GB1346618A - Data communication systems - Google Patents

Abstract

1346618 Electric selective signalling ALARM EQUIPMENT SUPPLIES Ltd 18 July 1972 [28 April 1971] 11933/71 Heading G4H In a security alarm system an alarm or line fault signal from a remote station is applied to one of inputs A1 ..., An; LF1 ..., LFn of a central station receiver, whence it passes to a matrix encoder whose outputs are scanned by decade counters LSD, HSD to produce a decimal output which corresponds to the local station number and which controls a digital display and a printer. The input signal, e.g. A2 or LF2 from station 2, passes to the matrix via a pulse lengthener D2 or D2A and a gate 11b opened by a pulse L2 from a shift register. The matrix input is fed to the junction of two forward biased diodes connected to respective co-ordinate lines (e.g. 02). The matrix outputs (lines 0 and 2) enable gates G1, G2 to admit oscillator S1 pulses to feed the counters; they also pass to two out of twenty gates 16 to which the counter outputs are connected. The counters scan gates 16 until coincidence of inputs at the two selected gates provides outputs which enable gates 14a, 14b and thus block gates G1, G2 to halt the counters. The counter outputs are displayed, and two slave counters provide outputs to control the printer. When a "1" appears in the matrix, a flip-flop B1 is caused to block a gate G3 between the shift register and its clock while the matrix is being scanned. After appropriate delays (caused by a timer, delay devices D10, D20 and monostables H3, H4) the printer is activated, the apparatus is reset, the matrix is cleared, and gate G3 is re-enabled. Input A2 or LF2 also activates an Alarm or a Line Fault Indicator via gate G7 (a) and bistable B2 (a). The disappearance of an alarm or line fault condition is shown by a Clear Line Indicator when gates G8, G9 are actuated by a signal Z from B1 and by the disappearance of the input signal LF2 or A2.