JP2000193621A - Gas detection method and device - Google Patents

Abstract

(57) [Summary] [Problem] With a simple configuration and low power consumption,
Provided is a gas detection element capable of stably performing accurate gas detection. [Solution] A pulse voltage is applied by applying a pulse voltage capable of heating the gas detection element to a temperature higher than a selected detection temperature capable of exhibiting selectivity for a gas to be detected. The temperature is controlled to be equal to or lower than the selected detection temperature by applying a voltage, and the detected gas is detected based on the output. At this time, the first purge voltage is applied to the gas detection element at every first set time, and when the output at that time exceeds the first set value, the second purge voltage is applied, After the purge voltage is applied, the concentration of the detected gas is known from the output after the elapse of the measurement standby time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse detecting device provided with a gas detecting element and capable of heating the gas detecting element to a temperature higher than a selected detection temperature at which the gas detecting element can exhibit selectivity for a gas to be detected. A voltage is applied, and the rise in the apparent temperature of the gas detection element due to the application of the pulse voltage is controlled so as to be equal to or lower than the selected detection temperature, and the detection is performed by the output from the gas detection element based on the application of the pulse voltage. A gas detection method for detecting gas, and a pulse voltage capable of providing a gas detection element and heating the gas detection element to a temperature equal to or higher than a selected detection temperature at which the gas detection element can exhibit selectivity for a gas to be detected. And a supply voltage control device for controlling an increase in an apparent temperature of the gas detection element due to the application of the pulse voltage so as to be equal to or lower than the selected detection temperature. The output from the gas sensing elements based on application of the pulse voltage, a gas detection device for detecting a gas to be detected.

[0002]

2. Description of the Related Art Conventionally, as this kind of gas detection method,
A gas detection method is known in which the gas concentration is monitored based on the output of the pulse voltage during normal times, and when the output for the gas to be detected reaches a certain level, the gas to be detected is detected. In such a case, a gas detection device provided with a supply voltage control device for controlling the application of the pulse voltage has been proposed.

[0003] With such a configuration, the amount of electric power supplied to the gas detecting element is only required to supply the pulse voltage for a very short time, so that the gas to be detected can be detected with low power consumption. Had become.

[0004]

However, according to such a configuration, the gas detecting element operates at room temperature, and the activity of oil smoke, dust and the like is reduced under the environment where the gas detecting element is placed. When a factor adheres to the gas detection element, the response performance for detecting the gas to be detected tends to decrease, and it is difficult to recover. Therefore, there is room for improvement in terms of the reliability of detection of the gas to be detected. .

Therefore, at normal times, the gas to be detected is monitored by the above-described detection method, and when the detection signal indicates that the gas to be detected exists at a predetermined concentration or more, a second gas different from the gas detection element is used. Using the sensing element, the second gas sensing element is used in a high-temperature environment, and even if there is an activity reducing factor such as the oil smoke and dust, it is eliminated by the high-temperature operation and is stably operated, and the detection target gas is removed. There has been proposed a configuration in which an accurate concentration can be detected and an accurate gas concentration to be detected can be known. In other words, a pair of gas detection elements are used as a monitoring gas detection element that operates constantly by supplying a pulse voltage and a concentration measurement gas detection element that accurately measures the concentration of a gas to be detected.
Attempts have been made to achieve both stable and accurate concentration measurements.

However, when such a configuration is employed, the use of two gas detecting elements inevitably complicates the structure and necessitates a gas detecting element requiring high-temperature operation. There was also a limit to power saving.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a gas detection element which has a simple configuration, consumes little power, and can stably perform accurate gas detection in view of the above-mentioned situation.

[0008]

In order to achieve the above object, a gas detecting method according to the present invention is characterized in that a gas detecting element is provided, and the gas detecting element is provided with respect to the gas to be detected. Apply a pulse voltage that can be heated to a temperature higher than or equal to the selection detection temperature capable of exhibiting selectivity, and control the rise in the apparent temperature of the gas detection element by applying the pulse voltage to be equal to or lower than the selection detection temperature, By the output from the gas detection element based on the application of the pulse voltage,
When detecting the gas to be detected, the gas detection element is provided with a first purge voltage for heating the gas detection element so that an activity reducing factor that reduces the activity of the gas detection element can be removed from the gas detection element for a first set time. When the output in the first operating state exceeds the first set value,
After applying a second purge voltage to apply a second purge voltage to a heating state in which a concentration measurement error generation factor for the gas detection element such as humidity and temperature can be removed from the gas detection element, and after a measurement standby time has elapsed, Is to know the concentration of the gas to be detected from the output. Note that the measurement standby time is preferably from 5 seconds to 60 seconds.

In order to achieve the above object, a gas detecting apparatus according to the present invention is characterized in that a gas detecting element is provided, and the gas detecting element exhibits selectivity to a gas to be detected with respect to the gas detecting element. A supply voltage control device that applies a pulse voltage that can be heated to a temperature higher than or equal to a selectable detection temperature and controls an increase in the apparent temperature of the gas detection element due to the application of the pulse voltage to be equal to or lower than the selectable detection temperature. In order to detect a gas to be detected by an output from a gas detection element based on the application of the pulse voltage, the gas detection element is provided with an activity reducing factor that reduces the activity of the gas detection element. A first operating state in which a first purge voltage for setting a heating state that can be removed from the gas detecting element is applied every first set time, and a concentration measurement error of the gas detecting element is set every second set time. A second purge voltage for applying a heating state capable of removing a generation factor is applied, and switching is performed to switch between a second operation state for measuring the concentration of the gas to be detected after a lapse of a measurement standby time from the application of the second purge voltage. A mechanism is provided, when the output in the first operating state exceeds a first set value, while switching from the first operating state to the second operating state, the output in the second operating state exceeds the second set value. When an alarm signal is issued, and the output in the second operating state falls below a first set value, a switching control mechanism that switches the switching mechanism from the second operating state to the first operating state is provided. is there. Further, the gas sensing element is provided with a gas sensing portion made of a metal oxide semiconductor to which at least one noble metal of gold, platinum and palladium is added in an amount of 0.05 mol% or more and 5 mol% or less, covering the noble metal wire coil. It is preferable that the gas detection element is a hot-wire semiconductor type gas detection element, and the metal oxide semiconductor is a tin oxide semiconductor or an indium oxide semiconductor. It is preferable that the measurement standby time is 5 seconds to 60 seconds.

[Effects] That is, a gas detecting element is provided, and a pulse voltage capable of heating the gas detecting element to a temperature higher than a selected detection temperature at which the gas detecting element can exhibit selectivity for a gas to be detected is provided. Control, so that the rise of the apparent temperature of the gas detection element due to the application of the pulse voltage is controlled to be equal to or lower than the selected detection temperature, and the output of the gas detection element based on the application of the pulse voltage causes the detected gas to be detected. Upon detection, the gas detection element can be operated with low power consumption, as in the above-described conventional example.
Further, when applying a first purge voltage for heating the gas sensing element to a heating state in which an activity reducing factor for reducing the activity of the gas sensing element can be removed from the gas sensing element at a first set time, the gas The sensing element is exposed to a high temperature every the first set time, and even if various activity reducing factors are attached to the gas sensing element, the attached matter can be volatilized and removed, The gas detecting element can be regenerated to a state of high activity, and a state in which the gas to be detected can be detected with high sensitivity is maintained. By repeating such gas detection in the first operation state, it becomes possible to continue monitoring the gas to be detected with low power consumption. Therefore,
When the output in the first operating state exceeds the first set value, it can be seen that the detected gas is present at a predetermined concentration or higher in the atmosphere to which the gas detecting element is exposed. Here, if an accurate gas concentration corresponding to the output can be known, an alarm for the leakage of the detected gas can be issued. Therefore, in order to eliminate the humidity, temperature and other concentration measurement error generating factors and to provide a stable concentration measurement condition, a second purge voltage for applying a heating state capable of removing the concentration measurement error generating factor from the gas sensing element is applied. Then, the gas detection element can accurately measure the concentration of the gas to be detected. After the application of the second purge voltage,
After a predetermined time after this, a measurement standby time can be set in which accurate concentration can be easily measured. The measurement standby time varies depending on the characteristics of the gas detection element. For example, the gas detection element contains at least one noble metal of gold, platinum, and palladium in an amount of 0.05 mol% or more and 5 mo or more.
In the case of a hot-wire semiconductor type gas detection element provided with a noble metal wire coil and covered with a gas sensing portion made of a metal oxide semiconductor to which 1% or less is added, about 15% after application of the second purge voltage. It is known that in seconds, a state is obtained in which the output and the concentration of the gas to be detected exhibit a high correlation, while being hardly affected by temperature and humidity. In other words, the present inventors have obtained the knowledge that the gas detection element once purged cancels out various sensitivity dependencies in a relatively short time, thereby obtaining a state in which the gas concentration can be measured with high sensitivity.
Based on this knowledge, by setting the measurement standby time, it is possible to monitor the gas to be detected at normal times with low power consumption and to measure the gas concentration with high accuracy with a single gas detection element. The configuration was completed. As a result, by adopting the above-described configuration, a stable and accurate concentration measurement can be expected with a simple configuration, and a gas detection element with low power consumption can be provided.

Further, the gas detecting apparatus of the present invention for realizing such a method is provided with a gas detecting element, and the gas detecting element exhibits selectivity to the gas to be detected with respect to the gas detecting element. A supply voltage control device is provided that applies a pulse voltage that can be heated to a temperature equal to or higher than a selectable detection temperature and controls an increase in an apparent temperature of the gas detection element due to the application of the pulse voltage to be equal to or lower than the selectable detection temperature. Therefore, the monitor of the detected gas in the normal state can appropriately control the power-saving normal temperature operation, and can accurately know the presence of the detected gas based on the detected gas output obtained in a pulsed manner. Therefore, a first operation of applying a first purge voltage to the gas sensing element at a first set time to bring the gas sensing element into a heating state in which an activity reducing factor that reduces the activity of the gas sensing element can be removed from the gas sensing element. If it operates in the state,
The detected gas can be continuously monitored while saving power. In addition, while applying the second purge voltage every second set time, operating in the second operation state of measuring the concentration of the gas to be detected after the elapse of the measurement standby time from the application of the second purge voltage, After the application of the second purge voltage and after the measurement standby time, it is possible to obtain an advantage such that an accurate concentration of the detected gas can be known and an accurate alarm can be issued. In addition, if a switching mechanism for switching these operating states is provided, normally, at the normal temperature operation in the first operating state, the detected gas can be monitored, and when measuring the concentration of the detected gas, The second operating state is switched by the switching mechanism, and the state can be switched to a state where the concentration can be measured. Therefore, the suitable operating conditions can be maintained at all times, so that the monitoring of the gas to be detected can be performed with low power consumption while saving the power and the gas concentration can be measured with high accuracy by one gas detection element. It became so. Specifically, when the output in the first operating state exceeds the first set value, the output is switched from the first operating state to the second operating state, and the output in the second operating state exceeds the second set value. When a warning signal is issued when the output in the second operating state is below a second set value, a switching control mechanism is provided so as to switch the switching mechanism from the second operating state to the first operating state. If this is the case, the frequency of applying the second purge voltage can be suppressed to the minimum necessary under the situation where the presence of the gas to be detected is recognized but not at the level at which an alarm is issued, further reducing power consumption. Can contribute.

Further, the gas detecting element may be gold, platinum,
0.05 m of at least one noble metal of palladium
More preferably, the metal oxide is a hot-wire semiconductor type gas detection element provided with a gas-sensitive portion made of a metal oxide semiconductor added in an amount of at least 5 mol% and not more than 5 mol%, covering the noble metal coil. When the semiconductor is a tin oxide semiconductor or an indium oxide semiconductor, the detection sensitivity of the detected gas in the first operation state is high, and the gas detection sensitivity in the second operation state is excellent in humidity stability and the like,
It can demonstrate stable performance. The measurement standby time is 5
It is known from an experimental example described later that it is preferably from 60 seconds to 60 seconds.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. The gas detection device of the present invention covers the platinum wire coil 2 having a diameter of about 20 μm as the gas detection element 1, provides a tin oxide semiconductor with a diameter of 0.5 mm, and fires the tin oxide semiconductor at 600 ° C. for 1 hour. , Gas sensing part 3
Is formed, and palladium is applied to the gas sensitive portion 3 by 0.05 m.
A hot-wire semiconductor gas detecting element, which is a normal-temperature-operating type and carbon monoxide gas selective element to which ol% is added, is provided (see FIG. 2). Further, when the voltage is continuously applied to the gas detecting element, the temperature of the gas detecting element becomes 350 ° C. to 550 ° C.
A voltage control mechanism 4 capable of applying a voltage that can be applied is provided, and the voltage control mechanism 4 is connected to the detection circuit section 5. The voltage control mechanism 4 applies voltage of the pulse voltage, stops application of the pulse voltage, and A switching control mechanism 6 for switching between application and stoppage of the purge voltage is provided. Further, an alarm device 7 for generating an alarm sound when an output accompanying application of the pulse voltage exceeds a certain set value (a second set value described later) is provided.

The gas detecting element 1 has a characteristic of detecting carbon monoxide gas as a gas to be detected at normal temperature and generating an output with respect to the concentration of the carbon monoxide gas when energized. The output corresponding to the concentration is determined based on changing the resistance value according to the concentration of carbon monoxide when the sensitive portion 3 comes into contact with the carbon monoxide gas. The value can be converted to a carbon monoxide concentration.

The control rules are as follows, and are controlled by a microcomputer having a voltage control mechanism 4, a switching control mechanism 6, and the like (see FIG. 3). ◎ First operation rule <1-1>: When the duration of the voltage application stop state (OFF) reaches 10 seconds (application cycle), a pulse voltage is applied for 1 millisecond (first operation state) ). At this time,
The gas detection element is driven such that a pulse voltage value to be heated to a selected detection temperature or higher capable of exhibiting selectivity with respect to a gas to be detected is selected, and that the gas detection element is operated at a normal temperature in consideration of an average voltage application cycle. <1-2>: Irrespective of the rule, once every hour (first set time), the state of application of the first purge voltage for one second (O
N). Thus, the activity reducing factor such as oil smoke and dust attached to the surface of the gas detection element is volatilized or eliminated, and high activity can be maintained through the first operation state. <1-3>: When the first sensitivity output from the gas detection element exceeds the first set value in the pulse voltage application state, the switching mechanism switches to the second operation rule. That is, the first sensitivity output quickly responds to the presence of the gas to be detected, and the gas to be detected can be monitored with high reliability by power-saving driving for supplying a pulse voltage. ◎ Second operation rule <2-1> When switching from the first operation state, the second purge voltage is applied (ON) for 0.5 seconds. This allows
The gas detecting element is in a state where the concentration of the gas to be detected can be accurately measured. <2-2>: After stopping application of the second purge voltage, a pulse voltage for concentration measurement is applied to the gas detection element for 1 millisecond after 15 seconds (measurement standby time). This makes it possible to know the concentration of the detected gas accurately. <2-3>: When the concentration measurement sensitivity output by application of the concentration measurement pulse voltage exceeds the second set value, the alarm device emits an alarm sound. <2-4>: When the density measurement sensitivity output falls below the first set value, the process proceeds to the first operation rule. <2-5>: When the density measurement sensitivity output is equal to or more than the first set value and equal to or less than the second set value, three minutes (third set time)
After the elapse, the second operation rule is repeated (second operation state). By judging the sensitivity output and selecting one of these operations, the detection target gas can be accurately and quickly monitored to perform an alarm function.

That is, if the control is performed in accordance with the first operating state, only a pulse voltage is applied to the gas detecting element, so that the gas detecting element is prevented from being heated and the sensitivity is periodically increased. While healing,
Continue to monitor the leak of the detected gas. Further, when determining whether or not to issue an alarm, the second operation state is repeated to quickly and accurately measure the concentration of the detected gas, so that an alarm can be immediately issued.

The specific composition of the gas sensing element,
The specific numerical value of each set time is an example, and is not limited to this. The specific time can be appropriately set according to the characteristics of the gas detection element. Specifically, the sensitive layer of the gas detection element is tin oxide. Instead of forming from, it can be formed from indium oxide, and the measurement standby time can be determined based on the sensor characteristics as shown in the embodiments described later.
When both characteristics can be satisfied under substantially the same conditions such as the first and second purge voltages, the control by the control mechanism can be simplified by setting the same conditions. Similarly, control can be simplified by associating the measurement standby time with the pulse voltage application cycle. (For example, the measurement standby time is 1
If the application period of the pulse voltage is set to 15 seconds when set to 5 seconds, the output based on the pulse voltage 15 seconds after the application of the second purge voltage is used to accurately indicate the concentration of the gas to be detected. It can be handled and the voltage application cycle can be kept constant. Although the third set time is not essential, when the sensitivity output is maintained between the first set value and the second set value, the application of the second purge voltage is performed. Since it is possible to suppress the alarm to the minimum necessary to quickly issue the alarm, it contributes to the power saving operation of the gas detection element.

[0018]

Embodiments of the present invention will be described below.

[Gas detecting element] An aqueous solution in which antimony chloride is added at a predetermined ratio to a tin chloride aqueous solution having a predetermined concentration is prepared. Aqueous ammonia is added dropwise to this aqueous solution to obtain a precipitate of hydroxide. The tin oxide is pulverized to a fine powder and kneaded with water to obtain a tin oxide paste.

The tin oxide paste is applied so as to cover the periphery of the platinum wire coil 2, dried and fired at 600 ° C. for 1 hour to provide a gas sensing portion made of a tin oxide semiconductor and covering the platinum wire coil 2. . The gas sensitive part 3 is impregnated with an aqueous palladium chloride solution to obtain the gas sensing element 1 in which 0.05 mol% of palladium is carried on the gas sensitive part.

[Sensor Characteristics] The gas detecting element is shown in FIG.
5 and 6 that the carbon monoxide gas selectivity at room temperature is high, and the dependence of the sensor output on carbon monoxide concentration is linear from 5 to 20 seconds after purging. In addition, it can be seen that the output 15 seconds after the purge exhibits a high output ratio in a wide concentration range of about 50 ppm to 500 ppm of carbon monoxide, and the conditions for measuring the concentration are suitable. 7 and 8, according to such a gas detection element, the sensor output is
It can be seen that it is hardly dependent on environmental conditions and is stable under various conditions. In particular, according to FIG. 7, it can be seen that the response of the sensor output intersects with each other at about 15 seconds, and a measurement standby time region where the output can be optimally stabilized is found in the vicinity. Further, it can be seen from FIG. 8 that such a tendency does not greatly differ depending on the gas concentration.

[Detection Accuracy] When such a gas detection element was employed in the above-described gas detection device, and under various conditions, the dependence of the sensor output on the concentration of carbon monoxide was examined, FIG. 4 and FIG. 9 show a comparison between one operating condition and the second operating condition according to the second operating rule. In other words, under the first operating condition, a high output can be obtained even for a low-concentration gas, which is advantageous. It can be seen that, because of the high density dependency, it works advantageously to know the exact density from the output.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a gas detection device.

FIG. 2 is a schematic diagram of a gas detection element.

FIG. 3 is a schematic diagram showing a relationship between a voltage supply and an output in first and second operating states.

FIG. 4 is a graph showing the concentration dependency of the output of the gas detection element under the first operation rule (a) is due to a difference in gas type, and (b) is due to a difference in environmental atmosphere.

FIG. 5 is a graph showing a difference in response speed of a sensor output due to a difference in carbon monoxide concentration.

FIG. 6 shows the dependence of sensor output on carbon monoxide concentration due to differences in measurement standby time.

FIG. 7 is a graph showing a difference in response speed of a sensor output due to a difference in various environmental atmospheres.

FIG. 8: Dependence of sensor output on carbon monoxide concentration due to differences in various environmental atmospheres

FIG. 9 is a graph showing the concentration dependency of the output of the gas detection element under the second operation rule (a) is due to a difference in gas type, and (b) is due to a difference in environmental atmosphere.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas detection element 2 Platinum wire coil 3 Gas sensing part

Continued on front page F-term (reference) 2G046 AA11 BA02 BA03 BA06 BE02 DA05 DB01 DB04 DB05 DC07 DC09 DD04 EB06 FB02 FE15 FE29 FE31 FE39 5C086 AA02 BA11 CB12 DA04 DA08 EA02 EA45 FA02

Claims (6)

[Claims] A gas detection element is provided, and a pulse voltage that can be heated to a selected detection temperature or higher at which the gas detection element can exhibit selectivity to a gas to be detected is applied to the gas detection element, Gas detection for controlling an increase in the apparent temperature of the gas detection element due to the application of the pulse voltage so as to be equal to or lower than the selected detection temperature, and detecting the gas to be detected based on the output from the gas detection element based on the application of the pulse voltage. A method, wherein a first purge voltage is applied to the gas sensing element at a first set time interval to set a heating state in which an activity reducing factor that reduces the activity of the gas sensing element can be removed from the gas sensing element. When the output in the first operating state exceeds a first set value, the second purge is set to a heating state in which a concentration measurement error generating factor of the gas detecting element can be removed. By applying a pressure, the second purge after the application of a voltage, a gas detection method to know the concentration of the gas to be detected by an output after the lapse of the measurement standby time. 2. The gas detection method according to claim 1, wherein the measurement standby time is 5 seconds to 60 seconds. 3. A gas detection element is provided, and a pulse voltage that can be heated to a temperature equal to or higher than a selected detection temperature at which the gas detection element can exhibit selectivity to a gas to be detected is applied to the gas detection element, A supply voltage control device for controlling an increase in an apparent temperature of the gas detection element due to the application of the pulse voltage to be equal to or lower than the selected detection temperature, and the detection is performed by an output from the gas detection element based on the application of the pulse voltage. A gas detection device for detecting a gas, wherein the gas detection element has a first purge voltage for heating the gas detection element so that an activity reduction factor that reduces the activity of the gas detection element can be removed from the gas detection element. A first operating state applied every set time and a second purge voltage for heating the gas sensing element to remove a concentration measurement error generating factor at every second set time are applied. Then, after the application of the second purge voltage, while applying a second purge voltage that knows the concentration of the gas to be detected by the output after the elapse of the measurement standby time, and after the elapse of the measurement standby time from the application of the second purge voltage A switching mechanism for switching between a second operating state for measuring the concentration of the detected gas and a second operating state when the output in the first operating state exceeds a first set value is provided. A warning signal is issued when the output in the second operation state exceeds a second set value, and when the output in the second operation state falls below the first set value, the first operation state is changed from the second operation state to the first set value. A gas detection device provided with a switching control mechanism for switching the switching mechanism to an operating state. 4. The gas detection element contains 0.05 mol% of at least one noble metal of gold, platinum, and palladium.
The gas detection device according to claim 3, wherein the gas detection device is a hot-wire semiconductor type gas detection element in which a gas sensing portion made of a metal oxide semiconductor added in an amount of not less than 5 mol% is provided so as to cover the noble metal wire coil. 5. The gas detection device according to claim 4, wherein the metal oxide semiconductor is a tin oxide semiconductor or an indium oxide semiconductor. 6. The gas detection device according to claim 3, wherein the measurement standby time is 5 seconds to 60 seconds.