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U.S. COUNCIL OF EMC LABORATORIES
TECHNICAL GUIDANCE NOTE
PAGE 1 OF 2
ISSUE NO: 20
PRIMARY ISSUE DATE:
FINAL ISSUE DATE:
August 14, 2000
August 21, 2000
NO RESPONSIBILITY OR LIABILITY CAN BE ACCEPTED BY THE US COUNCIL OF EMC LABORATORIES, ITS SECRETARIAT OR ANY OF ITS
OFFICERS OR MEMBERS FOR THE CONTENTS, SPECIFICATIONS AND/OR ADVICE REFERRED TO OR CONTAINED IN THIS TECHNICAL
MEMORANDUM AND/OR ACTIONS TAKEN AS A RESULT OF INFORMATION CONTAINED HEREIN.
THIS TECHNICAL GUIDANCE NOTE MUST BE USED IN ITS ENTIRETY. THE GUIDELINE AS STATED MUST BE CONSIDERED IN THE
CONTEXT OF THE ISSUE, RATIONALE, ASSUMPTIONS AND THE REFERENCE DOCUMENT STATED.
NOTE THAT:
(1) USCEL IS NOT SUPPLYING THIS TECHNICAL MEMORANDUM, PROVIDING PROFESSIONAL ADVICE OR GUIDANCE, TO ANY SPECIFIC
PARTY ON ANY SPECIFIC MATTER AND NO LEGAL RELATIONSHIP IS CREATED BY THE PROVISION OF THIS TECHNICAL MEMORANDUM.
(2) PARTIES SHOULD CONSULT THEIR OWN PROFESSIONAL ADVISORS IN THIS MATTER.
BACKGROUND:
Standard:
EN 55024: 1998, paragraph 4.2.1, Particular Requirements, Electrostatic
Discharges
The standard states: “The discharges shall be applied in two ways:
a)
contact discharges to the conductive surfaces and to coupling planes. The EUT shall be exposed to at least 200
discharges, 100 each at positive and negative polarity, at a minimum of four test points (a minimum of 50
discharges at each point). One of the test points shall be subjected to at least 50 indirect discharges (contact) to
the center of the front edge of the horizontal coupling plane. The remaining three test points shall each receive at
least 50 direct contact discharges. If no direct contact test points are available, then at least 200 indirect
discharges shall be applied in the indirect mode (see IEC 61000-4-2 for use of the Vertical Coupling Plane
(VCP)). Tests shall be performed at a maximum repetition rate of one discharge per second.
b) air discharge at slots and apertures, and insulating surface. On those parts of the EUT where it is not possible to
perform contact discharge testing, the equipment should be investigated to identify user accessible points where
breakdown may occur; examples are openings at edges of keys, or in the covers of keyboards and telephone
handsets. Such points are tested using the air discharge method. See also IEC 61000-4-2 regarding painted
surfaces. This investigation should be restricted to those areas normally handled by the user.
A minimum of 10 single air discharges shall be applied to the selected test point for each such area.”
ISSUE AS SUBMITTED:
In paragraph a) If the total number of test points (N) is greater than 4, how many discharges should be applied at each test
point? 50 or 200/N?
In paragraph b) Should the minimum number be 10 discharges (5+ 5-) or 20 discharges (10+ 10-)?
Should the total number of discharges be considered to mean per test level or total EUT exposure? And should the test level be
stepped as in EN 61000-4-2.
ASSUMPTIONS IN DEVELOPING GUIDELINE:
None.
GUIDELINE:
The requirements of paragraph a) will be met if the number of discharges applied to each of N points (N > 4) is a
minimum of 50, with 25 of each polarity.
The requirements of paragraph b) will be met with a minimum of 10 discharges of the most sensitive polarity, as
determined during pre-testing.
The total number of discharges relates to the type test level; lower levels are exploratory. Test levels should be
stepped, as in EN 61000-4-2. Additional testing beyond 4 points must be considered. The four (4) or more test points can be chosen by
doing pre-testing on the EUT at a lower level, to find the sensitive areas. These lower levels meet the requirements in EN 61000-4-2
while also being potentially less damaging to the equipment. The sensitive areas might manifest themselves by flashing lights that might
not constitute a failure, but show sensitivity to ESD. If pre-testing at a lower level reveals certain areas of sensitivity, these areas should
be tested with 50 contact discharges at the full compliance voltage level. During pre-testing it is not necessary to test all intermediate
discharge levels, nor at the slow repetition rate defined in the standard, nor with the full number of discharges.
The final test choices must be performed according to the standard. All work and decisions made should be documented in the
test report.
REFERENCE DOCUMENTS: EN 55024:1998; EN 61000-4-2:1995+A1:1998
Note: All members are free to deviate from the above guidelines where they think it appropriate, unworkable, or not commercially
viable. Under these circumstances the Executive Committee should be informed of the decision to deviate from their guidelines, so that
the matter can be reviewed. This document is copyrighted by the United States Council of EMC Laboratories (USCEL). This document
is for the use of USCEL members. Members may use it as they see fit, but are not permitted to sell it.