Survey of conducted transients in the electrical system of a passenger automobile

As part of an effort to develop automotive electromagnetic compatibility (EMC) test procedures for evaluating conducted emissions and conducted susceptibility at the component level, an extensive survey of the electrical transients was conducted at various locations within the electrical/electronic system of a late-model automobile. Simultaneous measurements were made at selected potential sources of transients and at power-line inputs of potentially susceptible electronic modules. The recorded signals were then analyzed to arrive at a reduced set of fundamental types of waveforms. The implications of the results reported here on component EMC test procedures developed are discussed. It is concluded that there are three main types of conducted transient waveforms: glow discharge, inductive kick, and damped sinusoid. The glow-discharge type had the highest voltage amplitude and shortest risetime; the inductive-kick type had lower amplitude, much slower rise, but very long pulse width; the damped-sinusoid type had the lowest amplitude. These transients were highly attenuated as they reached sensitive electronic receivers. The survey results, although based only on one car, clearly indicated that the glow-discharge transients are the most severe, followed by the inductive kicks