Patent GB-1257729-A (GB)
IPC: G08B29/18
Filed: 1969-07-09
Abstract: 1,257,729. Alarm signalling systems. AMERICAN DISTRICT TELEGRAPH CO. 9 July, 1969 [31 Oct., 1968], No. 34652/69. Heading G4H. In an electrical protection system of the kind in which operation of one or more condition sensing devices at a protected place is signalled to a central station by one or more rounds of coded signals, the system comprises a power supply unit having a first D.C. source, current and voltage responsive means coupled across the D.C. source and having transfer contacts normally connecting it to an output terminal, a second D.C. source normally disconnected which when the first source has a voltage below a given level, is connected to the output terminal, a transmitter connectible to the output terminal to apply operating potential thereto, and electrical control means associated with the condition sensing means for connecting the output terminal to the transmitter so that the coded signals are transmitted to the central station. The power supply unit 10, Fig. 1A, consists of a 12-volt battery 14 charged from a 110-volt A.C. source by a transformer and rectifier. Normally the 12-volt supply is sufficient to break down a Zener diode REC-1 so that transistor TRN-1 is conductive and relay PS energized. Contact PS-1 is then open, and battery, which is the second source, is then disconnected. If the voltage of the battery 14 falls the Zener diode switches off, de-energizing relay PS and switching contacts PS-1 to connect battery 22 to the alarm transmitter 11 but not to the supervisory transmitter 12. The alarm transmitter is designed to produce signals indicating an urgent condition, such as water flowing in a sprinkler system. Supervisory transmitter 12 produces signals indicating less urgent conditions such as low water level or low temperature in the tanks of the system. Normally current flows from battery 14 via contacts PS-1, resistor R-4, the A loop, front contact A-2, relay A, contact PS-2 and the B loop to earth 19. If any of the detectors operate, the corresponding contacts 24 close, shorting relay A which drops out, causing contacts A-2 to transfer and establish a circuit for motor 23 through the loops A and B and the operated contacts 24 contacts A-1 transfer to establish and second motor circuit via control contacts K3-1. When motor 23 starts a camoperated switch K1 transfers to provide a third motor circuit. As the motor rotates the coded signals are transmitted by code wheel. Contacts K3-2, K3-3 and K3-4 are controlled by cam also driven by the motor; to shortcircuit loops A and B and break the connection to ground. At the end of 5 rounds of signals contact K2-1 moves to a control position and de-energizes the motor. When the contacts 24 are again opened the alarm transmitter is returned to its; initial position by momentary closure of contact RS-1. This may be operated either locally, or from the remote station. If either of the loops A, B is broken, relay A falls out, contacts A-1 and A-2 transfer and motor 23 starts to transmit the coded signal. In this case the motor stops again after one round of signals has been transmitted by the opening of contact K3-1. An earth fault on the A loop has the same results, i.e. the transmission of one round of signals. If an alarm condition occurs at the same time as a fault the motor starts and transmits four rounds before it is stopped. If the A.C. source fails, battery 14 in due course becomes discharged until relay PS falls out and contacts PS-1 transfer to connect the battery 22 to the alarm transmitter. When contact PS-2 opens the alarm transmitter transmits a oneround signal. On restoration of the normal power source the alarm transmitter transmits four rounds of coded signals followed by one round. In addition to the alarm transmitter there are one or more supervisory transmitters 12, Fig. 1B. Contacts 26 open when any reportable condition appears and de-energizes relay S. This causes motor 25 to start and transmit a two-round signal of the supervisory code. The transmitter is returned to normal automatically or manually. An open or earth fault also causes a two-round signal to be sent but in the event of power failure no signal is sent. Visible and audible indicators may be provided at the protected premises, to show that the signals have been received at the central station.