Military use of commercial equipment has grown exponentially over the last decade; and not just in the area of whole equipment, which is easy to see.
The use of commercial components and subassemblies within systems has grown as well, so that parts of what look like a full military development effort are actually commercial items. What’s an DoD EMC engineer to do? I wish there was better news, and we’ve been down this road before, but it bears repeating. There just isn’t a good, up to date comparison of MIL-STD-461 (US military system level EMI compliance requirements) and commercial EMI standards. The Joint Spectrum Center (part of DISA) undertook a comparison effort back in the late 1990s and in March 2001 published Engineering Practices Study 0178, “Results of Detailed Comparison of Individual EMC Requirements and Test Procedures Delineated in Major National and International Commercial Standards with Military Standard MIL-STD-461E.” THAT’S a mouthful! So there’s essentially one useful tool to help EMI engineers attempt to correlate commercial EMI test results with MIL-STD-461 requirements in the development of military systems. Unfortunately its woefully out of date now (although the information in it is still good). I invite you to check it out in the E3 library at acc.dau.mil/library.
Another tool at our disposal is an informal but effective Commercial Items EMC Risk Assessment Process, developed under the auspices of the DoD E3 IPT several years ago. Based on some initial work by the UK EMC community, the process attempts to walk the EMC engineer through a step-by-step procedure from an assessment of the system initial Military operational EMC requirements, through the actual EMI requirements imposed on the commercial item, assigning a risk category for each requirement based on comparison of the actual commercial test results to the desired military test requirements. Not an easy task under ideal circumstances and exceptionally difficult without a good comparison tool such as the EPS 0178 document discussed above. This document is available at acc.dau.mil/e3, do a search for “DoD COTS E3 Risk Assessment Process.” I invite you to check this one out also.
So what’s a good EMI engineer to do when assessing COTS for military applications? First and most importantly, set good requirements and stick to them. Obviously none of us get our way 100 percent of the time and you may be overruled. But that’s why the PMs get the big bucks – to make the trade-offs between performance, schedule and money. And any EMI engineer who’s been around for a while will understand that performance, especially a black magic art like EMI compliance, can take a back seat to money and schedule pressure. Make sure to document any EM-related requirements changes or waivers. It’s very possible that it could come back to haunt the system once it gets out in the operational electromagnetic environment.
– Brian Farmer
