JPS6323599B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an ionization type smoke detector that detects the presence of smoke based on changes in ion current and notifies the occurrence of a fire or the like.

Conventionally, this type of smoke detector uses a rectangular pulse with a constant duty to cause an ion current to flow through an ion chamber in which air is ionized with radioactive isotopes, and the signal generated by this ion current is detected. The voltage is amplified and added to the capacitor of the rectifier circuit, and the voltage of this capacitor and the reference voltage are used as two inputs of a comparator, and as the ion current decreases due to smoke entering the ion chamber, the voltage of the capacitor changes to the reference voltage. When the voltage drops below that level, a high level output is obtained from the comparator, the switching circuit connected to the output terminal is closed, and the alarm is activated.

However, in this smoke detector, the duty of the signal voltage applied to the capacitor of the rectifier circuit changes due to variations in components such as the pulse generation circuit and changes over time, so the charging and discharging time of this capacitor changes and the capacitor The voltage deviates from a predetermined level, resulting in a disadvantage that the detection sensitivity changes, such as a longer time from sensing smoke to operating the switching circuit.

The present invention has been proposed in view of the above points, and its purpose is to apply a pulse whose duty is always constant to a capacitor of a rectifier circuit to keep the voltage of the capacitor as a signal voltage constant;
An object of the present invention is to provide an ionization type smoke detector that prevents changes in detection sensitivity by waiting in this state.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a pulse generating circuit that generates four types of pulses, and one embodiment thereof is shown in FIG. In Fig. 2, 2 is an astable multivibrator, in which the voltage of capacitor C ₁ charged via feedback resistor R ₁ changes with respect to the reference voltage given to comparator 3 by a voltage dividing resistor. ,
The output of the comparator 3 is inverted when the two voltages become equal, and is constituted by a so-called operational amplifier. This output voltage is shown in Figure 3B.
As shown below. An inverting circuit 4 consisting of a D-type flip-flop _F1 having S and R input terminals is connected to the output side of the astable multivibrator 2. A power supply voltage is applied to the S input terminal of the flip-flop _F1 , the clock input terminal and the D input terminal are both switched to the S input terminal, and the R input terminal is connected to the output terminal of the comparator 3. Therefore, the S input of flip-flop _F1 becomes high level, and this flip-flop _F1 becomes R
It operates as an inverter that simply inverts the input and outputs it from the Q output terminal. A 1/2 frequency divider circuit ₅ consisting of a D-type flip-flop F2 having S and R terminals is connected to the Q output terminal of the inverting circuit 4. The S and R input terminals of this flip-flop _F2 are both grounded and always at a low level, and the Q output terminal of the inverting circuit 4 is connected to the clock input terminal, and its inverting output terminal is connected to the D input terminal. ing. This causes flip-flop
As shown in Figure 3A, _F2 has a duty of 50% that changes between high level and low level at twice the period of the clock pulse which is the Q output of the inverting circuit 4.
The Q output is obtained by reducing the clock input by 1/2.
A frequency-divided Q output and its inverted output (FIG. 3C) are generated. In addition, as shown by D in FIGS. 1 and 2, the output of the flip-flop _F1 is branched,
It is also possible to input the signal to an AND circuit (not shown) together with the output of a comparator 9, which will be described later, and operate the switching circuit 11 based on the output.

The Q output terminal of the 1/2 frequency divider 5 of the pulse generating circuit 1 is connected to the anode of the ion chamber 6. This rectangular pulse is used to cause an ion current to flow inside the ion chamber 6. By making the ion current pulse-like, the impedance inside the ion chamber 6 can be lowered and the load resistance can be selected to be small, thereby stabilizing the sensitivity. This makes it possible to The cathode of the ion chamber 6 is
It is connected to the gate electrode of an N-channel FET (Q ₁ ) which is used as a source follower to perform impedance conversion. Note that R ₂ is a resistor that provides gate voltage. A load resistor R ₃ is connected in series to the source electrode of the FET (Q ₁ ), and the source electrode is connected to a comparator,
It is connected to the input terminal of a non-inverting voltage amplification circuit 7 consisting of a transistor or the like. The output terminal of this amplifier circuit 7 has a switch S ₁ , a capacitor C ₂ , and a resistor.
R ₄ , switch S ₂ are connected in series, switch S ₂
One end of is connected to the negative input terminal of the coiperator 9. In addition, a switch _S3 is inserted between the resistor _R4 , the switch _S2 , and the ground wire, and a capacitor is connected between the negative input terminal of the comparator 9 and the ground wire.
C ₃ is connected. These switches S ₁ , S ₂ , S ₃ ,
_The capacitors C ₂ and C ₃ and _the resistor R ₄ form a signal processing circuit ₈ that rectifies the amplified signal voltage. It consists of an analog switch. Each switch S ₁ , S ₂ , S is controlled to open or close by the output of the pulse generating circuit 1, and the switch S ₁ is controlled by the pulse shown in FIG. 3B, that is, by the output voltage of the comparator 3. Switch S ₂
is the pulse of FIG. 3A, that is, the flip-flop F ₂
According to the Q output voltage of , the switch S ₃ is also
, respectively, by the inverted output voltage of flip-flop _F2 . which switch
S ₁ , S ₂ , and S ₃ are also configured to close when the applied pulse is at high level and open when the applied pulse is at low level.

The positive input terminal of the comparator 9 is connected to the voltage dividing point of the voltage dividing resistors R ₅ and R ₆ connected to the constant voltage circuit 10 of the power supply V, and the comparator 9 converts the voltage at this voltage dividing point into a reference voltage. As, the signal processing circuit 8
output signal voltage, i.e. the capacitor of the integrating circuit
It is set to produce a high level output when the voltage of _C3 falls below the reference voltage. A switching circuit 11 such as a switching transistor is connected to the output terminal of the comparator 9.
The high-level output of the controller is used to activate alarms, etc.

Note that the circuit shown in FIG. 4 is an embodiment showing a specific configuration of the present invention, and a detailed description of the circuit configuration will be omitted.

Next, this operation will be explained with reference to FIG. Incidentally, time charts indicated by a, b, c, and d in the same figure show changes in voltage at corresponding points in FIG. 1.

The pulse shown in FIG. 3A is applied to the ion chamber 6, where an ion current flows through the air ionized by the radioactive isotope, and this ion current flows between the cathode of the ion chamber 6 and the ground wire. A voltage is applied to the gate electrode of the FET (Q ₁ ) through the resistor R ₂ connected between the Q 1 and Q 1 . In the FET (Q ₁ ), impedance conversion is performed between the ion chamber 6 as a signal source with high internal resistance and the load resistance R ₃ to obtain an output voltage that is in phase with the input voltage, and this voltage is passed to the amplifier circuit 7.
The signal voltage is amplified by . Here, since the ion chamber 6 has a capacitor-like structure consisting of an anode and a cathode as described above, when a pulse from the pulse generation circuit 1 is applied to it, the output voltage of the amplifier circuit 7 becomes as shown in FIG. 3a. As shown, spike noise based on the charging/discharging current of the ion chamber 6 appears. However, during the period when spike noise is occurring, that is, for a certain period from the rise and fall of the pulse applied to the ion chamber 6 (Fig. 3A), the signal processing circuit 8 is activated as shown in Fig. 3B. Switch S ₁
Since the pulse controlling the capacitor C3 is at a low level, the switch _S1 is in an open state and no signal voltage is transmitted to the capacitor _C3 , and this spike noise has no effect on the circuit described below.

In the signal processing circuit 8, while the pulse shown in FIG. 3B is at a high level and the switch _S1 is closed,
One of the mutually opposite phase pulses shown in FIG. 3A and C is at a high level,
Either one of the switches S ₂ and S ₃ is closed. Now, for example, switch S ₁ is closed and the third
If the pulse in Figure A is at a high level and closes switch _S2 , then switch _S3 is open. Therefore, the signal voltage that is the output of the amplifier circuit 7 is applied to the capacitors C ₂ and C ₃ via the resistor R ₄ and charges these capacitors C ₂ and C ₃ . Then, in the next period of the pulse shown in FIG. 3B, the switch S ₁ is turned on.
is closed again, at this time the pulse of FIG. 3A, which is the signal voltage and is also the control pulse of switch S ₂ , becomes low level and opens switch S ₂ , and at the same time the control pulse of switch S ₃ Figure 3C
The pulse of is reversed to high level and closes switch _S3 . Therefore, the switches S ₁ and S ₃ are closed when the output of the amplifier circuit 7 is at a low level and there is no signal voltage, and the capacitor C ₂ that had been charged with the signal voltage is discharged and its both ends are discharged. Let the voltage of be zero. During this time, since the switch S ₂ is open, the charging voltage of the capacitor C ₃ in which charge is accumulated due to the closing of the switch S ₂ is applied to the negative input terminal of the comparator 9. each capacitor
The time constant due to C ₂ , C ₃ and resistor R ₄ is determined by the signal voltage (third
By setting the value to be sufficiently larger than the half cycle in Figure A), the capacitor voltage will gradually increase to reach a predetermined value after several 10 cycles of the signal voltage, and thereafter as shown in Figure 3 d. It remains at an almost constant level. The voltage of this capacitor _C3 , that is, the signal voltage, decreases as the ion current decreases due to adhesion of ions and smoke particles, which are combustion products, when smoke enters the ion chamber 6 due to a fire or the like. However, when the voltage falls below the reference voltage of the comparator 9, a high level output is generated in the comparator 9, and a switching circuit 11 such as an alarm is operated.

As described above, according to the present invention, the pulse generating circuit 1 is formed by the astable multivibrator 2, the inverting circuit 4 consisting of flip-flops F ₁ and F ₂ , and the 1/2 frequency dividing circuit 5, and the comparator 9 The switches S ₂ and S ₃ of the signal processing circuit 8, which provide a signal voltage to the capacitor C ₃ of the integrating circuit that serves as the signal input, are connected to the pulses from the pulse generation circuit 1 whose duty is always constant (Fig. 3 A, C). As a result _{, a signal voltage with a constant duty is applied to capacitor C 3 ,} and the signal voltage based on conventional component variations etc. There is no risk of sensitivity deterioration due to voltage duty deviation, and there is an advantage that the system can stand by in a state where immediate action can be taken to detect the occurrence of smoke. In addition, since the spike noise generated in the output of the amplifier circuit 7 is also removed by the pulse from the pulse generator circuit 1 (Fig. 3B), a noise-free signal voltage can be obtained, and the sensor This can further contribute to improving sensitivity.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; Fig. 1 is an overall circuit diagram, Fig. 2 is a configuration diagram of a pulse generation circuit, and Fig. 3 is a time diagram showing voltages at corresponding points in Fig. 1. FIG. 4 is a circuit diagram of an embodiment showing a specific configuration of the present invention. 1... Pulse generation circuit, 2... Astable multivibrator, 3... Comparator, 4... Inverting circuit, 5... 1/2 frequency dividing circuit, 6... Ion chamber, 7...
...Amplification circuit, 8 ... Signal processing circuit, 9 ... Comparator, 10 ... Constant voltage circuit, 11 ... Switching circuit, F ₁ , F ₂ ... Flip-flop, Q ₁ ...
…FET, V…power supply, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ ,
R ₆ ... Resistor, C ₁ , C ₂ , C ₃ ... Capacitor, S ₁ ,
S ₂ , S ₃ ... switch.

Claims (1)

[Claims] 1. In order to flow an ion current, connect the output terminal of the pulse generation circuit to one electrode of the ion chamber, connect the other electrode of the ion chamber to the input terminal of the amplifier circuit, and connect the output terminal of the amplifier circuit to the output terminal of the amplifier circuit to rectify the amplified output. Connect the output terminal of the signal processing circuit to the signal input terminal of the comparator, apply a reference voltage to the other input terminal of the comparator, and connect the output terminal of this comparator to the input terminal of the signal processing circuit, such as an alarm device, etc. In addition to connecting the switching circuit that operates the
In the smoke detector, the comparator compares and detects that the signal voltage replacing the ion current changes due to smoke that has entered the ion chamber, and operates the switching circuit. A vibrator, an inverting circuit consisting of a flip-flop that inverts the phase of the output pulse of the astable multivibrator, a pulse having half the frequency of the inverting circuit using the output of the inverting circuit as a clock input, and a pulse with the phase of the pulse inverted. One of the output pulses of the 1/2 frequency divider circuit is used as the constant duty first pulse to be applied to the ion chamber, and the output pulse of the 1/2 frequency divider circuit is The other of the pulses is a second pulse, and the output pulse of the astable multivibrator, which is at a low level for a certain period from the rising and falling points of the first pulse, is a third pulse, and the signal processing circuit is configured to: A first switch, a first capacitor, a resistor, and a second switch are connected in series between the output terminal of the amplifier circuit and the input terminal of the comparator, and the resistor and the second switch are connected in series. A third switch is connected between the intermediate point and the ground line, and a second capacitor is connected between the signal input terminal of the comparator and the ground line, and the first pulse is connected to the second switch. The ionization method is characterized in that the second pulse is applied to the third switch and the third pulse is applied to the first switch as control pulses, respectively, and each corresponding switch is closed when each pulse is at a high level. Smoke detectors.