US3564524A

US3564524A - Fire alarm system having a diode coupled checking circuit means

Info

Publication number: US3564524A
Application number: US636174A
Authority: US
Inventors: Beat Walthard; Andreas Scheidweiler; Max Kuhn
Original assignee: Cerberus AG
Current assignee: Cerberus AG
Priority date: 1966-05-09
Filing date: 1967-05-04
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16
Also published as: AT279431B; SE338527B; US3678510A; SE365327B; BE698199A; US3530450A; GB1140294A; DE1281321B; NL6706275A; ES340611A1; IL27907A; NL162763C; NL162763B; DK136839C; DK136839B; AT278599B; CH473431A

Abstract

A FIRE ALARM SYSTEM INCLUDING A PLURALITY OF FIRE ALARMS ARRANGED IN GROUPS. ALARM-SIMULTING CONDITIONS ARE PRODUCED IN EACH FIRE ALARM BY AN ELECTRIC TEST SIGNAL, THE RESPONSE OF EACH FIRE ALARM BEING SENT TO AN EVALUATION DEVICE AT A CENTRAL SIGNAL STATION THROUGH A LOGIC CIRCUIT COUPLING THE FIRE ALARMS TOGETHER.

Description

Feb.16, 1971 BWALTHARDETAL 3,5641'524 FIRE ALARM SYSTEM HAVING A DIODE COUPLED CHECKING CIRCUIT MEANS Filed May 1967 United States Patent @Hice U.S. Cl. 340-214 Claims ABSTRACT OF THE DISCLOSURE A re alarm system including a plurality of tire alarms arranged in groups. Alarm-simulating conditions are produced in each tire alarm by an electric test signal, the response of each re alarm being sent to an evaluation device at a central signal station through a logic circuit coupling the re alarms together.

BACKGROUND OF THE INVENTION The present invention relates to an improved re alarm system comprising a central signal station to which electric re alarms are connected in groups, wherein the number of conductors between the central signal station and the fire alarms is independent of the number of re alarms. Furthermore, the inventive re alarm system additionally includes an apparatus for producing electrical test signals by means of which alarm-simulating conditions are produced at the tire alarms which, in turn, bring about an electrical change in condition at an intact iire alarm, and further, the inventive system includes an apparatus for evaluating such changes and conditions.

In re alarm installations, there generally exist the requirements of checking the operational reliability of the individual re alarms at regular intervals. To this end, and in accordance with a workable method, alarmsimulating conditions are manually delivered to the individual fire alarms one after the other or in series. The response of the relevant alarm is controlled at its locality or at the central station. However, this technique is, above all, extremely time-consuming and uneconornical, if the installation consists of a larger number of tire alarms, for instance, one hundred re alarms or more. In such case, a regular manual monitoring at shorter time intervals can no longer come under consideration for practical reasons.

It is for these reasons that methods have been developed in which it is possible to achieve from the central station alarm-simulating conditions at the tire alarms through use of special electronic means, and to check the response conditions of all re alarms at the central station. The diculty with such method, above all, resides in the reliable determination of whether all tire alarms of a group have actually responded.

In a known system, a separate conductor is led from each tire alarm back to the central station. During the checking operation, a signal appears at such conductor which is characteristic of the response condition of the 3,564,524 Patented Feb. 16, 1971 relevant fire alarm. This system has the drawback that it requires extensive additional installations, which becomes of particular importance if such a monitoring device should be subsequently installed in an already existing re alarm system.

Consequently, it is desirable to provide a monitoring device in which the number of conductors leading from the central station to the re alarms is independent of the number of connected re alarms. In a known arrangement of this type, all of the tire alarms are simultaneously caused to respond from the location of the central station. Further, by means of a current measuring device at the central station which is provided at one of both current delivery conductors of the fire alarm, the response of all tire alarms is monitored, whereby there is checked the coincidence of the total current with some predetermined reference value. Apart from the great current consumption which has an adverse eitect upon the choice and dimensioning of the conductors, the network devices, the emergency power groups, etc., this arrangement is limited to groups having relatively few tire alarms. Because of the diversity of the electrical characteristics of the structural elements in the re alarms as well as because of the limited measuring accuracy during comparison of the total current with the reference value based upon an analogous measurement, this technique is unreliable with a larger number of tire alarms and often times results in false alarms.

SUMMARY O'F THE INVENTION Accordingly, it is a primary object of the present invention to provide an improved monitoring device for a re alarm system of the previously mentioned type in which it is possible to reliably check or monitor an optional large number of re alarms per group.

It is another object of the present invention to provide a monitoring system which may be installed in existing re alarm systems.

It is a further object of the present invention to provide a monitoring system which requires low additional power.

It is an additional object of the present invention to provide a monitoring system which makes use of digital techniques.

Generally speaking, the present invention is characterized by the features that the tire alarms of a group are coupled with one another by means of a logic circuit and that the logic circuit, during the checking operation, then delivers a signal to the evaluation device when all tire alarms of a group have responded (AND-gate) or at least one re alarm has not responded (OR-gate).

A number of diierent embodiments of the invention as well as further inventive features will be described in greater detail hereinafter in conjunction with the figures of the drawing. In this regard, it will be appreciated that while the exemplary fire alarm installations depicted herein are in each instance equipped with ionization re alarms, it would be equally well possible to also employ optical llame detecting alarms, smoke detecting alarms or temperature detecting alarms.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood, and objects other than those set forth above, will become apparent,

when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawing wherein:

FIG. 1 illustrates a circuit diagram of a first embodiment of the invention in which the individual lire alarms have associated therewith diode means for coupling the individual vfire alarms to one another; and

yFIG. 2 is a circuit diagram of an exemplary embodiment of the invention in which the individual tire alarms have associated therewith oscillation generators.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawing, in .FIG. 1 there are depicted two

fire alarms

39 and 40 of identical construction. These

lire alarms

39 and 40 are connected parallel to one another via the supply conductors or leads 35 and 36 as well as being connected Lvia an additional signal conductor 29 with a central station 41. As already remarked, these

re alarms

39 and 40 are of identical construction and preferably consist of two

ionization chambers

21 and 22, the air content of which can be rendered completely or partially conductive through an appropriate radioactive preparation as is known in the art. Furthermore, these

tire alarms

39 and 40 each incorporate a switch element 23 which, in this case, is a ieldeffect transistor. The ionization chamber 21 operates as a measuring chamber, whereas the ionization chamber 22 is used as a reference chamber. `Chamber 22 can be replaced by a high-ohm resistor or an equivalent high ohm element. Likewise, in lieu of a field-effect transistor 23 it is possible to use other semi-conductor devices or a diderent switch element with high-ohm input resistance or impedance, for instance a cold-cathode tube.

The drain or anode of the field-effect transistor 23 is connected via a resistor 25 with the negative supply conductor 35, the cathode or source via the tap of a potentiometer 24 with the positive supply conductor 36. Furthermore, at the drain or anode of the field-effect transistor 23 there is connected the gate of a controlled rectifier 26, the cathode of which is coupled with the negative supply conductor 35 and the anode of which, on the one hand, is connected via a resistor 44 to the negative supply conductor 35 and, on the other hand, via a resistor 45 with the positive supply conductor 36. The anode of the controlled rectifier 26 is furthermore connected with the signal conductor 29 through the series circuit or connection incorporating the indicating lamp 31 and the Zener diode 28. A resistor 34 is connected parallel with the indicating lamp 31. This resistor 34 maintains the connection between the controlled rectifier 26 and the Zener diode 28 during breakdown of the indicating lamp 31.

The potential at the tap of the potentiometer 24 is adjusted in such a manner that the tield-etect transistor 23 and thereby the controlled rectier 26 block in the normal condition. The signal conductor 29 is connected at the central station 41 via a contact of the switch 43 and a resistor with the positive pole of the voltage source designated by reference numeral 100. The Zener voltage of the diode 28 is selected in such a manner that when the rectitier 26- is blocked, in which case its anode has a potential determined by the

voltage divider

44, 45, this diode 28 likewise blocks.

The signal conductor 29 is then without current and the voltage at point 200 equals the voltage of source 100.

Now if combustion gas enter the measuring the measuring chamber 21, then the field-effect transistor 23 and the controlled rectifier 26 change their switched condition. More precisely, the potential at the anode of the controlled rectifier 26 practically drops to that of the supply conductor (ground), so that the voltage across the diode 28 now exceeds the Zener voltage and the diode begins to conduct. At the central station 4.1 the point 200 or voltage at point 200 or the contact of the switch 43 drops from the value voltage of source 100 to a new value approximately corresponding to the Zener Voltage ot' the diode 28. In so doing, the resistor 30 is selected in such a manner that the current flowing through the indicating lamp 31 initially does not cause such to light up or indicate. By closing a switch 33 arranged parallel the resistor 30, the indicating lamp 31, in the case of the alarm, can be caused to ignite from the central station, whereby the tire alarm receives a receipt or acknowledgement of the proper reception of the alarm signal at the central station.

The Zener diodes 28 of the individual tire alarms commonly form, in the normal operating condition, an OR- gate, whereby an alarm signal of the one or other fire alarm arrives via the common conductor at the central station without having any etect upon the remaining ire alarms. In accordance with the invention, the OR-gate is coupled or switched during the checking operation in such a manner that a signal only appears in the central station if at least one tire alarm has not responded. This can be realized in that, the conductor 29 is supplied by a voltage source 300 by means of the switch 43. The value of voltage source 300 is smaller than the Zener voltage otthe diodes 28. Since voltage of source 300 is smaller than voltage of source 100, the Zener diodes 28 are poled in the forward direction via the resistor 45 and the indicating lamps .31 and a current tiows through the signal conductor. The alarm-simulating conditions are produced through opening for a short time the switch 37 to thus introduce a voltage reducing Zener diode 38 in the supply conductor 36 which initially causes the capacitor 42 to partially discharge. Upon closing of the switch 37, a momentary over-voltage is produced be tween the gate and cathode of the iield-etfect transistor 23. The alarm-simulating conditions thus bring about a. response of the held-effect transistor 23 and thereby the controlled rectifier 26. Then, as a practical matter, the voltage of source 300 appears across the Zener diodes 28 of the intact tire alarms, which Voltage of source 300 by definition is smaller than the Zener voltage. If all of the tire alarms of a group have properly responded then the conductor 29 is without current. On the other hand, a signal appearing at the conductor 29 means that one or more tire alarms have not responded.

The return of the iire alarm can likewise take place by means of the signal conductor 29. To this end, the switch 43 is thrown or applied for a short time to a negative voltage source 400.

Naturally, it is also possible to apply numerous rnoditications to the circuit of FIG. l. Thus, for instance, it is possible to employ conventional diodes instead of Zener diodes, whereby the measures which must be undertaken in such case will be apparent to those skilled in the art.

FIG. 2 depicts a circuit diagram of an embodiment of the invention which is essentially based upon the same principles as the circuit diagram of FIG. 1. In this circuit arrangement the individual fire alarms are connected with one another into a logical circuit and an additional signal conductor is dispensed with.

By referring to FIG. 2 in greater detail it will be recognized that the individual lire alarms 50 embody a measuring ionization chamber 52 and a reference ionization chamber 54, the common connection point of which is coupled with the starter electrode of a cold-cathode tube 56. The anode of the cold-cathode tube 56 is coupled via a resistor 58 with the supply conductor 60, and the cathode is directly connected with the supply conductor 62. Furthermore, between both of the conductors 62 and 60 a series connection of a capacitor 64 and a resistor 66 is disposed. At the common juncture point or point of connection of the capacitor 64 and the resistor 66 one electrode of the measuring ionization chamber 52 is connected. The diode 68 is connected in parallel with the resistor 66. Finally, the anode of the cold-cathode tube 56 is connected via a resistor 70 with the connection point of a series connection of a further capacitor '72 and a glow-discharge tube 74 disposed between the

supply conductors

60 and 62. Glow-discharge tube 74, capacitor 72 and resistors 58 and 70 form an impulse transmitter. A current flows through the glow-discharge tube 74 which charges the capacitor 72 for such length of time until the voltage is dropped via the glow-discharge tube 74 to the extinguishing voltage, whereafter the capacitor 72 discharges via the resistor 58 and 70. As a result, the voltage across the glow-discharge tube 74 again increases until it reaches the ignition voltage, and a new cycle is initiated. The individual current surges can be registered at the secondary winding of a transformer 76 provided in the supply conductor 62 at the central station 78.

If combustion gases enter the measuring ionization chamber 52, then the cold-cathode tube 56 ignites because of an increase of the starter potential and draws a current through the resistor 58. In the event the operating voltage of the cold-cathode tube 56 is larger than the ignition voltage of the glow-discharge tube 74 then the oscillations of the associated

impulse transmitter

74, 70, 72 stop. The current surge during ignition of the cold-cathode tube 56 can be employed in known manner for triggering a relay `80 or another alarm-transmitting device.

The checking operation is initiated by dropping the supply voltage 500 for a short period of time. In so doing, the capacitor 64 discharges during the reduction in voltage across the diode 68 to the new supply voltage. Now, if the supply voltage 500 is instantaneously increased again to the old value, then the diode 68 once again blocks and the capacitor 64 slowly charges via the high-ohm resistor `66. In so doing, however, the potential at the starter of the cold-cathode tube 56 initially is at an increased value determined by the capacitor 64 and the series connection incorporating the ionization chamber 52-54 and the resistor 53. The value of this potential is measured in such a manner that the coldcathode tube igntes. 'Ihe saw-tooth oscillations stop in the intact tire alarms, so that a signal only appears at the secondary winding of the transformer 76--which at the same time forms the input of a valuation circuit or device 19-when one or more re alarms have not responded. Consequently, the transformer 76 provides in such case an impulse-type OR-gate.

After completion of the checking operation, the supply voltage 500 is dropped slightly below the operating voltage of the tube 56 and thereafter slowly again increased to the full value.

-In each case, the checking operation is repeated at appropriate time intervals.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Accordingly, what is claimed is:

1. A ire alarm system comprising:

a plurality of tire alarms connected in parallel together in at least one group;

a central signal station;

conductor means connecting said central signal sta- .tion with said plurality of fire alarms, the number of said conductors being independent of the number of said re alarms of each group;

means for generating an electric test signal during an alarm checking operation;

said re alarms including means responsive to said electric test signal to produce alarm-simulating conditions;

means connecting each of said plurality of fire alarms of at least one group to said central signal station, said means including diode coupling circuit means for producing no alarm-checking response signals when all ire alarms of a group have responded to said electric test signal and producing an alarmchecking response signal when at least one re alarm of a group has not responded to said electric test signal; and

means for sensing at least one of said respective response signals.

2. A fire alarm system as claimed in claim 1, wherein said diode coupling circuit means includes diodes which are coupled .to a common conductor connected to said diode coupling circuit means and to said central signal station; said fire alarm system further including means for applying a lrst voltage to said common conductor during said alarm checking operation.

3. A re alarm system as claimed in claim 2, wherein said diodes comprise Zener diodes and wherein said first voltage is of a value less than the breakdown voltage of said Zener diodes.

4. A fire alarm system as claimed in claim 2, further including means for applying a second voltage to said common conductor during normal alarm operation, said diode coupling circuit means producing an actual alarmchecking response signal at said central signal station when at least one re alarm is actuated.

5. A re alarm system as claimed in claim 4, wherein said diodes comprise Zener diodes and wherein said second voltage is of a value greater than the breakdown voltage of said Zener diodes.

6. A re alarm system as claimed in claim 2, wherein a visual indicating element is provided for each tire alarm, said visual indicating elements being connected between said re alarms and said diodes included in said diode coupling circuit means, said visual indicating elements having a current threshold value below which they will not indicate.

7. A ire alarm system as claimed in claim 6, further including an additional voltage source, said additional voltage source being provided at said central signal station; resistance means connected between said additional voltage source and said common conductor, said resistance means limiting current flow to said visual indicating element of an actuated re alarm to a value less than the threshold value of said visual indicating element; and switch means tor short-circuiting said resistance means thus causing current to ilow to said indicating element having a value greater than said threshold value.

8. A tire alarm system as claimed in claim 2, including a source of negative voltage and means for resetting said plurality of tire alarms aftercompletion of said alarm checking operation, said means for resetting including switch means for connecting said common conductor with said source of negative voltage.

9. A re alarm system as claimed in claim 2, further including:

a positive and a negative supply conductor;

a measuring ionization chamber and a reference ionization chamber connected in series across said positive and negative supply conductors;

a eld-eiect transistor having a drain, a source and a gate electrode;

a first resistor;

a variable resistor;

means connecting said drain of said eld-eifect transistor to said negative supply conductor through said rst resistor;

means connecting said source of said field-effect transistor to said positive supply conductor through said variable resistor;

means connecting said gate of said field-effect transistor to the junction of said measuring ionization chamber and said reference ionization chamber;

a controlled rectien'having an anode, a cathode and a gate;

a second resistor;

means connecting said anode of said controlled recf References Cited tifier to said positive supply conductor through said Y UNITED STATES PATENTS second resistor; means connecting said gate of said controlled rectier 215891869 3/1952 Rum@ 340-214 to said drain of said field-effect transistor; 5 2,647,237 7/1953 Herbst 340214 means connecting said cathode of said controlled rec- 3,099,824 7/ 1963 Vitt 340-214 tier to said negative supply conductor; and 3,248,721 4/1966 Cockrell 340-214 a visual indicating element connected ibetween said 3,278,920 10/1966 Sargent 340-214 anode of said controlled rectifier and the associated 3,422,414 1/1969 Margreiter AF 340 214 diode of said diode coupling circuit means. 10 10. A re alarm system as claimed in claim 9, further THOMAS B HABECKER, primal-y Examiner including a capacitor in parallel with said reference ionization chamber and wherein said electric test signal U.S. Cl. X.R. comprises a reduction in potential of said positive supply 340-228 conductor.