Alarm devices for interconnected multi-device systems

Alarm devices are provided with circuit means for permitting interconnection of the alarm devices into an alarm system in which each of the alarm devices continually senses for an adverse condition, such as smoke in a smoke detection alarm system, and in which all of the alarm devices signal an alarm in response to the sensing of an adverse condition. The interconnections for the alarm devices are such that the alarm devices not directly coupled to operative sources of electric power will, nevertheless, sense adverse conditions and signal alarms when any one of the alarm devices senses an adverse condition.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to alarm devices for use in interconnected alarm 
systems and, more particularly, to alarm devices and systems in which an 
adverse condition such as smoke sensed by one or more of the devices 
causes all of the interconnected devices to signal an alarm. 
2. Description of Prior Art 
Alarm devices such as smoke or intrusion alarm devices are often used to 
signal the existence of an adverse condition. Such devices are typically 
self-contained in that the sensing apparatus and the alarm apparatus are 
combined in a single unit which may be placed wherever required to protect 
the premises. In the case of smoke detection, it is common to locate a 
number of smoke alarm devices throughout the premises. For example, in a 
typical home installation, one unit may be placed in the bedroom area 
while other units may be located in the living area, the garage, and the 
basement. If the units are totally self-contained, only the unit sensing 
an adverse condition will signal an alarm. This is undesirable under 
certain conditions in that the alarm signalling the alarm may be located 
where it cannot be seen or heard, e.g., people sleeping in the bedroom 
area may not be awakened by a horn alarm sounding in the basement area. To 
overcome this problem, it has been suggested in the past that alarm 
devices be provided with remote alarms, thereby substantially extending 
the warning range of the detection equipment. In this respect, a smoke 
alarm located in a basement area may be provided with an auxiliary alarm 
in a bedroom area. While this certainly extends the warning range of the 
detection equipment, it has a disadvantage of adding significantly to the 
cost of the overall system since it requires multiple alarm devices for 
detection in a single location. Furthermore, the resulting system is 
totally disabled in the event that the power supply to the primary unit is 
disrupted for some reason. 
The cost problem can be largely overcome by connecting the individual alarm 
units in parallel such that an adverse condition sensed by any one of the 
alarm devices will produce a warning signal on all of the interconnected 
units that are individually connected to operative sources of electric 
power. In such systems, however, an alarm device not connected to an 
operative source of electric power will neither sense for the presence of 
an adverse condition nor signal an alarm in response to the sensing of an 
adverse condition by another of the interconnected units. If, for example, 
in a home installation of a smoke detection system, a detector in a 
basement detects smoke, an interconnected detector located in the bedroom 
area will sound an alarm only if the bedroom unit is connected to an 
operative source of electric power. Similarly, the bedroom unit under such 
circumstances will not sense for smoke. 
SUMMARY OF THE INVENTION 
It is therefore a primary object of the invention to provide an improved 
alarm system for sensing the adverse conditions at a number of locations 
and for operating all of the alarms in response to the sensing of an 
adverse condition at only one location. 
Another object of the invention is to provide alarm devices which may be 
used individually or interconnected into an alarm system in which units 
not directly coupled to operative sources of electric power nevertheless 
sense for adverse conditions and signal alarms. 
Yet another object is to provide alarm devices for use in an interconnected 
alarm system in which units not directly coupled to operative sources of 
electric power will nevertheless signal an alarm in response to the 
sensing of an adverse condition by another of the interconnected alarm 
devices. 
A still further object of the invention is to provide an improved smoke 
detection alarm system having operating characteristics as set forth by 
the foregoing statements of objects. 
Briefly stated, in carrying out the invention in one form, an alarm device 
adopted for use in a multidevice alarm system includes terminal means for 
connection to a source of electric power, an alarm circuit coupled to the 
terminal means and including a normally conductive alarm means and a 
normally non-conductive (OFF) switching means connected in series, energy 
storage means coupled to the terminal means and connected in series with 
the alarm circuit, control means coupled to both the terminal means and 
the switching means for sensing an adverse condition and supplying an 
output signal to the switching means when an adverse condition is sensed. 
The switching means is selected such that it switches to its conductive 
state only while an output signal is being supplied to it by the control 
means. Circuit means are connected to the switching means so as to permit 
the interconnection of the switching means in parallel with the switching 
means of other alarm devices. In this manner, a source of electric power 
connected to at least one interconnected alarm device will charge the 
energy storage means of all of the interconnected alarm devices. Also in 
accordance with the invention, each energy storage means has sufficient 
energy storage capacity to operate the associated alarm means for a 
discernible period of time. As a result, all of the interconnected alarm 
devices will operate in response to the sensing of an adverse condition by 
any one of the interconnected alarm devices. 
By a further aspect of the invention, the energy storage means is a 
capacitor, and the alarm device includes power supply means for converting 
alternating current electric power to direct current electric power. By 
still further aspects of the invention, the control means comprises at 
least one detection element for detecting the presence of combustion and 
an electronic control circuit for producing the output signal. The 
switching means is a semi-conductor element, preferably a silicon 
controlled rectifier (SCR), having a control input connected to the 
control circuit for receiving output signals therefrom.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring first to FIG. 1, an alarm system 10 having four alarm devices 12 
interconnected in accordance with the invention is illustrated. Each of 
the alarm devices 12, which may be a smoke alarm or an intrusion alarm or 
the like, is provided with a power cord 14 which may be connected to a 
suitable source of electric power, such as normal house current. The alarm 
devices 12 are interconnected by leads 16 and 18 in a manner hereinafter 
described. The function of the leads 16 and 18 is to assure that the 
entire alarm system 10 remains operative so long as a single one of the 
alarm devices 12 is operatively connected to a source of electric power. 
More particularly, this means that each of the alarm devices 12 will 
provide sensing for an adverse condition, such as smoke, even though only 
one of the devices is connected to a source of electric power. 
Furthermore, upon the sensing of the adverse condition by any one of the 
alarm devices, whether or not it is directly connected to a source of 
electric power, all of the alarm devices will signal an alarm. 
Referring now to FIG. 2, two of the alarm devices 12 are disclosed in 
somewhat greater detail, the second one of the alarm devices and its 
components being identified by primed numerals for convenience. As 
illustrated, each of the alarm devices 12 has a pair of terminals 20 
through which internal electric power may be supplied to the device. As 
indicated above, their power is preferably alternating current electric 
power. The terminals 20 are coupled through a power supply 22, which 
converts alternating current supplied to the terminals 20 to direct 
current power, to an alarm circuit comprising a normally conductive horn 
24 and a normally non-conductive (OFF) semi-conductor switch 26 preferably 
a silicon controlled rectified (SCR) as shown. The terminals 20 are 
additionally coupled to a capacitor 28, which also forms a series circuit 
with the horn 24 and the switch 26. A control circuit 30 is also coupled 
to the terminals 20, the function of the control circuit 30 being to sense 
for an adverse condition, such as smoke, and to produce an output signal 
on line 32 whenever smoke is sensed. The gate of the SCR 26 is connected 
to receive output signals over line 32 and to maintain the SCR 26 in its 
conductive (ON) state so long as an output signal is produced by the 
control 30. 
The general mode of operation of the alarm system 10 will not be described 
with reference to FIGS. 1 and 2. If each of the power cords 14 is 
connected to a suitable source of alternating current electric power, the 
power supply 22 of each device 12 will provide direct current electric 
power of suitable voltage, such as 10 volts, to the capacitor 28, the 
alarm circuit comprising the horn 24 and the SCR 26, and the control 
circuit 30. So long as an adverse condition is not sensed by the control 
circuit 30 of any one of the units 12, all of the SCR's 26 will remain OFF 
and no alarm signal will be produced. If, however, circuit 30 of any one 
of the alarm devices 12 produces an output signal on line 32 indicative of 
the presence of an adverse condition, the associated SCR 26 will turn ON, 
thereby closing the alarm circuit of that alarm device and causing its 
horn 24 to sound. In addition, the horns 24 of each of the other 
interconnected devices 12 will also sound. This will be better understood 
from consideration of the two alarm devices 12 and 12' illustrated by FIG. 
2. Thus, if the control circuit 30 of the alarm device 12 senses an 
adverse condition, it will produce an output signal on line 32 and turn ON 
the SCR 26. The turning ON of the SCR 26 closes the alarm circuit coupled 
to the terminals 20 through the direct current power supply 22 such that 
current flows through the alarm circuit so as to sound the horn 24. The 
turning ON of the SCR 26 also closes a circuit across the output of the 
power supply 22'. As a result, both the horn 24 and the horn 24' operate 
with the SCR 26 carrying the total current, SCR 26' remaining OFF. 
Similarly, the alarms of all of the units 12 of FIG. 1 will sound whenever 
one units senses an adverse condition, the total alarm current flowing 
through the SCR 26 of the unit which senses the adverse condition. The 
SCR's 26 must therefore be selected for the maximum possible current load. 
Still referring to FIG. 2, let it now be assumed that alarm device 12' is 
not being supplied by the power supply 22' with direct current power. This 
could occur if the terminals 20' are not connected to a suitable source of 
electric power or if the power supply 22' is for some reason defective or 
otherwise disabled. In the absence of an adverse condition at both devices 
12 and 12', the power supply 22 will charge the capacitor 28' through horn 
24, line 16 and horn 24' to a voltage within the normal operating range. 
Since the capacitor 28' maintains a normal operating voltage, the control 
circuit 30' will be operative even though the power supply 22' is not 
operative. If an adverse condition should be sensed by the device 12', an 
output signal will be produced on line 32' and the SCR 26' will turn ON. 
When this occurs, the capacitor 28' discharges through the horn 24' and 
the SCR 26', thereby sounding the horn 24', the control circuit 30' will 
become inoperative upon discharge of the capacitor 28' , the result being 
the disappearance of the output signal on line 32' (even if the adverse 
condition continues), the switching OFF of the SCR 26', and the silencing 
of the horn 24'. In accordance with the invention, it is essential that 
the energy storage capacity of the capacitors 28 be sufficient to operate 
the associated alarm 24 for a discernible period of time, say one to two 
seconds, so that a meaningful warning of an adverse condition will be 
provided. 
If the control circuit 30' senses an adverse condition and turns ON the SCR 
26' and the horn 24' for the period of time required to discharge the 
capacitor 28; the horn 24 of the other alarm device 12 will also sound 
since, for the time SCR 26' is ON, a circuit will be completed across the 
output of power supply 22 through the horn 24, line 16, SCR 26', and line 
18. As soon as SCR 26' turns OFF, both horns 24' and 24 will stop 
sounding. As soon as SCR 26' turns OFF, however, the capacitor 28' will 
again be charged by the power supply 22, and the horn 24 and 24' will 
thereafter again be sounded (assuming that the control circuit 30' still 
senses an adverse condition). 
Let is now be assumed that only the alarm device 12 of FIG. 2 is connected 
to an operative source of electric power. As in the previous example, both 
the device 12 and the device 12' will be capable of sensing for an adverse 
condition. If, however, it is the powered unit 12 that senses the adverse 
condition, the operation is somewhat different than that of the previous 
example in which the adverse condition was sensed by the non-powered unit. 
If the powered unit senses the adverse condition, an output signal on line 
32 will turn ON SCR 26, which will remain ON so long as the adverse 
condition is sensed by the control circuit 30 (continuously). As a result, 
the horn 24 will sound continuously since the horn 24 and the SCR 26 from 
a closed circuit across the power supply 22. When the SCR 26 first turns 
ON, the capacitor 28' of the device 12' will discharge through the horn 
24', line 16, SCR 26, and line 18 to sound the horn 24' for the 
discernible period of time that it takes to discharge the capacitor 28'. 
Following discharge, the capacitor 28' will not recharge until the SCR 26 
turns OFF. Since the SCR 26 remains ON for the duration of the adverse 
condition, the horn 24' will therefore sound only one time. 
From the foregoing, it will be seen that the entire alarm system 10 will be 
operative so long as at least one of the alarm devices 12 is connected to 
an operative source of electric power. The mode of alarm signaling differs 
somewhat in accordance with the power and sensing characteristics of the 
system. Specifically, if all units are powered and the adverse condition 
is sensed by one or more units, all units will produce an alarm signal 
which continues as long as the adverse condition is sensed. If one or more 
units are powered and the adverse condition is sensed by a non-powered 
unit, all units will produce an intermittent alarm signal. If one or more 
units are powered and the adverse condition is sensed by a powered unit, 
all of the powered units will produce a continuous alarm signal and all of 
the non-powered units will produce a single relatively short initial alarm 
signal. 
Referring now to FIG. 3, a smoke detector 40 incorporating the present 
invention is illustrated, the smoke detector 40 being capable of operation 
as a single unit or as an alarm device 12 in an alarm system 10 as 
illustrated by FIGS. 1 and 2. The smoke detector 40 includes a pair of 
terminals 42 connected to a direct current power supply comprising a power 
transformer 46 and a diode 50. The terminals 42 are connected to the 
primary winding 44 of the transformer 46, and the secondary winding 48 is 
connected in series with the diode 50 to provide direct current output 
power when a switch 52 is closed (shown open). If, during normal 
operation, the switch 52 is opened; the unit 40 will not be operative in 
accordance with the invention whether or not it is interconnected in an 
alarm system in which other units are powered. Switch 52, connected to the 
cover interlock, allows the owner to disconnect a false-alarming unit from 
the system. By having lead 18 connected intermediate the switch 52 and the 
secondary winding 48, all interconnected units will be silenced when the 
switch 52 of the unit that is false-alarming is opened by removing the 
cover. If the cover of any of the other units is removed, the opening of 
the associated switch 52 will only silence the unit that is opened. The 
false-alarming unit and all of the other interconnected units will 
continue to sound an alarm. In this manner, it is relatively easy to 
identify and remove a false-alarming unit from the interconnected system. 
So long as the switches 52 of the other units are not opened, they will 
continue to operate to detect smoke. 
A zener diode 54 is connected across the output of the power supply to 
maintain a substantially fixed supply voltage, typically 10 volts. In 
accordance with the previous description of FIGS. 1 and 2, the alarm 
device 40 includes energy storage means in the form of a capacitor 60 
connected across the power supply, an alarm circuit comprising a horn 62 
and an SCR 64 connected across the power supply, and a control circuit 
connected across the power supply, the control circuit being identified by 
the circuitry enclosed within the outlined block 66. The output of the 
power supply is also connected across the series circuit comprising a 
resistor 67 and a light-emitting diode (LED) 68, which glows to indicate a 
power ON condition where power is being supplied by the power supply; the 
LED 68 will not glow when the switch 52 is open but will glow when switch 
52 is closed and operating power is being supplied by another 
interconnected smoke alarm. 
Referring now to FIG. 3, a smoke detector incorporating the present 
invention is illustrated, the smoke detector being suitable for use as one 
of the alarm devices 12. The control circuit 66 includes an ionization 
chamber 70 and a resistor 72 connected in series across the power supply. 
The chamber 70 is open to the atmosphere and its interior is thus freely 
accessible to air and airborne products of combustion or aerosols. For 
reasons which will become apparent as this description proceeds, the 
chamber 70 is a measuring chamber and the resistor 72 is a substantially 
fixed reference. 
As illustrated, the measuring chamber 70 includes a pair of spaced-apart 
electrodes 76 and 78 and a source 80 of alpha radiation such as Americium 
241 for ionizing the air in the interior space between the electrodes 76 
and 78. An ion current will flow between the electrodes 76 and 78 when a 
voltage is applied thereacross. If aerosols or products of combustion 
enter the interior space of the chamber 70, the current flow will be 
reduced if the voltage across the electrodes is maintained constant. In 
other words, the introduction of combustion aerosols increases the 
electrical resistance of the chamber 70, the amount of resistance change 
being indicative of the amount of combustion products present in the 
chamber 70. Since the zener diode 54 maintains a fixed voltage and the 
resistor 72 has a substantially fixed resistance, the introduction of 
smoke or other products of combustion into the chamber 70 will cause a 
reduction in the voltage at junction 82. 
A MOSFET field effect transistor 86 of the enhancement type has its gate 87 
coupled to the junction 82 intermediate the chamber 70 and the resistor 
72. The source 88 of the MOSFET 86 is connected to a relative positive 
voltage through the resistive network comprising resistors 90 and 92, and 
the drain 94 of the MOSFET 86 is connected to a relative positive voltage 
through the resistive network comprising resistors 90 and 92, and the 
drain 94 of the MOSFET 86 is connected through resistor 96 and capacitor 
98 to the negative output of the power supply. The drain 94 of the MOSFET 
86 is also connected to the gate of the SCR 64 through junction 100. 
The normally conductive horn 62 is illustrated in more detail by FIG. 4, 
the horn being represented by a coil 100 in series with the SCR 64 and a 
pair of normally closed contacts 112 mechanically connected to the horn 
mechanism for being rapidly opened and closed during sounding of the horn. 
A resistor 114 and a capacitor 116 are provided in parallel across the 
horn coil 54 to prevent large inductive spikes, which could damage other 
circuit components, from being generated by the coil when the horn is 
sounding. 
When there is no smoke or other airborne products of combustion within the 
measuring chamber 70, the voltage at junction 82 relative to the voltage 
on the source 88 is less than the threshold voltage of the MOSFET 86. 
Since the MOSFET 86 is of the enhancement type, this means that the MOSFET 
is essentially OFF (not conducting) under these conditions. Since the 
MOSFET 86 is essentially OFF, there is substantially no current flow 
through the resistor 96 and the junction 100 is maintained at a voltage 
substantially identical to that of the negative output of the power 
supply. As a result, the SCR 64 is also maintained in its OFF or 
non-conductive condition, and the horn 62 is not sounded. 
If smoke or other combustion products enter the chamber 70, the voltage 
across the chamber 70 and the source-to-gate voltage of the MOSFET 86 will 
increase and progressively turn on the MOSFET 86. Once the MOSFET 86 
reaches a preselected conduction level, current flow through the resistor 
96 causes the voltage at junction 100 to increase sufficiently to turn on 
the SCR 64 and sound the horn 62. The horns of any smoke detectors 
interconnected by lines 16 and 18 will also be turned on in the manner 
described above. If the smoke level in the chamber 70 subsequently drops 
below the preselected trigger point, the voltage at the junction 82 will 
rise, and the source-to-gate voltage on the MOSFET 86 will therefore fall 
below the level required to maintain the preselected level of conduction 
through the MOSFET 86 and the resistor 96. This means that the voltage at 
junction 100 will also fall and the SCR 64 will turn OFF when its current 
falls below its holding level (due to periodic opening during horn 
operation of the normally closed contacts 120). This in turn will cause 
the horn 62 and any interconnected horns to turn off. 
It will be noted that the smoke detector 40 is capable of functioning as an 
individual smoke detector not connected to any other alarm device. To 
function as an individual unit, the terminals 42 must, of course, be 
connected to a suitable source of electric power. Alternatively, the lines 
16 and 18 of two or more units may be interconnected into an alarm system 
as described above with respect to FIGS. 1 and 2. In this latter case, one 
or more of the detectors must be connected to a source of electric power 
in order for all of the interconnected units to function in the manner 
described above. 
As described herein, the terminals 42 of the smoke detectors 40 are adapted 
to be connected to a source of alternating current electric power, the 
power supply including the power transformer 46 and the diode 50 
converting the alternating current input into a lower voltage direct 
current output. It would, of course, be possible to eliminate the power 
supply, connecting the terminals 42 to a direct current source such as a 
battery. When interconnected into an alarm system, however, such an 
arrangement would not be entirely satisfactory under all conditions since 
the life of all of the batteries would be tied to the life of the weakest 
battery in the system. For this reason, it may be desirable to 
interconnect battery-operated alarm devices in the manner disclosed and 
claimed by copending patent application Ser. No. 968,426 entitled "Alarm 
Devices for Interconnected Multi-Device Systems", filed on Dec. 11, 1978, 
and assigned to the assigned hereof, General Electric Company. 
Smoke detectors having the circuitry of FIGS. 3 and 4 have been built and 
successfully operated in interconnected alarm systems. These smoke 
detectors 40 include a measuring chamber 70 having a 2 microcurie source 
of Americium 241, a Phillips BZX79010 zener diode 54 providing a voltage 
of 10 volts, a special MOSFET 86, a GEC103B SCR 64, and a capacitor 60 
having an energy storage capacity of 330 microfarads, with a 0.04 
microfarad capacitor 116 and a resistor 114 having a resistance of 1,000 
ohms and the diode 50 is an A14A rectifier. The resistance values of the 
resistors are as follows: 72-100,000 megohms; 96-15,000 ohms; 90 and 
92-5,000 ohm potentiometer; 67-1,500 ohms; 99-470 ohms; and the LED 68 is 
a XCITON SC111. It has been found that as many as ten smoke detectors may 
be interconnected with above components such that all alarms sound when 
smoke is detected by a single detector. Under such conditions, the SCR 64 
of the unit sensing smoke must carry currents of up to 2.5 amps during 
start-up and up to 0.6 amps during steady-state alarm conditions. 
From the foregoing, it will be seen that this invention provides alarm 
devices which may be used individually or interconnected into an alarm 
system in which units not directly coupled to operative sources of 
electric power nevertheless (1) sense for adverse conditions and signal 
alarms and (2) signal an alarm when an adverse condition is sensed by 
another unit. 
While the invention has been particularly shown and described with 
reference to a preferred embodiment thereof, it will be understood by 
those skilled in the art that various changes in form, details, and 
application may be made therein without departing from the spirit and 
scope of the invention. Accordingly, it is intended that all such 
modifications and changes be included within the scope of the appended 
claims.