EMC Question of the Week: August 22, 2022

Illustration of conducted emissions, ESD, EFT and BCI testing

The substitution method and closed-loop method describe two types of  

  1. ESD tests
  2. conducted emissions tests
  3. electrical fast transient tests
  4. bulk current injection tests


The correct answer is “d.” Bulk current injection (BCI) tests specify a common-mode current to be injected on the wire harness of the device under test. The closed-loop method uses two current probes. One probe, connected to the source, is used to inject the noise current. The other probe, connected to a measurement device, is used to determine how much current is being injected.

At low-frequencies (or at certain system resonances), it may be difficult to inject sufficient current at the monitoring point without exceeding the power limits of the injection source or probe. For this reason, some BCI measurement procedures call for (or allow) the substitution method. This method monitors the forward power to the injection probe while the DUT is replaced by a matched load. During the measurement of the DUT, the same forward power is applied without directly monitoring the current injected on the harness. 

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