Patent GB-1013489-A (GB)
Title: Remote alarm system
IPC: G08B26/00
Filed: 1964-06-18
Abstract: 1,013,489. Selective signalling - systems. MOTOROLA Inc. June 18, 1964 [July 3, 1963], No. 25264/64. Heading G4H. General.-In a system for indicating at a central station the states of alarm devices at remote stations, groups of tones are sequentially transmitted from the central station to select the remote stations in turn. The tones in each group also correspond to alarm devices making up a group at the selected remote station whereby each tone group interrogates a group of alarms, and in response to the interrogations, the tone group is retransmitted to the central station, those tones corresponding to actuated alarms being shifted in frequency. Transmission may take place over wire or radio links or a combination of both. Generation of scanning sequence.-Each tone group comprises three tones selected from 14 available tones. A fast clock source 56, Fig. 2, feeds a 14-stage binary counter 29 through a gate 57. When three of the counter stages are in the " 1 " state, gates 51-53 switch bi-stable circuit 58 to state 2 to close gate 57 and open gate 64, whereupon slow clock source 65 supplies pulses to a ring counter 66 to initiate an interrogation cycle. At count 1, counter 66 switches circuit 40 to apply the 3-out-of-14 group registered in counter 29 to 14 gates 26-28 so as to select 3 of the tones from oscillators 20. Gate 77 is opened from count 2 to count 5 to pass the selected tone group to the transmission link. Gates 30-33 are closed at count 6. The remainder of the interrogation cycle is used for receiving the response from the selected alarm group. When counter 66 reaches zero, gate 64 is closed and gate 57 is opened to allow counter 29 to advance to the next 3-out-of-14 combination. Reception of tone group by remote station and alarm response.-The remote station shown in Fig. 4 is associated with 12 alarms (not necessarily in the same locality) arranged in 4 groups of 3 to correspond to the four 3-tone groups selectable from tones A, B, C, D to which the station responds. For example, one alarm group corresponds to tone group ABC, and the 3 individual alarms in this group respectively correspond to tones A, B, C. When an appropriate tone group is received, e.g. ABC, the corresponding gate 215 is enabled, sets the associated circuit 220 to state 2 and starts timing triggers 226-230. After the end of the interrogating tone groups ABC, trigger 227 activates transmitter 201 and keys on oscillators 204-206 corresponding to interrogating group ABC. The fourth oscillator 207 is not activated owing to the inhibit connection from circuit 220 to gate 243. Circuit 220 gates out the selected alarm group conditions from network 242, and if one of these alarms is in the actuated condition, the corresponding oscillator 204, 205 or 206 is forced to produce a tone which is shifted in frequency from the normal tone A, B or C. The response tone group is transmitted to the central station. Trigger 228 inhibits response of the remote station to received tones for 100 M/s. after the end of the interrogating group. Indication of alarms at central station.-A tone group received at the central station, Fig. 2, is applied to 28 filters and detectors corresponding to the 14 normal tones A-N and the associated shifted tones. Verification circuit 74, which comprises a plurality of gating circuits connected in series, Fig. 8 (not shown), produces an error signal if the received tones, either normal or shifted, do not correspond to the transmitted tones represented by the count held in counter 29. If the response is acceptable, three lamps in a panel corresponding to the interrogated alarm group are selectively energized in console 73 to indicate the states of the alarms in this group. A main alarm is also operated if a remote alarm has been actuated. Indication of alarm group power failure.-In addition to the tone group representing the conditions of the selected group of alarms, each remote station, Fig. 4, also normally transmits an extra tone (X function) indicating that the power supply of that alarm group is operating correctly. In the case of interrogating tone group ABC, gate 249 is conditioned by timing trigger 227 and circuit 220, and if the power supply of this alarm group has failed, X1 is energized to inhibit gate 256, whereby the output of generator 255, common to all alarm groups of the station, is removed from the response group. This causes a corresponding lamp on the selected alarm group panel of console 73 to be lit at the central station. Resetting selected alarm group.-This is performed by transmitting a long interrogating tone group from the central station. Each panel of console 73 Fig. 2 includes reset test switches. When one of the switches is moved to the reset position, circuit 72 is switched to state 2, and the enabling signal from console 73 to gate 59 is removed so that counter 29 is stepped continuously by the fast clock pulses. When counter 29 reaches the count corresponding to the alarm group to be reset, a signal issues from console 73 to open gate 59 and thus close gate 57 so that counter 29 is stopped. At the same time, gates 63, 64 open to start passing slow clock pulses to counter 66, but when count 2 is reached, gate 70 inhibits gate 63 and opens gate 71. Slow clock pulses then pass to ring counter 68 until circuit 72 is reset after a predetermined count is attained. The interrogation cycle then continues normally under control of counter 66. While a reset operation is in progress, all indications from the other alarm groups are inhibited. At the remote station, Fig. 4, time delay 229 enables gates 232-235 during the reset period, and a reset signal is obtained from the gate opened by the appropriate circuit 220-223. Testing selected alarm group.-This is performed by transmitting the interrogation tone group for an indefinite period, and the operation is similar to the reset procedure. Operation of a console switch to the test position energizes line 86, Fig. 2, instead of line 87. Counter 29 is stopped at the desired count as in the reset operation. When counter 66 reaches count 2, however, gate 69 inhibits gate 63 and the interrogating tone group is continuously transmitted until the test command is removed from line 86. At the remote station delay 230 enables the selected test gate 237-240. Repeated interrogation of selected alarm group.-Switch 75 is opened and the appropriate console switch moved to the test or reset position. Selection of the desired tone group proceeds as in the test and reset operations, but now neither of gates 69, 70 is opened when counter 66 reaches count 2, and therefore counter 66 is recycled continuously to repeatedly initiate interrogation of the selected alarm group.