| 摘要 |
An arc fault detector includes an average instantaneous current generator which averages the current over the fundamental period and produces a substantial output only where there are substantial variations in waveform between half-cycles which is indicative of an arc. To discriminate over inrush currents, a pulse generator generates a pulse in response to the step increase in current caused by striking of an arc. An output circuit generates an arc signal when the time attenuated accumulation of pulses occurring in half-cycles in which the average instantaneous current is above a selected threshold reaches a predetermined level. To further discriminate over dimmers during turn on of a cold tungsten bulb, the ANDing with the average instantaneous current is delayed until a time attenuated accumulation of the pulses reaches a threshold value. The average instantaneous current can be approximated by a bandpass filter with a center frequency below the fundamental of the ac current. A second bandpass filter with a center frequency above the fundamental can be used as the pulse generator. <IMAGE> |
