Conducted Emissions – Filter incorrect install
A proposed EMC solution needs to provide the EMC solution it is intended for!
A manufacturer of industrial process machinery had Cranage conduct an on-site EMC assessment of one of their production manufacturing lines as part of technical file evidence in support of UKCA/CE obligations.
The client has always considered testing and conformity services as essential and values the Kudos it brings to them, not only for reputation but overall performance.
In readiness for the EMC testing, the customer understood the importance of fitting a mains EMI filter to clean up common-mode noise disturbances, often referred to as 'Conducted Emissions' in the EMC testing world. However, measurements on both live and neutral lines highlighted that emissions amplitudes had exceeded the required limits for industrial-based systems, even with the inclusion of a belt-and-braces approach led by the client
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It was found that the mains inlet supply filter, which was spec'd to attenuate the frequencies in the problematic frequency band, was not providing the expected performance. The investigation began, and immediately the solution was presented. Unfortunately, it was the filter installation that led to the ineffective performance. The filter had simply been installed back to front, with the filter output side being wired into the supply input side. This mistake meant that any high radio frequency noise was simply not being diverted back into the input supply or the common-mode ground path. A quick reversal of the filter, resumption of the equipment under test's operation mode and a re-scan of the supply lines confirmed that the solution worked and a pass was obtained against Class A, EN 55011 limits.
The client was extremely delighted that Cranage had found a solution whilst on-site and was able to confirm the effectiveness promptly, thus allowing for the EMC test program to continue. The valuable information gained by the customer enabled them to check other systems that were not under assessment at the time to confirm that the same mistake was present. Unfortunately, the mistake was made every day, and remedial work was needed in preparation for future EMC assessments. This avoided any wasted test and measurement time due to an incorrect installation of a mains EMI filter.
