Abstract: Disclosed is a dual-gap protector wherein both gaps will break down essentially simultaneously when a pulse of either polarity having a sufficient magnitude appears. An annular electrode is provided in the housing so as to form parallel gaps with respective end electrodes. The electrodes include a surface coating of a photoemissive and/or thermionic material so that light emission or heat resulting from the breakdown of one gap will influence the breakdown of the other gap.

Abstract: Disclosed is a method of improving the coating on electrodes (11 and 12) in spark gap devices which minimizes filament formation, densifies the coating, and ensures a good bond between the coating and underlying electrode. The device is coupled to a circuit (FIG. 2) which includes appropriate components so that a rapid sequence of current pulses having large amplitudes during arc initiation is passed through the device. The coating bonds with a different area of the cathode for each current pulse. The signal may be applied with appropriate reversal of polarities so that essentially the entire surface of both electrodes is thus reacted. Subsequently, the device may be subjected to an additional pulse in order to leave asperities on the surface which will increase field emission and ensure a low surge limiting voltage.