T­¬ng thÝch ®iÖn tõ (emc) miÔn nhiÔm ®èi víi hiÖn t­îng phãng tÜnh ®iÖn ph­¬ng ph¸p ®o vµ thö

Phô lôc B

CÊu tróc chi tiÕt cña bé c¶m biÕn dßng

CÊu t¹o chi tiÕt cña bé c¶m biÕn dßng ®­îc cho trong c¸c h×nh tõ B.1 ®Õn B.7.

Thñ tôc l¾p r¸p nh­ sau:

1. 
   Hµn 25 ®iÖn trë t¶i “7” (51 , 5%, 0,25 W) vµo mÆt ra cña ®Üa “3” vµ lµm s¹ch c¸c ®Çu cuèi ®­îc hµn.
   
2. 
   Hµn 05 ®iÖn trë ghÐp “8” (240 , 5%, 0,25 W) theo h×nh ngò gi¸c vµo ®Çu nèi lèi ra kiÓu N ®ång trôc.
   
3. 
   L¾p mÆt ra cña ®Üa “3” (®· cã ®ñ c¸c ®iÖn trë t¶i) vµo gê næi cña ®Çu nèi lèi ra “1” b»ng 4 ®inh vÝt M2,5 Pan Hd 6,5 mm.
   
4. 
   L¾p ®Çu nèi lèi ra (®· cã ®ñ c¸c ®iÖn trë ghÐp) víi gê næi ®Çu nèi lèi ra “1” b»ng 4 ®inh vÝt M3.
   
5. 
   Hµn ®Üa vµo “4”, víi ®inh vÝt hç trî ®iÖn cùc “6” ®· ®­îc b¾t vÝt vµ ®­îc hµn, trªn c¶ hai nhãm ®iÖn trë ghÐp vµ ®iÖn trë t¶i. Lµm s¹ch c¸c ®Çu cuèi ®­îc hµn.
   
6. 
   B¾t vÝt ®Üa ®iÖn cùc ph¼ng “5” trªn ®inh vÝt hç trî ®iÖn cùc “6”, sau ®ã l¾p g¸ gi÷ cè ®Þnh “2” b»ng 8 ®inh vÝt M3 Pan Hd 6,5 mm.
   

M« t¶ vµ cÊu t¹o chi tiÕt ®ang ®­îc nghiªn cøu.

VËt liÖu: ®ång m¹ b¹c hoÆc ®ång thau m¹ b¹c

H×nh B.6

TCN 68 - 207: 2002

Electrostatic discharge immunity

Testing and measurement techniques

FOREWORD
The technical standard TCN 68 - 207: 2002 “ElectroMagnetic compatibility (EMC) - Electrostatic discharge immunity - Testing and measurement techniques” is based on IEC 61000-4-2 (05/1999). A few of amendaments have been made to the scope to suit the specific application in Vietnam.

The technical standard TCN 68 - 207: 2002 is drafted by Research Institute of Posts and Telecommunications (RIPT) at the proposal of Department of Science & Technology of Ministry of Post and Telematics. The Technical standard is adopted by the Decision No. 28/2002/QD-BBCVT of the Minister of Posts and Telematics dated 18/12/2002.

The technical standard TCN 68 - 207: 2002 is issued in a bilingual document (Vietnamese version and English version). In cases of interpretation disputes, Vietnamese version is applied.

The ministry of posts and telematics No.: 34/2002/QD-BBCVT

The socialist republic of Vietnam Independent - Freedom - Happiness Hanoi, 31 December 2002

• 
  Pursuant to the Ordinance on Goods Quality of January 04, 2000;
  
• 
  Pursuant to the Government's Decree No. 90/2002/ND-CP of November 11, 2002 on the functions, tasks, powers and organizational structure of the Ministry of Posts and Telematics;
  
• 
  Pursuant to the Decision No. 27/2001/QD-TCBD of January 09, 2001 of the Department General of Posts and Telecommunications (now the Ministry of Posts and Telematics) on establishing, promulgating and adopting standards;
  
• 
  At the proposal of the Director General of the Department of Science Technology,
  

1. 
   ElectroMagnetic Compatibility (EMC) - Electrostatic discharge immunity - Testing and measurement techniques.
   

2. 
   ElectroMagnetic Compatibility (EMC) - Voltage dips, short interruptions and voltage variations immunity - Testing and measurement techniques.
   

3. 
   ElectroMagnetic Compatibility (EMC) - Surge immunity - Testing and measurement techniques.
   

4. 
   ElectroMagnetic Compatibility (EMC) - Power frequency magnetic field immunity - Testing and measurement techniques.
   

For the minister of posts and telematics

This Standard relates to the immunity requirements and test methods for electrical and electronic equipment subjected to static electricity discharges, from operators directly, and to adjacent objects. It additionally defines ranges of test levels which relate to different environmental and installation conditions and establishes test procedures.

The object of this standard is to establish a common and reproducible basis for evaluating the performance of electrical and electronic equipment when subjected to electrostatic discharges. In addition, it includes electrostatic discharges which may occur from personnel to objects near vital equipment.

This standard defines:

• 
  Typical waveform of the discharge current;
  
• 
  Range of test levels;
  
• 
  Test equipment;
  
• 
  Test set up;
  
• 
  Test procedure.
  

This standard does not intend to specify the tests to be applied to particular apparatus or systems. Its main aim is to give a general basic reference to all concerned product committees. The product committees (or users and manufacturers of equipment) remain responsible for the appropriate choice of the tests and the severity level to be applied to their equipment.

2. Normative references

[1] IEC 60050(161):1990, International Electrotechnical Vocabulary (IEV)   Chapter 161: Electromagnetic compatibility

[2] IEC 60068 1:1988, Environmental testing   Part 1: General and guidance

3. General

This standard relates to equipment, systems, sub systems and peripherals which may be involved in static electricity discharges owing to environmental and installation conditions, such as low relative humidity, use of low conductivity (artificial fibber) carpets, vinyl garments, etc., which may exist in allocations classified in standards relevant to electrical and electronic equipment (for more detailed information, see clause A.1 of annex A).

The tests described in this standard are considered to be a first step in the direction of commonly used tests for the qualitative evaluation of the performance of all electrical arid electronic equipment as referred to in clause 1.

Note: From the technical point of view the precise term for the phenomenon would be "static electricity discharge". However, the term "electrostatic discharge" (ESD) is widely used in the technical world and in technical literature. Therefore, it has been decided to retain the term ESD in the title of this standard.

4. Definitions

For the purpose of this section, the following definitions and terms apply and are applicable to the restricted field of electrostatic discharge; not all of them are included in IEC 60050(161) [IEV].

An undesired departure in the operational performance of any device, equipment or system from its intended performance. [IEV 161 01 19]

Note: The term "degradation" can apply to temporary or permanent failure.

4.2 Electromagnetic compatibility (EMC)

The ability of an equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment. [IEV 161 01 07]

Material exhibiting properties which minimize charge generation when rubbed against or separated from the same or other similar materials

The capacitor of the ESD generator representing the capacity of a human body charged to the test voltage value. This may be provided as a discrete component, or a distributed capacitance.

Electrostatic discharge (see 4.10).

Equipment under test.

A flat conductive surface whose potential is used as a common reference. [IEV 161 04 36].

A metal sheet or plate, to which discharges are applied to simulate electrostatic discharge to objects adjacent to the EUT. HCP: Horizontal Coupling Plane; VCP: Vertical Coupling Plane.

Interval of time within which the decrease of the test voltage due to leakage, prior to the discharge, is not greater than 10%.

A transfer of electric charge between bodies of different electrostatic potential in proximity or through direct contact. [IEV 161 01 22]

The ability of a device, equipment or system to perform without degradation in the presence of an electromagnetic disturbance. [IEV 161 01 20]

A method of testing, in which the electrode of the test generator is held in contact with the EUT, and the discharge actuated by the discharge switch within the generator.

A method of testing, in which the charged electrode of the test generator is brought close to the EUT, and the discharge actuated by a spark to the EUT.

Application of the discharge directly to the EUT.

Application of the discharge to a coupling plane in the vicinity of the EUT, and simulation of personnel discharge to objects which are adjacent to the EUT.

5. Test levels

The preferential range of test levels for the ESD test is given in table 1.

Testing shall also be satisfied at the lower levels given in table 1.

Details concerning the various parameters which may influence the voltage level to which the human body may be charged are given in clause A.2 of annex A. Clause A.4 also contains examples of the application of the test levels related to environmental (installation) classes.

Contact discharge is the preferred test method. Air discharges shall be used where contact discharge cannot be applied. Voltages for each test method are given in tables la and 1b. The voltages shown are different for each method due to the differing methods of test. It is riot intended to imply that the test severity is equivalent between test methods.

Further information is given in clauses A.3, A.4 and A.5 of annex A.

6. Test generator

The test generator consists, in its main parts, of:

• 
  Charging resistor R_c;
  
• 
  Energy storage capacitor C_s;
  

• 
  Distributed capacitance C_d;
  
• 
  Discharge resistor R_d;
  
• 
  Voltage indicator;
  
• 
  Discharge switch;
  
• 
  Interchangeable tips of the discharge electrode (see figure 4);
  
• 
  Discharge return cable;
  
• 
  Power supply unit.
  

The generator shall meet the requirements given in 6.1 and 6.2.

Specifications

• 
  Energy storage capacitance (C_s + C_d): 150 pF  10%
  
• 
  Discharge resistance (R_d): 330   10%
  
• 
  Charging resistance (R_c): between 50 M and 100 M;
  
• 
  Output voltage (see note 1): up to 8 kV (nominal) for contact discharge;
  

• 
  Tolerance of the output voltage indication:  5%;
  

• 
  Polarity of the output voltage: positive and negative (switchable);
  
• 
  Holding time: at least 5s;
  
• 
  Mode of operation (see note 2): single discharge (time between successive discharges at
  least 1s);
  

• 
  Waveshape of the discharge Current: see 6.2.
  

The energy storage capacitor, the discharge resistor, and the discharge switch shall be placed as close as possible to the discharge electrode.

The dimensions of the discharge tips are given in figure 4.

For the air discharge test method the same generator is used and the discharge switch has to be closed. The generator shall be fitted with the round tip shown

The discharge return cable of the test generator shall be in general 2 m long, and constructed to allow the generator to meet the waveform specification. It shall be sufficiently insulated to prevent the flow of the discharge current to personnel or conducting surfaces other than via its termination, during the ESD test.

In cases where a 2 m length of the discharge return cable is insufficient, (e.g. for tall EUTs) a length not exceeding 3 m may be used, but compliance with the waveform specification shall be verified.

6.2 Verification of the characteristics of the ESD generator

In order to compare the test results obtained from different test generators, the characteristics shown in table 2 shall be verified using the discharge return cable to be used in the testing.

The waveform of the output current of the ESD generator during the verification procedure shall conform to figure 3.

The values of the characteristics of the discharge current shall be verified with 1000 MHz bandwidth measuring instrumentation.

A lower bandwidth implies limitations in the measurement of rise time and amplitude of the first current peak.

For verification, the tip of the discharge electrode shall be placed in direct contact with the current sensing transducer, and the generator operated in the contact discharge mode.

The typical arrangement for the verification of the ESD generator performance is given in figure 2. The bandwidth of the target has to be more than 1 GHz. Constructional details of a possible design for the current sensing transducer are given in annex B.

Other arrangements that imply the use of a laboratory Faraday cage having dimensions different from those in figure 2 are allowed; separation of the Faraday cage from the target plane is also allowed, but in both cases the distance between the sensor and the grounding terminal point of the ESD generator shall be respected (1 m), as well as the layout of the discharge return cable.

The ESD generator shall be re calibrated in defined time periods in accordance with a recognized quality assurance system.

7. Test set up

The test set up consists of the test generator, EUT and auxiliary instrumentation necessary to perform direct and indirect application of discharges to the EUT in the following manner:

1. 
   Contact discharge to the conductive surfaces and to coupling planes;
   
2. 
   Air discharge at insulating surfaces.
   

• 
  Type (conformance) tests performed in laboratories;
  
• 
  Post installation tests performed on equipment in its final installed conditions.
  
• 
  he preferred test method is that of type tests performed in laboratories.
  
• 
  The EUT shall be arranged in accordance with the manufacturer's instructions for installation (if any).
  

The following requirements apply to tests performed in laboratories under environmental reference conditions outlined in 8.1.

A ground reference plane shall be provided on the floor of the laboratory. It shall be a metallic sheet (copper or aluminium) of 0.25 mm minimum thickness; other metallic materials may be used but they shall have at least 0.65 mm minimum thickness.

The minimum size of the reference plane is 1 m2, the exact size depending on the dimensions of the EUT. It shall project beyond the EUT or coupling plane by at least 0.5 m an all sides, and shall be connected to the protective grounding system.

Local safety regulations shall always be met.

The EUT shall be arranged and connected according to its functional requirements.

A distance of 1 m minimum shall be provided between the equipment under test and the walls of the laboratory and any other metallic structure.

The EUT shall be connected to the grounding system, in accordance with its installation specifications. No additional grounding connections are allowed.

The positioning of the power and signal cables shall be representative of installation practice.

The discharge return cable of the ESD generator shall be connected to the ground reference plane. The total length of this cable is in general 2 m.

In cases where this length exceeds the length necessary to apply the discharges to be selected points, the excess length shall, where possible, be placed non inductively off the ground reference plane and shall not come closer than 0.2 m to other conductive parts in the test set up.

The connection of the earth cables to the ground reference plane and all bonding shall be of low impedance, for example by using clamping devices for high frequency applications.

Where coupling planes are specified, for example to allow indirect application of the discharge, they shall be constructed from the same material type and thickness as that of the ground reference plane, and shall be connected to the GRP via a cable with a 470 k resistor located at each end. These resistors shall be capable of withstanding the discharge voltage and shall be insulated to avoid short circuits to the GRP when the cable lies on the GRP.

Additional specifications for the different types of equipment are

The test set up shall consist of a wooden table, 0,8 m high, standing on the ground reference plane.

A horizontal coupling plane (HCP), 1.6 m x 0.8 m, shall be placed on the table. The EUT and cables shall be isolated from the coupling plane by an insulating support 0.5 mm thick.

If the EUT is too large to be located 0.1 m minimum from all sides of the HCP, an additional identical HCP shall be used, placed 0.3 m from the first, with the short sides adjacent. The table has to be. enlarged or two tables may be used. The HCPs shall not be bonded together, other than via resistive cables to the GRP.

Any mounting feet associated with the EUT shall remain in place.

An example of the test set up for table top equipment is given in figure 5.

The EUT and cables shall be isolated from the ground reference plane by an insulating support about 0.1 m thick.

An example of the test set up for floor standing equipment is given
in figure 6.

Any mounting feet associated with the EUT shall remain in place.

These tests are optional, and not mandatory for certification tests; they may be applied only when agreed between manufacturer and customer. It has to be considered that other co located equipment may be unacceptably affected.

The equipment or system shall be tested in its final installed conditions.

In order to facilitate a connection for the discharge return cable, a ground reference plane shall be placed on the floor of the installation, close to the EUT at about 0.1 m distance. This plane should be of copper or aluminium not less than 0.25 mm thick. Other metallic materials may be used, providing the minimum thickness is 0.65 mm. The plane should be approximately 0.3 m wide, and 2 m in length where the installation allows.

This ground reference plane should be connected to the protective earthing system. Where this is not possible, it should be connected to the earthing terminal of the EUT, if available.

The discharge return cable of the ESD generator shall be connected to the reference plane at a point close to the EUT. Where the EUT is installed an a metal table, the table shall be connected to the reference plane via a cable with a 470 k resistor located at each end, to prevent a build up of charge.

An example of the set up for post installation tests is given in figure 7.

8. Test procedure

In order to minimize the impact of environmental parameters on test results, the tests shall be carried out in climatic and electromagnetic reference conditions as specified in 8.1.1 and 8.1.2.

In the case of air discharge testing, the climatic conditions shall be within the following ranges:

• 
  Ambient temperature: 15⁰C to 35⁰C
  
• 
  Relative humidity: 30% to 60%;
  
• 
  Atmospheric pressure: 86 kPa (860 mbar) to 106 kPa (1060 mbar).
  

The electromagnetic environment of the laboratory shall not influence the

The test programs and software shall be chosen so as to exercise all normal modes of operation of the EUT. The use of special exercising software is encouraged, but permitted only where it can be shown that the EUT is being comprehensively exercised.

For conformance testing, the EUT shall be continually operated in its most sensitive mode (program cycle) which shall be determined by preliminary testing.

If monitoring equipment is required, it should be decoupled in order to reduce the possibility of erroneous failure indication.

The testing shall be performed by direct and indirect application of discharges to the EUT according to a test plan. This should include:

• 
  Representative operating conditions of the EUT;
  
• 
  Whether the EUT should be tested as table top or floor standing;
  
• 
  The points at which discharges are to be applied;
  
• 
  At each point, whether contact or air discharges are to be applied;
  
• 
  The test level to be applied;
  
• 
  The number of discharges to be applied at each point for compliance testing;
  
• 
  Whether post installation tests are also to be applied.
  

The static electricity discharges shall be applied only to such points and surfaces of the EUT which are accessible to personnel during normal usage.

Inside the EUT, only the points and/or surfaces which have to be acceded to perform customer's maintenance are included unless clear instructions for the use of electrostatic discharges precautions (e.g. use of wrist straps) are prescribed by the manufacturer (see clause A.5 of annex A).

The application of discharges to any point of the equipment which is accessible only for maintenance purposes, excluding customer's maintenance, is not allowed unless different prescription is given in the dedicated product specification.

The test voltage shall be increased from the minimum to the selected test level, in order to determine any threshold of failure (see clause 5). The final test level should not exceed the product specification value in order to avoid damage to the equipment.

The test shall be performed with single discharges. On preselected points at least ten single discharges (in the most sensitive polarity) shall be applied.

For the time interval between successive single discharges an initial value of 1s is recommended. Longer intervals may be necessary to determine whether a system failure has occurred.

Note: The points to which the discharges should be applied may be selected by means of an exploration carried out at a repetition rate of 20 discharges per second, or more.

The ESD generator shall be held perpendicular to the surface to which the discharge is applied. This improves repeatability of the test results.

The discharge return cable of the generator shall be kept at a distance of at least 0.2 m from the EUT whilst the discharge is being applied.

In the case of contact discharges, the tip of the discharge electrode shall touch the EUT, before the discharge switch is operated.

In the case of painted surfaces covering a conducting substrate, the following procedure shall be adopted:

If the coating is not declared to be an insulating coating by the equipment manufacturer, then the pointed tip of tile generator shall penetrate the coating so as to make contact with the conducting substrate. Coating declared as insulating by the manufacturer shall only be submitted to the air discharge. The contact discharge test shall not be applied to such surfaces.

In the case of air discharges, the round discharge tip of the discharge electrode shall be approached as fast as possible (without causing mechanical damage) to touch the EUT. After each discharge, the ESD generator (discharge electrode) shall be removed from the EUT. The generator is then retriggered for a new single discharge. This procedure shall be repeated until the discharges are completed. In the case of an air discharge test, the discharge switch, which is used for contact discharge, shall be closed.

Discharges to objects placed or installed near the EUT shall be simulated by applying the discharges of the ESD generator to a coupling plane, in the contact discharge mode.

In addition to the test procedure described in 8.3.1, the requirements given in

8.3.2.1 and 8.3.2.2 shall be met.

8.3.2.1 Horizontal coupling plane (HCP) under the EUT

Discharge to the HCP shall be made horizontally to the edge of the HCP.

At least 10 single discharges (in the most sensitive polarity) shall be applied at the front edge of each HCP opposite the center point of each unit (if applicable) of the EUT and 0.1 m from the front of the EUT. The long axis of the discharge electrode shall be in the plane of the HCP and perpendicular to its front edge during the discharge.

The discharge electrode shall be in contact with the edge of the HCP

In addition, consideration should be given to exposing all sides of the EUT to this test,

8.3.2.2 Vertical coupling plane

At least 10 single discharges (in the most sensitive polarity) shall be applied to the centre of one vertical edge of the coupling plane (figures 5 and 6). The coupling plane, of dimensions 0.5 m  0.5 m, is placed parallel to, and positioned at a distance of 0.1 m from, the EUT.

Discharges shall be applied to the coupling plane, with sufficient different positions such that the four faces of the EUT are completely illuminated.

9. Test results and test report

This clause gives a guide for the evaluation of the test results and for the test report, related to this standard.

The variety and diversity of equipment and systems to be tested make the task of establishing the effects of this test on equipment and systems difficult.

The test results shall be classified on the basis of the operating conditions and the functional specifications of the equipment under test, as in the following, unless different specifications are given by product committees or product specifications:

1. 
   Normal performance within the specification limits;
   
2. 
   Temporary degradation or less of function or performance which is
   self   recoverable;
   
3. 
   Temporary degradation or loss of function or performance which requires operator intervention or system reset;
   
4. 
   Degradation or loss of function which is not recoverable due to damage of equipment (components) or software, or loss of data.
   

In the case of acceptance tests, the test program and the interpretation of the test results have to be described in the specific product standard.

As general rule, the test result is positive if the equipment shows its immunity, for all the period of application of the test, and at the end of the tests the EUT fulfils the functional requirements established in the technical specification.

The technical specification may define effects on the EUT, that may be considered insignificant and therefore acceptable.

For these conditions it shall be verified that the equipment is able to recover its operative capabilities by itself at the end of the test; the time interval during which the equipment has lost its functional capabilities shall be therefore recorded. These verifications are binding for the definitive evaluation of the test result.

The test report shall include the test conditions and the test results.

Note: The discharge switch (e.g. vacuum relay) shall be mounted as close as possible to the tip of the discharge electrode.

(Informative)

Explanatory notes
A.1 General considerations

The problem of protecting equipment against the discharge of static electricity has gained considerable importance for manufacturers and users.

The extensive use of microelectronic components has emphasized the need to define the aspects of the problem and to seek a solution in order to enhance products/system reliability.

The problem of static electricity accumulation and subsequent discharges becomes more relevant for uncontrolled environments and the widespread application of equipment and systems in a wide range of industrial plants.

Equipment may also be subjected to electromagnetic energies whenever discharges occur from personnel to nearby objects. Additionally, discharges can occur between metal objects, such as chairs and tables, in the proximity of equipment. However, based on limited experience available to date, it is considered that the tests described in this standard may adequately simulate the effects of the latter phenomenon. This aspect will be investigated and may lead to an amendment of this standard.

The effects of the operator discharge may be a simple malfunction of the equipment or damage of electronic components. The dominant effects can be attributed to the parameters of the discharge current (rise time, duration, etc.).

The knowledge of the problem and the necessity to have a tool to assist in the prevention of undesirable effects due to the discharge of static electricity on equipment, have initiated the development of the standard testing procedure described in this standard.

A.2 Influences of the environmental conditions on the levels of charge

The generation of electrostatic charges is especially favored by the combination of synthetic fabrics and dry atmosphere. There are many possible variations in the charging process. A common situation is one in which an operator walks over a carpet and at each step loses or gains electrons from his body to the fabric. Friction between the operator's clothing and his chair can also produce an exchange of charges. The operator's body may be charged either directly or by electrostatic inductions; in the latter case a conducting carpet will give no protection unless the operator is adequately earthed to it.

The graphic representation of figure A.1 shows the voltage values to which different fabrics may be charged depending on the relative humidity of the atmosphere.

Equipment may be directly subjected to discharges of voltage values up to several kilovolts, depending on the type of synthetic fabric and the relative humidity of the environment.

A.3 Relationship of environmental levels to air and contact discharge

As a measurable quantity, static voltage levels found in user environments have been applied to define immunity requirements. However, it has been shown that energy transfer is a function of the discharge current rather than, as well as, of the electrostatic voltage existing prior to the discharge. Further, it has been found that the discharge current typically is less than proportional to the pre discharge voltage in the higher level ranges.

Possible reasons for non proportional relationship between pre discharge voltage and discharge current are:

The discharge of high voltage charges typically should occur through a long arcing path which increases the rise time, hence keeping the higher spectral components of the discharge current less than proportional to the pre discharge voltage.

High charge voltage levels will more likely develop across a small capacitance, assuming the amount of charge should be constant for a typical charge generation event. Conversely, high charge voltages across a large capacitance would need a number of successive generation events which is less likely to occur. This means that the charge energy tends to become constant between the higher charge voltages found in the user environment.

As a conclusion from the above, the immunity requirements for a given user environment need to be defined in terms of discharge current amplitudes.

Having recognized this concept, the design of the tester is eased. Trade off in the choice of tester charge voltage and discharge impedance can be applied to achieve desired discharge current amplitudes.

A.4 Selection of test levels

The test levels should be selected in accordance with the most realistic installation and environmental conditions; a guideline is given in table A.1.

The installation and environmental classes recommended are related to the test levels outlined in clause 5 of this standard.

For some materials, for example wood, concrete and ceramic, the probable level is not greater than level 2.

The test points to be considered may, for example, include the following locations as applicable:

• 
  Points on metallic sections of a cabinet which are electrically isolated from ground;
  
• 
  Any point in the control or keyboard area and any other point of man machine communication, such as switches, knobs, buttons, and other operator accessible areas;
  
• 
  Indicators, LEDs, slots, grilles, connector hoods, etc.
  

In general the reproducibility of the previous test method (air discharge) was influenced by, for example, the speed of approach of the discharge tip, humidity, and construction of the test equipment, leading to variations in pulse rise time and magnitude of the discharge current.

In previous designs of ESD testers, the ESD event was simulated by discharging a charged capacitor through a discharge tip onto the EUT, the discharge tip forming a spark gap at the surface of the EUT.

The spark is a very complicated physical phenomenon. It has been shown that with a moving spark gap the resulting rise time (or rising slope) of the discharge current can vary from less than 1 ns and more than 20 ns, as the approach speed

Keeping the approach speed constant does not result in constant rise time.

One proposed way to stabilize the rise time is to use a mechanically fixed spark gap. Although the rise time is stabilized with this method, it cannot be recommended because the resulting rise time is much slower than the rise time of the natural event to be simulated.

The high frequency content of the real ESD event is not properly simulated with this method. Using various types of triggering devices (e.g. gas tubes or thyratrons) instead of the open spark, is another possibility, but such kinds of triggering devices produce rise times which are still too low compared to the rise times of the real ESD event.

The only triggering device known today which is able to produce repeatable and fast rising discharge currents is the relay. The relay should have sufficient voltage capability and a single contact (to avoid double discharges in the rising part). For higher voltages, vacuum relays prove to be useful. Experience shows that by using a relay as the triggering device, not only the measured discharge pulse shape is much more repeatable in its rising part, but also the test results with real EUTs are more reproducible.

Consequently the relay driven impulse tester is a device that produces a specified current pulse (amplitude and rise time).

This current is related to the real ESD voltage, as described in clause A.3.

A storage capacitance shall be used which is representative of the capacitance of the human body. A nominal value of 150 pF has been determined suitable for this purpose.

A resistance of 330  has been chosen to represent the source resistance of a human body holding a metallic object such as a key or tool. It has been shown that this metal discharge situation is sufficiently severe to represent all human discharges in the field.


Figure A.1: Maximum values of electrostatic voltages to which operators
may be charged while in contact with the materials mentioned in clause A.2

Annex B

(Informative)

Constructional details
B.1 Current sensing transducer

The constructional details for a possible current sensing transducer are shown in the figures B.1 to B.7.

The following sequence of assembly should be followed:

1. 
   Solder the 25 load resistors “7" (51 , 5%, 0.25 W) onto the output side disc "3” and shave the soldered terminals.
   
2. 
   Solder the 5 matching resistors "8" (240 , 5%, 0.25 W) in a pentagonal disposition onto the output connector, of Type N coaxial construction.
   
3. 
   Assemble the output side disc "3", complete with load resistors, onto the output connector flange "1" using 4 screws M2.5 Pan Hd 6.5 mm long.
   
4. 
   Assemble the output connector complete with matching resistors, “'7" onto the output connector flange "l " using 4 screws M3.
   
5. 
   Solder the input disc “4”, with the screw support for electrode "6" screwed and soldered, on both the load and matching resistors group. Shave the soldered terminals.
   
6. 
   Screw the flat electrode disc "5" on the screw support for electrode "6", then assemble the support for fixing "2" using 8 screws M3 Pan Hd
   6.5 mm long.
   

Description and constructional details are under consideration.