How to conduct the ESD test?

 What is ESD test?

Electrostatic discharge immunity test is a basic EMC test. Standard IEC61000-4-2 provide the immunity requirements and test methods for electrical and electronic equipment subjected to static electricity discharges, from operators directly, and to adjacent objects. The standard establish a common and reproducible basis for evaluating the performance of electrical and electronic equipment when subjected to electrostatic discharges.

Electrostatic discharge is a transfer of electric charge between bodies of different electrostatic potential in proximity or through direct contact. The standard IEC61000-4-2 does not intend to specify the tests to be applied to particular apparatus or system, it is to give a general basic reference to all concerned product.  So before conduct the test, an appropriate test level should be selected according to the product's characters and its working occasion.

 

Contact discharge and air discharge methods

The test levels has been specified in table 1 of standard IEC61000-4-2, and there are 2 discharge methods indicates on the table 1: contact discharge and air discharge:

--In contact discharge method, the electrode of the test generator is held in contact with EUT, and the discharge actuated by the discharge switch within the generator. In direct application, the discharge electrode directly contact with EUT, and the test objects include any parts that the user may touch during use, including any parts that can only be accessed for live maintenance and correction, such as: control keyboards, display screens, knobs, power cords, Chassis, indicator lights, etc..

--In air discharge method, the charged electrode of the test generator is brought close to the EUT, and the discharge actuated by a spark to the EUT. In indirect application, discharge to a coupling plane in the vicinity of the EUT, and simulation of personnel discharge to objects which are adjacent to the EUT. In the ESD test, indirect discharge can discharge to vertical coupling plane and horizontal coupling plane. The air discharge method normally apply to test the objects covered with or hiding by insulating material.

In electrostatic discharge testing, contact discharge is the preferred testing method. Whenever possible, contact discharge is used for testing. The severity of contact discharge is much greater than air discharge.

 

ESD generator is the tool to conduct the ESD test

The ESD generator is a special equipment to conduct ESD test, it is consisted by charging resistor, energy-storage capacitor, distributed capacitance, discharge resistor, voltage indicator, discharge switch, interchangeable tip of the discharge electrodes, discharge return cable and power supply unit. The energy storage capacitance is 150pF which simulates human body capacitance, the discharge resistance is 330Ω which simulates human body resistance. The energy storage capacitance and discharge resistance specified in the standard IEC61000-4-2 is to reproduce human body discharge, but in some product standards, it will has different requirements.

 

How to select the ESD generator?

Before testing, the following points need to be clarified:

1). What test method should be applied? contact discharge or air discharge. The direct discharge should be applied to accessible points and air discharge should be applied to inaccessible points or insulating surfaces.

2). What test level should be applied?

3). How many discharges should be applied to each test point?

4). In indirect application, how to place the coupling planes?

5). Is it necessary to perform ESD testing under final installation conditions?

6). The EUT should be tested as table-top equipment or floor-standing equipment?

7). Apply discharges to EUT with speed 20 times/s to pre-sweep first, and and conduct key tests on the doubtful parts. 

For the ESD test requirements, PEGO has launched two models ESD generators: ESD-2000 and ESD-2000Q. The test voltage can up to 20KV and 30KV, and can simulate contact discharge and air discharge. Compare with ESD-2000, ESD-2000Q is controlled by touch screen, and with memory function to meet the preferences of different customers.