JP4116989B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detection device that detects incomplete combustion gases such as flammable gases and carbon monoxide generated during incomplete combustion in general households and industrial fields.

Conventionally, as a gas detection device for detecting gas leaks of flammable gases such as city gas and propane gas, a gas sensitive body mainly composed of tin oxide (SnO ₂ ) and sensitive to flammable gases has been used. A device for detecting combustible gas from a change in resistance value of a gas body is provided.

Such a gas detection device has a heater for heating the gas sensitive body, controls energization to the heater, and alternately provides a high temperature heating period and a low temperature heating period at a predetermined cycle. Using the property that the resistance value changes due to the oxidation-reduction reaction when it comes into contact with the gas to be detected, while detecting incomplete combustion gas such as carbon monoxide (CO) generated during incomplete combustion in the low temperature heating period, A flammable gas such as methane (CH ₄ ) is detected during a high-temperature heating period, and a gas leak alarm or incomplete combustion alarm is output when the concentration of combustible gas or incomplete combustion gas exceeds a predetermined alarm level. (See, for example, Patent Document 1). Note that the gas concentration of the gas to be detected (flammable gas, etc.) is actually detected indirectly by comparing the resistance value of the gas sensitive body with the resistance value in the clean atmosphere. By comparing the value with the resistance value corresponding to the alarm level described above, the presence or absence of gas leakage was determined.
JP 2002-82083 A

  By the way, when the above-described gas detection device is used for detection of methane and carbon monoxide, it is necessary to prevent misdetection of hydrogen gas, which is a miscellaneous gas, and issue a gas leak alarm. When both the detection target gas and hydrogen gas are present in the atmosphere, the resistance value of the gas sensitive body is lower than when only the detection target gas is present due to the influence of hydrogen gas. In this case, the sensitivity to hydrogen has been reduced, but deterioration of the catalytic action over time has been a problem.

  Accordingly, the inventors pay attention to a period in which the hydrogen gas immediately after switching from the high temperature heating period to the low temperature heating period is discriminating, and in this period, the hydrogen gas concentration obtained from the resistance value of the gas sensor is predetermined. When the above judgment level is exceeded, the malfunction level due to hydrogen gas is prevented by correcting the alarm level of the combustible gas so as to shift to the high concentration side. The gas concentration of hydrogen gas is also detected indirectly by comparing the resistance value of the gas sensitive body with the resistance value in the clean atmosphere, and the resistance value of the gas sensitive body corresponds to the above-mentioned determination level. If it falls below, the alarm level is corrected. In the case of the gas sensitive body described above, the resistance value when hydrogen gas is present is lower than the resistance value when combustible gas is present in the atmosphere, so the resistance value corresponding to the determination level of hydrogen gas is It is set to a value lower than the resistance value corresponding to the alarm level of combustible gas.

  However, when the alarm level of the combustible gas is corrected according to the resistance value of the gas sensitive body for a predetermined period immediately after switching to the low temperature heating period, it is detected that the concentration of the combustible gas has become higher than the alarm level. After the gas leak alarm is output, if the hydrogen gas leaks and the hydrogen gas concentration exceeds the judgment level, the alarm level of the combustible gas is corrected to the high concentration side, causing the gas leak alarm to stop sounding. There was a problem to do. Further, when the gas concentration of the combustible gas exceeds the alarm level and further increases, the resistance value of the gas sensor further decreases. Therefore, the resistance value of the gas sensor during the predetermined period is a resistance corresponding to the determination level of hydrogen gas. In this case, the alarm level of the combustible gas is corrected to the high concentration side, which causes a problem that the gas leak alarm stops sounding.

  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 device that prevents malfunction due to hydrogen gas and prevents a gas leak alarm from stopping. is there.

To achieve the above object, a first aspect of the invention, a gas-sensitive member which changes the resistance value depending on the gas concentration, the gas concentration determined from the resistance value of the gas-sensitive body, a combustible other than hydrogen gas and alarm means for warning level on sexual gas or incomplete combustion gases for outputting an alarm is exceeded, determining the concentration of the hydrogen gas calculated from the resistance value of the gas-sensitive body during a period in which a discrimination to hydrogen gas is given A correction means for correcting the alarm level so as to shift the alarm level to a higher concentration side when exceeding the level, and means for setting the alarm level to an initial value when the alarm means outputs an alarm are provided. .

The invention according to claim 2 is the invention according to claim 1, wherein the alarm target gas is methane gas and incomplete combustion gas, and the heating means for heating the gas sensitive body and the heating amount by controlling the heating amount of the heating means are used. and heating control means for providing a time and a low temperature heating period alternately provided, the alarm means includes a gas leak gas concentration methane gas obtained from the resistance value of the gas-sensitive member at high temperature heating period is exceeded the first warning level and it outputs an alarm, and outputs a super-El and incomplete combustion alarm gas concentration of incomplete combustion gas obtained from the resistance value of the gas-sensitive body a second warning level in the low temperature heating period.

  According to a third aspect of the present invention, in the second aspect of the present invention, the correcting means is configured to detect the hydrogen gas from the resistance value of the gas sensitive body in a period in which the correction is made with respect to the hydrogen gas immediately after switching from the high temperature heating period to the low temperature heating period. The density | concentration of is calculated | required.

  The invention according to claim 4 is the invention according to claim 2 or 3, wherein the correction means shifts at least one of the first and second alarm levels to the high concentration side when the hydrogen gas concentration exceeds the determination level. It corrects so that it may be made.

As described above, according to the present invention, when the concentration of the hydrogen gas obtained from the resistance value of the gas sensitive body exceeds a predetermined determination level in a period in which the hydrogen gas is discriminative, the correction means detects the alarm level. Is corrected to the high concentration side, so that misdetection due to hydrogen can be prevented even in the presence of miscellaneous hydrogen, and when the alarm means outputs an alarm , the alarm level is set to the initial value. Stops the alarm level correction process by the correction means, so even if hydrogen gas leaks after the alarm is output and the hydrogen gas concentration exceeds the judgment level, the alarm level is shifted to the high concentration side. It is possible to prevent the alarm from stopping midway. Further, if the gas concentration of the detection target gas further increases after the alarm is output, the resistance value of the gas detection body decreases due to the increase of the detection target gas concentration, and the resistance of the gas detection body during the period in which the gas detection is discriminating. Although there is a possibility that the value falls below the resistance value corresponding to the judgment level, the alarm stops sounding halfway because the alarm level is prevented from shifting to the high concentration side by means of setting the alarm level as the initial value. Can be prevented.

  In addition, the heating control means controls the heating amount of the heating means to alternately provide a high temperature heating period and a low temperature heating period, and the alarm means makes an alarm judgment of methane gas during the high temperature heating period and is not effective during the low temperature heating period. If the complete combustion gas alarm determination is performed, it is possible to perform both a gas leak alarm and an incomplete combustion alarm using one gas sensitive body.

  Further, it is preferable that the correcting means obtains the concentration of the hydrogen gas from the resistance value of the gas sensitive body in a period in which the hydrogen gas immediately after switching from the high temperature heating period to the low temperature heating period is discriminated.

  Furthermore, the correcting means preferably corrects so that at least one of the first and second alarm levels is shifted to the high concentration side when the concentration of hydrogen gas exceeds the determination level. It is possible to prevent a gas leak alarm or an incomplete combustion alarm from being detected.

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

  The gas detection device of this embodiment is a gas detection device for gas lighter than air (excluding those for 12A and 13A gas lighter than air), and the gas detection elements used in this gas detection device are shown in FIGS. (A) As shown in (b), a substantially disk-shaped resin base 11, three terminals 12 a to 12 c penetrating the base 11 and projecting to the front side and the back side of the base 11, and terminals A sensing element A attached to 12a to 12c via lead wires 13a to 13c, and a cover 14 formed in a substantially cylindrical shape having a ceiling surface 14a and attached to the base 11 so as to cover the sensing element A; And a stainless steel wire mesh 15 attached to a round hole 14b in the ceiling surface 14a of the cover 14.

As shown in FIG. 5, the sensing element A has a so-called sintered body type gas sensitive body 20 which is mainly spherical and has a spherical shape (spherical or elliptical sphere), which is mainly composed of a metal oxide semiconductor such as tin oxide (SnO ₂ ). The heater-sensitive electrode 21 made of coiled platinum is embedded in the gas-sensitive body 20, and the central electrode 22 made of a noble metal wire is gas-sensitive so as to penetrate the center of the coil of the heater-cumulative electrode 21. It is embedded in the body 20 and formed. Here, the above-described lead wires 13a and 13c are configured from both end portions of the heater combined electrode 21 protruding from the gas sensitive body 20, and the lead wire 13b is extended from one end portion (lower end portion) of the center electrode 22 protruding from the gas sensitive body 20. Is configured. 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 formed in a substantially cylindrical shape and a coil is embedded in the cylinder. Thus, the gas sensitive body 20 can be reduced in size, and the heat capacity of the gas sensitive body 20 can be reduced.

  A method for manufacturing the gas sensor having the above configuration will be described below. First, after the three terminals 12a to 12c are formed simultaneously with the base 11 by insert molding, both ends (lead wires 13a and 13c) of the heater electrode 21 are connected to the tips of the terminals 12a and 12c, and the center electrode is connected to the tip of the terminal 12b. One end (lead wire 13b) of 22 is electrically and mechanically connected by welding or brazing, respectively, and a rust inhibitor 18 is applied to the connection portion between each terminal 12a-12c and each lead wire 13a-13c. Next, a paste made by adding a solvent (sulfuric acid, nitric acid, etc.) to a tin oxide powder to which a catalyst such as Pd and Pt is added is applied to the electrodes 21 and 22, and both electrodes 21 and 22 are embedded inside. The oval spherical gas sensitive body 20 is formed and sintered at about 600 ° C., and then a silica-based binder is applied to increase the mechanical strength of the gas sensitive body 20 and fired again at about 600 ° C. Then, the metal cap 14 is fitted to the base 11 so as to cover the gas sensitive body 20, and is fixed to the base 11 by caulking the metal cap 14, and the assembly of the sensing element A is completed. Conventionally, an alloy of iron and nickel is used as the material of the terminals 12a, and the surface of the terminals 12a is not subjected to solder plating in order to weld the lead wires 13a, so the gas sensitive body 20 is fired. At that time, sulfuric acid or nitric acid as a solvent may scatter and adhere to the terminals 12a, and rust may be generated on the terminals 12a. Therefore, as a material of the terminal 12a, for example, a material such as copper, nickel, zinc alloy (so-called white) or pure nickel, particularly preferably a copper content of 54.0 to 58.0% and a nickel content of 16. 5 to 19.5%, and the balance is zinc copper, nickel, and a zinc alloy (JIS H 3130 C7701), and these materials are resistant to rust, so the gas sensitive body 20 is fired. In this case, even if the sulfuric acid or nitric acid as a solvent scatters and adheres to the terminals 12a, it is possible to prevent rust from being generated on the terminals 12a.

  Next, the circuit configuration of the control unit 2 will be described with reference to FIG. The control unit 2 obtains the heating control means for controlling the amount of heat generated by controlling the energization of the heater combined electrode 21 and the resistance value of the gas sensitive body 20 in the high temperature heating period (period in which the methane gas has discrimination). When the concentration of methane gas exceeds the first alarm level, a gas leak alarm is output, and carbon monoxide determined from the resistance value of the gas sensitive body 20 during the low-temperature heating period (a period in which carbon monoxide has discrimination) Alarm means for outputting an incomplete combustion alarm when the concentration of the gas exceeds the second alarm level, in a period in which the gas sensitive body 20 is discriminated against hydrogen gas immediately after switching from the high temperature heating period to the low temperature heating period. Correction means for correcting the alarm level so that the first and second alarm levels are shifted to a higher concentration side when the hydrogen gas concentration obtained from the resistance value exceeds a predetermined determination level; When fine warning means outputs the gas leakage alarm or incomplete combustion alarm comprises a microcomputer 3 functions, such as correction stop means for stopping the correction of the alarm levels by the correction means performs control processing of the entire apparatus is programmed. Note that the gas concentration of the detection target gas (methane gas, carbon monoxide, hydrogen gas, etc.) is actually obtained indirectly by detecting the resistance value of the gas sensitive body 20, and the resistance value of the gas sensitive body 20 is detected. Is compared with threshold values set corresponding to the first and second alarm levels and the determination level, thereby determining the gas concentration level.

  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, respectively. The voltage rectified by the one diode bridge DB2 is a smoothing capacitor. After being smoothed by C1, it is stabilized at a predetermined voltage by a three-terminal regulator IC1 and supplied to the microcomputer 3.

  The heater electrode 21 of the sensing element A is connected between the output terminals of the three-terminal regulator IC1 through a parallel circuit of a PNP transistor Q1 and a resistor R0. The base of the transistor Q1 is connected to the output port O1 of the microcomputer 3. It is connected. On the other hand, the center 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, a series circuit of a PNP transistor Q22 and a load resistor R22, and a diode D1. And an input port I1 of the microcomputer 3 are connected. The bases of the transistors Q21 and Q22 are connected to the output ports O21 and O22 of the microcomputer 3, respectively. When the voltage level of the output port O21 or O22 becomes low level, the transistor Q21 or Q22 is turned on and the load resistance R21 or R22 is turned on. Is connected to the center electrode 22.

  The output ports O3 to O5 of the microcomputer 3 are connected to the cathodes of the light emitting diodes LED1 to LED3 for display, respectively, and the cathodes of the light emitting diodes L1 and L2 of the photocouplers PC1 and PC2 are connected to the output ports O6 and O7, respectively. Has been. The anodes of these light emitting diodes LED1 to LED3 and L1 and L2 are connected to the output terminal of the three-terminal regulator IC1 via current limiting resistors, respectively.

  Here, 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 stabilization circuit 4 for outputting the voltage signal is connected between both ends of a smoothing capacitor C2 for smoothing the rectified output of the diode bridge DB1, and applies a reference voltage applied to the base of the series control transistor Q3. The photocouplers PC1 and PC2 are switched by turning on / off the phototransistors PT1 and PT2.

  This reference voltage is obtained by dividing the voltage across the Zener diode ZD connected to both ends of the smoothing capacitor C2 via the resistor R4 by the resistors R11 to R13. When the phototransistor PT1 is turned on, the resistors R11 to R13 A voltage across the series circuit, that is, a voltage across the Zener diode ZD is applied as a reference voltage to the base of the transistor Q3. When the phototransistor PT2 is turned on, a voltage obtained by dividing the voltage across the Zener diode ZD by the resistor R11 and the series circuit of the resistors R12 and R13 is applied to the base of the transistor Q3 as a reference voltage. Thus, voltage signals corresponding to the respective reference voltages are output to the outside as gas detection signals in accordance with 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. By the signals output alternately from the output ports O8 and O9, the signal levels of the outputs of the comparators CP1 and CP2 are alternately inverted to the low level / high level, and the polarity of the voltage applied to the buzzer 6 comprising the piezoelectric buzzer is alternated. The alarm sound is oscillated and output. 1 is a reference clock oscillation circuit for supplying a reference clock to the microcomputer 3, and IC2 is a reset IC for resetting the microcomputer 3 when the power is turned on.

  A series circuit of a temperature compensation thermistor TH1 and a resistor R25 is connected between the output terminals of the three-terminal regulator IC1, and the potential at the connection point of the thermistor TH1 and the resistor R25 is input to the input port I2 of the microcomputer 3. ing. 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 across the gas sensitive 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, and the input ports I3 and I4 of the microcomputer 3 are connected. Are respectively input with set voltages set by the variable resistors VR1 and VR2. Note that the voltages input to the input ports I3 and I4 are set values of the both-end voltages of the gas sensing body 20 when the gas concentration of methane or carbon monoxide, which is the detection target gas, reaches a warning level, and are variable. It is set using resistors VR1 and VR2.

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

  Thus, in normal times, 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 of the resistors R6 and R7, and the comparator CP1. The signal level of the output of becomes a high level, turning off the transistor Q4. At this time, the transistor Q1 is turned off, the current applied to the heater electrode 21 of the sensing element A is reduced, and the heating amount is reduced.

  Further, in normal times, 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 combined 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 through the resistor R8, and the voltage at both ends of the capacitor 3 decreases. Due to the time constant, the voltage across the capacitor C0 does not fall below the potential at the connection point of the resistors R6 and R7 until the predetermined time elapses. Therefore, the output of the comparator CP1 remains low until the predetermined time elapses. The transistor Q4 is kept off. Therefore, the transistor Q1 is turned on, the current applied to the heater electrode 21 is increased, and the heating amount is increased.

  Thereafter, at the normal time, when the predetermined time ends, the microcomputer 3 sets the output port O1 to the high level to turn off the transistor Q1, thereby reducing the heating amount of the heater electrode 21.

  In this way, by performing duty control to energize the heater combined electrode 21 for a predetermined time every predetermined period, the average value of the voltage applied to the heater combined electrode 21 is set to about 0.9 V, and the gas sensitive body 20 is set to about 400 ° C. The high-temperature heating period for heating the gas sensitive body 20 to about 60 ° C. can be alternately set with the average value of the voltage applied to the heater serving electrode 21 being about 0.2 V (see FIG. 3).

  By the way, FIG. 4 has shown the response characteristic with respect to various gas at the time of heating at low temperature, after heating the temperature of the gas sensitive body 20 to high temperature for 5 second by controlling the heating to the heater combined electrode 21, The horizontal axis represents time (seconds), and the vertical axis represents the resistance value Rs (kΩ) of the gas sensitive body 20.

In FIG. 4, (x) is the measurement result for the atmosphere, (b) is the measurement result for 100 ppm carbon monoxide, (c) is the measurement result for 300 ppm carbon monoxide, and (ii) is for 1000 ppm methane. Measurement results: E (◯) is the measurement result for 3000 ppm of methane, F (▲) is the measurement result for 3000 ppm of hydrogen gas, G (△) is the measurement result for 6000 ppm of hydrogen gas, and Z (▼) is 100 ppm monoxide Measurement results for a mixed gas of carbon and 50 ppm hydrogen gas, Li (▽) is a measurement result for a mixed gas of 100 ppm carbon monoxide and 5000 ppm hydrogen gas, Nu (■) is 3000 ppm methane and 5000 ppm The measurement results for the mixed gas in which hydrogen gas is mixed are shown. As is clear from this measurement result, in the case of a high-concentration hydrogen gas or a mixed gas containing hydrogen gas, about 0.6 seconds have elapsed since the switching from the high temperature heating period to the low temperature heating period (FIG. 4). The resistance value of the gas sensitive body 20 is abruptly decreased at the point B), and the presence or absence of hydrogen gas can be detected by detecting the resistance value at this point.

  Here, the alarm determination operation of the microcomputer 3 will be described with reference to the flowchart of FIG.

  During the high temperature heating period, the microcomputer 3 sets the signal level of the output port O21 to high and the signal level of O22 to low to turn on the transistor Q21 and turn off Q22, whereby the resistance detection electrode 22 of the sensing element A is connected via the load resistor R21. And a predetermined detection voltage is applied between the heater combined electrode 21. Then, during a period of discrimination (approximately 4 to 5 seconds after the start of the high temperature heating period) with respect to methane gas immediately before switching from the high temperature heating period to the low temperature heating period (point A in FIG. 4), the microcomputer 3 senses The voltage of both ends of the gas body 20 is taken in from 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, and the resistance of the gas body 20 at the end of the high temperature heating period. A value is detected, and the resistance value at this time is stored as a resistance value (ch4) corresponding to the methane gas concentration (S11).

  Thereafter, the microcomputer 3 takes in the voltage across the gas sensitive body 20 from the input port I1 at about 0.6 seconds after the switching from the high temperature heating period to the low temperature heating period (point B in FIG. 4). Temperature compensation is performed based on the divided voltage of the thermistor TH1 and the resistor R25 taken from the port I2, and the resistance value of the gas sensitive body 20 at this time is detected, and the resistance value at this time is a resistance corresponding to the hydrogen gas concentration. Store as a value. Here, the microcomputer 3 has set the correction coefficients Kh1 and Kh2 for correcting the alarm levels of methane gas and carbon monoxide, respectively, according to the resistance value of the gas sensitive body 20 at the point B, and the gas leak alarm has already been output. If the hydrogen gas concentration is less than the judgment level, the correction coefficients Kh1 and Kh2 are set to 1. When the gas leak alarm is not output, the correction coefficients Kh1 and Kh2 are set to 1. When it is set to 1 and exceeds the determination level (that is, when the resistance value of the gas sensitive body 20 falls below the resistance value corresponding to the determination level), the correction coefficients Kh1 and Kh2 are respectively set to predetermined values greater than 1. (S12). The correction coefficients Kh1 and Kh2 can be individually set according to the sensor characteristics and specifications, and may be set to different values or the same value.

  Next, the microcomputer 3 turns off the transistor Q21 and turns on the Q22 by setting the signal level of the output port O21 to be low and the signal level of the O22 to be high when about 1 second has elapsed after switching to the low temperature heating period. Then, a predetermined detection voltage is applied between the resistance detection electrode 22 of the sensing element A and one heater combined electrode 21 via the load resistor R22 (S13). And both ends of the gas sensitive body 20 in a period (point C in FIG. 4 after about 10 seconds from the start of the low temperature heating period) that is discriminating with respect to carbon monoxide immediately before switching from the low temperature heating period to the high temperature heating period. The voltage is read from the input port I1, temperature compensation is performed to determine the resistance value of the gas sensitive body 20, and this resistance value is stored as a resistance value (co) corresponding to the gas concentration of carbon monoxide (S14).

  When the detection of methane gas, hydrogen gas, and carbon monoxide gas is completed as described above, the microcomputer 3 first sets the resistance value (ch4) corresponding to the methane gas concentration by the correction coefficient Kh1 and the first alarm level. When the value of the resistance value (ch4) multiplied by the correction coefficient Kh1 falls below the threshold value (alch) (that is, the resistance value of the gas sensitive body 20). When the methane gas concentration obtained from (1) exceeds the first alarm level), a gas leak alarm is output (S16), and if it is equal to or greater than the threshold (alch), the routine proceeds to a carbon monoxide determination routine. As a result of the determination in S12, if the hydrogen gas concentration exceeds the determination level, the correction coefficient Kh1 is set to a predetermined value greater than 1, and if it is less than the determination level, the correction coefficient Kh1 is set to 1. When the gas concentration exceeds the determination level, the resistance value (ch4) when the gas concentration falls below the threshold (alch) becomes a smaller value, so that the alarm level of methane gas is shifted to the high concentration side, and hydrogen gas Can prevent malfunction.

  When the microcomputer 3 finishes determining methane gas, it determines carbon monoxide. That is, the microcomputer 3 compares the value obtained by multiplying the resistance value (co) corresponding to the carbon monoxide concentration by the correction coefficient Kh2 with the threshold value (alco) corresponding to the second alarm level (S17). When the value obtained by multiplying the resistance value (co) by the correction coefficient Kh2 falls below the threshold value (alco) (that is, when the carbon monoxide concentration obtained from the resistance value of the gas sensitive body 20 exceeds the second alarm level), An incomplete combustion alarm is output (S18), and if it is equal to or greater than the threshold value (alco), the alarm is not output and the monitoring operation is continued (S19). As a result of the determination in S12, if the hydrogen gas concentration exceeds the determination level, the correction coefficient Kh2 is set to a predetermined value greater than 1, and if it is less than the determination level, the correction coefficient Kh2 is set to 1. As in the case of the leak alarm, when the hydrogen gas concentration exceeds the judgment level, the resistance value (co) when it falls below the threshold value (alco) becomes a smaller value, so that the carbon monoxide alarm level. Can be shifted to a higher concentration side to prevent malfunction due to hydrogen gas.

  Here, when the microcomputer 3 outputs a gas leak alarm or an incomplete combustion alarm, the predetermined output ports O3 to O5 are set to a low level, the corresponding light emitting diodes LED1 to LED3 are turned on or blinked, and the output ports O6 to O6 O7 is set to a low level, the corresponding photocoupler PC1 or PC2 is turned on, and a predetermined voltage signal is output from the stabilization circuit 4 to the outside. Further, the microcomputer 3 alternately reverses the outputs of the output ports O8 and O9 and sounds the buzzer 6 to issue an alarm.

  As described above, in the present embodiment, the gas concentration of the hydrogen gas is detected during a period in which the hydrogen gas immediately after switching from the high temperature heating period to the low temperature heating period is discriminated, and the hydrogen gas concentration reaches a predetermined determination level. In the case of exceeding, the alarm level of methane gas and carbon monoxide is corrected so as to shift to the high concentration side, so that erroneous detection by hydrogen gas can be prevented. Furthermore, once the gas leak alarm is output, the microcomputer 3 stops the alarm level correction operation. Therefore, after the gas leak alarm is output, the hydrogen gas leaks and the hydrogen gas concentration exceeds the judgment level, or the methane gas gas Even when the concentration becomes high and the resistance value of the gas sensitive body 20 in the hydrogen gas determination period falls below the determination level, correction is performed to shift the alarm level of methane gas and carbon monoxide to the high concentration side. Therefore, it is possible to prevent the gas leak alarm from stopping midway.

  In this embodiment, the gas concentration level determination of the detection target gas (a combustible gas such as methane gas, an incomplete combustion gas such as carbon monoxide, or hydrogen gas) is actually performed using the gas sensitive body 20 and the detection resistance. The resistance value of the gas sensing body 20 that changes according to the target gas concentration is obtained from the voltage at both ends, and a resistance value (threshold value set in accordance with the alarm level or determination level) is applied. The level determination is performed by comparing the values (alch, alco) and the level. However, the level determination method is not limited to the above-described method. For example, a series circuit of the gas sensitive body 20 and the detection resistor is used. The level may be determined by applying a constant voltage and comparing the voltage between both ends of the gas sensitive body 20 with a reference voltage value, or by applying a constant voltage to the gas sensitive body 20. Electricity flowing through the gas body 20 The level may be determined by detecting the value and comparing the level of this current value with the reference current value, and the gas obtained from the resistance value during a period in which the gas to be detected is discriminative. The level determination may be performed by any method as long as it can be detected whether the density exceeds a predetermined level.

  Further, in the present embodiment, methane gas is detected at the end of the high temperature heating period to determine a gas leak alarm, and carbon monoxide gas is detected at the end of the low temperature heating period to perform an incomplete combustion alarm determination. However, the timing of performing the gas leakage alarm and the incomplete combustion alarm is not limited to the end of the high temperature heating period and the low temperature heating period, but if it is a period that is discriminative with respect to methane gas or incomplete combustion gas, A gas leak alarm or incomplete combustion alarm may be performed during the high temperature heating period and the low temperature heating period. Further, when the hydrogen gas concentration exceeds the determination level, the microcomputer 3 as the correcting means sets both the alarm level for the gas leak alarm (first alarm level) and the alarm level for the incomplete combustion alarm (second alarm level). Although both are shifted to the high concentration side, only one of the alarm levels may be shifted to the high concentration side. The microcomputer 3 serving as the correction stop means stops the alarm level correction process when the gas leak alarm is output, but corrects the alarm level when outputting at least one of the gas leak alarm and the incomplete combustion alarm. Processing may be stopped.

  By the way, in the circuit configuration of the present embodiment, when the microcomputer 3 runs away due to external noise or the like and the output port O1 of the microcomputer 3 is fixed at a low level, the charge charged in the capacitor C0 of the protection circuit 5 causes the resistor R8 to be charged. Since the voltage across the capacitor C0 eventually falls below the potential at the connection point of the resistors R6 and R7, the output of the comparator CP1 is inverted from the high level to the low level, the transistor Q4 is turned on, and the base potential of the transistor Q1 Is raised to the power supply voltage to forcibly turn off the transistor Q1. Therefore, even if the microcomputer 3 runs away, the protection circuit 5 forcibly turns off the transistor Q1 and forcibly stops energization of the heater combined electrode 21, so that the heater combined electrode 21 is energized more than necessary. By appropriately setting the time constants of the capacitor C0 and the resistor R8, disconnection of the heater combined electrode 21 due to the runaway of the microcomputer 3 can be prevented.

  Moreover, the time settings for the high temperature heating period and the low temperature heating period may be set to appropriate values depending on the heat capacity of the sensing element A, and the period of the high temperature heating period and the low temperature heating period is preferably approximately 60 seconds or less. For example, if the high-temperature heating period is about 5 seconds and the low-temperature heating period is about 15 seconds, the detection cycle can be set to 20 seconds or less. "Inspector Inspection Rules (JIA E 001-99)" and "Incomplete Combustion Alarm Inspection Rules".

Further, as shown in FIG. 7, a gas flows into the sensing element A from the outside by attaching a cylindrical cap 16 having a ceiling surface to which an external filter 17 made of activated carbon is attached to the cover 13. An external filter 17 is disposed in the path, and alcohol vapor as a miscellaneous gas and silicon vapor as a poisoning gas are adsorbed by the external filter 17 to reduce the alcohol sensitivity of the sensing element A and sense from a poisoning substance such as silicon. By protecting the element A, the sensing element A can be made less susceptible to the influence of alcohol vapor or silicon vapor. In this embodiment, the external filter 17 made of activated carbon is used, but the material of the external filter 17 is not limited to activated carbon, and the material of the external filter 17 may be silica gel (SiO ₂ ). A combination of activated carbon and silica gel may be used.

It is a circuit diagram of the gas detection apparatus of Embodiment 1. It is a flowchart explaining alarm operation | movement same as the above. It is explanatory drawing explaining the heating cycle of a gas sensitive body same as the above. It is a figure which shows the responsiveness with respect to various gas same as the above. It is a front view of the state which removed the cover of the gas detection element used for the same as the above. (A) is a partially broken front view of the same, (b) is a top view of the same partially broken. The state which attached the filter to the same as the above is shown, (a) is a sectional view which breaks partially, (b) is a bottom view.

Explanation of symbols

A Sensing element 3 Microcomputer 20 Gas sensitive body 21 Heater combined electrode

Claims (4)

A gas-sensitive member which changes the resistance value depending on the gas concentration, gas concentration determined from the resistance value of the sense gas body, the alarm level for the combustible gas or incomplete combustion gas other than hydrogen gas when obtaining super an alarm means for outputting an alarm, shift the concentration of the hydrogen gas calculated from the resistance value of the sense gas body in a period in which a discrimination against hydrogen gas exceeds a predetermined decision level the alarm level to a high density side A gas detection apparatus comprising: correction means for correcting an alarm level so as to cause the alarm level to be set to an initial value when the alarm means outputs an alarm . The alarm target gas is methane gas and incomplete combustion gas, and heating means for heating the gas sensitive body, and heating control means for alternately providing a high temperature heating period and a low temperature heating period by controlling the heating amount of the heating means the door is provided, the alarm means may have a gas concentration of methane gas obtained from the resistance value of the gas-sensitive body a first warning level and outputs a is exceeded and gas leak alarms at high temperature heating period, sensitive in the low-temperature heating period gas body gas detector of claim 1 wherein the gas concentration of the incomplete combustion gas obtained from the resistance value, characterized in that the second alarm level output is exceeded and incomplete combustion alarm.   The said correction | amendment means calculates | requires the density | concentration of hydrogen gas from the resistance value of a gas sensitive body in the period which has a discrimination property with respect to hydrogen gas immediately after switching from a high temperature heating period to a low temperature heating period. Gas detection device.   The correction means corrects so that at least one of the first and second alarm levels is shifted to a high concentration side when the concentration of hydrogen gas exceeds the determination level. Or the gas detection apparatus of 3.

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