JP4271979B2

JP4271979B2 - Ultrasonic gas concentration flow measurement method and apparatus

Info

Publication number: JP4271979B2
Application number: JP2003115333A
Authority: JP
Inventors: 直登志藤本
Original assignee: Teijin Ltd
Current assignee: Teijin Ltd
Priority date: 2003-04-21
Filing date: 2003-04-21
Publication date: 2009-06-03
Anticipated expiration: 2023-04-21
Also published as: CN100374826C; JP2004317459A; CN1777791A

Description

【０００１】
【発明の属する技術分野】
本発明は、超音波により、サンプルガスの濃度及び流量を測定する装置に関するものである。さらに詳細には、例えば医療目的で使用される酸素濃縮器から送り出されたサンプルガス中の酸素濃度、流量の測定に適する装置に関するものである。
【０００２】
【従来の技術】
サンプルガス中を伝播する超音波の伝播速度は、サンプルガスの濃度、温度の関数として表されることが広く知られている。サンプルガスの平均分子量をM、温度をT[K]とすれば、サンプルガス中の超音波伝播速度C[m/sec]は、次式で表される。
【０００３】
【数１】

【０００４】
ここで、k、Rは定数（k：定積モル比熱と定圧モル比熱の比、R：気体定数）である。すなわち、サンプルガス中の超音波伝播速度C[m/sec]とサンプルガスの温度T[K]が測定できれば、サンプルガスの平均分子量Mを決定できる。該サンプルガスが、例えば酸素と窒素の２分子からなるガスであれば、k = 1.4となることが知られている。該サンプルガスの平均分子量Mは、酸素の分子量を32、窒素の分子量を28として、例えば酸素100×P[%](0≦P≦1)と窒素100×(1−P)[%]の場合においては、M = 32P＋28 (1−P)と記述することができ、測定された平均分子量Mから酸素濃度Pを決定できる。また、サンプルガス中の超音波伝播速度がC[m/sec]、サンプルガスの流速がV[m/sec]であったとき、サンプルガスの流れに対して順方向に超音波を送信したときに測定される超音波伝播速度V₁[m/sec]は、V₁= C＋V、逆方向に超音波を送信したときに測定される超音波伝播速度V₂[m/sec]は、V₂= C−Vとなるので、サンプルガスの流速V[m/sec]は、次式２で求めることができる。
【０００５】
【数２】

【０００６】
これにサンプルガスの流れている配管の内面積[m²]を乗じることで、サンプルガスの流量[m³/sec]を求めることができる。さらに体積換算、時間換算を行えば、流量を[L/min]で求めることも容易である。該原理を利用し、サンプルガス中を伝播する超音波の伝播速度もしくは伝播時間からサンプルガスの濃度、流量を測定する方法及び装置に関しては、種々の提案が行われている。たとえば、特開平6−213877号公報には、サンプルガスが通る配管中に超音波振動子２つを対向させて配置し、該超音波振動子間を伝播する超音波の伝播時間を計測することによってサンプルガスの濃度及び流量を測定する装置が記載されている。また、特開平7−209265号公報や特開平8−233718号公報には、超音波振動子１つを使用した音波反射方式でセンシングエリア内を伝播する超音波の伝播速度もしくは伝播時間を測定することにより、サンプルガスの濃度を測定する装置が記載されている。
【０００７】
【特許文献１】
特開平６−２１３８７７号公報
【特許文献２】
特開平７−２０９２６５号公報
【特許文献３】
特開平８−２３３７１８号公報
【特許文献４】
特開平９−３１８６４４号公報
【特許文献５】
特開昭６０−１３８４２２号公報
【０００８】
【発明が解決しようとする課題】
このような超音波の伝播速度を用いてサンプルガスの濃度および流量を正確に測定する方法および装置においては、超音波の伝播時間を正確に検出しなければならない。しかしながら、超音波の受信波形には常にノイズ成分が含まれており、超音波を受信した瞬間の時間を直接検出することは非常に困難であり、一般的に複雑な信号処理手法や、複雑なハ−ドウェアを搭載することにより、超音波伝播時間を推定する方法が用いられている。たとえば、特開平9−318644号公報には、受信された超音波波形を積分し、その積分出力が基準値に達したのちにおける受信波のゼロクロス時間を流速測定のための超音波伝播時間とする方法が記載されている。該方法により、受信波形の振幅が多少変動したとしてもゼロクロスのタイミングが変動しないため、受信波の到達時間に比較的近い位置でのゼロクロス時間を獲得できるが、残念ながら獲得されるゼロクロス時間は真の超音波伝播時間ではなく、とりわけ濃度測定においては真の超音波伝播時間と検出されたゼロクロス時間との差異が測定誤差に大きく影響する。また、たとえば特開昭60−138422号公報には、受信波形の包絡線波形から算出された近似式に基づいて包絡線波形の立ち上がり時間を検出し、真の超音波伝播時間とする方法が記載されている。しかしながら、包絡線波形から超音波伝播時間を推定する方法においては、包絡線波形を得るために受信波形をサンプリングするためのハ−ドウェアを必要とし、また、包絡線を計算するために複雑な信号処理を必要とするため、安価で小型の装置を作成することが困難であった。
【０００９】
本発明は、複雑な信号処理やハ−ドウェアを必要とせずにサンプルガスの濃度および流量を測定する方法、および、必要最小限の部品のみを用いることで安価かつ小型の超音波式ガス濃度流量測定装置を提供することを目的としている。
【００１０】
【課題を解決するための手段】
本発明者らは、かかる目的を達成するために鋭意研究した結果、サンプルガスの流れる配管中に、対向させて配置した超音波振動子２つ、受信超音波のゼロクロス時間検出回路、温度センサを具備する超音波式ガス濃度流量測定方法および装置において、サンプルガスの取り得る濃度範囲、および、温度範囲から、サンプルガス中を伝播する超音波の音速の取り得る範囲を事前に知ることで好適な超音波振動子間距離を設定し、さらに、サンプルガスの取り得る流量範囲から好適な配管内半径を設定すれば、サンプルガス温度と連続した２つ以上のゼロクロス時間のみを検出することで、受信超音波の波形情報を獲得することなく、静止サンプルガス中における超音波伝播時間、および、サンプルガスの流れに対し順逆双方向での超音波伝播時間差を正確に検出でき、サンプルガスの濃度、および流量を測定することができることを見出したものである。
【００１１】
【発明の実施の形態】
以下に実施例を示す。本実施例においては、酸素と窒素の２分子からなるサンプルガスの、酸素濃度と流量を測定する方法および装置に関して示す。さらに、本実施例では、サンプルガスの酸素濃度範囲が0[%O₂]〜100[%O₂]、流量範囲が0〜10[L/min]であり、また、サンプルガスの温度範囲は、5[℃]〜35[℃]である場合に関して示す。また、本実施例では、中心周波数が40[kHz]の超音波振動子を使用する。本発明によって測定できるサンプルガスは、本実施例に示す酸素と窒素からなるサンプルガスだけに限定されるものではなく、他の分子によって構成されるガスに対しても容易に適用できる。また、サンプルガスの取り得る濃度範囲、温度範囲も本実施例における範囲に限定されるものではなく、他の範囲においても容易に適用できる。さらに、超音波振動子の中心周波数も40[kHz]に限定されるものではなく、他の中心周波数を持つ超音波振動子に対しても容易に適用できる。
【００１２】
超音波式酸素濃度流量測定手段の構成は図１に示すとおりである。サンプルガスの流れる配管1の中に２つの超音波振動子2を対向させて配置し、該超音波振動子2の送受信を切り替える切り替え器4、該超音波振動子2に超音波送信パルスを伝えるドライバ5、超音波受信波形のゼロクロス時間を検出するゼロクロス時間検出回路6、サンプルガスの濃度、流量を算出するためのマイクロコンピュ−タ7、及び、配管1の中にサンプルガスの温度を測定する温度センサ3を備える。
【００１３】
超音波の送受信により、受信超音波のゼロクロス時間を検出する方法は各種提案されている。最も簡便な方法は、ゼロクロスコンパレ−タを搭載し、コンパレ−タ出力の立ち上がりエッジ、もしくは、立ち下りエッジを検出するものである。図２に超音波受信波形の一例を示す。超音波の受信波形には各種ノイズ成分が含まれるため、正確にゼロクロス時間を検出するためには、受信振幅が十分大きくなったところにてゼロクロスコンパレ−タの出力を獲得することが望ましい。すなわち、獲得されるゼロクロス時間は受信超音波の第一波目ではなく、それ以降の例えば第3波目や、第4波目にて得られることになる。図３に、本実施例でのゼロクロス時間検出回路６におけるゼロクロス時間検出方法を示す。ゼロクロス検出回路６には、ノイズレベルよりも十分大きい電圧値にて受信波形の存在を検出するためのトリガコンパレ−タ、および、トリガコンパレ−タの出力が発生した時間（図３中のトリガ検出位置）以降のゼロクロス時間を検出できるゼロクロスコンパレ−タを含む。獲得するゼロクロス時間は1点ではなく、連続した数点を取ることが望ましい。本実施例においては、連続した3点のゼロクロス時間（図３中のZc1、Zc2、Zc3）を獲得することとした。
【００１４】
受信超音波のゼロクロス間隔は、常に中心周波数から計算される１周期分の時間間隔となるはずである。中心周波数40[kHz]の超音波振動子を用いる場合の１周期分の時間は、1/40000[sec]＝25[μsec]となる。すなわち、ゼロクロス検出回路６にて得られた先頭のゼロクロス時間は超音波受信時間そのものではないが、該ゼロクロス時間から25[μsec]の整数倍を巻き戻した時間のいずれかに真の超音波受信時間が存在することになる。
【００１５】
すなわち、獲得されたゼロクロス時間が第何波目以降のゼロクロス時間であるか不明であっても、先述の超音波伝播時間の取り得る範囲内に、該ゼロクロス時間から１周期の整数倍だけ巻き戻して得られる時間が常に１つだけ存在する振動子間距離Lを設定することで、容易に真の超音波伝播時間を推定できることになる。
【００１６】
以下、超音波振動子間の距離を好適に設定する方法に関して示す。サンプルガスの濃度範囲が既知であれば、各温度での流速ゼロにおけるサンプルガス中を伝播する音速の範囲は、式１を用いて容易に計算できる。酸素の分子量を32、窒素の分子量を28とすれば、例えば、温度20℃の場合において、酸素濃度0%の場合の音速は式１より、349.1[m/sec]となり、酸素濃度100%の場合の音速は、326.6[m/sec]と計算される。すなわち、サンプルガスの酸素濃度が変化した場合において、20℃におけるサンプルガス中の音速は、常に324.6[m/sec]〜349.1[m/sec]の範囲に収まることになり、該範囲の両端を音速の上限、下限とする。サンプルガス温度の取り得る範囲である5℃〜35℃において計算される、温度と音速の関係をグラフ化したものを、図４に示す。図４にて明らかなように、音速Ｃの上限、下限は温度Ｔの関数として表すことができ、温度Ｔにおける音速の上限をＣ_max(T)、下限をＣ_min(T)とする。
【００１７】
次に好適にしたい振動子間距離をL_s[m]とする。音速の取り得る範囲が先述の通りあらかじめ分かっているため、超音波伝播時間の取り得る範囲は、L_sを用いて表すことができる。すなわち超音波伝播時間の取り得る範囲は、L_s/Ｃ_max(T)[sec] 〜 L_s/Ｃ_min(T)[sec]である。
【００１８】
該超音波伝播時間の取り得る範囲に、ゼロクロス時間検出回路6にて得られる該ゼロクロス時間から１周期の整数倍だけ巻き戻して得られる時間が常に１つだけにするためには、伝播時間の取り得る範囲が超音波の１周期分の時間未満であれば良い（図９）。超音波の周波数をfr[Hz]とすれば、１周期の時間は1/fr[sec]となる。すなわち、下記式３を常に満たすL_sを選定すれば良い。
【００１９】
【数３】

【００２０】
“L_s/ Ｃ_min(T) − L_s/ Ｃ_max(T)”の値を最大にする温度Tは、本実施例においてはサンプルガスの温度範囲下限の5℃である。5℃におけるＣ_max(5℃)、Ｃ_min(5℃)はそれぞれ、Ｃ_max(5℃)＝340.1[m/sec]、Ｃ_min(5℃)＝318.1[m/sec]となる。さらに、本実施例における超音波の周波数frは、fr＝40[kHz]＝40000[Hz]であるため、式３を満たす振動子間距離L_sは、L_s＜12.3[cm]となり、およそ12[cm]未満の振動子間距離となるように２つの超音波振動子２を設置すれば良いことになる。本実施例においては、振動子間距離として10[cm]を採用した。
【００２１】
流量を測定するためには、サンプルガスの流れに対して、順逆双方向に超音波送受信を実施し、双方でのゼロクロス時間を必要とする。順逆双方にて得られるゼロクロス時間が、常に同じトリガ位置にて獲得されたものであれば、図５に示すとおり、ゼロクロス時間の間隔（図５中のAの間隔）＝超音波の伝播時間差（図５中のt_d）となり得る。しかしながら、超音波の受信波形は順逆双方向で全く同一になる保証はなく、ゼロクロス検出回路6内のトリガコンパレ−タで検出されるトリガ位置が順逆にてずれる可能性がある。そこで、順逆双方向にて得られる超音波の伝播時間差t_dが、常に受信超音波の１周期分未満の時間となるようにサンプルガスの流れる配管１の内半径を設定すれば、トリガ位置が順逆にてずれた場合においても容易にトリガ位置合わせが可能となる。例えば、サンプルガスの流れに対して順方向に超音波送受信を実施して得られたトリガ位置に対し、逆方向に超音波送受信した場合に得られたトリガ位置が１周期分だけ前方であった場合を図６に示す。順逆にてトリガ位置が揃っていたと仮定してゼロクロス時間の差を計算すると、その値は負の値となる（図６中のA）。サンプルガスの流量範囲が0〜10[L/min]であれば、伝播時間の差が負になることはありえないため、容易にトリガがずれていたことを検出でき、図６中のBを真の伝播時間差として採択することが可能となる。逆に、サンプルガスの流れに対して順方向に超音波送受信を実施して得られたトリガ位置に対し、逆方向に超音波送受信した場合に得られたトリガ位置が１周期分だけ後方であった場合を図７に示す。順逆にてトリガ位置が揃っていたと仮定してゼロクロス時間の差を計算すると、その値は超音波の１周期分の時間を上回る値となる（図７中のA）。しかしながら、超音波の伝播時間差t_dが、常に受信超音波の１周期分未満の時間となるように設計されていれば、伝播時間の差が受信超音波の１周期分以上になることはありえないため、この場合も容易にトリガがずれていたことを検出でき、図７中のBを真の伝播時間差として採択することが可能となる。
【００２２】
以下、サンプルガスの流れる配管1の内半径を好適に設定する方法に関して示す。サンプルガスの流量をQ[L/min]とすれば、サンプルガスの流れる配管1の内半径をr[m]とした場合、該配管1中の流速V[m/sec]は、次の式４の範囲にて表される。
【００２３】
【数４】

【００２４】
サンプルガスの流れに対して順方向に超音波を送信した場合に観測される音速V₁[m/sec]は、サンプルガスが静止している場合の音速をC[m/sec]として、V₁＝C+V、また、サンプルガスの流れに対して逆方向に超音波を送信した場合に観測される音速V₂[m/sec]は、V₂＝C−V、として観測される。サンプルガスの流れに対して順逆双方向に超音波送受信を実施した際に観測される伝播時間の差をt_d[sec]とすると、t_dは振動子間距離をL_s[m]として、式５で表すことができる。
【００２５】
【数５】

【００２６】
したがって、伝播時間の差t_dが常に受信超音波の１周期分未満の時間となるようにするためには、常に式６を満たす内半径rを選定すれば良い。
【００２７】
【数６】

【００２８】
本実施例において、式６の左項を最大とするC、Qの条件は、C＝Ｃ_min(5℃)＝318.1[m/sec]、Q＝10[LPM]である。さらに、振動子間距離L_s＝10[cm]＝0.1[m]、超音波の周波数fr＝40[kHz]＝40000[Hz]を式６に代入すると、r＞2.05[mm]となり、配管1の内半径が2.05[mm]を上回るようにすれば良いことになる。本実施例においては、配管1の内半径として2.5[mm]を採用した。
【００２９】
以下、本実施例におけるサンプルガスの酸素濃度、および、流量測定方法に関して述べる。サンプルガス投入中において、マイクロコンピュ−タ7より超音波の送信パルスをドライバ5に送り、送受信切り替え器4によってサンプルガスの流れと順方向に超音波を送信するように選択された超音波振動子2にパルス電圧が印加され、超音波が送信される。もう一方の超音波振動子2によって受信された超音波は、送受信切り替え器4を介して、ゼロクロス検出回路6に入力され、得られたゼロクロス時間３つ（ZcF1、ZcF2、ZcF3）をマイクロコンピュ−タ7に送る。その後、マイクロコンピュ−タ7より超音波の送信パルスをドライバ5に送り、送受信切り替え器4によってサンプルガスの流れと逆方向に超音波を送信するように選択された超音波振動子2にパルス電圧が印加され、超音波が送信される。もう一方の超音波振動子２によって受信された超音波は、送受信切り替え器4を介して、ゼロクロス検出回路6に入力され、得られたゼロクロス時間３つ（ZcB1、ZcB2、ZcB3）をマイクロコンピュ−タ７に送る。
【００３０】
以上の操作によってサンプルガスの流れに対して順逆双方向にて得られたゼロクロス時間から、図５〜図７に示した方法により、トリガ位置のズレを補正して超音波の伝播時間の差t_dを算出する。t_dの算出には、図５中に示されたAの値、もしくは、図６、図７中に示されたBの値を加算平均することで、時間検出誤差を減少させることが可能である。さらに、順逆双方向での超音波送受信にて得られるゼロクロス時間のトリガ位置を揃えた最初のゼロクロス時間の平均Zｃ_aveを算出する。Zc_aveは、サンプルガスの流量がゼロの時に超音波送受信を行った際に得られるゼロクロス時間であると見なすことができる。例えば図５に示した状態であれば、Zc_aveは次の式７で求めることができる（図８）。
【００３１】
【数７】

【００３２】
同様に図６に示した状態であれば、式８にて求めることができる（図示せず）。
【００３３】
【数８】

【００３４】
更に図７に示した状態であれば、式９にて求めることができる（図示せず）。
【００３５】
【数９】

【００３６】
続いて、マイクロコンピュ−タ7は、２つの超音波振動子間の距離をL_s[m]とし（本実施例においては、L_s＝0.1[m]）、温度センサ3の出力T℃を読み取り、サンプルガスの温度T℃に応じた超音波伝播時間の範囲L_s/Ｃ_max(T)[sec]〜L_s/Ｃ_min(T)[sec]を計算する。さらに、該ゼロクロス時間の平均Zc_aveから該超音波伝播時間の範囲に入るまで、受信超音波の１周期分の時間＝25[μsec]の整数倍を巻き戻していき、超音波伝播時間t_s[sec]を確定する（図９）。この結果より、静止したサンプルガス中の超音波伝播速度C_s[m/sec]は次式10にて求めることができる。
【００３７】
【数１０】

【００３８】
ここで、酸素の分子量をM_O2、窒素の分子量をM_N2、温度センサ出力のT[℃]を単位変換してT_s[K]とし、求めたい酸素濃度をP_sとして式１を変形すると、次式が得られる。
【００３９】
【数１１】

【００４０】
式11より、サンプルガスの酸素濃度は100×P_s[%]として測定できる。もしくは、サンプルガスの酸素濃度は、サンプルガス中の超音波伝播速度と、酸素100%、窒素100%のガス中の超音波伝播速度の比として求めることも可能である。すなわち、式１を用いれば温度T_s[K]における酸素100%中の超音波伝播速度C_O2[m/sec]、窒素100%中の超音波伝播速度C_N2[m/sec]は容易に求めることができ、サンプルガス中の超音波伝播速度C_s[m/sec]を使い、以下の式12によっても、P_sを計算できる。
【００４１】
【数１２】

【００４２】
上記の計算は、マイクロコンピュ−タ7にて実施され、濃度測定結果は表示器8に表示される。
【００４３】
流量測定時には、先に求めた静止したサンプルガス中の超音波伝播時間t_sと、超音波伝播時間差t_dを用いて、サンプルガスの流れに対して順方向に超音波の送受信を実施した際の超音波伝播時間t_s1、逆方向に超音波の送受信を実施した際の超音波伝播時間t_s2を式13、式14によって求める。
【００４４】
【数１３】

【００４５】
【数１４】

【００４６】
すなわち、サンプルガスの流れに対して順方向に超音波を送信したときに測定される超音波伝播速度V_s1[m/sec]、逆方向に超音波を送信したときに測定される超音波伝播速度V_s2[m/sec]は、それぞれ次式によって求めることができる。
【００４７】
【数１５】

【００４８】
【数１６】

【００４９】
さらに、式２より、サンプルガスの流速V_s[m/sec]は次式で求めることができる。
【００５０】
【数１７】

【００５１】
流速V_s[m/sec]が求まれば、サンプルガスの流れる配管１の内半径をr_s[m]とすれば、流量Q_s[L/min]は式18によって求めることができる。
【００５２】
【数１８】

【００５３】
上記の計算は、マイクロコンピュ−タ7において実施され、流量測定結果は表示器8に表示される。
【図面の簡単な説明】
【図１】本発明の超音波式酸素濃度流量測定手段の構成を示す概略図。
【図２】超音波受信波形の一例。
【図３】ゼロクロス時間検出回路によるゼロクロス時間検出方法の例。
【図４】温度と音速の関係。
【図５】トリガ位置が揃っている場合の超音波伝播時間差とゼロクロス時間の間隔との関係。
【図６】順方向に超音波送受信を実施して得られたトリガ位置に対し、逆方向に超音波送受信した場合に得られたトリガ位置が１周期分だけ前方であった場合の超音波伝播時間差とゼロクロス時間の間隔との関係。
【図７】順方向に超音波送受信を実施して得られたトリガ位置に対し、逆方向に超音波送受信した場合に得られたトリガ位置が１周期分だけ後方であった場合の超音波伝播時間差とゼロクロス時間の間隔との関係。
【図８】静止したサンプルガス中にて超音波送受信を行った際に得られるゼロクロス時間を求める例。
【図９】静止したサンプルガス中の超音波伝播時間を求める例。
【符号の説明】
１配管
２超音波振動子
３温度センサ
４送受信切り替え器
５ドライバ
６ゼロクロス検出回路
７マイクロコンピュ−タ
８表示器
９不揮発性メモリ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for measuring the concentration and flow rate of a sample gas using ultrasonic waves. More specifically, the present invention relates to an apparatus suitable for measuring oxygen concentration and flow rate in a sample gas delivered from, for example, an oxygen concentrator used for medical purposes.
[0002]
[Prior art]
It is widely known that the propagation speed of ultrasonic waves propagating in a sample gas is expressed as a function of the concentration and temperature of the sample gas. If the average molecular weight of the sample gas is M and the temperature is T [K], the ultrasonic propagation velocity C [m / sec] in the sample gas is expressed by the following equation.
[0003]
[Expression 1]

[0004]
Here, k and R are constants (k: ratio of constant volume molar specific heat and constant pressure molar specific heat, R: gas constant). That is, if the ultrasonic propagation velocity C [m / sec] in the sample gas and the temperature T [K] of the sample gas can be measured, the average molecular weight M of the sample gas can be determined. For example, if the sample gas is a gas composed of two molecules of oxygen and nitrogen, it is known that k = 1.4. The average molecular weight M of the sample gas is such that the molecular weight of oxygen is 32 and the molecular weight of nitrogen is 28. For example, oxygen 100 × P [%] (0 ≦ P ≦ 1) and nitrogen 100 × (1−P) [%] In some cases, M = 32 P + 28 (1-P) can be described, and the oxygen concentration P can be determined from the measured average molecular weight M. Also, when the ultrasonic wave velocity in the sample gas is C [m / sec] and the flow velocity of the sample gas is V [m / sec], when ultrasonic waves are transmitted in the forward direction with respect to the sample gas flow The ultrasonic propagation velocity V ₁ [m / sec] measured at ₁ is V ₁ = C + V, and the ultrasonic propagation velocity V ₂ [m / sec] measured when ultrasonic waves are transmitted in the opposite direction is V ₂ Since C−V, the flow velocity V [m / sec] of the sample gas can be obtained by the following equation 2.
[0005]
[Expression 2]

[0006]
By multiplying this by the inner area [m ² ] of the pipe through which the sample gas flows, the flow rate [m ³ / sec] of the sample gas can be obtained. Furthermore, if volume conversion and time conversion are performed, the flow rate can be easily obtained in [L / min]. Various proposals have been made regarding methods and apparatuses for measuring the concentration and flow rate of a sample gas from the propagation speed or propagation time of an ultrasonic wave propagating in the sample gas using the principle. For example, in Japanese Patent Laid-Open No. 6-213877, two ultrasonic transducers are arranged facing each other in a pipe through which a sample gas passes, and the propagation time of ultrasonic waves propagating between the ultrasonic transducers is measured. Describes an apparatus for measuring the concentration and flow rate of a sample gas. In Japanese Patent Application Laid-Open Nos. 7-209265 and 8-233718, the propagation speed or propagation time of ultrasonic waves propagating in a sensing area is measured by a sound wave reflection method using one ultrasonic transducer. Thus, an apparatus for measuring the concentration of a sample gas is described.
[0007]
[Patent Document 1]
JP-A-6-213877 [Patent Document 2]
JP 7-209265 A [Patent Document 3]
JP-A-8-233718 [Patent Document 4]
JP-A-9-318644 [Patent Document 5]
Japanese Patent Application Laid-Open No. 60-138422
[Problems to be solved by the invention]
In such a method and apparatus for accurately measuring the concentration and flow rate of the sample gas using the ultrasonic wave propagation speed, the ultrasonic wave propagation time must be accurately detected. However, the received waveform of an ultrasonic wave always contains a noise component, and it is very difficult to directly detect the time at which the ultrasonic wave is received. Generally, a complicated signal processing method or a complicated A method of estimating the ultrasonic propagation time by installing hardware is used. For example, in Japanese Patent Laid-Open No. 9-318644, the received ultrasonic waveform is integrated, and the zero-cross time of the received wave after the integrated output reaches the reference value is used as the ultrasonic propagation time for flow velocity measurement. A method is described. With this method, even if the amplitude of the received waveform varies slightly, the zero cross timing does not vary, so the zero cross time at a position relatively close to the arrival time of the received wave can be obtained. The difference between the true ultrasonic wave propagation time and the detected zero-crossing time greatly affects the measurement error, particularly in the concentration measurement, not the ultrasonic wave propagation time. Further, for example, Japanese Patent Application Laid-Open No. 60-138422 describes a method of detecting a rise time of an envelope waveform based on an approximate expression calculated from an envelope waveform of a received waveform and obtaining a true ultrasonic wave propagation time. Has been. However, in the method of estimating the ultrasonic wave propagation time from the envelope waveform, hardware for sampling the received waveform is required to obtain the envelope waveform, and a complicated signal is required for calculating the envelope. Since processing is required, it has been difficult to produce an inexpensive and small device.
[0009]
The present invention provides a method for measuring the concentration and flow rate of a sample gas without requiring complicated signal processing and hardware, and an inexpensive and small ultrasonic gas concentration flow rate by using only the minimum necessary components. The object is to provide a measuring device.
[0010]
[Means for Solving the Problems]
As a result of diligent research to achieve the above object, the present inventors have found that two ultrasonic transducers, a zero-crossing time detection circuit for receiving ultrasonic waves, and a temperature sensor are arranged opposite to each other in a pipe through which a sample gas flows. In the ultrasonic gas concentration flow rate measuring method and apparatus provided, it is preferable to know in advance the possible range of the sound velocity of the ultrasonic wave propagating in the sample gas from the concentration range that the sample gas can take and the temperature range. By setting the distance between ultrasonic transducers and setting a suitable pipe radius from the flow rate range that can be taken by the sample gas, it is possible to receive only by detecting two or more zero-crossing times that are continuous with the sample gas temperature. Without acquiring ultrasonic waveform information, ultrasonic propagation time in stationary sample gas and ultrasonic propagation in both directions forward and backward with respect to sample gas flow During difference can be accurately detected and it has been found that the concentration of the sample gas, and the flow rate can be measured.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Examples are shown below. In this embodiment, a method and apparatus for measuring the oxygen concentration and flow rate of a sample gas composed of two molecules of oxygen and nitrogen will be described. Further, in this embodiment, the oxygen concentration range of the sample gas is 0 [% O ₂ ] to 100 [% O ₂ ], the flow rate range is 0 to [L / min], and the temperature range of the sample gas is , 5 [° C.] to 35 [° C.]. In this embodiment, an ultrasonic transducer having a center frequency of 40 [kHz] is used. The sample gas that can be measured according to the present invention is not limited to the sample gas composed of oxygen and nitrogen shown in the present embodiment, but can be easily applied to gases composed of other molecules. Further, the concentration range and temperature range that the sample gas can take are not limited to the ranges in the present embodiment, and can be easily applied to other ranges. Furthermore, the center frequency of the ultrasonic vibrator is not limited to 40 [kHz], and can be easily applied to ultrasonic vibrators having other center frequencies.
[0012]
The configuration of the ultrasonic oxygen concentration flow rate measuring means is as shown in FIG. Two ultrasonic transducers 2 are arranged opposite to each other in the pipe 1 through which the sample gas flows, a switch 4 for switching between transmission and reception of the ultrasonic transducer 2, and an ultrasonic transmission pulse is transmitted to the ultrasonic transducer 2 The driver 5, the zero cross time detection circuit 6 for detecting the zero cross time of the ultrasonic reception waveform, the microcomputer 7 for calculating the concentration and flow rate of the sample gas, and the temperature of the sample gas in the pipe 1 are measured. A temperature sensor 3 is provided.
[0013]
Various methods for detecting the zero-cross time of received ultrasonic waves by transmitting and receiving ultrasonic waves have been proposed. The simplest method is to mount a zero cross comparator and detect the rising edge or falling edge of the comparator output. FIG. 2 shows an example of the ultrasonic reception waveform. Since various noise components are included in the received waveform of the ultrasonic wave, it is desirable to acquire the output of the zero cross comparator when the reception amplitude becomes sufficiently large in order to accurately detect the zero cross time. That is, the acquired zero crossing time is obtained not at the first wave of the received ultrasonic wave but at, for example, the third wave or the fourth wave thereafter. FIG. 3 shows a zero cross time detection method in the zero cross time detection circuit 6 in the present embodiment. The zero-cross detection circuit 6 includes a trigger comparator for detecting the presence of a received waveform at a voltage value sufficiently larger than the noise level, and the time when the trigger comparator output is generated (trigger detection in FIG. 3). It includes a zero cross comparator that can detect the zero cross time after the position). It is desirable to take several consecutive points instead of one for the zero crossing time to be acquired. In this embodiment, three consecutive zero crossing times (Zc1, Zc2, and Zc3 in FIG. 3) are obtained.
[0014]
The zero-crossing interval of the received ultrasonic wave should always be a time interval for one cycle calculated from the center frequency. The time for one cycle when using an ultrasonic transducer with a center frequency of 40 [kHz] is 1/40000 [sec] = 25 [μsec]. In other words, the leading zero-crossing time obtained by the zero-crossing detection circuit 6 is not the ultrasonic reception time itself, but the true ultrasonic reception is received at any time obtained by rewinding an integral multiple of 25 [μsec] from the zero-crossing time. There will be time.
[0015]
That is, even if it is unclear how many times the zero-crossing time acquired is the zero-crossing time after the first wave, it is rewound by an integral multiple of one cycle from the zero-crossing time within the possible range of the ultrasonic propagation time described above. By setting the inter-vibrator distance L in which only one time is always obtained, the true ultrasonic wave propagation time can be easily estimated.
[0016]
Hereinafter, a method for suitably setting the distance between the ultrasonic transducers will be described. If the concentration range of the sample gas is known, the range of the sound velocity that propagates through the sample gas at a flow velocity of zero at each temperature can be easily calculated using Equation 1. If the molecular weight of oxygen is 32 and the molecular weight of nitrogen is 28, for example, at a temperature of 20 ° C., the sound velocity when the oxygen concentration is 0% is 349.1 [m / sec] from Equation 1, and the oxygen concentration is 100%. The speed of sound in this case is calculated as 326.6 [m / sec]. That is, when the oxygen concentration of the sample gas changes, the speed of sound in the sample gas at 20 ° C. always falls within the range of 324.6 [m / sec] to 349.1 [m / sec]. The upper and lower limits of sound speed. FIG. 4 shows a graph of the relationship between the temperature and the speed of sound, which is calculated in the range of 5 to 35 ° C. that can be taken by the sample gas temperature. As apparent from FIG. 4, the upper and lower limits of the sound speed C can be expressed as a function of the temperature T, and the upper limit of the sound speed at the temperature T is C _max (T) and the lower limit is C _min (T).
[0017]
Next, let L _s [m] be the distance between the transducers that is desired to be suitable. Since the possible range of the sound velocity is known in advance as described above, the possible range of the ultrasonic propagation time can be expressed using L _s . That is, the possible range of the ultrasonic wave propagation time is L _s / C _max (T) [sec] to L _s / C _min (T) [sec].
[0018]
In order to always have only one time obtained by rewinding from the zero cross time obtained by the zero cross time detection circuit 6 by an integral multiple of one cycle within the possible range of the ultrasonic propagation time, The range which can be taken should just be less than the time for 1 period of an ultrasonic wave (FIG. 9). If the frequency of the ultrasonic wave is fr [Hz], the time of one cycle is 1 / fr [sec]. That is, L _s that always satisfies Equation 3 below may be selected.
[0019]
[Equation 3]

[0020]
The temperature T at which the value of “L _s / C _min (T) −L _s / C _max (T)” is maximized is 5 ° C., which is the lower limit of the temperature range of the sample gas in this embodiment. C _max (5 ° C.) and C _min (5 ° C.) at 5 ° C. are C _max (5 ° C.) = 340.1 [m / sec] and C _min (5 ° C.) = 318.1 [m / sec], respectively. Furthermore, since the frequency fr of the ultrasonic wave in this embodiment is fr = 40 [kHz] = 40000 [Hz], the inter-vibrator distance L _s satisfying Expression 3 is L _s <12.3 [cm], which is approximately The two ultrasonic transducers 2 may be installed so that the inter-vibrator distance is less than 12 [cm]. In this example, 10 [cm] was adopted as the inter-vibrator distance.
[0021]
In order to measure the flow rate, ultrasonic wave transmission / reception is performed in both forward and reverse directions with respect to the flow of the sample gas, and zero cross time is required for both. If the zero cross time obtained in both the forward and reverse directions is always acquired at the same trigger position, as shown in FIG. 5, the zero cross time interval (interval A in FIG. 5) = the difference in ultrasonic propagation time ( It can be t _d ) in FIG. However, there is no guarantee that the received waveform of ultrasonic waves will be exactly the same in both forward and reverse directions, and the trigger position detected by the trigger comparator in the zero cross detection circuit 6 may be shifted in forward and reverse directions. Therefore, if the inner radius of the pipe 1 through which the sample gas flows is set so that the ultrasonic propagation time difference t _d obtained in the forward and reverse bidirectional directions is always less than one period of the received ultrasonic wave, the trigger position is set. Even when the positions are shifted in the forward and reverse directions, the trigger position can be easily adjusted. For example, the trigger position obtained when ultrasonic transmission / reception is performed in the reverse direction is forward by one cycle with respect to the trigger position obtained by performing ultrasonic transmission / reception in the forward direction with respect to the flow of the sample gas. The case is shown in FIG. If the difference in the zero crossing time is calculated assuming that the trigger positions are aligned in the forward and reverse directions, the value becomes a negative value (A in FIG. 6). If the flow rate range of the sample gas is 0 to 10 [L / min], the difference in propagation time cannot be negative. Therefore, it can be easily detected that the trigger has shifted, and B in FIG. It is possible to adopt as the propagation time difference. Conversely, the trigger position obtained when ultrasonic transmission / reception is performed in the reverse direction is behind the trigger position obtained by performing ultrasonic transmission / reception in the forward direction with respect to the flow of the sample gas. This case is shown in FIG. If the difference in zero crossing time is calculated assuming that the trigger positions are aligned in the forward and reverse directions, the value exceeds the time corresponding to one ultrasonic cycle (A in FIG. 7). However, if the ultrasonic propagation time difference t _d is always designed to be less than one period of the received ultrasonic wave, the difference in propagation time cannot be more than one period of the received ultrasonic wave. Therefore, in this case as well, it can be easily detected that the trigger has shifted, and B in FIG. 7 can be adopted as the true propagation time difference.
[0022]
Hereinafter, a method for suitably setting the inner radius of the pipe 1 through which the sample gas flows will be described. If the flow rate of the sample gas is Q [L / min] and the inner radius of the pipe 1 through which the sample gas flows is r [m], the flow velocity V [m / sec] in the pipe 1 is It is expressed in the range of 4.
[0023]
[Expression 4]

[0024]
The sound velocity V ₁ [m / sec] observed when ultrasonic waves are transmitted in the forward direction with respect to the flow of the sample gas is expressed as V [m / sec] when the sample gas is stationary. ₁ = C + V, and the sound velocity V ₂ [m / sec] observed when the ultrasonic wave is transmitted in the opposite direction to the flow of the sample gas is observed as V ₂ = C−V. When t _d [sec] is the difference in propagation time observed when ultrasonic transmission / reception is performed in both forward and reverse directions with respect to the flow of the sample gas, t _d is the distance between transducers L _s [m] It can be expressed by Equation 5.
[0025]
[Equation 5]

[0026]
Therefore, in order to ensure that the difference in propagation time t _d is always less than one period of the received ultrasonic wave, it is sufficient to always select an inner radius r that satisfies Equation 6.
[0027]
[Formula 6]

[0028]
In the present embodiment, the conditions of C and Q that maximize the left term of Expression 6 are C = C _min (5 ° C.) = 318.1 [m / sec] and Q = 10 [LPM]. Furthermore, when the inter-vibrator distance L _s = 10 [cm] = 0.1 [m] and the ultrasonic frequency fr = 40 [kHz] = 40000 [Hz] are substituted into Equation 6, r> 2.05 [mm] is obtained. The inner radius of 1 should be larger than 2.05 [mm]. In this example, 2.5 [mm] was adopted as the inner radius of the pipe 1.
[0029]
Hereinafter, the oxygen concentration of the sample gas and the flow rate measuring method in this embodiment will be described. While the sample gas is being fed, an ultrasonic transducer selected to send ultrasonic transmission pulses from the microcomputer 7 to the driver 5 and to transmit ultrasonic waves in the forward direction with the flow of the sample gas by the transmission / reception switch 4 A pulse voltage is applied to 2 and ultrasonic waves are transmitted. The ultrasonic wave received by the other ultrasonic transducer 2 is input to the zero cross detection circuit 6 via the transmission / reception switch 4, and the obtained three zero cross times (ZcF1, ZcF2, ZcF3) are used in the microcomputer. To 7 Thereafter, an ultrasonic transmission pulse is sent from the microcomputer 7 to the driver 5, and a pulse voltage is applied to the ultrasonic transducer 2 selected by the transmission / reception switch 4 to transmit the ultrasonic wave in the direction opposite to the flow of the sample gas. Is applied and ultrasonic waves are transmitted. The ultrasonic waves received by the other ultrasonic transducer 2 are input to the zero cross detection circuit 6 via the transmission / reception switch 4, and the three zero cross times (ZcB1, ZcB2, ZcB3) obtained are obtained by the microcomputer. To 7.
[0030]
From the zero cross time obtained in the forward and reverse directions with respect to the flow of the sample gas by the above operation, the deviation of the trigger position is corrected by the method shown in FIGS. _d is calculated. In calculating t _d , the time detection error can be reduced by averaging the values of A shown in FIG. 5 or the values of B shown in FIGS. 6 and 7. is there. Further, the average Zc_ave of the first zero cross time obtained by aligning the trigger positions of the zero cross time obtained by forward / reverse bidirectional ultrasonic transmission / reception is calculated. Zc_ave can be regarded as a zero cross time obtained when ultrasonic transmission / reception is performed when the flow rate of the sample gas is zero. For example, in the state shown in FIG. 5, Zc_ave can be obtained by the following Expression 7 (FIG. 8).
[0031]
[Expression 7]

[0032]
Similarly, if it is in the state shown in FIG. 6, it can obtain | require by Formula 8 (not shown).
[0033]
[Equation 8]

[0034]
Furthermore, if it is in the state shown in FIG. 7, it can obtain | require by Formula 9 (not shown).
[0035]
[Equation 9]

[0036]
Subsequently, the microcomputer 7 sets the distance between the two ultrasonic transducers to L _s [m] (in this embodiment, L _s = 0.1 [m]), and sets the output T ° C. of the temperature sensor 3 to Read, and calculate the ultrasonic propagation time range L _s / C _max (T) [sec] to L _s / C _min (T) [sec] according to the temperature T ° C. of the sample gas. Further, until the ultrasonic wave propagation time is within the range from the average Zc_ave of the zero crossing time to the ultrasonic wave propagation time, an integral multiple of the time of one period of the received ultrasonic wave = 25 [μsec] is rewound, and the ultrasonic wave propagation time t _s [ sec] is determined (FIG. 9). From this result, the ultrasonic propagation velocity C _s [m / sec] in the stationary sample gas can be obtained by the following equation 10.
[0037]
[Expression 10]

[0038]
Here, when the molecular weight of oxygen is M _O2 , the molecular weight of nitrogen is M _N2 , T [° C] of the temperature sensor output is converted to T _s [K], and the desired oxygen concentration is P _s. The following equation is obtained.
[0039]
[Expression 11]

[0040]
From Equation 11, the oxygen concentration of the sample gas can be measured as 100 × P _s [%]. Alternatively, the oxygen concentration of the sample gas can be obtained as a ratio of the ultrasonic propagation velocity in the sample gas and the ultrasonic propagation velocity in the gas of 100% oxygen and 100% nitrogen. That is, if Equation 1 is used, the ultrasonic propagation velocity C _O2 [m / sec] in 100% oxygen and the ultrasonic propagation velocity C _N2 [m / sec] in 100% nitrogen can be easily obtained at the temperature T _s [K]. can be obtained, using the ultrasonic propagation velocity C _s in the sample gas [m / sec], by equation 12 below, it can be calculated P _s.
[0041]
[Expression 12]

[0042]
The above calculation is performed by the microcomputer 7, and the concentration measurement result is displayed on the display 8.
[0043]
When the flow rate measurement, the ultrasonic wave propagation time t _s of the sample gas at rest previously obtained using the ultrasonic wave propagation time difference t _d, when carrying out the transmission and reception of ultrasonic waves in the forward direction to the flow of sample gas The ultrasonic propagation time t _s1 and the ultrasonic propagation time t _s2 when ultrasonic transmission / reception is performed in the opposite direction are obtained by Expressions 13 and 14.
[0044]
[Formula 13]

[0045]
[Expression 14]

[0046]
That is, the ultrasonic propagation velocity V _s1 [m / sec] measured when ultrasonic waves are transmitted in the forward direction with respect to the flow of the sample gas, and the ultrasonic propagation measured when ultrasonic waves are transmitted in the reverse direction The velocity V _s2 [m / sec] can be obtained by the following equations, respectively.
[0047]
[Expression 15]

[0048]
[Expression 16]

[0049]
Furthermore, from Equation 2, the flow velocity V _s [m / sec] of the sample gas can be obtained by the following equation.
[0050]
[Expression 17]

[0051]
If the flow velocity V _s [m / sec] is obtained, the flow rate Q _s [L / min] can be obtained from Equation 18 if the inner radius of the pipe 1 through which the sample gas flows is r _s [m].
[0052]
[Formula 18]

[0053]
The above calculation is performed in the microcomputer 7, and the flow measurement result is displayed on the display 8.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of ultrasonic oxygen concentration flow rate measuring means of the present invention.
FIG. 2 shows an example of an ultrasonic reception waveform.
FIG. 3 shows an example of a zero cross time detection method by a zero cross time detection circuit.
FIG. 4 shows the relationship between temperature and sound speed.
FIG. 5 shows the relationship between the ultrasonic propagation time difference and the zero cross time interval when the trigger positions are aligned.
FIG. 6 shows ultrasonic wave propagation in the case where the trigger position obtained when ultrasonic transmission / reception is performed in the reverse direction is one period ahead of the trigger position obtained by performing ultrasonic transmission / reception in the forward direction. Relationship between time difference and zero crossing time interval.
FIG. 7 shows ultrasonic wave propagation when the trigger position obtained when ultrasonic transmission / reception is performed in the reverse direction is behind the trigger position obtained by performing ultrasonic transmission / reception in the forward direction by one cycle. Relationship between time difference and zero crossing time interval.
FIG. 8 shows an example of obtaining a zero cross time obtained when ultrasonic transmission / reception is performed in a stationary sample gas.
FIG. 9 shows an example of obtaining ultrasonic propagation time in a stationary sample gas.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piping 2 Ultrasonic vibrator 3 Temperature sensor 4 Transmission / reception switching device 5 Driver 6 Zero cross detection circuit 7 Microcomputer 8 Display device 9 Non-volatile memory

Claims

Ultrasonic gas concentration flow rate measuring sample gas concentration and / or flow rate with two ultrasonic transducers arranged facing each other in pipe through which sample gas flows, zero-crossing time detection means of received ultrasonic wave, temperature sensor In the measuring apparatus, the zero-crossing time detecting means detects two or more consecutive zero-crossing times from the received waveform of ultrasonic waves transmitted and received in both forward and reverse directions with respect to the flow of the sample gas. Aligning the obtained trigger positions for each zero-crossing time, estimating the zero-crossing time obtained when ultrasonic transmission / reception is performed in a stationary sample gas from the average value of the zero-crossing time where the trigger positions are aligned, and the temperature Based on the output of the sensor, the possible range of the true ultrasonic propagation time is derived, and the estimated stationary until the ultrasonic propagation time is within the possible range. Ultrasonic gas concentration flow measuring apparatus characterized by comprising calculating means for calculating a true ultrasonic wave propagation time by unwinding integral multiple one period of time of the received ultrasonic waves from said zero crossing time in the Npurugasu.

Based on the concentration range and the temperature range of the sample gas, the range of the range of the true ultrasonic wave propagation time obtained when ultrasonic transmission / reception is performed in the sample gas is the time for one period of the received ultrasonic wave. The ultrasonic gas concentration flow measuring device according to claim 1, wherein the distance between the ultrasonic transducers is set so as to be less than the value.

The ultrasonic gas concentration flow rate measuring apparatus according to claim 1 or 2, wherein a distance (L) between the ultrasonic transducers satisfies the following formula.
L / C _min (T _min )-L / C _max (T _min ) <1 / fr
However,
C _min (T _min ): Lower limit value of the theoretical sound velocity range of ultrasonic waves propagating in a stationary sample gas calculated from the sample gas concentration range at the sample gas temperature lower limit value T _min ° C [m / sec]
C _max (T _min ): Upper limit value [m / sec] of the theoretical sound velocity range of the ultrasonic wave propagating through the stationary sample gas calculated from the sample gas concentration range at the sample gas temperature lower limit value T _min ° C.
fr: Received frequency [Hz] of ultrasonic wave propagating in sample gas

The calculation means further obtains a difference between the zero cross times at which the trigger positions are aligned , and reverses the flow of the sample gas based on the difference between the true ultrasonic propagation time in the already obtained stationary sample gas and the zero cross time. by obtaining the difference between the speed of sound in both directions, the reception ultrasonic wave without obtaining the waveform information, and Turkey to calculating the flow rate of sample gas according to any one of claims 1 to 3, characterized Ultrasonic gas concentration flow measurement device.

Based on the concentration range, temperature range, and flow rate range of the sample gas, the difference in the ultrasonic propagation time that is obtained in both forward and reverse directions with respect to the sample gas flow is one of the received ultrasonic waves. It sets so that it may become less than the time for a period, The ultrasonic type gas concentration flow measuring device of any one of Claims 1-4 characterized by the above-mentioned.

The ultrasonic gas concentration flow measuring device according to any one of claims 1 to 5, wherein an inner radius (r) of the pipe satisfies a condition of the following formula.
L / (C _min (T _min ) -Q _max / (60000πr ² )) − L / (C _min (T _min ) + Q _max / (60000πr ² )) <1 / fr
However,
C _min (T _min ): Lower limit value of the theoretical sound velocity range of ultrasonic waves propagating in a stationary sample gas calculated from the sample gas concentration range at the sample gas temperature lower limit value T _min ° C [m / sec]
Q _max : Upper limit of sample gas flow [L / min]
fr: Received frequency [Hz] of ultrasonic wave propagating in sample gas

Detecting two or more consecutive zero cross times from the received waveform of ultrasonic waves transmitted / received in both forward and reverse directions with respect to the flow of the sample gas, and aligning the trigger positions of the respective zero cross times obtained in the forward and reverse directions , A step of estimating a zero cross time obtained when ultrasonic wave transmission / reception is performed in a stationary sample gas from an average value of the zero cross time at which the trigger positions are aligned, a true ultrasonic wave propagation based on the temperature of the sample gas True time is derived by deriving the time range that can be taken, and by rewinding the time of one period of the received ultrasound from the zero-crossing time in the estimated stationary sample gas by an integral multiple until the time range is reached. Measuring the concentration of the sample gas without obtaining waveform information of the received ultrasonic wave Ultrasonic gas concentration flow measuring method.

Based on the concentration range and temperature range of the sample gas, the width of the range of the true ultrasonic wave propagation time obtained when ultrasonic transmission / reception is performed in the sample gas is equal to one period of the received ultrasonic wave. The ultrasonic gas concentration flow rate measuring method according to claim 7, wherein the distance between the ultrasonic transducers is set to be less than time.

9. The ultrasonic gas concentration flow rate measuring method according to claim 8, wherein a distance L satisfying the following equation is selected as a method of setting the distance between the ultrasonic transducers.
L / C _min (T _min ) − L / C _max (T _min ) <1 / fr
However,
C _min (T _min ): Lower limit value of the theoretical sound velocity range of ultrasonic waves propagating in a stationary sample gas calculated from the sample gas concentration range at the sample gas temperature lower limit value T _min ° C [m / sec]
C _max (T _min ): Upper limit value [m / sec] of the theoretical sound velocity range of the ultrasonic wave propagating through the stationary sample gas calculated from the sample gas concentration range at the sample gas temperature lower limit value T _min ° C.
fr: Received frequency [Hz] of ultrasonic wave propagating in sample gas

Detect two or more consecutive zero cross times from the received waveform of ultrasonic waves transmitted and received in both forward and reverse directions with respect to the flow of sample gas, and align the trigger positions of each zero cross time obtained in forward and reverse directions, The difference in the zero crossing time with the same trigger position is obtained, and the difference between the sound velocity in the forward and reverse directions with respect to the sample gas flow is determined from the difference between the true ultrasonic propagation time in the already obtained stationary sample gas and the zero crossing time. The ultrasonic gas concentration flow rate measuring method according to claim 8, wherein the flow rate of the sample gas is measured without obtaining waveform information of the received ultrasonic wave by obtaining the above.

Based on the concentration range, temperature range, and flow rate range of the sample gas so that the difference in ultrasonic propagation time obtained in both forward and reverse directions with respect to the sample gas flow is less than the time of one cycle of the received ultrasonic wave. The ultrasonic gas concentration flow rate measuring method according to any one of claims 8 to 10, wherein the trigger position of the zero crossing time is aligned by setting the inner radius of the pipe through which the sample gas flows.

The ultrasonic gas concentration according to any one of claims 8 to 11, wherein an inner radius (r) satisfying the following equation is selected as a method of setting an inner radius of a pipe through which the sample gas flows. Flow rate measurement method.
L / (C _min (T _min )) − Q _max / (60000πr ² )) − L / (C _min (T _min ) + Q _max / (60000πr ² )) <1 / fr
However,
C _min (T _min ): Lower limit value of the theoretical sound velocity range of ultrasonic waves propagating in a stationary sample gas calculated from the sample gas concentration range at the sample gas temperature lower limit value T _min ° C [m / sec]
Q _max : Upper limit of sample gas flow [L / min]
fr: Received frequency [Hz] of ultrasonic wave propagating in sample gas

Ultrasonic gas concentration flow rate measuring sample gas concentration and / or flow rate with two ultrasonic transducers arranged facing each other in pipe through which sample gas flows, zero-crossing time detection means of received ultrasonic wave, temperature sensor An ultrasonic gas concentration flow rate measuring device, wherein the distance (L) between the ultrasonic transducers is installed so as to satisfy the following formula.
L / C _min (T _min ) − L / C _max (T _min ) <1 / fr
However,
C _min (T _min ): Lower limit value of the theoretical sound velocity range of ultrasonic waves propagating in a stationary sample gas calculated from the sample gas concentration range at the sample gas temperature lower limit value T _min ° C [m / sec]
C _max (T _min ): Upper limit value [m / sec] of the theoretical sound velocity range of the ultrasonic wave propagating through the stationary sample gas calculated from the sample gas concentration range at the sample gas temperature lower limit value T _min ° C.
fr: Received frequency [Hz] of ultrasonic wave propagating in sample gas

The ultrasonic gas concentration flow rate measuring device according to claim 13, wherein the inner radius (r) of the pipe satisfies the following formula.
L / (C _min (T _min ) -Q _max / (60000πr ² )) − L / (C _min (T _min ) + Q _max / (60000πr ² )) <1 / fr
However,
C _min (T _min ): Lower limit value of the theoretical sound velocity range of ultrasonic waves propagating in a stationary sample gas calculated from the sample gas concentration range at the sample gas temperature lower limit value T _min ° C [m / sec]
Q _max : Upper limit of sample gas flow [L / min]
fr: Received frequency [Hz] of ultrasonic wave propagating in sample gas