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EMC Test Plans compliance tricks

8. November 2021 10:49 by Christian in EMC/EMI, EMC TEST PLAN, OEM Specs, Test Methods
How to cheat EMC requirements

FMC1278R3 specification mention that CI 280 (ESD Test Methods) must be carried out prior to any other test methods. If CI 280 fails, continuing the rest of EMC validation must be decided by FORD. The same 2 samples must theoretically withstand all FMC1278R3 test methods selected by EMC Test Plan.

The order of the test methods is critical, and the test results listed by laboratory report applies only to the two samples provided (Part Number, Serial Number, HW/SW revision). Some Europeans & Japanes automotive makers allow the use of multiple groups of samples to be used for simultaneously running test methods, probably to to speed up the completion of validation. This means that no sample is exposed to the full validation test list leaving room for insufficient EMC compliance evaluations.

Example of potentially destructive test methods:

  1. ESD on the first group of samples.
  2. Transients on supply lines on a second group of samples.
  3. Reverse Polarity on a third grtoup of samples

To compensate somehow such selective test methods allocation, the EMC Test Plan authors would require 3 samples per group instead of 2 samples per full validation. 

A parametric test is required following each immunity test method, and this may reveal some tolerances being pushed to one extreme if not outside the acceptable range. In a real scenario, following ESD powered one unit out of three was measured with 12 KΩ impedance on B+ line versus 16 KΩ prior to test. Other than that everything was functional, the DUT current consumption was the same before and after ESD. Theoretically this unit survived ESD and based on EMC Test Plan was not supposed to be tested for Transients on Supply Lines. By mistake this unit was tested for JASO Pulse B-2 (-260V) and the outcome was "sample damged on the second pulse". This EMC test plan trick was used to hide a poor DUT design performance for Honda that otherwise would have never pass FMC1278R3 spec.



Christian Rosu, Nov 8, 2021.