JP4132563B2

JP4132563B2 - Gas detector

Info

Publication number: JP4132563B2
Application number: JP2000095473A
Authority: JP
Inventors: 中丸　　哲也; 正記渡辺; 洋貝野; 勝彦相澤; 雅徳三好; 毅中村; 光輝西田; 謙次沢田
Original assignee: New Cosmos Electric Co Ltd; Osaka Gas Co Ltd
Current assignee: New Cosmos Electric Co Ltd; Osaka Gas Co Ltd
Priority date: 2000-03-30
Filing date: 2000-03-30
Publication date: 2008-08-13
Anticipated expiration: 2020-03-30
Also published as: JP2001281194A

Description

【０００１】
【発明の属する技術分野】
本発明は、検知対象ガスを導入するガス搬送路を設け、前記ガス搬送路に、主ガス検知素子を備えたガス検知機構を設け、検知対象ガスを前記ガス搬送路に流通させて前記主ガス検知素子に導くガス流通装置を設けたガス検知装置に関する。
【０００２】
【従来の技術】
従来、この種のガス検知装置は、単に前記ガス搬送路にガス検知素子を設けてガス検知機構を構成していた。
【０００３】
【発明が解決しようとする課題】
近年、このようなガス検知装置によって、低濃度から高濃度まで広い濃度領域において被検知ガスの濃度を測定したり検知対象ガス中の微量成分ガスについてその種類を特定したりするために、特に低濃度ガスに対するガス検知性能の高いガス検知素子を用いることが考えられている。また、このようなガス検知素子は、一般に高濃度ガスに対する暴露によって被検知ガスを検知する検知精度が低下する場合が多いことが知られている。
【０００４】
しかしながら、このような形態で前記ガス検知素子を用いると、検知対象ガス中に高濃度の被検知ガスが含まれる場合であっても前記ガス検知素子は高濃度の被検知ガスに晒されてしまうことになり、そのガス検知素子の精度の低下（劣化）は避けられないという現状にあった。
【０００５】
従って、本発明の目的は、上記実状に鑑み、特に低濃度ガスに対するガス検知性能の高いガス検知素子を、高濃度ガスが存在する可能性のある環境下でも劣化しにくく維持しつつ、その特性を発揮させられるガス検知装置を提供する事にある。
【０００６】
【課題を解決するための手段】
この目的を達成するための本発明のガス検知装置の特徴構成は、
検知対象ガスを導入するガス搬送路を設け、前記ガス搬送路に、主ガス検知素子を備えたガス検知機構を設け、検知対象ガスを前記ガス搬送路に流通させて前記主ガス検知素子に導くガス流通装置を設け、
その主ガス検知素子よりも高濃度ガス耐久性のある前置ガス検知素子を、前記主ガス検知素子が前記検知対象ガスを検知するよりも早い時点で、前記検知対象ガスを検知自在に設け、検知対象ガス中の被検知ガスを所定濃度以上に含有する高濃度ガスであることを、前記前置ガス検知素子が検知した場合、前記主ガス検知素子が前記高濃度ガスを検出しないようにする保護機構を設けたガス検知装置であって、
前記保護機構が、前記前置ガス検知素子が前記検知対象ガスを検知した時点の後、前記主ガス検知素子が前記検知対象ガスを検知する時点までに、前記前置ガス検知素子のガス検知結果に基づいて前記主ガス検知素子の通電を停止させる停止機構と、
前記停止機構による前記主ガス検知素子の通電停止後、前記主ガス検知素子が常温に復帰するまでの間、前記前置ガス検知素子に接触した前記被検知ガスが前記主ガス検知素子に到達することを遅延させる機構と、を備えた点にあり、
請求項２記載のように、前記被検知ガスが前記主ガス検知素子に到達することを遅延させる機構は、前記前置ガス検知素子と前記主ガス検知素子との間のガス搬送路に設けられた長尺部を備えるのが好ましく、
請求項３記載のように、前記前置ガス検知素子と前記主ガス検知素子との間のガス搬送路に設けられた大径のバッファー部を備えてもよい。
また、保護機構として更に、請求項４記載のように前記前置ガス検知素子のガス検知結果に基づいて、前記主ガス検知素子の上流側で、前記主ガス検知素子に検知対象ガスを導入する前記ガス搬送路を遮断する遮断機構を備えたものであってもよく、
請求項５記載のように前記前置ガス検知素子のガス検知結果に基づいて、前記主ガス検知素子の上流側で、前記主ガス検知素子に導かれる検知対象ガスを希釈する希釈機構を備えたものであってもよい。
【０００７】
〔作用効果〕
つまり、検知対象ガスを導入するガス搬送路を設け、前記ガス搬送路に、検知対象ガスを前記ガス搬送路に流通させるガス流通装置を設け、前記ガス搬送路にガス検知機構を設けてあるから、前記ガス検知機構にガス検知素子を備えてあれば、前記検知対象ガス中の被検知ガスを検知することが出来る。
前記ガス検知機構に、主ガス検知素子を設けると、前記ガス検知機構は、前記主ガス検知素子の特性に従って被検知ガスを検知することができる。
【０００８】
このとき、請求項１記載のように、その主ガス検知素子よりも高濃度ガス耐久性のある前置ガス検知素子を、前記主ガス検知素子が前記検知対象ガスを検知するよりも早い時点で、前記検知対象ガスを検知自在に設けてあれば、前記検知対象ガス中の被検知ガス濃度が前記主ガス検知素子に悪影響を及ぼさない程度に低いかどうかを、前記前置ガス検知素子によって検知させられることになる。そこで、検知対象ガス中の被検知ガス濃度が所定濃度以上の高濃度ガスであることを、前記前置ガス検知素子が検知した場合、保護機構を設けて前記主ガス検知素子が前記高濃度ガスを検出しないようにしてあれば、前記主ガス検知素子は、その能力を発揮するのに適した低濃度条件でのみ機能させられる。
そのため、前記主ガス検知素子は、劣化の原因になりやすい高濃度ガスを検出しなくなり、不必要に劣化するのを回避することができる。そのため、その主ガス検知素子の劣化の進行を緩和し、長期使用等に貢献することができる。
【０００９】
前記保護機構としては、前記前置ガス検知素子が前記検知対象ガスを検知した時点の後、前記主ガス検知素子が前記検知対象ガスを検知する時点までに、前記前置ガス検知素子のガス検知結果に基づいて前記主ガス検知素子の通電を停止させる停止機構を備えたものであれば、たとえば、前記主ガス検知素子が通電加熱により、被検知ガスを検出し、その際、前記被検知ガスの濃度に応じて劣化するような場合に、前記通電加熱を停止するような手法で作動停止することにより、高濃度の被検知ガスによる劣化の要因が発生しなくなるために、前記主ガス検知素子の劣化を緩和することが出来る。
【００１０】
ここで、前記停止機構による前記主ガス検知素子の通電停止後、前記主ガス検知素子が常温に復帰するまでの間、前記前置ガス検知素子に接触した前記被検知ガスが前記主ガス検知素子に到達することを遅延させる機構を備えたものであれば、遅延させられている時間（遅延時間）内に前記主ガス検知素子を常温に復帰させることにより、前記主ガス検知素子に高濃度の被検知ガスを検知させてしまうのをほぼ回避して、前記主ガス検知素子の劣化を緩和させることができる。
【００１１】
前記被検知ガスが前記主ガス検知素子に到達することを遅延させる機構としては、請求項２記載のように前記前置ガス検知素子と前記主ガス検知素子との間のガス搬送路に設けられた長尺部を備えるものであれば、被検知ガスが移動する距離を長くすることで遅延時間を確保することができる。なお、長尺部の長さを変えることにより、容易に遅延時間を変更することができる。
また、請求項３記載のように前記前置ガス検知素子と前記主ガス検知素子との間のガス搬送路に設けられた大径のバッファー部を備えるものであれば、バッファー部の容積を変えることにより、容積に対応した遅延時間を確保することができる。
【００１２】
また、請求項４記載のように保護機構として前記主ガス検知素子の上流側で、前記主ガス検知素子に検知対象ガスを導入する前記ガス搬送路を遮断する遮断機構を更に備えたものであれば、高濃度の被検知ガスを含む検知対象ガスを、前記主ガス検知素子に接触する前に上流側で遮断し、必要に応じてさらに別の経路に誘導することが出来る。その結果、たとえば、前記主ガス検知素子が通電加熱なしに、高濃度の被検知ガスと接触して劣化するようなものであっても、前記被検知ガスとの接触を避けることが出来、前記主ガス検知素子の劣化特性によらず、保護機構として作用させることが可能になる。
【００１３】
さらに、同様にして、請求項５記載のように保護機構として前記主ガス検知素子の上流側で、前記主ガス検知素子に導かれる検知対象ガスを希釈する希釈機構を更に備えたものであれば、高濃度の被検知ガスを含む検知対象ガスを、前記主ガス検知素子に接触する前に上流側で希釈する事が出来るから、高濃度の被検知ガスを含む検知対象ガスを、前記主ガス検知素子に接触する前に上流側で希釈して低濃度にし、前記ガス検知素子が高濃度の前記被検知ガスにさらされるのを防止することが出来、前記主ガス検知素子が、高濃度の被検知ガスによって劣化するのを防止することが出来る。
また、このとき、あらかじめ前記希釈機構のガス希釈率を定めておいて、前記主ガス検知素子が、希釈後の被検知ガス濃度を求められるように構成してあれば、希釈後の測定被検知ガス濃度を基に、検知対象ガス中の被検知ガス濃度を求めることが可能となる。
【００１４】
尚、前記主ガス検知素子と、前記前置ガス検知素子とは、前記ガス搬送路において分岐され、異なる管路内に配置されていたとしても、前記前置ガス検知素子が、前記主ガス検知素子が前記検知対象ガスを検知するよりも早い時点で、前記検知対象ガスを検知自在な位置、構造であれば良い。
また、本発明における主ガス検知素子の機能としては、検知対象ガス中の被検知ガス濃度を求めるものであっても良いし、検知対象ガス中の微量ガス成分のガス種を識別するものであっても良い。
【００１５】
【発明の実施の形態】
以下に本発明の実施の形態を図面に基づいて説明する。
図１に示すように、本発明のガス検知装置は、検知対象ガスを導入するガス搬送路１ａ、１ｂを設け、前記ガス搬送路１ａ、１ｂに、検知対象ガスを前記ガス搬送路１ａ、１ｂに流通させるためのガス流通装置としての吸引ポンプ２を設けてある。また、前記ガス搬送路１ａ、１ｂには、ガス検知機構３を設けるとともに、前記検知対象ガスを希釈する希釈用ガスを供給する検知対象ガス希釈機構４を設けてある。
前記ガス検知機構３には、前置ガス検知素子としての第一ガス検知素子３ａを主ガス搬送路１ａにおける前記希釈機構４の上流側に設け、主ガス検知素子としての第二ガス検知素子３ｂを、前記検知対象ガス希釈機構の上流側から分岐する副ガス搬送路１ｂに設けてあり、第三ガス検知素子３ｃを、前記ガス搬送路１における前記希釈機構４の下流側に設けて構成してある。さらに、前記ガス検知素子３ａ、３ｂ、３ｃには、前記被検知ガスとの接触に基づき、出力を得て、その被検知ガスの濃度を求めるガス検知回路３ｄを接続してある。また、前記ガス検知機構３には、得られたガス濃度情報に基づき、警報信号等を発生する警報機構３ｄを設けてある。
【００１６】
前記第一〜第三ガス検知素子３ａ、３ｂ、３ｃは、図２に示すように貴金属線コイル３１にアルミナを主成分とする金属酸化物からなる感応層３２を設けてある熱線型接触燃焼式ガス検知素子が有効に用いられる。このようなガス検知素子を用いた場合、前記多孔質担体３２が前記被検知ガスに接触すると、その多孔質担体３２に担持された白金属系触媒の触媒作用によって接触燃焼を起こし、その燃焼反応熱に伴う温度上昇により変化する貴金属線コイル３１の電気抵抗変化により前記被検知ガス濃度を知ることができる。
尚、前記貴金属線コイル３１は、前記出力を取出す導線として働くとともに、前記感応層３２を、前記被検知ガスに接触したときに接触燃焼を生起させられるように加熱する働きを兼ね備えるもので、前記ガス検知素子を微小かつ高性能なものとするのに役立つとともに、単純な構造であるから、装置全体をコンパクトに構成しやすくなっている。ここで、前記第二、第三ガス検知素子３ｂ、３ｃとしては、前記感応層の表面に白金触媒を担持させた触媒層３４を設け、低濃度の可燃性ガス（プロパン、ブタンなど）を精度良く検知して濃度を測定可能なもの、前記第一ガス検知素子３ａとしては、前記感応層の表面にパラジウム触媒を担持させた触媒層３４を設け、高濃度の可燃性ガス（メタン、プロパン、ブタンなど）にも劣化しにくく、応答性高く可燃性ガスを検出可能なものを採用する。
【００１７】
また、前記第一、第二ガス検知素子３ａ，３ｂの間は、副ガス搬送路１ｂを２００ｃｍにわたる長尺部Ａ１に形成してある。これにより、通常は、前記第一、第三ガス検知素子３ａ，３ｃ間を５ｃｍとした場合に、前記第一ガス検知素子に接触した検知対象ガスは、約０．１秒遅れで前記第三ガス検知素子３ｃに達するのに対し、前記第一ガス検知素子に接触した検知対象ガスは、約２秒遅れで前記第二ガス検知素子３ｂに達する構成とするとともに、前記第一ガス検知素子が高濃度の被検知ガスを検知した場合に、前記第二ガス検知素子３ｂの通電を停止させて作動を停止させる停止機構を設けて保護機構Ａを構成する。
【００１８】
前記希釈機構４は、前記ガス搬送路１ａにオリフィス部４ａを設け、その下流側に希釈用ガスの供給部としてのエア導入配管４ｂを接続してエア導入遮断切り替え自在に構成してあり、さらに、前記オリフィスの上流側には、余剰ガスを排出する排出路４ｃを設けてある。このような構成により、前記第三ガス検知素子は、常に希釈された被検知ガスのガス濃度を検知し続けることができるようになり、一時的に希釈された被検知ガスの濃度測定が不安定になるような状態が介在しなくなるため、安定したガス濃度測定が容易になる。
【００１９】
このようなガス検知装置を用いる場合には、前記ガス搬送路１の一端部側から前記吸引ポンプにより吸引し、前記第一ガス検知素子による出力をモニタし、ガス濃度を知ることが出来る。この出力があるしきい値を越えた場合には、前記検知対象ガス希釈機構により、希釈用ガスが導入され、希釈された検知対象ガス中の被検知ガス濃度を、前記第三ガス検知素子で知ることができるので、常時ガス濃度を正確に知ることができるようになった。
【００２０】
【実施例】
以下に本発明の実施例を図面に基づいて説明する。
（１）先の実施の形態における第二ガス検知素子のガス検知の際の通電に伴う温度変化を調べたところ、図３に示すようになった。これによると、このガス検知素子は、通電停止から約２秒で常温に復帰し、被検知ガスを検知しなくなるため、その被検知ガスによる劣化を伴わないことが読みとれる。
【００２１】
（２）前記副ガス搬送路１ｂの前記第一第二ガス検知素子３ａ，３ｂ間の距離を種々に変化させたときの前記第一、第二ガス検知素子３ａ，３ｂの応答速度を調べたところ、図４のようになった。この場合、被検知ガスとしては、１００％の都市ガス（１３Ａ）をポンプ流量５００ｍｌ／ｍｉｎで吸引して前記ガス搬送路に供給している。また、ガス検知素子としては、いずれも先述の第二ガス検知素子として用いたものを用いた。この結果から、前記副ガス搬送路１ｂの長さを変えることにより、ほぼ、長さと比例するようにガス検知応答時間が長くなっており、これにより、遅延させられている時間（遅延時間）内に、前記第二ガス検知素子を常温に復帰させれば前記第二ガス検知素子の劣化を緩和させられることがわかる。つまり、前記遅延時間が二秒以上あれば、前記第二ガス検知素子に高濃度の被検知ガスを検知させてしまうのをほぼ回避できることがわかる。
【００２２】
（３）上述の構成のガス検知装置と、従来のガス検知装置（図１３参照）とで、高濃度ガスの暴露によるガス検知素子の劣化がどの程度相違するかについて調べたところ、図５のようになった。この試験では、各ガス検知器に７．５％（ａ）、１５％（ｂ）の都市ガス（１３Ａ）を３分間検知させる動作を１０回繰り返して、試験前後において前記第二ガス検知素子の出力の被検知ガス濃度依存性がどの様に変化するかを調べた。ここでは、本発明のガス検知装置における第二ガス検知素子は、全く動作しなかったために、試験前後でほとんど特性が変化していなかった（試験前のグラフに一致する）のに対して、従来のガス検知素子における第二ガス検知素子は、いずれの場合であっても大きく出力低下が見られることが読みとれ、高濃度ガスによる劣化を受けていることがわかる。これにより、本発明のガス検知装置によれば、第二ガス検知素子は前記保護機構により保護されて、劣化しにくく、信頼性の高いガス検知が行えることがわかる。
【００２３】
〔別実施の形態〕
以下に別実施の形態を説明する。
先の実施の形態によれば、副ガス搬送路１ｂを長尺に設けて、前記前置ガス検知素子（第一ガス検知素子）に接触した被検知ガスが主ガス検知素子（第二ガス検知素子）に達するまでに、前記主ガス検知素子の作動を停止させるための遅延時間を確保したが、前記副ガス搬送路１ｂに大径のバッファー部Ａ２を設けて構成してあっても良い（図６参照）。このような場合、前記第一、第二ガス検知素子３ａ，３ｂの応答速度を調べたところ、図７のようになる。この場合、被検知ガスとしては、１００％の都市ガス（１３Ａ）をポンプ流量５００ｍｌ／ｍｉｎで吸引して前記ガス搬送路に供給している。また、ガス検知素子としては、いずれも先述の第二ガス検知素子として用いたものを用いた。この結果から、前記副ガス搬送路１ｂの容積を変えることにより、容積の増加に伴って、ガス検知応答時間が長くなっており、これにより、遅延させられている時間（遅延時間）内に、前記第二ガス検知素子を常温に復帰させれば前記代にガス検知素子の劣化を緩和させられることがわかる。
尚、このような形態をとった場合、前記主ガス検知素子の出力応答経過は、図８のようになり、経路を長くした場合には、前記主ガス検知素子の出力経過は、前記前置ガス検知素子の出力と、ほぼ同様の経過をとるのに対して、上述の場合出力がなだらかに上昇することになるため、後述の希釈機構の役割も果たす。
【００２４】
また、先の実施の形態によれば、保護機構として前記主ガス検知素子の動作を停止させる停止機構を採用したが、検知対象ガスが前記前置ガス検知素子に接触した後、前記主ガス検知素子に達するまでに、前記前置ガス検知素子のガス検知結果に基づいて、前記主ガス検知素子の上流側で、前記主ガス検知素子に検知対象ガスを導入する前記ガス搬送路を遮断する遮断機構を備えて構成しても良い。このような遮断機構としては、たとえば、図９に示すように、前記前置ガス検知素子の高濃度ガス検知に伴って、前記主ガス検知素子の上流側で検知対象ガスの流路を切り替えることにより、前記主ガス検知素子への検知対象ガス流入を遮断するように構成することが出来る。
【００２５】
さらに、前記保護機構として、検知対象ガスが前記前置ガス検知素子に接触した後、前記主ガス検知素子に達するまでに、前記前置ガス検知素子のガス検知結果に基づいて、前記主ガス検知素子の上流側で、前記主ガス検知素子に導かれる検知対象ガスを希釈する希釈機構を備えてもよい。このような希釈機構の例としては、図１０に示すように、前記主ガス検知素子の上流側で検知対象ガスを希釈するための希釈用ガス導入路を設けて、前記前置ガス検知素子の高濃度ガス検知に伴って、前記希釈用ガス導入路からの希釈用ガスの導入、停止を制御可能に構成してあっても良い。
【００２６】
尚、前記前置ガス検知素子としての前記第一ガス検知素子は、図１１に示すように副ガス搬送路に配置してあっても良い。さらに、第一、第二ガス検知素子は、主ガス搬送路と、副ガス搬送路との分岐部分の下流側でお互いに異なる搬送路内に配置してあってもよく、このような場合であっても前置ガス検知素子としての第一ガス検知素子が主ガス検知素子としての第二ガス検知素子よりも早い時点で検知対象ガスを検知自在に設けてあればよい。
【００２７】
また、上述の実施の形態における第三ガス検知素子が、前記第二ガス検知素子よりも早い時期に検知対象ガス中の被検知ガスを検知でき、その濃度が希釈前において前記第二ガス検知素子に悪影響を及ぼすほどに濃いか否かが判別できる場合、その第三ガス検知素子が前記第一ガス検知素子の機能を兼ね備えることになるので、図１２のように構成することが出来る。つまり、前記主ガス搬送路１ａに前記第一、第三ガス検知素子を兼ねるガス検知素子３ａ（３ｃ、３）を設け、その上流側に希釈機構４を設け、その停止機構よりも上流側で分岐する副ガス搬送路に保護機構としての長尺部Ａ１及び希釈機構を介在させて第二ガス検知素子３ｂを設けることにより、前記ガス検知素子３ａ（３ｃ、３）は、希釈された検知対象ガスを検知することにより、被検知ガスの濃度の大小を早期に判別し、希釈前の検知対象ガスが高濃度の被検知ガスを含んでいると判断できるときは、前記第二ガス検知素子に対する停止機構を働かせ、前記第二ガス検知素子が高濃度ガスに晒されるのを防ぐとともに、希釈前の検知対象ガスが被検知ガスを低濃度にしか含んでいないと判断できるときは、前記第二ガス検知素子を働かせたままにして、前記第二ガス検知素子で精度の高い濃度測定を可能とする。
【００２８】
そのため、本発明においては、主ガス検知素子と前置ガス検知素子との位置関係が、同じガス搬送路内１に存する場合のみならず、主ガス搬送路１ａと副ガス搬送路１ｂとに分配配置されているような場合であっても、前記前置ガス検知素子を、前記主ガス検知素子が前記検知対象ガスを検知するよりも早い時点で、前記検知対象ガスを検知自在に設けてあれば、検知対象ガス中の被検知ガスを所定濃度以上に含有する高濃度ガスであることを、前記前置ガス検知素子が検知した場合、前記主ガス検知素子が前記高濃度ガスを検出しないようにする保護機構を働かせるとともに、前記前置ガス検知素子が希釈された検知対象ガス中の被検知ガス濃度を求めて、希釈前の被検知ガス濃度を求めることが出来、本発明の目的とする作用効果を発揮させられる。また、ガス吸引ポンプ２は、ガス検知素子の上流側に設けることもできるし、上下流側両方に設けることもできる。さらに、前記第三ガス検知素子に対しても前置ガス検知素子を設け、濃度測定、ガス種識別等の主要な機能を担うガス検知素子をそれぞれ保護可能に保護機構を設けてあっても良い。
【図面の簡単な説明】
【図１】本発明のガス検知装置の概略図
【図２】ガス検知素子の概略図
【図３】ガス検知素子に対する通電と素子温度との関係を示すグラフ
【図４】ガス検知素子の応答速度を示すグラフ
【図５】主ガス検知素子の高濃度ガス暴露による劣化を示すグラフ
【図６】別実施の形態におけるガス検知装置の概略図
【図７】図６の実施の形態におけるガス検知素子の応答速度を示すグラフ
【図８】図６の実施の形態におけるガス検知素子の応答速度を示すグラフ
【図９】別実施の形態におけるガス検知装置の概略図
【図１０】別実施の形態におけるガス検知装置の概略図
【図１１】別実施の形態におけるガス検知装置の概略図
【図１２】別実施の形態におけるガス検知装置の概略図
【図１３】従来のガス検知装置を示す概略図
【符号の説明】
ガス搬送路１ａ、１ｂ
ガス流通装置２
主ガス検知素子３ｂ
前置ガス検知素子３ａ
保護機構Ａ１[0001]
BACKGROUND OF THE INVENTION
The present invention provides a gas conveyance path for introducing a detection target gas, a gas detection mechanism including a main gas detection element in the gas conveyance path, and circulates the detection target gas through the gas conveyance path. The present invention relates to a gas detection device provided with a gas flow device leading to a detection element.
[0002]
[Prior art]
Conventionally, this type of gas detection device simply configures a gas detection mechanism by providing a gas detection element in the gas transport path.
[0003]
[Problems to be solved by the invention]
In recent years, with such a gas detection device, in order to measure the concentration of a gas to be detected in a wide concentration range from a low concentration to a high concentration or to specify the type of a trace component gas in the detection target gas, it is particularly low. It is considered to use a gas detection element having a high gas detection performance for a concentration gas. In addition, it is known that such a gas detection element generally has a low detection accuracy for detecting a gas to be detected due to exposure to a high concentration gas.
[0004]
However, when the gas detection element is used in such a form, the gas detection element is exposed to the high concentration gas to be detected even when the gas to be detected contains a high concentration gas to be detected. In other words, there has been a current situation in which a decrease (deterioration) in accuracy of the gas detection element is unavoidable.
[0005]
Therefore, in view of the above situation, the object of the present invention is to maintain the characteristics of a gas detection element having a high gas detection performance especially for low-concentration gas in an environment where a high-concentration gas may exist, while maintaining its characteristics. The purpose of this invention is to provide a gas detector capable of exhibiting the above.
[0006]
[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 conveyance path for introducing a detection target gas is provided, a gas detection mechanism including a main gas detection element is provided in the gas conveyance path, and the detection target gas is circulated through the gas conveyance path to be guided to the main gas detection element. set the gas flow device,
The location gas sensing element before than the main gas sensing element of that a high concentration gas durable, early in than the main gas sensing element detects the detection target gas, disposed for free detect the detection target gas When the front gas detection element detects that the gas to be detected in the detection target gas is a high concentration gas containing a predetermined concentration or more, the main gas detection element does not detect the high concentration gas. A gas detection device provided with a protective mechanism for
Gas detection result of the pre-gas detection element after the time when the pre-gas detection element detects the detection target gas until the time when the main gas detection element detects the detection target gas. A stop mechanism for stopping energization of the main gas detection element based on
After the energization of the main gas detection element is stopped by the stop mechanism, the detected gas that has contacted the pre-gas detection element reaches the main gas detection element until the main gas detection element returns to normal temperature. And a mechanism for delaying that ,
According to a second aspect of the present invention, the mechanism for delaying the detection gas from reaching the main gas detection element is provided in a gas conveyance path between the pre-gas detection element and the main gas detection element. It is preferable to have a long part,
According to a third aspect of the present invention, a large-diameter buffer portion provided in a gas conveyance path between the pre-gas detection element and the main gas detection element may be provided.
Further, as a protection mechanism , a detection target gas is introduced into the main gas detection element upstream of the main gas detection element based on a gas detection result of the front gas detection element as described in claim 4. It may be provided with a blocking mechanism for blocking the gas transport path,
A dilution mechanism for diluting a detection target gas led to the main gas detection element on the upstream side of the main gas detection element based on the gas detection result of the front gas detection element as described in claim 5. It may be a thing.
[0007]
[Function and effect]
In other words, a gas conveyance path for introducing the detection target gas is provided, a gas distribution device that distributes the detection target gas to the gas conveyance path is provided in the gas conveyance path, and a gas detection mechanism is provided in the gas conveyance path. If the gas detection mechanism includes a gas detection element, the gas to be detected in the detection target gas can be detected.
When the main gas detection element is provided in the gas detection mechanism, the gas detection mechanism can detect the gas to be detected according to the characteristics of the main gas detection element.
[0008]
At this time, as described in claim 1, the pre-gas detecting element having a higher concentration gas durability than the main gas detecting element is detected at an earlier time point than the main gas detecting element detects the detection target gas. If the detection target gas is provided so as to be detectable, the pre-gas detection element detects whether the concentration of the gas to be detected in the detection target gas is low enough not to adversely affect the main gas detection element. Will be allowed to. Therefore, when the pre-gas detection element detects that the concentration of the gas to be detected in the detection target gas is a high concentration gas having a predetermined concentration or more, a protection mechanism is provided so that the main gas detection element is the high concentration gas. If the gas is not detected, the main gas detection element is allowed to function only under a low concentration condition suitable for exerting its ability.
For this reason, the main gas detection element does not detect a high-concentration gas that tends to cause deterioration, and can avoid unnecessary deterioration. Therefore, the progress of deterioration of the main gas detection element can be mitigated, and it can contribute to long-term use and the like.
[0009]
As the protection mechanism, the gas detection of the front gas detection element is performed after the time when the front gas detection element detects the detection target gas and before the time when the main gas detection element detects the detection target gas. If the main gas detection element is provided with a stop mechanism for stopping the energization of the main gas detection element based on the result, for example, the main gas detection element detects the detection gas by energization heating, and at that time, the detection gas In the case of deterioration depending on the concentration of the gas, the main gas detection element is prevented from being generated by the high concentration gas to be detected by stopping the operation by the method of stopping the energization heating. Can be alleviated.
[0010]
Here, after the energization of the main gas detection element is stopped by the stop mechanism, the detected gas in contact with the pre-gas detection element is the main gas detection element until the main gas detection element returns to normal temperature. If the main gas detection element is provided with a mechanism that delays the arrival of the gas, the main gas detection element is returned to room temperature within a delayed time (delay time). It is possible to substantially avoid the detection of the gas to be detected and to alleviate the deterioration of the main gas detection element.
[0011]
The mechanism for delaying the detection gas from reaching the main gas detection element is provided in a gas conveyance path between the pre-gas detection element and the main gas detection element as claimed in claim 2. If a long portion is provided, the delay time can be secured by increasing the distance that the gas to be detected moves. Note that the delay time can be easily changed by changing the length of the long portion.
Moreover, if it has a large diameter buffer part provided in the gas conveyance path between the said front gas detection element and the said main gas detection element like Claim 3, the volume of a buffer part is changed. Thus, a delay time corresponding to the volume can be ensured.
[0012]
In addition, according to a fourth aspect of the present invention, the protective mechanism further includes a shut-off mechanism for shutting off the gas conveyance path for introducing the detection target gas into the main gas detection element on the upstream side of the main gas detection element. For example, the gas to be detected including the gas to be detected having a high concentration can be blocked on the upstream side before contacting the main gas detection element, and can be guided to another path as necessary. As a result, for example, even if the main gas detection element is deteriorated by contact with a high-concentration detected gas without energization heating, contact with the detected gas can be avoided, Regardless of the deterioration characteristics of the main gas detection element, it is possible to act as a protection mechanism.
[0013]
Further, similarly, as long as the protection mechanism further includes a dilution mechanism for diluting the detection target gas led to the main gas detection element on the upstream side of the main gas detection element as a protection mechanism. Since the detection target gas containing the high concentration gas to be detected can be diluted upstream before contacting the main gas detection element, the detection gas containing the high concentration detection gas can be diluted with the main gas. Before contacting the sensing element, it can be diluted to a low concentration on the upstream side to prevent the gas sensing element from being exposed to the high concentration of the gas to be sensed. It is possible to prevent deterioration due to the gas to be detected.
At this time, if the gas dilution rate of the dilution mechanism is determined in advance and the main gas detection element is configured to obtain the concentration of the gas to be detected after dilution, the measurement target to be detected after dilution is obtained. Based on the gas concentration, the detected gas concentration in the detection target gas can be obtained.
[0014]
Even if the main gas detection element and the pre-gas detection element are branched in the gas conveyance path and are arranged in different pipes, the pre-gas detection element is not included in the main gas detection element. Any position and structure may be used as long as the element can detect the detection target gas at a point earlier than the detection of the detection target gas.
Further, the function of the main gas detection element in the present invention may be to obtain the concentration of the gas to be detected in the detection target gas, or to identify the gas type of the trace gas component in the detection target gas. May be.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the gas detection apparatus of the present invention is provided with gas conveyance paths 1a and 1b for introducing a detection target gas, and the detection target gas is supplied to the gas conveyance paths 1a and 1b. A suction pump 2 is provided as a gas flow device for circulating the gas. The gas transport paths 1a and 1b are provided with a gas detection mechanism 3 and a detection target gas dilution mechanism 4 for supplying a dilution gas for diluting the detection target gas.
The gas detection mechanism 3 is provided with a first gas detection element 3a as a pre-gas detection element on the upstream side of the dilution mechanism 4 in the main gas transport path 1a, and a second gas detection element 3b as a main gas detection element. Is provided in the secondary gas conveyance path 1b branched from the upstream side of the detection target gas dilution mechanism, and the third gas detection element 3c is provided on the downstream side of the dilution mechanism 4 in the gas conveyance path 1. It is. Furthermore, a gas detection circuit 3d is connected to the gas detection elements 3a, 3b, and 3c to obtain an output based on contact with the gas to be detected and obtain the concentration 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 to third gas detection elements 3a, 3b, 3c are each a hot-wire catalytic combustion type in which a noble metal wire coil 31 is provided with a sensitive layer 32 made of a metal oxide mainly composed of alumina as shown in FIG. A gas detection element is used effectively. 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 catalytic action of the white metal catalyst supported on the porous carrier 32, and the combustion reaction occurs. The concentration of the gas to be detected can be known from the change in electrical resistance of the noble metal wire coil 31 that changes due to the temperature rise caused by heat.
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. Here, as the second and third gas detecting elements 3b and 3c, a catalyst layer 34 supporting a platinum catalyst is provided on the surface of the sensitive layer, and low concentration combustible gas (propane, butane, etc.) is accurately used. As the first gas detection element 3a that can detect well and measure the concentration, a catalyst layer 34 supporting a palladium catalyst is provided on the surface of the sensitive layer, and a high concentration combustible gas (methane, propane, Butane, etc.) that does not deteriorate easily and that can detect flammable gas with high responsiveness is adopted.
[0017]
Further, between the first and second gas detection elements 3a and 3b, a sub gas transport path 1b is formed in a long portion A1 extending over 200 cm. Thus, normally, when the distance between the first and third gas detection elements 3a and 3c is 5 cm, the detection target gas that has contacted the first gas detection element is delayed by about 0.1 second. While the gas to be detected reaches the gas detection element 3c, the detection target gas that has contacted the first gas detection element reaches the second gas detection element 3b with a delay of about 2 seconds, and the first gas detection element A protection mechanism A is configured by providing a stop mechanism that stops the operation by stopping energization of the second gas detection element 3b when a high-concentration gas to be detected is detected.
[0018]
The dilution mechanism 4 is configured such that an orifice part 4a is provided in the gas transport path 1a, and an air introduction pipe 4b as a dilution gas supply part is connected to the downstream side of the gas conveyance path 1a so as to be capable of switching between air introduction and cutoff. A discharge passage 4c for discharging excess gas is provided on the upstream side of the orifice. With this configuration, the third gas detection element can always detect the gas concentration of the diluted gas to be detected, and the concentration measurement of the diluted gas to be detected is unstable. Therefore, stable gas concentration measurement is facilitated.
[0019]
When such a gas detection device is used, it is possible to know the gas concentration by sucking with the suction pump from one end side of the gas conveyance path 1 and monitoring the output by the first gas detection element. When this output exceeds a certain threshold value, a dilution gas is introduced by the detection target gas dilution mechanism, and the concentration of the detection target gas in the diluted detection target gas is determined by the third gas detection element. Since it is possible to know, it has become possible to know the gas concentration accurately at all times.
[0020]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
(1) When the temperature change accompanying energization at the time of gas detection of the second gas detection element in the previous embodiment was examined, it was as shown in FIG. According to this, since this gas detection element returns to room temperature in about 2 seconds from the stop of energization and does not detect the detected gas, it can be read that there is no deterioration due to the detected gas.
[0021]
(2) The response speeds of the first and second gas detection elements 3a and 3b when the distance between the first and second gas detection elements 3a and 3b in the sub gas conveyance path 1b was changed in various ways were examined. However, it became like FIG. In this case, as the gas to be detected, 100% city gas (13A) is sucked at a pump flow rate of 500 ml / min and supplied to the gas conveyance path. Further, as the gas detection element, the one used as the second gas detection element described above was used. From this result, by changing the length of the sub-gas transport path 1b, the gas detection response time becomes longer in proportion to the length, and within this time (delay time). In addition, it is understood that the deterioration of the second gas detection element can be alleviated by returning the second gas detection element to room temperature. That is, it can be seen that if the delay time is 2 seconds or longer, the second gas detection element can be substantially prevented from detecting a high-concentration gas to be detected.
[0022]
(3) When the gas detection device having the above-described configuration and the conventional gas detection device (see FIG. 13) are examined as to how much the deterioration of the gas detection element due to the exposure of the high-concentration gas is different, FIG. It became so. In this test, the operation of causing each gas detector to detect 7.5% (a) and 15% (b) city gas (13A) for 3 minutes was repeated 10 times, and before and after the test, We examined how the output gas concentration dependency changes. Here, since the second gas detection element in the gas detection device of the present invention did not operate at all, the characteristics hardly changed before and after the test (corresponding to the graph before the test), whereas It can be seen that the output of the second gas detection element in this gas detection element is greatly reduced in any case, and it has been deteriorated by the high concentration gas. Thereby, according to the gas detection apparatus of this invention, it turns out that the 2nd gas detection element is protected by the said protection mechanism, is hard to deteriorate, and can perform highly reliable gas detection.
[0023]
[Another embodiment]
Another embodiment will be described below.
According to the previous embodiment, the sub gas transport path 1b is provided long, and the gas to be detected that comes into contact with the preceding gas detection element (first gas detection element) is the main gas detection element (second gas detection element). The delay time for stopping the operation of the main gas detection element is ensured until reaching the element), but a large-diameter buffer portion A2 may be provided in the auxiliary gas transport path 1b. (See FIG. 6). In such a case, when the response speeds of the first and second gas detection elements 3a and 3b are examined, the result is as shown in FIG. In this case, as the gas to be detected, 100% city gas (13A) is sucked at a pump flow rate of 500 ml / min and supplied to the gas conveyance path. Further, as the gas detection element, the one used as the second gas detection element described above was used. From this result, by changing the volume of the auxiliary gas conveyance path 1b, the gas detection response time becomes longer as the volume increases, and within this time (delay time), It can be seen that if the second gas detection element is returned to room temperature, the deterioration of the gas detection element can be mitigated instead.
When such a configuration is adopted, the output response progress of the main gas detection element is as shown in FIG. 8, and when the path is lengthened, the output progress of the main gas detection element is In contrast to the output of the gas detection element, the output of the gas detection element rises gently in the above-mentioned case.
[0024]
Further, according to the previous embodiment, the stop mechanism that stops the operation of the main gas detection element is adopted as a protection mechanism. However, after the detection target gas comes into contact with the front gas detection element, the main gas detection is performed. Blocking the gas transport path for introducing the detection target gas into the main gas detection element upstream of the main gas detection element based on the gas detection result of the pre-gas detection element before reaching the element A mechanism may be provided. As such a shut-off mechanism, for example, as shown in FIG. 9, the flow path of the detection target gas is switched on the upstream side of the main gas detection element in accordance with the detection of the high concentration gas of the front gas detection element. Thus, the detection target gas can be blocked from flowing into the main gas detection element.
[0025]
Furthermore, as the protection mechanism, the main gas detection is performed based on the gas detection result of the front gas detection element after the detection target gas contacts the front gas detection element and before reaching the main gas detection element. A dilution mechanism for diluting the detection target gas guided to the main gas detection element may be provided upstream of the element. As an example of such a dilution mechanism, as shown in FIG. 10, a dilution gas introduction path for diluting the detection target gas is provided on the upstream side of the main gas detection element. Along with the detection of the high-concentration gas, the introduction and stop of the dilution gas from the dilution gas introduction path may be controllable.
[0026]
Note that the first gas detection element as the pre-gas detection element may be arranged in the auxiliary gas transport path as shown in FIG. Further, the first and second gas detection elements may be arranged in different conveyance paths on the downstream side of the branch portion between the main gas conveyance path and the sub gas conveyance path. Even if it exists, the 1st gas detection element as a pre-gas detection element should just detectably provide detection object gas at the time earlier than the 2nd gas detection element as a main gas detection element.
[0027]
In addition, the third gas detection element in the above-described embodiment can detect the gas to be detected in the detection target gas at an earlier time than the second gas detection element, and the concentration of the second gas detection element is before the dilution. When it can be determined whether the concentration is so high as to adversely affect the gas, the third gas detection element also has the function of the first gas detection element, so that the configuration can be configured as shown in FIG. That is, the gas detection element 3a (3c, 3) that also serves as the first and third gas detection elements is provided in the main gas transport path 1a, the dilution mechanism 4 is provided on the upstream side thereof, and the upstream side of the stop mechanism. The gas detection element 3a (3c, 3) is diluted by providing the second gas detection element 3b with the elongate portion A1 as a protection mechanism and the dilution mechanism interposed in the branching gas transport path. By detecting the gas, it is possible to quickly determine the level of the concentration of the gas to be detected, and when it can be determined that the detection target gas before dilution contains a high concentration of the gas to be detected. When the stop mechanism is activated to prevent the second gas detection element from being exposed to the high-concentration gas and it can be determined that the detection target gas before dilution contains only the low concentration of the gas to be detected, Working gas detection element And left to to allow a high concentration measurement accuracy by the second gas sensing element.
[0028]
Therefore, in the present invention, the positional relationship between the main gas detection element and the front gas detection element is distributed not only in the same gas transfer path 1 but also in the main gas transfer path 1a and the sub gas transfer path 1b. Even in such a case, the pre-gas detection element may be provided so that the detection target gas can be detected at an earlier time point than the main gas detection element detects the detection target gas. For example, when the front gas detection element detects that the gas to be detected in the detection target gas is a high concentration gas containing a predetermined concentration or more, the main gas detection element does not detect the high concentration gas. It is possible to obtain the concentration of the gas to be detected in the gas to be detected in which the pre-gas detection element is diluted, and to obtain the concentration of the gas to be detected before dilution. Demonstrate effect Is Sera. The gas suction pump 2 can be provided on the upstream side of the gas detection element, or can be provided on both the upstream and downstream sides. Further, a pre-gas detection element may be provided for the third gas detection element, and a protection mechanism may be provided so as to protect each of the gas detection elements that perform major functions such as concentration measurement and gas type identification. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a gas detection device according to the present invention. FIG. 2 is a schematic diagram of a gas detection element. FIG. 3 is a graph showing a relationship between energization of the gas detection element and element temperature. FIG. 5 is a graph showing the deterioration of the main gas detection element due to high-concentration gas exposure. FIG. 6 is a schematic diagram of the gas detection device in another embodiment. FIG. 7 is a gas detection in the embodiment of FIG. Fig. 8 is a graph showing the response speed of the element. Fig. 8 is a graph showing the response speed of the gas detection element in the embodiment of Fig. 6. Fig. 9 is a schematic diagram of the gas detection device in another embodiment. FIG. 11 is a schematic diagram of a gas detector in another embodiment. FIG. 12 is a schematic diagram of a gas detector in another embodiment. FIG. 13 is a schematic diagram of a conventional gas detector. [Explanation of symbols]
Gas transport path 1a, 1b
Gas distribution device 2
Main gas detection element 3b
Pre-gas detection element 3a
Protection mechanism A1

Claims

A gas conveyance path for introducing a detection target gas is provided, a gas detection mechanism including a main gas detection element is provided in the gas conveyance path, and the detection target gas is circulated through the gas conveyance path to be guided to the main gas detection element. set the gas flow device,
The location gas sensing element before than the main gas sensing element of that a high concentration gas durable, early in than the main gas sensing element detects the detection target gas, disposed for free detect the detection target gas When the front gas detection element detects that the gas to be detected in the detection target gas is a high concentration gas containing a predetermined concentration or more, the main gas detection element does not detect the high concentration gas. A gas detection device provided with a protective mechanism for
Gas detection result of the pre-gas detection element after the time when the pre-gas detection element detects the detection target gas until the time when the main gas detection element detects the detection target gas. A stop mechanism for stopping energization of the main gas detection element based on
After the energization of the main gas detection element is stopped by the stop mechanism, the detected gas that has contacted the pre-gas detection element reaches the main gas detection element until the main gas detection element returns to normal temperature. And a mechanism for delaying the gas detection.

The mechanism for delaying the detection target gas from reaching the main gas detection element includes a long portion provided in a gas transfer path between the pre-gas detection element and the main gas detection element. The gas detection device according to 1.

The mechanism for delaying the detection gas from reaching the main gas detection element includes a large-diameter buffer provided in a gas transfer path between the pre-gas detection element and the main gas detection element. The gas detection device according to claim 1 or 2.

Gas detection result of the pre-gas detection element after the time when the pre-gas detection element detects the detection target gas until the time when the main gas detection element detects the detection target gas. based on, upstream of the main gas sensing element, according to any one of claims 1 to 3 comprising a blocking mechanism for blocking the gas conveying path for introducing the detection target gas in the main gas sensing element Gas detector.

Gas detection result of the pre-gas detection element after the time when the pre-gas detection element detects the detection target gas until the time when the main gas detection element detects the detection target gas. based on, the main upstream side of the gas sensing element, the gas detection apparatus according to any one of 4 from claim 1, further comprising a dilution mechanism to dilute the detection target gas introduced into the main gas sensing element.