FIRE ALARM INSTALLATION

• US 3,603,949 A
• Filed: 06/18/1968
• Issued: 09/07/1971
• Est. Priority Date: 06/26/1967
• Status: Expired due to Term

• Current Assignee: Beat Walthard
• Original Assignee: Beat Walthard
• Inventors: Walthard, Beat
• Primary Examiner(s): Habecker, Thomas B.
• Application Number:
  US04/738,046
• Time in Patent Office: 1,176 Days
• Field of Search: 340/214,409
• 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 29/145 of fire detection circuits

Abstract

A fire alarm installation is disclosed which provides positive detection of the response or nonresponse of an individual fire alarm during the normal operational condition thereof as well as during a checking operation. Each of the individual fire alarms are provided with circuits which exhibit a high impedance for supply voltages of a first polarity and a low impedance for supply voltages of a second polarity during normal operational conditions. During alarm conditions, however, the impedancepolarity relationships reverse and such is detected at a remote central station.

Claims

1. A fire alarm installation comprising:

a. a central station;

b. a plurality of fire alarms;

c. a pair of common conductors for connecting said plurality of fire alarms in parallel to one another and to said central station;

d. each of said fire alarms comprising a detector element sensitive to fire phenomena and electric circuit means controlled by its associated detector element;

e. each of said circuit means possessing two stable conditions, defining a normal condition when the detector element assumes a normal operating state in a condition of readiness for detecting a fire and an alarm condition when said detector element assumes a response condition when it has been subjected to fire phenomena f. said circuit means possessing two parallel current paths for the respective flow of currents of different polarity;

g. each of said circuit means including switching means for connecting one of said parallel current paths to said two common conductors when the circuit means is in said normal condition and for connecting the other of said current paths across said two conductors when the circuit means is in said alarm condition;

h. said central station embodying means for generating a supply voltage of continuously and periodically alternating polarity which is delivered to said two conductors;

i. said central station further including means for generating a test signal applied to said two conductors;

said test signal controlling said electric circuit means in like manner as said detector elements; and

j. said central station further comprising measuring means for separately detecting the current in said two conductors during the phases of different polarity of said supply voltage.

2. A fire alarm installation as defined in claim 1, wherein each of said detector elements comprises a measuring ionization chamber accessible to the surrounding atmosphere, at least one resistance element connected in series with said measuring ionization chamber, the current flowing through said measuring ionization chamber changing when the atmosphere contains combustion aerosols or smoke, each of said circuit means being responsive to the thus produced voltage changes appearing across its associated measuring ionization chamber.

3. A fire alarm installation as defined in claim 1, wherein said parallel current paths of each of said circuit means comprises two circuit branches, each circuit branch being connected across said supply conductors via respective diode means of opposite polarity and via controllable semiconductor means, said controllable semiconductor means being connected in said circuit means such that one of said semiconductor means is conductive and the other semiconductor means is blocked during said normal condition of said electric circuit means, whereas said one semiconductor means is blocked and said other semiconductor means is conductive during said alarm condition of said electric circuit means.

4. A fire alarm installation as defined in claim 3, wherein each of said detector elements comprises a measuring ionization chamber accessible to the surrounding atmosphere connected in series with a reference ionization chamber by a common electrode, said one controllable semiconductor means being a field-effect transistoR having gate, source and drain electrodes, the gate electrode of which is electrically connected with said common electrode of both said ionization chambers, said other semiconductor means being a further transistor, said circuit means possessing voltage divider means for coupling both said ionization chambers with said further transistor such that said field-effect transistor is positively fed back by means of said further transistor as well as by said ionization chambers.

5. A fire alarm installation as defined in claim 4, wherein a Zener diode is connected in series with said source electrode of said field-effect transistor, said test signal generating means at said central station including control means for reducing the amplitude of said supply voltage during one polarity for a short period of time.

6. A fire alarm installation as defined in claim 1, wherein said parallel current paths of each of said circuit means comprise diode means of opposite polarity, at least one of said current paths possessing a bistable element containing at least two transistors and wherein the other current path possesses at least one further transistor, said transistors being coupled together to provide a switching arrangement controlling either both transistors of said bistable element to be conductive or said further transistor in said other current path to be conductive, said bistable element being connected with and controlled by its associated detector element, said further transistor being connected with and controlled by said bistable element.

7. A fire alarm installation as defined in claim 6, wherein each of said detector elements comprises a measuring ionization chamber accessible to the surrounding atmosphere connected in series with a reference ionization chamber by a common electrode, one of said two transistors of said bistable element being a field-effect transistor having gate, source and drain electrodes, the gate electrode of which is connected to said common electrode of both ionization chambers, said further transistor having a base electrode, the second transistor of said bistable element possessing a collector electrode connected with a second electrode of one of the ionization chambers and with said base electrode of said further transistor in the other current path and via a resistor with one of the supply conductors, said bistable element being connected via one of said diode means with the other of said supply conductors, one said electrode of said field-effect transistor being connected via a Zener diode with said one supply conductor, said further transistor in said other current branch being connected via the other of said diode means with said other supply conductor.

8. A fire alarm installation as defined in claim 1, wherein one of said current paths comprises a first diode and a first bistable element containing at least two transistors, said second current path comprises a second diode connected electrically antiparallel to said first diode and a second bistable element comprising at least two further transistors, said second bistable element being connected with and controlled by said first bistable element such that only one of said bistable elements is conductive and the other one is blocked.

9. A fire alarm installation as defined in claim 8, wherein each of said detector elements comprises a measuring ionization chamber accessible to the surrounding atmosphere connected in series with a reference ionization chamber by a common electrode, a field-effect transistor having a gate, drain and source electrode and controlling said first bistable element, said gate electrode of said field-effect transistor being connected to said common electrode of said two ionization chambers, a still further transistor providing an alarm threshold means connecting said field-effect transistor with said first bistable element, said field-effect transistor and said first bistable element being blocked when said circuit means is in said normal condition, saId second bistable element being further connected via a diode with a capacitor and with a voltage divider for connecting said second bistable element with the series connection of both of said ionization chambers, said further capacitor during the normal condition of said circuit means being charged and in said alarm condition discharges due to blocking of said second bistable element and thereby stores said alarm condition by displacing the potential at said gate electrode of said field-effect transistor.

10. A fire alarm installation as defined in claim 1, wherein said central station comprises control means for increasing as well as for decreasing the supply voltage during the phases of one polarity for short periods of time, said electric circuit means including circuitry for maintaining said electric circuit means in a self-holding state during the presence of said alarm condition.

11. A fire alarm installation as defined in claim 1, further including a conductor terminal element connected in parallel to the last fire alarm of said plurality of fire alarms, said conductor terminal element comprising an asymmetrical astable multivibrator having a higher pulse repetition frequency with respect to the repetition frequency of said supply voltage.

12. An alarm installation comprising a central station, a plurality of alarms, at least one pair of conductors for electrically connecting said plurality of alarms in a group in parallel with said central station, said central station including supply voltage means for said group of parallely connected alarms, a conductor terminal element means connected in parallel to the last alarm of said plurality of alarms for monitoring possible interruptions at the conductors of said plurality of alarms, said conductor terminal element means including means for applying to said conductors a signal having an alternating voltage component for periods during which said central station is delivering a supply voltage of a certain polarity to said conductors and different from the signals drawn by said plurality of alarms.

13. An alarm installation comprising a central station, a plurality of alarms, at least one pair of conductors for electrically connecting said plurality of alarms in a group in parallel with said central station, said central station including supply voltage means for said group of parallely connected alarms, a conductor terminal element means connected in parallel to the last alarm of said plurality of alarms for monitoring possible interruptions at the conductors of said plurality of alarms, said conductor terminal element means including means for applying to said conductors a signal different from the signal delivered by said supply voltage means to said plurality of fire alarms and different from the signals drawn by said plurality of alarms, said supply voltage means delivering signals of alternating polarity, said terminal element means applying to said conductors a signal of a different frequency than the signal frequency of said supply voltage means.

14. An alarm installation comprising a central station, a plurality of alarms, at least one pair of conductors for electrically connecting said plurality of alarms in a group in parallel with said central station, said central station including supply voltage means for said group of parallely connected alarms, a conductor terminal element means connected in parallel to the last alarm of said plurality of alarms for monitoring possible interruptions at the conductors of said plurality of alarms, said conductor terminal element means including means for applying to said conductors a signal different from the signal delivered by said supply voltage means to said plurality of fire alarms and different from the signals drawn by said plurality of alarms, said supply voltage means delivering a signal of alternating polarity, said means of said conductor terminal element means for applying said signal to said conductors comprises an asymmetrical astable multivibratOr having a higher pulse repetition frequency than the repetition frequency of said supply voltage means.