I seem to hear a never ending litany of complaints about how the US military acquisition community has to use more and more commercial equipment (COTS or CI) and that said equipment tends to be highly problematic from an EMC perspective. I tend to dwell on this subject in this blog space, hopefully from different angles, but at the end of the day, I don’t see much being done to help ensure that commercial items integrated into military systems are electromagnetically compatible. Hopefully I’m wrong! I’m sure there a some programs that levy good EMI requirements and avoid commercial equipment that doesn’t meet those requirements. But there are also programs that don’t impose good EMI (and other military specific) requirements, hiding behind the mantra of “costs less, gets fielded quicker.” There are many EMC engineers working in the civil service that are passionate about potential interference problems that can be passed on to front line troops, both from the lack of robust EMC requirements in general and the use of EMI-unproven commercial items specifically. So what can we do?
I’ve written before about the process of conducting a COTS EMI-related risk assessment and how a comparison of commercial EMI standards to MIL-STD-461 is a tool that is central to the ability to conduct such a risk assessment. I still believe that is a legitimate and valuable tool in the EMC engineers arsenal. Unfortunately there is no good comparison of commercial EMI standards to MIL-STD-461. An attempt to compare was made by the DoD’s Joint Spectrum Center in the late 1990’s with a document published in 2001 titled: “Results Of Detailed Comparisons Of Individual EMC Requirements And Test Procedures Delineated In Major National And International Commercial Standards With Military Standard MIL-STD-461E” or more affectionately known as Engineering Practices Study (EPS) 0178. The table shown below is the overall result of the study. For the different military platforms down the left side, an attempt was made to compare three primary categories of commercial standards (across the top) to the individual test methods of MIL-STD-461E. (that’s our first issue: we’re currently at Revision F of MIL-STD-461 and the TriService Working Group is working on Revision G as we speak!). You will notice from the legend that there is a small table corresponding to the individual MIL-STD-461E tests that is inserted into each intersection of a Platform and a Commercial Standards Group. You’d have to go into the details of the text of the document for specifics, but you will notice a great deal of red (high risk) and black (medium risk) and very little green (low risk) in the results of the comparisons. I invite you to make your own assessment of the document…its available online at acc.dau.mil/library.
So, we have a risk assessment process that needs a better tool (standards comparison) to be of any real use to EMC engineers and DoD programs. It’s not a trivial exercise but I believe it’s time that the DoD EMC community figured out some way to update this comparison in such a way as to enable the risk assessment process to actually work. Who’s with me?
– Brian Farmer