US 3530450 A
A fire alarm system including a plurality of fire alarms arranged in groups. Alarm-simulating 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 circuit coupling the fire alarms together.
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Description (OCR text may contain errors)
Sept. 22, 1970 B. WALTH 5 WITH MONI ARD EI'AL 3,530,450 TORING DEVICE FOR FIRE O A CENTRAL STATION FIRE ALARM SYSTEM ALARMS CONNECTED IN GROUPS T Filed May 4. 1967 Fig.1
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counterlonizah'oh/ Chambers United States atent ii ce 3,530,450 Patented Sept. 22, 1970 US. Cl. 340214 11 Claims ABSTRACT OF THE DISCLOSURE A fire alarm system including a plurality of individual fire alarms arranged in groups and connected to a central station. In response to a condition test signal, the fire alarms sequentially produce signals indicative of their condition which signals are counted in a system evaluation means which determines which fire alarm of a group is defective.
BACKGROUND OF THE INVENTION The present invention relates to an improved fire alarm system comprising a central signal station to which electric fire 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 fire alarms. Furthermore, the inventive fire alarm system additionally includes an apparatus for producing electrical test signals by means of which alarm-simulating conditions are produced at the fire alarms which, in turn, bring about an electrical change in condition at an intact fire alarm, and further, the inventive system includes an apparatus for evaluating such changes and conditions.
In fire alarm installations, there generally exist the requirement of checking the operational reliability of the individual fire alarms at regular intervals. To this end, and in accordance with a workable method, alarm-simulating 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 uneconomical, if the installation consists of a larger number of fire alarms, for instance, one hundred fire 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 fire alarms through use of special electronic means, and to check the response conditions of all fire alarms at the central station. The difiiculty with such method, above all, resides in the reliable determination of whether all fire alarms of a group have actually responded.
In a known system, a separate conductor is led from each fire 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 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 fire alarm system.
Consequently, it is desirable to provide a monitoring device in which the number of conductors leading from the central station to the fire alarms is independent of the number of connected fire alarms. In a known arrangement of this type, all of the fire 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 fire 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 effect upon the choice and dimensioning of the conductors, the network devices, the emergency tower groups, etc., this arrangement is limited to groups having relatively few fire alarms. Because of the diversity of the electrical characteristics of the structural elements in the fire alarms as well as because of the limited measuring accuracy during comparison of the total current with the reference value based upon an analagous measurement, this technique is unreliable with a larger number of fire alarms and often times results in false alarms.
SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide an improved monitoring device for a fire alarm system of the previously mentioned type in which it is possible to reliably check or monitor an optional large number of fire alarms per group.
It is another object of the present invention to provide a monitoring system which may be installed in existing fire 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 means are provided at the fire alarms which, during the checking operation, bring about a response of the individual fire alarms which is staggered in time. Further, the apparatus for evaluating the response conditions of the individual fire alarms determines by means of a counting operation if all fire alarms of a group have responded.
It will be understood that with the description to follow two different embodiment-s of the invention, as well as further inventive features will be described with greater detail in conjunction with the individual figures of the drawing. In this regard, it should be understood that while the fire alarm installations are, in each case, equipped with ionization fire alarms, there could also equally well be employed optical plane detecting alarms, smoke detecting alarms or temperature detecting alarms.
BRIEF DESCRIPTION OF THE DRAWING response of the fire alarm is obtained by time-delay elements:
DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawing, it will be unedstood that the fire alarm 17 depicted in FIG. 2 consists of two ionization chambers 1 and 2, the air content of which can be rendered completely or partially conductive by radioactive preparations as is known in the art. Further, this fire alarm 17 comprises a switch element 3, which in this instance is formed by a field-effect transistor 3. Ionization chamber 1 functions as a measuring chamber, whereas ionization chamber 2 is employed as. a reference chamber and can also be replaced by a high-ohm resistor or an equivalent high-ohm element. Likewise, it is possible to use instead of the field-effect transistor 3, a different switch element with high-ohm input resistance, for instance another semiconductor device or a cold cathode tube.
The ionization chambers 1 and 2 are connected in series with respect to one another and are coupled via the conductors 10 and 20, respectively, with the central station 18 and, at such location, are connected with the voltage source 100*. The gate of the field-effect transistor 3 is disposed at the point of juncture or connection of both ionization chambers 1 and 2. Its anode is coupled via a resistor 5 with the negative feed conductor 20, and its cathode via a resistor 5a with a positive feed conductor 10. The resistor 5a is, at the same time, a part of a voltage divider circuit incorporating the resitor 5a and the Zener diode 4, wherein the Zener voltage and the potential at the gate of the field-effect transistor 3 is selected in such a manner that this field-effect transistor 3 blocks during the normal operating condition.
The anode of the field-effect transistor 3 is coupled with the control gate of a control rectifier 6 (SCR), the cathode of which is connected to the negative feed conductor 20 and the anode of which is connected to the positive feed conductor 10 through the voltage divider incorporating the resistor 13 and the resistor 14. The indicating lamp 12 is arranged parallel to the resistor 13, and a Zener diode is connected parallel to the resistor 14. Hence, as the field-effect transistor 3 blocks during the normal operating condition, there is no voltage drop at the resistor 5, and the control rectifier 6 is likewise blocked.
Now, if combustion gases enter the measuring chamber 1, then the voltage between the cathode and the gate of the field-effect transistor 3 exceeds its response threshold value, whereby the field-effect transistor conducts and brings about a voltage drop at the resistor 5. Now a voltage appears between the gate and the cathode of the control rectifier 6 which causes same to ignite. As a result, the anode current essentially flows through the Zener diode 15 and the indicating lamp 12. In the event of a defect in the indicating lamp 12, the current passes through the resistor 13 and the circuit remains closed. The change in current appearing in the supply conductors 10 and 12 are employed at the central station 18 for triggering a relay A or another known alarm device.
The displacement of the potential at the gate of the field-effect transistor 3 which is brought about by the entry of combustion gases into the measuring chamber 1 also can be realized for checking or monitoring purposes in that, the potential of the supply conductor 10 is appropriately reduced. Such can be, for instance, realized by introducing a Zener diode '8 in the supply conductor within the central station 18, whereby the Zener diode 8 during normal operation is short-circuited by means of a switch 7. The response of the field-effect transistor 3 and the controlled rectifier 6 take place in the same manner as in the case of an actual alarm, with the exception that the Zener diode 15 now does not ignite because of the lower supply voltage, so that the anode current flows through the resistor 14 and is strongly reduced in comparison to the anode current in the event of an actual alarm. This current reduction is permissible for the reason that the fire alarm current which fiows during the chec king operation, as will be explained hereinafter, need not actuate any relay or similar alarm device. Since the further intact fire alarms of the group, which are connected parallel to the illustrated fire alarm 14 at the supply conductors 10 and 20', also are caused to respond during the checking operation, it is possible to limit, in this manner, the value of the total current in the supply conductors such that the total current is of the order of magnitude of the current which flows in the case of an actual alarm upon response of a single fire alarm. The normal anode current of the controlled rectifier 6 of the individual fire alarms can have relatively great tolerances, since the system evaluation does not take place in the previously utilized analog manner, rather it takes place in accordance with the invention in a digital manner.
Continuing, it will be recognized that at the central station 18, the primary winding of a transformer 11 is connected in the supply conductor 10, and the secondary winding of the transformer is coupled to the input of the evaluation circuit 19. Hence, during response of the individual controlled rectifiers, pulse-shaped signals appear at the input of the evaluation circuit. 19*, which characterize in binary form the response condition of a fire alarm (impulse: fire alarm has responded; no impulse: fire alarm has not responded). The evaluation of the binary signals takes place digitally in the form of a counting operation, whereby after a certain period of time the counting condition of the evaluation device 19 is read and compared with a reference value.
The capacitor 9 arranged in parallel to the reference chamber 2 assures that it is possible to freely select a staggering or sequencing of the periods of response time of the individual fire alarms. This sequencing occurs as follows. The potential of the conductor 10 is lowered by opening the switch 7, but the potential at the gate of the field-effect transistor 3 remains contsant for a moment. The period of time in which the capacitor 9 discharges to the new lower potential via the high-ohm ionization chambers and via the gate-anode path of the field-effect transistor is adjustable and can be selected by suitable dimensioning of the value of capacitor 9. Each capacitor in the individual fire alarms can be selected to have a graduated capacitance thus effecting a true sequential response through all fire alarms of a group.
Under certain circumstances, it is also possible to dispense with the capacitor 9, whereby the natural response delays of the individual fire alarms can be employed. In
- order to eliminate accidental coincidence with respect to the release capacity of the counter with respect to time, the checking operation in each instance can be carried out two or more times in succession.
The switch 16 which interrupts the current supply for a short period of time only serves to reset or return the fire alarm after a checking or monitoring operation has been completed.
Instead of simultaneously delivering the alarm-simulating conditions to all fire alarms and bringing about the staggered response of the fire alarms by delay elements, it is also possible to achieve in accordance with the embodiments of FIG. 1, a sequential response of the individual fire alarms. More precisely, in such case only a first fire alarm has delivered thereto from the central station alarm-simulating conditions, and the response of this fire alarm is used as the criterion for providing alarmsimulating conditions for the next fire alarm. In this manner, all fire alarms of a group are checked in series.
A single fire alarm of the n fire alarms depicted in FIG. 1 and represented by numeral M M M,,, for instance the fire alarm M again consists of two ionization chambers 104 and 106. The point of connection of these two ionization chambers 104 and 106 is conducted or lead to the starter electrode of a cold-cathode tube 108. The cold-cathode tube 108 (switch triode) in this case replaces the field-effect transistor 3 of FIG. 2. The cathode of the cold-cathode tube 108 is connected by a diode 110 to one current conductor 112, whereas the anode is coupled via a resistor R, to the other supply conductor 114. The cathode of the cold-cathode tube 108 is furthermore con ditionally connected by means of a capacitor 116 directly with the supply conductor L. The ionization chamber 104, functioning as a reference chamber, is situated between the starter electrode and anode of the cold-cathode tube. Each measuring ionization chamber 106 is connected via a separate conductor 118 with the cathode of the previous tube 108. In principle, all of the fire alarms are of identical construction. The only exception is the first fire alarm M in which the measuring chamber MK is directly connected to the supply conductor 112.
During the normal operating condition, the switch 120 in the central station SZ of the supply line 112 is closed, so that the fire alarms M M M are directly connected to the supply voltage 122. The capacitors 116 are charged via the diode 110 to the supply voltage. The coldcathode tubes are in the blocked condition. Now, if combustion gases enter one of the measuring chambers 106, there appears at the starter electrode of the corresponding cold-cathode tube 108 an increased potential whereby the tube responds and draws a current via the resistor 124 and the supply conductor 114. This current causes an alarm-triggering device at the central station SZ to respond, for instance, a relay. Only a minimum voltage increase appears across the diode 110 of the fire alarm M which has responded, so that the subsequent fire alarms M remain in the rest condition.
The checking operation is initiated by Opening the switch 120. The potential of the supply conductor 112 which now appears at the tap of a voltage divider circuit, namely, the resistor 126 and the resistor 128, is increased in such a manner that the cold-cathode tube 108 ignites because of the appropriate increase of the starter potential. The individual diodes 110 of each alarm are prebiased in the blocking direction. As a result, the increase in the potential of the conductor 112, in the first instance, does not have any effect upon the remaining fire alarms M M Now, a current flows in the closed circuit of the fire alarm M which comprises the capacitor 116, the conducting cold-cathode tube 108, and the resistor 124. This current discharges the capacitor 116 to the operating voltage of the tube 108. In so doing, the potential at the cathode of the cold-cathode tube 108 reaches the potential of the conductor 112, so that the diode 110 conducts and draws a current through the primary winding of a transformer 130 provided in the central station SZ at the supply conductor 114. In a manner analogous to the apparatus of FIG. 2, there appears at the secondary winding of the transformer 130, which again is situated at the input of the evaluation device 19, an impulse which represents a binary signal characterizing the response condition of the fire alarm M Also, in this case, the evaluation device 19 contains a digital counter at which the numeral 1 appears upon the current of the first impulse.
Now, at the same time, the potential of the supply conductor 112 is supplied via the conductor 118 to the one electrode of the next measuring chamber 106. The corresponding increase in potential at the starter electrode of the cold-cathode tube 108 causes such to conduct whereby after discharge of the capacitor 116 via the transformer 130, a second impulse appears at the input of the evaluation device 19.
Now, if one of the n fire alarms becomes non-functional because of a disturbance, then, on the one hand, a potential increase in the next fire alarm is suppressed, whereby the checking operation is temporarily completed, and, on the other hand, further counting impulses fail to arrive at the evaluation device 19. The counting condition which can be read in this case at the same time pinpoints the faulty fire alarm.
On the other hand, if all of the fire alarms are functional, then the count condition at the evaluation device 19 achieve a prescribed digital reference value. A further indication that all fire alarms of a group have responded resides in connecting a relay 132 in series with the capaci- 6 tor C of the last fire alarm M,,. This relay 132 is energized for a short interval upon response of the last fire alarm and closes a work contact 134. This work contact 134 can be, for instance, employed for triggering an appropriate indicating device at the central station.
If the possibility of localizing or pin-pointing a single faulty fire alarm is to be dispensed with, then it is also possible to do away with the transformer 130 and to connect the work contact 134 in the depicted manner as a shortcircuit connection between both of the supply conductors 112 and 114. Then a high current flows for a short period of time through the resistor 128, the diode and the alarm relay 136, which is caused to respond and indicate during the checking or the monitoring operation the proper functioning of all fire alarms. If the resistor 128 is dimensioned in such a manner to be large enough so that the short-circuit current no longer brings about energization of the relay 136, then an increase of the voltage at the test point or location 140 can be used as the criterion for the response for the relay 132 and, therefore, the last fire alarm M In this instance, the voltage increase at point 140 simultaneously brings about switching-off of the responsive fire alarm, so that after termination of the checking operation, only the switch has to be closed in order to again place the installation in normal operation. Of course, the transformer 130 and the relay 132 can also be combined with one another.
The checking operation which can last for up to several seconds, is repeated at appropriate time intervals.
The foregoing detailed description has been given for clearness of understanding and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art. Furthermore, it should be apparent from the foregoing detailed description that the objects set forth at the outset to this specification have been successfully achieved.
Accordingly, what is claimed is:
1. A fire alarm system comprising:
a plurality of fire alarms connected together in groups;
a central signal station;
conductor means connecting said central station with said plurality of fire alarms means, the number of said conductor means being independent of the number of said fire alarms;
means for generating an electric test signal;
said fire alarms including means responsive to said electric test signal to produce alarm-simulating conditions in a time sequential manner; and
means for evaluating said alarm-simulating conditions of each of said plurality of fire alarms, said means for evaluating including a counting means for counting said sequence of alarm-simulating conditions to determine whether all fire alarms of a group have responded.
2. A fire alarm system as claimed in claim 1, wherein a series connection exists between each fire alarm of each group, said fire alarms including means for transforming alarm-simulating conditions of a fire alarm into binary signals, said means for transforming also simultaneously bringing about the alarm-simulating condition in the next successive fire alarm to thus produce said time sequential response to said electric test signal.
3. A fire alarm system as claimed in claim 2, wherein said binary signals comprise stepwise current increases at said central signal station, said central signal station including means for differentiating said current increases into impulses, said means for evaluating including a digital counter.
4. A fire alarm system as claimed in claim 2, further including a power supply having positive and negative supply conductors, and wherein said fire alarms comprise:
a measuring ionization chamber;
a reference ionization chamber connected to said measuring ionization chamber;
7 a cold-cathode tube having anode, cathode and starter electrode; a resistor; a capacitor; a diode;
means connecting said measuring ionization chamber and said reference ionization chamber across said power supply;
means including 'said resistor connecting said anode electrode to said positive supply conductor;
means including said capacitor connecting said cathode electrode to said positive supply conductor;
means including said diode connecting said cathode electrode to said negative supply conductor; and,
conducting means connecting the junction of said measuring and reference ionization chambers to said starter electrode.
5. A fire alarm system as claimed in claim 4, wherein said means for generating an electric test signal which triggers the checking operation is located at said central signal station and brings about a reduction in supply voltage.
6. A fire alarm system as claimed in claim 2, wherein the last fire alarm of a group includes relay means responsive to the alarm-simulating condition produced in said last fire alarm for indicating said condition in said central signal station.
7. A fire alarm system as claimed in claim 4, wherein the last fire alarm of a group includes relay means responsive to the alarm-simulating condition produced in said last fire alarm for indicating said condition in said central signal station.
8. A fire alarm system as claimed in claim 7, wherein said relay means is in series with the capacitor of the last fire alarm, and wherein said relay means includes a work contact which is normally open and which upon response of said relay means short-circuits for a short period of time the positive and negative supply conductors.
9. A fire alarm system as claimed in claim 1, further including a power supply having positive and negative supply conductors, and wherein each of said fire alarms comprises;
a measuring ionization chamber and a reference ionization chamber connected together in series across said power supply;
a capacitor connected in parallel with said reference ionization chamber, the capacitance of said capacitor in each fire alarm being graduated; a field-effect transistor means coupled across said powe supply and including a gate electrode;
means connecting said gate electrode to the junction of said measuring ionization chamber and Said reference ionization chamber; and
wherein said means for generating an electric test signal includes means at said central signal station for dropping said supply voltage during the checking operation, whereby the response times of said fire alarms to said electric test signal is caused to be staggered. l
10. A fire alarm system as claimed in claim 9, wherein said fire alarms further include means for transforming said alarm-simulating conditions into binary signals comprising stepwise current increases at said central signal station, said central signal station including means for differentiating said current increases into impulsespsaid means for evaluating includinga digital counter.
11. A fire alarm system comprising:
a plurality of individual fire alarms connected together in groups;
a central signal station;
conductor means connecting said plurality of individual fire alarms to said central signal station;
means for generating an electric test signal for said plurality of individual fire alarms;
means included within said fire alarms responsive to said electric test signal to produce sequential condition response signals in each of said plurality of individual fire alarms; and
counting means included at said central signal station for counting each said sequential condition response signal and producing a system evaluation signal in response thereto.
References Cited UNITED STATES PATENTS 2,697,824 12/1954 Norton 340-410 3,438,019 4/1969 Gowan 340214 THOMAS B. HABECKER, Primary Examiner US. (:1. X.R. 25083.6