Time- and Frequency-Domain Characterization of Railgun Sliding Contact Noise

The noise in a railgun sliding contact is characterized in both the time and frequency domain in this investigation. Railgun operating parameters are typically 4 g projectiles traveling up to 100 m/s. The railgun is powered by a sequentially fired pulse forming network (PFN) consisting of eight electrolytic capacitor banks. Typical V-I characteristics of the PFN are approximately 20-kA peak current and 400-V peak voltage. The total pulsewidth is on the order of 6 ms. The noise is extracted from the muzzle voltage measurements using an improved method that can be applied to any electromagnetic launcher with a sliding contact. A variety of rail materials and rail coatings were investigated in regard to their effect on sliding contact noise. The noise is characterized in the time domain using statistical terms such as rms quantities. The Fourier transform is used to characterize the noise in the frequency domain. The results show that good and poor sliding contacts have particular average rms noise voltages and spectral signatures. The spectral signatures are used to quantitatively identify the point the difference between a good and a poor performing contact and to gain insight into the nature of the sliding contact's current conduction mechanisms.