ABSTRACT
The filter may test well using the specified test method and still fail to work as designed for many reasons, the most prevalent of which are discussed here. As mentioned in an earlier section, some filters are compromised by ground faults. The case discussed was a balanced filter with the bottom half shunted around. This reduced the loss by 50%. It was caused by lack of communication between two different engineering groups, resulting in double the weight, size, and cost for half the performance. More candidates for failure are discussed here.
12.1. SPECIFICATIONS-TESTING Filters are usually designed to pass the more prominent 220A test with 50 ohms load and source. An EMI filter was designed for the 220A specification but the new customer wanted to test using the current injection method described by Military Standard (MIL STD) 461. The filter failed. This test setup requires two 10-µF capacitors to ground on both the supply and return power leads. The filter was unbalanced with all the components on the supply, or hot, side. The test setup was detecting common mode noise, and even though common mode was added, the filter failed the tests, so the filter had to be redesigned.
