JP3814160B2 - Gas sensor with gas type separation function - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensor having a function of classifying gas species, and more particularly to a gas sensor using a catalytic combustion type gas sensor. To Related.
[0002]
[Prior art]
Conventionally, many gas detection devices that perform gas leakage detection using a highly versatile catalytic combustion type gas sensor have been proposed. An example of this will be described with reference to FIG. FIG. 13 is an overview of a catalytic combustion type gas sensor used in a conventional gas detection device. In particular, FIGS. 13A and 13B are schematic views of a sensitive element portion and a compensating element portion of a conventional catalytic combustion gas sensor, respectively.
[0003]
This type of catalytic combustion type gas sensor captures combustion heat obtained by burning combustible gas and oxygen in the air on the catalyst as a resistance change of the platinum coil. As shown in FIG. 13 (A), the sensitive element portion is made of Pd / Al so that it becomes a spherical shape having a diameter of about 1 mm on a (platinum) Pt coil 42A of 20 μm. ₂ O _Three A catalyst layer 43A is applied. Further, as shown in FIG. 13B, the compensation element portion is made of Al so that the same Pt coil 44A has a spherical shape with a diameter of about 1 mm. ₂ O _Three A catalyst layer 45A is applied. And practically, since the resistance change of the Pt coil 42A with respect to the flammable gas is very small, the sensitive element part and the compensating element part are incorporated in a bridge circuit, and a direct current or a pulse is applied to both ends of the bridge circuit. The change in the midpoint voltage of the bridge circuit relative to the combustible gas is measured as the sensor output.
[0004]
FIG. 14 is a graph showing the relationship between the gas concentration and the sensor output of the conventional catalytic combustion gas sensor described above. In the figure, Gc1 represents the output characteristics of isobutane, and similarly, Gc2 represents hydrogen, Gc3 represents ethanol, and Gc4 represents the output characteristics of methane. As shown in this figure, the sensor outputs corresponding to the above four kinds of gases monotonically increase with increasing gas concentration, and all have similar characteristics. Here, ethanol is an example of a harmless thing that frequently occurs in daily life caused by liquor. On the other hand, isobutane, hydrogen, methane, and the like are examples of what should be detected as harmful gases that are generated extraordinarily due to gas leakage and the like.
[0005]
[Problems to be solved by the invention]
However, since the conventional catalytic combustion type gas sensor described above has a large heat capacity, and its responsiveness and measurement accuracy are not good, as shown in FIG. It was difficult to separate and identify. Therefore, the gas sensor device using the conventional catalytic combustion type gas sensor has to set a gas detection reference value common to all the gas types, and has to detect the gas based on this reference value. As a result, there is a possibility that the gas sensor reacts to an innocuous gas such as an ethanol-based gas or an acetic acid-based gas caused by liquor, seasoning, etc. present in a normal household and gives a false alarm. Therefore, as another conventional example that improves this point, a gas sensor device in which a filter such as activated carbon is attached to a sensor cap has been proposed in order to provide selectivity for a gas type. Furthermore, as another conventional example, a gas sensor device or the like provided with a plurality of gas sensors having different characteristics corresponding to the gas type and driving them simultaneously is proposed. However, these conventional examples also require additional means for providing selectivity such as a filter, or require a plurality of gas sensors having different characteristics, which makes the apparatus more complex, larger, and consumes more power. There has been a problem in that the cost is increased due to the increase.
[0006]
Therefore, in view of the present situation described above, the present invention optimizes the structure of the catalytic combustion type gas sensor and the sensor output acquisition timing so that a plurality of gas types can be separated by using only one catalytic combustion type gas sensor. It is an object to provide a gas sensor that achieves cost reduction. Another object of the present invention is to provide a gas sensor that achieves high detection speed and low power consumption.
[0007]
[Means for Solving the Problems]
The gas sensor with a gas type separation function according to claim 1, which has been made in order to solve the above-described problem, is a sensor of the catalytic combustion gas sensor 40 from the start of energization of the catalytic combustion gas sensor 40 as shown in FIGS. 1 to 7. The sensor output is classified using the fact that the sensor output in the rising period until the steady time T300 when the output is stable exhibits a specific peak waveform for the specific gas. A gas sensor with a gas type separation function, the first rising period from the energization start time to a specific initial rise time T10 between the energization start time and the steady time, and from the initial rise time to the steady time A first gas having a peak waveform of the sensor output, a second gas having a peak waveform of the sensor output only in the second rising period, and the sensor output in the rising period, respectively. First gas presence / absence detecting means 12 for detecting the presence / absence of a peak waveform of the sensor output in the first rising period in a gas sensor with a gas type separation function that separates a third gas that monotonously increases and outputs a classification result; , Second peak presence / absence detection means 13, 1 for detecting the presence or absence of a peak waveform of the sensor output in the second rising period. And the first gas, the second gas, and the third gas are separated based on the respective peak waveform presence / absence detection results by the first peak presence / absence detection means 12 and the second peak presence / absence detection means 13 and 14. A gas type separation unit 15; and a gas detection output unit 30 that outputs a result of the classification by the gas type separation unit 15. It is characterized by that.
[0008]
According to the first aspect of the present invention, the gas output is classified by utilizing the fact that the sensor output during the rising period from the start of energization to the steady time exhibits a specific peak waveform for the specific gas. Therefore, a plurality of gas types can be separated by using only one catalytic combustion type gas sensor 40. Further, since the sensor output in the rising period is used, the gas type can be separated at high speed.
[0010]
Also, A first gas having a peak waveform in each of the first rising period and the second rising period, a second gas having a peak waveform only in the second rising period, and a third gas in which the sensor output monotonously increases in the rising period, The first peak presence / absence detection means 12 and the second peak presence / absence detection means 13 and 14 are classified based on the respective peak waveform presence / absence detection results. In other words, by focusing on the sensor output waveform during the rising period of the catalytic combustion type gas sensor 40, the three types of gases can be separated. Thus, paying attention to the sensor output during the rising period of the catalytic combustion type gas sensor 40, the presence / absence of the peak waveform is detected by the first peak presence / absence detecting means 12 and the second peak presence / absence detecting means 13, 14. The three types of gas can be separated by using only one catalytic combustion type gas sensor 40.
[0011]
Claims made to solve the above problems 2 As shown in FIGS. 1 to 7, the gas sensor with a gas type separation function described in claim 1 is a claim. 1 In the gas sensor with a gas type separation function described above, the first gas is a gas generated due to acetic acid, and the second gas is a gas generated due to ethanol.
[0012]
Claim 2 According to the described invention, a gas generated due to acetic acid, a gas generated due to ethanol, and other gases can be separated. Since the gas generated due to acetic acid and ethanol is likely to be generated from alcohol and seasonings on a daily basis, it is possible to prevent false alarms by separating them.
[0013]
Claims made to solve the above problems 3 As shown in FIG. 4, the gas sensor with a gas type separation function described in the claim 1 or 2 In the gas sensor with a gas type separation function described above, the catalytic combustion type gas sensor 40 includes a heater element and a catalyst layer formed on an insulating film supported on a silicon wafer, and further etched from the back surface of the silicon wafer to form a thin film diaphragm. It is formed.
[0014]
Claim 3 According to the described invention, in the catalytic combustion type gas sensor 40, the heater element and the catalyst layer are formed on the insulating film supported on the silicon wafer, and further, the thin film diaphragm Ds is formed by etching from the back surface of the silicon wafer. Therefore, the heat capacity can be reduced.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0028]
First embodiment
First, a first embodiment of the present invention will be described with reference to FIGS.
In the first embodiment, first, a basic configuration, a drive waveform, and a gas type separation method will be described with reference to FIGS. FIG. 1 is a block diagram showing a basic configuration of a first embodiment of a gas sensor with a gas type separation function according to the present invention. 2A and 2B are time charts showing examples of drive waveforms according to the first embodiment of the present invention. FIG. 3 is an explanatory diagram showing determination criteria and gas determination patterns for gas type separation according to the first embodiment of the present invention.
[0029]
As shown in FIG. 1, the controller 10 is connected to a drive power source 20, a gas detection output means 30, and a catalytic combustion type gas sensor 40 including a detection bridge circuit. In this gas sensor with a gas type separation function, a drive pulse as shown in FIG. 2 is supplied to control the energization of the catalytic combustion type gas sensor 40, and the gas type is separated by the controller 10 based on the sensor output of the sensor 40. Gas detection output. As shown in FIG. 6, this classification principle is based on the fact that the sensor output in a rising period from the start of energization of the catalytic combustion type gas sensor 40 to the steady time when the sensor output is stable is a specific type of gas (for example, acetic acid, ethanol, etc.). However, this will be described later again.
[0030]
As shown in FIG. 2 (A), the controller 10 is shown in FIG. 2 (B) in the drive pulse energization period D10, which is composed of a 10-second pulse OFF period and a 400 ms energization period D10. As described above, the sensor output is acquired at the time 5 ms T5, the time 10 ms T10, the time 20 ms T20, and the time T300 300 ms from the pulse ON. Each of these time points T5, T10, T20, and T300 is set based on data collected in advance so that a peak waveform unique to a specific gas can be easily identified and detected.
[0031]
The controller 10 includes a sensor output acquisition unit 11, first to third determination units 12 to 14, a gas type classification unit 15, a determination pattern storage unit 16, a sensor drive control unit 17, and a correction unit 18. The controller 10 includes a calculation unit, a storage unit, a timer unit, and the like as hardware, and each of the means 11 to 16 is a processing operation of FIG. 7 described later performed by the calculation unit according to a control program stored in the storage unit. It corresponds to.
[0032]
The sensor output acquisition means 11 acquires sensor outputs at the respective time points T5, T10, T20 and T300 shown in FIG. The sensor output acquisition unit 11 includes a first time point output acquisition unit 11a, a second time point output acquisition unit 11b, a third time point output acquisition unit 11c, and a fourth time point corresponding to the respective time points T5, T10, T20, and T300. It is comprised from the time point output acquisition means 11d. For example, the first time point output acquisition unit 11a acquires the sensor output at the time T5 5 ms from the pulse ON, and similarly, the second time point output acquisition unit 11b, the third time point output acquisition unit 11c, and the fourth time point output acquisition unit 11d. Also, sensor outputs at 10 ms time T10, 20 ms time T20, and 300 ms time T300 are obtained.
[0033]
The first to third determination means 12 to 14 receive the sensor output at each time point supplied from the sensor output acquisition means 11, and determine the determination result of Y or N according to the determination criteria shown in the explanatory diagram of FIG. Output. The first determination means 12, the second determination means 13 and the third determination means 14 in FIG. 1 respectively determine Y or N by a method corresponding to the first determination YN1, the second determination YN2 and the third determination YN3 in FIG. Down. For example, the first determination means 12 performs a 10 ms time point output S10 (sensor output at the time point T10) and a 5 ms time point output S5 (sensor output at the time point T5) according to the determination criterion indicated by the first determination YN1. In comparison, if the determination criterion is satisfied, Y is output, otherwise N is output. Similarly, the second determination unit 13 and the third determination unit 14 output Y or N according to the determination criterion, the second determination YN2, and the third determination YN3 shown in FIG.
[0034]
By the way, the first determination means 12 compares the 10 ms time point output S10 with the 5 ms time point output S5, and outputs Y or N. Although not shown in FIG. 3, when the 0 ms time point output (sensor output at the time of pulse ON) is compared with the 5 ms time point output S5, the 5 ms time point output S5 is better for any gas. growing. That is, the presence or absence of the peak waveform of the sensor output at the time of 0 to 10 ms (corresponding to the first rising period of claim 2) is detected by the Y or N output of the first determination means 12. Similarly, the presence or absence of the peak waveform of the sensor output at the time point of 10 to 300 ms (corresponding to the second rising period of claim 2) is detected by the second determination means 13 and the third determination means 14. That is, the first determination means 12 corresponds to the first peak presence / absence detection means described in claim 2, and the second determination means 13 and the third determination means 14 correspond to the second peak presence / absence detection means described in claim 2. Note that the 5 ms time point T5 corresponds to a specific rising initial time point according to claim 2, and the 300 ms time point T300 corresponds to a steady time point. These time points T5 and T300 are set in consideration of the characteristics and sensor performance of acetic acid and ethanol, which will be described later, in the first embodiment, and are appropriately changed when the separation gas is different or the sensor performance is different. May be.
[0035]
The gas type classification unit 15 receives the determination result of each Y or N output from the first to third determination units 12 to 14 and stores the gas determination pattern (shown in FIG. 3) stored in the determination pattern storage unit 16. By referring to the sensor output, acetic acid, ethanol or methane, H ₂ Or the like, and the determination result, that is, the gas separation result is output. For example, if the first determination YN1 is N, the second determination YN2 is Y, and the third determination YN3 is N, the gas type separation means 15 has detected and detected acetic acid from the sensor output at this time. Similarly, if the first determination YN1 is Y, the second determination YN2 is Y, and the third determination YN3 is N, ethanol, the first determination YN1 is Y, the second determination YN2 is Y, and the third determination YN3 is Y, methane, H ₂ And so on. This classification will be described more specifically using data in FIGS. 5 and 6.
[0036]
The sensor drive control means 17 controls the energization of the drive power supply 20 to the catalytic combustion type gas sensor 40, and has a 10-second pulse OFF period and a 400-ms energization period D10 as shown in FIGS. 2 (A) and 2 (B). A drive pulse comprising one cycle is continuously generated until the power is turned on and a predetermined trigger is present. In the drive pulses shown in FIGS. 2A and 2B, the level of the drive pulse corresponding to OFF is not necessarily zero. That is, a DC bias may be applied to the drive pulse so that a desired sensor output can be easily acquired by the sensor output acquisition unit 11.
[0037]
The correction means 18 supplies the sensor output acquisition means 11 with a sensor output obtained by performing a predetermined correction on a detection output from a bridge circuit described later. That is, the detection output from the bridge circuit in pure air by the drive pulse shown in FIG. 2 is measured in advance as an initial detection output, and this initial detection output is subtracted from the detection output actually obtained from the bridge circuit. Is supplied to the sensor output acquisition means 11 as the sensor output.
[0038]
As the drive power source 20, an existing battery or the like is used. Further, the gas detection output means 30 receives the gas type determination result from the gas type classification means 15 of the controller 10 and outputs the determination result. The gas detection output means 30 is composed of, for example, a known speaker or LED that emits a gas leak alarm by sound or light emission display, and a driver circuit thereof. If the determination result indicates acetic acid or ethanol, they are harmless to the human body, so that no alarm is issued from the gas detection output means 30. Or, do not issue a sound alarm only by display. The above judgment result is H ₂ In the case of indicating, etc., it is an abnormal situation, so that an audio alarm or both an audio alarm and a display alarm are issued. In addition, in order to distinguish the detection of acetic acid or ethanol, you may make it display LED of a different color.
[0039]
The catalytic combustion type gas sensor 40 is intermittently driven by being supplied with driving pulses as shown in FIGS. 2 (A) and 2 (B). The catalytic combustion gas sensor 40 basically includes a sensitive element portion Rs and a compensation element portion Rr. The sensitive element portion Rs is (platinum) Pt heater 42 and Pd / Al. ₂ O _Three It includes a catalyst layer 43, and the compensation element portion Rr includes a Pt heater 44 and (alumina) Al ₂ O _Three A catalyst layer 45 is included. The Pt heaters 42 and 44 constitute a bridge circuit together with the fixed resistors R1 and R2 and the variable resistor Rv. A driving pulse is intermittently supplied at predetermined intervals to the connection point between the Pt heater 44 and the fixed resistor R1 and the connection point between the Pt heater 42 and the fixed resistor R2 of the bridge circuit via the controller 10. . A voltage value as a sensor output is supplied to the controller 10 from the connection point of the Pt heaters 42 and 44 and the variable resistor Rv.
[0040]
When using this catalytic combustion type gas sensor 40, first, before starting the detection operation, the variable resistance Rv is adjusted so that the sensor output supplied from the correction means 18 to the sensor output acquisition means 11 becomes zero. In this state, when CO gas or the like touches the sensitive element portion Rs, it is oxidized on the surface of the element by a catalytic action to generate reaction heat. Due to this reaction heat, the resistance value of the Pt heater 42 rises, and the rise in the resistance value breaks the balance of the bridge circuit, and the sensor output is supplied to the controller 10. In this case, the Pt heater 44 compensates for the fluctuation of the resistance value of the Pt heater 42 due to the fluctuation of the ambient temperature so that only the fluctuation component of the resistance value of the Pt heater 42 caused by the reaction heat can be extracted. The structure of the catalytic combustion gas sensor 40 will be described later with reference to FIG.
[0041]
Next, the structure of the catalytic combustion type gas sensor 40 used in the first embodiment will be described with reference to FIG. 4A, 4B, and 4C are a plan view, a rear view, and a cross-sectional view taken along line AA of the catalytic combustion type gas sensor 40, respectively.
[0042]
As shown in FIGS. 4A and 4B, this catalytic combustion type gas sensor is formed on a (silicon) Si wafer 41 with (oxidized) SiO 2. ₂ Film 48c, (nitrided) SiN film 48b, and (hafnium oxide) HfO ₂ An insulating thin film made of the film 48a is formed on the film, and a (platinum) Pt heater 42 and a Pd / Al as the sensitive element portion Rs are formed thereon. ₂ O _Three (Platinum) Pt heater 44 and (Alumina) Al as catalyst layer 43 and compensation element Rr ₂ O _Three A catalyst layer 45 is formed. Further, as shown in FIG. 3C, the concave portions 46 and 47 are formed by anisotropic etching to form thin film diaphragms Ds and Dr, respectively, thereby reducing the heat capacity. By adopting such a configuration, it is possible to obtain a catalytic combustion type gas sensor capable of high-speed reaction and having improved measurement accuracy. In addition, since the heat capacity is reduced, power consumption is reduced.
[0043]
Next, the output characteristics of each gas by the catalytic combustion type gas sensor 40 used in the above embodiment will be described with reference to FIGS. 5 and 6. 5 and 6 are graphs showing sensor output characteristics of nonpolar gas and polar gas by the catalytic combustion type gas sensor 40, respectively. 5 and 6, the horizontal axis represents the elapsed time from the pulse ON point (time point 0 in the figure) when the driving pulse as shown in FIG. 2 is supplied to the catalytic combustion type gas sensor 40. Indicates.
[0044]
In FIG. 5, Sv1 indicates the sensor output characteristic of (carbon monoxide) CO gas, and similarly, Sv2, Sv3, and Sv4 are (methane) CH _Four Gas, (hydrogen) H ₂ Gas, (isobutane) i · C _Four H _Ten The sensor output characteristic of gas is shown. These gases are mainly generated at the time of gas leakage. Here, the concentration of each gas was 1000 ppm and data was collected. As shown in FIG. 5, the sensor output for four types of gases rises with a unique waveform until 100 ms elapses from the 0 time point (pulse ON time), but after 100 ms, the steady state of the specific output value. It turns out that it will be in a state. However, it can be seen that these nonpolar gases all increase monotonically from the pulse ON point to the point when 100 ms elapses, and thereafter have a common fluctuation pattern that is stable at a constant value unique to each gas. Utilizing such characteristics, the catalytic combustion gas sensor 40 can detect an abnormal situation such as gas leakage.
[0045]
In FIG. 6, Sv5 is (acetic acid) CH. _Three Indicates sensor output characteristics of COOH gas, Sv6 is (ethanol) C ₂ H _Five The sensor output characteristic of OH gas is shown. These gases are mainly generated in the daily life due to seasonings and liquors in the kitchen or the like. Here, the concentration of each gas was 1000 ppm and data was collected. As indicated by Sv5 in FIG. 6, the sensor output with respect to acetic acid rapidly increases until 5 ms elapses from the pulse ON time, reaches a first peak at this time, and then decreases rapidly. Then, after reaching the minimum at the time of 10 ms, it rapidly rises again and reaches the second peak at the time of 30 ms. After that, it monotonously decreases, and the steady state of the intrinsic output value is reached when 200 ms elapses. That is, it can be seen that the sensor output for acetic acid shown in Sv5 has a peak waveform having two peaks before reaching a steady state. This acetic acid corresponds to the first gas of claim 2.
[0046]
Further, as indicated by Sv6 in FIG. 6, the sensor output for ethanol rapidly increases until 30 ms elapses from the pulse ON point, and after reaching a peak at this point, it decreases monotonously and reaches the specific output when 200 ms elapses. A steady state of values. That is, it can be seen that the sensor output for ethanol shown in Sv6 has a peak waveform having one peak before the steady state is reached. Utilizing such a unique peak waveform characteristic, the catalytic combustion gas sensor 40 can separately detect acetic acid and ethanol. This ethanol corresponds to the second gas of claim 2.
[0047]
The reason why such a unique pulse waveform is generated is considered to be due to the attractive force. In other words, gas with a large polarity such as acetic acid and ethanol, and a large adsorption power, gas molecules are adsorbed on the sensor surface during the pulse OFF period, and when the pulse is turned on and the sensor is energized, the adsorbed gas burns instantly. Along with this, the sensor output also increases. At this time, the catalytic combustion reaction also occurs simultaneously. On the other hand, nonpolar or low polarity gases such as methane, hydrogen, and carbon monoxide have a small adsorption power, so the above phenomenon does not occur and the sensor output gradually increases until it stabilizes at a steady value. .
[0048]
As described above, the gas type is classified by utilizing the fact that a specific type of gas exhibits a unique peak waveform, so that it is possible to classify a plurality of gas types using only one contact combustion type gas sensor. Become. As a result, gas generated due to acetic acid and ethanol generated from alcohol and seasonings on a daily basis can be separated, and a highly reliable gas sensor with few false alarms can be obtained.
[0049]
The processing operation performed by the controller 10 to perform gas type separation using the sensor output characteristics of each gas as shown in FIGS. 5 and 6 will be described with reference to FIG.
[0050]
FIG. 7 is a flowchart showing the processing operation according to the first embodiment of the present invention. In this embodiment, sensor outputs are obtained at 5 ms time T5, 10 ms time T10, 20 ms time T20, and 300 ms time T300, respectively, in the energization period D10 using the drive pulses as shown in FIG. Then, after the sensor outputs acquired at the respective times T5, T10, T20, and T300 are determined as Y / N based on the determination criteria shown in FIG. 3, the gas type is determined with reference to the gas determination pattern shown in FIG. Is done. Thereby, one kind of gas is separated using one contact combustion type gas sensor.
[0051]
In Step P1 of FIG. 7, the sensor output of the catalytic combustion gas sensor 40 is acquired as the 5 ms time output S5 at the 5 ms time T5 in the drive pulse energization period D10 shown in FIG. Similarly, in Step P2, Step P3, and Step P4, the sensor output is 10ms point output S10 at 10ms point T10, 20ms point T20, and 300ms point T300, respectively, in the drive pulse energization period D10 shown in FIG. , 20 ms time point output S20 and 300 ms time point output S300. These outputs S5, S10, S20, and S300 are temporarily stored in the storage unit of the controller 10.
[0052]
Next, in step P5, the temporarily stored 5ms time point output S5 and 10ms time point output S10 are read, and these are stored in the determination pattern storage means 16 based on the determination criteria shown in FIG. N is determined. Similarly, in Step P6, the 10ms time output S10 and the 20ms time output S20 are read, and in Step P7, the 20ms time output S20 and the 300ms time output S300 are read and stored in the determination pattern storage means 16. Y / N determination is made based on the determination criteria shown in FIG. These Y / N determination results are also temporarily stored in the storage unit of the controller 10. Step P5 corresponds to the first peak presence / absence detecting means of claim 2. Steps P6 and P7 correspond to second peak presence / absence detection means.
[0053]
Then, in step P8, the temporarily stored determination results by the first determination YN1, the second determination YN2, and the third determination YN3 are read and stored in the determination pattern storage means 16 as shown in FIG. Compared with the gas determination pattern, the gas type is classified. If the determination in step P8 is N, Y, N in the order of the first determination YN1, the second determination YN2, and the third determination YN3, the process proceeds to the acetic acid detection output process of step P9, and if it is Y, Y, N, the step The process proceeds to the ethanol detection output process of P10, and if Y, Y, Y, the methane, H of Step P11 ₂ The process proceeds to the equal detection output process. The step P8 corresponds to the gas type separation means of claim 2.
[0054]
In the acetic acid detection output process and the ethanol detection output process in step P9 and step P10, since they are harmless to the human body, no alarm is issued from the gas detection output means 30. Or, do not issue a sound alarm only by display. Or in order to distinguish the detection of acetic acid or ethanol, you may make it display LED of a different color in step P9 and step P10.
[0055]
On the other hand, methane and H in Step P11 ₂ In the equal detection output processing, since there is a possibility of an abnormal situation, a sound alarm or both a sound alarm and a display alarm are issued from the gas detection output means 300. However, since this step P11 is also performed in a normal state that does not include any gas, the sensor output of the 300ms time point output S300 is monitored and an alarm is issued in the normal state in order to distinguish this normal state from the abnormal state. Do not. Steps P9, P10, and P11 correspond to the gas detection output means of claim 2.
[0056]
In this flowchart, only the process corresponding to one cycle of the drive pulse shown in FIG. 2 is shown. However, in reality, the above-described process is continuously performed by continuously generating the drive pulse. To. Thereby, gas separation can be performed more reliably.
[0057]
As described above, according to the first embodiment, focusing on the sensor output during the rising period of the catalytic combustion type gas sensor 40, the presence or absence of the peak waveform is detected by Step P5 and Steps P6 and 7. Three types of gases having different waveforms can be separated by using only one catalytic combustion type gas sensor. Further, a gas type separation filter or the like is not required. As a result, a small, low-cost and high-performance gas sensor with a gas type separation function can be obtained. In particular, gas generated due to acetic acid and ethanol generated from alcohol and seasonings on a daily basis can be separated from other gases, so that a highly reliable gas sensor with few false alarms can be obtained. Become. Furthermore, the contact combustion type gas sensor having a small heat capacity as shown in FIG. 4 is used to acquire the sensor output during the rising period and to use the instantaneous combustion reaction, so that the gas type can be separated at high speed. become.
[0058]
Second embodiment
Furthermore, 2nd Embodiment of this invention is described using FIGS. 8-12.
In the second embodiment, first, the basic configuration and drive waveforms will be described with reference to FIGS. FIG. 8 is a block diagram showing a basic configuration of the second embodiment of the gas sensor with a gas type separation function of the present invention. FIG. 9 is a time chart showing an example of drive waveforms according to the second embodiment of the present invention.
[0059]
As shown in FIG. 8, the controller 100 is connected to a driving power source 20, a catalytic combustion gas sensor 40 including a detection bridge circuit, and a gas detection output means 300. In this gas sensor with a gas type separation function, a drive pulse as shown in FIG. 9 is supplied to control the energization of the catalytic combustion type gas sensor 40, and the gas type is separated by the controller 100 based on the sensor output of the sensor 40. Gas detection output. As shown in FIG. 11, this classification principle is calculated by calculating the ratio between the maximum value of the sensor output during the rising period of the catalytic combustion gas sensor 40 and the steady value of the sensor output at the steady time, that is, the output ratio, and changing the energization interval. The gas type is sorted based on the variation of the output ratio accompanying this, which will be described later again.
[0060]
The controller 100 acquires sensor outputs in a 400 ms energization period D10 immediately after a 10 second pulse OFF period and a 400 ms energization period D30 immediately after a 30 second pulse OFF period as shown in FIG. The controller 100 includes a sensor output acquisition unit 101, first and second output ratio calculation units 102 and 103, first and second classification units 104 and 105, a sensor drive control unit 170 and a correction unit 180. The controller 100 includes a calculation unit, a storage unit, a timer unit, and the like as hardware, and each of the units 101 to 105 is performed by the calculation unit according to a control program stored in the storage unit. It corresponds to the operation.
[0061]
The sensor output acquisition unit 101 acquires the sensor output through the correction unit 180 during the energization periods D10 and D30 shown in FIG. These energization periods D10 and D30 are both 400 ms. During this period, for example, sensor outputs are acquired every 5 ms. That is, 80 times are sampled in each energization period D10 and D30. The sensor output acquisition unit 101 includes a first sensor output acquisition unit 101a and a second sensor output acquisition unit 101b corresponding to the energization periods D10 and D30, respectively. This first sensor output acquisition means 101a is based on the 80 sensor outputs in the energization period D10 of 400 ms immediately after the 10 seconds pulse OFF set based on the saturated adsorption time of polar gas such as acetic acid and ethanol. Get the maximum and steady values. The maximum value and the steady value will be described later. The second sensor output acquisition unit 101b acquires the maximum value and the steady value from the 80 sensor outputs in the energization period D30 of 400 ms immediately after the 30-second pulse OFF.
[0062]
The first output ratio calculation means 102 outputs the ratio between the maximum value and the steady value acquired by the first sensor output acquisition means 101a, that is, (maximum value−steady value) / steady value in the energization period D10. Calculate as a ratio. The second output ratio calculation means 103 outputs the ratio of the maximum value and the steady value acquired by the second sensor output acquisition means 101b, that is, (maximum value−steady value) / steady value in the energization period D30 as the second output. Calculate as a ratio. This maximum value−steady value corresponds to the maximum adsorption combustion output described later, and the steady value corresponds to the contact combustion output.
[0063]
Then, the first separation unit 104 separates the polar gas from the other gas based on the comparison of the first output ratio and the second output ratio. Based on the first output ratio or the second output ratio, the second fractionation means 105 is a first polar gas having an output ratio of about five times regardless of the energization interval, for example, ethanol. And a second polar gas having an output ratio of about 10 to 13 times, for example, acetic acid.
[0064]
The sensor drive control means 170 controls the energization of the drive power source 20 to the catalytic combustion type gas sensor 40, and a drive pulse having energization intervals of 10 seconds and 30 seconds as shown in FIG. It is generated continuously until there is. In the drive pulse shown in FIG. 9, the level of the drive pulse corresponding to OFF is not necessarily zero. That is, a DC bias may be applied to the drive pulse so that a desired sensor output can be easily acquired by the sensor output acquisition unit 101.
[0065]
The correcting unit 180 supplies a sensor output obtained by performing predetermined correction on a detection output from a bridge circuit described later to the sensor output acquiring unit 101. That is, the detection output from the bridge circuit in pure air by the drive pulse shown in FIG. 9 is measured in advance as an initial detection output, and this initial detection output is subtracted from the detection output actually obtained from the bridge circuit. Is supplied to the sensor output acquisition means 101 as the sensor output.
[0066]
Since the drive power supply 20 is the same as that described in the first embodiment of FIG. 1, the description thereof is omitted here. The gas detection output means 300 receives the gas type classification results from the first and second classification means 104 and 105 of the controller 100 and outputs the classification results. The gas detection output means 300 includes, for example, a known speaker or LED that emits a gas leak alarm by sound or light emission display, and a driver circuit thereof. If the determination result indicates acetic acid or ethanol, they are harmless to the human body, so that no alarm is issued from the gas detection output means 300. Or, do not issue a sound alarm only by display. The above judgment result is H ₂ In the case of indicating, etc., it is an abnormal situation, so that an audio alarm or both an audio alarm and a display alarm are issued. In addition, in order to distinguish the detection of acetic acid or ethanol, you may make it display LED of a different color.
[0067]
The catalytic combustion type gas sensor 40 has the same configuration as that shown in the first embodiment of FIG. 1 and FIG. 4, and only the drive pulses supplied are different. When using this catalytic combustion type gas sensor 40, the variable resistance Rv is adjusted so that the sensor output supplied from the correction means 180 to the sensor output acquisition means 101 becomes zero before the detection operation is started.
[0068]
Furthermore, the output ratio that is the determination criterion for the gas type classification of the gas sensor with the gas type classification function will be described with reference to FIGS. 10 and 11. FIG. 10 is a graph showing respective sensor outputs when ethanol is used as a test substance and the drive interval of the catalytic combustion type gas sensor is set to 1 second, 10 seconds, and 30 seconds. FIG. 11 is a graph showing output ratios of a plurality of gases when the gas concentration and the driving interval are changed. In FIG. 10, the horizontal axis indicates the elapsed time from the pulse ON point (time point 0 in the figure) when the drive pulse as shown in FIG. 9 is supplied to the catalytic combustion type gas sensor 40. Moreover, in FIG. 11, the numerical value below a horizontal axis shows a driving interval-gas concentration.
[0069]
In FIG. 10, H1 shows the sensor output characteristic of ethanol in the energization period D1 of 400 ms immediately after setting the driving interval to 1 second. Similarly, H10 represents the ethanol sensor output characteristic in the 400 ms energization period D10 immediately after the drive interval of 10 seconds, and H30 represents the ethanol sensor output characteristic in the 400 ms energization period D30 immediately after the drive interval of 30 seconds. . As shown in FIG. 10, when the pulse driving interval is changed from 1 second to 10 seconds, the sensor output, in particular, the peak value changes greatly, but even if the pulse driving interval is changed from 10 seconds to 30 seconds, the sensor output is not changed. It can be seen that there is a saturation characteristic that hardly fluctuates. This shows that the saturated adsorption time of ethanol is 10 to 30 seconds. It has been found that the saturation adsorption time of polar gases other than ethanol is almost 10 to 30 seconds. On the other hand, nonpolar gases such as methane, hydrogen, carbon monoxide and the like have been found to have no such characteristic of saturated adsorption time of 10 to 30 seconds because their adsorption power is smaller than that of polar gases. Thus, the polar gas can be separated by utilizing the fact that the polar gas has a saturated adsorption time of about 10 to 30 seconds.
[0070]
FIG. 11 shows output ratios of a plurality of types of gases when the gas concentration and the driving interval are changed. This output ratio is generally expressed by the maximum adsorption combustion output / contact combustion output. The contact combustion output (corresponding to the steady value of claim 5) is an output value when the sensor output is in a steady state, and the maximum adsorption combustion output is a value obtained by subtracting the contact combustion output from the peak output. In the example of this figure, the energization period is 400 ms, the catalytic combustion output is the sensor output when 300 ms elapses from the pulse ON, and the peak output is the maximum value of the sensor output during the energization period. Then, the drive pulse drive intervals are set to 10 seconds and 30 seconds, and data on the output ratio of ethanol, acetic acid, cotton wick, and wood smoke is collected and calculated. In addition, in each driving interval, data collected and calculated by setting three gas concentrations are also shown.
[0071]
As shown in FIG. 11, the output ratio of ethanol depends on the set driving interval and gas concentration, and the output ratio is almost 5 times and constant. The output ratio of acetic acid is about 10 to 13 times depending on the set driving interval and gas concentration. That is, since these polar gases have a saturation adsorption time of about 10 to 30 seconds, it can be seen that the output ratio is stable regardless of the driving interval. On the other hand, it can be seen that other cotton lanterns and wood smoke have a correlation between the driving interval and gas concentration in the above-described driving interval and gas concentration. Using such characteristics, polar gases such as ethanol and acetic acid can be separated from other types of gases and smoke. Furthermore, separation of ethanol and acetic acid becomes possible by utilizing the output ratio characteristics of ethanol and acetic acid. As described above, by using the output ratio, it is possible to classify the gas types only by using the contact combustion type gas sensor used for detecting one gas leak.
[0072]
The processing operation performed by the controller 100 to perform gas type separation using the output ratio characteristics of each gas as shown in FIG. 11 will be described with reference to FIG. FIG. 12 is a flowchart showing the processing operation according to the second embodiment of the present invention. In this embodiment, using the drive pulse as shown in FIG. 9, the catalytic combustion output is acquired when 300 ms elapses from the pulse ON, and the maximum value of the sensor output during the 400 ms energization period is acquired as the peak output. Then, ethanol, acetic acid and others are separated by comparing the output ratios of the driving intervals of 10 seconds and 30 seconds. The driving intervals of 10 seconds and 30 seconds are set based on the saturation adsorption time of a polar gas such as acetic acid or ethanol.
[0073]
In step P101 of FIG. 11, for example, a total of 80 sensor outputs W10 are acquired every 5 ms in the energization period D10 immediately after 10 seconds of the drive interval shown in FIG. In Step P102, similarly, a total of 80 sensor outputs W30 are acquired in the energization period D30. These acquired sensor outputs are temporarily stored in the storage unit of the controller 100.
[0074]
Next, in step P103, the maximum value and the steady value (contact combustion output) are acquired from the 80 sensor outputs W10 in D10 that are temporarily stored. In step P104, (maximum value−steady value) / steady value is calculated as the first output ratio using the maximum value and the steady value acquired in step P103. In addition, the said step P103 and step P104 are corresponded to the 1st sensor output acquisition means and 1st output ratio calculation means of Claim 6, respectively.
[0075]
Similarly, in step P105, the maximum value and the steady value (contact combustion output) are acquired from the 80 sensor outputs W30 in D30 stored temporarily, and in step P106, the maximum value acquired in step P105. Using the value and the steady value, (maximum value−steady value) / steady value is calculated as the second output ratio. The first output ratio and the second output ratio are temporarily stored in the storage unit of the controller 100. Steps P105 and P106 correspond to second sensor output acquisition means and second output ratio calculation means according to claim 6, respectively.
[0076]
In step P107, the temporarily stored first output ratio and second output ratio are read out, and the polar gas is separated from other gases based on the comparison of the first output ratio and the second output ratio. Is done. This separation is detected, for example, by using the output ratio characteristic shown in FIG. 11 if the first output ratio and the second output ratio are within a fluctuation range of about 20%, that is, detected. The gas is determined to be a polar gas such as acetic acid or ethanol, and the process proceeds to Step P108. Otherwise, there is a change, that is, the gas is determined to be a gas other than the polar gas, and the process proceeds to Step P111. The step P107 corresponds to the first sorting means of claim 6.
[0077]
In Step P108, the ethanol and acetic acid are separated based on either the first output ratio or the second output ratio using the output ratio characteristic shown in FIG. That is, if the first output ratio (or the second output ratio) is about 5, the detected gas is determined to be ethanol, and the process proceeds to Step P109. If it is about 10 to 13, the detected gas is acetic acid. Is determined, and the process proceeds to Step P110. As a precautionary explanation, both ethanol and acetic acid have a specific output ratio regardless of the energization interval. Therefore, the determination in step P108 may use either the first output ratio or the second output ratio. Good. The step P108 corresponds to the second sorting means of claim 7.
[0078]
When ethanol, acetic acid, and others are separated in this way, ethanol detection output processing, acetic acid detection output processing, and other detection processing are performed in Step P109, Step P110, and Step P111, respectively. In the ethanol detection output process and the acetic acid detection output process in Step P109 and Step P110, since they are harmless to the human body, no alarm is issued from the gas detection output means 300. Or, do not issue a sound alarm only by display. Or in order to distinguish ethanol detection and acetic acid detection, you may make it display LED of a different color in step P109 and step P110. Step P109, step P110 and step P111 correspond to the gas detection output means of claim 6.
[0079]
On the other hand, in the other detection output processing in Step P111, the detected gas is a cotton lantern shown in FIG. 11, smoke caused by combustion of wood, nonpolar gas such as methane gas or hydrogen gas, or polarity is very high. May correspond to a small gas. In reality, smoke caused by the burning of the above-mentioned cotton lantern or wood is generated at the time of fire, and nonpolar gas such as methane gas or hydrogen gas, or gas with very low polarity is generated at the time of gas leakage. Conceivable. In other words, since reaching step P111 may be an abnormal situation, the gas detection output means 300 issues a sound alarm or both a sound alarm and a display alarm. When issuing this alarm, for example, methane gas or hydrogen gas is detected using the method of the first embodiment, and the output ratio is as shown in the graph corresponding to the cotton wick and wood of FIG. A tendency to increase as the concentration increases may be detected, smoke due to fire may be detected, and the manner of alarming may be changed according to the result. However, since there is a possibility that the normal state which does not belong to such an abnormality detection may be the step P111, for example, in order to distinguish this normal state from the abnormal state, for example, a sensor output of a 300 ms time point output during the energization period. To prevent alarms in normal conditions.
[0080]
In this flowchart, only the process corresponding to one cycle of the drive pulse shown in FIG. 2 is shown. However, in reality, the above-described process is continuously performed by continuously generating the drive pulse. To. Thereby, gas separation can be performed more reliably.
[0081]
As described above, according to the second embodiment, when the conduction interval is set in consideration of the saturated adsorption time of polar gas such as acetic acid and ethanol, the fact that the output ratio of polar gas becomes stable is utilized. Thus, it is possible to separate polar gas from others only by using one catalytic combustion type gas sensor for detecting gas leakage. Further, among polar gases, there are a gas generated due to ethanol having an output ratio of about 5 regardless of the energization interval and a gas generated due to acetic acid having an output ratio of about 10-13. Separation is possible. That is, since it is possible to separate the gas generated due to ethanol and acetic acid generated from alcohol and seasonings on a daily basis and other gases, a highly reliable gas sensor with few false alarms can be obtained. Of course, gas separation can be performed by using only one catalytic combustion type gas sensor, and it is needless to say that a small, low-cost and high-performance gas sensor with a gas type separation function can be obtained as in the first embodiment. Furthermore, the contact combustion type gas sensor having a small heat capacity as shown in FIG. 4 is used to acquire the sensor output during the rising period and to use the instantaneous combustion reaction, so that the gas type can be separated at high speed. become.
[0082]
Note that the present invention does not limit the acquisition time, energization interval, energization time, and the like of each sensor output to the values exemplified in the first and second embodiments. These values can be changed as appropriate without departing from the scope of the present invention. In addition to ethanol and acetic acid exemplified as polar gases in the second embodiment, the present invention can be applied to a gas having a specific output ratio.
[0083]
【The invention's effect】
As described above, according to the first aspect of the present invention, the sensor output in the rising period from the energization start point to the steady point exhibits a peak waveform specific to a specific type of gas. Since the species are separated, a plurality of gas species can be separated by using only one contact combustion type gas sensor 40. Further, a gas type separation filter or the like is not required. As a result, a small, low-cost and high-performance gas sensor with a gas type separation function can be obtained. Furthermore, since the sensor output during the rising period is used, the gas type can be separated at high speed.
[0084]
Also, Paying attention to the sensor output during the rising period of the catalytic combustion type gas sensor 40, the presence / absence of the peak waveform is detected by the first peak presence / absence detection means 12 and the second peak presence / absence detection means 13, 14, so Three different kinds of gases can be separated by using only one catalytic combustion type gas sensor 40. As a result, a small, low-cost and high-performance gas sensor with a gas type separation function can be obtained.
[0085]
Claim 2 According to the described invention, a gas generated due to acetic acid, a gas generated due to ethanol, and other gases can be separated. Since the gas generated due to acetic acid and ethanol is likely to be generated from liquor and seasonings on a daily basis, the fact that these can be separated can provide a highly reliable gas sensor with few false alarms. It turns out that.
[0086]
Claim 3 According to the described invention, in the catalytic combustion type gas sensor 40, the heater element and the catalyst layer are formed on the insulating film supported on the silicon wafer, and further, the thin film diaphragm Ds is formed by etching from the back surface of the silicon wafer. Therefore, the heat capacity can be reduced. As a result, the power consumption is reduced, the gas response changes at high speed, and the measurement accuracy is further improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration of a first embodiment of a gas sensor with a gas type separation function according to the present invention.
FIGS. 2A and 2B are time charts showing examples of drive waveforms according to the first embodiment of the present invention.
FIG. 3 is an explanatory diagram showing determination criteria and gas determination patterns for gas type classification according to the first embodiment of the present invention.
4A, 4B, and 4C are a plan view, a rear view, and a cross-sectional view taken along line AA of the contact combustion gas sensor, respectively.
FIG. 5 is a graph showing sensor output characteristics of nonpolar gas by the catalytic combustion type gas sensor.
FIG. 6 is a graph showing sensor output characteristics of polar gas by the contact combustion type gas sensor.
FIG. 7 is a flowchart showing a processing operation according to the first embodiment of the present invention.
FIG. 8 is a block diagram showing a basic configuration of a second embodiment of the gas sensor with a gas type separation function of the present invention.
FIG. 9 is a time chart showing an example of a driving waveform according to the second embodiment of the present invention.
FIG. 10 is a graph showing sensor outputs when the driving interval of the catalytic combustion type gas sensor is changed.
FIG. 11 is a graph showing output ratios of a plurality of gases when the gas concentration and the driving interval are changed.
FIG. 12 is a flowchart showing a processing operation according to the second embodiment of the present invention.
FIGS. 13A and 13B are schematic views of a sensitive element portion and a compensating element portion of a conventional catalytic combustion gas sensor, respectively.
FIG. 14 is a graph showing the relationship between gas concentration and sensor output by a conventional catalytic combustion gas sensor.
[Explanation of symbols]
10, 100 controller
20 Drive power supply
30, 300 Gas detection output means
40 Contact combustion gas sensor
42, 44 Pt heater
43 Pd / Al ₂ O _Three Catalyst layer
45 Al ₂ O _Three Catalyst layer
Rs sensitive element part
Rr compensation element

Claims (3)

Utilizing the fact that the sensor output in the rising period from the start of energization of the catalytic combustion type gas sensor to the steady time when the sensor output of the catalytic combustion type gas sensor is stable exhibits a specific peak waveform for a specific type of gas. A gas sensor with a gas type separation function for separating gas types,
In the first rising period from the energization start time to the specific rising initial time point between the energization starting time and the steady time point, and in the second rising period from the initial rising time point to the steady time point, respectively, A first gas having a sensor output peak waveform, a second gas having a sensor output peak waveform only in the second rising period, and a third gas in which the sensor output monotonously increases in the rising period are separated. In the gas sensor with gas type separation function that outputs the separation result separately,
First peak presence / absence detecting means for detecting the presence / absence of a peak waveform of the sensor output in the first rising period;
Second peak presence / absence detecting means for detecting presence / absence of a peak waveform of the sensor output in the second rising period;
Gas type separation means for separating the first gas, the second gas, and the third gas based on the respective peak waveform presence / absence detection results by the first peak presence / absence detection means and the second peak presence / absence detection means;
A gas detection output means for outputting a classification result by the gas type separation means;
Gas species sorting function with a gas sensor characterized in that it comprises a. In the gas sensor with a gas type separation function according to claim 1,
The gas sensor with a gas type separation function, wherein the first gas is a gas generated due to acetic acid, and the second gas is a gas generated due to ethanol . In the gas sensor with a gas type separation function according to claim 1 or 2 ,
The catalytic combustion gas sensor is
A gas sensor with a gas type separation function, wherein a heater element and a catalyst layer are formed on an insulating film supported by a silicon wafer, and a thin film diaphragm is formed by etching from the back surface of the silicon wafer .

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