JP2010054230A - Gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detector for improving detecting accuracy of the poisoning amount. <P>SOLUTION: This gas detector 1 applies reference voltage to a contact combustion type gas sensor 21 so that a reference region as a part of the contact combustion type gas sensor 21 reaches a combustion temperature for combusting polar gas or higher, and acquires an output from the contact combustion type gas sensor 21 driven by the voltage application. The gas detector 1 applies a voltage higher than the reference voltage to the contact combustion type gas sensor 21 so that an extended region including the reference region of the contact combustion type gas sensor 21 reaches the combustion temperature for combusting polar gas or higher, and acquires an output from the contact combustion type gas sensor driven by the voltage application. A poisoning amount detecting section 14 detects the poisoning amount in the reference region based on the two acquired outputs. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas detection device.

Conventionally, a gas detector that calculates a gas concentration according to an output from a gas sensor is known. In such a gas detection device, the output from the gas sensor may decrease due to silicone poisoning or the like, and the accurate gas concentration may not be calculated. Therefore, a gas detection device has been proposed that detects the poisoning amount of a gas sensor and corrects the output from the gas sensor in accordance with the detected poisoning amount (see Patent Document 1).
JP 2003-232760 A

  However, in the gas detection device described in Patent Document 1, since the poisoning amount is determined from the change amount of the sensor resistance value after the heat cleaning, it is affected by the outside air temperature, and the detection accuracy of the poisoning amount is never high. That's not true.

  The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a gas detection device capable of improving the detection accuracy of the poisoning amount.

  The gas detection device of the present invention is a gas detection device that calculates the concentration of a polar gas from an output obtained by burning a polar gas with a catalytic combustion type gas sensor, and is a reference that is a part of the catalytic combustion type gas sensor. A first voltage applying means for applying a reference voltage to the contact combustion type gas sensor, and a contact combustion type gas sensor driven by voltage application by the first voltage application means so that the region is equal to or higher than a combustion temperature for burning the polar gas; A voltage higher than the reference voltage in the contact combustion type gas sensor so that the first output acquisition means for acquiring the output from the gas and the enlarged region including the reference region of the contact combustion type gas sensor is equal to or higher than the combustion temperature for burning the polar gas. A second voltage applying means for applying a second output, and a second output for obtaining an output from a catalytic combustion type gas sensor driven by voltage application by the second voltage applying means. An acquisition unit; and a poisoning amount detection unit that detects a poisoning amount in the reference region based on the output acquired by the first output acquisition unit and the output acquired by the second output acquisition unit. Features.

  In the gas detection device of the present invention, it is preferable that the second voltage applying unit applies a voltage higher than the reference voltage every time the operation in which the reference voltage is applied and the output is acquired is repeated for a certain period.

  Further, in the gas detection device of the present invention, the second voltage application means determines that the previous contact combustion type gas sensor was present in an atmosphere in which no polar gas exists based on the output acquired by the first output acquisition means. In this case, it is preferable to prohibit application of a voltage higher than the reference voltage even if the operation is repeated for a certain period.

  In the gas detection device of the present invention, the gas detection device further includes concentration calculation means for calculating the concentration of the polar gas based on the output from the contact combustion type gas sensor, wherein the second output acquisition means is a contact combustion type gas sensor. When the output from is acquired, it is preferable to calculate the concentration of the polar gas based on the output acquired by the second output acquisition means.

  According to the gas detection device of the present invention, the reference voltage is applied so that the reference region that is a part is equal to or higher than the combustion temperature at which the polar gas is burned, while the expanded region wider than the reference region contains the polar gas. A voltage higher than the reference voltage is applied so that the combustion temperature is equal to or higher than the combustion temperature, and the poisoning amount in the reference region is detected based on these outputs. Here, the comparison result between the output obtained so that only the reference region is equal to or higher than the combustion temperature and the output obtained so that the enlarged region is equal to or higher than the combustion temperature indicates that the poisoning of the reference region proceeds. The case where it is and the case where it is not are different. Therefore, the poisoning amount can be detected based on the comparison result. In particular, in the present invention, even when the outside air temperature is high, the amount of poisoning is detected from the comparison of the sensor outputs of the two, so that it is difficult to be affected by the outside air temperature and the amount of poisoning is detected. Can do. Therefore, the detection accuracy of the poisoning amount can be improved.

  In addition, a voltage higher than the reference voltage is applied every time the operation of acquiring the output by applying the reference voltage is repeated for a certain period. For this reason, every time acquisition of output for the reference region is performed for a certain period of time, output for the expansion region is acquired, and the reference region is burned at a frequency that makes the expansion region equal to or higher than the combustion temperature. The frequency can be less than the temperature. This makes it difficult for the enlarged area to be poisoned, and is obtained by the output obtained from the reference area (ie, the area where the degree of poisoning is unknown) and the enlarged area (ie, the area where poisoning is not progressing). The amount of poisoning in the reference area can be obtained with reference to the area where the poisoning is not progressing as an enlarged area, and the detection accuracy of the poisoning amount can be further improved. it can.

  Further, the second voltage applying means, when it is determined that the previous contact combustion type gas sensor was present in an atmosphere in which no polar gas exists, based on the output obtained by the first output obtaining means, the above operation is constant. Even if the period is repeated, application of a voltage higher than the reference voltage is prohibited. Here, the poisoning amount is obtained from a comparison between the output obtained so that only the reference region is equal to or higher than the combustion temperature and the output obtained so that the enlarged region is equal to or higher than the combustion temperature. If there is no polar gas, the two cannot be compared, and the detected poisoning amount may be incorrect. For this reason, if the previous output is an output obtained in an atmosphere where there is no polar gas, the detection of the poisoning amount is prohibited by prohibiting the application of a voltage higher than the reference voltage. , Can prevent detection of wrong poisoning amount.

  Further, when the second output acquisition means acquires the output from the catalytic combustion type gas sensor, the concentration of the polar gas is calculated based on the output acquired by the second output acquisition means. For this reason, when the second output acquisition means acquires the output from the catalytic combustion type gas sensor, the concentration of the polar gas is calculated based on the output result from the enlarged region where the poisoning does not proceed from the reference region. Thus, the calculated concentration of the polar gas can be improved while omitting the processing such as the poisoning correction.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. FIG. 1 is a configuration diagram illustrating a gas detection device according to an embodiment of the present invention. As shown in FIG. 1, the gas detection device 1 calculates the concentration of the polar gas based on the sensor output, and includes a control unit 10 and a gas sensor unit 20 having a catalytic combustion type gas sensor 21. ing. Here, the polar gas is a gas in which the molecules have an electric dipole because the centers of gravity of the positive charge and the negative charge do not coincide within the molecule, and are also simply referred to as a polar gas. Examples of such a polar gas include ethanol, acetic acid, formaldehyde, and toluene.

  The control unit 10 performs drive control of the gas sensor unit 20, calculation of gas concentration, and the like, and is configured by, for example, an MPU (Microprocessor Unit). The control unit 10 includes a sensor drive control unit 11, a sensor output acquisition unit (first output acquisition unit, second output acquisition unit) 12, a storage unit 13, a poisoning amount detection unit (toxic amount detection unit) 14, and , A density calculation unit (density detection means) 15 is provided.

  The sensor drive controller 11 controls the drive of the catalytic combustion gas sensor 21 by outputting a drive signal. The sensor output acquisition unit 12 acquires information on the output voltage of the catalytic combustion gas sensor 21 that is driven and controlled by the sensor drive control unit 11. The storage unit 13 is a non-volatile memory that stores a poisoning amount and a poisoning level, which will be described later. The poisoning amount detection unit 14 detects the poisoning amount of the catalytic combustion type gas sensor 21. The concentration calculation unit 15 calculates the concentration of the polar gas based on the output voltage value of the catalytic combustion type gas sensor 21 acquired by the sensor output acquisition unit 12. Further, the density calculation unit 15 includes a correction unit 15a. The correction unit 15 a corrects the output from the sensor output acquisition unit 12 according to the poisoning amount detected by the poisoning amount detection unit 14 and stored in the storage unit 13. Therefore, the concentration calculation unit 15 calculates an accurate gas concentration based on the output voltage corrected by the correction unit 15a.

  The gas sensor unit 20 includes various resistors R1 to R3, a bridge drive circuit 22, an instrumentation amplifier 23, and an A / D converter 24 in addition to the contact combustion gas sensor 21.

  As shown in FIG. 1, the contact combustion type gas sensor 21 has two resistors Rr and Rs, and these resistors Rr and Rs together with the resistors R1 and R2 form a bridge circuit. The resistor R1 has one end connected to the bridge drive circuit 22 side and the other end connected to the connection point B. The resistor R2 has one end connected to the bridge drive circuit 22 side and the other end connected to the connection point A. The sensor resistor Rs is connected in series with the resistor R2, one end connected to the connection point A, and the other end connected to the ground. The reference resistor Rr is connected in series with the resistor R1, one end connected to the connection point B, and the other end connected to the ground.

  The bridge drive circuit 22 controls the voltage applied to the bridge circuit based on the drive signal from the sensor drive control unit 11. For this reason, the bridge drive circuit 22 constitutes the first and second voltage application means for controlling the voltage applied to the catalytic combustion type gas sensor 21 together with the sensor drive control unit 11.

  FIG. 2 is an external view showing details of the catalytic combustion type gas sensor 21 shown in FIG. 1, wherein (a) shows a top view and (b) shows a cross-sectional view. FIG. 2B shows a cross section taken along the line AA in FIG.

  A catalytic combustion type gas sensor 21 shown in FIG. 2A and FIG. 2B is a micro sensor manufactured using a semiconductor manufacturing process technology. In this contact combustion type gas sensor 21, an insulating film 21b made of a silicon oxide film, a silicon nitride film, a hafnium oxide film or the like is formed on a silicon wafer 21a, and a sensor resistance Rs and a reference resistance Rr are formed on the insulating film 21b. Is provided.

The sensor resistor Rs is a resistor made of platinum, and a catalyst layer 21s is provided so as to enclose the resistor. The catalyst layer 21 s is made of, for example, Pd / Al ₂ O ₃ made of alumina supporting palladium. The reference resistor Rr is a resistor made of platinum like the sensor resistor Rs, and an alumina layer 21r is provided so as to enclose the resistor.

  In addition, three bonding pads 21c to 21e are formed on the silicon wafer 21a. The first bonding pad 21c is a connection point A. The second bonding pad 21d is grounded. Further, the third bonding pad 21e becomes the connection point B.

  Further, in the silicon wafer 21a, concave portions 21f and 21g are formed by anisotropic etching from the back surface at positions corresponding to the sensor resistance Rs and the reference resistance Rr. The catalytic combustion type gas sensor 21 has a small heat capacity due to the recesses 21f and 21g.

  Reference is again made to FIG. The instrumentation amplifier 23 amplifies the difference between the voltages input to the non-inverting input terminal and the inverting input terminal. The instrumentation amplifier 23 has a non-inverting input terminal connected to the connection point A and an inverting input terminal connected to the connection point B. For this reason, the instrumentation amplifier 23 amplifies the voltage difference between the connection point A and the connection point B. The instrumentation amplifier 23 is connected to a variable resistor R3. The variable resistor R3 is for adjusting the offset. The A / D converter 24 receives the analog voltage output from the instrumentation amplifier 23, performs A / D conversion, and outputs the analog voltage to the sensor output acquisition unit 12.

  Next, the basic operation of the gas detection device 1 according to this embodiment will be described. First, the sensor drive control unit 11 outputs a drive signal to the bridge drive circuit 22, and the bridge drive circuit 22 drives the catalytic combustion gas sensor 21 at a low temperature. As a result, the catalytic combustion type gas sensor 21 becomes lower than the combustion temperature of the polar gas, and in an atmosphere where the polar gas is present, the polar gas adheres to the catalyst layer 21s provided so as to surround the sensor resistance Rs. Thereafter, the bridge drive circuit 22 drives the catalytic combustion gas sensor 21 at a high temperature by a drive signal from the sensor drive control unit 11. Thereby, the contact combustion type gas sensor 21 reaches the combustion temperature of the polar gas, and in the atmosphere where the polar gas exists, the polar gas attached to the catalyst layer 21s at the time of low temperature driving burns.

  When switching from the low temperature drive to the high temperature drive, the temperature rise of the catalytic combustion gas sensor 21 depends on the energy supplied to the catalytic combustion gas sensor 21. For this reason, if both resistors Rs and Rr are driven at the same voltage in an atmosphere without a polar gas, the time required for both resistors Rs and Rr to reach a predetermined temperature becomes equal. On the other hand, when both resistances Rs and Rr are driven at the same voltage in an atmosphere where a polar gas exists, the sensor resistance Rs reaches a predetermined temperature earlier than the reference resistance Rr due to the energy during the combustion of the polar gas. And since a difference arises in temperature, a difference arises also in the resistance value of both resistances Rs and Rr, and the balance of a bridge circuit is broken. As a result, the output from the instrumentation amplifier 23 shows a value corresponding to the molecular weight (that is, the concentration) of the attached polar gas. Then, the concentration calculation unit 15 calculates the concentration of the polar gas based on the obtained output.

  In the above, when the catalytic combustion type gas sensor 21 is driven at a low temperature, a voltage is applied to the catalytic combustion type gas sensor 21, but this is not limiting, and the voltage is cut off when the catalytic combustion type gas sensor 21 is driven at a low temperature. It may be configured to.

  Next, details of the characteristic operation of the gas detection device 1 according to the present embodiment will be described. 3A and 3B are conceptual diagrams showing the temperature and the like of the catalyst layer 21s enclosing the sensor resistance Rs. FIG. 3A shows the temperature and the like during low temperature driving and high temperature driving, and FIG. 3B shows the region functioning as the sensor portion. ing. As described above, the catalytic combustion type gas sensor 21 performs the low temperature driving and burns the polar gas attached to the catalyst layer 21s during the high temperature driving to obtain an output. For this reason, only the region of the catalyst layer 21s that has an adsorption temperature lower than the combustion temperature during low-temperature driving and that is equal to or higher than the combustion temperature during high-temperature driving functions as a sensor portion.

  Specifically, as shown in FIG. 3, the gas detection device 1 according to the present embodiment sets only the first region 31 in the central portion of the catalyst layer 21 s as an adsorption temperature during low-temperature driving and as high as a combustion temperature during high-temperature driving. Yes. For this reason, only the first region 31 functions as a sensor portion. That is, the center portion of the catalyst layer 21s is easily warmed by the sensor resistance Rs, and the region outside the first region 31 is hardly warmed, so that only the first region 31 functions as a sensor portion.

Here, the contact combustion type gas sensor 21 is poisoned with silicone when three conditions are satisfied. Specifically, the catalytic combustion type gas sensor 21 is conditioned on (1) presence of siloxane in the test gas, (2) having a catalyst layer 21s, and (3) a high catalyst temperature. SiO ₂ is formed and silicone poisoning occurs. Therefore, the first region 31 on the catalyst layer 21s satisfying the three conditions is poisoned with silicone by long-term use.

  4A and 4B are second conceptual diagrams showing the temperature and the like of the catalyst layer 21s enclosing the sensor resistance Rs. FIG. 4A shows the temperature and the like during low temperature driving and high temperature driving, and FIG. 4B functions as the sensor portion. Indicates the area. When the first region 31 of the catalyst layer 21s has been poisoned with silicone, the gas detection device 1 according to this embodiment increases the temperature when the catalytic combustion gas sensor 21 is driven at a high temperature (see FIG. 4A). ). Thereby, the 2nd field 32 containing the 1st field 31 can be made to function as a sensor part (refer to Drawing 4 (b)). Furthermore, when the 2nd area | region 32 has been poisoned with silicone, the gas detection apparatus 1 raises the temperature at the time of the high temperature drive of the contact combustion type gas sensor 21 further. Thereby, the 3rd field 33 containing the 1st field 31 and the 2nd field 32 can be made to function as a sensor part (refer to Drawing 4 (b)). Thereafter, each time the region functioning as the sensor portion is poisoned with silicone, the temperature at the time of high temperature driving is increased, so that the outer region can function as the sensor portion.

  In the case of the example shown in FIG. 4, the gas detection device 1 increases the temperature at the low temperature driving in accordance with the increase in the temperature at the high temperature driving. You may make it raise the temperature at the time of high temperature drive, keeping it constant. If the temperature during low temperature driving is increased in conjunction with increasing the temperature during high temperature driving, it becomes possible to apply a temperature higher than the combustion temperature during low temperature driving to the poisoned area. Gas adsorption can be prevented. That is, when a slight gas sensitivity remains in the poisoned area, it can be prevented from being affected by the slight gas sensitivity. And even if any detection region is made to function as a sensor part, the variation in adsorption amount can be suppressed. On the other hand, when the temperature at the time of low temperature driving is constant, it is only necessary to increase the temperature at the time of high temperature driving, so that control can be facilitated. In this case, as the area that functions as the sensor portion becomes the outer area, the polar gas is adsorbed to the inner area and the adsorption of the polar gas increases, so it is desirable to adjust the detection area. .

  In addition, even if the voltage is constantly applied to the catalytic combustion type gas sensor 21 without performing the low temperature driving and the high temperature driving, by sequentially increasing the voltage applied to the catalytic combustion type gas sensor 21 as described above. An area that is not poisoned with silicone can also function as a sensor portion.

  In addition, in this embodiment, the poisoning amount of the first region 31 can be detected by using the first region 31 and the second region 32. First, it is assumed that the first region 31 is not poisoned. In this case, the value obtained by dividing the output when the second region 32 including the first region is controlled to be equal to or higher than the combustion temperature from the output when only the first region 31 is controlled to be equal to or higher than the combustion temperature is , C1 (C1 is a constant).

  On the other hand, it is assumed that the first region 31 is poisoned and hardly performs the sensor function. In this case, the value obtained by dividing the output when the second region 32 including the first region is controlled to be equal to or higher than the combustion temperature from the output when only the first region 31 is controlled to be equal to or higher than the combustion temperature is , C2 (C2 is a constant smaller than C1).

  Accordingly, the poisoning amount detection unit 14 according to the present embodiment controls the output voltage when only the first region 31 (reference region) is controlled to be equal to or higher than the combustion temperature, and the second region 32 (including the first region) ( The amount of poisoning in the first region 31 can be detected from a comparison with the output voltage when the control is performed so that the (expanded region) is equal to or higher than the combustion temperature. This theory is valid only when the poisoning amount of the second region 32 is small. For this reason, the gas detection device 1 detects the poisoning amount in the first region 31 by acquiring the output voltage in the second region 32 only once after performing concentration detection repeatedly in the first region 31 for a certain period of time, for example. It is desirable to do. This is because the number of uses of the second region 32 is less than the number of uses of the first region 31 and the progress of poisoning of the second region 32 is suppressed.

  In the above description, the first region 31 and the second region 32 have been described. However, the present invention is not limited to this, and the same applies to the second region 32 (reference region) and the third region 33 (enlarged region). The poisoning amount of the second region 32 can be detected. Furthermore, the poisoning amount can be similarly detected for the third region 33 (reference region) and the region outside the third region (enlarged region).

  Next, an outline of processing of the gas detection device 1 according to the present embodiment will be described. First, the sensor drive unit 11 and the bridge drive circuit 22 drive the contact combustion gas sensor 21 at a low temperature so that the first region 31 of the contact combustion gas sensor 21 is lower than the combustion temperature of the polar gas. Then, after a predetermined time elapses, the sensor drive unit 11 and the bridge drive circuit 22 apply the first voltage (reference voltage) to the contact combustion type gas sensor 21 so that the first region 31 becomes equal to or higher than the combustion temperature of the polar gas. Drive at high temperature.

  Next, after the gas detection device 1 repeatedly executes the above operation for a certain period, the poisoning amount detection unit 14 detects the poisoning amount in the first region 31. At this time, after driving the catalytic combustion gas sensor 21 at a low temperature, the sensor driving unit 11 and the bridge driving circuit 22 are connected to the catalytic combustion gas sensor 21 so that the second region 32 becomes equal to or higher than the combustion temperature of the polar gas. A second voltage higher than one voltage is applied to drive at a high temperature. Thereby, the poisoning amount detection part 15 detects the poisoning amount of the 1st area | region 31 based on an above-described theory. In detecting the poisoning amount, it is desirable to repeat a series of operations of applying the second voltage after driving the catalytic combustion gas sensor 21 at a low temperature twice, and to use the second output. When the first output is used, the polar gas continues to be adsorbed in the second region 32 while the detection was performed in the first region 31, and the first region 31 and the second region 32 This is because a large difference appears in the adsorption time.

  Next, the control unit 10 stores the detected poisoning amount in the storage unit 13. Further, when the detected poisoning amount is less than the predetermined value, the control unit 10 causes the storage unit 13 to store the poisoning level as the first level. On the other hand, when the detected poisoning amount is equal to or greater than the predetermined value, the control unit 10 causes the storage unit 13 to store the poisoning level as the second level.

  When the detected poisoning amount is less than the predetermined value, that is, when the poisoning level is the first level, the sensor driving unit 11 and the bridge driving circuit 22 operate to drive the first region 31 at a low temperature. Then, the operation of driving the first region 31 at a high temperature is repeatedly performed.

  On the other hand, when the detected poisoning amount is a predetermined value or more, that is, when the poisoning level is the second level, the sensor driving unit 11 and the bridge driving circuit 22 drive the catalytic combustion gas sensor 21 at a low temperature, The second voltage is applied to the catalytic combustion type gas sensor 21 so that the second region 32 is equal to or higher than the combustion temperature of the polar gas, and is driven at a high temperature. Then, the gas detection apparatus 1 causes the second region 32 to function as a sensor part in the future, and does not perform detection only by the first region 31 in which poisoning has progressed.

  Next, the poisoning amount detection unit 14 causes the second region 32 to function as a sensor portion, and after repeatedly performing low temperature driving and high temperature driving for a certain period of time, detects the poisoning amount of the second region 32. At this time, after driving the catalytic combustion gas sensor 21 at a low temperature, the sensor driving unit 11 and the bridge driving circuit 22 provide the catalytic combustion gas sensor 21 with the first temperature so that the third region 33 becomes equal to or higher than the combustion temperature of the polar gas. A third voltage higher than the second voltage is applied to drive at a high temperature. Thereby, the poisoning amount detection part 15 detects the poisoning amount of the 2nd area | region 32 based on an above-described theory. Even in this case, it is desirable to repeat the series of operations for applying the third voltage after driving the catalytic combustion gas sensor 21 at a low temperature twice, and to use the second output. This is because a large difference occurs in the adsorption time.

  Next, the control unit 10 stores the detected poisoning amount in the storage unit 13. Further, when the detected poisoning amount is less than the predetermined value, the control unit 10 causes the storage unit 13 to store the poisoning level as the second level. On the other hand, when the detected poisoning amount is equal to or greater than the predetermined value, the control unit 10 causes the storage unit 13 to store the poisoning level as the third level.

  Thereafter, when the gas detection device 1 detects the poisoning amount as described above and can determine that the poisoning is in progress, the region outside the region currently functioning as the sensor portion is the sensor portion. The applied voltage is adjusted so as to function as

  Next, detailed operation of the gas detection apparatus 1 according to the present embodiment will be described with reference to a flowchart. FIG.5 and FIG.6 is a flowchart which shows detailed operation | movement of the gas detection apparatus 1 which concerns on this embodiment.

  First, the control unit 10 reads information on the poisoning level and the poisoning amount stored in the storage unit 13 (S1). Next, the control unit 10 sets a voltage for driving the catalytic combustion gas sensor 21 at a high temperature (S2). At this time, the control unit 10 sets the voltage to be set as the first voltage when the poisoning level read in step S1 is the first level, and sets the voltage to be set as the first voltage when the poisoning level is the second level. If the voltage is 2 and the poisoning level is the third level, the voltage to be set is the third voltage. The temperature when the catalytic combustion type gas sensor 21 is driven by the voltage set in step S2 is referred to as “current detection temperature”.

  Thereafter, the control unit 10 sets a voltage for driving the catalytic combustion gas sensor 21 at a low temperature (S3). Then, the sensor drive control unit 11 and the bridge drive circuit 22 apply the voltage set by the control unit 10 to the bridge circuit to drive the catalytic combustion gas sensor 21 at a low temperature (S4). In the processing of Step S3 and Step S4, the control unit 10 may or may not change the voltage at the time of low temperature driving according to the poisoning level.

  After the process of step S4, the control unit 10 determines whether or not a predetermined time has elapsed (S5). When it is determined that the predetermined time has not elapsed (S5: NO), this process is repeated until it is determined that the predetermined time has elapsed. On the other hand, when it is determined that the predetermined time has elapsed (S5: YES), the process proceeds to step S6. As described above, the gas detection device 1 realizes an adsorption period in which the polar gas is adsorbed by the catalytic combustion gas sensor 21 by determining whether or not a predetermined time has elapsed.

  In step S6, the control unit 10 determines whether or not to execute a poisoning determination process for detecting the poisoning amount (S6). At this time, the control unit 10 performs the poisoning determination process when (1) the gas concentration is detected for a certain period at the current detection temperature, and (2) there is a gas reaction from the previous gas concentration detection value. Is determined to be executed. This is because if the poisoning determination process is executed when the gas concentration is not detected for a certain period at the current detection temperature, the poisoning determination process is frequently executed, which is inconvenient. That is, if the poisoning amount is frequently detected, as described above, the number of times of use of the region (for example, the second region 32) outside the region (for example, the first region 31) where the poisoning amount is desired to be detected increases. This is because the possibility that the poisoning of the outer region proceeds will increase. Further, if the poisoning amount is detected when there is no gas reaction from the detection value of the previous gas concentration, it becomes impossible to obtain the poisoning amount from the previous and current output voltages.

  If it is determined that the poisoning determination process is to be executed (S6: YES), the control unit 10 sets a new voltage in such a manner as to overwrite the voltage set in step S2 (S7). At this time, when the poisoning level is the first level, the control unit 10 sets the set voltage as the second voltage higher than the first voltage. The control unit 10 sets the voltage to be set to a third voltage higher than the second voltage when the poisoning level is the second level, and sets the voltage to be set to the third voltage when the poisoning level is the third level. The fourth voltage is higher than the voltage. Thereby, the control part 10 will function the area | region outside the area | region made to function as a sensor part by the present detection temperature as a sensor part. The temperature when the catalytic combustion type gas sensor 21 is driven by the voltage set in step S7 is referred to as “next detection temperature”.

  On the other hand, when it is determined not to execute the poisoning determination process (S6: NO), the process proceeds to step S8. In step S8, the sensor drive control unit 11 and the bridge drive circuit 22 apply the voltage set by the control unit 10 to the bridge circuit to drive the catalytic combustion gas sensor 21 at a high temperature (S8). That is, if it is determined in step S6 that the poisoning determination process is to be executed, the catalytic combustion gas sensor 21 is driven at the next detected temperature, and if it is determined not to execute the poisoning determination process, the contact combustion gas sensor 21 is determined. Is driven at the current detected temperature.

Thereafter, the control unit 10 determines whether or not the poisoning determination is currently being performed, and whether or not the H temperature driving in step S8 is the first driving (S9). If the poisoning determination is currently being performed and the H temperature drive in step S8 is the first drive (S9: YES), the process proceeds to step S3. On the other hand, when the poisoning determination is not currently being performed, or when the poisoning determination is currently being performed, but the H temperature driving in step S8 is the second driving (S9: NO), the control unit 10 performs step S8. The sensor output obtained by the high-temperature driving at is sampled at least once, and the obtained data is stored in the storage unit 13 as GAS _n (S10).

  And the control part 10 judges whether the temperature at the time of high temperature drive was the next detection temperature (FIG. 6: S11). That is, the control unit 10 determines whether or not the poisoning determination process is executed in step S6. When it is determined that the temperature at the time of high temperature driving is not the next detection temperature (S11: NO), since the poisoning determination process is not being executed, the gas detection device 1 determines the poisoning amount and the poisoning level after step S12. The process proceeds to step S18 without executing the detection process.

On the other hand, when it is determined that the temperature at the time of high temperature driving is the next detection temperature (S11: YES), since the poisoning determination process is being performed, the gas detection device 1 performs the poisoning amount and the amount of the poisoning after Step S12. Execute poison level detection processing. In this detection process, the poisoning amount detection unit 14 first divides GAS _n that is the current sampling data from GAS _n−1 that is the previous sampling data stored in the storage unit 13 to obtain the poisoning amount. Obtain (S12). Next, the control unit 10 determines whether or not the poisoning amount is less than a preset value α (S13).

  When it is determined that the poisoning amount is less than the preset set value α (S13: YES), that is, when the poisoning of the region functioning as the sensor portion is in progress by the current detected temperature, the control unit 10 Causes the poisoning level to be incremented and stored in the storage unit 13 so that the next detection temperature becomes the current detection temperature (S14). By this processing, the area outside the area that has been functioning as the sensor part until now is made to function as the sensor part. And the control part 10 resets the information of the poisoning amount memorize | stored in the memory | storage part 13 (S15), and a process transfers to step S18.

  When it is determined that the poisoning amount is not less than the preset set value α (S13: NO), that is, when the poisoning of the region functioning as the sensor portion is not progressing so much due to the current detected temperature, the control unit 10 Sets the voltage for driving the catalytic combustion gas sensor 21 at a high temperature as in step S2 (S16). Next, the control unit 10 causes the storage unit 13 to store information on the poisoning amount obtained in step S12 (S17). Thereafter, the process proceeds to step S18.

  In step S18, the correction unit 15a of the concentration calculation unit 15 performs poisoning correction (S18). In this process, the correction unit 15 a divides the output voltage acquired by the sensor output acquisition unit 12 by the poisoning amount stored in the storage unit 13. Thereby, the concentration calculation unit 15 can obtain the gas concentration in which the output voltage is corrected and the influence of poisoning is eliminated. However, if “YES” is determined in step S11 and the poisoning determination is being performed, the concentration calculation unit 15 obtains the gas concentration using the output voltage obtained by driving at the next detection temperature as it is. This simplifies the process without correcting the output voltage, and allows the gas concentration to be obtained from the output voltage detected by the outer region where the number of times of use is small, thereby improving the calculation accuracy of the gas concentration. Because you can.

  Thereafter, the control unit 10 outputs the gas concentration calculated in step S18 to an external device (for example, a gas alarm device) as necessary (S19). Then, the processing shown in FIGS. 5 and 6 ends. The processes shown in FIGS. 5 and 6 are repeatedly executed until the power of the gas detection device 1 is turned off.

  FIG. 7 is a graph showing the sensor output when the gas detection device 1 according to the present embodiment divides the catalyst layer 21 s into five regions and causes the outer region to function as a sensor portion each time poisoning proceeds. is there. The sensor output value on the vertical axis in FIG. 7 was obtained as follows. First, in an atmosphere where a polar gas with a certain concentration exists, the output from the catalytic combustion type gas sensor 21 is AD converted by an 11-bit A / D converter, and the obtained AD value is sampled at a predetermined timing and sampled. Accumulate AD values. After that, in a situation where no polar gas exists, the output from the catalytic combustion type gas sensor 21 is AD-converted by an 11-bit A / D converter, and the obtained AD value is sampled at the same timing as above and sampled. Accumulate AD values. Next, the integrated AD value obtained in the former is subtracted by the latter integrated AD value. As described above, the values on the vertical axis shown in FIG. 7 were obtained.

  As shown in FIG. 7, in the first area 31, the initial sensitivity, that is, the state where there is no poisoning, the value of the sensor output indicates about “16000”. When the first region 31 is poisoned, the sensor output value is almost “0”.

  However, as in the gas detection device 1 according to the present embodiment, by causing the second region 32 to newly function as a sensor portion, the value of the sensor output again indicates about “16000” (second region 32). Initial sensitivity). Thus, in this embodiment, it is clear from the experiment that the sensor output is recovered and can contribute to the extension of the lifetime of the sensor.

  When the second region 32 is poisoned, the sensor output value is almost “0”. However, by causing the third region 33 to newly function as a sensor portion, the value of the sensor output again indicates about “16000” (see the initial sensitivity of the third region 33). In other words, it is clear from experiments that it is possible to further contribute to the extension of the life of the sensor by dividing the area into three or more instead of two and changing the sensor function part each time the poisoning progresses. ing.

  Thereafter, similarly, every time the poisoning progresses and the sensor output value becomes substantially “0”, the sensor function value is changed, so that the sensor output value is restored to about “16000” again. Contributes to longer life.

  Thus, according to the gas detection apparatus 1 according to the present embodiment, the reference voltage (for example, the reference region (for example, the first region 31) is set so that the reference region (for example, the first region 31) becomes equal to or higher than the combustion temperature for burning the polar gas. While applying the first voltage), a voltage (for example, the second voltage) higher than the reference voltage so that an enlarged region (for example, the second region 32) wider than the reference region is equal to or higher than the combustion temperature at which the polar gas is combusted. And the amount of poisoning in the reference region is detected based on these outputs. Here, the comparison result between the output obtained so that only the reference region is equal to or higher than the combustion temperature and the output obtained so that the enlarged region is equal to or higher than the combustion temperature indicates that the poisoning of the reference region proceeds. The case where it is and the case where it is not are different. Therefore, the poisoning amount can be detected based on the comparison result. In particular, in this embodiment, even under conditions such as the outside air temperature being high, the poisoning amount is detected from the comparison of the sensor outputs of both, so that it is hardly affected by the outside air temperature and the poisoning amount is detected. be able to. Therefore, the detection accuracy of the poisoning amount can be improved.

  In addition, a voltage higher than the reference voltage is applied every time the operation of acquiring the output by applying the reference voltage is repeated for a certain period. For this reason, every time acquisition of output for the reference region is performed for a certain period of time, output for the expansion region is acquired, and the reference region is burned at a frequency that makes the expansion region equal to or higher than the combustion temperature. The frequency can be less than the temperature. This makes it difficult for the enlarged area to be poisoned, and is obtained by the output obtained from the reference area (ie, the area where the degree of poisoning is unknown) and the enlarged area (ie, the area where poisoning has not progressed). The amount of poisoning in the reference area can be obtained with reference to the area where the poisoning is not progressing as an enlarged area, and the detection accuracy of the poisoning amount can be further improved. it can.

  If it is determined that the previous contact combustion type gas sensor 21 was present in an atmosphere in which no polar gas exists, it is prohibited to apply a voltage higher than the reference voltage even if the above operation is repeated for a certain period of time. To do. Here, the poisoning amount is obtained from a comparison between the output obtained so that only the reference region is equal to or higher than the combustion temperature and the output obtained so that the enlarged region is equal to or higher than the combustion temperature. If there is no polar gas, the two cannot be compared, and the detected poisoning amount may be incorrect. For this reason, if the previous output is an output obtained in an atmosphere where there is no polar gas, the detection of the poisoning amount is prohibited by prohibiting the application of a voltage higher than the reference voltage. , Can prevent detection of wrong poisoning amount.

  Moreover, when the output based on the expansion area | region of the catalytic combustion type gas sensor 21 is acquired, the density | concentration of polar gas is calculated based on this output. For this reason, when the output based on the enlarged region of the catalytic combustion type gas sensor 21 is acquired, the concentration of the polar gas is calculated based on the output result from the enlarged region where the poisoning does not proceed from the reference region. The calculated concentration of the polar gas can be improved while omitting processing such as poisoning correction.

  As described above, the present invention has been described based on the embodiment, but the present invention is not limited to the above embodiment, and may be modified without departing from the gist of the present invention. For example, in the above embodiment, the contact combustion type gas sensor 21 forms a bridge circuit by the reference resistance Rr, the sensor resistance Rs, and the fixed resistances R1 and R2, but these arrangements can be changed as appropriate.

It is a block diagram which shows the gas detection apparatus which concerns on embodiment of this invention. It is an external view which shows the detail of the contact combustion type gas sensor shown in FIG. 1, (a) shows the top view, (b) has shown sectional drawing. It is a conceptual diagram which shows the temperature etc. of the catalyst layer which wraps sensor resistance, (a) shows the temperature at the time of low temperature drive and high temperature drive, etc., (b) has shown the area | region which functions as a sensor part. It is a 2nd conceptual diagram which shows the temperature etc. of the catalyst layer which wraps sensor resistance, (a) shows the temperature at the time of low temperature drive and high temperature drive, etc., (b) has shown the area | region which functions as a sensor part. It is a flowchart which shows detailed operation | movement of the gas detection apparatus 1 which concerns on this embodiment, and has shown the first half part. It is a flowchart which shows detailed operation | movement of the gas detection apparatus 1 which concerns on this embodiment, and has shown the second half part. In the gas detection apparatus which concerns on this embodiment, it is a graph which shows a sensor output at the time of dividing a catalyst layer into five area | regions and making an outer area | region function as a sensor part whenever poisoning advances.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gas detection apparatus 10 ... Control part 11 ... Sensor drive control part (1st voltage application means, 2nd voltage application means)
12 ... Sensor output acquisition unit 13 ... Storage unit 15 ... Toxic amount detection unit (toxic amount detection means)
15 ... Concentration calculation unit (concentration calculation means)
15a ... corrector 20 ... gas sensor 21 ... contact combustion gas sensor 21a ... silicon wafer 21b ... insulating films 21c-21e ... bonding pads 21f, 21g ... recess 21s ... catalyst layer 21r ... alumina layer 22 ... bridge drive circuit (first voltage) Application means, second voltage application means)
23 ... Instrumentation amplifier 24 ... A / D converter Rs ... Sensor resistance Rr ... Reference resistance R1-R3 ... Resistance

Claims (4)

A gas detection device that calculates the concentration of a polar gas from an output obtained by burning a polar gas with a contact combustion gas sensor,
First voltage applying means for applying a reference voltage to the catalytic combustion type gas sensor such that a reference region which is a part of the catalytic combustion type gas sensor is equal to or higher than a combustion temperature at which a polar gas is burned;
First output acquisition means for acquiring an output from a catalytic combustion gas sensor driven by voltage application by the first voltage application means;
A second voltage applying means for applying a voltage higher than the reference voltage to the catalytic combustion gas sensor so that an enlarged region including the reference region of the catalytic combustion gas sensor is equal to or higher than a combustion temperature at which a polar gas is burned;
Second output acquisition means for acquiring an output from a catalytic combustion gas sensor driven by voltage application by the second voltage application means;
A poisoning amount detection unit for detecting a poisoning amount in the reference region based on the output acquired by the first output acquisition unit and the output acquired by the second output acquisition unit;
A gas detection device comprising: The said 2nd voltage application means applies a voltage higher than the said reference voltage, whenever the operation | movement from which the said reference voltage is applied and an output is acquired is repeated for a fixed period. Gas detection device. When the second voltage application unit determines that the previous contact combustion type gas sensor was present in an atmosphere in which no polar gas exists, based on the output acquired by the first output acquisition unit, the operation is performed for a certain period of time. 3. The gas detection device according to claim 2, wherein even if it is repeated, application of a voltage higher than the reference voltage is prohibited. Concentration calculating means for calculating the concentration of the polar gas based on the output from the catalytic combustion gas sensor,
When the second output acquisition unit acquires the output from the catalytic combustion type gas sensor, the concentration calculation unit calculates the concentration of the polar gas based on the output acquired by the second output acquisition unit. The gas detection device according to any one of claims 2 and 3.

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