Test unit for sawdust extractor spark alarm - simulates flying sparks by diode emitted flashes with accurate rise and fall rates

摘要

The spark detecting alarm is for a sawdust extractor which is tested by light flashes of accurately defined waveform and intensity which simulate standard sparks flying past the detector in the duct. An amplifier drives light emitting diodes in the duct and feedback from a monitoring photo-diode makes the light intensity follow the driving waveform. A square wave (R) is integrated and limited to form a trapezium wave (Tr) and this is integrated to form the driving waveform (In). The essential features of the waveform are the linear rising (t1-t-2) and falling (t4-t5) slopes and the round transitions (t0-t1, t2-t4, t5-56). For calibration purposes, the waveform amplitude is adjustable and measured by a peak voltmeter.