JPS5920160B2 - Ionization fire detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ionization type fire detector that prevents malfunctions due to leakage current.

Leakage current is one of the major causes of malfunction of ionization fire detectors.

This is because the impedance of the internal and external ion chambers of the ionization fire detector is approximately 1010 to 1012 ohms.
The insulator that insulates a pair of electrodes in the ion chamber with high resistance and the insulator that insulates each lead wire of the FET (field effect transistor) that detects voltage changes between the inside and outside of the ion chamber are contaminated by dust and moisture. When this occurs, the insulation properties of the insulator deteriorate due to this contamination, and a leakage current flows through the surface of the insulator. This leakage current that flows between the electrodes of the ion chamber and between the FET lead wires has the same effect as when smoke enters the external ion chamber, causing the FET to deepen conduction and operate the switching circuit, which causes the ionization type fire detector to operate. will give rise to false alarms. Among the malfunctions caused by this leakage current, leakage current flowing between the electrodes of the ion chamber can be reduced by increasing the creepage distance by providing a guard electrode between the electrodes or by making the insulator have a labyrinth structure. Measures have already been taken and are proving to be effective. However, regarding FET leakage current, the spacing between each lead wire is only a few microliters, so it is not possible to provide a guard electrode or increase the creepage distance. It is installed inside the ion chamber. However, even if the FET is provided in the internal ion chamber, it is not effective against moisture, and therefore no effective measures have been taken to prevent leakage current from the FET. In view of the above points, this invention detects smoke during operation and determines whether the FET is operating normally or due to leakage current flowing through the FET, and outputs a fire signal only when smoke is detected and the FET operates. The purpose is to obtain an ionization type fire detector that can

First, the principle of this invention will be explained with reference to FIGS. 1 to 4.

The internal ion chamber CH1, which is a comparative impedance element, and the external ion chamber CH2, into which smoke does not enter, are connected in series to a power supply (not shown) with the polarities shown in FIG. When the -1 (voltage-current) characteristic 11 and the -1 characteristic 12 of the external ion chamber CH2 are measured, the characteristics shown in Fig. 2 are obtained. The gate potential of the FET is the voltage V at the intersection of 11 and 12. becomes. When smoke with a concentration of 10%, for example, enters the external ion chamber CH2, the ion current in the ion chamber CH2 decreases, and the characteristic changes from 12 to 13, and the potential at the connection point becomes V1. Also, if a leakage current i flows between the lead wires of the FET, for example between the drain and the gate, this leakage current 1
exists in parallel with the internal ion chamber CHl, and F
When considering the internal ion chamber CHl side from ET, a current equal to the sum of the ion current and the leak current flows through the internal ion chamber CH, and its characteristics are 11 when the leak current is large.
The voltage changes from 14 to 14, and the potential at the connection point reaches 1. By the way, as shown in FIG. 3, only the voltage applied to the series circuit of the internal ion chamber CHl and the external ion chamber CH2 is reversed without changing the polarity of the voltage applied to the FET. When we measured the -1 characteristic of , we obtained the characteristic shown in Fig. 4.

In other words, there is no smoke in the external ion chamber CH2 and the FET
The characteristics of the internal ion chamber CHl when no leakage current flows are l/, and the characteristics of the external ion chamber CH2 are I! The potential at the connection point is J, but there is a concentration of 10% in the external ion chamber CH2.
When smoke enters, its characteristics change from IJ to 135, and the potential at the connection point becomes V2, which is lower than J, whereas F
When a leakage current 1 flows between the input and source of the ET, this current 1 flows in parallel to the external ion chamber CH2, unlike the case in Fig. 1, and the characteristics of the external ion chamber CH2 change from IJ to 15.
The potential at the connection point changes to . ′ was found to be higher than . This invention focuses on the above fact, and the detection output of a field effect transistor that detects a potential change at a series connection point of a series circuit of an internal ion chamber or a comparison impedance element such as a resistor and an external ion chamber is the first one. The polarity of the applied voltage of the series circuit is reversed when a predetermined smoke concentration level is reached, and the detection output of the field effect transistor when the polarity of the series circuit is reversed is equal to or higher than a second predetermined smoke concentration level. By determining whether or not there is a field effect transistor, it is possible to determine whether the operating state has been reached by detecting smoke of a predetermined concentration or whether the operating state has been entered by leakage current of the field effect transistor. This is to obtain an ionization type fire detector.

Hereinafter, one embodiment of this invention will be explained with reference to FIG.
The drain of an FET, which is an impedance element for comparison and whose gate is connected to the intermediate electrode 1 of the internal ion chamber CH1 and the external ion chamber CH2, is connected to the positive terminal 2, and the source is connected to the negative terminal 3 through the resistor R.

Further, the source of the FET is connected to the first discrimination circuit and the second discrimination circuit. The first discrimination circuit includes a first comparator C1 and a monostable multivibrator M1 provided as necessary.
and a switching circuit SW for outputting a caution signal, and the non-inverting input of the comparator C is connected to the source of the FET, and the inverting input for reference is connected between the positive terminal 2 and the negative terminal 3. It is connected to the movable terminal of variable resistor R2 for reference signal. The output of the comparator C1 is connected to a monostable multivibrator M1, and the output thereof is connected to a switching circuit SW1 and N1 of inverters N1 and N2 connected in series forming a polarity reversing circuit. In addition, the output of multivibrator M1 is AND circuit A, and the operating time is
, is connected to a shorter monostable multivibrator M2, and the output of this multivibrator M2 is connected to an AND circuit A via an inverter N3. The second discrimination circuit includes a second comparator C2, an inverter N4, and an AND circuit A.
2 and a switching circuit SW2 for fire signal output, the non-inverting input of the comparator C2 is the source of the FET, and the inverting input is a variable resistor R3 for reference signals connected between the positive terminal 2 and the negative terminal 3. Connected to the movable terminal of Also, the output of comparator C2 is connected to inverter N4, and its output is connected to the above AND
The output of the circuit A1 is connected to an AND circuit A2, and the output thereof is connected to a switching circuit SW2 having a self-holding function. Further, in the polarity reversing circuit, the output of the inverter N1 is connected to the internal electrode 4 of the internal ion chamber CH, and the output of the inverter N2 is connected to the external electrode 5 of the external ion chamber CH2, thereby configuring the ionization type fire detector DE. . Note that 6 is a radiation source provided on the intermediate electrode 1, 7 is a smoke inlet of the external ion chamber CH2 provided on the external electrode 5, RE is a receiver, 8 is a high-sensitivity relay that receives a small current caution signal, 9 is a low sensitivity relay that receives large current fire signals, L1 is a caution light, L
2 is a fire indicator light. Note that the first comparator C1 is an FET.
The gate potential of is V in FIG.

The second comparator is designed so that it does not operate normally, but operates when a predetermined concentration of smoke, for example, 10% smoke enters the external ion chamber CH2 and the gate potential of the FET reaches 1 in Fig. 2. C2 does not operate under normal conditions, and when the polarity of the series circuit of internal ion chamber CHl and external ion chamber CH2 is reversed, the smoke concentration in external ion chamber CH2 is 10% or less and FE is activated.
Variable resistors R2 and R3 are adjusted so that the device operates when the gate potential of T is 2 or more in FIG. 4, or in other words, it becomes inactive when the smoke density is 10% or more. Next, the operation of this ionization type fire detector DE will be explained.

During normal operation, when there is no smoke in the external ion chamber CH2 and no leakage current in the FET, the first and second comparators C1 and C
2 are both inactive, and monostable multivibrators M1 and M2 are also inactive.

As a result, inverters Nl, N2 and N4 produce high potential outputs, inverter N2 produces a low potential output, and electrode 4 of internal ion chamber CH1 has a positive and external ion chamber C.
A voltage of negative polarity is applied to the electrode 5 of H2. Also, AND circuits Al, A2 and switching circuits SWl, S
W2 is inactive. If smoke enters the external ion chamber CH2 due to a fire, or a leakage current flows between the FET lead wires, the gate potential of the FET will decrease to V1 as shown in Figure 2.
When it reaches, comparator C1 operates and produces an output, and monostable multivibrator M, operates and produces an output.

The switching circuit SWl is operated by the output of the multivibrator M1, and a small current as a caution signal flows through the signal lines 11 and 12. This caution signal operates the high-sensitivity relay 8 and closes its make contact 81, thereby issuing a caution signal. Light L1 lights up. Furthermore, the multivibrator M2 is operated by the output of the multivibrator M1, and the inverter N3 is made to have a low output, thereby maintaining the non-operating state of the AND circuit A2. Furthermore, the output of the multivibrator M1 causes the inverter N1 of the polarity reversing circuit to have a low output and the inverter N2 to have a high output, so that the polarity of the voltage applied to the electrodes 4 and 5 is reversed.
If this polarity reversal is caused by leakage current of the FET, the source potential of the FET becomes higher than 2 due to the polarity reversal, and the comparator C2 operates to produce an output.

The output of the comparator C2 causes the inverter N4 to have a low output. Then, when the multivibrator M2 reaches the O output after the operating time has elapsed, the inverter N3 becomes a high output, and the AND circuit A1 operates with the output of this inverter N3 and the output of the multivibrator M1, which is still operating, and outputs an output. comes out. However, the AND circuit A2 does not operate because the inverter N4 has a low output, and the switching circuit SW2 does not operate. Then, when the monostable multivibrator M becomes low output after the operating time, the inverter N1 becomes high output and N2 becomes low output, and the polarity of the internal electrode 4 and the external electrode 5 returns to the state before polarity reversal. At the same time, the switching circuit SWl stops operating, the relay 8 is restored, and the caution light L is turned off. At this time, if leakage current is still flowing through the FET, the comparator C1 operates again and repeats the above operation, blinking the caution light L1, and notifying that the sensor DE is malfunctioning due to the leakage current. However, if the polarity reversal is caused by smoke having a predetermined concentration entering the external ion chamber CH2, the gate potential of the FET decreases to 2 or less due to the polarity reversal.

Therefore, comparator C2 does not operate and multivibrator M
When 2 becomes O output after the operating time, inverter N3
produces high output. The AND circuit A1 is operated by the output of the inverter N3 and the output of the multivibrator M, which is still operating, to produce an output. This AND
Due to the output of circuit A1 and the high output of isoverter N4, AN
D circuit A2 operates and switching circuit SW2 operates. Due to the operation of this switching circuit SW2, the signal line 1
A large current flows through 1 and 12, causing low sensitivity relay 9 of receiver Re.
operates, and the warning light L is activated by opening the break contact 92.
, is turned off, the make contact 91 is closed, and the fire indicator light L2 is turned on to indicate the occurrence of a fire. In the above embodiment, the characteristics of the internal ion chamber CH and the external ion chamber CH2 constituting the series circuit are such that the potential 1 at the series connection point at the predetermined smoke concentration to be detected before polarity reversal is the same as that of the predetermined smoke concentration chamber after polarity reversal. Although we have explained the case where the potential V1 at the series connection point is lower than the potential 2 at the series connection point at the predetermined smoke concentration before polarity reversal, the characteristics of the series circuit are such that the potential V1 at the series connection point at the predetermined smoke concentration before polarity reversal is higher than the potential 2 at the predetermined smoke concentration after polarity reversal. When this is selected, the second comparator C2 is supplied with the lower reference potential V2 from the resistor R3, so that it is in an operating state and produces an output under normal conditions.

For this reason, the inverter N4 outputs a high output only when smoke at a specific concentration enters the external ion chamber CH2 and becomes a polarity inversion state, so the high output of the inverter N4 directly controls the fire signal output circuit SW2. is completed, monostable multivibrator M2, inverter N3 and AND circuit Al,
A2 can be omitted. In the above embodiment, the internal ion chamber CH was used as a comparison impedance element.
An impedance element such as a resistor may be used in place of l, and if the warning signal is to be output continuously, the switching circuit SWl should have a self-holding function, and if only the fire signal is to be output, the switching circuit SWl should have a self-holding function. The switching circuit SWl may be omitted from the first discrimination circuit, and each electrode 1
, 4 and 5 as shown by the dotted line in FIG.
It is also possible to provide In the above embodiment, the first and second
The comparators C1 and C2 detect potential changes at the same concentration level before and after polarity reversal in the series circuit, but the detection level of the second comparator C2 is set higher than the detection level of the first comparator C1. By detecting potential changes at a low concentration level, it is possible to remove the influence of leakage current and detect smoke at a predetermined concentration even when some leakage current is flowing between the FET lead wires. can. According to this invention, the sensor itself detects whether the FET has become active due to smoke having a predetermined concentration entering the external ion chamber or whether the FET has become active due to leakage current flowing through the FET. The fire signal is determined by reversing the polarity of the series circuit connected to the ion chamber, and a fire signal is output only when smoke at a predetermined concentration is detected and the operating state is reached.This prevents malfunctions caused by leakage current. This provides an ionization type fire detector that prevents

[Brief explanation of drawings]

Figures 1 to 4 are diagrams explaining the principle of the ionization type fire detector according to the present invention, and Figure 1 is a circuit diagram before polarity change;
FIG. 3 is a circuit diagram after polarity reversal, and FIGS. 2 and 4 are −1 characteristic diagrams of the comparison impedance element and external ion chamber in FIGS. 1 and 3. Fig. 5 shows one of the ionization type fire detectors according to the present invention.
It is a circuit diagram of an example. DE...Ionization fire detector, RE...Receiver, CHl...
・Comparison impedance element, CH2... External ion chamber, 1... Intermediate electrode, 4... Internal electrode, 5... External electrode, FET...・・・・・・
Field effect transistor, C1...first comparator, C2...second comparator, SWl...
Caution signal output circuit, SW2...Fire signal output circuit, Nl, N2...Inverter that constitutes the polarity reversal circuit.

Claims (1)

[Claims] 1. Ionization type fire detection comprising a series circuit of a comparison impedance element and an external ion chamber through which smoke freely enters and exits, and a field effect transistor that detects potential changes at the series connection points of this series circuit. The device includes a first discrimination circuit for determining whether the detection output of the field effect transistor has reached a first predetermined smoke concentration level, and a voltage applied to the series circuit controlled by the first discrimination circuit. a polarity reversing circuit for reversing the polarity; and determining whether or not the detection output of the field effect transistor is equal to or higher than a second predetermined smoke concentration level when the polarity of the series circuit is reversed by the polarity reversing circuit. A second discriminating circuit is provided, the first discriminating circuit and the second discriminating circuit
An ionization type fire detector characterized in that it can be determined whether the detector is activated by detecting smoke of a predetermined concentration or by leakage current of a field effect transistor based on a difference in the output of the discrimination circuit. 2. The first discriminator circuit includes a first comparator that detects a first predetermined smoke concentration level, and the second discriminator circuit includes a second comparator that detects a second predetermined smoke concentration level and a second comparator that detects a second predetermined smoke concentration level. The ionization type fire detector according to claim 1, comprising a fire signal output circuit operated by a second comparator. 3. The first discrimination circuit consists of a first comparator that detects a first predetermined smoke concentration level and a caution signal output circuit operated by the first comparator, and the second discrimination circuit consists of a second a second comparator for detecting a predetermined smoke density level of the second comparator;
2. The ionization type fire detector according to claim 1, comprising a fire signal output circuit operated by a comparator. 4. Claim 1, wherein the first predetermined smoke density level and the second predetermined smoke density level are the same smoke density level.
The ionization type fire detector according to any one of Items 1 to 3. 5. The ionization fire detector according to any one of claims 1 to 3, wherein the second predetermined smoke density level is a lower smoke density level than the first predetermined smoke density level.