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ESD: IEC 61000-4-2, MIL-STD-461 CS118, ISO 10605, et. al.
Several standards cover ESD testing in similar ways. This article gives an overview plus places to look for additional guidance and alternate discharge models.
The basis for most ESD (electrostatic discharge) tests comes from IEC 61000-4-2, “Testing and measurement techniques–Electrostatic discharge immunity test”. The active 2008 version can be purchased here, with a new version expected in 2025. ISO 10605, “Road vehicles — Test methods for electrical disturbances from electrostatic discharge” (purchase 2023 version here) adopted the test method for the automotive industry. MIL-STD-461 included ESD testing for the first time with Rev G (freely available here) with the CS118 test method–and it looked pretty familiar. See comparisons below.
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If you have questions about ISO10605 or IEC 61000-4-2, you can see if there are answers in the freely available MIL-STD-461G CS118 or related appendix (Section A.5.16) before purchasing from IEC or ISO.
Testing is specified for units that are powered off (representing the danger from discharge when being handled or installed) and when turned on (representing threats present in its operating environment). They also include air and contact discharge, with air discharge generally being more severe. Contact discharge is mating two conductive objects at different potentials together and seeing the surge of charge transfer. Air discharge is when you reach for a metal doorknob on a dry/cold day and feel an actual spark just before you touch the door. Maximum testing voltages should be adjusted based on the expected operating conditions (how often humans interact with the unit, if it is installed in a humidity-controlled environment, etc.).
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ANSI C63.16, “Guide for Electrostatic Discharge Test Methodologies and Acceptance Criteria for Electronic Equipment”, is an available guidance document for ESD testing (the 2016 version is available for purchase here; a new version has been drafted and is currently going through ANSI approvals). It gives additional context
Almost all ESD test standards and commercially available ESD test guns/simulators base their waveforms off the human body model (HBM). The CS118 version is below.
However, there are cases where the main threat does not come from human interaction. Generally speaking the industries have determined that testing based on the HBM is adequate to identify most hardware weaknesses to ESD (although the ANSI C63.16 working group will tell that’s definitely not 100% true). I was once looking into a case where the main threat to a satellite orbiting in Low Earth Orbit was definitely going to be spacecraft charging, and did some research to see if there were other standard models available.
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The only one I was able to find was from an outdated military standard, MIL-STD-1541A (1987) (freely available here). You can see an alternate discharge model below, and the document has information about ways to vary different parts of the circuit to address different threat waveforms.
MIL-STD-331D (download here) includes circuit values for helicopter-based discharges for fuzing systems and ignition protection devices as well, to be inserted into a more traditional IEC 61000-4-2 circuit setup. Appendix A.5.8.3.2 of MIL-STD-464D also has information on helicopter-borne discharges & ordnance.
ANSI C63.16: “Guide for Electrostatic Discharge Test Methodologies and Acceptance Criteria for Electronic Equipment”
This is a guidance document for ESD testing that helps the users of IEC 61000-4-2 (as well as ISO 10605 and MIL-STD-461 CS118)
ANSI C63.16 is a useful document meant to provide guidance for engineers and technicians conducting ESD testing to IEC 61000-4-2. Which means it is also useful for people testing to ISO 10605 and MIL-STD-461 CS118 by extension, since those documents are close to identical with the IEC standard. The 2016 version of C63.16 can be purchased here, but you might want to wait. A new version is expected to be published in late 2024/early 2025, which will have several technically substantial updates. I’m on the working group for this revision, so it’s near and dear to my heart.
Some of the topics addressed in C63.16:
Climate conditions during testing
The use of air vs. contact discharges
Test setups
Considerations for the ESD gun return cable
Considerations for the bleed resistors (in the revision, issues of degradation over time are raised)
Test procedures
Selecting test points
Handling large EUTs or those with complex peripheral arrangements
Approach speed for air discharges
In situ testing
Pin discharges
A lot of the guidance found in this document is based on decades worth of lessons learned. It points out things that are easy to miss until they go wrong.
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There have been a large number of cases where customers report issues in the field that hadn’t been caught and can’t be replicated in the lab. C63.16 aims to add to the minimum number of tests and test conditions called for in IEC 61000-4-2 in order to reduce these situations.
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The new revision contains an extensive discussion of relative humidity. Humidity can vary dramatically between indoors and outdoors, as well as different locations within a building, so knowing what the conditions are specifically where testing is occuring helps with repeatability. ESD events, in particular air discharges, are known to be sensitive to humidity conditions. On many occasions, the fact that equipment is used in environments far outside the 30 - 60% relative humidity called for by IEC 61000-4-2 is the cause for disconnects between field issues and lab testing as noted above.
MIL-STD-461: “Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment”
MIL-STD-461 is one of the core EMC standards, having evolved with military applications since WWII. It is widely used in the aerospace and defense sectors.
MIL-STD-461 is a landmark document in the world of EMC standards, and there are a lot of other standards that derive from this one. The easiest place to find a copy of MIL-STD-461 (free, as most government standards are) is here, or the official site is here. The current edition is Rev G, and the working group for the standard is currently drafting Rev H.
MIL-STD-461 is more of a document that specifies test methods than a strict requirements document, and while it has suggested limits for many of the tests, in most cases those limits should be tailored. For general aerospace and defense projects MIL-STD-464 is the actual requirements document, and the tests in MIL-STD-461 are how you document compliance to the EMC requirements.
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Tailor, tailor, tailor! Beware of any project that simply tells you to “meet 461”--even accepting 461 as the overarching requirement, tailoring 461 is key for saving testing time and budget and not wasting resources designing to inappropriate or inapplicable requirements. I’ll discuss this more in articles dedicated to each test method.
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Read the appendices! More than most standards, the committee behind MIL-STD-461 documents background information for every section of the main document. This includes context, lessons learned, and why different changes have been made over time. There’s a wealth of information in there.
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MIL-STD-461 does not have a requirement to perform testing in a certified lab. While many of the labs that have the equipment needed to perform 461 testing are certified (to ISO, by ANLAB or A2LA, etc), that is not required. Testing in an uncertified lab or your own facility is allowed as long as you can meet the test equipment and test reporting requirements.