Single station type ionization smoke sensor
BACKGROUND OF THE INVENTION 
     The present invention relates to a single station type ionization smoke sensor consisting of an ionization-type smoke sensor, a fire alarming device and a battery-replacement alarming device, which are accommodated in a single housing and which work with one or two normal dry batteries, and particularly to a single station type ionization smoke sensor which is capable of performing these three functions using a power-supply battery which produces a voltage smaller than the voltage required for widely available ionization-type smoke sensors. 
     A conventional battery-powered smoke sensor has been disclosed, for example, in U.S. Pat. No. 4,030,086, having three functions such as detection of combustion, generation of a fire alarm, and generation of an alarm for indicating that the battery is depleted. The smoke sensor disclosed in this U.S. patent is powered by a Mallory Battery, Model No. 304116 having an initial voltage of 12.3 volts, which voltage decreases to 10.6 volts when 60% of its power is consumed. The ionization-type sensors for detecting combustion are usually supplied with a voltage higher than 9 volts. In order to drive such a conventional ionization-type smoke sensor using normal dry batteries having an initial voltage of 1.5 volts, it is necessary to use six or more such batteries occupying a space which can not be accommodated in a housing of the usually employed size. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a single station type ionization smoke sensor which is powered by a few dry batteries which supply a voltage smaller than the 9 volts which is required for energizing an ionization-type smoke sensor, and which also indicates drop of the required operation voltage, said single station type ionization smoke sensor having one electrode of the ionization-type smoke sensor connected to a terminal of a d-c power supply through a power feed conductor and the other electrode of the ionization-type smoke sensor connected through a booster conductor to one terminal of a branch resistor element which has its other terminal connected to the power feed conductor, a booster means having an input terminal connected to said booster conductor to boost the booster conductors between two resistors of said ionization-type smoke sensor and branch resistor element, a voltage detector means connected between the input terminal of said booster means and said branch resistor element, a signal transmission circuit which connects an intermediate electrode of said ionization-type smoke sensor to a fire alarm means, and means for applying the output of the voltage detector means to the signal transmission circuit. 
     Referring to the power feed conductor connected between one terminal of the d-c power supply and one electrode of the ionization-type smoke sensor, the very high impedance possessed by the ionization-type smoke sensor makes it possible to boost the voltage of a secondary conductor which branches from the power feed conductor and which is connected to the other electrode of the ionization-type smoke sensor. That is, if a resistor element is inserted in a branched portion between the secondary conductor and the power feed conductor, the resistance between the two terminals of the secondary conductor enables the voltage of the secondary conductor itself to be boosted substantially independent of the power feeding conductor. Particularly, in order to connect the power feed conductor and the secondary conductor in a branched manner, connection of a resistor and a Zener diode in series between them is recommended. If the connection point between the resistor and the Zener diode is connected to the input terminal of the voltage detector means, the voltage detector means detects the boosted voltage instead of the battery voltage. A voltage multiplying rectifier circuit REC is desirably used as a booster means. 
     According to the present invention, a household ionization-type smoke sensor employing an ionization-type smoke sensor can be operated using one or two ordinarily used dry batteries. Commonly available ionization-type smoke sensors require a power supply voltage of 9 volts to 12  volts to detect the smoke produced by a fire. To supply such a high voltage, therefore, particular batteries, such as the mercury batteries used so far, are required. Therefore, these particular batteries must be obtained when the batteries are to be renewed. Furthermore, the battery operation of ionization-type sensors of this kind should be tested once a week, and the life expectancy of the battery is desirably as long as at least one year. 
     In view of the abovementioned facts, the present invention is to provide an ionization-type smoke sensor which operates using commercially available 1.5-volt dry batteries as a power supply, which functions to indicate of the depletion of the power supply, and which can be safely used at home, having a good appearance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit diagram of an ionization-type smoke sensor according to the present invention; and 
     FIG. 2, FIG. 3 and FIG. 4 are perspective views showing in a disassembled manner the ionization-type smoke sensor according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first embodiment of the ionization-type smoke sensor according to the present invention. The symbol E represents a power supply consisting of one or two 1.5-volt dry batteries, and l 1  a conductor connected to the positive electrode of the power supply E. The negative electrode is grounded. An alarming device I, a booster circuit II, a battery capacity monitoring circuit III, an alarm energizer circuit IV, and a smoke detector V are connected between the conductor l 1  and the ground. Referring to the alarming device I, a relay contact a, and a buzzer consisting of a buzzer breaker contact point b and a coil L 3  surrounded by a dotted line B, are connected between conductor l 1  and the ground, and a capacitor C 6  and a resistor R 9  are connected in series from the connection point of the contact b and coil L 3  to ground. With reference to the smoke detector V, an outer electrode 3 of an outer ionization chamber OC is connected to the conductor l 1  via a resistor R 7 , and a test switch SW and a resistor R 8  are connected in series between the electrode 3 and ground. Further, an inner electrode 1 of an inner ionization chamber IC is connected to an output terminal R of the booster circuit via a conductor l 3 , and this terminal R is connected to the conductor l 1  via a Zener diode ZD having the polarity shown and a resistor R 10 . An intermediate electrode 2 is connected to the gate of a field effect transistor F 2  which performs a switching function. The source of field effect transistor F 2  is connected to the conductor l 1 , and the drain thereof is connected to a first input terminal of a NOR circuit N 3  of the alarm energizer circuit IV via a resistor R 15 . As is well known, the inner ionization chamber IC may be replaced by a high resistance. Referring to the alarm energizer circuit Iv, a resistor R 16  is connected between the first input terminal of the NOR circuit N 3  and ground, and a resistor R 14  is connected between the other input terminal and ground. An oscillator circuit OSC 2  surrounded by a dotted line is connected to the second input terminal of NOR circuit N 3  via a capacitor C 8  and is further connected to a connecting point Q between resistor R 10  and Zener diode ZD. 
     The oscillator circuit OSC 2  consists of a NOR circuit N 4 , inverters In 1  and In 2 , resistors R 11  to R 13  and a capacitor C 7 . The input terminal of the inverter In 1 , i.e., the input terminal of this oscillator circuit is connected to connection point Q, and the output terminal of the inverter In 2 , i.e., the output terminal of this oscillator circuit is connected to the second input terminal of the NOR circuit N 3  via the capacitor C 8 . The resistor R 11  is connected between the output terminal of the NOR circuit N 4  and the input terminal of the inverter In 1 , resistors R 12  and R 13  are connected in series between one input terminal and the output terminal of said NOR circuit, and the capacitor C 7  is connected between the output terminal of the inverter In 2  and the connection point between the resistors R 12  and R 13 . 
     With this oscillator circuit OSC 2 , when a low level input signal is fed to the inverter In 1 , its output becomes a high level signal which is fed to the NOR circuit N 4  to close it. That is, the NOR circuit N 4  always produces a low level output signal, so that the output of the inverter In 2  always becomes a high level signal; the oscillator circuit does not oscillate. When the input turns from a low level to a high level, the inverter In 1  produces a low level output signal, causing the NOR circuit N 4  to open so that the oscillator circuit oscillates; the inverter In 2  alternately produces a high level signal and a low level signal. 
     In the alarm energizer circuit IV, the output terminal of the NOR circuit N 3  is connected to one input terminal of the NOR circuit N 2 , and an inverter In 3 , a resistor R 17  and a capacitor C 9  are connected in series between this output terminal of NOR circuit N 2  and the ground. The connecting point between the resistor R 17  and the capacitor C 9  is connected to one input terminal of NOR circuit N 1 . The output terminal of oscillator circuit OSC 1  of the booster circuit II is connected to the other input terminal of the NOR circuit N 1 , the output terminal of the NOR circuit N 1  is connected to the other input terminal of the NOR circuit N 2 , and the output terminal of said NOR circuit N 2  is connected to the base of a transistor Tr 2  for exciting an alarm relay A. 
     The oscillator circuit OSC 1  consists of inverters In 4  to In 6 , resistors R 18  and R 19 , and a capacitor C 15 , wherein these inverters are connected in series as shown, the inverter In 5  having a feedback voltage applied thereto by the resistors R 18  and R 19 , and the inverters In 4  and In 5  having a feedback voltage applied thereto by the capacitor C 15 . Consequently, the circuit is always placed in an unstable state, whereby the output terminals of the inverters In 4  and In 6  produce voltages which alternately change between a high level signal and a low level signal. The voltages are rectified through a voltage multiplying rectifier circuit REC (multiplied four fold in this example) composed of diodes d 3  to d 7 , and capacitors C 10  to C 14 , whereby a high negative voltage is produced on the output terminal R. These oscillator circuits OSC 1  and OSC 2  are powered by the power supply E. 
     The operation of the circuit of FIG. 1 is described below. The oscillating output of the oscillator circuit OSC 1  under ordinary conditions is rectified and boosted by the voltage multiplying rectifier circuit REC, and a high negative potential produced on the output terminal R is applied to the inner electrode 1 of the inner ionization chamber IC, whereby the intermediate electrode 2 is maintained at a predetermined potential under the influence of the potential of the conductor l 1  applied to the outer electrode 3. In this state, the field effect transistor F 2  is turned off, and a low level input signal is fed to one input terminal of the NOR circuit N 3  through the resistor R 16 . Referring to the oscillator circuit OSC 2 , on the other hand, the input level thereof is pulled toward the high negative potential side of the output terminal R by means of the Zener diode ZD and becomes a low level signal. The output of the oscillator circuit OSC 2 , therefore, is always a high level signal as mentioned earlier. The high level output signal, however, is interrupted by the capacitor C 8 , whereby a low level input signal is fed to the other input terminal of the NOR circuit N 3  through the resistor R 14 . Therefore, the NOR circuit N 3  produces a high level output signal which is applied to one input terminal of the NOR circuit N 2 , causing the NOR circuit N 2  to produce a low level output signal and rendering the transistor Tr 2  nonconductive. The relay A therefore is not energized, and an alarm is not produced. The high level output signal of the NOR circuit N 3  is inverted into a low level signal by the inverter In 3 , and is fed to one input terminal of the NOR circuit N 1  via the resistor R 17 . Alternate low and high signal levels produced by the oscillator circuit OSC 1  are fed to the other input terminal of the NOR circuit N 1 . The NOR circuit N 1 , accordingly, produces alternate high and low signal levels correspondingly and applies them to the other input terminal of the NOR circuit N 2 . However, since a high level input signal has been applied to one input of said circuit N 2 , the outputs of the NOR circuit N 1  are all ineffective. 
     When the smoke is detected, the potential of the intermediate electrode 2 is decreased causing the field effect transistor F 2  to be turned on, whereby a high level input signal enters the input terminal of the NOR circuit N 3  via the resistor R 15 , and the output of the NOR circuit N 3  because a low level. Consequently, the NOR circuit N 2  is opened to produce alternate low and high output signal levels responsive to the alternate high and low output signal levels produced by the NOR circuit N 1 , thereby causing the transistor Tr 2  to be turned alternately on and off. As a result, the relay A is intermittently energized. Thereafter, an input which is obtained by inverting the low level output signal of the NOR circuit N 3  into a high level signal by the inverter In 3  is applied to one input terminal of the NOR circuit N 1  and delayed by the resistor R 17  and the capacitor C 9 . After a predetermined period of time has passed, the NOR circuit N 1  is closed to always produce a low level output signal, and the NOR circuit N 2  produces a high level output signal to maintain the transistor Tr 2  in a conductive state continuously. The relay A therefore is continuously energized to close the contact a. Thus, the contact a is first intermittently closed and is, thereafter, continuously closed to energize the buzzer B consuming less electric power. 
     When the capacity of the battery is decreased, the output voltage of the oscillator circuit OSC 1  is lowered causing the Zener diode ZD to be turned off. The input fed to the oscillator circuit OSC 2  is then switched from a low level to a high level, whereby the oscillator circuit OSC 2  starts to oscillate. When the smoke detector is not detecting the smoke, its output remains in the low level as mentioned earlier, and the NOR circuit N 3  produces an output which alternates from a low level signal to a high level signal in synchronism with the output of the oscillator circuit OSC 2 . The NOR circuit N 2  receives the outputs of both oscillator circuits OSC 1  and OSC 2 , and produces a high level output when these two outputs are both a low level and produces a low level output when these two outputs are not simultaneously high level signals. As a result, the relay A is intermittently energized causing the buzzer B to be intermittently energized, thereby indicating the depletion of the battery. Although the oscillator circuits OSC 1  and OSC 2  are not particularly synchronized, if the output frequencies differ slightly, the states in which the two outputs are both in a low level state or not in a low level state are periodically repeated. 
     According to the circuit of the present invention which performs the oscillation and the voltage multiplying rectification, the smoke detector V can be properly operated using only one or two dry batteries. Further, since the smoke detector which requires the high voltage is the only load for the booster circuit, and the other circuits are directly connected to the dry batteries, it is possible to reduce the electric power required by the booster circuit. In addition, the power loss caused by the booster circuit can be minimized. Furthermore, since the potential at the point Q, which is related to the potential at the point R, or in other words, since the boosted potential of the battery is monitored, it is possible to detect the voltage variation or the reduction of capacity of the battery with a high sensitivity. 
     The test switch SW is to test whether the ionization-type smoke sensor properly operates or not. If the test switch SW is turned on, the voltage of the power supply E applied to the electrode 3 of the outer ionization chamber OC is reduced, and the potential of the intermediate electrode 2 becomes the same potential as when smoke flows into the outer ionization chamber OC; the buzzer B is energized by the same procedure as when smoke is detected. It is convenient if the test switch SW is so constructed that the testing can be performed simply by pressing it from the exterior of the housing. 
     FIG. 2, FIG. 3 and FIG. 4 are perspective views showing in a disassembled manner the ionization-type smoke sensor to which the present invention is applied. FIG. 2 shows a cover 10 of the smoke sensor. FIG. 3 shows a depression portion 11 of the test switch SW, a contact 12, a spring 13, a switch holder 14, the outer electrode 3 of the outer ionization chamber of the smoke detector, the intermediate electrode 2 and the inner ionization chamber 1. FIG. 4 shows a substrate 15, the buzzer B, dry battery E, a holder 16 for holding the dry battery, a flag 17 for indicating that the battery is depleted, a circuit 18, a support plate 19 for supporting the smoke detector, a screw 20, a source of radiation, and the inner electrode 21. 
     According to the present invention as illustrated in detail in the foregoing, the ionization-type smoke sensor can be operated with the low voltage produced by one or two ordinarily used dry batteries, making it possible to produce a fire sensor for household use in a small size accommodating all necessary parts in a housing. In addition, the reduced capacity of the battery is indicated utilizing the alarming bell, enabling the sensor itself to be reliably used.