Properties of High-Frequency Conducted Noise from Automotive Electrical Accessories

This paper describes generation mechanisms and electrical characteristics of high-frequency conducted noise from electrical contacts and accessory drive/control motors, which may cause logic errors in automotive electronic devices. High-frequency conducted noise due to contacts in both horn sounding and lighting circuits results from spark discharge initiated by breakdown across the contacts; and a showering arc which sustains spark discharge for hundreds of microseconds was observed at contacts in lighting circuits. High-frequency conducted noise due to accessory drive/control motors was caused by reactance voltage fluctuations and commutator sparks. To analyze electrical characteristics of high-frequency conducted noise, a measuring system for amplitude distributions in both the time domain and the frequency domain was developed, and an attempt was made to fit a distribution pattern to observed data in each domain. In the time domain, the noise voltages due to contact breaking were distributed between 360 and 530 V. The distribution pattern in the time domain fitted closely to the normal distribution curve, while the pattern in the frequency domain fitted to the lognormal distribution curve.