GB1360957A - Apparatus for the early detection of arcs - Google Patents

Abstract

1360957 Spark-erosion PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 5 Dec 1972 [8 Dec 1971] 56050/72 Heading B3V An apparatus for detecting arcing during a spark-erosion process comprises means 34 for comparing the no load voltage time of each discharge with a reference time interval, a counter 38 for counting the number of consecutive discharges having no load voltage times less than the reference time interval and a comparator 39 for producing an error signal if the number exceeds a predetermined value. The spark gap 1, 2 is connected to a power source 3 via a switching transistor 4 which is controlled by two monostable multivibrators 8, 9 via an amplifier 10. The multivibrator 8 is controlled by a current discriminator 7 to supply a pulse P 1 for controlling the duration of the machining discharge whilst the multivibrator #1 is triggered by the trailing edge of the pulse from the multivibrator 8 to produce a pulse P 0 for determining the cut off time of the transistor 4. The pulse P 0 is fed, via an element 33 for increasing its duration by an amount equal to the reference time interval, to a logic gate 34 having another input supplied with the pulse P 1 . If the pulse P 1 appears before the delayed trailing edge of the pulse P 0 , a counting pulse is produced which is fed to a counter 38. If a number of consecutive counting pulses occur which exceed a predetermined number set by an element 40, an output signal is produced from a comparator 39 and applied to a multivibrator 42 which applies a pulse to the multivibrator 9 to increase the interval between the discharges. The counter 38 is reset to zero by the output from the comparator 39. The pulses P 0 , P 1 are also applied via inverters 36, 37 to a logic gate 35 which produces an output signal for resetting the counter 38 to zero when an acceptable discharge is produced.