Patent GB-1005568-A (GB)
Title: Annunciator system
Inventor: BEGUIN RICHARD FRANCOIS
IPC: G08B23/00
Filed: 1962-04-24
Abstract: 1,005,568. Annunciators. ISI Inc. April 24, 1962, No. 15589/62. Heading G4F. [Also in Division H3] An annunciator circuit (Fig. 1) includes a bistable flip-flop 6 and a pair of alarm lamps L 1 , L 2 , a switch 8 being responsive to an abnormal condition of a monitored variable to close path 15 and make device 10a conductive thus lighting lamp L 1 ; lamp L 2  being lit and L 1  extinguished when acknowledgement switch 2 is closed to reverse circuit 6 into its other state. Elements 10a, 10b are transistors, Fig. 3 (not shown), although magnetic core elements or thermionic valves are also referred to. A flasher may be included in the circuit of lamp L 1 . In the embodiment of Fig. 4, contacts 30<SP>1</SP> are normally closed and control a transistor gate 49 normally held in a non-conducting state by diode 57. When the variable goes abnormal, contacts 30<SP>1</SP> open causing transistor 49 and thus transistor 10a to conduct and lamp L 1  to flash, the acknowledgement switch 2 being arranged as before to trigger the bi-stable circuit. The circuit may be operated by using normally open contacts across terminals 67-67<SP>1</SP>, closed when the variable goes abnormal, and omission of contacts 30<SP>1</SP>. Stability of the circuit at high temperatures is obtained by making resistors 22a<SP>1</SP>, 22b<SP>1</SP> interconnecting the transistor bases and collectors of the same high value and resistors 24a<SP>1</SP>, 24b<SP>1</SP> connecting the base electrodes to the point 43 of the same low value. Initial conduction of the left hand transistor 10a is ensured by capacitor 41 which by-passes resistor 22a<SP>1</SP> under transient conditions. A voltage supply stabilizing diode 45 is also included in the circuit. Fig. 5 shows two interconnected annunciator circuits A 1 , A 2  to monitor two variables. A lock-in (preferably transistor) gate 72 maintains the gate 49 open once it has responded to an abnormal condition of the variable, provided one of switches 86, 82 in paths 80, 78, respectively is closed, when the voltage drop across resistor 61 resulting from the current flowing through either path is sufficient to maintain gate 49 open irrespective of the position of the variable responsive contacts 30<SP>1</SP>. Initial lock-in operation.-The circuit goes back to normal once acknowledgement switch 2 is pressed. Switch 82 in path 78 is closed, switch 86 in path 80 open. Gate 49 is held open as above mentioned, but current through path 78 and lamp L 2  is not sufficient to light the latter; transistor 10b is non-conductive. On acknowledgement, transistor 10b conducts and gate control device 74 interrupts the biasing current in gate 49 so closing the latter, provided contacts 30<SP>1</SP> have resumed the normal position. Manual reset operation.-Both switches 82, 86 are closed so that the initial alarm condition of lamp L 1  is locked-in before acknowledgement and the acknowledged condition of lamp L 2  is locked-in after acknowledgement until the reset switch 89 is closed. Lock-out operation to identify the variable which first becomes abnormal.-Switch 93 is opened so connecting a gate 97 in circuit. Lock-in gate 72 is also connected. Gate 97 is open until the variable goes abnormal when the resultant positive voltage on bus R due to opening of gate 49 is fed via line 98 to the control terminal of gate 97 which closes to prevent operation of all subsequent annunciator circuits until acknowledgement switch 2 is operated to remove the + ve voltage from R. A testing circuit is completed by a switch 104 Fig. 8a, which applies negative voltage to the gate control transistors 49 to simulate an abnormal condition of all the variables to initiate conduction of all the left-hand transistors 10a to energize all the lamps L 1 , if the circuits are operating properly. A remote light 119, is energized when any of the paths 15<SP>1</SP> of the bi-stable circuits are closed. Operation of all annunciator circuits except that associated with the first variable to become abnormal is prevented even after acknowledgement until the variable returns to normal by connecting line 98, Fig. 8a (as shown dotted at 98<SP>1</SP>) to lock-out transistor 97 to bus A instead of bus R. Flasher circuit (Fig. 8a).-The bias across diode 122 cuts off transistor 120 until transistor 111 becomes conductive by a positive potential applied to base 111b. The resultant current through resistor 113 causes a negative bias on the base of 120, the latter then becoming conductive thereby connecting a +ve voltage from bus H to the base of flasher transistor 109 to keep it cut off. Capacitor 118 thereupon charges up to a potential determined by 115, 116 keeping transistor 111 conducting until the capacitor is fully charged. The potential across 116 will then cut off 111, no current will flow through resistor 113 and transistor 120 will cut off. Capacitor 118 discharges through resistors 115, 117 and 123 thus momentarily switching on a transistor 109 and causing the appropriate lamp L 1  to flash. Transistor 111 is stabilized by a thermistor 114<SP>1</SP>. Horn supply circuit (Fig. 8b).-A positive signal is applied to the base of transistor 126 from the R bus when a variable becomes abnormal, so that the transistor 126 becomes conductive. The resultant current through resistor 136 causes a potential on the base of transistor 138 to render this conducting and energize the horn 4<SP>1</SP>.