GB1209304A - Improvements in or relating to electrical pulse monitoring circuits - Google Patents

Abstract

1,209,304. Magnetic drum stores. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. 8 Nov., 1967 [10 Nov., 1966], No. 50531/66. Heading G4C. [Also in Divisions G1, H2 and H3] In an arrangement for providing an indication of the failure of one of n sources of identical pulse trains S1-S3, pulses from these sources are applied as strobe pulses to a plurality of pairs of associated bi-stable circuits TA-TF and failure of one of the sources S1-S3 is indicated by operation of detection devices such as relays 1ALR-3ALR associated with each pair of bi-stable circuits to which the failed source is applied. The outputs of the bi-stable circuits TA, TB of each pair are set to opposite states by momentarily operating reset key KR to apply earth potential via isolating diodes DADF to the outputs of the bi-stable circuits. This causes the bi-stable circuits TA, TB to be in the " 1 " and " 0 " state so that a " 0 " output is applied from both bi-stable circuits TA, TB to the associated relay 1ALR which is not energized. When the strobe inputs S1 and S2 occur at the strobe inputs X, Y (Fig. 1) of each bi-stable circuit TA, TB the state of each bistable circuit changes so that a " 1 " output is applied to each terminal of the relay 1ALR. If one of these strobe pulses fails then the state of one of the bi-stable circuits remains unchanged and the outputs applied to the relay 1ALR become 1, 0 or 0, 1 and the relay 1ALR is energized to close its contact 1ALR1 and operate a strobe fail alarm SFA. Failure of both S1 and S2 will not operate relay 1ARL but will operate relay 2ALR. Similar operation occurs for failure of S3 and combinations of S1, S2 and S3 except that failure of all three will not be detected. The circuit operates to fail safe since if one of the bi-stable circuits fails the next strobe pulse applied to it will result in the failure alarm being given. The alarm relays may be replaced by a gate arranged to detect the same output state of the bi-stables. Each bi-stable circuits (Fig. 1) have input gates DA, DB, DS which only allow signals at the control inputs I/PS and I/PR to change the state of the bistable circuit provided a strobe pulse is applied to both X and Y strobe inputs. The arrangement may detect the failure of a strobe source or the omission of a single strobe pulse, e.g. due to a flaw in an oxide coating where the strobe sources are derived from three sync. tracks on a magnetic drum by means of a sync. track reading head. Three strobe or clock pulse sources may be combined in a two-out of three majority gate, the output of which is used to drive a strobe distribution amplifier supplying a strobe controlled system.