JP2004279288A

JP2004279288A - Gas-detecting apparatus and gas concentration measurement method

Info

Publication number: JP2004279288A
Application number: JP2003073099A
Authority: JP
Inventors: Tsuneyoshi Matsugi; 常義眞継
Original assignee: New Cosmos Electric Co Ltd
Current assignee: New Cosmos Electric Co Ltd
Priority date: 2003-03-18
Filing date: 2003-03-18
Publication date: 2004-10-07
Anticipated expiration: 2023-03-18
Also published as: JP3989390B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas-detecting apparatus which is driven by a low voltage and reduces the power consumption. <P>SOLUTION: The gas-detecting apparatus is provided with: a gas sensor element 1 and a temperature compensating element 2 connected to a current supply terminal 300a of a power supply 300 via resistors R1, R2 in parallel; a switch 3 disposed in a current supply path 7 from the current supply terminal 300a to the gas sensor element 1 and the temperature compensating element 2 and switching to a conduction state and a non-conduction state; and a driving part 100 for intermittently driving the switch 3 so as to switch to the conduction state and a sensing part 200 for sensing gas, based on a detected voltage V1 of the gas sensor 1 and a compensated voltage V2 of the temperature compensating element, when the switch 3 is switched to the conduction state. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、ガスセンサ素子と温度補償素子を備え、ガスセンサ素子の出力である検出電圧と温度補償素子の出力である補償電圧に基づいてガス検知を行うガス検知装置、及び、このガス検知装置を用いたガス濃度測定方法に関する。
【０００２】
【従来の技術】
上記ガスセンサ素子は、例えば白金又は白金合金のコイルに可燃性ガスに対して感度を有する触媒をコーティングした接触燃焼式のセンサ素子であり、その素子表面でガスが燃焼反応を起こしてセンサ素子の温度が上昇し、その温度上昇でセンサ素子の抵抗が変化することを利用してガス濃度を測定することができる。具体的には、図９に示すように、検出対象ガスに対して感度がある上記ガスセンサ素子１と検出対象ガスに対して感度がない温度補償素子２を直列に接続してその両端に一定の電圧を印加し、ガスが反応して生じた熱によるセンサ素子１の抵抗値の変化を、センサ素子１の検出電圧の変化として検出してガス濃度を測定していた。なお、図９は、直列接続したガスセンサ素子１と温度補償素子２をブリッジ回路の一方の辺に配置し、他方の辺に直列接続した２つの抵抗Ｒａ，Ｒｂを配置した検知回路の例を示す。
【０００３】
上記温度補償素子は、ガスセンサ素子と同じコイルに触媒をコーティングしていない構造のもので、周囲温度の変化の影響を相殺するために使用する。すなわち、センサ素子のガスとの反応による温度変化は数１０℃程度と小さく、周囲温度が例えば０℃〜４０℃の範囲で変化すると、ガスとの反応によるセンサ出力変化と周囲温度の変化によるセンサ出力変化が区別できないため、センサ素子と同程度の抵抗値を有し周囲温度に対して同じような抵抗変化をする温度補償素子をセンサ素子と直列に接続して、センサ素子の検出電圧に周囲温度の影響が現れないようにしている。
【０００４】
ここで問題となるのは、上記のようにガスセンサ素子と温度補償素子を直列に接続するので、ガスセンサ素子に印加される電圧の約２倍の電源電圧が必要となることであり、具体的には１．６Ｖ〜２．５Ｖ程度の電源電圧が必要となる。そのため、従来では、携帯用のガス検出機器等で駆動電圧の低電圧化を進めて、例えば電池１セルや２セルの機器を作ろうとした場合、低電圧駆動のガス検知機器の設計が難しいという問題があった。
【０００５】
一方、別の従来技術として、上記ガスセンサ素子と温度補償素子を夫々抵抗を介して電源端子に並列接続させ、そのセンサ素子と温度補償素子の各抵抗との接続点の両電圧信号に基づいてガス検知を行うようにしたガス検知装置が提案されている（特許文献１参照）。
【０００６】
【特許文献１】
特開平８−８２６１１号公報（第１−４頁、図１−図５）
【０００７】
【発明が解決しようとする課題】
上記特許文献１には記載されていないが、ガスセンサ素子と温度補償素子に接続した各抵抗の値をガスセンサ素子や温度補償素子の抵抗値に比べて小さくすることで、電源電圧をガスセンサ素子の印加電圧の２倍の電圧よりも低くできる可能性がある。ただし、特許文献１に記載のガス検知装置では、電源部から検知回路に常時電流供給される構成であるので装置使用時の消費電力が大きくなり、例えば電池駆動する場合の電池の消耗が激しくなるおそれがある。
【０００８】
本発明は、上記実情に鑑みてなされたものであり、その目的は、低電圧駆動と消費電力の低減が可能となるガス検知装置、及び、このガス検知装置に適したガス濃度測定方法を提供することにある。
【０００９】
【課題を解決するための手段】
上記目的を実現するための本発明に係るガス検知装置の第１の特徴構成は、請求項１に記載したように、ガスセンサ素子と温度補償素子が抵抗を介して電源部の電流供給端子に並列接続され、前記電流供給端子から前記ガスセンサ素子及び前記温度補償素子への電流供給路に配置され且つ非導通状態と導通状態とに切り替え可能なスイッチと、前記スイッチを間欠的に導通状態に切り替え駆動する駆動部と、前記スイッチを導通状態に切り替えたときの前記ガスセンサ素子の検出電圧及び前記温度補償素子の補償電圧に基づいてガス検知を行う検知部が備えられている点にある。
【００１０】
すなわち、ガスセンサ素子及び温度補償素子と電源部の電流供給端子との間に介在させた抵抗の値をガスセンサ素子や温度補償素子の抵抗値に比べて小さくして、電源部の駆動電圧を低くする。また、検知部がガス検知を行うときだけ、駆動部がスイッチを導通状態に切り替えてガスセンサ素子及び温度補償素子に電流を供給し、検知部がガス検知を行うとき以外は、駆動部がスイッチを非導通状態に切り替えてガスセンサ素子及び温度補償素子に電流を供給しない。
従って、低電圧駆動と消費電力の低減が可能となるガス検知装置を提供することができる。
【００１１】
同第２の特徴構成は、請求項２に記載したように、第１の特徴構成において、前記スイッチが、前記ガスセンサ素子への電流供給を断続する第１スイッチと、前記温度補償素子への電流供給を断続する第２スイッチとからなり、前記駆動部が、前記第１スイッチ及び第２スイッチを一方が導通状態のときに他方が非導通状態となるように駆動し、前記検知部が、前記第１スイッチを導通状態に切り替えたときのガスセンサ素子の検出電圧及び前記第２スイッチを導通状態に切り替えたときの温度補償素子の補償電圧の両電圧信号を保持して、その両電圧信号に基づいてガス検知を行う点にある。
【００１２】
すなわち、駆動部が第１スイッチを導通状態に切り替えてガスセンサ素子へ電流供給するとともに、第２スイッチを非導通状態に切り替えて温度補償素子への電流供給を遮断し、検知部がガスセンサ素子の検出電圧信号を入力して保持する。また、駆動部が第１スイッチを非導通状態に切り替えてガスセンサ素子への電流供給を遮断するとともに、第２スイッチを導通状態に切り替えて温度補償素子へ電流供給し、検知部が温度補償素子の補償電圧信号を入力して保持する。
従って、ガスセンサ素子と温度補償素子に同時に電流供給せず、片方だけに電流供給するので、電源部からの供給電流が少なくなり、一層の消費電力の低減が可能となる。そして、供給電流が少なくなると、電源部に電池を使用したときの電池出力端子での電圧降下も小さくなり、電池の消耗も少なくなって電池の使用可能期間も長くなるため、ガス検知装置の好適な実施形態が提供される。
【００１３】
同第３の特徴構成は、請求項３に記載したように、第２の特徴構成において、前記ガスセンサ素子と前記温度補償素子が、共通の抵抗を介して前記電流供給端子に並列接続されている点にある。
【００１４】
すなわち、検知部がガスセンサ素子の検出電圧信号を入力するときは、駆動部が第１スイッチを導通状態に第２スイッチを非導通状態に夫々切り替えて、共通の抵抗を介してガスセンサ素子だけに電流供給し、また、検知部が温度補償素子の補償電圧信号を入力するときは、駆動部が第１スイッチを非導通状態に第２スイッチを導通状態に夫々切り替えて、共通の抵抗を介して温度補償素子だけに電流供給する。
従って、ガスセンサ素子及び温度補償素子と電源部の電流供給端子との間に介在させる抵抗が１個の共通抵抗になるので、回路構成が簡素化され、同時に、両素子と電源部の電流供給端子との間に別々の抵抗を介在させた場合に、両抵抗の特性の違いが、ガスセンサ素子の検出電圧と温度補償素子の補償電圧に異なる影響を及ぼすおそれを有効に回避することが可能となり、ガス検知装置の好適な実施形態が提供される。
【００１５】
同第４の特徴構成は、請求項４に記載したように、第１から第３の特徴構成のいずれかにおいて、前記電源部が、前記ガスセンサ素子及び前記温度補償素子に対して定電流状態で電流供給する点にある。すなわち、定電流で電流供給する場合は、電源部をオンしてガスセンサ素子及び温度補償素子に電圧印加する電源投入時に一定電流しか流れないので、ガスセンサ素子等に過大電流が流れるのを抑制して、素子の特性劣化を起こり難くすることができる。また、電源投入時の検知回路側の突入電流が一定であるので、電源部に電池を使用した場合でも、電源投入時に電源電圧が一時的に大きく低下するような不都合も発生しない。
従って、電源部が定電流で電流供給することにより、ガスセンサ素子及び温度補償素子の特性劣化を防止するとともに、電池使用に適したガス検知装置の好適な実施形態が提供される。
【００１６】
同第５の特徴構成は、請求項５に記載したように、第１から第３の特徴構成のいずれかにおいて、前記電源部が、前記ガスセンサ素子及び前記温度補償素子に対して定電圧状態で電流供給する点にある。すなわち、定電圧で電流供給する場合は、電源部をオンしてガスセンサ素子及び温度補償素子に電圧印加する電源投入時に各素子が冷えていて大きな電流が流れるため、定電流で小さな電流を供給する場合に比べて、各素子の立ち上がり特性を早くすることが可能となる。
従って、電源部が定電流で電流供給することにより、立ち上がり特性が良好なガス検知装置の好適な実施形態が提供される。
【００１７】
本発明に係るガス濃度測定方法の特徴構成は、請求項６に記載したように、上記第１から第５の特徴構成のいずれかのガス検知装置を用いたガス濃度測定方法であって、前記ガスセンサ素子及び前記温度補償素子に対して電流供給を開始した後、電圧値が安定化する前の前記ガスセンサ素子の検出電圧及び前記温度補償素子の補償電圧に基づいてガス濃度を測定する点にある。
【００１８】
すなわち、電源部から抵抗を介してガスセンサ素子及び温度補償素子に電流が流れると、各素子の温度は上昇して素子の抵抗値が変化し、ガスセンサ素子の検出電圧及び温度補償素子の補償電圧の各電圧値は安定状態に達するまで変化する。しかし、抵抗と接続されたガスセンサ素子側と温度補償素子側の各検知回路が同一構成であって電源部に並列接続されているので、上記検出電圧と補償電圧は同じ傾向で変化し、ガス濃度に対応する両電圧の差は各素子への電流供給開始時点と安定状態に達した時点とでほぼ等しくなる。その結果、両電圧が安定状態に達する前の段階でガス濃度の測定を行うことができる。
従って、第１から第５の特徴構成のいずれかのガス検知装置を用いて、検知動作開始後の早い段階で迅速にガス濃度を測定することができるガス濃度測定方法が提供される。
【００１９】
【発明の実施の形態】
本発明に係るガス検知装置及びガス濃度測定方法の実施の形態を、基本となる第１実施形態から順次、図面に基づいて説明する。
〔第１実施形態〕
図１に示すように、本発明のガス検知装置では、ガスセンサ素子１と温度補償素子２が抵抗Ｒ１，Ｒ２を介して電源部３００の電流供給端子３００ａに並列接続され、前記電流供給端子３００ａからガスセンサ素子１及び温度補償素子２への電流供給路７に配置され且つ非導通状態と導通状態とに切り替え可能なスイッチ３と、前記スイッチ３を間欠的に導通状態に切り替え駆動する駆動部１００と、前記スイッチ３を導通状態に切り替えたときの前記ガスセンサ素子１の検出電圧Ｖ１及び前記温度補償素子２の補償電圧Ｖ２に基づいてガス検知を行う検知部２００が備えられている。
【００２０】
前記電源部３００には、電池６と電池出力をバッファーするオペアンプ５が設けられ、オペアンプ５の出力端子が電流供給端子３００ａに対応する。具体的には、電池６として１セル又は２セルが使用され、電源部３００からは０．８Ｖ〜１．３Ｖ程度の電源電圧が検知回路側に供給される。
【００２１】
なお、上記ガスセンサ素子１及び温度補償素子２は従来技術で説明した構造のものである。また、抵抗Ｒ１，Ｒ２の抵抗値は、同一の抵抗値で、ガスセンサ素子１及び温度補償素子２の抵抗値の数分の１から１０分の１程度に設定する。
【００２２】
上記スイッチ３はトランジスタで構成され、そのトランジスタを非導通状態と導通状態に切り替えるために制御回路４から矩形波状の駆動信号が出力されている。従って、制御回路４内に前記駆動部１００が構成されている。
【００２３】
また、上記制御回路４内に前記検知部２００が構成され、検知部２００は、ガスセンサ素子１の検出電圧Ｖ１と温度補償素子２の補償電圧２の補償電圧Ｖ２の差から検知対象ガスの濃度を測定する。ここで、一定濃度のガスがある状態での検出電圧Ｖ１及び補償電圧Ｖ２は、図２に示すように、ガス検知装置の電源スイッチ（図示せず）をオンして測定動作を開始した後、または間欠駆動でセンサ駆動動作を開始した後、安定するまで時間がかかるが、抵抗と接続された同一構成のガスセンサ素子１側と温度補償素子２側の各回路を電源部３００に並列接続している（図１参照）ので、両電圧Ｖ１，Ｖ２は同じ傾向で変化し、そのガス濃度に対応する差電圧ΔＶはセンサの電源オン時点またはセンサ駆動動作の開始時点と安定状態に達した時点とでほぼ等しくなる。その結果、両電圧Ｖ１，Ｖ２が安定状態に達する前の早い段階でガス濃度の測定を行うことができる。
【００２４】
〔第２実施形態〕
第２実施形態では、図３に示すように、前記スイッチ３が、前記ガスセンサ素子１への電流供給を断続する第１スイッチ３ａと、前記温度補償素子２への電流供給を断続する第２スイッチ３ｂとからなり、前記駆動部１００が、前記第１スイッチ３ａ及び第２スイッチ３ｂを一方が導通状態のときに他方が非導通状態となるように駆動し、前記検知部２００が、前記第１スイッチ３ａを導通状態に切り替えたときの前記ガスセンサ素子１の検出電圧Ｖ１及び前記第２スイッチ３ｂを導通状態に切り替えたときの前記温度補償素子２の補償電圧Ｖ２の両電圧信号Ｖ１，Ｖ２を保持して、その両電圧信号Ｖ１，Ｖ２に基づいてガス検知を行う。なお、図中、７ａはガスセンサ素子１への電流供給路であり、７ｂは温度補償素子２への電流供給路である。
【００２５】
上記検知部２００における検出電圧信号Ｖ１と補償電圧信号Ｖ２の保持は、前記制御回路４に所謂サンプルホールド回路を備えて、アナログ信号として保持することが実現できる。また、前記制御回路４がマイクロコンピュータを備える場合は、マイクロコンピュータ内のメモリー部に、ＡＤ変換された検出電圧信号Ｖ１と補償電圧信号Ｖ２のデジタルデータを記憶させることで実現できる。
【００２６】
〔第３実施形態〕
第３実施形態は、第２実施形態（図３）の変形構成であり、図４に示すように、前記ガスセンサ素子１と前記温度補償素子２が、共通の抵抗Ｒ３を介して前記電流供給端子３００ａに並列接続されている点が異なる。即ち、ガスセンサ素子１及び温度補償素子２と電源部３００の電流供給端子３００ａとの間に介在させる抵抗が個別の抵抗Ｒ１，Ｒ２ではなく、１個の共通抵抗Ｒ３に置き換えられている。
【００２７】
そして、図４においては、前記第１スイッチ３ａを導通状態に切り替え、前記第２スイッチ３ｂを非導通状態に切り替えたときの入力電圧Ｖ３を前記ガスセンサ素子１の検出電圧信号Ｖ３ａとして保持し、前記第１スイッチ３ａを非導通状態に切り替え、前記第２スイッチ３ｂを導通状態に切り替えたときの入力電圧Ｖ３を前記温度補償素子２の補償電圧信号Ｖ３ｂとして保持し、その両電圧信号Ｖ３ａ，Ｖ３ｂに基づいてガス検知を行う。
【００２８】
〔第４実施形態〕
第４実施形態は、ガスセンサ素子１及び温度補償素子２自身に一定電圧が印加される定電圧駆動の電源部３００の回路例である。
具体的には、図５に示す回路において、オペアンプ５の反転入力端子と非反転入力端子が同電位になるように動作するので、ガスセンサ素子１及び温度補償素子２に加わる電圧は電池６の出力電圧ＶＢと同じになる。検知回路側には、オペアンプ５の出力端子から抵抗Ｒ５を通して電流供給され、この抵抗Ｒ５に生じる電圧降下Ｖ４をガスセンサ素子１の検出電圧信号Ｖ４ａ及び温度補償素子２の補償電圧信号Ｖ４ｂとして制御回路４に入力する。なお、ガスセンサ素子１及び温度補償素子２に過大な電流が流れないように、抵抗Ｒ５の抵抗値を設定する必要がある。
【００２９】
また、図５の回路の変形例として、図示はしないが、オペアンプ５の出力端子側に抵抗Ｒ５を設けずに出力端子と非反転端子間を短絡させ、代わりにオペアンプ５の電源端子側に抵抗Ｒ５に相当する抵抗Ｒ５ａを配置し、センサ素子１の抵抗変化による電流変化を上記抵抗Ｒ５ａでの電圧降下として取り出し、ガスセンサ素子１の検出電圧及び温度補償素子２の補償電圧を入力する構成でもよい。
【００３０】
〔第５実施形態〕
上記第１〜第４の実施形態では、電源部３００が検知回路側に定電圧状態で電流供給していたが、第５実施形態では、電源部３００Ａが、前記ガスセンサ素子１及び前記温度補償素子２に対して定電流状態で電流供給する。
具体的には、図６に示すように、電池６の出力がオペアンプ５Ａの非反転入力端子に接続され、オペアンプ５Ａの出力端子と反転入力端子との間に、ガスセンサ素子１と第１スイッチ３ｃ及び温度補償素子２と第２スイッチ３ｄを並列接続させて配置し、オペアンプ５Ａの非反転入力端子を抵抗Ｒ４によって接地する。この回路において、オペアンプ５Ａの非反転入力端子は電池６の出力電圧ＶＢと等しくなるように動作するので、抵抗Ｒ４には電池６の出力電圧ＶＢが印加され、抵抗Ｒ４を流れる電流、即ち、上記ガスセンサ素子１及び温度補償素子２を流れる電流は一定値（ＶＢ／Ｒ４）となる。ここで、各素子１，２を流れる電流が一定であるので、電池６の出力電圧ＶＢを低くして、抵抗Ｒ４の抵抗値を小さくすることができる。なお、この図６では、第１及び第２スイッチ３ａ，３ｂはリレー等で構成する。
【００３１】
〔第６実施形態〕
第６実施形態は、定電流状態で電流供給する電源部３００Ａの別の回路例であり、電流制限抵抗を電源側に配置して、前記ガスセンサ素子１及び前記温度補償素子２をグランド（接地）側に配置するようにしている。
具体的には、図７に示すように、電源電圧端子から抵抗Ｒ６及びトランジスタ８を通して検知回路側に電流供給されるが、出力端子がトランジスタ８のベースに接続されたオペアンプ９の非反転入力端子と電源電圧端子の間に比較電圧源１０が配置され、オペアンプ９の反転入力端子とトランジスタ８のエミッタの間が短絡されている。この回路においても、オペアンプ９の反転入力端子と非反転入力端子は同電位になるように動作するので、抵抗Ｒ６による電圧降下が比較電圧源１０の電圧Ｖｒｅｆと等しくなり、上記ガスセンサ素子１及び温度補償素子２には、Ｖｒｅｆ／Ｒ６で定まる値の一定電流が供給される。
そして、図７の回路では、ガスセンサ素子１及び温度補償素子２がグランド側に配置されているので、第１スイッチ３ａ及び第２スイッチ３ｂとして、トランジスタやＦＥＴ等のスイッチ素子が使用できる。
【００３２】
〔第７実施形態〕
第７実施形態は、第６実施形態と基本的には同じであるが、比較電圧源１０を電源端子側を基準とするのではなく、グランドを基準とする点が相異する。そして、一般的な電子回路の場合、グランドを基準とすることで、比較電圧源１０として汎用の電源基準ＩＣ等を使用して簡単に構成することができ、より実用的な回路が得られる。
具体的には、図８に示すように、電源電圧端子から抵抗Ｒ７及びトランジスタ８を通して検知回路側に電流供給されるが、出力端子がトランジスタ８のベースに接続されたオペアンプ９の非反転入力端子は、電源電圧を抵抗値が等しい２つの抵抗Ｒ１０と抵抗Ｒ１１で分圧した電圧が入力され、電源電圧の１／２に固定される。オペアンプ９の反転入力端子は、抵抗Ｒ８を介してトランジスタ８のエミッタに接続されるとともに、抵抗Ｒ８と同じ抵抗値の抵抗Ｒ９及び比較電圧源１０を介して接地されている。
【００３３】
図８の回路においても、オペアンプ９の反転入力端子の電位が非反転入力端子の電位（電源電圧の１／２）と同電位になるように動作するので、抵抗Ｒ８，Ｒ９の抵抗値が抵抗Ｒ７の抵抗値に対して十分大きい条件、又は、比較電圧源１０の内部抵抗が抵抗Ｒ７と同じである条件が成立する場合には、抵抗Ｒ７を流れる電流で生じる電圧降下が比較電圧源１０の電圧Ｖｒｅｆと等しくなり、上記ガスセンサ素子１及び温度補償素子２には、Ｖｒｅｆ／Ｒ７定まる値の一定電流が供給される。
なお、図８の回路では、オペアンプ９の反転入力端子と非反転入力端子が電源電圧の１／２の電位になるように動作するので、電源電圧の値とは無関係にセンサ素子等に定電流が供給できる。
【００３４】
〔別実施の形態〕
上記実施形態では、ガスセンサ素子１を温度で抵抗値が変化する接触燃焼式のガスセンサ素子で構成したが、接触燃焼式以外の各種ガスセンサ素子を用いることができる。
【００３５】
上記実施形態では、電源部３００，３００Ａの電圧源として電池６を用いたが、電池ではなく、商用電源を整流した直流回路の出力を用いてもよい。
【００３６】
上記実施形態では、スイッチ３，３ａ〜３ｄとして、トランジスタやＦＥＴやリレーを用いたが、これ以外の各種導通・非導通の切り替え可能なスイッチを用いることができる。
【図面の簡単な説明】
【図１】第１実施形態のガス検知装置の全体構成を示す電気回路図
【図２】ガスセンサの出力電圧特性を示すグラフ
【図３】第２実施形態のガス検知装置の全体構成を示す電気回路図
【図４】第３実施形態のガス検知装置の全体構成を示す電気回路図
【図５】第４実施形態のガス検知装置の全体構成を示す電気回路図
【図６】第５実施形態のガス検知装置の全体構成を示す電気回路図
【図７】第６実施形態のガス検知装置の全体構成を示す電気回路図
【図８】第７実施形態のガス検知装置の全体構成を示す電気回路図
【図９】従来のガス検知装置の構成を示す電気回路図
【符号の説明】
１ガスセンサ素子
２温度補償素子
３スイッチ
３ａ第１スイッチ
３ｂ第２スイッチ
３ｃ第１スイッチ
３ｄ第２スイッチ
７電流供給路
１００駆動部
２００検知部
３００電源部
３００Ａ電源部
３００ａ電流供給端子
Ｒ１抵抗
Ｒ２抵抗
Ｒ３抵抗
Ｒ４抵抗
Ｒ５抵抗
Ｒ６抵抗
Ｒ７抵抗[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a gas detection device that includes a gas sensor element and a temperature compensation element, performs gas detection based on a detection voltage output from the gas sensor element and a compensation voltage output from the temperature compensation element, and uses the gas detection apparatus. Gas concentration measurement method.
[0002]
[Prior art]
The gas sensor element is, for example, a contact combustion type sensor element in which a platinum or platinum alloy coil is coated with a catalyst having sensitivity to combustible gas, and the gas causes a combustion reaction on the element surface and the temperature of the sensor element increases. The gas concentration can be measured by utilizing the fact that the resistance of the sensor element changes due to the temperature rise. Specifically, as shown in FIG. 9, the above-mentioned gas sensor element 1 having sensitivity to the gas to be detected and the temperature compensating element 2 having no sensitivity to the gas to be detected are connected in series, and fixed at both ends thereof. When a voltage is applied, a change in the resistance value of the sensor element 1 due to heat generated by the reaction of the gas is detected as a change in the detection voltage of the sensor element 1, and the gas concentration is measured. FIG. 9 shows an example of a detection circuit in which the gas sensor element 1 and the temperature compensating element 2 connected in series are arranged on one side of a bridge circuit, and two resistors Ra and Rb connected in series are arranged on the other side. .
[0003]
The temperature compensating element has a structure in which the same coil as the gas sensor element is not coated with a catalyst, and is used to cancel the influence of a change in ambient temperature. That is, the temperature change due to the reaction of the sensor element with the gas is as small as about several tens of degrees Celsius. Since a change in output cannot be distinguished, a temperature compensating element that has the same resistance value as the sensor element and has the same resistance change with respect to the ambient temperature The effect of temperature is not shown.
[0004]
The problem here is that since the gas sensor element and the temperature compensation element are connected in series as described above, a power supply voltage that is about twice the voltage applied to the gas sensor element is required. Requires a power supply voltage of about 1.6 V to 2.5 V. Therefore, conventionally, it is difficult to design a low-voltage-driven gas detection device when a portable gas detection device or the like is used to reduce the driving voltage and, for example, to make a one-cell or two-cell battery device. There was a problem.
[0005]
On the other hand, as another conventional technique, the gas sensor element and the temperature compensation element are connected in parallel to a power supply terminal via respective resistors, and the gas sensor element and the temperature compensation element are connected based on both voltage signals at a connection point between the sensor element and each resistor of the temperature compensation element. A gas detection device that performs detection has been proposed (see Patent Document 1).
[0006]
[Patent Document 1]
JP-A-8-82611 (pages 1-4, FIGS. 1-5)
[0007]
[Problems to be solved by the invention]
Although not described in Patent Document 1, the value of each resistor connected to the gas sensor element and the temperature compensation element is made smaller than the resistance values of the gas sensor element and the temperature compensation element, so that the power supply voltage is applied to the gas sensor element. There is a possibility that the voltage can be made lower than twice the voltage. However, the gas detection device described in Patent Literature 1 has a configuration in which current is constantly supplied from the power supply unit to the detection circuit, so that power consumption during use of the device becomes large, and, for example, battery consumption when driving with a battery becomes severe. There is a risk.
[0008]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas detection device capable of driving at a low voltage and reducing power consumption, and a gas concentration measurement method suitable for the gas detection device. Is to do.
[0009]
[Means for Solving the Problems]
According to a first characteristic configuration of a gas detection device according to the present invention for achieving the above object, as described in claim 1, a gas sensor element and a temperature compensation element are connected in parallel to a current supply terminal of a power supply unit via a resistor. A switch connected to a current supply path from the current supply terminal to the gas sensor element and the temperature compensation element, the switch being switchable between a non-conductive state and a conductive state; and a switch for intermittently switching the switch to a conductive state. And a detection unit that performs gas detection based on the detection voltage of the gas sensor element and the compensation voltage of the temperature compensation element when the switch is switched to the conductive state.
[0010]
That is, the value of the resistance interposed between the gas sensor element and the temperature compensating element and the current supply terminal of the power supply unit is made smaller than the resistance value of the gas sensor element and the temperature compensating element, thereby lowering the driving voltage of the power supply unit. . Also, only when the detection unit performs gas detection, the drive unit switches the switch to the conductive state to supply current to the gas sensor element and the temperature compensation element, and except when the detection unit performs gas detection, the drive unit turns on the switch. The current is not supplied to the gas sensor element and the temperature compensation element by switching to the non-conductive state.
Therefore, it is possible to provide a gas detection device capable of driving at a low voltage and reducing power consumption.
[0011]
A second feature configuration according to the first feature configuration, wherein the switch is a first switch that interrupts current supply to the gas sensor element, and a current that flows to the temperature compensation element. A second switch for interrupting the supply, wherein the drive unit drives the first switch and the second switch such that when one of the switches is in a conductive state, the other is in a non-conductive state; It holds a voltage signal of both the detection voltage of the gas sensor element when the first switch is switched to the conductive state and the compensation voltage of the temperature compensation element when the second switch is switched to the conductive state, and based on the two voltage signals. Gas detection.
[0012]
That is, the drive unit switches the first switch to the conductive state to supply current to the gas sensor element, and switches the second switch to the non-conductive state to cut off the current supply to the temperature compensation element. Input and hold a voltage signal. Further, the driving unit switches the first switch to a non-conducting state to cut off current supply to the gas sensor element, and switches the second switch to a conducting state to supply current to the temperature compensating element. Input and hold the compensation voltage signal.
Therefore, current is not supplied to the gas sensor element and the temperature compensating element at the same time, but is supplied to only one of the gas sensor element and the temperature compensating element. Therefore, the supply current from the power supply unit is reduced, and the power consumption can be further reduced. When the supply current is reduced, the voltage drop at the battery output terminal when the battery is used for the power supply unit is reduced, and the consumption time of the battery is reduced, and the usable period of the battery is extended. Embodiments are provided.
[0013]
According to a third characteristic configuration, as described in claim 3, in the second characteristic configuration, the gas sensor element and the temperature compensation element are connected in parallel to the current supply terminal via a common resistor. On the point.
[0014]
That is, when the detection unit inputs the detection voltage signal of the gas sensor element, the driving unit switches the first switch to the conducting state and the second switch to the non-conducting state, and the current is applied only to the gas sensor element via the common resistor. When the detection unit inputs the compensation voltage signal of the temperature compensation element, the driving unit switches the first switch to the non-conducting state and the second switch to the conducting state, respectively, and outputs the temperature through the common resistor. A current is supplied only to the compensation element.
Therefore, the resistance interposed between the gas sensor element and the temperature compensating element and the current supply terminal of the power supply unit becomes a single common resistance, so that the circuit configuration is simplified, and at the same time, the current supply terminals of both elements and the power supply unit are provided. When a separate resistor is interposed between the two, it is possible to effectively avoid the possibility that the difference between the characteristics of the two resistors affects the detection voltage of the gas sensor element and the compensation voltage of the temperature compensation element differently. A preferred embodiment of the gas detection device is provided.
[0015]
According to a fourth feature configuration, as set forth in claim 4, in any one of the first to third feature configurations, the power supply unit is in a constant current state with respect to the gas sensor element and the temperature compensation element. The point is to supply current. In other words, when supplying a constant current, only a constant current flows when the power is turned on to turn on the power supply unit and apply a voltage to the gas sensor element and the temperature compensation element, so that an excessive current is suppressed from flowing to the gas sensor element and the like. In addition, it is possible to make the characteristics of the element hardly deteriorate. In addition, since the inrush current on the detection circuit side when the power is turned on is constant, even when a battery is used in the power supply unit, there is no inconvenience that the power supply voltage temporarily drops significantly when the power is turned on.
Therefore, the power supply unit supplies a constant current to prevent deterioration of the characteristics of the gas sensor element and the temperature compensation element, and to provide a preferred embodiment of a gas detection device suitable for use with a battery.
[0016]
According to a fifth feature configuration, as set forth in claim 5, in any one of the first to third feature configurations, the power supply unit is in a constant voltage state with respect to the gas sensor element and the temperature compensation element. The point is to supply current. That is, when supplying a current at a constant voltage, the power supply unit is turned on to apply a voltage to the gas sensor element and the temperature compensating element. As compared with the case, the rising characteristics of each element can be made faster.
Therefore, a preferred embodiment of the gas detection device having a good start-up characteristic is provided by supplying a constant current from the power supply unit.
[0017]
The characteristic configuration of the gas concentration measuring method according to the present invention is, as described in claim 6, a gas concentration measuring method using the gas detection device according to any one of the first to fifth characteristic configurations, After starting current supply to the gas sensor element and the temperature compensation element, the gas concentration is measured based on the detection voltage of the gas sensor element and the compensation voltage of the temperature compensation element before the voltage value is stabilized. .
[0018]
That is, when a current flows from the power supply unit to the gas sensor element and the temperature compensation element via the resistor, the temperature of each element rises, the resistance value of the element changes, and the detection voltage of the gas sensor element and the compensation voltage of the temperature compensation element are changed. Each voltage value changes until it reaches a stable state. However, since the detection circuits on the gas sensor element side connected to the resistor and the temperature compensation element side have the same configuration and are connected in parallel to the power supply, the detection voltage and the compensation voltage change in the same tendency, and the gas concentration Is substantially equal between the time when the current supply to each element is started and the time when a stable state is reached. As a result, the gas concentration can be measured before both voltages reach a stable state.
Therefore, there is provided a gas concentration measuring method capable of quickly measuring the gas concentration at an early stage after the start of the detecting operation by using the gas detecting device having any one of the first to fifth characteristic configurations.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of a gas detection device and a gas concentration measurement method according to the present invention will be described sequentially from the first embodiment, based on the drawings.
[First Embodiment]
As shown in FIG. 1, in the gas detection device of the present invention, the gas sensor element 1 and the temperature compensation element 2 are connected in parallel to the current supply terminal 300a of the power supply unit 300 via the resistors R1 and R2. A switch 3 arranged in a current supply path 7 to the gas sensor element 1 and the temperature compensation element 2 and capable of switching between a non-conductive state and a conductive state, and a driving unit 100 for switching the switch 3 to a conductive state intermittently. And a detection unit 200 that performs gas detection based on the detection voltage V1 of the gas sensor element 1 and the compensation voltage V2 of the temperature compensation element 2 when the switch 3 is switched to the conductive state.
[0020]
The power supply unit 300 is provided with a battery 6 and an operational amplifier 5 for buffering the battery output, and the output terminal of the operational amplifier 5 corresponds to the current supply terminal 300a. Specifically, one or two cells are used as the battery 6, and a power supply voltage of about 0.8 V to 1.3 V is supplied from the power supply unit 300 to the detection circuit side.
[0021]
The gas sensor element 1 and the temperature compensating element 2 have the structures described in the related art. Further, the resistance values of the resistors R1 and R2 are set to be approximately the same as the resistance values of the gas sensor element 1 and the temperature compensating element 2 in the order of several tenths to tenths.
[0022]
The switch 3 is composed of a transistor, and a control signal is output from the control circuit 4 to switch the transistor between a non-conductive state and a conductive state. Therefore, the driving unit 100 is configured in the control circuit 4.
[0023]
Further, the detection unit 200 is configured in the control circuit 4, and the detection unit 200 determines the concentration of the gas to be detected from the difference between the detection voltage V1 of the gas sensor element 1 and the compensation voltage V2 of the compensation voltage 2 of the temperature compensation element 2. Measure. Here, as shown in FIG. 2, the detection voltage V1 and the compensation voltage V2 in the presence of a gas having a constant concentration are measured by turning on a power switch (not shown) of the gas detection device and starting the measurement operation. Alternatively, after the sensor driving operation is started by the intermittent driving, it takes time to stabilize, but each circuit of the same configuration of the gas sensor element 1 and the temperature compensation element 2 connected to the resistor is connected in parallel to the power supply unit 300. (See FIG. 1), the two voltages V1 and V2 change in the same tendency, and the difference voltage ΔV corresponding to the gas concentration is determined when the power of the sensor is turned on or when the sensor driving operation is started and when the sensor reaches a stable state. Is almost equal. As a result, the gas concentration can be measured at an early stage before both voltages V1 and V2 reach a stable state.
[0024]
[Second embodiment]
In the second embodiment, as shown in FIG. 3, the switch 3 includes a first switch 3a for interrupting the current supply to the gas sensor element 1 and a second switch for interrupting the current supply to the temperature compensation element 2. 3b, the drive unit 100 drives the first switch 3a and the second switch 3b such that when one of the switches is in a conductive state, the other is in a non-conductive state. Holds both voltage signals V1 and V2 of the detection voltage V1 of the gas sensor element 1 when the switch 3a is switched to the conducting state and the compensation voltage V2 of the temperature compensation element 2 when the second switch 3b is switched to the conducting state. Then, gas detection is performed based on the two voltage signals V1 and V2. In the figure, 7a is a current supply path to the gas sensor element 1, and 7b is a current supply path to the temperature compensation element 2.
[0025]
The holding of the detection voltage signal V1 and the compensation voltage signal V2 in the detection unit 200 can be realized by providing a so-called sample-and-hold circuit in the control circuit 4 and holding them as analog signals. When the control circuit 4 includes a microcomputer, the control circuit 4 can be realized by storing digital data of the detection voltage signal V1 and the compensation voltage signal V2, which have been AD-converted, in a memory unit in the microcomputer.
[0026]
[Third embodiment]
The third embodiment is a modified configuration of the second embodiment (FIG. 3). As shown in FIG. 4, the gas sensor element 1 and the temperature compensation element 2 are connected to the current supply terminal via a common resistor R3. The difference is that they are connected in parallel to 300a. That is, the resistance interposed between the gas sensor element 1 and the temperature compensation element 2 and the current supply terminal 300a of the power supply unit 300 is replaced with one common resistor R3 instead of the individual resistors R1 and R2.
[0027]
In FIG. 4, the input voltage V3 when the first switch 3a is switched to the conducting state and the second switch 3b is switched to the non-conducting state is held as the detection voltage signal V3a of the gas sensor element 1, The input voltage V3 when the first switch 3a is switched to the non-conductive state and the second switch 3b is switched to the conductive state is held as the compensation voltage signal V3b of the temperature compensating element 2, and the two voltage signals V3a and V3b Gas detection is performed based on the detected gas.
[0028]
[Fourth embodiment]
The fourth embodiment is a circuit example of a constant-voltage-driven power supply unit 300 in which a constant voltage is applied to the gas sensor element 1 and the temperature compensation element 2 themselves.
Specifically, in the circuit shown in FIG. 5, since the inverting input terminal and the non-inverting input terminal of the operational amplifier 5 operate so as to have the same potential, the voltage applied to the gas sensor element 1 and the temperature compensation element 2 It becomes the same as the voltage VB. A current is supplied to the detection circuit side from an output terminal of the operational amplifier 5 through a resistor R5, and a voltage drop V4 generated in the resistor R5 is used as a detection voltage signal V4a of the gas sensor element 1 and a compensation voltage signal V4b of the temperature compensation element 2 for the control circuit 4. To enter. It is necessary to set the resistance value of the resistor R5 so that an excessive current does not flow through the gas sensor element 1 and the temperature compensation element 2.
[0029]
As a modified example of the circuit of FIG. 5, although not shown, a resistor R5 is not provided on the output terminal side of the operational amplifier 5 and the output terminal and the non-inverting terminal are short-circuited. A configuration may be adopted in which a resistor R5a corresponding to R5 is arranged, a current change due to a resistance change of the sensor element 1 is taken out as a voltage drop at the resistor R5a, and a detection voltage of the gas sensor element 1 and a compensation voltage of the temperature compensation element 2 are input. .
[0030]
[Fifth Embodiment]
In the first to fourth embodiments, the power supply unit 300 supplies a current to the detection circuit side in a constant voltage state. However, in the fifth embodiment, the power supply unit 300A includes the gas sensor element 1 and the temperature compensation element. 2 is supplied in a constant current state.
Specifically, as shown in FIG. 6, the output of the battery 6 is connected to the non-inverting input terminal of the operational amplifier 5A, and the gas sensor element 1 and the first switch 3c are connected between the output terminal and the inverting input terminal of the operational amplifier 5A. The temperature compensating element 2 and the second switch 3d are arranged in parallel, and the non-inverting input terminal of the operational amplifier 5A is grounded by the resistor R4. In this circuit, since the non-inverting input terminal of the operational amplifier 5A operates so as to be equal to the output voltage VB of the battery 6, the output voltage VB of the battery 6 is applied to the resistor R4, and the current flowing through the resistor R4, that is, The current flowing through the gas sensor element 1 and the temperature compensation element 2 has a constant value (VB / R4). Here, since the current flowing through each of the elements 1 and 2 is constant, the output voltage VB of the battery 6 can be lowered, and the resistance value of the resistor R4 can be reduced. In FIG. 6, the first and second switches 3a and 3b are configured by relays or the like.
[0031]
[Sixth embodiment]
The sixth embodiment is another circuit example of a power supply unit 300A that supplies a current in a constant current state, in which a current limiting resistor is disposed on the power supply side, and the gas sensor element 1 and the temperature compensation element 2 are grounded (grounded). It is arranged on the side.
Specifically, as shown in FIG. 7, a current is supplied from the power supply voltage terminal to the detection circuit side through the resistor R6 and the transistor 8, but the output terminal is a non-inverting input terminal of the operational amplifier 9 connected to the base of the transistor 8. A comparison voltage source 10 is arranged between the power supply voltage terminal and the inverting input terminal of the operational amplifier 9 and the emitter of the transistor 8 is short-circuited. Also in this circuit, since the inverting input terminal and the non-inverting input terminal of the operational amplifier 9 operate so as to have the same potential, the voltage drop due to the resistor R6 becomes equal to the voltage Vref of the comparison voltage source 10, and the gas sensor element 1 and the temperature A constant current having a value determined by Vref / R6 is supplied to the compensation element 2.
In the circuit of FIG. 7, since the gas sensor element 1 and the temperature compensation element 2 are arranged on the ground side, switch elements such as transistors and FETs can be used as the first switch 3a and the second switch 3b.
[0032]
[Seventh embodiment]
The seventh embodiment is basically the same as the sixth embodiment, except that the comparative voltage source 10 is not based on the power supply terminal side but on the ground. In the case of a general electronic circuit, by using the ground as a reference, it is possible to easily configure a general-purpose power supply reference IC or the like as the comparison voltage source 10, and to obtain a more practical circuit.
Specifically, as shown in FIG. 8, current is supplied from the power supply voltage terminal to the detection circuit side through the resistor R7 and the transistor 8, but the output terminal is connected to the non-inverting input terminal of the operational amplifier 9 connected to the base of the transistor 8. Is supplied with a voltage obtained by dividing the power supply voltage by two resistors R10 and R11 having the same resistance value, and is fixed to 電源 of the power supply voltage. The inverting input terminal of the operational amplifier 9 is connected to the emitter of the transistor 8 via a resistor R8, and is grounded via a resistor R9 having the same resistance value as the resistor R8 and a comparison voltage source 10.
[0033]
The circuit of FIG. 8 also operates such that the potential of the inverting input terminal of the operational amplifier 9 becomes the same as the potential of the non-inverting input terminal (電圧 of the power supply voltage). When a condition that is sufficiently large with respect to the resistance value of R7 or a condition that the internal resistance of the comparison voltage source 10 is the same as that of the resistor R7 is satisfied, a voltage drop caused by a current flowing through the resistor R7 causes a voltage drop of the comparison voltage source 10. The voltage becomes equal to the voltage Vref, and a constant current having a value determined by Vref / R7 is supplied to the gas sensor element 1 and the temperature compensation element 2.
In the circuit shown in FIG. 8, since the inverting input terminal and the non-inverting input terminal of the operational amplifier 9 operate so as to have a potential of 1/2 of the power supply voltage, a constant current is supplied to the sensor element or the like regardless of the value of the power supply voltage. Can be supplied.
[0034]
[Another embodiment]
In the above embodiment, the gas sensor element 1 is a contact combustion type gas sensor element whose resistance value changes with temperature, but various gas sensor elements other than the contact combustion type can be used.
[0035]
In the above embodiment, the battery 6 is used as the voltage source of the power supply units 300 and 300A. However, instead of the battery, an output of a DC circuit obtained by rectifying a commercial power supply may be used.
[0036]
In the above embodiment, transistors, FETs, and relays are used as the switches 3, 3a to 3d. However, other switches that can be switched between conducting and non-conducting can be used.
[Brief description of the drawings]
FIG. 1 is an electric circuit diagram showing an overall configuration of a gas detection device according to a first embodiment. FIG. 2 is a graph showing output voltage characteristics of a gas sensor. FIG. 3 is an electric diagram showing an overall configuration of a gas detection device according to a second embodiment. FIG. 4 is an electric circuit diagram showing the entire configuration of the gas detection device according to the third embodiment. FIG. 5 is an electric circuit diagram showing the entire configuration of the gas detection device according to the fourth embodiment. FIG. 6 is a fifth embodiment. FIG. 7 is an electric circuit diagram showing the entire configuration of the gas detection device of FIG. 7. FIG. 8 is an electric circuit diagram showing the entire configuration of the gas detection device of the sixth embodiment. FIG. 8 is an electric diagram showing the entire configuration of the gas detection device of the seventh embodiment. Circuit diagram [Figure 9] Electric circuit diagram showing configuration of conventional gas detection device [Explanation of reference numerals]
DESCRIPTION OF SYMBOLS 1 Gas sensor element 2 Temperature compensation element 3 Switch 3a 1st switch 3b 2nd switch 3c 1st switch 3d 2nd switch 7 Current supply path 100 Drive section 200 Detecting section 300 Power supply section 300A Power supply section 300a Current supply terminal R1 Resistance R2 Resistance R3 Resistance R4 Resistance R5 Resistance R6 Resistance R7 Resistance

Claims

The gas sensor element and the temperature compensation element are connected in parallel to the current supply terminal of the power supply via a resistor,
A switch disposed in a current supply path from the current supply terminal to the gas sensor element and the temperature compensation element and capable of switching between a non-conducting state and a conducting state, and a drive unit for intermittently switching and driving the switch to a conducting state And a detection unit that performs gas detection based on a detection voltage of the gas sensor element when the switch is switched to a conductive state and a compensation voltage of the temperature compensation element.

The switch comprises a first switch for interrupting the current supply to the gas sensor element, and a second switch for interrupting the current supply to the temperature compensation element;
The drive unit drives the first switch and the second switch such that when one of the switches is in a conductive state, the other is in a non-conductive state;
The detection unit holds both a voltage signal of a detection voltage of the gas sensor element when the first switch is turned on and a compensation voltage of the temperature compensation element when the second switch is turned on. 2. The gas detection device according to claim 1, wherein gas detection is performed based on the two voltage signals.

The gas detection device according to claim 2, wherein the gas sensor element and the temperature compensation element are connected in parallel to the current supply terminal via a common resistor.

The gas detection device according to claim 1, wherein the power supply unit supplies a current to the gas sensor element and the temperature compensation element in a constant current state.

The gas detection device according to any one of claims 1 to 3, wherein the power supply unit supplies a current to the gas sensor element and the temperature compensation element in a constant voltage state.

A gas concentration measurement method using the gas detection device according to any one of claims 1 to 5, wherein current supply to the gas sensor element and the temperature compensation element is started, and before a voltage value is stabilized. A gas concentration measuring method for measuring a gas concentration based on a detection voltage of the gas sensor element and a compensation voltage of the temperature compensation element.