BS 7506-1-1995 Methods for measurement in electrostatics - Guide to basic electrostatics《静电学的测量方法 基本静电学指南》.pdf

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1、BRITISH STANDARD BS 7506-1: 1995 Methods for Measurements in electrostatics Part 1: Guide to basic electrostaticsBS7506-1:1995 This British Standard, having been prepared under the directionof the Materials and Chemicals Sector Board (I/-), waspublished under the authorityof the Standards Boardand c

2、omes into effect on 15June1995 BSI 03-1999 The following BSI references relate to the work on this standard: Committee reference PRI/25 Draft for comment 93/305298DC ISBN 0 580 23891 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technica

3、l Committee PRI/25, Electrical properties of rubber and plastics, upon which the following bodies were represented: British Floor Covering Manufacturers Association British Plastics Federation British Rubber Manufacturers Association Ltd. ERA Technology Ltd. Electrical and Electronic Insulation Asso

4、ciation (BEAMA Ltd.) European Electrostatic Discharge Association Federation of the Electronics Industry Federation of Resin Formulators and Applicators Ltd. Health and Safety Executive Ministry of Defence RAPRA Technology Ltd. Tyre Manufacturers Conference (Service Committee) Amendments issued sinc

5、e publication Amd. No. Date CommentsBS7506-1:1995 BSI 03-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 References 1 3 Definitions 1 4 List of symbols 4 5 Fundamentals of static electricity 4 6 Problems and hazards associated with electrostatic charges 9 7 Sol

6、utions 12 8 Applications dependent on electrostatic effects 13 9 General aspects of measurements 13 Figure 1 Equivalent electrical circuit for an electrostatically charged conductor 5 Figure 2 Potential wells and charge migration 7 Figure 3 Schematic diagram of a metal-insulator-metal sandwich 8 Tab

7、le 1 Typical electrical capacitances 10 Table 2 Perception levels and physical responses of people to discharges 12 List of references Inside back coverBS7506-1:1995 ii BSI 03-1999 Foreword This Part of BS 7506 was prepared by Technical Committee PRI/25. This Part is related to BS 5958 and BS EN 100

8、015 which are codes of practice concerned with hazards arising from electrostatic phenomena. Electrostatic problems are experienced in a wide spectrum of industry and measurements are made by technologists who are not necessarily experts in electrostatics. Part2 of this British Standard describes me

9、thods for measuring electrostatic effects and quantifying the relevant properties of materials and gives guidance on implementation of the methods. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct

10、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 20, an inside back cover and a back cover. This standard has been updated (see copyright

11、 date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside front cover.BS7506-1:1995 BSI 03-1999 1 1 Scope This Part of BS 7506 provides information and guidance on methods for making reliable measurements of electrostatic phenomena and the relevant p

12、roperties of materials. This Part comprises the following: review of basic electrostatics; outline of the range of problems caused by static; consideration of the role of materials and description of methods to minimize charge generation and achieve safe dissipation of static charge; consideration o

13、f electrostatic applications; recommendations for the control of the test environment conditions; general consideration of the basic recommendations for reliable measurement of electrostatic parameters. 2 References 2.1 Normative references This British Standard incorporates, by reference, provision

14、s from specific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on the inside back cover. Subsequent amendments to, or revisions of, any of these publications apply to this British Standard only when incorpora

15、ted in it by updating or revision. 2.2 Informative references This British Standard refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the

16、 latest editions. 3 Definitions For the purposes of this British Standard the following definitions apply. 3.1 antistatic material or treatment a material or treatment which allows easy migration of charge so that when bonded to earth the material does not retain static charge or one which does not

17、easily acquire charge by contact NOTEAn antistatic material will satisfy the quantitative requirements of either a dissipative or an astatic material (see3.12 and3.3). 3.2 antistatic additive or filler a substance added to a liquid or a solid in order to promote more rapid charge migration and so re

18、duce its ability to retain significant electrostatic charge when in contact with earth 3.3 astatic material a material with low tendency for charge separation by contact or by rubbing against other materials NOTEAs a means to control static risks it is essential that the maximum surface charge gener

19、ated in an approved test procedure should remain below the relevant hazard threshold value. 3.4 bonding the use of an additional independent connection between conductors to provide electrical continuity when this cannot otherwise be ensured 3.5 breakdown the annihilation, at least temporary, of the

20、 insulating properties of an insulating medium under electric stress 3.6 breakdown voltage the voltage at which breakdown occurs, under prescribed conditions of test or use 3.7 charge decay the migration of charge across or through a material leading to a reduction of charge density or surface poten

21、tial at the point where the charge was deposited NOTEIt is usually measured by observation of the timescale for decay of surface voltage. 3.8 charge decay time constant the time required for the local charge density or surface potential to fall to 1/e of its initial value NOTEFor characterizing mate

22、rials the initial value should be the relevant hazard threshold value. 3.9 conductive material a material of relatively high conductivity or charge carrier mobility. Materials of surface resistivity below 10 67 or volume resistivity below10 77m are usually implied 3.10 conductivity the reciprocal of

23、 resistivity (Sm 1 , equal to (7m) 1 )BS7506-1:1995 2 BSI 03-1999 3.11 conductor a material providing a sufficiently high conductivity that all parts of it are always at the same potential 3.12 dissipative material a material which allows charge to migrate over its surface and/or through its volume

24、in a time which is short compared to the timescale of the actions creating the charge or the time within which this charge will cause a problem. For normal applications the decay time constant for a patch of deposited charge downwards from the hazard threshold value should be within the range0.01s t

25、o0.5s 3.13 earth/earthing electrical connection (bonding) of a conductor to the main body of the earth to ensure that it is at earth potential 3.14 earth bonding point a dedicated point for connecting equipment and people to earth 3.15 electrostatic discharge (ESD) the sudden transfer of electrostat

26、ic charge between bodies at different electrostatic potentials by direct contact or by breakdown 3.16 electrostatic discharge sensitive device (ESDS) a discrete device, semiconductor, integrated circuit or other assembly that can be damaged by an electrostatic discharge directly to the device or nea

27、rby 3.17 ESD common earth bonding point a common connection point to which all items in an ESD protected area are connected 3.18 ESD protected area (EPA) an area with a defined boundary within which an ESDS can be handled without risk of damage from electrostatic discharges or fields 3.19 ESDS volta

28、ge sensitivity the maximum voltage at which the ESDS does not suffer any ESD damage 3.20 ESDS voltage sensitivity of an assembly the ESDS voltage sensitivity of the most sensitive device in an assembly will determine the sensitivity of the assembly 3.21 field work handling ESDS within a temporary EP

29、A with controlled boundaries 3.22 flammable material a gas, vapour, liquid, dust or solid that can react continuously with atmospheric oxygen and that may, therefore, sustain fire or explosion when such reaction is initiated by a suitable spark, flame or hot surface NOTEIn normal usage gas and vapou

30、r are synonymous. 3.23 flammable mixture a mixture of a gas, mist or suspension of dust with air (or air enriched with oxygen) in which combustion will propagate 3.24 flammable range the range of concentrations in air of a flammable material within which combustion can occur 3.25 garment a coat, jac

31、ket, smock, hood, trousers, overall or cap 3.26 ground this is synonymous with earth 3.27 ground cord a flexible electrical connection between the earth bonding point and the ESD earth facility 3.28 hazard threshold voltage the minimum capacitively stored voltage at which an electrostatic hazard or

32、risk will exist 3.29 hazardous area an area in which flammable or explosive gas-air mixtures are, or may be expected to be, present in quantities such as to require special precautions against ignition 3.30 incendive capable of igniting a prescribed flammable mixtureBS7506-1:1995 BSI 03-1999 3 3.31

33、insulator a material with very low mobility of charge so that any charge on the surface will remain there for a long time NOTEThe charge decay time constant is generally greater than10s. 3.32 ion an atomic or molecular particle carrying electrical charge 3.33 mass charge density the net quantity of

34、charge carried by unit mass of a material (Ckg 1 ) 3.34 minimum ignition energy the smallest amount of energy released in a spark that can ignite a mixture of a specified flammable material with air or oxygen, measured by a standard procedure 3.35 packaging material any material in which ESDS are pa

35、cked in intimate contact or close proximity for transportation or storage; including bags, boxes, crates, wraps, magazines, cushioning, foams, loose fill, etc 3.36 relaxation the migration of charge over and/or through a solid, liquid or gaseous material causing a reduction in surface charge density

36、 and potential 3.37 relaxation time constant charge decay time constant 3.38 shielding material a material which when formed into an enclosure provides strong attenuation of fast electric field transients associated with spark discharges to, or in the vicinity of, the outside of the enclosure 3.39 s

37、hielding bag/container a bag or container made from shielding material which provides protection for the storage or transport of ESDS NOTEFor normal applications it is necessary to provide1000:1 voltage attenuation ratio over the frequency range10Hz to1GHz between the inside and outside region. This

38、 may be affected by both the material and the construction. 3.40 surface charge density the net quantity of charge per unit area of surface of a solid or liquid (C m 2 ) 3.41 surface resistivity the resistance between opposing sides of a square on the surface of a material with account taken of all

39、current flow paths 3.42 triboelectric charging the separation of charge occurring at relative contact movement between two surfaces 3.43 volume charge density the net quantity of charge per unit volume of a solid, liquid or gas (C m 3 ) 3.44 volume resistivity the resistance between opposing sides o

40、f a cube of the material with account taken of fringing field effects 3.45 permittivity (absolute) the quantity whose product by the electric field strength is the electric flux density or surface charge density 3.46 electric constant ” 0 the value of the permittivity in a vacuum, sometimes referred

41、 to as the permittivity of free space 3.47 relative permittivity the ratio of the absolute permittivity to the electric constant. The permittivity is often taken to mean relative permittivity. It is also the ratio of the capacitance of an electrode system filled with a dielectric to that where the i

42、nterelectrode space is free of all material (i.e.in a vacuum)BS7506-1:1995 4 BSI 03-1999 4 List of symbols The following symbols are used in this standard: 5 Fundamentals of static electricity 5.1 General The most common cause of electrostatic charge is contact electrification. Conducting objects ca

43、n become charged by induction if they reside in an electric field produced by other charged objects or conductors at high potential in the vicinity. Any object can become charged if charged particles or ionized molecules accumulate on it. 5.2 Contact electrification Contact electrification can occur

44、 at solid/solid, liquid/liquid or solid/liquid interfaces. Clean gases cannot be charged in this way. If a gas contains solid particles or liquid droplets in suspension, however, these may be charged by contact so that such a gas can carry an electrostatic charge by virtue of these particles. In the

45、 case of dissimilar solids, initially uncharged and normally at earth potential, a small amount of charge is transferred from one material to the other when they make contact. The two materials are, therefore, oppositely charged and consequently there is an electric field between them. If the materi

46、als are then separated, work has to be done to overcome the attraction between the opposing charges and the potential difference between them, therefore, increases linearly with distance. This higher potential difference tends to drive charge back to any point of residual contact. In the case of two

47、 conductors the recombination of charges is virtually complete and no significant amount of charge remains on either material after separation. If one material, or both, is a non-conductor, the recombination cannot take place completely and the separating materials retain part of their charge. There

48、 may only be a small amount of charge involved but, because the distance between the charges when the surfaces are in contact is extremely small, the potential generated on separation can easily reach many kilovolts. In practice, surfaces are usually rough and so the charging is enhanced if the cont

49、act and separation involves rubbing since the area of real contact is increased. Contact electrification in liquids is essentially the same process but it can depend on the presence of ions or sub-microscopic charged particles. Ions (or particles) of one polarity may be adsorbed at the interface and they then attract ions of opposite polarity forming a diffuse layer of charge in the liquid, close to the surface. If the liquid is then moved relative to the interface, it carries away some of this diffuse layer, thereby bringing about separation of