JP2002082083A - Gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detector having a gas leakage alarming function of detecting methane gas and hydrogen gas and an incomplete combustion alarming function of detecting carbon monoxide gas. SOLUTION: A sensing element A is provided with a gas sensing body constructed of a metal oxide semiconductor such as tin oxide, while a coil type electrode 21 serving as a heater is buried in the gas sensing body, and a resistance detecting electrode 22 is buried through the center of the electrode 21 serving as a heater. A microcomputer 3 controls current supply to the electrode 21 serving as a heater so that a high-temperature period for heating the gas sensing body at a high temperature and a low-temperature period for heating it at a low temperature are arranged alternately, and in the end of the high-temperature period, gas leakage alarming operation is carried out, while in the end of the low-temperature period, incomplete combustion alarming operation is carried out. Just after a switch to the low-temperature period, a hydrogen gas concentration is detected by means of the microcomputer 3, and if the hydrogen gas concentration is above a predetermined level, an alarm at hydrogen gas is determined in the end of the low-temperature period in which sensitivity to the hydrogen gas is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detector for detecting inflammable gas and incompletely combusted gas such as carbon monoxide generated during incomplete combustion in the general household and industrial fields.

[0002]

2. Description of the Related Art Conventionally, as a gas detecting device for detecting a gas leak of a flammable gas such as a city gas or a propane gas, a gas-sensitive material mainly composed of tin oxide (SnO ₂ ) is used. In some cases, the flammable gas is detected from a change in resistance of the gas-sensitive body due to the attachment of the flammable gas to the surface of the gas sensor. Such a gas detection device has a heater for heating the gas-sensitive body, and controls the energization of the heater to increase the temperature of the gas-sensitive body to a high temperature period. A low-temperature period and a low-temperature period are alternately provided in a predetermined cycle, and the resistance is reduced when the gas-sensitive body comes into contact with the gas to be detected. In addition to detecting incomplete combustion gas such as carbon monoxide (CO), the incomplete combustion gas adhering to the surface of the gas-sensitive body is burned during the high-temperature period of the gas-sensitive body, and after removing dirt on the surface, methane is removed. (CH ₄ )
And other flammable gases.

[0003]

By the way, for gas lighter than air (12A lighter than air) stipulated in the Japanese Gas Appliance Inspection Association's "Rules for Inspection of Gas Alarms for City Gas (JIA E 001-99)" , 13A gas), it is required to distinguish and detect hydrogen. However, it has been difficult to selectively detect hydrogen with a conventional semiconductor gas sensor. Further, in semiconductor gas sensors used for detecting natural gas, in order to prevent malfunction due to hydrogen gas which is a miscellaneous gas, the sensitivity to hydrogen was reduced by supporting a gas-sensitive body with a catalyst. However, there is a problem that the effect of reducing the sensitivity is insufficient.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a gas leak alarm function for detecting methane gas and hydrogen gas and a function for detecting carbon monoxide gas. An object of the present invention is to provide a gas detection device in which both of the incomplete combustion warning functions are provided in one gas sensitive body. It is another object of the present invention to provide a gas detection device which prevents erroneous detection by hydrogen gas.

[0005]

To achieve the above object, according to the first aspect of the present invention, there is provided a gas-sensitive body whose resistance value changes by adsorbing a gas, a heater for heating the gas-sensitive body, A control unit for making an alarm judgment by comparing the level of the alarm level with the concentration of the detection target gas obtained from the resistance value of the gas body, wherein the control unit controls the energization of the heater, A high-temperature period in which the temperature of the gas sensor is high and a low-temperature period in which the temperature is low are alternately provided to detect the concentration of methane gas during the high-temperature period of the gas-sensitive body and perform a gas leak alarm judgment. Incomplete combustion alarm determination by detecting the concentration of carbon monoxide gas to perform, and,
When the concentration of hydrogen gas detected during a period having a discrimination characteristic with respect to hydrogen gas at the time of switching to the low temperature period exceeds a predetermined level, at least one of the latter half of the low temperature period or the latter half of the high temperature period in which the sensitivity to hydrogen gas is stabilized. On the other hand, it is characterized by detecting the concentration of hydrogen gas and making a gas leak alarm judgment, and determines whether hydrogen gas is present or not from the resistance value of the gas-sensitive body during a period that is distinguishable from hydrogen gas at the time of switching to a low temperature period. Judgment, when hydrogen gas is present, since the alarm judgment for the hydrogen gas is performed in at least one of the latter half of the low temperature period or the latter half of the high temperature period in which the sensitivity to the hydrogen gas is stable, the hydrogen gas is accurately detected. Can be detected. Therefore, a gas leak alarm function for detecting methane gas and hydrogen gas and an incomplete combustion alarm function for detecting carbon monoxide gas can be provided in one gas-sensitive body. For gases lighter than air (12A, 1A lighter than air) specified in the “Gas Alarm Test Rules for City Gas (JIA E 001-99)”
3A gas) (except for 3A gas).

According to the second aspect of the present invention, a gas-sensitive body whose resistance value changes by adsorbing a gas, a heater for heating the gas-sensitive body, and a concentration of a gas to be detected obtained from the resistance value of the gas-sensitive body A control unit for making an alarm judgment by comparing the level with an alarm level, wherein the control unit controls energization of the heater to increase the temperature of the gas-sensitive body during a high temperature period and to decrease the temperature of the gas sensitive body during a low temperature period. Are alternately provided to detect a gas leak alarm by detecting the concentration of methane gas during the high-temperature period of the gas sensitive body, and detect the concentration of carbon monoxide gas generated during incomplete combustion during the low-temperature period to detect incomplete combustion. If an alarm determination is made and the concentration of hydrogen gas detected during a period of discrimination from the hydrogen gas at the time of switching to the low-temperature period exceeds a predetermined level, the alarm levels of the gas leak alarm and the incomplete combustion alarm are set to the hydrogen gas level. It is characterized by correcting each to prevent malfunction due to, the presence or absence of hydrogen gas is determined from the resistance value of the gas sensitive body during the period that is distinguishable from hydrogen gas at the time of switching to the low temperature period, and the presence of hydrogen gas is determined. When present, the alarm levels of the gas leak alarm and the incomplete combustion alarm are each corrected, so that even when hydrogen, which is a miscellaneous gas, exists, erroneous detection due to hydrogen can be prevented, and the accuracy of the alarm is improved. be able to.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the cycle of the high temperature period and the low temperature period is about 60 seconds or less, and the "Gas Inspection Association of Japan" defines " It can satisfy the “Gas alarm inspection rules for city gas” and “Incomplete combustion alarm inspection rules”.

According to a fourth aspect of the present invention, in the first or second aspect of the invention, the control unit applies a predetermined voltage to the gas-sensitive body via a load resistor, and determines the resistance of the gas-sensitive body from the voltage generated in the gas-sensitive body. The characteristic value is detected, and the resistance value of the load resistance is switched for each gas detection. By appropriately setting the resistance value of the load resistance, the optimal voltage is applied to the gas sensitive body and different types of Gas can be detected with high accuracy.

According to a fifth aspect of the present invention, in the first or second aspect of the present invention, a temperature sensor for detecting an ambient temperature is provided, and based on an output of the temperature sensor, the control unit controls the gas-sensitive body in a high temperature period and a low temperature period. The temperature compensation of the resistance value of the gas sensing element is performed by the control unit based on the output of the temperature sensor, so that the detection target gas can be accurately detected in the high temperature period and the low temperature period. It is possible to perform temperature compensation in a high temperature period and a low temperature period with one temperature sensor.

According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, a filter for removing alcohol vapor or silicon vapor from a gas in contact with the gas-sensitive body is provided in the gas flow path from the outside to the gas-sensitive body. Claim 7
In the invention of claim 6, in the invention of claim 6, the filter is made of either activated carbon or silica gel, and alcohol vapor or silicon vapor is removed from the gas in contact with the gas-sensitive body by the filter layer, The alcohol sensitivity of the gas-sensitive body can be reduced, and the gas-sensitive body can be protected from silicon vapor which is a poisoning substance.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 Embodiment 1 of the present invention will be described with reference to the drawings. The gas detection device of the present embodiment is a gas detection device for gas lighter than air (except for 12A and 13A gas lighter than air), and the gas detection element used in this gas detection device is shown in FIGS. (A) (b)
As shown in FIG. 5, a substantially disk-shaped resin base 11, three terminals 12 a to 12 c penetrating the base 11 and protruding toward the front side and the back side of the base 11, and the terminals 12 a to 12
c, a cover 14 formed in a substantially cylindrical shape having a ceiling surface 14a and covered with the base 11 so as to cover the sensing element A, and a cover. And a stainless steel wire net 15 for gas introduction, which is attached to a round hole 14b formed on the ceiling surface 14a of the device 14.

As shown in FIG. 5, the sensing element A has a so-called sintered body-type gas-sensitive body 20 which is made of a metal oxide semiconductor such as tin oxide (SnO ₂ ) as a main component and is formed in a substantially spherical shape. A coil-shaped heater / electrode 21 made of platinum is embedded in the gas-sensitive body 20, and the resistance detecting electrode 22 made of a noble metal wire is passed through the center of the coil of the heater / electrode 21 so that the gas-sensitive body 20 It is formed by being buried in 20. Here, the above-described lead wires 13a, 13a are connected from both ends of the heater / electrode 21 protruding from the gas-sensitive body 20.
3c, and a lead wire 13b is formed from one end of the resistance detection electrode 22 protruding from the gas-sensitive body 20. Note that the outer diameter of the gas-sensitive body 20 is 0.8 mm or less, compared to the case where the gas-sensitive body 20 is formed in a substantially flat plate shape or in a substantially cylindrical shape and a coil is embedded in a cylinder. As a result, the gas sensitive body 20 can be reduced in size, and the heat capacity of the gas sensitive body 20 can be reduced.

Here, the gas-sensitive body 20 is made of tin oxide (SnO).
_Two) As the main component and SnO_TwoAgainst palladium (Pd)
1.7 wt%. Below is SnO_Twoof
The adjustment will be briefly described. First, tin chloride (SnC
l_Four) With ammonia (NH_Three) Hydrolyzed with tin
An acid sol is obtained, and the obtained stannic sol is air-dried and then put in the air.
Baking at 500 ° C. for 1 hour,_TwoGet
You. This SnO_TwoImpregnated with an aqueous solution of Pd
For example, baking in air at 500 ° C. for 1 hour to convert Pd
It is carried. SnO supporting Pd_TwoAs aggregate
For example, an equal amount of 1000 mesh alumina is mixed and
After adding terpineol to the paste to make a paste,
Apply to dual-purpose electrode 21 and resistance detection electrode 22
By baking in air at about 500 ° C for 1 hour.
The gas sensing body 20 is formed. Here, SnO_TwoCarried on
Pd improves the response speed to various gases (speed
Plays a role as a catalyst, in addition to Pd
5wt% tungsten (W) supported on tin oxide
And platinum (Pt), rhodium in addition to Pd and W
(Rh), cerium (Ce), molybdenum (Mo)
One or more of _Two0.5wt% supported
You may let it.

The heater / electrode 2 of the sensing element A
FIG. 1 shows a circuit configuration of the control unit 2 that controls the heating of the gas sensor 1 and detects a gas to be detected from a change in the resistance value of the gas-sensitive body 20. In this circuit, the AC voltage of the AC commercial power supply AC is stepped down by a step-down transformer Tr, and the stepped-down voltage is full-wave rectified by diode bridges DB1 and DB2, respectively.
The voltage rectified by one diode bridge DB2 is smoothed by a smoothing capacitor C1, then stabilized at a predetermined voltage by a three-terminal regulator IC1, and supplied to a 4-bit microcomputer (hereinafter referred to as a microcomputer) 3. .

The heater / electrode 21 of the sensing element A
Is connected between the output terminals of a three-terminal regulator IC1 via a PNP transistor Q1.
When 1 is turned on, the heater / electrode 21 is energized, and the heater / electrode 21 generates heat. Also,
The resistance detecting electrode 22 of the sensing element A is connected to a three-terminal regulator IC1 via a series circuit of a PNP transistor Q21 and a load resistor R21 and a series circuit of the PNP transistor Q22 and a load resistor R22 and a diode D1. And to the input port I1 of the microcomputer 3.

The output port O1 of the microcomputer 3 is connected to the base of the transistor Q1, and the output ports O21 and O2
2, the bases of the transistors Q21 and Q22 are connected. Also, the output ports O3 to
O5 includes light emitting diodes LED1 to L for display, respectively.
The cathode of the ED3 is connected, and the output ports O6 and O7 are connected to the cathodes of the light emitting diodes L1 and L2 of the photocouplers PC1 and PC2, respectively. The anodes of the light-emitting diodes LED1 to LED3 and L1 and L2 are connected to a three-terminal regulator IC through current-limiting resistors, respectively.
1 output terminal.

Here, the photocouplers PC1 and PC2 are used as switching elements for outputting a gas detection signal corresponding to the concentration of the detected gas or the like as a voltage signal. The series control type stabilizing circuit 4 for outputting this voltage signal is connected between both ends of a smoothing capacitor C2 for smoothing the rectified output of the diode bridge DB1, and a reference voltage applied to the base of the series control transistor Q3 is obtained by: Photo coupler P
Switching is performed by turning on and off the phototransistors PT1 and PT2 of C1 and PC2.

This reference voltage is supplied to a Zener diode ZD connected to both ends of a smoothing capacitor C2 via a resistor R4.
Is divided by resistors R11 to R13. When the phototransistor PT1 is turned on, the voltage across the series circuit of the resistors R11 to R13, that is, the voltage across the Zener diode ZD is applied to the base of the transistor Q3 as a reference voltage. Applied. When the phototransistor PT2 is turned on, the resistor R11 and the resistors R12, R13
Is applied as a reference voltage to the base of the transistor Q3. Thus, the phototransistors PT1, PT
In response to the on / off operation of 2, the voltage signals corresponding to the respective reference voltages are output to the outside as gas detection signals.

The output port O8 of the microcomputer 3 is connected to the non-inverting input terminal of the comparator CP2, and the output port O9 is connected to the inverting input terminal of the comparator CP3. The signals output from the output ports O8 and O9 alternately invert the signal levels of the outputs of the comparators CP1 and CP2 to low level / high level, and the polarity of the voltage applied to the buzzer 6 comprising a piezoelectric buzzer alternates. And an alarm sound is oscillated and output. In FIG. 1, reference numeral 7 denotes a reference clock oscillation circuit for supplying a reference clock to the microcomputer 3, and IC2 denotes a reset IC for resetting the microcomputer 3 when power is turned on.

On the other hand, a pull-up resistor R2 is connected between the emitter and the base of the transistor Q1, and a PNP transistor Q4 is connected to both ends of the pull-up resistor R2. The transistor Q4, together with the comparator CP1 and the like, constitutes a protection circuit 5 for the heater / electrode 21. In the protection circuit 5, the resistors R6, R
7 is connected to the output terminal of the three-terminal regulator IC1 via the diode D1, the output voltage is divided by the resistors R6 and R7, and the connection point of the resistors R6 and R7 is connected to the inverting input terminal of the comparator CP1. Connected to A series circuit of a resistor R8 and a capacitor C0 is connected between the output port O1 of the microcomputer 3 and the ground of the circuit. A connection point of the resistor R8 and the capacitor C0 is connected to a non-inverting input terminal of the comparator CP1. The output terminal is connected to a transistor Q via a resistor R9.
4 connected to the base.

Between the output terminals of the three-terminal regulator IC1, a series circuit of a thermistor TH1 for sound and humidity compensation, which is a temperature sensor, and a resistor R25 is connected, and the potential of the connection point of the thermistor TH1 and the resistor R25 is set to the microcomputer 3
Is input to the input port I2. The microcomputer 3 takes in the divided voltage of the thermistor TH1 and the resistor R25 from the input port I2, and performs temperature compensation of the voltage between both ends of the gas sensing body 20 taken in from the input port I1.

A series circuit of a resistor R23 and a variable resistor VR1 and a series circuit of a resistor R24 and a variable resistor VR2 are connected between the output terminals of the three-terminal regulator IC1. , I4 are supplied with set voltages set by the variable resistors VR1 and VR2, respectively. The input ports I3, I
The voltage input to each of the variable resistors VR1 and V4 corresponds to the voltage between both ends of the gas sensitive body 20 when the gas concentration of methane or carbon monoxide as the detection target gas reaches the warning level.
This is set using R2.

In the normal state, when the output of the output port O1 of the microcomputer 3 is at a high level, the capacitor C0 is charged via the resistor R8, and the charged voltage exceeds the potential at the connection point between the resistors R6 and R7. Comparator CP
The signal level of the output of the output 1 becomes high level, and the transistor Q4 is turned off. At this time, the transistor Q
1 turns off and the heater / electrode 21 of the sensing element A
The power supply to is stopped.

In the normal state, when the output of the output port O1 of the microcomputer 3 becomes low level for a predetermined time, the transistor Q1 is turned on and the heater / electrode 21 of the sensing element A is energized. On the other hand, when the output of the output port O1 of the microcomputer 3 becomes low level, the charge charged in the capacitor C0 of the protection circuit 5 is discharged via the resistor R8, and the voltage across the capacitor C0 decreases. Due to the time constant, the voltage across the capacitor C0 does not fall below the potential of the connection point between the resistors R6 and R7 until the predetermined time elapses. Therefore, the output of the comparator CP1 is low level until the predetermined time elapses. And the off state of the transistor Q4 is maintained.
Therefore, the transistor Q1 is turned on, and the heater electrode 21 is energized.

Thereafter, in a normal state, when the predetermined time is over, the microcomputer 3 sets the output port O1 to a high level to turn off the transistor Q1, and the heater / electrode 21
Stop supplying power to

By performing the duty control to energize the heater / electrode 21 for a predetermined time at predetermined intervals in this manner, the average value of the voltage applied to the heater / electrode 21 is set to about 0.9 V, and the gas-sensitive body 20 is turned on. A high-temperature period for heating to about 400 ° C. and a low-temperature period for heating the gas-sensitive body 20 to about 60 ° C. with the average value of the voltage applied to the heater / electrode 21 set to about 0.2 V can be set alternately ( (See FIG. 2).

FIG. 3 shows that the temperature of the gas-sensitive body 20 is controlled by controlling the heating of the heater / electrode 21.
After heating to a high temperature for 2 seconds, the response characteristics to various gases when heating at a low temperature are shown. The horizontal axis represents time (second),
The vertical axis represents the resistance value Rs (kΩ) of the gas-sensitive body 20. FIG.
(A) is the measurement result for the atmosphere, and (b) is 100
As a result of the measurement on carbon monoxide (ppm),
The measurement result for 0 ppm carbon monoxide,
As a result of the measurement for methane of 000 ppm,
The measurement results for 000 ppm methane,
(△) is the measurement result for 6000 ppm hydrogen gas, and H (▼) is the measurement result for 6000 ppm hydrogen gas.
Is a measurement result of a mixed gas obtained by mixing 100 ppm of carbon monoxide and 50 ppm of hydrogen gas.
ppm of carbon monoxide and 5000 ppm of hydrogen gas were mixed, the result was 3,000 (p)
The measurement results for a mixed gas obtained by mixing pm methane and 5000 ppm hydrogen gas are shown. As is apparent from the measurement results, in the case of high-concentration hydrogen gas or a mixed gas containing hydrogen gas, approximately 0.5 seconds have elapsed since the switch from the high-temperature period to the low-temperature period (see FIG. 3). At point B), the resistance value of the gas-sensitive body 20 sharply decreases, and the presence or absence of hydrogen gas is detected by detecting the resistance value at this point.

Here, the alarm judging operation of the microcomputer 3 is shown in FIG.
This will be described with reference to the flowchart of FIG. When the high temperature period is reached, the microcomputer 3 sets the output of the output port O21 to a high level to turn on the transistor Q21, and thereby the resistance detection electrode 2 of the sensing element A via the load resistance R21.
A predetermined detection voltage is applied between 2 and one of the heater / electrodes 21. Immediately before switching from the high-temperature period to the low-temperature period (about 4 to 5 seconds after the start of the high-temperature period) (point A in FIG. 3), the microcomputer 3 takes in the voltage across the gas-sensitive body 20 to the input port I1, Temperature compensation is performed based on the divided voltage of the thermistor TH1 and the resistor R25 taken in from the input port I2, the resistance value of the gas sensitive body 20 at the end of the high temperature period is detected, and the methane concentration is detected from the resistance value. . Then, the microcomputer 3 makes an alarm determination for methane by comparing the level of the methane concentration obtained from the resistance value of the gas sensing body 20 with a preset alarm level (S11). When the methane concentration exceeds the alarm level, a gas leak alarm is issued (S1).
5). At this time, the microcomputer 3 outputs predetermined output ports O3 to
O5 is set to low level and the corresponding light emitting diode LED
1 to LED3 are turned on or blinked, the output ports O6 to O7 are set to low level, the corresponding photocouplers PC1 or PC2 are turned on, and a predetermined voltage signal is output from the stabilization circuit 4 to the outside. Further, the microcomputer 3 alternately inverts the output of the output ports O8 and O9, sounds the buzzer 6, and issues an alarm.

On the other hand, if the detected concentration of methane is lower than the alarm level, the microcomputer 3 determines that at about 0.5 second after the switch to the low temperature period (point B in FIG. 3).
The voltage between both ends of the gas sensing body 20 is taken into the input port I1,
The resistance value of the gas-sensitive body 20 is obtained by performing temperature compensation, and the concentration of the hydrogen gas is detected from the resistance value. Then, the microcomputer 3 determines the presence or absence of the hydrogen gas by comparing the concentration of the hydrogen gas obtained from the resistance value of the gas sensing body 20 with a predetermined level (S12).

Here, if the concentration of the hydrogen gas detected in S12 is lower than the predetermined level, the microcomputer 3 determines that there is no hydrogen gas, and immediately before switching from the low-temperature period to the high-temperature period (about 15 minutes from the start of the low-temperature period). Seconds later, C in FIG.
(Point), the voltage between both ends of the gas-sensitive body 20 is read from the input port I1, the temperature is compensated, and the resistance value of the gas-sensitive body 20 is obtained. Then, the microcomputer 3 makes an alarm determination for carbon monoxide by comparing the level of the alarm level with the concentration of carbon monoxide obtained from the resistance value of the gas sensing body 20 (S1).
3) If the detected concentration exceeds the alarm level, an incomplete combustion alarm is issued (S16). At this time, the microcomputer 3 sets the predetermined output ports O3 to O5 to low level, turns on or off the corresponding light emitting diodes LED1 to LED3, sets the output ports O6 to O7 to low level, and sets the corresponding photocoupler PC1 to low. Alternatively, the PC 2 is turned on, and a predetermined voltage signal is output from the stabilizing circuit 4 to the outside. Further, the microcomputer 3 alternately inverts the output of the output ports O8 and O9, sounds the buzzer 6, and issues an alarm. On the other hand, if the concentration of carbon monoxide detected in S13 is lower than the alarm level, the microcomputer 3 continues the monitoring operation without issuing an alarm (S17).

When the concentration of hydrogen gas detected in S12 exceeds a predetermined level, the microcomputer 3 determines that hydrogen gas is present, and at the end of a low-temperature period in which sensitivity to hydrogen gas is high and stable (monoxide). An alarm judgment is made for hydrogen gas at the carbon detection point). That is, immediately before switching from the low-temperature period to the high-temperature period (about 15 seconds after the start of the low-temperature period), the voltage between both ends of the gas-sensitive body 20 is read from the input port I1, and the temperature is compensated to obtain the resistance value of the gas-sensitive body 20. From this resistance value, the concentration of hydrogen gas is detected. Then, the microcomputer 3 makes a warning judgment for the hydrogen gas by comparing the level of the warning level with the concentration of the hydrogen gas obtained from the resistance value of the gas sensing body 20 (S1).
4) If the detected hydrogen gas concentration exceeds the alarm level, a gas leak alarm is issued (S15). At this time, the microcomputer 3 sets the predetermined output ports O3 to O5 to low level,
The corresponding light emitting diodes LED1 to LED3 are turned on or blinked, and the output ports O6 to O7 are set to low level, so that the corresponding photocoupler PC1 or PC2 is set.
Is turned on to output a predetermined voltage signal from the stabilizing circuit 4 to the outside. Further, the microcomputer 3 alternately inverts the output of the output ports O8 and O9, sounds the buzzer 6, and issues an alarm. On the other hand, if the concentration of the hydrogen gas detected in S14 is lower than the alarm level, the microcomputer 3 continues the monitoring operation without issuing an alarm (S17). At about one second after the switch to the low-temperature period (after the determination of the presence or absence of hydrogen gas), the microcomputer 3 sets the output of the output port O21 to low and the output of the output port O22 to high, By turning off the transistor Q21 and turning on the transistor Q22, a predetermined detection voltage is applied between the resistance detection electrode 22 of the sensing element A and one of the heater / electrodes 21 via the load resistance R22. The microcomputer 3 performs an alarm operation for hydrogen or carbon monoxide at the end of the low temperature period. After performing either alarm operation, the microcomputer 3 performs an incomplete combustion alarm operation for detecting carbon monoxide and a hydrogen alarm operation. The gas leak alarm operation for detecting gas may be performed alternately.

As described above, in the gas detection device of the present embodiment, an alarm operation for methane gas is performed at the end of the high-temperature period, and an alarm operation for carbon monoxide gas is performed at the end of the low-temperature period. The presence or absence of hydrogen gas is determined during a period that is distinctive from hydrogen gas immediately after switching to the low-temperature period, and if hydrogen gas is present, hydrogen is detected in the second half of the low-temperature period during which the sensitivity to hydrogen gas is high and stable. Since the alarm judgment is performed on the gas, one gas sensitive body 20 can have a gas leak alarm function for detecting methane and hydrogen and an incomplete combustion alarm function for detecting carbon monoxide gas. ) Japan Gas Appliance Inspection Association's “Gas Alarm Test Rules for City Gas (JIA
E 001-99) "for gases lighter than air (except for 12A and 13A gases lighter than air)
Gas alarm can be realized.

In this circuit, the variable resistors VR1 and VR2
Can be used to adjust the gas concentration at the time of issuing an alarm in the high temperature period and the low temperature period, so that one thermistor TH1 can perform temperature compensation in the high temperature period and the low temperature period. In addition, in this circuit, each time a detection target gas (carbon monoxide gas, methane gas, and hydrogen gas) is detected, a load resistor R2 connected to the sensing element A is detected.
1 and R22, and different types of gases can be detected with high accuracy by appropriately setting the resistance values of the load resistors R21 and R22 according to the gas to be detected. For example, in the present embodiment, the load resistance R21 for methane gas detection is used during the high temperature period, and the load resistance for methane gas detection is set for one second (the period for determining the presence or absence of hydrogen gas) immediately after switching from the high temperature period to the low temperature period. R21 is also used for detecting hydrogen gas, and a load resistor R22 for detecting carbon monoxide gas is used during a low temperature period thereafter.

In the present embodiment, the gas leak alarm is determined by detecting the concentration of hydrogen gas at the end of the low temperature period. However, the timing of detecting hydrogen gas is limited to the end of the low temperature period. Instead, the hydrogen gas may be detected at any timing as long as the sensitivity to the hydrogen gas is stable in the latter half of the low temperature period. Also, as can be seen from the data in FIG. 3, since the sensitivity to hydrogen gas is high and stable in the second half of the high temperature period, the resistance value Rs of the gas sensitive body 20 in the second half of the high temperature period is detected. The presence or absence of hydrogen gas may be detected from the resistance value Rs, or the resistance value Rs of the gas sensitive body 20 may be detected in both the latter half of the low temperature period and the latter half of the high temperature period, and hydrogen may be detected from this resistance value Rs. The presence or absence of gas may be detected.

At the end of the high-temperature period, methane gas is detected to make a gas leak alarm judgment, and at the end of the low-temperature period, carbon monoxide gas is detected to make an incomplete combustion alarm judgment. The timing for performing the leak alarm and the incomplete combustion alarm is not limited to the end of the high-temperature period and the low-temperature period, and the gas leak alarm and the incomplete combustion alarm may be performed during the high-temperature period and the low-temperature period. .

In the circuit configuration of the present embodiment, the microcomputer 3 runs away due to external noise or the like, and the microcomputer 3
Is fixed to a low level, the electric charge charged in the capacitor C0 of the protection circuit 5 is discharged through the resistor R8, and the voltage across the capacitor C0 eventually reduces the potential of the connection point between the resistors R6 and R7. As a result, the output of the comparator CP1 is inverted from the high level to the low level, turning on the transistor Q4, raising the base potential of the transistor Q1 to the power supply voltage, and forcibly turning off the transistor Q1. Therefore, even if the microcomputer 3 goes out of control, the protection circuit 5 forcibly turns off the transistor Q1 and forcibly stops energization to the heater / electrode 21, so that the heater / electrode 21 is energized more than necessary. By setting the time constants of the capacitor C0 and the resistor R8 appropriately, disconnection of the heater / cumulative electrode 21 due to runaway of the microcomputer 3 can be prevented.

The time setting of the high temperature period and the low temperature period may be set to appropriate values depending on the heat capacity of the sensing element A, etc., and is not particularly limited to the above values. By setting the time to about 15 seconds, the detection cycle can be set to 20 seconds or less, such as the “Gas Alarm Test Rules for City Gas (JIA E 001-99)” stipulated by the Japan Gas Appliance Inspection Association. "Incomplete combustion alarm inspection rules" can be satisfied.

As shown in FIG. 7, a cylindrical cap 16 having a ceiling surface on which an external filter 17 made of activated carbon is mounted is mounted on the cover 13 so that gas can be externally sent to the sensing element A. An external filter 17 is arranged in the path where the gas flows, and alcohol vapor as a miscellaneous gas and silicon vapor as a poisoning gas are removed from the external filter 17.
To reduce the sensitivity of the sensing element A to alcohol, protect the sensing element A from poisonous substances such as silicon, and make the sensing element A less susceptible to alcohol vapor or silicon vapor. . In this embodiment, the external filter 1 made of activated carbon is used.
7, the material of the external filter 17 is not limited to activated carbon. The material of the external filter 17 may be silica gel (SiO ₂ ) or a combination of activated carbon and silica gel.

(Embodiment 2) Embodiment 2 of the present invention is shown in FIG.
This will be described with reference to FIG. The gas detection device of the present embodiment is a gas detection device used for natural gas (12A, 13A gas lighter than air). The configuration and operation of the gas detection device other than the alarm operation of the microcomputer 3 are the same as those of the first embodiment. Therefore, only different portions will be described below.

As in the first embodiment, the microcomputer 3 performs duty control to energize the heater / electrode 21 for a predetermined time at predetermined intervals, thereby reducing the average value of the voltage applied to the heater / electrode 21 to about 0.1. Gas sensitive body 20 as 9V
High temperature period for heating the heater to about 400 ° C., and the heater / electrode 2
The low-temperature period in which the gas-sensitive body 20 is heated to about 60 ° C. with the average value of the voltage applied to 1 being about 0.2 V is alternately provided (see FIG. 2).

Here, the alarm judging operation of the microcomputer 3 is shown in FIG.
This will be described with reference to the flowchart of FIG. When the high temperature period is reached, the microcomputer 3 sets the output of the output port O21 to a high level to turn on the transistor Q21, and thereby the resistance detection electrode 2 of the sensing element A via the load resistance R21.
A predetermined detection voltage is applied between 2 and one of the heater / electrodes 21. Immediately before switching from the high-temperature period to the low-temperature period (approximately 4 to 5 seconds after the start of the high-temperature period), the microcomputer 3 takes in the voltage between both ends of the gas-sensitive body 20 to the input port I1, and thermistor TH1 taken in from the input port I2.
And temperature compensation based on the divided voltage of the resistor R25, and the resistance value R of the gas sensitive body 20 at the end of the high temperature period
The channel is detected (S21).

Next, after switching to the low-temperature period, about 0.
At the time when 5 seconds have elapsed, the microcomputer 3 takes in the voltage between both ends of the gas-sensitive body 20 into the input port I1, performs temperature compensation, finds the resistance value of the gas-sensitive body 20, and detects the concentration of hydrogen gas from the resistance value. I do. And the microcomputer 3 is a gas sensitive body 2
The presence or absence of hydrogen gas is determined by comparing the level of the hydrogen gas concentration obtained from the resistance value of 0 with a predetermined level, and the alarm level coefficients Kh1 and Kh2 are determined according to the presence or absence of hydrogen gas (S22). ).

Then, immediately before switching from the low-temperature period to the high-temperature period (about 15 seconds after the start of the low-temperature period), the microcomputer 3 reads the voltage between both ends of the gas sensitive body 20 from the input port I1 and performs temperature compensation to perform the temperature compensation. The resistance value Rco of the gas sensing body 20 at the time of the end of the process is detected (S23).

When the microcomputer 3 detects the resistance values Rch and Rco of the gas sensitive body 20 at the end of the high-temperature period and the low-temperature period, respectively, it firstly sets the resistance value R at the end of the high-temperature period.
By comparing the level (Rch × Kh1) obtained by multiplying the channel by the coefficient Kh1 with a preset methane threshold Ralch, it is determined whether or not the methane concentration exceeds the alarm level (S24). The detection value (Rch × Kh1) is equal to the threshold Ralch
If it is smaller than the threshold value (that is, if the methane concentration exceeds the alarm level), a gas leak alarm is issued (S25).
At this time, the microcomputer 3 sets the predetermined output ports O3 to O5 to low level, and sets the corresponding light emitting diodes LED1 to L5.
Turns on or off the ED3 and outputs the output port O6.
O7 is set to a low level to turn on the corresponding photocoupler PC1 or PC2, and a predetermined voltage signal is output from the stabilization circuit 4 to the outside. Further, the microcomputer 3 alternately inverts the output of the output ports O8 and O9, sounds the buzzer 6, and issues an alarm.

On the other hand, if the detected value (Rch × Kh1) is equal to or greater than the threshold value Ralch in S24, the microcomputer 3 multiplies the resistance value Rco at the end of the low-temperature period by the coefficient Kh2 (Rco).
× Kh2) and a preset carbon monoxide threshold Ralco
It is determined whether or not the concentration of carbon monoxide has exceeded the alarm level (S26). When the detected value (Rco × Kh2) becomes smaller than the threshold value Ralco (ie, the concentration of carbon monoxide). (If exceeds the alarm level), an incomplete combustion is signaled (S27). At this time, the microcomputer 3
Sets the predetermined output ports O3 to O5 to low level, turns on or blinks the corresponding light emitting diodes LED1 to LED3, sets the output ports O6 to O7 to low level, and turns on the corresponding photocoupler PC1 or PC2. Then, a predetermined voltage signal is output from the stabilizing circuit 4 to the outside. Further, the microcomputer 3 alternately inverts the output of the output ports O8 and O9, sounds the buzzer 6, and issues an alarm. On the other hand, in S26, the detection value (Rco × Kh2) is
If it is equal to or greater than co, the microcomputer 3 does not issue an alarm signal,
Returning to step 21, the monitoring operation is continued (S28).

When the microcomputer 3 determines in step S22 that there is no hydrogen gas, the microcomputer 3 sets, for example, 1 as the coefficient Kh2 and determines that hydrogen is present. Then, a value larger than 1 is set as the coefficient Kh2. Therefore, when hydrogen gas is present, the alarm levels for methane and carbon monoxide are each higher than when there is no hydrogen gas, which substantially lowers the sensitivity. It is possible to prevent a gas leak alarm or an incomplete combustion alarm from being issued, thereby improving the accuracy of the alarm.

[0048]

As described above, according to the first aspect of the present invention, a gas-sensitive body whose resistance value changes by adsorbing a gas;
A heater that heats the gas-sensitive body, and a control unit that performs an alarm determination by comparing the level of the alarm level with the concentration of the detection target gas obtained from the resistance value of the gas-sensitive body. The high-temperature period in which the temperature of the gas-sensitive body is high and the low-temperature period in which the temperature of the gas-sensitive body is low are alternately provided, and the concentration of methane gas is detected during the high-temperature period of the gas-sensitive body to perform a gas leak alarm determination. At the same time, the concentration of carbon monoxide gas generated at the time of incomplete combustion in the low temperature period is detected to make an incomplete combustion alarm judgment, and the hydrogen detected during the period that is distinguishable from the hydrogen gas at the time of switching to the low temperature period When the gas concentration exceeds a predetermined level, a gas leak alarm determination is made by detecting the hydrogen gas concentration in at least one of the latter half of the low temperature period or the latter half of the high temperature period in which the sensitivity to hydrogen gas is stable. It is characterized by the fact that the presence or absence of hydrogen gas is determined from the resistance value of the gas-sensitive body during a period that is distinguishable from hydrogen gas at the time of switching to the low temperature period, and if hydrogen gas is present, the sensitivity to hydrogen gas is stabilized Since the alarm determination for the hydrogen gas is performed in at least one of the latter half of the low temperature period or the latter half of the high temperature period, there is an effect that the hydrogen gas can be accurately detected. Therefore, a gas leak alarm function for detecting methane gas and hydrogen gas and an incomplete combustion alarm function for detecting carbon monoxide gas can be provided in one gas-sensitive body. "Gas Alarm Test Rules for City Gas (J
IA E001-99) "can be realized as a gas alarm device for gas lighter than air (except for 12A and 13A gas lighter than air).

According to a second aspect of the present invention, there is provided a gas-sensitive body whose resistance value changes by adsorbing a gas, a heater for heating the gas-sensitive body, and a detection target gas concentration obtained from the resistance value of the gas-sensitive body. A control unit for making an alarm judgment by comparing the level with an alarm level, wherein the control unit controls energization of the heater to increase the temperature of the gas-sensitive body during a high temperature period and to decrease the temperature of the gas sensitive body during a low temperature period. Are alternately provided to detect a gas leak alarm by detecting the concentration of methane gas during the high-temperature period of the gas sensitive body, and detect the concentration of carbon monoxide gas generated during incomplete combustion during the low-temperature period to detect incomplete combustion. Perform an alarm judgment,
In addition, when the concentration of hydrogen gas detected during a period that is distinguishable from hydrogen gas at the time of switching to the low temperature period exceeds a predetermined level, the malfunction level of the gas leak alarm and the incomplete combustion alarm is prevented by the hydrogen gas. It is characterized in that the presence or absence of hydrogen gas is determined from the resistance value of the gas sensitive body during a period that is distinguishable from hydrogen gas at the time of switching to the low temperature period, and if hydrogen gas is present, Since the alarm levels of the leak alarm and the incomplete combustion alarm are each corrected, it is possible to prevent erroneous detection due to hydrogen even when hydrogen as a miscellaneous gas is present, and to improve the accuracy of the alarm. There is.

The invention of claim 3 is characterized in that, in the invention of claim 1 or 2, the cycle of the high temperature period and the low temperature period is about 60 seconds or less, and is defined by the Japan Gas Appliance Inspection Association. There is an effect that the "inspection rules for gas alarm for city gas" and the "inspection rules for incomplete combustion alarm" can be satisfied.

According to a fourth aspect of the present invention, in the first or second aspect of the invention, the control section applies a predetermined voltage to the gas-sensitive body via a load resistor, and determines the resistance of the gas-sensitive body from the voltage generated in the gas-sensitive body. The characteristic value is detected, and the resistance value of the load resistance is switched for each gas detection. By appropriately setting the resistance value of the load resistance, the optimal voltage is applied to the gas sensitive body and different types of There is an effect that gas can be detected with high accuracy.

According to a fifth aspect of the present invention, in the first to fourth aspects, a temperature sensor for detecting an ambient temperature is provided, and based on an output of the temperature sensor, the control unit controls the gas-sensitive body in a high temperature period and a low temperature period. The temperature compensation of the resistance value of the gas sensing element is performed by the control unit based on the output of the temperature sensor, so that the detection target gas can be accurately detected in the high temperature period and the low temperature period. In addition, there is an effect that temperature compensation in a high temperature period and a low temperature period can be performed by one temperature sensor.

According to a sixth aspect of the present invention, in the first to fourth aspects of the present invention, a filter for removing alcohol vapor or silicon vapor from a gas in contact with the gas-sensitive body is provided in the gas flow path from the outside to the gas-sensitive body. The invention according to claim 7 is characterized in that, in the invention according to claim 6, the filter is made of either activated carbon or silica gel,
Since alcohol vapor and silicon vapor are removed from the gas in contact with the gas-sensitive body by the filter layer, the alcohol sensitivity of the gas-sensitive body can be reduced, and the gas-sensitive body can be protected from silicon poison, which is a poisonous substance. effective.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a gas detection device according to a first embodiment.

FIG. 2 is a time chart for explaining the operation of the above.

FIG. 3 is a diagram showing responsiveness to various gases of the above.

FIG. 4 is a flowchart illustrating an operation of the above.

FIG. 5 is a front view showing a state where a cover of the gas detection element used in the first embodiment is removed.

6A and 6B show a gas detection element of the above, wherein FIG. 6A is a partially broken front view and FIG. 6B is a partially broken top view.

7A and 7B show another gas detection device of the above, wherein FIG. 7A is a cross-sectional view in which a part is broken, and FIG. 7B is a bottom view.

FIG. 8 is a flowchart illustrating an operation of the gas detection device according to the second embodiment.

[Explanation of symbols]

 A sensing element 3 microcomputer 21 electrode also serving as heater 22 electrode for detecting resistance

Continued on the front page F term (reference) 2G046 AA03 AA05 AA11 AA19 BA01 BA09 BC03 BC05 BC09 BD02 BD06 BE02 BE08 BJ02 CA09 DB07 DC12 DD02 EA02 EA04 FB00 FB01 FB02 FE00 FE18 FE29 FE31 FE34 FE39 FE46 2G060 AB07 AB03 BD02 HB06 HD01 HE03 KA03

Claims (7)

[Claims] 1. A gas-sensitive body whose resistance value changes by adsorbing a gas, a heater for heating the gas-sensitive body, and a difference between the concentration of a detection target gas obtained from the resistance value of the gas-sensitive body and an alarm level. And a control unit that performs an alarm determination by comparing the temperature of the gas-sensitive body with a high-temperature period in which the temperature of the gas-sensitive body is high and a low-temperature period in which the temperature of the gas-sensitive body is low. Detecting the concentration of methane gas during the high temperature period of the gas sensitive body to make a gas leak alarm judgment, and detecting the concentration of carbon monoxide gas generated during incomplete combustion during the low temperature period to make an incomplete combustion alarm judgment, And, when the concentration of the hydrogen gas detected during a period having a discriminating property with respect to the hydrogen gas at the time of switching to the low temperature period exceeds a predetermined level, the sensitivity to the hydrogen gas is stabilized in the second half of the low temperature period or the second half of the high temperature period. Small Kutomo gas detection apparatus which is characterized in that the detected gas leak alarms determined the concentration of either one with hydrogen gas. 2. A gas-sensitive body whose resistance value changes by adsorbing a gas, a heater for heating the gas-sensitive body, and high and low levels of a concentration of a detection target gas and an alarm level obtained from the resistance value of the gas-sensitive body. And a control unit that performs an alarm determination by comparing the temperature of the gas-sensitive body with a high-temperature period in which the temperature of the gas-sensitive body is high and a low-temperature period in which the temperature of the gas-sensitive body is low. Detecting the concentration of methane gas during the high temperature period of the gas sensitive body to make a gas leak alarm judgment, and detecting the concentration of carbon monoxide gas generated during incomplete combustion during the low temperature period to make an incomplete combustion alarm judgment, In addition, when the concentration of hydrogen gas detected during a period that is distinguishable from hydrogen gas at the time of switching to the low temperature period exceeds a predetermined level, the malfunction level of the gas leak alarm and the incomplete combustion alarm is prevented by the hydrogen gas. Gas detecting apparatus and correcting each so that. 3. The gas detection device according to claim 1, wherein a cycle of the high temperature period and the low temperature period is about 60 seconds or less. 4. The control unit applies a predetermined voltage to the gas-sensitive body via a load resistor and detects a resistance value of the gas-sensitive body from a voltage generated in the gas-sensitive body. 3. The gas detection device according to claim 1, wherein a resistance value of the resistance is switched. 5. The apparatus according to claim 1, further comprising a temperature sensor for detecting an ambient temperature, wherein the control unit performs temperature compensation of a resistance value of the gas-sensitive body in a high temperature period and a low temperature period based on an output of the temperature sensor. Item 3. The gas detection device according to item 1 or 2. 6. A gas flow path from the outside to a gas-sensitive body is provided with a filter for removing alcohol vapor or silicon vapor from gas in contact with the gas-sensitive body.
6. The gas detection device according to any one of claims 5 to 5. 7. The gas detector according to claim 6, wherein said filter is made of either activated carbon or silica gel.