JP2003185611A - Gas detection method and gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detection method capable of certainly detecting the presence of a plurality of gases even if the circumferential temperature varies, and a gas detector therefor. <P>SOLUTION: In a microcomputer 3, a high temperature period for heating a gas-sensitive body to a first set temperature, and a low temperature period for heating the gas-sensitive body to a second set temperature lower than the first set temperature, are alternately provided by controlling the applied voltage to an electrode 21 also used as a heater. The microcomputer 3 takes in the resistance value of the gas-sensitive body immediately before the low temperature period is completed to detect an imperfect combustion gas such as carbon monoxide or the like. Herein, the microcomputer 3 changes timing for taking in the resistance value of the gas-sensitive body to timing making the ratio of the resistance value of the gas-sensitive body in an atmosphere containing gas to be detected and the resistance value of the gas-sensitive body in an atmosphere containing gas other than the gas to be detected almost same on the basis of the detection result of the circumferential temperature in the low temperature period. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a gas detector for detecting gas leakage of combustible gas such as city gas or propane gas, a gas sensitive body containing tin oxide (SnO ₂ ) as a main component has been used. In some cases, flammable gas is detected by utilizing the property that the resistance value decreases due to the redox action when a reducing gas such as flammable gas contacts the surface. There is also provided a device that detects both an incompletely combustible gas such as carbon monoxide (CO) generated during incomplete combustion and a combustible gas by appropriately combining the temperature and materials of the gas-sensitive body.

Such a gas detecting device has a heater for heating the gas-sensitive body, and a high temperature period in which the temperature of the gas-sensitive body is raised by controlling the energization of the heater, and the gas-sensitive body. A low temperature period for lowering the temperature of the gas sensitive body is alternately provided at a predetermined cycle to detect an incomplete combustion gas such as carbon monoxide during the low temperature period of the gas sensitive body, and at the time of the high temperature period of the gas sensitive body. After burning the incomplete combustion gas adhering to the surface and removing the dirt on the surface, methane (CH ₄ )
Such as flammable gas was detected.

[0004]

In the above-described gas detection device, the presence or absence of the gas to be detected is determined by comparing the resistance value of the gas-sensitive body with the level of a predetermined alarm level at the end of the low temperature period or the high temperature period. Although it is determined, the resistance value of the gas-sensitive body greatly varies depending on the ambient temperature, and the influence of the ambient temperature becomes remarkable especially in the low temperature period.
There is a possibility that the detection target gas may be erroneously detected due to a change in ambient temperature.

Therefore, a temperature sensor for detecting the ambient temperature of the gas-sensitive body is provided, and the resistance value of the gas-sensitive body is multiplied by a correction coefficient according to the temperature detected by the temperature sensor to compensate for the change in resistance value due to the ambient temperature. Things have been proposed.

FIG. 14 is a flow chart of such a temperature compensating method. First, the heater voltage VH is switched to a set voltage at high temperature and held for 5 seconds (S11), and the gas sensitive body is detected at 5 seconds of the high temperature period. Of the combustible gas is compared with the resistance level of the combustible gas to determine the presence or absence of the combustible gas (S12). Next, the heater voltage is switched to the set voltage for low temperature and held for 15 seconds (S13).
After detecting the resistance value Rs of the gas sensitive body at the 5th second (S1
4) The ambient temperature is detected (S15), and the correction coefficient h corresponding to the ambient temperature is applied to the resistance value Rs to obtain the correction value Rs' (S16). Then, the presence or absence of carbon monoxide is determined by comparing the level of the carbon monoxide alarm level and the correction value Rs ′.

By the way, FIG. 15 shows the temperature change of the resistance value of the gas-sensitive material at the 20th second in the low temperature period.
(◯) in 5 indicates the resistance value Rs of the gas-sensitive body 20 in the atmosphere,
(▼) is the resistance value Rs of the gas-sensitive body 20 in the atmosphere containing 100 ppm of carbon monoxide (C0), and (Δ) is 100.
Gas-sensitive body 20 in an atmosphere containing 0 ppm hydrogen (H ₂ ).
Resistance value Rs, (●) is 1000 ppm of methane (C
It is the resistance value Rs of the gas sensitive body 20 in the atmosphere containing H ₄ ).

FIG. 16 shows the low temperature period at the 20th second.
The resistance value Rs of the gas sensitive body 20 is calculated by multiplying it by a correction coefficient.
The correction value Rs ′ is shown, and (◯) in FIG. 16 indicates the feeling in the atmosphere.
A correction value Rs ′ obtained from the resistance value Rs of the gas body 20,
(▼) is an atmosphere containing 100 ppm of carbon monoxide (C0)
Correction value R obtained from the resistance value Rs of the gas-sensing body 20 in the air
s', (△) is 1000 ppm hydrogen (H₂)including
Correction value obtained from the resistance value Rs of the gas-sensitive body 20 in the atmosphere
Rs', (●) is 1000 ppm of methane (CH _Four)
Calculated from the resistance value Rs of the gas-sensitive body 20 in an atmosphere containing
It is a correction value Rs'.

As can be seen from FIG. 15, the rate of change in resistance value with respect to temperature change varies depending on the type of gas to be detected, and as shown in FIG. 16, the resistance value in an atmosphere containing 100 ppm carbon monoxide is substantially constant. Even if the temperature coefficient (correction coefficient) is applied to the resistance value of the gas-sensing body to obtain temperature compensation, the resistance value in the other gases will change according to the ambient temperature change. There is a problem in that it is necessary to change the correction coefficient in order to perform temperature compensation, which takes time and effort for temperature compensation.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a gas detection method and an apparatus therefor capable of reliably detecting the presence or absence of a plurality of gases even when the ambient temperature changes. To provide.

[0011]

In order to achieve the above object, in the invention of claim 1, the gas to be detected is determined from the resistance value of the gas-sensing body whose resistance value changes when the gas to be detected comes into contact with the surface. A gas detection method for detecting, wherein the temperature of the gas-sensitive body is heated to a first set temperature, and the temperature of the gas-sensitive body is detected after detecting the first detection target gas from the resistance value of the gas-sensitive body. The ambient temperature of the gas-sensitive body is detected in a state where the temperature is lowered to the second set temperature lower than the first set temperature,
Ratio of the resistance value of the gas-sensitive body in the atmosphere containing the second detection target gas to the resistance value of the gas-sensitive body in the atmosphere containing the gas other than the second detection target gas, based on the detection result of the ambient temperature. To detect the second gas to be detected by changing the timing of taking in the resistance value of the gas-sensitive body so that the ratio becomes approximately the same regardless of the ambient temperature, and taking in the resistance value of the gas-sensitive body at the changed timing. In the state where the temperature of the gas-sensing body is lowered to the second set temperature, the timing of detecting the resistance value of the gas-sensing body is changed according to the ambient temperature, so that the second gas to be detected is The sensing is performed at such a timing that the ratio between the resistance value of the gas-sensitive body in the atmosphere containing the gas and the resistance value of the gas-sensitive body in the atmosphere containing the gas other than the second detection target gas is substantially the same regardless of the ambient temperature. The resistance value of the gas body can be detected. It can be, because the temperature can be compensated at the same time for a plurality of gas including the detection target gas can be prevented erroneous detection due to ambient temperature changes.

According to a second aspect of the invention, in the first aspect of the invention, a high temperature period in which the temperature of the gas-sensing body is heated to the first set temperature and a low temperature period in which the temperature is raised to the second set temperature are alternately repeated. Wherein the resistance value of the gas sensitive body is detected immediately before the end of the low temperature period, and the timing is changed by changing the time width of the low temperature period based on the detection result of the ambient temperature. The same operation as that of the invention of Item 1 is achieved.

According to a third aspect of the invention, in the first aspect of the invention, a high temperature period in which the temperature of the gas-sensitive material is heated to a first set temperature and a low temperature period in which the temperature is heated to a second set temperature are alternately repeated. The timing is changed while keeping the time width of the low temperature period substantially constant, and the same operation as the invention of claim 1 is achieved.

According to a fourth aspect of the present invention, a gas-sensitive material, the resistance value of which changes when the gas to be detected comes into contact with the surface,
A heating unit for heating the gas-sensitive body, a high temperature period in which the temperature of the gas-sensitive body is heated to a first set temperature by controlling the heating state of the heating unit, and a second set temperature lower than the first set temperature. A heating control unit that alternately provides a low temperature period for heating up to, and a gas detection unit that detects the detection target gas from the resistance value of the gas-sensitive body in the high temperature period and the low temperature period, respectively,
The temperature sensor unit that detects the ambient temperature of the gas-sensitive body and the timing at which the gas detection unit detects the resistance value of the gas-sensitive body in the low temperature period include the detection target gas based on the ambient temperature detected by the temperature sensor unit. And a detection timing variable unit that changes the timing so that the ratio of the resistance value of the gas-sensitive body in the atmosphere to the resistance value of the gas-sensitive body in the atmosphere containing a gas other than the gas to be detected becomes approximately the same. The variable detection timing unit changes the timing of detecting the resistance value of the gas-sensitive body in the low temperature period in accordance with the ambient temperature detected by the temperature sensor unit, in an atmosphere containing the gas to be detected. When the resistance value of the gas-sensitive body is approximately the same as the resistance value of the gas-sensitive body in an atmosphere containing a gas other than the gas to be detected, the resistance value of the gas-sensitive body becomes almost the same regardless of the ambient temperature. Since the detected values, for a plurality of gas including the detection target gas can be temperature compensated at a time, it can be prevented erroneous detection due to ambient temperature changes.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the gas detecting section detects the resistance value of the gas sensitive body at the end of the low temperature period, and the detection timing changing section detects the resistance value of the low temperature period. The timing is changed by changing the time width, and the same operation as the invention of claim 4 is achieved.

According to a sixth aspect of the present invention, in the fourth aspect of the present invention, the detection timing changing section changes the timing while keeping the time width of the low temperature period substantially constant. Has the same effect.

[0017]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. As shown in FIGS. 12 (a) and 12 (b), the gas detection element used in the gas detection device of the present embodiment has a substantially disk-shaped resin base 11 and a surface side of the base 11 penetrating the base 11. And three terminals 12a to 12c protruding to the back side, a sensing element A attached to the terminals 12a to 12c via lead wires 13a to 13c, and a sensing element formed in a substantially cylindrical shape having a ceiling surface 14a. A cover 14 is attached to the base 11 so as to cover A, and a metal net 15 for introducing gas, which is attached to a circular hole 14b formed in a ceiling surface 14a of the cover 14.

As shown in FIG. 13, the sensing element A has a so-called sintered body type gas sensitive body 20 which is formed in a substantially spherical shape and contains a metal oxide semiconductor such as tin oxide (SnO ₂ ) as a main component. A heater / electrode 21 made of platinum in the form of a coil is embedded in the gas-sensing body 20, and the resistance-sensing electrode 22 made of a noble metal wire is formed so as to penetrate through the center of the coil of the heater / simultaneous electrode 21. It is formed by being embedded in 20. Here, from the both ends of the heater / electrode 21 protruding from the gas sensitive body 20, the lead wire 13a,
13c is formed, and the lead wire 13b is formed from one end of the resistance detection electrode 22 protruding from the gas sensitive body 20.

Electrode 2 also serving as a heater of this sensing element A
FIG. 1 shows the circuit configuration of the control unit 2 that controls the heating of No. 1 and detects the gas to be detected from the 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 the step-down transformer Tr, and the stepped-down voltage is full-wave rectified by the diode bridges DB1 and DB2.
The voltage rectified by one diode bridge DB2 is smoothed by the smoothing capacitor C1, stabilized by the three-terminal regulator IC1 to a substantially constant voltage, and supplied to the microcomputer (hereinafter, referred to as a microcomputer) 3.

The electrode 21 which also serves as the heater of the sensing element A
Is connected between the output terminals of the three-terminal regulator IC1 via a parallel circuit of a PNP type transistor Q1 and a resistor R10, and the voltage applied to the heater / electrode 21 is divided into two levels, high and low, according to the on / off state of the transistor Q1. It is designed to switch. The resistance detection electrode 22 of the sensing element A includes a diode D1 and a series circuit of a PNP transistor Q21 and a load resistor R21, a series circuit of a PNP transistor Q22 and a load resistor R22.
And the output terminal of the three-terminal regulator IC1 and the input port I1 of the microcomputer 3.

The base of the transistor Q1 is connected to the output port O1 of the microcomputer 3, and the output ports O21 and O2 are connected.
The bases of transistors Q21 and Q22 are connected to 2, respectively. A pull-up resistor R2 is connected between the emitter and base of the transistor Q1, and an emitter-collector of a PNP type transistor Q4 is connected between both ends of the pull-up resistor R2. The transistor Q4 constitutes the protection circuit 5 for the heater / electrode 21 together with the comparator CP1 and the like.

In the protection circuit 5, the three-terminal regulator IC
1 through the diode D1 to the resistor R6, R7
Connected to a series circuit of three-terminal regulator IC1
Is divided by 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. A resistor R8 and a capacitor C0 are provided between the output port O1 of the microcomputer 3 and the circuit ground.
Is connected in series, the connection point of the resistor R8 and the capacitor C0 is connected to the non-inverting input terminal of the comparator CP1, and the output terminal of the comparator CP1 is connected to the base of the transistor Q4 via the resistor R9.

When the output of the output port O1 of the microcomputer 3 is inverted from low to high, the transistor Q1 is turned off and the heater / electrode 21 is connected via the resistor R10.
Since a voltage is applied to the heater / electrode 21, the voltage applied to the heater / electrode 21 decreases. When the output port O1 of the microcomputer 3 becomes high, the capacitor C0 is charged via the resistor R8, and when the charging voltage exceeds the potential at the connection point of the resistors R6 and R7, the output of the comparator CP1 becomes high, The transistor Q4 turns off.

Next, when the output port O1 of the microcomputer 3 is inverted from high to low, the transistor Q1 is turned on,
Since the voltage is applied to the heater / electrode 21 via the transistor Q1, the voltage applied to the heater / electrode 21 increases. When the output port O1 of the microcomputer 3 is inverted from high to low, the electric charge charged in the capacitor C0 is discharged through the resistor R8, and the voltage across it is gradually reduced. Then, after a lapse of a predetermined time determined by the time constant of the capacitor C0 and the resistor R8, the voltage across the capacitor C0 falls below the potential at the connection point of the resistors R6 and R7, the output of the comparator CP1 becomes low, and the transistor Q4 is turned on. Turn on. At this time, the base and emitter of the transistor Q1 are short-circuited, so that the transistor Q1 is turned off and the voltage applied to the heater / electrode 21 decreases.

In this way, the microcomputer 3 as the heating control unit
However, the average value of the heater voltage VH applied to the heater / electrode 21 is set to about 0.9 V by performing duty control such that the voltage applied to the heater / electrode 21 is switched to a high voltage for each predetermined period for a predetermined time. A high temperature period in which the gas-sensitive body 20 is heated to approximately 400 ° C. and a low-temperature period in which the average value of the heater voltage VH is approximately 0.2 V and the gas-sensitive body 20 is heated to approximately 60 ° C. can be provided alternately (FIG. 11).

When the output port O1 of the microcomputer 3 is fixed at a low level due to a runaway of the microcomputer 3 due to external noise or the like, the electric charge stored in the capacitor C0 of the protection circuit 5 is discharged through the resistor R8. Then, the voltage across the capacitor C0 falls below the potential at the connection point between the resistors R6 and R7, and the output of the comparator CP1 is inverted from the high level to the low level to turn on the transistor Q4 and the base potential of the transistor Q1 to the power supply voltage. And the transistor Q1 is forcibly turned off. Therefore, even if the microcomputer 3 runs away and the transistor Q1 is turned on, the protection circuit 5 forcibly turns off the transistor Q1 and forcibly stops the energization of the heater / electrode 21. The dual-purpose electrode 21 is not energized more than necessary, and the capacitor C0 and the resistor R
By setting the time constant of 8 appropriately, the microcomputer 3
It is possible to prevent the heater / electrode 21 from being disconnected due to runaway of the electrode.

By the way, between the output terminals of the three-terminal regulator IC1, a series circuit of a temperature sensor / humidity compensating thermistor TH1 and a resistor R25 is connected, and the potential at the connection point of the thermistor TH1 and the resistor R25 is connected. It is input to the input port I2 of the microcomputer 3. The microcomputer 3 takes in the divided voltage of the thermistor TH1 and the resistor R25 from the input port I2, and temperature-compensates the resistance value of the gas sensing body 20 according to this voltage value. The method of temperature compensation will be described later.

2 to 4 show response characteristics to various gases when the gas-sensitive body 20 is heated at a high temperature for 5 seconds and then at a low temperature for a predetermined time. Shows the response characteristic when the ambient temperature is 20 ° C., FIG. 3 shows the response characteristic when the ambient temperature is −10 ° C., and FIG. 4 shows the response characteristic when the ambient temperature is 50 ° C. Further, in each figure, (○) indicates the resistance value Rs of the gas sensitive body 20 in the atmosphere, (▼) indicates the resistance value Rs of the gas sensitive body 20 in the atmosphere containing 100 ppm of carbon monoxide, (△).
Is a gas-sensitive body 20 in an atmosphere containing 1000 ppm of hydrogen.
Indicates the resistance value Rs of the gas sensitive body 20 in the atmosphere containing 1000 ppm of methane.

From these measurement results, it was found that the response characteristics of the resistance value Rs with respect to various gases differ depending on the ambient temperature in the low temperature period. That is, when the ambient temperature is lower than room temperature (20 ° C.), the response speed of the resistance value Rs becomes slow, and when the ambient temperature is higher than room temperature (20 ° C.), the response speed of the resistance value RS becomes faster. . Thus, the microcomputer 3 as the detection timing variable unit determines the timing of detecting the resistance value Rs during the low temperature period from the resistance value Rs in the atmosphere containing the gas to be detected (100 ppm carbon monoxide) and the other values. The ratio with the resistance value Rs in the atmosphere containing a gas (for example, 1000 ppm hydrogen or 1000 ppm methane) is changed according to the ambient temperature so that the ratio becomes substantially the same regardless of the ambient temperature, and the sensitivity in the low temperature period is increased. Since the detection result of the resistance value of the gas body 20 can be made substantially the same value, temperature compensation can be performed at once for a plurality of types of gas. Here, assuming that the resistance value Rs of the gas sensitive body 20 is detected immediately before the end of the low temperature period, the relationship between the ambient temperature t of the gas sensitive body 20 and the time width TL of the low temperature period is expressed by the following equation.

TL = 0.0039 × t ² −0.5056 × t + 23.556 (1) From equation (1), when the ambient temperature is 20 ° C., the time width TL≈15 (seconds) of the low temperature period, −10 In the case of ℃, time width TL ≒ 29
(Seconds), in the case of 50 ° C., the time width TL≈8 (seconds).
Note that FIG. 8 shows the relationship between the ambient temperature t and the time width TL of the low temperature time. Further, in FIGS. 5 to 7, the ambient temperature is 20 ° C., −10
Detection point t of heater voltage and resistance value Rs at ℃ and 50 ℃
The relationship with a, tb, and tc is shown, respectively.

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, and the input port of the microcomputer 3 is connected. I3, I4
A set voltage set by the variable resistors VR1 and VR2 is input to each. The input port I3,
The voltage input to I4 is set to the voltage corresponding to the resistance value of the gas sensing body 20 when the gas concentration of methane or carbon monoxide as the detection target gas reaches the warning level.

Further, the output ports O3 to O5 of the microcomputer 3
Each has a light-emitting diode for display LED1 to LED
3 is connected to the cathode, and the light emitting diodes L of the photocouplers PC1 and PC2 are connected to the output ports O6 and O7, respectively.
The cathodes of 1 and L2 are connected. The anodes of the light emitting diodes LED1 to LED3 and L1 and L2 are connected to the output terminals of the three-terminal regulator IC1 via current limiting resistors.

The photocouplers PC1 and PC2 are used as switch elements for outputting a gas detection signal corresponding to the concentration of the detection gas as a voltage signal. The series control type stabilizing circuit 4 for outputting this voltage signal is a smoothing capacitor C2 for smoothing the rectified output of the diode bridge DB1.
Of the reference voltage applied to the base of the series control transistor Q3, which is connected between both ends of the photocouplers PC1 and P3.
Switching is performed by turning on / off the phototransistors PT1 and PT2 of C2.

This reference voltage is applied to the Zener diode ZD connected across the smoothing capacitor C2 via the resistor R4.
Is obtained by dividing the voltage across the resistors R11 to R13, and when the phototransistor PT1 is on, the voltage across the series circuit of the resistors R11 to R13, that is, the voltage across the Zener diode ZD is used as a reference voltage at the base of the transistor Q3. Is applied. When the phototransistor PT2 is turned on, the resistance R11 and the resistances R12 and R13 are
A voltage obtained by dividing the voltage across the Zener diode ZD is applied as a reference voltage to the base of the transistor Q3. When the phototransistors PT1 and PT2 are turned on, the series circuit of the resistors R11 and R12 and the resistor R13 are connected.
A voltage obtained by dividing the voltage across the Zener diode ZD is applied as a reference voltage to the base of the transistor Q3. Thus, voltage signals corresponding to the respective reference voltages are output to the outside as gas detection signals according to ON / OFF of the phototransistors PT1 and PT2.

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 signal levels of the outputs of the comparators CP1 and CP2 are alternately inverted to the low level / high level by the signals alternately output from the output ports O8 and O9, and the polarities of the voltage applied to the buzzer 6 formed of the piezoelectric buzzer alternate. The alarm sound is oscillated and output. Reference numeral 7 in FIG. 1 is a reference clock oscillation circuit for giving a reference clock to the microcomputer 3, and IC2 is a reset IC for resetting the microcomputer 3 when the power is turned on.

Here, the alarm determination operation of the microcomputer 3 is shown in FIG.
This will be described with reference to the flowchart of No. 0. First, the microcomputer 3 switches the output of the output port O1 to high / low and controls the on / off of the transistor Q1 to set the average value of the heater voltage VH to about 0.9 V and the gas sensing body 20 to about 400 ° C. Is heated in the high temperature state (S1).
At this time, the microcomputer 3 sets the output of the output port O21 to high and turns on the transistor Q21, so that the resistance detecting electrode 22 of the sensing element A and one of the heater / cumulative electrodes 21 are connected via the load resistor R21. A predetermined detection voltage is applied.

The microcomputer 3 as a gas detection unit takes in the voltage across the gas sensing body 20 from the input port I1 immediately before switching from the high temperature period to the low temperature period (about 5 seconds after the start of the high temperature period) and changes the temperature during the high temperature period. Sensitive gas body 2 at the end
A resistance value of 0 is detected, and the concentration of methane is detected from this resistance value (S2). Then, in the microcomputer 3, the gas sensitive body 2
The methane concentration obtained from the resistance value of 0 is compared with a preset alarm level to make an alarm determination for methane (S3).

Here, when the detected concentration of methane exceeds the alarm level, the microcomputer 3 causes the predetermined output ports O3 ...
O5 is set to low level and the corresponding light emitting diode LE
The D1 to LED3 are turned on or blinked, the output ports O6 to O7 are set to low level, the corresponding photocoupler PC1 or PC2 is turned on, and the stabilization circuit 4 outputs a predetermined voltage signal to the outside. Also the microcomputer 3
Alternately inverts the outputs of the output ports O8 and O9, causes the buzzer 6 to ring, and issues an alarm.

Next, the microcomputer 3 takes in the divided voltage of the thermistor TH1 and the resistor R25 from the input port I2, detects the ambient temperature t from the resistance value of the thermistor TH1 (S4), and uses the above equation (1). The time width (low temperature time) TL of the low temperature period is obtained from the ambient temperature t (S5).

When the microcomputer 3 obtains the time width TL of the low temperature period from the detected value of the ambient temperature, it switches the output of the output port O1 to high / low to control the on / off of the transistor Q1 to thereby control the heater voltage. The average value of VH is set to about 0.2 V, and the gas sensitive body 20 is heated at a low temperature of about 60 ° C. for the time width TL (S6). When the high temperature period is switched to the low temperature period, the microcomputer 3 outputs the output port O2.
By setting the output of No. 1 to low, the output of the output port O22 to high, and turning off the transistor Q21 and turning on the transistor Q22, the resistance detection electrode 22 of the sensing element A and one of the heater / combined electrodes 21 via the load resistor R22. A predetermined detection voltage is applied between and.

After that, the microcomputer 3 takes in the voltage across the gas sensing body 20 from the input port I1 immediately before switching from the low temperature period to the high temperature period (about 15 seconds after the start of the low temperature period when the ambient temperature is 20 ° C.). Then, the resistance value Rs of the gas sensitive body 20 at the end of the low temperature period is detected, and the concentration of carbon monoxide is detected from this resistance value Rs (S7). Then, the microcomputer 3 makes an alarm determination for carbon monoxide by comparing the concentration of carbon monoxide obtained from the resistance value of the gas-sensitive body 20 with a preset alarm level (S8).

When the detected concentration of carbon monoxide exceeds the alarm level, an incomplete combustion alarm is issued. At this time,
The microcomputer 3 sets the predetermined output ports O3 to O5 to the low level, lights or blinks the corresponding light emitting diodes LED1 to LED3, and sets the output ports O6 to O7 to the low level to set the corresponding photocoupler PC1 or PC2. The stabilization circuit 4 is turned on to output a predetermined voltage signal to the outside. Further, the microcomputer 3 outputs the output port O8,
The output of O9 is alternately inverted and the buzzer 6 is sounded to issue an alarm. On the other hand, if the concentration of carbon monoxide detected in S13 is lower than the alarm level, the microcomputer 3 does not issue an alarm and continues the monitoring operation.

By repeating the operations of S1 to S8 described above by the microcomputer 3, the warning determination of methane and carbon monoxide is repeatedly performed.

As described above, in the gas detection method of the present embodiment, carbon monoxide is detected immediately before the end of the low temperature period, and the time width TL of the low temperature period changes according to the ambient temperature of the gas-sensitive body 20. By doing so, the ratio of the resistance value Rs in the atmosphere containing the gas to be detected to the resistance value Rs in the atmosphere containing the other gas can be made substantially constant regardless of the ambient temperature, and a plurality of gas to be detected can be detected. About temperature compensation can be done at once. In the present embodiment, carbon monoxide is detected immediately before the end of the low temperature period, and the timing for detecting the resistance value Rs is changed by changing the time width of the low temperature period according to the ambient temperature. However, the time width of the low temperature period may be a sufficiently long constant value, and the timing of detecting the resistance value Rs may be changed according to the ambient temperature.

[0046]

As described above, the invention of claim 1 is a gas detection method for detecting a gas to be detected from the resistance value of a gas-sensing body whose resistance value changes when the gas to be detected comes into contact with the surface. Then, after detecting the first detection target gas from the resistance value of the gas-sensitive body in a state where the temperature of the gas-sensitive body is heated to the first set temperature, the temperature of the gas-sensitive body is set to be higher than the first set temperature. The ambient temperature of the gas-sensitive body is detected in a state where the temperature is lowered to the second low set temperature, and the resistance value of the gas-sensitive body in the atmosphere including the second detection target gas is detected based on the detection result of the ambient temperature. The timing of taking in the resistance value of the gas-sensitive material is changed and changed so that the ratio with the resistance value of the gas-sensitive material in the atmosphere containing a gas other than the second detection target gas becomes substantially the same regardless of the ambient temperature. The resistance value of the gas sensitive material is taken in at the timing of By detecting the gas to be detected, by changing the timing of detecting the resistance value of the gas-sensitive body according to the ambient temperature in a state where the temperature of the gas-sensitive body is lowered to the second set temperature, The ratio of the resistance value of the gas-sensitive body in the atmosphere containing the second detection target gas and the resistance value of the gas-sensitive body in the atmosphere containing the gas other than the second detection target gas is substantially the same regardless of the ambient temperature. It is possible to detect the resistance value of the gas sensitive body at the timing such that
Since a plurality of gases including the gas to be detected can be temperature-compensated at once, there is an effect that erroneous detection due to a change in ambient temperature can be prevented.

According to a second aspect of the invention, in the first aspect of the invention, a high temperature period in which the temperature of the gas-sensitive material is heated to the first set temperature and a low temperature period in which the temperature is raised to the second set temperature are alternately repeated. Wherein the resistance value of the gas sensitive body is detected immediately before the end of the low temperature period, and the timing is changed by changing the time width of the low temperature period based on the detection result of the ambient temperature. The same effect as that of the invention of Item 1 is achieved.

According to a third aspect of the invention, in the first aspect of the invention, a high temperature period in which the temperature of the gas-sensing body is heated to the first set temperature and a low temperature period in which the temperature is raised to the second set temperature are alternately repeated. The timing is changed while keeping the time width of the low temperature period substantially constant, and the same effect as the invention of claim 1 is achieved.

According to a fourth aspect of the present invention, by controlling the gas sensitive body whose resistance value changes when the gas to be detected comes into contact with the surface, the heating section for heating the gas sensitive body, and the heating state of the heating section. A heating control unit for alternately providing a high temperature period for heating the temperature of the gas-sensitive body to a first set temperature and a low temperature period for heating to a second set temperature lower than the first set temperature, and a high temperature period and a low temperature period. The gas detection unit that detects the detection target gas from the resistance value of the gas-sensitive body, the temperature sensor unit that detects the ambient temperature of the gas-sensitive body, and the gas detection unit detects the resistance value of the gas-sensitive body in the low temperature period. The timing is based on the ambient temperature detected by the temperature sensor, and is the ratio of the resistance value of the gas-sensitive body in the atmosphere containing the gas to be detected to the resistance value of the gas-sensitive body in the atmosphere containing a gas other than the gas to be detected. Are almost the same It is characterized by comprising a detection timing variable unit for changing the timing to obtain a ratio, and the detection timing variable unit detects the timing of detecting the resistance value of the gas-sensitive body in the low temperature period by the temperature sensor unit. It is changed according to the ambient temperature, and the ratio of the resistance value of the gas-sensitive body in the atmosphere containing the detection target gas to the resistance value of the gas-sensitive body in the atmosphere containing the gas other than the detection target gas is related to the ambient temperature. Since the resistance value of the gas-sensitive body is detected at such a timing that the ratio becomes substantially the same, temperature compensation can be performed at once for a plurality of gases including the gas to be detected, and erroneous detection due to ambient temperature change can be prevented. There is an effect.

According to a fifth aspect of the present invention, in the fourth aspect of the invention, the gas detecting section detects the resistance value of the gas sensitive body at the end of the low temperature period, and the detection timing changing section detects the resistance value of the low temperature period. The timing is changed by changing the time width, and the same effect as the invention of claim 4 is obtained.

The invention according to claim 6 is characterized in that, in the invention according to claim 4, the detection timing varying section changes the timing while keeping the time width of the low temperature period substantially constant. Has the same effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a gas detection device of the present embodiment.

FIG. 2 is a diagram showing response characteristics in various gases when the ambient temperature is 20 ° C. in the above.

FIG. 3 is a diagram showing response characteristics in various gases when the ambient temperature is −10 ° C. in the above.

FIG. 4 is a diagram showing response characteristics in various gases when the ambient temperature is 50 ° C. in the above.

FIG. 5 is a time chart showing the heater voltage and the detection timing when the ambient temperature is 20 ° C. in the above.

FIG. 6 is a time chart showing the heater voltage and the detection timing when the ambient temperature is −10 ° C. in the above.

FIG. 7 is a time chart showing the heater voltage and the detection timing when the ambient temperature is 50 ° C. in the above.

FIG. 8 is a diagram showing a relationship between an ambient temperature and a time width of a low temperature period in the above.

FIG. 9 is a diagram showing temperature characteristics of resistance values of the above gas-sensitive body.

FIG. 10 is a flowchart illustrating a gas detection method of the above.

FIG. 11 is a time chart of the heater voltage of the above.

12A and 12B show the above gas detection element, wherein FIG. 12A is a partially cutaway front view, and FIG. 12B is a partially broken top view.

FIG. 13 is a front view showing a state in which a cover of the above gas detection element is removed.

FIG. 14 is a flowchart illustrating a conventional gas detection method.

FIG. 15 is a diagram showing a temperature characteristic of a resistance value of a gas sensitive body used in a conventional gas detection device.

FIG. 16 is a diagram showing a temperature characteristic of a resistance value after temperature compensation in the above.

[Explanation of symbols]

3 Microcomputer 21 Heater and electrode

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G01N 27/04 G01N 27/04 P QF term (reference) 2G046 AA02 AA05 AA11 AA19 BA02 BA09 BB01 BC03 BC05 BE02 BF05 BG01 BH10 BJ02 BJ08 BJ10 DA03 DB05 DC02 DC09 DC12 DC14 DC16 DC17 DC18 DD02 EB06 FA01 FB02 FE10 FE12 FE25 FE31 FE39 2G060 AA01 AB03 AB08 AB17 AE19 AF03 AF07 AG01 BA01 BB02 BB09 BD02 BD06 BD08 HA02 HB06 HC03 HC07 HC13 HC19 HC21 HC22 HC26 HD01 HD02 HE03 KA01 3K003 QA01 TB04 TB06 TC01

Claims (6)

[Claims] 1. A gas detection method for detecting a target gas to be detected from the resistance value of the target gas, the resistance value of which changes when the target gas comes into contact with the surface, the temperature of the target gas being set to a first value. With heating to temperature,
After detecting the first detection target gas from the resistance value of the gas-sensing body, the ambient temperature of the gas-sensing body in a state where the temperature of the gas-sensing body is lowered to the second setting temperature lower than the first setting temperature. And the resistance value of the gas-sensitive body in the atmosphere containing the second detection target gas and the resistance of the gas-sensitive body in the atmosphere containing a gas other than the second detection target gas based on the detection result of the ambient temperature. The timing of taking in the resistance value of the gas-sensitive body is changed so that the ratio with the value becomes substantially the same regardless of the ambient temperature, and the resistance value of the gas-sensitive body is taken in at the changed timing to obtain the second detection target gas. A method for detecting a gas, which comprises: 2. A high-temperature period in which the temperature of the gas-sensitive body is heated to a first set temperature and a low-temperature period in which the temperature is heated to a second set temperature are alternately repeated, and the temperature of the gas-sensitive body is changed immediately before the end of the low-temperature period. The gas detection method according to claim 1, wherein the resistance value is detected, and the timing is changed by changing the time width of the low temperature period based on the detection result of the ambient temperature. 3. A high temperature period in which the temperature of the gas-sensitive material is heated to a first set temperature and a low temperature period in which it is heated to a second set temperature are alternately repeated, and the time width of the low temperature period is substantially constant. The gas detection method according to claim 1, wherein the timing is changed. 4. A gas-sensitive body whose resistance value changes when a gas to be detected comes into contact with a surface, a heating unit for heating the gas-sensitive body, and a temperature of the gas-sensitive body by controlling a heating state of the heating unit. A heating control unit for alternately providing a high temperature period for heating the first set temperature and a low temperature period for heating the second set temperature lower than the first set temperature; The temperature sensor detects the gas detection unit that detects the gas to be detected from the resistance value, the temperature sensor unit that detects the ambient temperature of the gas-sensitive body, and the timing when the gas detection unit detects the resistance value of the gas-sensitive body in the low temperature period. Based on the ambient temperature detected by the unit, the ratio of the resistance value of the gas-sensitive body in the atmosphere containing the gas to be detected to the resistance value of the gas-sensitive body in the atmosphere containing the gas other than the gas to be detected is approximately the same ratio. To be Gas detecting apparatus characterized by comprising a detection timing variable unit for changing the timing. 5. The gas detection unit detects the resistance value of the gas sensitive body at the end of the low temperature period, and the detection timing variable unit changes the timing by changing the time width of the low temperature period. The gas detection device according to claim 4, wherein 6. The gas detection device according to claim 4, wherein the detection timing varying unit changes the timing while keeping a time width of the low temperature period substantially constant.