JP4528638B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detection device, and more particularly to an improved gas detection device for temperature compensation.

  Many catalytic combustion type gas sensors and semiconductor type gas sensors are used as gas sensors for reducing gas leak alarms or incomplete combustion gas alarms.

FIG. 1 shows the structure of a semiconductor gas sensor that is currently widely used. The semiconductor gas sensor 1 is mainly formed of a metal oxide such as tin oxide (SnO ₂ ), and is formed of a gas sensitive body 1a that exhibits a resistance change when a gas is present, and a metal resistor such as platinum (Pt). A heater 1b for heating the gas sensitive body 1a, heater electrodes 1b1 and 1b2 led out of the sensor from the heater 1b, and a sensor electrode 1c for detecting a resistance change of the gas sensitive body 1a Have

  Basically, when detecting combustible gas (reducing gas) such as city gas or LPG gas, it is necessary to heat the element temperature of the gas sensor to a high temperature of about 300 to 500 ° C. Used by heating. Further, in order to detect incomplete combustion gas such as carbon monoxide generated during incomplete combustion, the element temperature is heated to a low temperature of 100 ° C. or lower.

  That is, the semiconductor gas sensor needs to be heated to a more optimal element temperature for each gas to be detected, and has a characteristic that fluctuates with changes in ambient temperature.

Therefore, in order to correct the ambient temperature, for example, as disclosed in Japanese Patent Application Laid-Open No. 2000-193623 (Patent Document 1), in a gas detection apparatus having a semiconductor gas sensor, the ambient temperature is detected. A temperature sensor such as an NTC thermistor or a resistance temperature detector is installed in the apparatus, and the ambient temperature is corrected based on the relationship between the temperature sensor information and the ambient temperature of the gas sensor measured in advance.
JP 2000-193623 A ([0021], FIG. 3)

  However, when a high detection accuracy is required for the gas concentration of about 100 ppm, there is a problem that it is difficult to accurately detect the ambient temperature with a temperature sensor such as a thermistor or a resistance temperature detector.

  Therefore, in view of the conventional problems described above, the present invention can accurately detect the ambient temperature and perform temperature compensation without providing a temperature sensor when high detection accuracy is required for the gas concentration. An object of the present invention is to provide a gas detection device.

  The invention according to claim 1 is a gas detection device that detects the presence of gas in a state where the gas is installed in a gas atmosphere, and detects the concentration of the gas in a state where the gas is installed in a gas atmosphere to output a sensor output. The level of the gas sensor to be generated and the voltage for operating the gas sensor are alternately changed in a pulse manner between a constant high level for detecting the gas concentration and a constant low level for detecting the gas concentration. A voltage source for supplying a voltage to be detected, a current detection means for detecting a current flowing through the gas sensor, and a current value detected by the current detection means while the voltage at the low level is supplied from the voltage source. Temperature information signal generating means for determining and generating a temperature information signal indicating the ambient temperature based on a predetermined correlation between the current value, the ambient temperature of the gas sensor, and the sensor output Based on the temperature information signal generated by said temperature information signal generating means, characterized in that and a gas concentration data generating means for generating a gas concentration data by performing temperature compensation for the sensor output.

  The invention according to claim 2 is a gas detection device for detecting the presence of gas in a state of being installed in a gas atmosphere, the gas sensitive body, a heater for heating the gas sensitive body, and a resistance change of the gas sensitive body. The semiconductor gas sensor having a sensor electrode for taking out the gas and the heater alternately in a pulse at a constant high level for detecting the gas concentration and a constant low level not detecting the gas concentration. A heater power supply for supplying a heater voltage that changes in level, a plate power supply for intermittently supplying a plate voltage at a constant level to the sensor electrode, a heater voltage at the high level is supplied to the heater, and the plate power supply Sensor output detection means for detecting sensor output while plate voltage is supplied to the sensor electrode, and heater current flowing in the heater Current detection means for detecting, determining a current value detected by the current detection means while the heater voltage at the low level is supplied to the heater and the plate voltage is not supplied to the sensor electrode, A temperature information signal generating means for generating a temperature information signal indicating an ambient temperature based on a correlation obtained in advance between an electric current value, an ambient temperature of the semiconductor gas sensor, and the sensor output; and Gas concentration data generating means for generating gas concentration data by performing temperature compensation on the sensor output based on the generated temperature information signal.

  The invention according to claim 3 is a gas detection device that detects the presence of gas in a state where it is installed in a gas atmosphere, and the resistance value changes according to the concentration of the gas in a state where it is installed in a gas atmosphere. A catalytic combustion type gas sensor that detects a concentration of the gas and generates a sensor output; a constant high level for detecting the concentration of the gas; and a concentration of the gas A voltage source that supplies a voltage that alternately changes in level to a certain low level that does not detect current, current detection means that detects a current flowing in the sensor element, and a voltage at the low level in the sensor element A current value detected by the current detection means while being supplied, and based on a correlation obtained in advance between the current value, the ambient temperature of the catalytic combustion gas sensor, and the sensor output, Temperature information signal generating means for generating a temperature information signal indicating temperature, and gas for generating gas concentration data by performing temperature compensation on the sensor output based on the temperature information signal generated by the temperature information signal generating means Density data generating means.

  According to a fourth aspect of the present invention, in the gas detection device according to any one of the first to third aspects, the low level of the voltage is a level for detecting a concentration of a gas of a different type from the gas. It is characterized by.

  According to a fifth aspect of the present invention, in the gas detection device according to the second aspect, the current detection means is a fixed resistor having a temperature coefficient sufficiently smaller than the temperature coefficient of the heater.

  According to a sixth aspect of the present invention, in the gas detection device according to the third aspect, the current detection means is a fixed resistor having a temperature coefficient sufficiently smaller than the temperature coefficient of the sensor element.

  According to the first aspect of the present invention, it is possible to obtain a temperature information signal indicating the ambient temperature without using a temperature sensor that is a separate component from the gas sensor. Further, since the temperature information signal is obtained during a period other than the gas detection period of the gas sensor, the ambient temperature can be accurately detected. Further, based on the obtained temperature information signal, gas concentration data in which the sensor output is temperature-compensated with high accuracy can be generated.

  According to the second aspect of the present invention, a temperature information signal indicating the ambient temperature can be obtained without using a temperature sensor that is a separate component from the semiconductor gas sensor. Moreover, since the temperature information signal is obtained during a period other than the gas detection period of the semiconductor gas sensor, the ambient temperature can be accurately detected. Further, based on the obtained temperature information signal, it is possible to generate gas concentration data in which the sensor output of the semiconductor gas sensor is temperature-compensated with high accuracy.

  According to the third aspect of the present invention, a temperature information signal indicating the ambient temperature can be obtained without using a temperature sensor which is a separate component from the catalytic combustion type gas sensor. Further, since the temperature information signal is obtained in a period other than the gas detection period of the catalytic combustion type gas sensor, the ambient temperature can be accurately detected. Further, based on the obtained temperature information signal, gas concentration data in which the sensor output of the catalytic combustion type gas sensor is temperature-compensated with high accuracy can be generated.

  According to the fourth aspect of the present invention, it is possible to obtain a temperature information signal indicating the ambient temperature without using a temperature sensor that is a separate component from the gas sensor. Further, since the temperature information signal is obtained during a period other than the gas detection period of the gas sensor, the ambient temperature can be accurately detected. Further, based on the obtained temperature information signal, it is possible to generate gas concentration data relating to two types of gases in which the sensor output is temperature-compensated with high accuracy.

  According to the fifth aspect of the present invention, it is possible to accurately detect the ambient temperature by reducing the influence of the ambient temperature on the current detecting means.

  According to the invention described in claim 6, it is possible to accurately detect the ambient temperature by reducing the influence of the ambient temperature in the current detecting means.

  The best mode of the present invention will be described below with reference to the drawings.

  (First Embodiment) FIG. 2 is a circuit diagram of a gas detector according to a first embodiment of the present invention. In FIG. 2, the gas detection apparatus 10 uses a semiconductor gas sensor 1, and includes a plate power source 11, a heater power source 12 as a voltage source, a plate voltage application unit 13, a heater voltage application unit 14, and a sensor as sensor output detection means. An output detection unit 15, a current detection unit 16 as current detection means, and a microcomputer (CPU) 20 are included.

  The plate voltage application unit 13 includes an npn transistor Q1. The collector of the transistor Q1 is connected to the plate power supply 11, and the emitter is connected to the sensor electrode 1c of the gas sensor 1 via the detection resistor R8 that constitutes the sensor output detection unit 15.

  The heater voltage application unit 14 includes an npn transistor Q2, a pnp transistor Q3, an operational amplifier OP1, resistors R1 to R7, and a switch SW1.

  The collector of the transistor Q2 is connected to the heater power supply 12 via the resistor R1, and the emitter is connected to the heater electrode of the heater 1b of the gas sensor 1 via the detection resistor R9 that constitutes the current detection unit 16.

  Between the connection point between the resistor R1 and the transistor Q2 and the installation, a series circuit of the resistors R2 and R3 and the switch SW1, a series circuit of the resistors R4, R5 and R6, and an emitter of the transistor Q3 are connected. The base of the transistor Q3 is connected to the connection point between the resistors R2 and R3, and the collector is connected to the connection point between the resistors R4 and R5.

  The non-inverting input terminal of the operational amplifier OP1 is connected to the connection point between the resistors R5 and R6, and the inverting input terminal is connected to the connection point between the detection resistor R9 of the current detection unit 16 and the heater electrode of the heater 1b of the gas sensor 1, The output terminal is connected to the base of the transistor Q2 via the resistor R7.

  The CPU 20 includes a plate voltage control unit 20a, a voltage switching control unit 20b, a current detection determination unit 20c as a temperature information signal generation unit, and a sensor output determination unit 20d as a gas concentration data generation unit. A power supply voltage is supplied from 11.

  The plate voltage control unit 20a outputs a plate voltage control signal and applies it to the base of the transistor Q1 of the plate voltage application unit 13. The voltage switching control unit 20b outputs a voltage switching control signal and performs on / off control of the switch SW1 of the heater voltage applying unit 14. The switch SW1 can be an analog electronic switch or a relay. The current detection determination unit 20c detects the heater current flowing through the heater 1b as a voltage drop generated across the detection resistor R9 of the current detection unit 16, and determines the magnitude thereof. The sensor output determination unit 20d determines the magnitude of the sensor output detected as a voltage drop generated at both ends of the detection resistor R8 based on the plate current flowing through the detection resistor R8 constituting the sensor output detection unit 15.

  Next, the operation of the gas detection device having the above-described configuration will be described. When the gas detector is used, the heater voltage application unit 14 applies a heater voltage whose level is alternately changed in two stages of a high level (Hi) and a low level (Lo) to the heater 1b of the gas sensor 1.

  That is, when the switch SW1 is controlled to be turned on by the voltage switching control signal supplied from the voltage switching control unit 20b of the CPU 20, the transistor Q3 is turned on and the resistor R4 is short-circuited. As a result, the divided voltage by the resistors R5 and R6 is input to the non-inverting input terminal of the operational amplifier OP1, the transistor Q2 is turned on, and the detection resistor R9 connected to the inverting input terminal and the heater electrode of the heater 1b of the gas sensor 1 The potential at the connection point, i.e., the heater voltage, becomes equal to the divided voltage by the resistors R5 and R6 and becomes Hi level.

  On the other hand, when the switch SW1 is controlled to be turned off by the voltage switching control signal supplied from the voltage switching control unit 20b of the CPU 20, the transistor Q3 is turned off. As a result, the divided voltage by the resistors R4 and R5 and the resistor R6 is input to the non-inverting input terminal of the operational amplifier OP1, and the connection potential between the detection resistor R9 connected to the inverting input terminal and the heater electrode of the heater 1b of the gas sensor 1, That is, the heater voltage becomes equal to the divided voltage by the resistors R4 and R5 and the resistor R6 and becomes the Lo level.

  The current detection unit 16 detects the current flowing through the heater 1b, and the current detection determination unit 20c determines the magnitude of the current value detected by the current detection unit 16, and is obtained in advance and is a memory of the CPU 20 (not shown). The temperature corresponding to the magnitude of the current value determined based on the lookup table indicating the correlation between the current value, the ambient temperature of the semiconductor gas sensor 1 and the sensor output, stored in FIG. Is generated.

  For example, when the heater 1b is made of platinum (Pt), the Pt line alone has a temperature coefficient of 3920 ppm / ° C., but the gas sensitive body 1a is formed around the heater 1b, and the Pt line The temperature coefficient is smaller than that of a simple substance. Although the temperature coefficient of the heater 1b varies depending on the size of the gas sensitive element 1a and the like, it is about 3000 ppm / ° C., and temperature information indicating the ambient temperature can be read by this temperature coefficient.

However, there are problems as described below, and it is difficult to accurately read temperature information.
(1) The gas-sensitive body 1a is a catalyst and has a very strong oxidizing action against reducing gas. Therefore, if the gas to be detected is present in the atmosphere, the resistance of the heater 1b increases due to the reaction heat. , Accurate temperature information can not be read.
(2) In order to measure the resistance change of the gas sensitive body 1a as the gas sensor 1, as shown in FIG. 2, the plate voltage applying unit 13 naturally applies a plate voltage as a constant voltage to the gas sensitive body 1a. Then, the resistance change of the gas sensitive body 1a is measured based on the both-end potential of the detection resistor R8. Although there is no problem in clean air, in the reducing gas, the resistance of the gas sensing element 1a is lowered, Joule heat is generated, the resistance of the heater 1b is increased, and accurate temperature information cannot be read.

  In view of the above-described problem, a driving condition for accurately detecting temperature information indicating the ambient temperature using the temperature coefficient of the metal resistor used in the heater 1b of the gas sensor 1 is shown in the timing chart of FIG.

  In order to detect periodically, the heater 1b of the gas sensor 1 is heated to a high temperature at which the gas concentration can be measured more selectively. For example, if the detection target gas is a reducing gas such as methane or butane, the gas is heated to about 450 ° C., and if it is hydrogen or the like, it is heated to about 350 ° C. However, the above-described problem occurs when a plate voltage for constantly maintaining this warmed state and constantly measuring the resistance change of the gas sensitive body 1a is applied.

  Therefore, as shown in FIG. 3A, the heater voltage has a certain high level voltage (Hi) for heating to a high temperature at which the detection target gas, for example, reducing gas, can be detected, and the detection target gas. As a voltage whose level changes alternately in a predetermined cycle in a pulsed manner to a temperature at which the concentration is not detected, that is, a constant low level voltage (Lo) for lowering to a temperature at which the gas sensitive body 1a does not cause a catalytic reaction. And applied to the heater 1b.

  Thereby, as shown in FIG. 3B, the temperature of the gas sensitive body 1a of the gas sensor 1 changes between a high temperature period in which the temperature is high around 400 ° C. and a low temperature period in which the temperature is 100 ° C. or less.

  In addition, the plate voltage is a plate voltage control signal that becomes the Hi level from the plate voltage control unit 20a of the CPU 20 as shown in the sensor output measurement timing in FIG. 3C immediately before the heater voltage is switched from the Hi level to the Lo level. Is applied to the sensor electrode 1c of the gas sensor 1 from the plate power supply 11 by switching the transistor Q1 from the off state to the on state. The plate current flowing thereby is detected by the detection resistor R8 of the sensor output detection unit 15, and is taken into the sensor output determination unit 20d as a sensor output.

  On the other hand, after the heater voltage is switched from the Hi level to the Lo level, if the temperature of the gas sensitive body 1a is sufficiently cooled, no plate voltage is applied, as shown in the temperature information measurement timing in FIG. During the period when the heater voltage is at the Lo level and indicated by the temperature information measurement timing signal Hi, the current detection determination unit 20c measures the heater current with the detection resistor R9 of the current detection unit 16 and determines the current value. And the resistance of the heater 1b is detected.

  The temperature at which the resistance value of the heater 1b is measured basically depends on the ability of the gas sensitive body 1a. However, if the heating temperature in the heater 1b is 100 ° C. or less in the low temperature period, Pt with respect to the ambient temperature When the wire is used, the resistance change based on the temperature coefficient of about 3000 ppm / ° C. of the heater 1b is measured by the heater current value, and temperature information for temperature compensation is sufficiently obtained based on the measured heater current value.

  As the detection resistor R9 of the current detection unit 16, a temperature coefficient sufficiently small with respect to the temperature coefficient of about 3000 ppm / ° C. of the heater 1b, for example, 100 ppm / ° C. or less (preferably several tens ppm) in this first embodiment. A fixed resistor having a temperature coefficient of / ° C or less) is used. By using such a fixed resistor, the resistance change rate due to the change in the ambient temperature generated in the detection resistor R9 itself becomes a sufficiently small value with respect to the resistance change rate due to the change in the ambient temperature of the heater 1b. The influence of the ambient temperature on the detection accuracy can be made little.

  Then, the sensor output determination unit 20d performs temperature compensation on the determined plate current value (that is, sensor output) based on the temperature information signal generated by the current detection determination unit 20c, and generates gas concentration data. Note that the detection resistor R8 of the sensor output detection unit 15 also uses a fixed resistor having a temperature coefficient equivalent to that of the detection resistor R9 so that the influence of the ambient temperature on the sensor output detection accuracy is hardly affected. be able to.

  As described above, according to the first embodiment of the present invention, the temperature information is obtained based on the temperature coefficient of the metal resistor used in the heater 1b of the semiconductor gas sensor 1, and the temperature compensation of the sensor output of the gas sensor is performed. Can be performed with high accuracy. Therefore, by using the temperature coefficient of the metal resistor of the heater 1b as information of the temperature sensor without using a temperature sensor that has been used conventionally, a gas detection device capable of highly accurate temperature compensation of the gas sensor is constructed. It becomes possible to do.

  (Second Embodiment) In the first embodiment described above, the gas detection device is configured to detect the reducing gas. In the second embodiment described below, the reducing gas and incomplete combustion are performed. It is configured to detect gas. In the second embodiment, the configuration of the gas detection device is the same as that of the first embodiment shown in FIG. 2, but the driving conditions are different as shown in the timing chart of FIG.

  A heater voltage for periodically detecting a reducing gas such as methane and an incomplete combustion gas such as carbon monoxide is applied to the heater 1b of the gas sensor 1. That is, as shown in FIG. 4A, the heater voltage is a constant high level voltage (Hi) for heating to a high temperature at which the reducing gas can be detected, and the reducing gas does not detect the reducing gas. Different kinds of gases, for example, a constant low level voltage (Lo) for detecting incomplete combustion gas, are applied to the heater 1b as a voltage whose level changes alternately in a predetermined cycle in a pulse manner.

  Thereby, as shown in FIG. 4B, the temperature of the gas sensitive body 1a of the gas sensor 1 changes between a high temperature period in which the temperature is about 400 ° C. and a low temperature period in which the temperature is about 100 ° C.

  Further, the plate voltage is the plate voltage of the CPU 20 immediately before the heater voltage is switched from the Hi level to the Lo level and immediately before the heater voltage is switched from the Lo level to the Hi level, as shown in the sensor output measurement timing of FIG. A plate voltage control signal which becomes Hi level is supplied from the control unit 20a to switch the transistor Q1 from the off state to the on state, so that it is applied from the plate power source 11 to the sensor electrode 1c of the gas sensor 1. The plate current flowing thereby is detected by the detection resistor R8 of the sensor output detection unit 15, and is taken into the sensor output determination unit 20d as a sensor output.

  On the other hand, after the heater voltage is switched from the Hi level to the Lo level, when the temperature of the gas sensitive body 1a is sufficiently cooled, the plate voltage is not applied, as shown in the temperature information measurement timing in FIG. During the period when the heater voltage is at the Lo level and indicated by the temperature information measurement timing signal Hi, the current detection determination unit 20c measures the heater current with the detection resistor R9 of the current detection unit 16 and determines the current value. And the resistance of the heater 1b is detected.

  Thereby, as in the first embodiment, the resistance change based on the temperature coefficient of the heater 1b is measured by the heater current value, and sufficient temperature information for temperature compensation is obtained based on the measured heater current value. .

  Then, the sensor output determination unit 20d performs temperature compensation on the plate current value (that is, sensor output) determined in the high temperature period based on the temperature information signal generated by the current detection determination unit 20c, thereby reducing the reducing gas. Gas concentration data is generated, and temperature compensation is performed on the plate current value (that is, sensor output) determined in the low temperature period to generate gas concentration data of incomplete combustion gas.

  Thus, according to the second embodiment of the present invention, the temperature information is obtained based on the temperature coefficient of the metal resistor used in the heater 1b of the semiconductor gas sensor 1, and the reducing gas and incomplete combustion are obtained. It is possible to accurately compensate the temperature of the sensor output corresponding to the gas. Therefore, by using the temperature coefficient of the metal resistor of the heater 1b as information of the temperature sensor without using a temperature sensor that has been used conventionally, a gas detection device capable of highly accurate temperature compensation of the gas sensor is constructed. It becomes possible to do.

  (Third Embodiment) In the first and second embodiments described above, the gas detection device uses a semiconductor type gas sensor. However, the present invention will be described below as a third embodiment. Can also be used.

  FIG. 5 is a circuit diagram of a gas detection device according to the third embodiment of the present invention. In FIG. 5, the gas detection device 10 uses a catalytic combustion type gas sensor 19 and includes a drive power supply 17 as a voltage source, a drive voltage application unit 18, a sensor output detection unit 15, a current detection unit 16, and a CPU 20.

  The catalytic combustion gas sensor 19 has a sensor element 19a that detects the presence of gas in a state where it is installed in a gas atmosphere. The sensor element 19a is formed by, for example, winding a platinum (Pt) resistance wire having a wire diameter of 20 to 50 μm to form a coil shape, applying a catalyst such as palladium-alumina around the coil, and firing it, It is formed with a double mesh of about 100 mesh.

  The drive voltage application unit 18 has the same configuration as the heater voltage application unit shown in FIG. 2, and includes an npn transistor Q2, a pnp transistor Q3, an operational amplifier OP1, resistors R1 to R7, and a switch SW1.

  The collector of the transistor Q2 is connected to the drive power supply 17 via the resistor R1, and the emitter is connected to the sensor element 19a of the catalytic combustion type gas sensor 19 via the detection resistor R9 constituting the current detector 16.

  Between the connection point between the resistor R1 and the transistor Q2 and the installation, a series circuit of the resistors R2 and R3 and the switch SW1, a series circuit of the resistors R4, R5 and R6, and an emitter of the transistor Q3 are connected. The base of the transistor Q3 is connected to the connection point between the resistors R2 and R3, and the collector is connected to the connection point between the resistors R4 and R5.

  The non-inverting input terminal of the operational amplifier OP1 is connected to the connection point between the resistors R5 and R6, and the inverting input terminal is connected to the connection point between the detection resistor R9 of the current detection unit 16 and the sensor element 19a of the contact combustion type gas sensor 19. The output terminal is connected to the base of the transistor Q2 via the resistor R7.

  The CPU 20 includes a voltage switching control unit 20 b, a current detection determination unit 20 c, and a sensor output determination unit 20 d, and a power supply voltage is supplied from the drive power supply 17.

  The voltage switching control unit 20b outputs a voltage switching control signal and performs on / off control of the switch SW1 of the drive voltage applying unit 18. The switch SW1 can be an analog electronic switch or a relay. The current detection determination unit 20c detects the current flowing through the sensor element 19a of the catalytic combustion gas sensor 19 as a voltage drop generated at both ends of the detection resistor R9, and determines the magnitude thereof. The sensor output determination unit 20d detects the sensor output as a voltage drop generated at both ends of the sensor element 19a due to the resistance change of the sensor element 19a, and determines the magnitude of the sensor output.

  Next, the operation of the gas detection device of FIG. 5 having the above-described configuration will be described with reference to the timing chart shown in FIG. When the gas detection device is used, the drive voltage application unit 18 applies a heater voltage that alternately changes the level of the sensor element 19a of the catalytic combustion type gas sensor 19 in two steps of a high level (Hi) and a low level (Lo). Apply.

  The current detection unit 16 detects a current flowing through the sensor element 19a, and the current detection determination unit 20c determines the magnitude of the current value detected by the current detection unit 16, and is obtained in advance and a memory (not shown) of the CPU 20 ), Which is stored in the lookup table showing the correlation between the current value, the ambient temperature of the catalytic combustion type gas sensor 19 and the sensor output, and based on this, corresponds to the magnitude of the determined current value. A temperature information signal indicating the temperature to be generated is generated.

  As shown in FIG. 6 (A), the drive voltage includes a constant high level voltage (Hi) for heating to a high temperature at which a detection target gas, for example, a reducing gas can be detected, and a reducing gas. However, it is applied to the sensor element 19a as a voltage whose level changes alternately in a predetermined cycle to a temperature at which the concentration is not detected, that is, a constant low level voltage (Lo) for lowering to a temperature at which no catalytic reaction occurs. The

  Thereby, as shown in FIG. 6B, the temperature of the sensor element 19a of the catalytic combustion type gas sensor 19 changes between a high temperature period of about 400 ° C. and a low temperature period of 100 ° C. or less. .

  Further, as shown in the sensor output measurement timing in FIG. 6C, a voltage drop across the sensor element 19a is detected immediately before the drive voltage is switched from the Hi level to the Lo level, and the sensor output determination unit 20d is detected as the sensor output. Is taken in.

  On the other hand, after the drive voltage is switched from the Hi level to the Lo level, when the temperature of the sensor element 19a is sufficiently cooled, the drive voltage becomes the Lo level as shown in the temperature information measurement timing of FIG. During the period indicated by the temperature information measurement timing signal Hi, the current detection determination unit 20c measures the current flowing through the sensor element 19a by the detection resistor R9 of the current detection unit 16 and captures the current value. Thereby, the resistance change based on the temperature coefficient of the sensor element 19a is measured as a current value, and temperature information for temperature compensation is sufficiently obtained based on the measured current value.

  Then, the sensor output determination unit 20d generates gas concentration data by performing temperature compensation on the sensor output based on the temperature information signal generated by the current detection determination unit 20c.

  As described above, according to the third embodiment of the present invention, the temperature information is obtained based on the temperature coefficient of the sensor element 19a of the catalytic combustion type gas sensor 19, and the temperature compensation of the sensor output of the gas sensor can be accurately performed. Is possible. Therefore, it is possible to construct a gas detection device capable of accurately compensating the temperature of the gas sensor by using the temperature coefficient of the sensor element 19a as information of the temperature sensor without using a temperature sensor that has been conventionally used. It becomes possible.

  (4th Embodiment) In 3rd Embodiment mentioned above, although the gas detection apparatus is comprised so that a reducing gas can be detected using a catalytic combustion type gas sensor, in 4th Embodiment demonstrated below, It is configured to detect reducing gas and incomplete combustion gas. In the fourth embodiment, the configuration of the gas detection device is the same as that of the first embodiment shown in FIG. 5, but the driving conditions are different as shown in the timing chart of FIG.

  A driving voltage for periodically detecting a reducing gas such as methane and an incomplete combustion gas such as carbon monoxide is applied to the sensor element 19a of the catalytic combustion type gas sensor 19. That is, as shown in FIG. 7A, the driving voltage is a constant high level voltage (Hi) for heating to a high temperature at which the reducing gas can be detected, and the reducing gas is detected without detecting the reducing gas. And a constant low level voltage (Lo) for detecting different types of gas, for example, incomplete combustion gas, are applied as a voltage whose level changes alternately in a predetermined cycle.

  Thereby, as shown in FIG. 7B, the temperature of the sensor element 19a changes between a high temperature period in which the temperature is high at around 400 ° C. and a low temperature period in which the temperature is as low as about 100 ° C.

  Further, as shown in the sensor output measurement timing in FIG. 7C, a voltage drop across the sensor element 19a is detected immediately before the drive voltage is switched from the Hi level to the Lo level and immediately before the drive voltage is switched from the Lo level to the Hi level. The sensor output is taken into the sensor output determination unit 20d.

  On the other hand, after the driving voltage is switched from the Hi level to the Lo level, when the temperature of the sensor element 19a is sufficiently cooled, the driving voltage becomes the Lo level as shown in the temperature information measurement timing of FIG. In the period indicated by the temperature information measurement timing signal Hi, the current detection determination unit 20c measures the current flowing through the sensor element 19a by the detection resistor R9 of the current detection unit 16 and captures the current value. Thereby, similarly to the third embodiment, the resistance change based on the temperature coefficient of the sensor element 19a is measured by the current value, and the temperature information for temperature compensation is sufficiently obtained based on the measured current value.

  Then, the sensor output determination unit 20d performs temperature compensation on the sensor output determined in the high temperature period based on the temperature information signal generated by the current detection determination unit 20c, and generates gas concentration data of the reducing gas, Temperature compensation is performed on the sensor output determined in the low temperature period to generate gas concentration data of incomplete combustion gas.

  Thus, according to the fourth embodiment of the present invention, the temperature information is obtained based on the temperature coefficient of the sensor element 19a of the catalytic combustion type gas sensor 19, and the sensor output corresponding to the reducing gas and the incomplete combustion gas is obtained. It is possible to accurately perform temperature compensation. Therefore, it is possible to construct a gas detection device capable of accurately compensating the temperature of the gas sensor by using the temperature coefficient of the sensor element 19a as information of the temperature sensor without using a temperature sensor that has been conventionally used. It becomes possible.

  The catalytic combustion type gas sensor normally includes a temperature compensating element having the same structure as the sensor element and subjected to a desensitization process on the gas, in addition to the sensor element, but the third and fourth embodiments of the present invention. In the embodiment, since the temperature information signal is obtained by using the temperature coefficient of the sensor element 19a of the catalytic combustion type gas sensor 19, the temperature compensation element is unnecessary, and the structure of the catalytic combustion type gas sensor is simple and inexpensive. There is.

  As described above, the embodiment of the present invention has been described. However, the present invention is not limited to this, and various modifications and applications are possible.

  For example, the present invention can be applied to all gas sensors using a material such as a heater material having a certain level of temperature coefficient.

1 is a schematic diagram showing the structure of a semiconductor gas sensor. 1 is a circuit diagram of a gas detection device according to a first embodiment of the present invention. (First embodiment) It is a timing chart explaining the drive conditions in the gas detection apparatus which concerns on 1st Embodiment of this invention. (First embodiment) It is a timing chart explaining the drive conditions in the gas detection apparatus which concerns on 2nd Embodiment of this invention. (Second Embodiment) It is a circuit diagram of the gas detection apparatus which concerns on 3rd Embodiment of this invention. (Third embodiment) It is a timing chart explaining the drive conditions in the gas detection apparatus which concerns on 3rd Embodiment of this invention. (Third embodiment) It is a timing chart explaining the drive conditions in the gas detection apparatus which concerns on 4th Embodiment of this invention. (Fourth embodiment)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor type gas sensor 1a Gas sensitive body 1b Heater 1c Sensor electrode 10 Gas detection apparatus 11 Plate power supply 12 Heater power supply (voltage source)
15 Sensor output detector (sensor output detector)
16 Current detection determination unit (current detection means)
17 Drive power supply (voltage source)
19 catalytic combustion type gas sensor 19a sensor element 20 microcomputer (CPU)
20c Current detection determination unit (temperature information signal generation means)
20d sensor output determination unit (gas concentration data generating means)

Claims (6)

A gas detection device that detects the presence of gas in a state installed in a gas atmosphere,
A gas sensor that detects the concentration of the gas in a state installed in a gas atmosphere and generates a sensor output;
A voltage for operating the gas sensor, a voltage that alternately changes in level between a constant high level for detecting the gas concentration and a constant low level for detecting the gas concentration is supplied. A voltage source;
Current detecting means for detecting a current flowing through the gas sensor;
The current value detected by the current detection means is determined while the voltage at the low level is supplied from the voltage source, and the current value, the ambient temperature of the gas sensor, and the sensor output are obtained in advance. Temperature information signal generating means for generating a temperature information signal indicating the ambient temperature based on the correlation;
Gas concentration data generation means for generating gas concentration data by performing temperature compensation on the sensor output based on the temperature information signal generated by the temperature information signal generation means;
A gas detection device comprising: A gas detection device that detects the presence of gas in a state installed in a gas atmosphere,
A gas sensor, a heater for heating the gas sensor, and a semiconductor gas sensor having a sensor electrode for taking out a resistance change of the gas sensor;
A heater power supply for supplying a heater voltage that alternately changes the level of the heater to a constant high level for detecting the gas concentration and a constant low level not detecting the gas concentration;
A plate power source that intermittently supplies a constant level of plate voltage to the sensor electrode;
Sensor output detection means for detecting a sensor output while the heater voltage is supplied to the heater and the plate voltage is supplied to the sensor electrode from the plate power supply;
Current detecting means for detecting a heater current flowing in the heater;
A current value detected by the current detection means while the heater voltage at the low level is supplied to the heater and the plate voltage is not supplied to the sensor electrode is determined, and the current value and the semiconductor gas sensor Temperature information signal generating means for generating a temperature information signal indicating the ambient temperature based on a correlation obtained in advance between the ambient temperature of the sensor and the sensor output;
Gas concentration data generation means for generating gas concentration data by performing temperature compensation on the sensor output based on the temperature information signal generated by the temperature information signal generation means;
A gas detection device comprising: A gas detection device that detects the presence of gas in a state installed in a gas atmosphere,
A contact combustion type gas sensor having a sensor element whose resistance value changes according to the concentration of the gas in a state installed in a gas atmosphere, and detecting the concentration of the gas to generate a sensor output;
A voltage source that supplies the sensor element with a voltage that alternately changes in level between a constant high level for detecting the gas concentration and a constant low level that does not detect the gas concentration;
Current detecting means for detecting a current flowing in the sensor element;
The current value detected by the current detection means is determined while the low-level voltage is supplied to the sensor element, and the current value, the ambient temperature of the catalytic combustion gas sensor, and the sensor output are preliminarily determined. Temperature information signal generating means for generating a temperature information signal indicating the ambient temperature based on the obtained correlation;
Gas concentration data generation means for generating gas concentration data by performing temperature compensation on the sensor output based on the temperature information signal generated by the temperature information signal generation means;
A gas detection device comprising: In the gas detection device according to any one of claims 1 to 3,
The low level of the voltage is a level for detecting a concentration of a gas of a different type from the gas. The gas detection device according to claim 2,
The gas detection device, wherein the current detection means is a fixed resistor having a temperature coefficient sufficiently smaller than a temperature coefficient of the heater. The gas detection device according to claim 3,
The gas detection device, wherein the current detection means is a fixed resistor having a temperature coefficient sufficiently smaller than a temperature coefficient of the sensor element.

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