IEC 61000-4-2 / EN 61000-4-2
This is the basic immunity test method for personnel ESD and is often called up as a basic test method by immunity standards listed under the Electromagnetic Compatibility (EMC) Directive.
ESD Simulator tips
Direct contact ESD discharge – Pointed tip
4kV typ test voltage. Put tester in contact with a metal object on EUT then activate tester.
Contact discharges remove the variability associated with the breakdown of the air gap and are the preferred method when the location being tested is conducting (e.g. not coated or painted providing an insulating layer).
Air ESD discharge – Rounded tip
8kV typ test voltage. Activate tester, bring close to EUT, discharge can be seen occurring as an arc.
Preferred method for insulating surfaces. The tip remains live until a discharge occurs. Favourite locations are seams and apertures in plastic enclosures and gaps between buttons and around displays.
When handling the tip should be perpendicular to the surface being tested and the gun handled positively and quickly, i.e. the tip approached as fast as possible without causing mechanical damage, as any spark occurring is affected by approach speed.
Obviously you must obtain a copy of EN/IEC 61000-4-2 and follow its specifications exactly when testing. The following is simply a very basic guide on basic self testing – it is not thorough or in any way intended to replace it!
Read the specification for the requirements of the ground reference plane, they are specific. For a simple non standard complaint test you can simply place the EUT (Equipment Under Test) over a ground reference plane, with it insulated, but a standard complaint test has more detailed requirements. The proper setup is a ground reference plane on the floor which is larger than the EUT all round by at least 0.5m. Connect the plane to the ground connection of the ESD simulator. Then for desktop equipment a wooden bench is placed over it, a second ground plane – a horizontal coupling plane (HCP) on top of it and connected to the reference ground plane via resistors, followed by an insulating later on top of that and then the EUT (Equipment Under Test). A VCP (vertical coupling plane) is also needed for some of the tests.
Keep the ESD simulator ground lead away from the EUT by at least 200mm at all times and away from the test engineers body.
Mains / Safety Earth
The ground reference plane should be connected to mains / safety earth. If the EUT has a mains earth connection this should also be connected to mains earth
Choice of test points can be difficult as having to test every possible area of a product to find all the weak points can take a very log time. This doesn’t have to be done, instead EST test engineers are expected to learn which areas are most likely to cause failures and test those.
At each identified test point and for each test voltage apply at least 10 discharges in each polarity, allowing at least 1 second between each and checking the EUT is still functioning correctly each time.
For each set of discharges start off at the lowest test level of +-2kV and increase through the other test levels until the maximum specified test level is reached. This is usually 4kV for contact discharge and 8kV for air discharge. In real life ESD discharges with lower voltages than the max test level are more common and therefore testing at the lower voltages is a requirement as there can be differences in response of the EUT.
RF field test can be done with a vertical grounded / coupling plane (VCP) nearby and the tester sparking to it through air. The RF field produced can affect EUT.
Using The Teseq NSG435 Tester
Turn on auto polarity, to change every 10 discharges.
Checklist for each test
- Contact / Air discharge selected correct for fitted tip
- Correct test voltage selected
- Counter reset
- Ensure ground cable screw thumb still tightened!
- Ensure ground cable still connected to ground plane (not pulled off)!!
Useful Documents & Resources
https://www.emcstandards.co.uk/handbook-on-en-61000-4-2-personnel-electrostat – A brilliant guide on ESD generally and on performing ESD testing to EN 61000-4-2
UL 2 minute tutorials: #2 – Electrostatic Discharge Testing – Some quick and simply examples of basic testing
Don’t worry, it’s just ESD! – Funny and useful what not to do