Designing Commercial Equipment for Conducted Susceptibility

Although no national regulatory agency has required a noise immunity limit or standard, the commercial equipment manufacturer must design for almost error free operation in a hostile electromagnetic environment. The major problem of noise immunity today is power mains susceptibility rather than radiation interference or static discharge from humans. It was shown that power main susceptibility must be based upon inferential statistics and the integral of the transients above the product threshold. In modeling the transient source and when testing the four transient propagation modes, separate injection test setups are required. Using the typical measured product input impedances (as described in the paper) and the present state of the art test generators, one can easily see why series transient injection is used. However, this series arrangement doesn't test all transient propagation modes. The 1.25 MHz ringing transient pulse was found to be a better test than the unidirectional pulse. Upon determining that an improvement in susceptibility level is needed and if the fix is to harden or reduce the coupling path(s), one finds the most serious measurement problem is the voltage measurements of the two types of voltage measurements, the differential measurement is especially difficult.