ESD TEST SETUP From: 61000-4-2 . IEC:1995 +A1:1998 +A2:2000
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:
a) contact discharge to the conductive surfaces and to coupling planes;
b) air discharge at insulating surfaces.
Two different types of tests can be distinguished:
– type (conformance) tests performed in laboratories;
– post installation tests performed on equipment in its final installed conditions.
The 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).
7.1 Test set-up for tests performed in laboratories
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 aluminum) 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 on 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 bondings 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 kW 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 given below.
7.1.1 Table-top equipment
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 × 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.
7.1.2 Floor-standing equipment
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.
7.1.3 Test method for ungrounded equipment
The test method described in this subclause is applicable to equipment or part(s) of equipment whose installation specifications or design preclude connection to any grounding system. Equipment, or parts thereof, includes portable, battery-operated and double-insulated equipment (class II equipment).
Rationale: Ungrounded equipment, or ungrounded part(s) of equipment, cannot discharge itself similarly to class I mains-supplied equipment. If the charge is not removed before the next ESD pulse is applied, it is possible that the EUT or part(s) of the EUT be stressed up to twice the intended test voltage. Therefore, double-insulated equipment could be charged at an unrealistically high charge, by accumulating several ESD discharges on the capacitance of the class II insulation, and then discharge at the breakdown voltage of the insulation with a much higher energy.
The general test set-up shall be identical to the ones described in 7.1.1 and 7.1.2 respectively.
To simulate a single ESD event (either by air or by contact discharge), the charge on the EUT shall be removed prior to each applied ESD pulse.
The charge on the metallic point or part to which the ESD pulse is to be applied, for example, connector shells, battery charge pins, metallic antennae, shall be removed prior to each applied ESD test pulse.
When one or several metallic accessible parts are subject to the ESD test, the charge shall be removed from the point where the ESD pulse is to be applied, as no guarantee can be given about the resistance between this and other accessible points on the product.
A cable with 470 kW bleeder resistors, similar to the one used with the horizontal and vertical coupling planes, shall be used; see 7.1.
As the capacitance between EUT and HCP (table-top) and between EUT and GRP (floorstanding) is determined by the size of the EUT, the cable with bleeder resistors may remain installed during the ESD test when functionally allowed. In the discharge cable, one resistor shall be connected as close as possible, preferably less than 20 mm from the EUT test point. The second resistor shall be connected near the end of the cable attached to the HCP for table-top equipment (see figure 8), or GRP for floor-standing equipment (see figure 9).
The presence of the cable with the bleeder resistors can influence the test results of some equipment. In case of dispute, a test with the cable disconnected during the ESD pulse takes precedence over the test with the cable installed during the test, provided that the charge has sufficiently decayed between the successive discharges.
As an alternative, the following options can be used:
. the time interval between successive discharges shall be extended to the time necessary to allow natural decay of the charge from the EUT;
. a carbon fibre brush with bleeder resistors (for example, 2 × 470 k.) in the grounding cable;
. an air-ionizer to speed-up the "natural" discharging process of the EUT to its environment.
The ionizer shall be turned off when applying an air-discharge test. The use of any alternative method shall be reported in the test report.
NOTE In case of dispute concerning the charge decay, the charge on the EUT can be monitored by a noncontacting electric field meter. When the charge has decayed below 10 % of the initial value, the EUT is considered to be discharged.
The tip of the ESD generator shall be held normal (perpendicular) to the surface of the EUT.
126.96.36.199 Table-top equipment
For table-top equipment, the EUT is placed on the horizontal coupling plane on top of the insulating foil (0,5 mm thick), as described in 7.1.1 and figure 5.
When a metallic accessible part, to which the ESD pulse is to be applied, is available on the EUT, this part shall be connected to the HCP via the cable with bleeder resistors; see figure 8.
188.8.131.52 Floor-standing equipment
Floor-standing equipment without any metallic connection to the ground reference plane shall be installed similarly to 7.1.2 and figure 6.
A cable with bleeder resistors shall be used between the metallic accessible part, to which the ESD pulse is to be applied, and the ground reference plane (GRP); see figure 9.
7.2 Test set-up for post-installation tests
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 on a metal table, the table shall be connected to the reference plane via a cable with a 470 kW 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.
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