JPH04363795A - Ionized system smoke sensor - Google Patents

Abstract

PURPOSE:To permit time till the output of an alarm issuing signal after smoke reaches an alarm issuing level to be fixed. CONSTITUTION:An inner electrode 13b, an outer electrode 13c surrounding the inner electrode so as to form an ion room 13e and an intermediate electrode 13d formed between the inner electrode and the outer electrode are provided, the potential of the intermediate electrode changing by smoke flowed into the ion room is inputted to the gate G of an electric field effect-type transistor FET, a capacitor C is charged by current flowing with the electric field effect- type transistor and a trigger output is executed when the charged voltage of the capacitor becomes more than a specified voltage so that the alarm issuing signal is outputted in an ionized system smoke sensor 1. In the sensor, the first transistor Tr1 and the second transistor Tr2 are provided, current flowing with the electric field effect type transistor is inputted to the base of the first transistor and the second transistor is turned on at the time of turning on the first transistor so that the second transistor charges the capacitor.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ionization smoke detector.

0002

2 shows a circuit diagram of a conventional ionization type smoke detector 1. The ionization type smoke detector 1 has a signal line connection terminal 1a connected to a fire receiver (not shown) via a signal line. ，
1a. The ionization smoke detector 1 is constantly supplied with voltage from a fire receiver (not shown) via a signal line (not shown). The diode bridge 10 rectifies the supplied voltage and inputs the rectified voltage to the power supply circuit 12 via the alarm signal circuit 11. The power supply circuit 12 converts the voltage inputted from the diode bridge 10 via the alarm signal circuit 11 into an appropriate voltage and supplies the drive voltage Vcc to the smoke detection circuit 14 and the smoke detection section 13.

The smoke sensing section 13 includes an inner electrode 13b on which a radiation source 13a is placed and an ion chamber 1 surrounding the inner electrode 13b.
3e, and an intermediate electrode 13d formed between the inner electrode 13b and the outer electrode 13c. The outer electrode 13c is connected to the driving voltage Vcc side of the power supply circuit 12, the inner electrode 13b is connected to the ground side of the power supply circuit 12, and the intermediate electrode 13d is connected to the gate of the field effect transistor FET.

The collector of the transistor Tr for sensitivity adjustment is connected to the drive voltage Vcc side, the emitter of the transistor Tr is connected to the source S of the field effect transistor FET, and the drain D of the field effect transistor FET is connected to the resistor R1 and the resistor. Connected to R2. Further, the other resistor R1 is connected to the ground side, and the other resistor R2 is connected to the positive side of the electrolytic capacitor C and the anode of the silicon-controlled rectifier PUT which is the trigger element. The negative side of the electrolytic capacitor C is connected to the ground side, and the cathode of the silicon-controlled rectifying element PUT is connected to the alarm signal circuit 11.

The gate of the silicon-controlled rectifier PUT is connected to the connection point between the resistors R3 and R4 connected in series, the other resistor R3 is connected to the driving voltage Vcc side, and the other resistor R4 is connected to the ground side. ing. Further, the base of the transistor Tr is connected to a sliding terminal of a variable resistor VR, one of which is connected to the driving voltage Vcc side and the other to the ground side.

Therefore, the ionization type smoke detector 1 outputs an alarm signal as follows. When smoke flows into the ion chamber 13e, the potential of the intermediate electrode 13d drops. That is, the gate voltage (hereinafter referred to as VG) of the field effect transistor FET drops. On the other hand, field effect transistor FE
The source voltage of T (hereinafter referred to as VS) decreases as the gate voltage VG of the field effect transistor FET drops, but the source voltage of transistor Tr (hereinafter referred to as VB) decreases from the base voltage of transistor Tr (hereinafter referred to as VB) adjusted by variable resistor VR.・The voltage does not drop below the voltage obtained by subtracting the emitter voltage (hereinafter referred to as VBE).

However, due to the inflow of smoke, the gate voltage VG of the field effect transistor FET further drops.
The difference between the source voltage VS and gate voltage VG of the field effect transistor FET (hereinafter referred to as gate-source voltage V
GS) is a constant value (hereinafter referred to as threshold voltage VGS (th
) or above, it is a field effect transistor FET.
turns on and current flows from source S to drain D. Then, electrolytic capacitor C is charged via resistor R2, and the voltage of electrolytic capacitor C increases. and,
When the voltage of the electrolytic capacitor C exceeds the gate voltage of the silicon-controlled rectifier PUT divided by the resistors R3 and R4, the silicon-controlled rectifier PUT turns on and triggers the alarm signal circuit 11, causing ionization smoke. Sensor 1
outputs an alarm signal.

[0008] The adjustment of the variable resistor VR is performed using the intermediate electrode 1.
This is to prevent the alarm sensitivities of the individual ionization type smoke detectors 1 from differing due to variations in the potential change with respect to the 3d smoke and variations in the threshold voltage VSG(th) of the field effect transistor FET. Also, the time from when the field effect transistor FET is turned on and the electrolytic capacitor C begins to be charged via the resistor R2 until the silicon-controlled rectifier PUT is turned on and triggers the alarm signal circuit 11 is called a delay time. .

[0009]

[Problem to be Solved by the Invention] By the way, the drain voltage (hereinafter referred to as V
D) is the voltage obtained by subtracting the base-emitter voltage VBE and the source-drain voltage (hereinafter referred to as VSD) of the field effect transistor FET from the base voltage VB. Even if the concentration is different, the variable resistance VR is adjusted depending on each ionization type smoke sensor 1 and the base voltage VB is different, so the drain voltage VD is different depending on each ionization type smoke sensor 1.

Therefore, as shown in FIG. 3, after the voltage of the electrolytic capacitor C, which is charged towards the drain voltage VD, begins to be charged via the resistor R2, the gate voltage of the silicon-controlled rectifier PUT (hereinafter referred to as VPG) increases. ), when the drain voltage VD is high, it is time t1 as shown by the curve L1, and the time when the drain voltage VD is high.
When D is low, the time is t2 as shown by curve L2. That is, the ion chamber 1 of each ionization smoke detector 1
Even if the smoke density within 3e is the same, the drain voltage VD
In the ionization type smoke detector 1, which has a low
There is a long delay before it turns on.

Further, even if the ionization type smoke detector 1 is the same, if the smoke concentration in the ion chamber 13e after the field effect transistor FET is turned on is different, the amount of potential drop at the intermediate electrode 13d will be different, and the smoke concentration will be different. When is low, the amount of potential drop at the intermediate electrode 13d is small. And the gate-source voltage VG
When S is different, the source-drain resistance (hereinafter referred to as RSD) of the field effect transistor FET is also different, and when the gate-source voltage VGS is low, the source-drain resistance RSD is high.

Therefore, as shown in FIG. 4, the time period from when electrolytic capacitor C starts being charged via resistor R2 until the voltage of electrolytic capacitor C exceeds the gate voltage VPG of silicon-controlled rectifying element PUT is When the resistance RSD is low, the time is t3 as shown by the curve L3, and when the source-drain resistance RSD is high, the time is t4 as shown by the curve L4. In other words, even if the ionization type smoke detector 1 is the same, if the smoke density is low and the source-drain resistance RSD is high, the delay time from when the field effect transistor FET turns on until the ionization type smoke detector 1 triggers an alarm. is long.

Furthermore, in order to reliably turn on the silicon-controlled rectifying element PUT, it is necessary to flow a current higher than the peak current (hereinafter referred to as IP) of the silicon-controlled rectifying element PUT to the anode of the silicon-controlled rectifying element PUT. However, since the current flowing through the resistor R2 is determined by the drain voltage VD of the field effect transistor FET, it changes depending on variations in the ion chamber 13e and the threshold voltage VGS(th), and the setting of the variable resistor VR. In addition, the peak current IP of the silicon-controlled rectifier PUT itself also depends on the ambient temperature and the gate resistance of the silicon-controlled rectifier PUT (in Fig. 2, the gate resistance RG is RG = R3 R4
/(R3 +R4)), and it is difficult to balance the required peak current IP with the current actually flowing to the anode to ensure reliable ON operation of the silicon-controlled rectifier PUT.

[0014] There were problems as described above. The present invention
This was done to improve the above problems, and its purpose is to reduce the difference in delay time between individual ionization smoke detectors when smoke of the same concentration flows in, and to ensure that the same Even with ionization type smoke detectors, it reduces the difference in delay time due to differences in smoke concentration, and also ensures that alarms are issued even if the characteristics of the ion chamber and field effect transistor vary and the ambient temperature changes. An object of the present invention is to provide an ionization type smoke detector that outputs a signal.

[0015]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an inner electrode on which a radiation source is placed, an outer electrode surrounding the inner electrode to form an ion chamber, and an inner electrode and an outer electrode. The potential of the intermediate electrode, which is changed by the smoke flowing into the ion chamber, is input to the gate of the field effect transistor, and the current flowing through the field effect transistor is used to drive the capacitor. In an ionization smoke detector that is charged and outputs a trigger signal when the charging voltage of the capacitor reaches a predetermined voltage or higher,
A first transistor and a second transistor are provided, a current flowing through the field effect transistor is inputted to the base of the first transistor, and when the first transistor is turned on, the second transistor is turned on. The capacitor is turned on and the capacitor is charged by the second transistor.

[0016]

[Operation] With the above configuration, when smoke flows into the ion chamber and the potential of the intermediate electrode changes and the field effect transistor is turned on, the first transistor is turned on; The second transistor turns on and the current flowing through the second transistor charges the capacitor.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit diagram of an embodiment of an ionization type smoke detector according to the present invention, and FIG. 1 differs from the conventional example shown in FIG. 2 only in the smoke detection circuit 14. Therefore, the smoke detection circuit 14
The connection relationship will be explained, and then the operation will be explained.

The collector of the transistor Tr for sensitivity adjustment is connected to the drive voltage Vcc side, the emitter of the transistor Tr is connected to the source S of the field effect transistor FET, and the drain D of the field effect transistor FET is connected to the drive voltage Vcc side through a resistor R8. The resistor R7 is connected to the base of the transistor Tr1 corresponding to the first transistor and the resistor R7, and the other end of the resistor R7 is connected to the ground side of the power supply circuit 12. Further, the base of the transistor Tr for sensitivity adjustment is connected to a sliding terminal of a variable resistor VR, one of which is connected to the driving voltage Vcc side and the other to the ground side.

One end of the resistor R5 is connected to the driving voltage Vcc side, the other end of the resistor R5 is connected to the base of the transistor Tr2 corresponding to the second transistor and the resistor R6, and the other end of the resistor R6 is connected to the collector of the transistor Tr1. However, the emitter of the transistor Tr1 is connected to the ground side. Further, the emitter of the transistor Tr2 is connected to the drive voltage Vcc side, and the emitter of the transistor Tr2 is connected to the drive voltage Vcc side.
The collector of is connected to a resistor R1 and a resistor R2, and the other of the resistor R1 is connected to the ground side. The other end of the resistor R2 is connected to the positive side of the electrolytic capacitor C and the anode of the silicon-controlled rectifier PUT.
The negative side of is connected to the ground side. The cathode of the silicon-controlled rectifying element PUT is connected to the alarm signal circuit 11.

The gate of the silicon-controlled rectifier PUT is connected to the connection point between the resistors R3 and R4 connected in series, the other resistor R3 is connected to the driving voltage Vcc side, and the other resistor R4 is connected to the ground side. ing.

Therefore, when smoke flows into the ion chamber 13e, the potential of the intermediate electrode 13d drops and the gate voltage VG of the field effect transistor FET drops, causing the gate-source voltage VGS to exceed the threshold voltage VGS(th). Then, the field effect transistor FET turns on and the source S
Current flows from the drain D to the drain D. Then, the base voltage of the transistor Tr1 becomes High, so the transistor Tr1 is turned on, and the base voltage of the transistor Tr2 becomes Low, so the transistor Tr2 is turned on.

Then, the electrolytic capacitor C has a driving voltage Vc
C is charged via transistor Tr2 and resistor R2, and the voltage of electrolytic capacitor C increases. Then, the voltage of electrolytic capacitor C is between resistor R3 and resistor R4.
When the gate voltage of the silicon-controlled rectifier PUT becomes equal to or higher than VPG, the voltage of the silicon-controlled rectifier PUT
turns on and triggers the alarm signal circuit 11, and the ionization type smoke detector 1 outputs an alarm signal.

Therefore, the field effect transistor FET
When turned on, the electrolytic capacitor C is charged to a voltage obtained by subtracting the base-emitter voltage of the transistor Tr2 from the drive voltage Vcc, and the ion chamber 13e is charged as in the conventional case.
Since the charge is not made to a different drain voltage VG due to variations in the characteristics of the field effect transistor FET, it is possible that the delay time will differ between individual ionization smoke detectors 1 when smoke of the same concentration flows in. do not have.

Although the charging resistance of the electrolytic capacitor C changes depending on the on state of the transistor Tr2,
The transistor Tr2 turns from off to on with a much smaller amount of change in the potential of the intermediate electrode 13d than in the conventional case. Therefore, even if the ionization type smoke sensor is the same, the delay time is less likely to differ due to a difference in the smoke concentration in the ion chamber 13e after the field effect transistor FET is turned on.

Furthermore, since current can flow from the drive voltage Vcc to the anode of the silicon-controlled rectifying element PUT via the transistor Tr2 and the resistor R2, when the field effect transistor FET is turned on, the current flowing into the anode flows into the ion chamber 13e. and field effect transistor FET
The variation in the characteristics of the transistor Tr and the base voltage VB of the transistor Tr
is determined almost independently of the adjustment of Furthermore, the current flowing into the anode can flow from a higher voltage (that is, the voltage obtained by subtracting the base-emitter voltage of transistor Tr2 from the drive voltage Vcc) than in the past, and the design can withstand changes in ambient temperature. can. Therefore, even if there are variations in the characteristics of the ion chamber 13e and the field effect transistor FET, the alarm signal can be reliably output even if the ambient temperature changes.

[0026]

[Effects of the Invention] Since the ionization type smoke detector of the present invention is configured as described above, there is no difference in delay time between individual ionization type smoke detectors when smoke of the same concentration flows in. In addition, even if the same ionization type smoke detector is used, the delay time will not differ depending on the smoke concentration, and furthermore, even if there are variations in the characteristics of the ion chamber and field effect transistor, the detection will occur reliably even if the ambient temperature changes. This has the effect of providing an ionization type smoke detector that outputs a warning signal.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an ionization type smoke detector according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional ionization smoke detector.

FIG. 3 is a charging characteristic diagram illustrating variations in charging characteristics of an electrolytic capacitor of a conventional ionization type smoke detector.

FIG. 4 is a charging characteristic diagram illustrating variations in charging characteristics of an electrolytic capacitor of a conventional ionization type smoke sensor.

[Explanation of symbols]

1 Ionization type smoke detector 13a Radiation source 13b Inner electrode 13c Outer electrode 13d Intermediate electrode 13e Ion chamber C Capacitor FET Field effect transistor Tr1
First transistor Tr2 Second transistor

Claims (1)

[Claims] Claim 1: An inner electrode on which a radiation source is placed, an outer electrode surrounding the inner electrode to form an ion chamber, and an intermediate electrode formed between the inner electrode and the outer electrode. The potential of the intermediate electrode, which changes due to the inflow of smoke, is input to the gate of the field effect transistor, and the capacitor is charged with the current flowing through the field effect transistor, and when the charging voltage of the capacitor exceeds a predetermined voltage. In an ionization type smoke detector that outputs a trigger signal to output an alarm signal, a first transistor and a second transistor are provided,
A current flowing through the field effect transistor is input to the base of the first transistor, and when the first transistor is turned on, the second transistor is turned on, and the second transistor charges the capacitor. An ionization type smoke detector characterized by: