Patent GB-1356673-A (GB)
Title: Automatic telephone dialling and signalling systems
IPC: H04M11/04
Filed: 1971-08-11
Abstract: 1356673 Automatic exchange equipment NATRONICS PTY Ltd 11 Aug 1971 [13 Aug 1970] 37649/71 Heading H4K An alarm system includes at least one alarm station connectible over an automatic telephone network to a control station where the alarm station on comprehending an abnormal situation operates to obtain a connection to the control station the control station on being connected sends an identity signal which causes the alarm station to transmit signals corresponding to a coded message whose receipt is acknowledged by the transmission of a signal from the control station to the alarm station. In the preferred system and if the identity signal is not received the alarm station repeats the calling procedure. The number of repeats is limited to three by a 3 call counter. Alarm station Fig. 1.-The alarm contacts cause the alarm trigger and latch to be operated and start the 3 minute timer and start the sequence counter which comprises a twisted ring counter. Initially the line is looped and a 10 second counter started. At the end of this time the sequence counter is stepped and the pulse counter, as coded by the coding plug, operates the dialling relay to send the first digit of the control station number. When the digit is sent the 1-second timer operates and the sequencer is stepped to send the second digit until the whole number has been transmitted. At this stage the 10 sec. timer operates and within this time an identity tone should be received to step on the sequencer. If no tone is received a "repeat" instruction is made and the sequencer restored to its initial state and a count of one inserted in the 3-call counter. When the identity tone is received the telephone line is switched to the coupling transformer and the alarm message transmitted as a sequence of tone pulses. The 10 second timer again operates until an acknowledgement tone signal is received which causes the alarm station to display a flag or other visual display and remain inoperative until a reset button is operated. If no acknowledgement tone is received the sequencer will recycle repetitively until a total of 3 calls have been made. Control station Fig. 2.-Ringing tone is detected by a full wave rectifier arrangement and causes connection to be made so that the tone generator can send the identity tone, a 1 second pulse tone, to the calling alarm station. The incoming message tone pulses are decoded and displayed with the actuation of an audible alarm and subsequently a further tone pulse is sent as an acknowledgement signal to shut the alarm station down. A reset button is provided to reset the visual and audible alarms. A test sequence can be made by altering the last digit of the coded message tones to a special test digit and this is recognized at the control station. Additionally the alarm station is stated to be capable of dialling an alternative number if no identity response is received on the first number. A permanent record of the alarm may be made at the control station using punched or printed tape or magnetic recording. The type of alarm may also be identified by use of different coded messages and the communication link may include a carrier telephony system or a radio link.