1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7506 : Part 2 : 1996 I
2、ncorporating Amendment No. 1 ICS 29.020 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Methods for Measurements in electrostatics Part 2. Test methodsBS 7506 : Part 2 : 1996 Issue 2, December 1997 This British Standard, having been prepared under the direction of the Sector B
3、oard for Materials and Chemicals, was published under the authority of the Standards Board and comes into effect on 15 March 1996 BSI 1997 The following BSI references relate to the work on this standard: Committee reference PRI/25 Draft for comment 94/304285 DC ISBN 0 580 24636 1 Amendments issued
4、since publication Amd. No. Date Text affected 9720 December 1997 Indicated by a sideline in the margin Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee PRI/25, Electrical properties of rubber and plastics, upon which the f
5、ollowing bodies were represented: British Plastics Federation British Resilient Flooring Manufacturers Association British Rubber Manufacturers Association ERA Technology Ltd. Electrical and Electronic Insulation Association (BEAMA Ltd.) European Electrostatic Discharge Association Federation of Res
6、in Formulators and Applicators (FeKFA) Federation of the Electronics Industry Health and Safety Executive RAPRA Technology Ltd.Issue 1, December 1997 BS 7506 : Part 2 : 1996 BSI 1997 a Summary of pages The following table identifies the current issue of each page. Issue 1 indicates that a page has b
7、een introduced for the first time by amendment. Subsequent issue numbers indicate an updated page. Vertical sidelining on replacement pages indicates the most recent changes (amendment, addition, deletion). Page Issue Page Issue Front cover Inside front cover a b i ii 1 2 3 4 5 6 7 8 9 10 11 12 13 1
8、4 15 2 2 1 blank 2 2 2 2 original original original original original 2 2 original original original original original 2 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 Inside back cover Back cover original 2 original original original original original original 2 2 original original origin
9、al original original original original original original original 2b blankIssue 2, December 1997 BS 7506 : Part 2 : 1996 BSI 1997 i Contents Page Foreword ii 1 Scope 1 2 Informative references 1 3 Measurement of electric field 1 4 Measurement of potential 4 5 Measurement of charge 5 6 Measurement of
10、 charge density 8 7 Measurement of charge decay 9 8 Measurement of resistance and resistivity 12 9 Measurement of chargeability 15 10 Measurement of shielding performance of materials 20 11 Measurement of d.c. breakdown voltage 23 Annexes A (informative) Methods for the calibration of electrostatic
11、instruments 27 B (informative) Bibliography 33 List of references Inside back coverii BSI 1997 BS 7506 : Part 2 : 1996 Issue 2, December 1997 | | | Foreword This Part of BS 7506 was prepared by Technical Committee PRI/25. BS 7506 Methods for measurement in electrostatics comprises two Parts: Part 1:
12、 Guide to basic electrostatics Part 2: Test methods The test methods described are those considered most appropriate for electrostatic measurements. Several methods described in this Part are simplified versions of existing British Standards, since for the purposes of electrostatics the range of val
13、ues of significance may be restricted. The methods described give adequate accuracy and precision in these ranges. In many cases more precise or accurate procedures are available, and for these more specialized standards should be consulted. Part 1 of this standard provides information and guidance
14、on methods for making reliable measurements. Annex A describes procedures for calibration of the instruments used in the test methods specified. Although calibration is not always deemed to be necessarily prescribed, it is considered advisable to provide guidance. Annex B provides useful references
15、for additional information. Compliance with a British Standard does not of itself confer immunity from legal obligations. BSI 1997 1 Issue 2, December 1997 BS 7506 : Part 2 : 1996 Shield Sensor C R Figure 1. Induction probe fieldmeter 1 Scope This Part of BS 7506 comprises standard methods of measur
16、ement, providing reliable means of determining the values of those properties of materials relevant to electrostatic phenomena. The range of values of a property which is significant to electrostatic effects is limited, and it is only useful to measure such a property within this range (for example
17、resistance values between 10 6 V and 10 10 V). For this reason, simpler procedures are acceptable, and fewer problems of interpretation arise. For precise measurements of properties outside these ranges reference should be made to more specialized standard methods and to relevant scientific literatu
18、re. 2 Informative references This Part of BS 7506 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 latest editions. | | 3 Measuremen
19、t of electric field 3.1 Principle 3.1.1 General Electric fields are measured from the charge induced on a conducting surface. Fieldmeters (used for measuring the field) are of two main types: induction probe and field mill instruments. 3.1.2 Induction probe instruments Induction probe instruments ar
20、e simple and of relatively low cost. They consist, as shown in figure 1, of a sensing surface with a defined capacitance to earth connected to a very high input impedance amplifier. The signal V (volts) observed at the preamplifier input when a sensing surface of effective area A (m 2 ) with an inpu
21、t capacitance C (F), is exposed to an electric field E (Vm 21 )i s given by: V = e 0 EA/C where e 0 is the electric constant (8.853 10 212 Fm 21 ). The effective sensing area will depend on the screening arrangements, and should be calibrated in situ. Zero drift can arise from variation of the bias
22、currents and offset voltages at the preamplifier input. Induction probe instruments have a finite input time constant arising from the input capacitance and inevitable input leakage resistance. Consequently, induction probe instruments are used for relatively short term measurements (tens of seconds
23、) and require to be adjusted to zero reading in a zero electric field environment.2 BSI 1997 BS 7506 : Part 2 : 1996 Issue 2, December 1997 Figure 2. Field mills with rotating and oscillating shutters | 3.1.3 Field mill instruments Field mill fieldmeters overcome the limitations of induction probes
24、by using a rotating chopper, which is normally earthed, to modulate the coupling of the electric field to the sensing surface. The general arrangement is shown in figure 2. So long as the timescale of modulation is suitably shorter than the product of the input capacitance, C, and the effective inpu
25、t resistance to earth, R, then an alternating signal is generated which is independent of the rate of chopping and the value of the input resistor. The response then depends only on the area of the sensing surface A and the value of the input capacitance C. The change of charge induced on the sensin
26、g surface is given by dQ: dQ = A e 0 dE The peak-to-peak signal V (volts) generated will be: V = dQ/C For a depth of modulation, f, of the observed electric field by the rotation of the chopper: dE =fE | and V = e 0 f E A/C Phase sensitive detection of the observed alternating signal after amplifica
27、tion generates an output signal whose strength and polarity relate proportionally and directly to the observed electric field. 3.2 Fieldmeters 3.2.1 Construction The case of the fieldmeter shall be of a conductive or static dissipative material. No insulating materials shall be visible on or near th
28、e sensing aperture. NOTE. Insulating materials acquire and retain static charge which will affect the readings and the zero setting. This is particularly important for high sensitivity instruments and for instruments used near air ionizer units. The sensing aperture of the fieldmeter shall be define
29、d within a flat conducting region of the case, mounted flush with a surrounding surface for application measurements and for calibration. Readings shall relate to the electric field at this aperture. BSI 1996 3 BS 7506 : Part 2 : 1996 Fieldmeter instruments shall include provision for external adjus
30、tment of the zero reading when observing a zero electric field environment. This shall be the only adjustment of basic instrument operation directly accessible by the user. 3.2.2 Reference potential An earth bonding point shall be provided and be clearly identified. The fieldmeter shall be bonded to
31、 a defined reference potential, usually earth potential, before and during use. 3.2.3 Susceptibility to interference Operation shall not be adversely affected by exposure to high value or fast changing electric fields; for example from nearby spark discharges. 3.2.4 Sensitivity Fieldmeter instrument
32、s are categorized in terms of sensitivity and accuracy. High sensitivity fieldmeters are able to measure and display values of electric field of 100 Vm 21 with the zero stable within 50 Vm 21 over at least 1000 s. A reading of 100 Vm 21 shall be at least 10 % of an analogue scale reading or at least
33、 the second decimal digit of a digital display. For accurate measurements with field mill instruments the time constant of the input resistance and capacitance shall be at least five times the half cycle time of the minimum chopping frequency of the instrument. Also, the time constants of any high p
34、ass noise reduction filtering in signal amplification shall be four to five times the half cycle time multiplied by the number of such filtering stages. To avoid interaction with alternating mains supply signals the chopping frequency shall be at least three times the frequency of the supply. 3.2.5
35、Display The instrument display, and any signal output, shall give a linear response to electric field, symmetrical with polarity and with no hysteresis. For high accuracy instruments these properties of the instrument shall be within 1 % of full scale reading of the operating range and for lower acc
36、uracy instruments within 5 %. The output time constant at the display shall be less than 1 s. NOTE. This is particularly important for handheld instruments used to search for sources of static charge. The display shows electric field values with polarity. Scale readings are to be given in Vm 21 or k
37、Vm 21 as appropriate. In battery powered instruments warning shall be given when the battery voltage is at a level at which readings may become unreliable. 3.3 Procedure If using an induction probe fieldmeter, switch on in a region free of electric fields. Before starting measurements check and reco
38、rd the zero reading and stability. Check the zero with the fieldmeter looking into a clean metal chamber in which the nearest surfaces are at least 50 mm away from the sensing apertures, avoiding the influence of contact potential and contamination effects. Make readings relative to the instrument z
39、ero. When using an induction probe instrument make measurements within a shorter time relative to the input decay time constant and without re-zeroing. Ensure that surfaces around the sensing region are clean. NOTE 1. This is particularly important with high sensitivity instruments and in work invol
40、ving insulating particles. Insulating particles readily become charged and any such particles deposited in or around the sensing region will offset the instrument zero. Air purging helps prevent particle deposition. Check the zero reading at appropriate intervals (see item b) and record its value. N
41、OTE 2. On first use of a particular fieldmeter it is important for the user to carry out the following checks. a) Bond the instrument to earth. b) Switch the instrument on in a region free of static charges and electric fields and check the stability of the zero reading over times comparable to the
42、times needed for the measurements. c) Switch the instrument on in a field-free region and move it to observe a constant high value of electric field, for example a steady voltage on a metal plate at a stable distance. Observe the rate of change of reading and estimate the input decay time constant.
43、After a time return it to a field-free region and check if the zero reading has changed. 3.4 Expression of results The results of electric field measurements are the values of electric field observed at particular times in Vm 21 . 3.5 Test report The report shall include at least the following infor
44、mation: a) the number and date of this standard; b) date and time of measurements; c) location, arrangement and time when measurements made; d) ambient temperature and relative humidity in measurement region; e) identification of instrumentation used and date of most recent calibration.4 BSI 1996 BS
45、 7506 : Part 2 : 1996 4 Measurement of potential 4.1 Principle The potential of a conducting object may be measured by direct connection to an electrostatic voltmeter or voltmeter with a suitably high input impedance. The potential of a charged surface, insulating or conducting, may be measured by t
46、he electric field which it creates at a nearby fieldmeter held at a fixed potential, usually earth. A more accurate measure is obtained if the potential of the fieldmeter is adjusted to give zero field at the fieldmeter, the potential of the meter then being equal to that of the surface or location
47、in the volume, described usually as the voltage follower configuration. The potential of a localized region in a volume can be measured using a fieldmeter in either a simple or a voltage follower configuration as above. 4.2 Fieldmeters and voltmeters 4.2.1 Simple configuration fieldmeter The potenti
48、al of a surface is calculated from the electric field at a nearby electrostatic fieldmeter at earth or a defined potential. Induction or field mill fieldmeter instruments shall be as described in 3.2. The electric field between the body and the fieldmeter is usually non-uniform and the surface volta
49、ge is not a simple product of the electric field E (Vm 21 ) and the separation distance d (m). A geometric factor f may need to be used; for plane surfaces which have a radial extent less than five times the separation gap the correction factor will be affected by the size and form of the surface on which the potential is measured. NOTE. In these circumstances the factor f may be determined by calibration (see annex A) or computer modelling of the particular geometric arrangement. The potential is is given by: V = Efd For accurate measurements it is necessary tha
