Tailoring Guidance

Some requirements are set in stone. But many of them need to be tailored for your specific hardware. If you apply standards blindly, you’ll run into all kinds of schedule-delaying problems: test methods and setups that don’t make sense, test failures that aren’t important and need to be waived, and missing problems that will pop up later during integration and checkout. Some standards, such as MIL-STD-464 and MIL-STD-461, are explicit that they must be tailored. When a standard needs to be so general that it can cover everything from a walkie-talkie to an aircraft carrier, you need to make sure that you’re applying it in a way that makes sense for your hardware.

So, when you’re sitting down to tailor your program requirements down to a specific set of hardware to be tested, where should you start? Here are some suggestions.

1. The document itself. It’s worth the time to sit down and read, in detail, as much of the original text as possible. It may have a table showing which requirements apply to different applications (such as Table V of MIL-STD-461 Rev G). There may be notes or footnotes that mention exceptions or specific configuration types to include or avoid.
2. The appendices of the document. As I’ve said many times in many venues, it’s always worth the time to read informative as well as normative appendices and annexes. They often have context and guidance that can help you work out how a specific standard applies to your project.
3. Parent documents. Sometimes, you’re looking at a document derived from another source. For instance, in the automotive sector, you might be looking at an OEM spec that has been lightly modified from ECE Reg 10, CISPR 25, or ISO 11452. Tracing a requirement back to a parent and seeing how (and with luck, understanding why) it has been modified can give you valuable insight. The parent document may also have additional context or rationale to help you understand the “why” behind the requirement’s purpose, allowing you to apply it most effectively.
4. Other documents tackling similar projects. There are some standards out there that are already-tailored versions of their parents. Seeing how (and why) they did their tailoring can be invaluable. Here are a few examples:
   1. GSFC-STD-7000 is a version of MIL-STD-461 specifically tailored to small science satellites. Its “app notes” section (functioning as an appendix) has a wealth of information about exactly why they made the modifications they did. I found their commentary on LISN selection particularly enlightening, among others.
   2. AIAA-S-121, SMC-S-008 and SMC-T-008 are tailored versions of MIL-STD-464 for space systems. (Just a note, that’s MIL-STD-464 covering the broad range of electromagnetic environmental effects requirements, not just EMC.) I recommend particularly looking at SMC-S-008. It has technically been superseded by SMC-T-008, but the S version is much easier to read. In addition, the SMC documents are freely available, while the S-121 document must be purchased from AIAA.
   3. MIL-STD-461 CS118 and JLR-EMC-CS CI 280 are lightly tailored versions of IEC 61000-4-2.

Being a die-hard standards geek, tailoring requirements is one of my favorite things to do professionally. It may not be everyone’s idea of beach reading, but I’ve learned that every time I’ve put in the effort to read a standard or its appendices closely, I’ve found useful nuggets that help make my testing more efficient and effective.