Electrical Noise in Machine Tool Controls

The most troublesome electrical noise source in industrial control systems, the ``showering arc,´´ and the resulting induced noise in adjacent lines is characterized by oscillograms and other measurements. It is shown that shunt capacitance due to wiring can increase the severity of this noise. Transient voltage peaks of 17 000 V have been observed; 2000-V peaks are common in 120-V ac systems. Malfunction of control systems due to these transients can be prevented by proper isolation shielding techniques or elimination of the noise at its source. A method to provide assistance in the selection of a capacitor quench circuit is presented, showing that capacitors of not more than 0.5 µF are adequate.