JP2002168820A - Smoke detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a larger change in resistance than that of a heater as a resistor with an eventual combustion heat transmitted to the heater by causing an instantaneous burning of particles of smoke adsorbing on the surface of a catalyst during the OFF period of a pulse voltage by heat generated with the pulse voltage turned ON. SOLUTION: This apparatus is provided with a smoke sensor S which has a heater built therein with sensing parts, containing a catalyst detecting smoke SM to generate a reaction heat, installed on the circumference thereof, a pulse voltage generation means EP which applies a pulse voltage with a specified duty ratio to the heater and a sensor signal processing means SP which detects the generation of smoke to be notified to an annunciation means A based on a resistance value of the heater varying with a combustion heat of particles of the smoke on the surface of the catalyst as burned by heat generated from the heater by the pulse voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a smoke detection device for detecting smoke generated in a fire using a conventional catalytic combustion type gas sensor which is a gas sensor for LP gas and city gas.

[0002]

2. Description of the Related Art As a type of detecting smoke using a sensor used in a fire alarm, a dimming type and an ionizing type smoke sensor are typical. However, the conventional smoke sensor has a problem that the structure is complicated and the cost is relatively high. Further, since a 100 V commercial power supply is required for operating the sensor, there is a problem that it is difficult to easily install the sensor at a location without power supply equipment. These problems cause the fire alarm device using the smoke sensor not to spread widely.

In order to solve these problems, there is a smoke sensor that detects smoke using a contact combustion type gas sensor that is a gas sensor for LP gas and city gas. In recent years, it has become possible to reduce the size and power consumption of the sensor by using micromachining technology. Therefore, it has become possible to detect smoke using a contact combustion gas sensor driven by a battery.

FIG. 6 is a sectional view of the catalytic combustion type gas sensor, and FIG. 7 is a top view of the catalytic combustion type gas sensor when the cap C is removed in FIG. As shown in FIG. 6, in the contact combustion type gas sensor, a housing for accommodating the sensor element COS includes a sensor pedestal (stem) SB and a cap C formed of a wire mesh. The sensor element COS is fixed to the pedestal SB, and the electrode EL on the electrode pad EP to which the heater H of the sensor element COS is connected and the pins P1 and P3 serving as external lead leads are connected to the thin metal wire W.
By the bonding method. After the connection, the cap C is put on the stem SB and welded to complete the catalytic combustion type gas sensor module. This sensor module is mounted on a wiring board by pins P1 to P4 and arranged in a fire monitoring area.

[0005] Sensor element COS are configured with a crystal orientation of silicon (Si) substrate B as shown in the sectional view of FIG. 6, on the upper surface of the silicon substrate B SiO ₂
A heat insulating film is formed in the order of the film M2 and the Si ₃ N ₄ film M1. On the upper surface of the Si ₃ N ₄ film M1, a thin Pt film (about 2500 to 5000 °) laminated by a sputtering method.
The two heaters H1 and H2 (see FIG. 7) are disposed with a predetermined gap. These heaters H1, H
7, a thin thin film resistance film (not shown) is bent many times into a rectangular shape at the center to form a heater body, as is apparent from FIG.

The heaters H1 and H2 are connected to pins P1 to P1.
4 and an electrode of an area that can be bonded and connected by metal wire W
Connected to pad EP. The adjacent heater H
1 and H2 are prevented from being short-circuited, and the heaters H1 and H2 are
Sensing part (detection element) and temperature compensation part (comparative element)
Sensor element COS in order to prevent
On the surface of SiO by CVD, sputtering, etc. _Two, S
i_ThreeN_FourOr single layer or multiple layers of PSG (phosphosilicate glass)
It is also possible to form a layer film.

On top of the heater H1, Pd is deposited on the protective film.
(5-15% by weight) on the catalyst layer C
The sensitive part TS used as T is formed. Further, a temperature compensating portion TC using γ or α-alumina as the catalyst layer CT is formed above the heater H2. The temperature compensating unit TC is for compensating for a change in the resistance value of the heater H1 due to a change in the ambient temperature. It is formed so as to have the same heat capacity as the sensitive part TC. Also, the heater H
1 and H2 are kept energized at all times to keep the sensitive part at 300 ° C. or more and maintain appropriate gas-sensitive characteristics.

The diaphragm DI is formed by forming a concave portion (not shown) on the back surface of the silicon substrate B at the position where the sensitive portion TS and the temperature compensating portion TC are provided.

The heater H1 corresponding to the sensitive section TS and the heater H2 corresponding to the temperature compensating section TC constitute a bridge circuit together with a fixed resistor R1, a fixed resistor R2 and a variable resistor Rv as shown in FIG. Heater H
A detection circuit DT for detecting a bridge unbalanced current flowing due to a change in the resistance value as smoke generated by a fire, and a drive power supply E2 by a DC power supply for continuous conduction are connected.

When using the sensor element COS, first, the variable resistor Rv is adjusted so as to prevent a current from flowing to the detection circuit DT in a state where smoke is not flowing, and a bridge circuit is balanced. In this state, the smoke particles move to the sensitive part T
When the S catalyst layer is touched, it is oxidized by the catalytic action on the surface of the sensitive portion TS to generate reaction heat. The resistance value of the heater H1 increases due to the reaction heat, and the balance of the bridge circuit is broken due to the increase in the resistance value, so that a current flows through the detection circuit DT. The detection circuit DT measures this current value to calculate the gas concentration in the smoke.

FIG. 10 shows the output characteristics of a continuously energizing contact combustion type gas sensor when the gas concentration of carbon monoxide, methane, hydrogen, acetic acid and the like is changed from 0 to 1000 ppm. As for carbon monoxide generated during incomplete combustion and methane generated when city gas leaks, both gas concentrations are 1000 ppm.
However, the sensor output is about 150 mV.

Regarding the smoke detection sensitivity, as shown in FIG. 11, for example, filter paper (175 × 175 mm)
After the smoke smoked at 00 ° C. was injected into a 50 L (little) chamber for 1 minute by a pump, a gas sensor was set in the chamber, and the sensor output was measured for 5 minutes. Set one cigarette on fire 5
A gas sensor was set in the chamber and the sensor output was measured when it was left in the 0 L (little) chamber for 5 minutes. The output was about 130 mV. After leaving it for 5 minutes, a gas sensor was set in the chamber and the sensor output was measured. The result was about 150 mV.

[0013]

As shown in FIGS. 10 and 11, a conventional continuous-current contact-combustion type gas sensor has a sensitivity of detecting carbon monoxide and methane of about 1000 ppm and about 1 ppm.
50 mV, and various smoke detections were 15 minutes even after 5 minutes of ignition.
0 mV, and the sensitivity to various detection objects is relatively low, and the sensitivity characteristics are almost the same. Therefore, from the sensor output, it is impossible to distinguish between fire detection due to smoke detection and incomplete gas combustion due to carbon monoxide detection or city gas leakage due to methane gas detection. There is a problem that it is difficult to use it for a fire alarm which performs fire detection by detection.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and uses a known contact combustion type gas sensor to reduce the smoke generated at the time of fire and the carbon monoxide generated at the time of incomplete combustion of gas. It is an object of the present invention to obtain a smoke detection device capable of detecting with high sensitivity by distinguishing between methane gas and the like generated at the time of city gas leakage.

[0015]

As shown in the basic configuration diagram of FIG. 1, a smoke detecting device according to the present invention has a sensitive portion including a catalyst that generates a reaction heat upon detecting smoke SM around its periphery. A smoke sensor S having a built-in heater, pulse voltage generating means EP for applying a pulse voltage having a predetermined duty ratio to the heater, and combustion heat of smoke particles on the catalyst surface burned by the heat generated by the heater due to the pulse voltage. Means for detecting smoke based on the changing resistance value of the heater and informing means A
And a sensor signal processing means SP for notifying the user. According to the present invention, the smoke molecules adsorbed on the catalyst during the pulse voltage OFF period are burned by the heat generated by the heater during the pulse voltage ON period, and the high combustion heat transmitted to the heater at this time causes a large resistance change of the heater. Therefore, an output larger than that of the sensor can be obtained.

The smoke sensor S of the smoke detector according to the present invention
In the method, the smoke SM particles adsorbed on the surface of the catalyst during the OFF time of the pulse voltage are burned at once by the heat generated by the heater when the pulse voltage is ON, and the combustion heat is transmitted to the heater. According to the present invention, smoke particles are adsorbed on the surface of the catalyst during the off time of the pulse voltage, and the adsorbed smoke particles are burned at once by the heat generated by the heater when the pulse voltage is turned on, so that the high combustion heat is used as a resistor as a heater. To obtain a large resistance change.

The smoke sensor S of the smoke detector according to the present invention
Treats the heater as a resistor, forms a bridge circuit with other resistors, applies a pulse voltage, and generates smoke based on an output signal of the bridge circuit accompanying a change in resistance of the heater when the pulse voltage is turned on. This is to detect the presence or absence of. According to the present invention, the resistance value of the heater rises due to the reaction heat of the catalyst when the pulse voltage is turned on, and the rise in the resistance value breaks the balance of the bridge circuit and causes the current to flow, thereby detecting smoke.

The voltage generating means EP of the smoke detecting apparatus according to the present invention is provided with a duty ratio control means DC for varying the ON-OFF duty ratio of the pulse voltage. According to the present invention, the OFF time of the pulse voltage for adsorbing smoke molecules on the catalyst surface and the ON time for burning the adsorbed smoke molecules are adjusted by varying the ON-OFF duty ratio of the pulse voltage. .

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, a smoke detector according to an embodiment of the present invention will be described with reference to the accompanying drawings. The configuration of the contact combustion type gas sensor used as the smoke sensor in the present embodiment is the same as that shown in FIGS. The present invention uses a catalytic combustion type gas sensor as a catalytic combustion type smoke sensor, and is not affected by carbon monoxide generated at the time of incomplete combustion or methane gas generated at the time of city gas leakage, and smoke generated at the time of fire (mainly, Cellulose, lignin, xylan, glucomannan, which are substances generated during the thermal decomposition of wood, etc.
VOL, 41, No. Ten. p. 879, 886 (19995) See the thermal decomposition kinetics of wood and cellulose) with high sensitivity to determine the occurrence of fire.

FIG. 2 is a basic configuration diagram of the smoke detector according to the present embodiment. According to this configuration, the heater H1 corresponding to the sensitive unit TS and the heater H corresponding to the temperature compensating unit TC
2 forms a bridge circuit by the fixed resistor R1, the fixed resistor R2, and the variable resistor Rv as shown in FIG. This bridge circuit includes a detection circuit (sensor signal processing means) DT
a, a drive power supply (pulse voltage generation means, duty ratio control means) E1 that can vary the duty cycle of the pulse voltage Vout applied to the bridge circuit is connected.
Further, although not shown, the detection circuit DTa has a built-in notification means for notifying the occurrence of a fire.

When using the bridge circuit composed of the sensor element COS, first, the variable resistor Rv is adjusted so that the current when the pulse voltage is ON does not flow to the detection circuit DTa when smoke is not flowing. Balance the bridge circuit. In this equilibrium state, when the smoke particles touch the sensitive part TS when the pulse voltage is turned off, the particles burn at once with the catalyst heated by the heater H1 that generates heat when the pulse voltage is turned on. The resistance value of the heater H1 as a resistor increases due to the combustion heat, and the balance of the bridge circuit is broken by the increase in the resistance value, so that a pulse current flows to the detection circuit DTa. The detection circuit DTa peak-holds and measures the pulse current, converts the measured value into a voltage, and calculates the gas concentration in the smoke. Alternatively, the pulse current may be integrated for a certain period of time and the integrated value may be used as the measured value of the gas concentration. Generally, the sensor output E is represented by the following equation.

E = E0 (((R _F1 + ΔR _F1 ) / (R _F1 +
R _F2 + ΔR _F1 ))-(R1 / (R1 + R2))) Here, E0 is a voltage applied to both ends of the bridge, R _F1 is a resistance value of the heater H1 in the sensitive part TS, and R _F is a heater in the temperature compensation part TC. The resistance value of H2, ΔR _F1 is the resistance change of the heater H1, and ΔR _F is the resistance change of the heater H2.

FIG. 3 shows an example of the configuration of the driving power source E1.
There is a duty variable pulse circuit shown in FIG. According to this circuit, the time constant R for charging and discharging the timing capacitor C1
4.C1 and R5.C1 are exactly the same because R4 = R5 is initially set. Using the diodes DI and D2, the current input to and output from the timing capacitor C1 is divided into a charging current and a discharging current to form a discharging circuit (diode D2).
2. It comprises a variable resistor R5 and a timing capacitor C1. ) And charging circuit (diode D1, variable resistor R)
4. It is composed of a timing capacitor C1. If the resistance values of the variable resistors R4 and R5 in () are changed, the values of the charging time and the discharging time of the timing capacitor C1 differ.

In this circuit, the timing capacitor C
Since the charging current of 1 flows through the variable resistor R4 and the diode D2, if the charging time constant is determined together with the timing capacitor C1 by changing the resistance value of the variable resistor R4, the pulse voltage Vou
The ON time t1 of t is determined. Since the discharge current of the timing capacitor C1 flows through the variable resistor R5 and the diode D2, if the resistance value of the variable resistor R5 is changed, the pulse voltage Vou
The OFF time t2 of t changes.

Therefore, by independently changing the values of the variable resistors R4 and R5, the ON time t1 of the pulse voltage Vout and the OF time
Since the F time t2 can be changed independently, the amount of smoke particles attached at the time of OFF can be adjusted. Further, the amount of battery consumption can be adjusted by adjusting the ON time t1 of the pulse voltage Vout required for smoke particle combustion. The ON time t1 and the OFF time t2 of the pulse voltage Vout are derived from the following equations.

T1 = −R4 · C1ln (1/2) ≒ 0.
694R4 · C1 t2 = −R5 · C1ln (1/2) ≒ 0.694R5 ·
C1

As described above, the charging time constant and the discharging time constant are changed, and a pulse voltage having an OFF time of about 30 seconds and an ON time of about 100 msec is applied to the bridge circuit from the driving power source E2.
Once every 0 seconds, the heaters H1 and H2 are energized for about 100 msec to burn the smoke particles adsorbed on the catalyst when the pulse voltage is turned off at once when the pulse voltage is turned on. Shows a similar reaction. As a result,
As shown in the sensor output characteristic diagram of FIG. 5, it is possible to obtain a smoke detection sensitivity 10 times or more as compared with the smoke detection sensitivity of the conventional contact combustion type gas sensor by continuous energization.

Further, it is possible to obtain a greater sensitivity than each conventional gas detection sensitivity of the contact combustion type gas sensor by continuous energization shown in FIG. As a result, a large detection sensitivity is obtained for smoke, so that it is possible to distinguish between carbon monoxide generated during incomplete combustion and methane gas generated during city gas leakage and smoke generated at the time of fire. Also, even if carbon monoxide and methane gas are detected by a contact combustion type smoke sensor using pulsed electricity, the concentration of these gases is 6000.
If it does not reach ppm or more, the sensor output does not reach 1000 mV.

The reason why the contact combustion type smoke sensor by the pulsed current can obtain a large detection sensitivity to various types of smoke generated at the time of fire is as follows. For ordinary gases (methane and oxygen), even if the pulse voltage applied to the heater is turned on and off, the sensitivity is almost the same as in the case of continuous energization, since gas particles hardly adsorb to the catalyst layer when the pulse voltage is turned off. . However, the smoke particles generated in the event of a fire always cause a combustion reaction in the catalyst layer during continuous energization, so the sensitivity does not increase so much.
Sometimes adsorbed particles are turned on because they are adsorbed on the surface of the catalyst layer
High sensitivity can be obtained by sometimes performing contact combustion at once.
For the above reasons, the smoke particles are adsorbed on the surface of the catalyst layer constituting the sensitive part TS during the OFF time of the pulse voltage Vout, and the smoke particles adsorbed during the OFF time during the ON time of the pulse voltage Vout. A high combustion temperature is obtained when the heater H1 generates heat at once, and the resistance change ΔR of the heater H1 as a resistor changes according to the following relational expression.

ΔR = kCQ (k is a constant) where Q is the heat of molecular combustion and C is the gas (smoke) concentration

As is apparent from the above equation, the heater H
Heat of combustion (Q) of smoke particles in contact with catalyst due to heat generated in (1)
, A large resistance change ΔR can be obtained.
A large output can be obtained from a bridge circuit using the heater H1 as a resistor. As a result, a higher detection sensitivity can be obtained than in the conventional continuous combustion type gas sensor of the contact combustion type.

The sensitivity adjustment of the contact combustion type smoke sensor is OFF.
The time, that is, the discharge time is adjusted by the variable resistor R5. The present invention can be applied to a contact combustion type sensor using a Pt coil without using micromachining technology. In addition, as a catalyst of the sensitive part for detecting smoke, in addition to γ or α-alumina, even if a noble metal catalyst containing Pt is used, smoke detection is possible although there is a slight difference in the output from which the reaction temperature can be obtained.

As described above, according to the present invention, the heater is energized instead of the conventional energization to the contact combustion type gas sensor by continuous energization, instead of continuous energization by intermittent energization by a pulse voltage, and the smoke adsorbed on the catalyst layer is removed. Particles were burned at once by the heat generated by the heater when the pulse was turned on, and a large change in resistance was obtained by transmitting the high combustion heat at this time to the heater, so that an output larger than that of the bridge circuit was obtained. As a result, the smoke at the time of the fire is detected with high sensitivity and notified to the notification means (see FIG. 1).
Issue a fire alarm.

[0034]

According to the present invention, the pulse voltage is turned off.
The smoke molecules adsorbed on the catalyst during the period are burned by the heat generated by the heater during the ON period of the pulse voltage, and the high combustion heat is transmitted to the heater to obtain a large resistance change of the heater, so that the output of the sensor is larger. And the detection sensitivity to smoke is improved.

According to the present invention, the smoke particles adsorbed on the surface of the catalyst during the OFF time of the pulse voltage are removed by the pulse voltage of O.
By causing the heat generated by the heater to burn at once and transferring the heat generated during the combustion to the heater, a larger resistance change than the heater as a resistor can be obtained. There is an effect that smoke can be detected.

According to the present invention, the resistance value of the heater rises due to the combustion heat of the catalyst when the pulse voltage is ON, and the bridge circuit breaks due to the rise in the resistance value, and current flows, thereby detecting smoke. In addition, there is an effect that smoke detection can be performed with a simple configuration using a conventional contact combustion type gas sensor.

According to the present invention, the OFF time of the pulse voltage for adsorbing the smoke particles on the catalyst surface and the ON time for burning the adsorbed smoke particles are defined as ON-O of the pulse voltage.
By varying and adjusting the FF duty ratio, there is an effect that the sensitivity of smoke detection can be easily adjusted.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a smoke detection device according to the present invention.

FIG. 2 is a schematic configuration diagram of a smoke sensor according to the present embodiment.

FIG. 3 is an internal configuration of a drive power supply according to the present embodiment.

FIG. 4 is an output characteristic diagram of the drive power supply according to the present embodiment.

FIG. 5 is a sensitivity characteristic diagram of the smoke sensor according to the present embodiment.

FIG. 6 is an internal configuration diagram of the smoke sensor according to the present embodiment.

FIG. 7 is an internal plan view of the smoke sensor shown in FIG. 6;

FIG. 8 is a schematic configuration diagram of a conventional catalytic combustion type gas sensor.

9 is a perspective view, partly in section, of the catalytic combustion type gas sensor shown in FIG. 8;

FIG. 10 is a diagram showing various gas detection sensitivity characteristics of a conventional contact combustion type gas sensor.

FIG. 11 is a diagram showing various smoke detection sensitivity characteristics of the conventional contact combustion type gas sensor.

[Explanation of symbols]

 S smoke sensor (contact combustion type smoke sensor) EP pulse voltage generation means DC duty ratio control means SP sensor signal processing means A notification means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G060 AA02 AE19 AF09 BA03 BB02 HA03 HC02 HC10 5C085 AA03 AB01 AC03 BA17 CA07 CA30 EA11

Claims (4)

[Claims] 1. A smoke sensor having a built-in heater provided around a sensitive portion including a catalyst that generates reaction heat upon detecting smoke, and a pulse voltage generating means for applying a pulse voltage having a predetermined duty ratio to the heater. And sensor signal processing means for detecting smoke generation based on the resistance value of the heater which changes due to the combustion heat of the smoke particles on the catalyst surface burned by the heat generated by the heater due to the pulse voltage and informing the notification means. A smoke detector characterized by the above-mentioned. 2. The smoke sensor burns smoke particles adsorbed on the surface of the catalyst during the OFF time of the pulse voltage by the heat generated by the heater when the pulse voltage is ON, and transmits the combustion heat to the heater. The smoke detection device according to claim 1, wherein: 3. The smoke sensor regards the heater as a resistor, forms a bridge circuit together with another resistor, applies a pulse voltage, and applies a pulse voltage to the bridge due to a change in resistance of the heater when the pulse voltage is turned on. The smoke detection device according to claim 1, wherein the presence or absence of smoke is detected based on an output signal of the circuit. 4. The smoke detecting apparatus according to claim 1, wherein said pulse voltage generating means includes a duty ratio control means for varying an ON-OFF duty ratio of the pulse voltage.