APPARATUS FOR MONITORING THE CONDUCTORS OR LINES OF FIRE ALARM INSTALLATIONS

• US 3,665,461 A
• Filed: 09/10/1970
• Issued: 05/23/1972
• Est. Priority Date: 09/16/1969
• Status: Expired due to Term

• Current Assignee: Alex Gnagi, Peter Muller
• Original Assignee: Alex Gnagi, Peter Muller
• Inventors: Gnagi, Alex, Muller, Peter
• Primary Examiner(s): Habecker, Thomas B.
• Application Number:
  US05/071,111
• Time in Patent Office: 621 Days
• Field of Search: 340/409
• US Class Current: 340/509
• CPC Class Codes: G08B 17/06 Electric actuation of the alarm, e.g. using a thermally-operated switch
• CPC Class Codes: G08B 29/06 Monitoring of the line circuits, e.g. signalling of line faults

Abstract

An apparatus for supervising the continuity of the conductors of an alarm installation, especially a fire alarm installation, comprising a central signal station and a plurality of fire alarms each of which draws a quiescent current during normal operation and an alarm current when in an actuated condition. At least one pair of conductors electrically couples the fire alarms in parallel with one another and with such central signal station. A direct-current voltage supply is provided for the parallely connected fire alarms. Terminating element means serves to monitor the continuity of the conductors, such terminating element means being connected across the ends of the conductors located remote from the central signal station and generates and applies to such conductors a signal containing at least an alternating-current component, said signal being distinguishable from the signal delivered by said direct-current voltage supply to said fire alarms and further being distinguishable from the quiescent and alarm current signals drawn by said fire alarms. Also, the central signal station is provided with means responding to the presence of the signal applied to the conductors by the terminating element means.

Claims

1. An apparatus for supervising the continuity of the conductors of an alarm installation, especially a fire alarm installation, comprising a central signal station, a plurality of fire alarms each of which draws a quiescent direct current during normal operation and an alarm direct current when in an actuated condition, at least one pair of conductors for electrically coupling said plurality of fire alarms in parallel with one another and with such central signal station, a direct-current voltage supply for said plurality of parallely connected fire alarms, terminating element means for monitoring the continuity of said pair of conductors, said terminating element means being connected across said pair of conductors at the ends thereof located remote from said central signal station and generating and applying to said conductors a signal containing at least an alternating-current component, said signal being distinguishable from the signal delivered by said direct-current voltage supply to said fire alarms and further being distinguishable from the quiescent and alarm current signals drawn by said fire alarms, and means provided at said central signal station for responding to the presence of said signal applied to said conductors by said terminating element means.

2. The apparatus as defined in claim 1, wherein said central signal station contains said direct-current voltage supply.

3. The apparatus as defined in claim 2, wherein said signal produced by said terminating element means constitutes a train of pulses.

4. The apparatus as defined in claim 3, wherein the duration of said pulses is less by at least a factor of 10 than the separation between pulses.

5. The apparatus as defined in claim 3, wherein the maximum current of a pulse differs by not more than a factor of two from the alarm current of an individual fire alarm.

6. The apparatus as defined in claim 3, wherein said terminating element means includes a unijunction transistor generating said pulses.

7. The apparatus as defined in claim 3, wherein said terminating element means comprises a multivibrator incorporating at least two mutually cross-coupled transistors.

8. The apparatus as defined in claim 2, wherein said terminating element means comprises a sawtooth-wave generator incorporating at least a gas-discharge tube, capacitor means and resistor means.

9. The apparatus as defined in claim 1, wherein said terminating element means is equipped with an individual voltage source.

10. The apparatus as defined in claim 1, wherein said central signal station contains both means for providing an indication of an alarm current provided by at least one of said fire alarms and said means for indicating the presence or absence of signals provided by said terminating element means.

11. The apparatus as defined in claim 10, wherein said central signal station contains at least one common alarm amplifier stage for both the alarm signals and for the signals supplied by said terminating element means.

12. The apparatus as defined in claim 10, wherein said means for indicating an alarm current is operable only with a predetermined time-delay after the appearance of an alarm signal.

13. The apparatus as defined in claim 10, wherein said central signal station contains means for switching off said supply voltage in the event the current in said conductors exceeds a predetermined value.

14. The apparatus as defined in claim 10, wherein said central signal station includes means for fault indication for producing a fault indication only when the signals provided by said terminating element means have been absent for a period in excess of a predetermined minimum.

15. An apparatus for supervising the continuity of the conductors of a fire alarm installation, comprising a central signal station, a plurality of fire alarms each of which draws a quiescent current during normal operation and an alarm current when in an actuated condition, at least one pair of conductors for electrically coupling said plurality of fire alarms in parallel with one another and with such central signal station, a direct-current voltage supply for said plurality of parallely connected fire alarms, terminating element means for monitoring the continuity of said pair of conductors, said terminating element means being connected across said pair of conductors at the ends thereof located remote from said central signal station and generating and applying to said conductors a signal in the form of a train of pulses, the duration of said pulses being less by a factor of 10 than the separation between pulses, said pulse train signal being distinguishable from the signal delivered by said direct-current voltage supply to said fire alarms and further being distinguishable from the quiescent and alarm current signals drawn by said fire alarms, and means provided at said central signal station for responding to the presence of said signal applied to said conductors by said terminating element means.