JP4162352B2 - Gas detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas detection device, wherein a gas conveyance path for introducing a detection target gas is provided, a gas distribution device that distributes the detection target gas to the gas conveyance path is provided, and a gas detection mechanism is provided in the gas conveyance path. The present invention relates to a gas detection device.
[0002]
[Prior art]
Conventionally, as this type of gas detection device, as described in Japanese Utility Model Laid-Open No. 60-17440 and Japanese Utility Model Publication No. 1-31951 is used, the gas detection element provided in the gas conveyance path is diluted, non-diluted. It is known that the concentration of the gas to be detected can be measured in a wide range from the low concentration region to the high concentration region by switching and supplying the diluted gas to be detected to enable measurement of the concentration of the gas to be detected. ing.
On the other hand, a pair of gas detection elements having different gas detection characteristics are provided in the gas conveyance path and the gas detection path is exposed to the detection target gas flowing in the gas conveyance path. In addition, there is known a configuration that can measure the gas concentration (see, for example, Japanese Patent Laid-Open No. 6-300727), and further, a dilution mechanism that enables dilution of the detection target gas is provided to select gases having different concentrations. It is known that the concentration of the gas to be detected can be measured in a wide range from a low concentration region to a high concentration region by switching between them (see FIG. 5). According to such a configuration, it is known that it can be used to identify a gas type by calculating an output ratio or an output difference based on a difference in gas detection characteristics of the pair of gas detection elements. .
[0003]
[Problems to be solved by the invention]
However, even when high-concentration gas detection based on dilution as described above is performed, when switching from detection in an undiluted state to detection in a diluted state, the phenomenon that the output value is greatly disturbed is temporarily observed. In particular, a state in which accurate gas concentration measurement is impossible is observed, and a gas detection device that can continue to output accurately even when gas detection is switched is desired. In addition, when identifying a gas type, if the identification operation is performed in a specific concentration region of the detection target gas to be measured, an erroneous identification result may be derived from the inaccuracy of the concentration measurement. It is done.
[0004]
Accordingly, an object of the present invention is to eliminate the above-mentioned transient phenomenon in view of the above-described actual situation.
[0005]
[Means for Solving the Problems]
In order to achieve this object, the characteristic configuration of the gas detector of the present invention is:
A gas detection apparatus provided with a gas conveyance path for introducing a detection target gas, provided with a gas distribution device for distributing the detection target gas through the gas conveyance path, and provided with a gas detection mechanism in the gas conveyance path In
As described in claim 1 of the claims, the gas detection mechanism is configured by providing first and second gas detection units each including a gas detection element, and the output from each gas detection element is based on the output. in conjunction with providing the gas detection circuit for measuring the gas concentration, the gas conveying path, said first gas detector, a dilution mechanism to test feeding the dilution gas to dilute the detection target gas, the second gas detector Are provided in series in this order from upstream to downstream.
Moreover, you may provide the said gas detection element of the same detection characteristic in said 1st gas detection part and 2nd gas detection part like Claim 2.
Preferably, as described in claim 3, the throttle mechanism is provided in the gas transport path, and an introduction pipe for introducing a dilution gas is provided downstream of the throttle path to form the dilution mechanism. It is desirable that
[0006]
[Function and effect]
In other words, the gas detection mechanism is provided with first and second gas detection units provided with gas detection elements, and a gas detection circuit is provided that can measure the gas concentration based on the output from each gas detection element. in case,
If a dilution mechanism for supplying a dilution gas for diluting the detection target gas is provided in the gas conveyance path, the detection gas in the low concentration region is detected without diluting, and the gas in the high concentration region is detected. It can be detected by diluting, and accurate gas detection can be performed in the gas detection concentration range of a general gas detection element.
As a general gas detection element, gas is detected accurately in a low concentration region, but there are few gas detection elements that can perform simple and accurate concentration measurement for high concentration gas, and from ppm level to% order. In order to make gas detection possible in all concentration areas, there is a concentration area that does not have an appropriate gas detection element, and accurate gas concentration measurement in all concentration areas is possible with a small number of gas detection elements. Have difficulty. On the other hand, if the gas to be detected in the high concentration range is diluted to a low concentration region, the gas detection element of the same type as the gas detection element used to detect the low concentration detected gas can be used. The gas to be detected can be detected.
[0007]
Here, the present inventors analyzed the above-mentioned conventional problems from the aspect of output stability, and after supplying the dilution gas in the gas transport path, the detection target diluted with the dilution gas In the transition period until the gas reaches the gas detection element, the gas detection element has empirically obtained knowledge that the output becomes unstable.
This phenomenon is caused by the gas remaining between the dilution mechanism and the gas detection element being disturbed by the introduction of the dilution gas. When it reaches the element, it is supposed to give an output that is significantly different from the concentration equivalent output, that is, the diluted gas and the detected gas that has been diluted and mixed in the transition period are sufficiently diluted and mixed. When the gas detection element is reached without having a stable composition, gas detection unevenness occurs in the gas detection element, and it is considered that an accurate gas concentration cannot be measured.
[0008]
That is, as described in claim 1, the first gas detection unit is provided on the upstream side of the dilution mechanism in the gas conveyance path, and the second gas detection unit is provided on the downstream side of the dilution mechanism in the gas conveyance path. If it is provided on the side, it is possible to know the concentration of the gas to be detected based on the output from the first gas detector when detecting the gas to be detected that does not require dilution. On the other hand, when the concentration of the gas to be detected is high, the concentration of the gas to be detected can be known based on the output from the second gas detection unit that detects the diluted gas to be detected.
Moreover, if the gas detection element having the same detection characteristics is provided in the first gas detection unit and the second gas detection unit as in claim 2, the concentration of the gas to be detected from a low concentration to a high concentration Can be measured.
[0009]
Furthermore, as described in claim 3, the throttle mechanism is provided in the gas conveying path, and the dilution mechanism is formed by providing an introduction pipe for introducing a dilution gas downstream of the throttle path. In this case, while the first gas detection unit detects the gas to be detected before dilution, the second gas detection unit can continuously detect the diluted gas to be detected, and outputs a stable output. Since the configuration can be continued, the concentration of the gas to be detected before and after dilution can always be monitored, and accurate concentration measurement can be stably performed.
[0010]
In the present invention, when the first gas detection unit is provided on the upstream side of the dilution mechanism, the detection target gas can be detected before the detection target gas led to the dilution mechanism is diluted. Since the first gas detection unit is provided in a branch path that is branched upstream of the dilution mechanism in the gas transport path, the gas detection element is upstream of the dilution mechanism. It is assumed that it is provided on the side.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(1) As shown in FIG. 1, the gas detection device of the present invention is provided with a gas transport path 1 for introducing a detection target gas, and causes the detection target gas to flow through the gas transport path 1 in the gas transport path 1. A suction pump 2 is provided as a gas flow device for this purpose. The gas transport path 1 is provided with a gas detection mechanism 3 and a dilution mechanism 4 for supplying a dilution gas for diluting the detection target gas. The first gas is provided with a first gas detection element 31a. The detection unit 3a is provided on the upstream side of the dilution mechanism 4 in the gas transport path 1, and the second gas detection unit 3b including the second gas detection element 31b is connected to the dilution mechanism 4 in the gas transport path 1. The gas detection mechanism 3 is configured on the downstream side. Further, each gas detection element 31a, 31b is connected to a gas detection circuit 3c which obtains an output based on contact with the detected gas and obtains the concentration of the detected gas. The gas detection mechanism 3 is provided with an alarm mechanism 3d that generates an alarm signal or the like based on the obtained gas concentration information.
[0012]
As the gas detection elements 31a and 31b, a hot-wire catalytic combustion type gas detection element in which a noble metal wire coil 31 is provided with a sensitive layer 32 made of a metal oxide as shown in FIG. 4 is effectively used. When such a gas detection element is used, when the sensitive layer 32 comes into contact with the gas to be detected, the electrical resistance of the sensitive layer 32 changes with the contact combustion of the gas to be detected in the sensitive layer 32. In addition, the detected gas concentration can be known by taking out and outputting the change in resistance value as a current value from the noble metal wire coil 31. The noble metal wire coil 31 functions as a conducting wire for extracting the output, and also has a function of heating the sensitive layer 32 so as to cause contact combustion when it comes into contact with the gas to be detected. It is useful for making the gas detection element minute and high-performance, and since it has a simple structure, the entire apparatus can be easily made compact.
[0013]
The dilution mechanism 4 is configured such that a throttle channel 4a is provided in the gas conveyance path 1, and an air introduction pipe 4b as a dilution gas supply unit is connected to the downstream side of the gas conveyance path 1 so that air introduction can be cut off and switched. Furthermore, a discharge passage 4c for discharging the excess detected gas is provided on the upstream side of the throttle passage 4a. With such a configuration, the second gas detection element can always detect the gas concentration of the diluted detection gas, and the concentration measurement of the diluted detection gas is unstable. Therefore, stable gas concentration measurement is facilitated.
[0014]
When such a gas detection device is used, the gas is sucked from the one end of the gas conveyance path 1 by the suction pump, the output from the first gas detection element is monitored, and the gas concentration is known. When this output exceeds a certain threshold, the dilution mechanism introduces a dilution gas, dilutes the gas to be detected, and knows the concentration of the diluted gas to be detected by the second gas detection element. This makes it possible to know the gas concentration accurately at all times and monitor the atmosphere.
[0015]
(2) The gas detection device of the present invention can also be configured as shown in FIG. That is, the gas conveyance path 1 for introducing the detection target gas is provided, and the gas conveyance path 1 is provided with a suction pump 2 as a gas distribution device for distributing the detection target gas to the gas conveyance path 1. The gas transport path 1 is provided with a gas detection mechanism 3 and a dilution mechanism 4 for supplying a dilution gas for diluting the detection target gas, and the first gas detection unit 3a is connected to the gas transport path 1. The gas detection mechanism 3 is configured by providing the second gas detection unit 3 b on the downstream side of the dilution mechanism 4 in the gas transport path 1. Further, a gas detection circuit 3c is connected to the gas detection units 3a and 3b to obtain an output based on contact with the gas to be detected and to obtain the concentration and gas type of the gas to be detected. The gas detection mechanism 3 is provided with an alarm mechanism 3d that generates an alarm signal or the like based on the obtained gas concentration information.
[0016]
The first and second gas detectors 3a, 3b are provided with a pair of catalytic combustion gas detectors 31a, 32a (3a), 31b, 32b (3b), and each gas detector 31a, 32a, 31b, As shown in FIG. 4, a catalytic combustion type gas detection element in which a porous carrier 32 mainly composed of alumina, silica or the like with a catalyst such as platinum or palladium attached on the surface is provided on a noble metal wire coil 31 as shown in FIG. Used for. When such a gas detection element is used, when the porous carrier 32 comes into contact with the gas to be detected, catalytic combustion is caused by the action of the catalyst carried on the porous carrier 32, and the temperature associated with the heat of combustion reaction. The detected gas concentration can be known from the change in electrical resistance of the noble metal wire coil 31 that changes due to the rise.
Here, as the gas detection elements 31a and 31b, those using palladium as the catalyst, and those using platinum as the catalyst as the gas detection elements 32a and 32b are adopted, and detection is performed for each gas detection element. When the target gas is introduced, the sensor output ratio of each pair of gas detection elements is obtained, and when the sensor output ratio is in a predetermined region (identification region), the detected gas contains the gas to be detected. The configuration can be identified as being
[0017]
The dilution mechanism 4 is provided with a throttle channel portion 4a in the gas transport path 1 and connects an air introduction pipe 4b as a dilution gas supply portion downstream of the gas conveyance path 1 as in the above (1), and shuts off air introduction. Further, a discharge path 4c for discharging excess detected gas is provided on the upstream side of the throttle flow path.
[0018]
When using such a gas detection device, suction is performed by the suction pump from one end side of the gas conveyance path 1, and the outputs of the gas detection elements 31a and 32a of the first gas detection unit 3a are monitored, Know the gas concentration and its ratio. When this output exceeds a certain threshold value, a dilution gas is introduced by the dilution mechanism, the gas to be detected is diluted, and diluted by the gas detection elements 31b and 32b of the second gas detection unit 3b. By knowing the concentration of the detected gas and its ratio, it is now possible to know the gas concentration and gas type accurately at all times.
[0019]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
Using the gas detection device described in the above (1), the state of the output change when the gas to be detected whose concentration changes with time is detected, and the conventional gas detection device (see FIG. 5) and the present invention. When compared with the gas detection element, the results are as shown in FIGS.
6 and 7, the upper diagram shows the change over time in the concentration of the detected gas supplied, and the lower diagram shows the change over time in the output.
[0020]
As a result, in the conventional gas detection element, the output is destabilized immediately after switching, but in the present invention, the destabilization is not observed.
[0021]
Using the gas detector described in (2) above, the state of the output change when the gas to be detected whose concentration changes with time is detected, and the conventional gas detector (see FIG. 5) When compared with a gas detector, the results are as shown in FIGS.
8 and 9, (a) shows the change over time in the concentration of the gas to be detected, (b) shows the change over time in the output, and (c) shows the gas type identification determination based on those outputs. Is shown.
[0022]
As a result, in the conventional gas detection element, there is an error in identifying the gas type based on the destabilization of the output immediately after switching, but in the present invention, the destabilization is not observed and the stable gas type identification is performed. It turns out that it is possible.
[0023]
[Another embodiment]
In the previous embodiment, an example in which the catalytic combustion type gas detection element is applied has been described. However, a semiconductor type gas detection element may be applied.
[0024]
The first gas detection unit 3a only needs to be configured to be able to detect the detection target gas before the detection target gas led to the dilution mechanism is diluted. As shown in FIG. The first gas detection unit may be provided in a branch path that is branched on the upstream side of the dilution mechanism, and the gas detection element provided in the first gas detection unit also has such a configuration. If the detection target gas can be detected earlier than the gas detection element provided in the second gas detection unit, the same effect can be obtained, and the first gas detection unit is provided in the branch path. Even if it exists, it will be considered that said 1st gas detection element is provided in the upstream of the said dilution mechanism in the said gas conveyance path.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a gas detection device according to an embodiment (1) of the present invention. FIG. 2 is a schematic diagram of a gas detection device according to an embodiment (2) of the present invention. FIG. 4 is a schematic diagram of a gas detection element. FIG. 5 is a schematic diagram of a conventional gas detection device. FIG. 6 is a graph showing instability of gas detection output in the conventional gas detection device. FIG. 7 is a graph showing the stabilized gas detection output in the embodiment (1). FIG. 8 is a graph showing the instability of the gas discrimination ability in the conventional gas detection device. FIG. 9 is the embodiment (2). Graph showing stabilized gas discrimination ability in Japan 【Explanation of symbols】
DESCRIPTION OF SYMBOLS 1 Gas conveyance path 2 Suction pump 3 Gas detection mechanism 3a First gas detection part 31a, 32a Gas detection element 3b Second gas detection part 31b, 32b Gas detection element 3c Gas detection circuit 4 Dilution mechanism

Claims (3)

A gas detection device provided with a gas conveyance path for introducing a detection target gas, provided with a gas distribution device for distributing the detection target gas through the gas conveyance path, and provided with a gas detection mechanism in the gas conveyance path;
The first and second gas detection units each including a gas detection element are provided to constitute the gas detection mechanism, and a gas detection circuit for measuring a gas concentration based on an output from each gas detection element is provided. the gas conveying path, said first gas detector, a dilution mechanism to test feeding the dilution gas to dilute the detection target gas, and the second gas detector is, from the upstream side in this order in series downstream Gas detection device.   The gas detection device according to claim 1, wherein the first gas detection unit and the second gas detection unit include the gas detection element having the same detection characteristics.   The gas detection device according to claim 1 or 2, wherein a throttle channel is provided in the gas conveyance path, and an introduction pipe for introducing a dilution gas is provided downstream of the throttle channel to form the dilution mechanism. .

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