeated on separate200cm 2areas of the sample for each of the rubbing materials. Between successive tests, the sample shall be discharged as des

34、cribed in 4.1. Careful consideration shall be given to any charges on the sample which may not be removed by the procedures described. 6 Test results The test results are expressed by the output of the recording device under the following conditions. 6.1 Residual charge When no discharge has been ob

35、served, the pattern of the recording is smooth as is shown in Figure 2. The value recorded on the charge meter at the end of the experiment shall be less than1nC (residual charge): Q r= C %V r . 6.2 Transferred charge When a discharge has occurred, the pattern of the recording shows a form similar t

36、o the one reproduced in Figure 3. The sudden increase in voltage on the recorder is used to calculate the transferred charge Q t : Q t= C %V t where %V tis the increase in voltage and C the capacitance of the charge meter. The value of the distance at which the spark occurred shall be measured. NOTE

37、Only the first discharge is to be taken into account, but if more than one discharge occurs, then an investigation with a larger sphere is advisable.BS7815:1995 BSI 10-1999 3 7 Acceptance conditions The acceptance conditions shall be specified in individual standards. 8 Test report The test report s

38、hall include: description of the product, including dimensions; description of the device used to ground the product, if any, and dimensions of the ground plate; description of the charging device and procedure; distance at which the spark occurred, if any; Q ras defined in 6.1 and polarity, or Q ra

39、s defined in 6.2 and polarity; reference to any relevant particular specification on specific conditions; conditioning; environment conditions during the test; record of the number of tests and of the number of discharges. NOTEThis test has been shown to be repeatable in a given laboratory when cond

40、ucted by experienced operators. The reproducibility between laboratories is still under examination. Figure 1 Test specimen and test electrodeBS7815:1995 4 BSI 10-1999 Figure 2 Typical trace without discharges Figure 3 Typical trace with dischargesBS7815:1995 BSI 10-1999 List of references See natio

41、nal foreword.BS 7815:1995 IEC 1087:1991 BSI 389 Chiswick High Road 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

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