GB1260121A - An improved system for detecting the healthy condition of a rectifier diode in an electrical control or proving circuit - Google Patents

Abstract

1,260,121. Protective arrangements. WALLACETOWN CONTROL SYSTEMS Ltd. 11 Feb., 1969 [22 Jan., 1968], No. 3224/68. Heading H2K. A remote control or cable proving circuit of the kind having an auxiliary supply transformer 10 and at a distant point a rectifying diode 16, the transformer and diode being interconnected by a cable conductor 13 and a conductor 17 which may be an earth connection, is provided with series resistors 11, 12, a short-circuit detector 20 and an open-circuit detector 21 connected to the junction 18 between the resistors and a bi-stable. multi-vibrator 22 connected to the outputs of both detectors. Normally, the potential at 18 is such that on positive half cycles one detector produces output pulses and on negative half cycles the other detector produces output pulses, the resulting output of the multivibrator being amplified at 23, transformed at 24, rectified at 24a and applied to a closed loop circuit 25 controlling a switch 27. A short circuit, an open circuit or incorrect polarity of the diode 14 causes the half cycle pulses from one or other detector to cease so that the multivibrator ceases to provide an output. In the arrangement shown, the upper circuit functions as remote control circuit being provided with a starting switch 14, a resistor 15 and a time switch 17a. A start circuit detector 26 provides half cycle pulses when the switch 14 is closed and these pulses together with pulses from the short circuit detector are applied to a further multivibrator 29 connected to the loop circuit 25 through an amplifier 30, transformer 31 and rectifier 32. A cable proving circuit with diode 42, resistors 40, 41, open and short circuit detectors 43, 44 and multivibrator 45 is connected to the loop circuit 25 which has to receive an output from the three circuits shown to control the switch 27.