What is the most common failure seen in EMC Testing ?

I would guess from experience that emissions failures are most common place. Certainly in my previous experience as a test engineer, radiated emissions seems to be the failure most seen. On the flip side a lot of the failures have been sorted quickly and have come down to simple errors rather than inherent design faults. For example, I was testing a large unit which was covered with metal panelling to shield the unit from emitting emissions. When it was tested it came in at some frequencies at 3dB’s over the test limit. The client and myself removed some of the panels and found that whilst each panel had been fitted with an earth stud, the implementation of the ground straps to the earth studs had been poorly executed with studs painted over, nuts used on one side only without washers and nuts hand tight at best. We removed all the ground straps, cleaned all the studs to bare metal and then used a nut, washer, ground strap, washer and nut configuration to get the ground straps bonded firmly to the ground studs. When we put everything back together and retested we had gained about 6dB of additional shielding and the unit passed so it had been a simple assembly quality issue. Consideration also has to be given to how simply

can the equipment be operated. Whilst you want the equipment under test to be fully functional, any additional equipment that’s required to get it to operating correctly should be simplified down to the bare minimum as there’s always a chance of passing emissions through interconnecting cables between drive equipment and the actual equipment under test.

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