JPH0330955Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Fields> The present invention relates to a composite fire detector that is activated by four phenomena: flame, heat, smoke, and gas.

<Prior Art> Conventionally, there are two types of fire detectors used in Japan (approved by the Fire Service Act): heat detectors and smoke detectors. Heat detectors include constant temperature type, differential type, compensation type, etc. For example, the bimetal type used in constant temperature and differential types uses a bimetal made by laminating a low expansion metal and a high expansion metal.
When a bimetal fixed at one end receives heat, it curves toward the metal with a lower coefficient of expansion, causing a displacement proportional to the temperature. As a result, when the bimetal reaches a certain temperature, it closes the contacts and activates the sensor.
Furthermore, there are two types of smoke detectors: photoelectric type and ionization type, and the former photoelectric type includes dimming type and scattered light type.
For example, the light emitting unit 31 is of a dimming type as shown in FIG. The part 40 is a lens 41,
It has a configuration including an aperture 42 and a light receiving element 43. Now, when smoke 36 enters the optical path 35 emitted from the light projector 31, the amount of light received by the light receiving element 43 decreases by an amount proportional to the amount of smoke 36 that has entered, and the amount of light decreases to a predetermined value. The sensor is activated when it reaches . Secondly, flame detectors are intended for early fire detection, and are recognized as fire detectors by the US UL standards and NFPA. In addition to an ultraviolet sensor and an infrared sensor, this flame detector includes a visible light sensor that the applicant previously proposed, and is a device that can detect flame and smoke with a single detection element (patent application). (Sho 58-69752).

On the other hand, typical gas detectors include catalytic combustion type sensors and semiconductor type sensors. For example, the semiconductor method utilizes changes in the electrical conductivity of the semiconductor due to gas adsorption and desorption phenomena that occur on the surface of metal oxides (SnO ₂ , ZnO, etc.), and its structure is as shown in Figure 6. . The electrodes 51 are embedded in a metal oxide semiconductor 52, one of which is used as a heater, and the other electrode is used to measure the electrical resistance of the semiconductor present between the electrodes. Here, the heater is provided to heat the semiconductor surface to a temperature (200 to 400° C.) at which gas can be easily adsorbed and desorbed. . As mentioned above, conventionally,
There were separate sensors for detecting heat, smoke, flame, and gas, but they were independent and had no relation to each other.

<Problems to be solved by the invention> In view of the above-mentioned circumstances, the purpose of the invention is to provide a simple composite fire detector that can detect heat, smoke, flame, and gas and can be applied to ordinary houses. That is.

<Means for solving the problems> The present invention consists of a first sensing element made of a pyroelectric element that responds to changes in incident infrared rays, and a semiconductor whose electrical conductivity changes due to gas adsorption/desorption phenomena. a second sensing element, and a first and a second sensing element for determining the magnitude of the output of the first and second sensing elements;
a comparison circuit is provided, the reference voltages of the first and second comparison circuits are set to different values, and the outputs of the first and second detection elements are respectively set to the first and second detection elements.
and a second comparison circuit, and further leads to a third comparison circuit that compares the output of the third sensing element with a reference value to correct for changes in electrical conductivity due to ambient temperature of the second sensing element. Composition: gas, smoke,
The timing at which the alarm is issued can be changed depending on the state of flame and heat generation.

<Example> Shown in FIG. P and N are DC positive and negative potentials, respectively. Reference numeral 10 denotes a semiconductor element that senses smoke and gas, and is, for example, a metal oxide semiconductor such as _SnO2 . 21 is a pyroelectric element that senses heat and flame.

20 is a temperature correction sensing element, for example a thermistor. R1 to R8 are resistors (R2, R3, R4
is a variable resistance) C1 is a capacitor, D1, D2,
D3 is a diode, and 1, 2, 3 and 4 are comparators. This operation will now be explained. When smoke or gas comes into contact with the element 10, the electrical conductivity of the element 10 increases due to an adsorption/desorption reaction with the gas on the element surface, that is, the resistance decreases as shown in FIG. A due to decreased resistance
The potential V1 at the point increases to a value determined by 10 and R1. 1 is a comparator whose reference voltage is set to an arbitrary value V3 by adjusting a variable resistor R3. Now V1 is V
When the voltage is higher than 3, an output 1' of the comparator 1 is generated.
Here, R6 and C1 constitute a delay circuit, so
The voltage V6 changes as shown in FIG. Therefore V
By inputting Vc to another comparator 4 and appropriately setting its reference voltage V7 using R7 and R8, the output Vc of the comparator 4 can be delayed as desired. An alarm circuit 5 consisting of a buzzer etc.
You can lead to Its function is to prevent alarms from being triggered due to gases generated during spraying or cooking, cigarette smoke, etc. However, when a large amount of gas ejects rapidly and diffuses, V1 rises rapidly, but due to the delay effect of R6 and C1, Vc
This may not occur immediately and may lead to a serious accident. Here, R so that V2>V3
2 and R3, and when V1>V2, the output 2' of the comparator 2 is output and VD is generated without delay. If this output VD is led to an alarm circuit 5 consisting of a buzzer or the like, the buzzer will immediately sound if a large amount of gas or smoke is generated. Here, a buzzer connected to Vc and a buzzer connected to VD may be provided separately, or a single buzzer may be used in common.

In addition, when flame or heat is generated (when no smoke or gas is generated), charges essentially based on spontaneous polarization appear on the surface of the pyroelectric element 21, but in the atmosphere, floating charges appear. Therefore, it is neutralized and no apparent charge is observed. In this state, when the surface of the pyroelectric element 21 is irradiated with infrared rays (heat rays) caused by flame, heat, etc., the charge is absorbed and the temperature of the pyroelectric element 21 increases. The magnitude of this spontaneous polarization decreases as the temperature rises, and the magnitude of the spontaneous polarization of the pyroelectric element 21 changes instantaneously due to temperature changes. However, it takes time for this surface charge to reach equilibrium, and it remains in a non-equilibrium state for some time. This unbalanced surface charge is detected as a voltage.
For example, if the pyroelectric element 21 receives incident heat as shown in FIG. 2a, the output will be as shown in FIG. 2b. Therefore, when there is no temperature change, this pyroelectric element 21 has only the DC bias voltage shown in FIG. 2b. Of course, when the temperature change is gradual, the change in the output signal is also gradual, and no output is output from the comparison circuits 1 and 2. In this way, when the output 21' of the element 21 changes significantly beyond a certain level, the outputs 1' and 2' are generated (the set voltage increases). In this case, since 1' and 2' do not continue for a long time, the output Vc is not generated at the output 1' which passes through the delay circuit. On the other hand, the output VD is generated by issuing the output 2'.

Next, the operation of 20 will be explained.

When the ambient temperature increases (e.g. due to seasonal changes), 1
0 is affected by this, for example in the case of SnO ₂ , the fourth
As shown in the figure, the element resistance decreases. Therefore, if the reference voltages 1 and 2 are fixed, in summer when the ambient temperature is high, the sensitivity will increase due to the increase in V1, and in some cases, 1' will occur even when no smoke or gas is generated. This may cause false alarms. In order to correct the influence of this ambient temperature, a thermistor (negative characteristic), for example, is used as the temperature sensing element 20. The resistance-temperature characteristics of this thermistor are similar to those of the element 10, and the resistance decreases as the temperature increases.
When the ambient temperature rises, V1 rises, and the potential at point B rises accordingly, causing V3 and V2 to rise. Therefore, by optimally selecting the 20 characteristics, it is possible to correct the ambient temperature. This thermistor 20 is a necessary element to accurately detect gas and smoke without false alarms, but in the present invention, this thermistor for compensating ambient temperature is also used to detect heat in the event of a fire. .

Fires generally generate poisonous gases and smoke, so 10 is effective, but 10 does not work if the concentration of smoke or gas is low due to the influence of wind or a fire in a neighboring house. However, when the temperature rises due to heat, the resistance of 20 decreases as described above, and the potential at point B increases. Therefore, if the reference voltage V4 of the comparator 3 is appropriately determined by the resistor R4 in consideration of the surrounding environment, etc., and the output 3' is generated at a temperature of 60°C, for example, if the temperature exceeds 60°C, then immediately without delay
VD is output and the alarm circuit 5 is activated. Here, the function of the diodes D1, D2, and D3 is to prevent the outputs 3', 2', and 21' from being affected by the equivalent output resistances (not shown) of the comparators 2, 3, and 21, respectively. This is provided to stabilize VD.

<Effects of the invention> As mentioned above, the composite fire detector of the invention has the following advantages by using inexpensive and highly reliable semiconductor elements and pyroelectric elements, and devising a combination of comparison circuits and delay circuits.
It can detect gas, smoke, flame, and heat with extremely high accuracy. i.e. gas from spraying and cooking;
Although it does not detect smoke, flames, or heat, it is able to sense a rapidly spreading fire and issue an immediate warning with great accuracy and no delay.

Furthermore, regarding heat, it has an excellent feature in that it can detect not only a sudden temperature rise but also a gradual rise in temperature if it exceeds a set value. Therefore, this device can exhibit great effects as a detector suitable for general homes.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention: Fig. 1 is a block diagram, Fig. 2, a and b are explanatory diagrams of the operation of the semiconductor element and the pyroelectric element, and Fig. 3 shows the operating characteristics of the delay circuit. FIG. 4 is an explanatory diagram showing the resistance-temperature characteristics of a temperature sensing element, FIG. 5 is an explanatory diagram showing a conventional dimming type sensor, and FIG. 6 is an explanatory diagram of the same semiconductor element. 1, 2, 3, 4...comparison circuit, 1', 2', 3',
4'...Same output, 5...Alarm circuit, 10...Semiconductor element, 20...Temperature detection element, 21...Pyroelectric element, R1, R5, R6, R7, R8...Resistance,
R2, R3, R4...Variable resistor, C1...Capacitor, D1, D2, D3...Diode, V2,
V3, V4, V7... Reference voltage of comparison circuit, V1
... Potential at point A, V5... Potential at point D, V6...
Potential at point C, Vc...Delay circuit output, VD...Immediate circuit output.

Claims (1)

[Claims for Utility Model Registration] (1) A first sensing element that responds to changes in incident infrared rays, a second sensing element whose electrical conductivity changes due to a gas adsorption/desorption phenomenon, and a first sensing element that responds to changes in incident infrared rays; A first and a second detector which combine the output of the sensing element and the output of the second sensing element and compare the magnitude of the output with a reference value.
a comparison circuit, a delay circuit that delays only the output of the first comparison circuit for a predetermined period of time, a third detection element that corrects a change in electrical conductivity due to ambient temperature of the second detection element, The output of the sensing element is guided to a third comparison circuit for comparing with a reference value, and the output of the third comparison circuit is combined with the output of the second comparison circuit, and the output of the first comparison circuit is combined with the output of the second comparison circuit.
The reference setting value of the comparison circuit is set lower than the reference setting value of the second comparison circuit, and when a fire is detected, the output of the second or third comparison circuit or the output of the first comparison circuit is set lower than the reference setting value of the second comparison circuit. A composite fire detector that activates the alarm circuit. (2) The composite fire detector according to claim 1, wherein the first detection element is a pyroelectric element. (3) The composite fire detector according to claim 1, wherein the second and third detection elements are oxide semiconductor elements.