Patent GB-1007793-A (GB)
Title: Electric annunciator system
IPC: G08B19/00
Filed: 1961-09-19
Abstract: 1,007,793. Annunciators. ISI. Inc. Sept. 19, 1961 [Sept. 19, 1960], No. 33508/61. Heading G4F. [Also in Divisions H2 and H3] A system for monitoring a number of variables has, for each variable, a control circuit including a bi-stable circuit which is set to one state by a control signal voltage to actuate an alarm when the associated variable is abnormal. Reset pulses are applied to the bi-stable circuit continuously but are effective only when the variable has returned to normal to remove the control signal voltage. Fig. 1 shows a single control circuit 1, in which, when the associated variable goes abnormal, switch 22 is reversed to apply a control signal continuously to the input 66 of a bi-stable circuit 4 which is thereby set to feed positive potential over line 69 to an " and " gate 181 the other input 187 of which receives positive pulses from a flasher bus 193 over rectifier 191. This gate controls an alarm lamp 182 which thus flashes at the frequency of the flasher source to indicate the abnormality. As the bi-stable circuit 4 is set the positive potential over line 69 develops a positive pulse across resistor 96 of a differentiating circuit 90, 96 which over rectifier 209, sets a second bistable circuit 4<SP>1</SP>. In this set condition circuit 4<SP>1</SP> applies positive potential over line 199 to the input 189 of " and " gate 184. This gate has its other input 182 energized from line 69 and now opens to extend negative potential from the bus 28 over the horn bus 94 and amplifier 203 to actuate an audible signal (horn H) common to all the variable control circuits. These conditions obtain until an " acknowledge " key 14 is manually operated to reset the second bi-stable circuit 4<SP>1</SP> by connecting the negative bus 28 to its common input 78<SP>1</SP>. In this reset condition negative potential is applied to line 199 to close " and " gate 184 and stop the HORN H, and positive potential is fed over line 194 to the input 187 of " and " gate 181 so that the alarm lamp 182 now no longer flashes but glows continuously. A selector switch 206 is provided for either " non lock in " operation (position 1) or " lock in " (position 2) operation. " Non-lock in " operation.-In this case the lamp 182 is extinguished as soon as the variable in question returns to normal (and removes + ve from input 66) by resetting of the bi-stable circuit 4 as follows. The positive pulses from the flasher bus 193 are fed over rectifier 216 and capacitor 212 to produce positive pulses at the input 78 of the bi-stable circuit 4 but these are blocked by the rectifier 218. However, as these flasher pulses disappear the capacitor 212 recharges to a negative voltage over potentiometer 211, 211<SP>1</SP> connected to the - ve bus 28. The consequential negative pulses continuously produced at the upper end of resistor 214 then reset the bi-stable circuit 4 as soon as +ve is removed from its other input 66, i.e. when the variable reverts to normal. " Lock-in " operation.-With the bi-stable circuit 4<SP>1</SP> set, +ve is connected over line 199, rectifier 213 and switch 206 to the upper plate of capacitor 212 and this prevents resetting of the bi-stable circuit 4 as above described when the variable reverts to normal. Only after the acknowledge switch 14 has been operated to reset the bi-stable circuit 4<SP>1</SP> (whenve is applied to line 199) is the bi-stable circuit 4 reset as described above. A detailed transistorized circuit, Figs. 2, 3 (not shown) is described.