JP4212374B2

JP4212374B2 - Ultrasonic flow meter

Info

Publication number: JP4212374B2
Application number: JP2003031978A
Authority: JP
Inventors: 真司平野
Original assignee: Ricoh Elemex Corp
Current assignee: Ricoh Elemex Corp
Priority date: 2003-02-10
Filing date: 2003-02-10
Publication date: 2009-01-21
Anticipated expiration: 2023-02-10
Also published as: JP2004239868A

Description

【０００１】
【発明の属する技術分野】
本発明は、超音波流量計に関する。
【０００２】
【従来の技術】
従来、都市ガス、水などの流体の流量を計測する流量計測装置として、超音波を利用して流速を測定する超音波流量計が知られている。その際の測定原理として、一般には「伝搬時間差法」が用いられる。これは、流路の流体流れ方向上手側及び下手側に一対の超音波送受信部を設け、超音波信号の送受信を交互に切り替えて、流れ方向上手側の超音波送信部（送信側振動子）から流れ方向下手側の超音波受信部（受信側振動子）に到達するまでの時間（以下、順方向到達時間という）と、流れ方向下手側の超音波送信部（送信側振動子）から流れ方向上手側の超音波受信部（受信側振動子）に到達するまでの時間（以下、逆方向到達時間という）とを計測して、両者の時間差から流路を流れる流体の平均流速及び流量を求める方法である。
【０００３】
そして、超音波受信信号波形は受信初期においてはノイズ混入等の影響により十分な振幅レベルを有しない不規則波形部分を有するので、順方向到達時間（又は逆方向到達時間）を計測するためのトリガー波（例えば第３波）を適切に定め、測定精度を向上させるための種々の試みがなされている。例えば、特許文献１には、トリガーレベル（比較レベル）の最適化を行うことにより、測定精度を向上させる技術が開示されている。
【０００４】
【特許文献１】
特開２００２−１３９５８号公報
【０００５】
【発明が解決しようとする課題】
しかし、特許文献１等に開示された改良は与えられた超音波受信信号波形に対する信号処理に留まり、受信開始からトリガー波までに経過した時間（トリガー波が第３波の場合には１．５周期分）は、以前と同様に計測された順方向到達時間（又は逆方向到達時間）から減算補正しなければならない。ところが、超音波振動子の発振周波数（固有振動数）は温度依存性を有するため、周囲の環境温度変化に伴って補正値を修正し直す必要があり、根本的な測定精度の向上には至っていなかった。また、信号処理の複雑化に伴って、測定スピードが遅くなったり測定用電池の消耗が激しくなったりするおそれもあった。
【０００６】
そこで本発明の課題は、測定スピードを低下させたり測定用電池を著しく消耗させたりすることなく、測定精度の大幅な向上を図ることのできる超音波流量計を提供することにある。
【０００７】
【課題を解決するための手段及び発明の効果】
上記課題を解決するために本発明に係る超音波流量計は、
流体を通過させるための流路と、
その流路に、流体の流れ方向上手側又は下手側に向けて超音波を発振した後、流れ方向上手側又は下手側から到来する超音波を受信する送受信振動子が取り付けられた超音波送受信部と、
その超音波送受信部の流れ方向上手側又は下手側の前記流路に、前記送受信振動子から発振された超音波を受信し、かつ少なくともその超音波の一部を前記送受信振動子に向けて反射する受信反射振動子が取り付けられた超音波受信反射部と、
前記送受信振動子が超音波を発振してから前記受信反射振動子がその超音波を受信するまでの直接到達時間を計測するとともに、その受信反射振動子に超音波が到達した時点から当該受信反射振動子で反射された超音波を前記送受信振動子が受信するまでの反射到達時間を計測する時間計測手段と、
を備えることを特徴とする。
【０００８】
この超音波流量計によれば、反射到達時間は、受信反射振動子に超音波が到達して受信した時点から受信反射振動子で反射された超音波を送受信振動子が受信するまでの時間であるから、受信開始からトリガー波までに経過した時間を減算補正する必要がなくなり、測定精度の大幅な向上を図ることができる。また、超音波受信信号波形に対して複雑な信号処理を要しないので、測定スピードが遅くなったり測定用電池が消耗したりすることを防止できる。
【０００９】
なお、従来の超音波流量計（例えば上記特許文献１参照）においても、超音波受信部において超音波を受信する際、受信側振動子では超音波送信部（送信側振動子）へ向けて超音波の反射が必然的に発生している。しかしながら、これまで反射波はノイズ成分として取り扱われ、測定精度を向上させるためには除外すべきものと考えられるのが一般的であった。これに対して、本発明では、超音波受信信号波形そのものから誤差・補正の要素を取り除き、時間計測手段での反射到達時間の測定精度を向上させるために、超音波流量計において反射超音波を積極的に活用することとしている。
【００１０】
また、上記課題を解決するために本発明に係る超音波流量計を反射型Ｖ字配列に適用した場合、
流体を通過させるための流路と、
その流路の壁に、流体の流れ方向上手側又は下手側に向けて超音波を発振した後、流れ方向上手側又は下手側から到来する超音波を受信する送受信振動子が取り付けられた超音波送受信部と、
流体の流れ方向軸線と前記送受信振動子とを含む流路断面において、流れ方向上手側又は下手側の前記流路の壁に、前記送受信振動子から発振され当該流路の内壁面で少なくとも１回反射された超音波を受信し、かつ少なくともその超音波の一部を前記送受信振動子に向けて反射する受信反射振動子が取り付けられた超音波受信反射部と、
前記送受信振動子が超音波を発振してから前記受信反射振動子がその超音波を受信するまでの直接到達時間を計測するとともに、その受信反射振動子に超音波が到達した時点から当該受信反射振動子で反射された超音波を前記送受信振動子が受信するまでの反射到達時間を計測する時間計測手段と、
を備えることを特徴とする。
【００１１】
反射型Ｖ字配列の超音波流量計に用いた場合にも、上記と同様に反射到達時間に減算補正する必要がないので、測定精度の大幅な向上を図ることができる。しかも、送受信振動子から超音波を発振するのみで、受信反射振動子からは超音波を発振しなくてすむので、超音波受信信号波形に対して複雑な信号処理を要しないこととあわせて、コストの低減、測定スピードの向上及び測定用電池の消耗防止に効果を発揮する。加えて、反射型Ｖ字配列では相対的に伝搬距離を長くできるので、時間計測手段での反射到達時間の測定精度をさらに向上させることができる。
【００１２】
したがって、流路が流体の流れ方向に直交する断面において矩形状に形成されるとともに、流路の流れ方向直交断面のうち短辺の一方を形成する壁面に送受信振動子及び受信反射振動子が流れ方向に所定距離を隔てて取り付けられ、かつ他方の短辺を形成する壁面を反射面とすることにより、流路に配置される超音波測線が反射型Ｖ字配列に構成される。このように、矩形断面流路の短辺側壁面を振動子取付面及び反射面に形成することによって、薄型の小型コンパクトな計測部を有する超音波流量計とすることができる。
【００１３】
さらに、上記課題を解決するために本発明に係る超音波流量計を透過型Ｚ配列に適用した場合、
流体を通過させるための流路と、
その流路の壁に、流体の流れ方向上手側又は下手側に向けて超音波を発振した後、流れ方向上手側又は下手側から到来する超音波を受信する送受信振動子が取り付けられた超音波送受信部と、
流体の流れ方向軸線と前記送受信振動子とを含む流路断面において、流れ方向上手側又は下手側の前記超音波送受信部の設置側と対向する前記流路の壁に、前記超音波送受信部から発振された超音波を受信し、かつ少なくともその超音波の一部を前記送受信振動子に向けて反射する受信反射振動子が取り付けられた超音波受信反射部と、
前記送受信振動子が超音波を発振してから前記受信反射振動子がその超音波を受信するまでの直接到達時間を計測するとともに、その受信反射振動子に超音波が到達した時点から当該受信反射振動子で反射された超音波を前記送受信振動子が受信するまでの反射到達時間を計測する時間計測手段と、
を備えることを特徴とする。
【００１４】
透過型Ｚ配列の超音波流量計に用いた場合にも、反射型Ｖ字配列と同様に反射到達時間に減算補正する必要がないので、測定精度の大幅な向上を図ることができる。しかも、送受信振動子から超音波を発振するのみで、受信反射振動子からは超音波を発振しなくてすむので、超音波受信信号波形に対して複雑な信号処理を要しないこととあわせて、コストの低減、測定スピードの向上及び測定用電池の消耗防止に効果を発揮する。加えて、透過型Ｚ配列では相対的に伝搬距離を短くできるので、反射波での減衰を気にせずに実施することができる。
【００１５】
そして、これらの超音波流量計において、超音波送受信部が超音波受信反射部よりも流れ方向下手側に配置され、送受信振動子は流れ方向上手側に配置された受信反射振動子に向け超音波を発振するように構成するのが好ましい。一般に、流路内に流体の流れがある場合に、流れに沿う方向（流れ方向下手側）に超音波が発振されると超音波出力が減少し、流れに逆らう方向（流れ方向上手側）に超音波が発振されると超音波出力が増加することが知られている。そこで、上記のように送受信振動子が受信反射振動子に向け超音波を発振することによって超音波出力が増加するので、受信反射振動子から送受信振動子に向う反射波の出力減少分を補って受信レベルの低下及び測定精度の低下を抑制することができる。
【００１６】
さらに、これらの超音波流量計において、時間計測手段により直接到達時間及び反射到達時間を計測するために、送受信振動子から発振され受信反射振動子で受信された直接受信信号、及び受信反射振動子で反射され送受信振動子で受信された反射受信信号を増幅する増幅手段を設け、増幅手段では、直接受信信号の増幅率よりも反射受信信号の増幅率を大に設定するとよい。送受信振動子を流れ方向下手側、受信反射振動子を流れ方向上手側に配置した場合でも、通常、反射受信信号のレベルは直接受信信号のレベルより低下する傾向にある。そこで、到達時間の計測を実行する前に反射受信信号を相対的に大なる増幅率で信号増幅しておくことにより、反射受信信号のレベル低下及び測定精度の低下をさらに抑制することができる。
【００１７】
そのために、超音波送受信部及び超音波受信反射部と増幅手段との間には、増幅手段に対して直接受信信号又は反射受信信号を切り替えて供給するための受信信号切替手段を設け、受信信号切替手段は、直接受信信号と反射受信信号との信号切替に伴い増幅手段に対して増幅率の変更指令を発するように構成することができる。これにより、反射受信信号に対して相対的に大なる増幅率で安定した信号増幅が実行される。
【００１８】
また、流路を流れる流体の流れ方向を検出する流れ検出手段を設け、流れ検出手段が、流体流れ方向の変化を検出したときに受信信号切替手段に対して直接受信信号と反射受信信号との信号切替のタイミング変更指令を発するように構成してもよい。これにより、流路内を流体が逆流する事態が発生したときにも、素早く検知して受信信号レベルの調整が行われるので、信号レベルや測定精度が低下したりするのを抑制できる。なお、流れ検出手段として、本発明の構成要件である時間計測手段（の計測データ）を用いたり、超音波流量計とは別個に差圧式、面積式、渦式等の周知の流量計（又は流速計）を用いたりしてもよい。また、逆流を検出したときに、受信信号切替手段を用いて直接受信信号と反射受信信号とを切り替える手法（第一手法）に代えてあるいは加えて、計測切替手段を用いて超音波送受信部と超音波受信反射部とを切り替える手法（第二手法）を採用してもよい。その際、逆流流量小のときには第一手法を実施しつつ警告表示、逆流流量大のときにはまず第二手法の実施、さらに流量増加で遮断弁作動、のように使い分けることもできる。
【００１９】
次に、上記課題を解決するために本発明に係る超音波流量計は、
流体を通過させるための流路と、
流れ方向上手側又は下手側に向けて超音波を発振する機能と、流れ方向上手側又は下手側から到来する超音波を受信する機能と、少なくとも到来した超音波の一部を流れ方向上手側又は下手側に向けて反射する機能とを有する送受信反射振動子を具備し、相互に超音波の発振・受信・反射が行えるように、前記流路の流れ方向上手側と下手側とに配置された一対の超音波送受信反射部と、
前記一対の送受信反射振動子のうち一方の前記送受信反射振動子（以下、第一振動子という）を発振・受信側とし他方の前記送受信反射振動子（以下、第二振動子という）を受信・反射側とする第一回計測と、前記第二振動子を発振・受信側とし前記第一振動子を受信・反射側とする第二回計測とを切り替える計測切替手段と、
前記第一回計測において、前記第二振動子に超音波が到達した時点から当該第二振動子で反射された超音波を前記第一振動子が受信するまでの第一回反射到達時間を計測するとともに、前記第二回計測において、前記第一振動子に超音波が到達した時点から当該第一振動子で反射された超音波を前記第二振動子が受信するまでの第二回反射到達時間を計測する時間計測手段と、
を備えることを特徴とする。
【００２０】
この超音波流量計によれば、第一回計測において第一回反射到達時間は、第二振動子に超音波が到達して受信した時点から第二振動子で反射された超音波を第一振動子が受信するまでの時間である。一方、第二回計測において第二回反射到達時間は、第一振動子に超音波が到達して受信した時点から第一振動子で反射された超音波を第二振動子が受信するまでの時間である。したがって、順方向到達時間と逆方向到達時間とに第一回反射到達時間及び第二回反射到達時間を当てはめれば、順方向到達時間と逆方向到達時間の計測値のいずれにおいても、受信開始からトリガー波までに経過した時間を減算補正する必要がなくなり、測定精度はさらに大幅に向上する。また、超音波受信信号波形に対して複雑な信号処理を要しないので、測定スピードが遅くなったり測定用電池が消耗したりすることを防止できる。
【００２１】
【発明の実施の形態】
（実施例１）
次に、本発明の実施の形態を図面を用いて説明する。図１は、一般住宅用ガスメータ等として用いられる超音波流量計の一実施例の基本構成を示す。この超音波流量計１００の流量測定用の流路１には、流量測定用ガス（流体）が流れ方向軸線Ｏに沿って図示の流れ方向に流通（平均流速ｖ）している。流路１の壁１０には、流れ方向下手側の超音波送受信部２と流れ方向上手側の超音波受信反射部３とが取り付けられ、図１に示すように、流れ方向軸線Ｏと超音波送受信部２とを含む流路断面において、超音波受信反射部３は超音波送信部２設置側の壁１０に位置している。
【００２２】
測定用の流路１は、少なくとも超音波送受信部２―超音波受信反射部３間において流れ方向軸線Ｏが直線状であり、軸断面の形状及び断面積が流れ方向において同一に形成されている。測定対象がガスの場合、測定用流路１の軸断面形状は壁１０により閉鎖された空間を形成するものであればよく、例えば、円形状、楕円形状、正方形状、矩形状等のいずれを採用してもよい。図１に示す流路１は矩形状に形成され、流路１の流れ方向直交断面のうち一方の短辺１１ａを形成する壁面（取付面）に送受信振動子２１及び受信反射振動子３１が流れ方向に所定距離を隔てて取り付けられ、かつ他方の短辺１１ｂを形成する壁面を反射面とすることにより、流路１に配置される超音波測線Ｍが反射型Ｖ字配列に構成される。なお、測定対象が水等の液体であれば、測定用流路１の軸断面形状として壁１０の天頂部が大気中に開放されたオープン形状（例えば半円形状等）を採用できる場合がある。
【００２３】
超音波送受信部２は、流路１の壁１０に固定され、圧電素子、振動板、電極板等から構成される送受信振動子２１と、この送受信振動子２１を発振させるための駆動電圧回路等から構成される送信手段２２とを備えている。送受信振動子２１は、流体の流れ方向上手側（超音波受信反射部３側）に向けて超音波を発振した後、後述する受信反射振動子３１で反射され流れ方向上手側から到来する超音波を受信する。
【００２４】
超音波受信反射部３は、超音波送受信部２（送受信振動子２１）よりも流れ方向上手側の壁１０に固定され、圧電素子、振動板、電極板等から構成される受信反射振動子３１と、この受信反射振動子３１又は送受信振動子２１の発生電圧を検出するための電圧検出回路等から構成される受信手段３２とを備えている。受信反射振動子３１は、送受信振動子２１から発振され流路１の内壁面（反射面１２）で１回反射された超音波を受信し、かつ少なくともその超音波の一部を送受信振動子２１に向けて反射する。受信反射振動子３１で反射された超音波は測線Ｍに沿ってもと来た径路を逆戻りし、送受信振動子２１で受信される。
【００２５】
図１において、ガスの平均流速をｖ、ガス中を伝搬する音速をｃ、超音波の進行方向（測線Ｍ）とガスの流れ方向（流れ方向軸線Ｏ）とのなす角をθ（以下、測線角という）、超音波の伝搬距離をＬ（＝Ｄ／ｃｏｓθ）とすると、順方向到達時間Ｔｄ及び逆方向到達時間Ｔｕはそれぞれ次のように表わされる。
Ｔｄ＝Ｌ／（ｃ＋ｖ・ｃｏｓθ）（１）
Ｔｕ＝Ｌ／（ｃ−ｖ・ｃｏｓθ）（２）
（１）、（２）式の逆数をとり、その差をとれば次式が得られる。
１／Ｔｄ−１／Ｔｕ＝２ｖ・ｃｏｓθ／Ｌ（３）
したがって、順方向到達時間Ｔｄと逆方向到達時間Ｔｕの測定から、ガスの平均流速ｖと流量Ｑが次式により求められる。ただし、Ａは流路１の断面積である。
ｖ＝（１／Ｔｄ−１／Ｔｕ）Ｌ／２ｃｏｓθ （４）
Ｑ＝ｖ・Ａ（５）
このように、ガスの温度・含有成分等に依存する音速ｃを（４）式から消去することで、測定値（到達時間Ｔｄ，Ｔｕ）と一定値（伝搬距離Ｌ，測線角θ）とから流速ｖが得られる利点を有している。
【００２６】
そこで、図１に示すように、超音波流量計１００には、計測部として、受信反射振動子３１又は送受信振動子２１により得られる受信側振動子出力を増幅する増幅手段４と、後述する「ゼロクロス法」により出力波形から超音波到達時点を検出するゼロクロスポイント検出手段５と、超音波到達時間を測定する時間計測手段６と、受信手段３２で処理すべき信号を切り替える受信信号切替手段７１（切替手段７）とが備えられている。
【００２７】
増幅手段４は、送受信振動子２１から発振され受信反射振動子３１で受信された直接受信信号、及び受信反射振動子３１で反射され送受信振動子２１で受信された反射受信信号を増幅する。そして、直接受信信号の増幅率よりも反射受信信号の増幅率が大となるように設定されている（図３参照）。
【００２８】
受信信号切替手段７１（切替手段７）は、超音波送受信部２及び超音波受信反射部３と増幅手段４との間に設けられ、増幅手段４に対して、受信反射振動子３１で受信された直接受信信号又は送受信振動子２１で受信された反射受信信号を受信手段３２で切り替えて供給する。また、受信信号切替手段７１は、これら直接受信信号と反射受信信号との信号切替に伴い増幅手段４に対して増幅率の変更指令を発する。
【００２９】
時間計測手段６は、送受信振動子２１が超音波を発振してから受信反射振動子３１がその超音波を受信するまでの直接到達時間（図１では上記式（２）の逆方向到達時間Ｔｕに相当する）を計測する。また、時間計測手段６は、受信反射振動子３１に超音波が到達した時点から受信反射振動子３１で反射された超音波を送受信振動子２１が受信するまでの反射到達時間（図１では上記式（１）の順方向到達時間Ｔｄに相当する）を計測する。
【００３０】
ところで、前述の式（１），（２）からも明らかな通り、時間計測手段６で計測される順方向到達時間Ｔｄは逆方向到達時間Ｔｕよりも小さくなる。したがって、時間計測手段６は、流路１を流れる流体の流れ方向を検出する流れ検出手段としての機能をも有することができる。つまり、流れ検出手段６は、流体流れ方向の変化を検出したときに受信信号切替手段７１に対して直接受信信号と反射受信信号との信号切替のタイミング変更指令を発することにより、以後の信号処理が流体の流れ方向に沿って行われるように修正する。
【００３１】
次に、図２に一例として示す計測部のブロック図と図３に示すタイミングチャートとに基づいて、超音波流量計１００の作動を説明する。図２に示すように、受信側振動子出力（ここでは、送受信振動子２１出力Ｖ0d又は受信反射振動子３１出力Ｖ0u）は、増幅手段４を構成する増幅器４１（例えばオペアンプ）で電圧増幅（例えば非反転増幅）され、増幅信号Ｖａがゼロクロスポイント検出手段５に入力される。ゼロクロスポイント検出手段５において、増幅信号Ｖａはゼロクロス型コンパレータ５１（第一コンパレータ）に入力（例えば非反転入力）され、差動型コンパレータ５２（第二コンパレータ）に入力（例えば反転入力）される。コンパレータ出力Ｖｂ，Ｖｃは、ＲＳフリップフロップ回路（以下、ＲＳＦＦ回路という）５３のポート＃Ｓ，＃Ｒへ各々入力される。ＲＳＦＦ回路５３のポート＃Ｑ出力Ｖｄにより、単安定マルチバイブレータ等で構成されるゼロクロスポイントパルス発生回路５４が出力波形Ｖａにおける超音波到達時点を検出し、ゼロクロスポイント検出信号Ｖｅを時間計測手段６に出力する。時間計測手段６では、ゼロクロスポイント検出信号Ｖｅに基づき、クロックパルス発生回路６２（例えば水晶発振子、無安定マルチバイブレータ）からのクロックパルス数をパルスカウンタ回路６１（例えばＪＫフリップフロップ回路）でカウントして到達時間検出信号Ｖｆが出力される。なお、差動型コンパレータ５２出力Ｖｃ，ＲＳＦＦ回路５３のポート＃Ｑ出力Ｖｄ，ゼロクロスポイント検出信号Ｖｅの各出力は、受信信号切替出力Ｖｇにより各々１回のみの出力で終了するように制御されている（図３参照）。
【００３２】
（１）直接到達時間Ｔｕ（逆方向到達時間）の計測
図３において、受信手段３２では受信信号切替手段７１により、受信側振動子出力（図２参照）として、まず受信反射振動子３１の出力Ｖ0uが選択される。
増幅信号Ｖａ（受信反射振動子３１の直接受信信号）は、受信初期においてはノイズ混入等の影響により十分な振幅（発生電圧）レベルを有しない不規則波形信号であり、先頭から第ｎ番目（図では第▲３▼番目）の波形部分においてようやく安定して測定可能な振幅レベルに達するのが通常である。そこで、超音波受信出力の増幅信号Ｖａにおいて精度のよい時間測定を可能にするために、以下に述べるゼロクロス法が一般に採用されている。つまり、「差動型コンパレータ５２（図２参照）に入力設定された閾値ＶSを超える（又は下回る）に至る波形部分（図では第▲３▼波）をトリガー波とし、このトリガー波の振幅（又は位相）がゼロとなるゼロクロス点を、増幅信号Ｖａ（又はその派生信号）の波形上でゼロクロスポイントパルス発生回路５４（図２参照）により検出する方法」である。
【００３３】
具体的には、増幅信号Ｖａの波形に対してゼロクロス法は次のように適用される。増幅信号Ｖａが非反転入力されたゼロクロス型コンパレータ５１では、増幅信号Ｖａの波形のうち振幅（発生電圧）が正の波形部分（第▲１▼波，第▲３▼波，第▲５▼波…）に対応してＨとなるパルスが、第一コンパレータ出力Ｖｂとして断続的に出力される。一方、負極性の増幅信号Ｖａと正極性の閾値ＶSとが入力された差動型コンパレータ５２では、閾値ＶSを超える波形部分（第▲３▼波，第▲５▼波…の頂部）に対応してＬとなるパルスが、第二コンパレータ出力Ｖｃとして断続的に出力される。
【００３４】
第二コンパレータ出力Ｖｃで最初に閾値ＶSを超えるトリガー波（第▲３▼波）のパルス信号が入力されるまではＲＳＦＦ回路５３のポート＃ＲにはＨが継続して入力されるので、ＲＳＦＦ回路５３のポート＃Ｑ出力ＶｄはＬに維持される。第一コンパレータ出力Ｖｂから第▲３▼波の波形検出パルス信号がＲＳＦＦ回路５３のポート＃Ｓに入力（Ｈ）されている状態において、第二コンパレータ出力Ｖｃからトリガー波（第▲３▼波）の閾値ＶS検出パルス信号がポート＃Ｒに入力（Ｌ）されたとき、ポート＃Ｑ出力ＶｄはＨに変化する。そして、第一コンパレータ出力Ｖｂから第▲３▼波の波形検出パルス信号がＲＳＦＦ回路５３のポート＃Ｓに入力されなくなるまでポート＃Ｑ出力ＶｄはＨに維持され、ポート＃Ｓへの入力がＬとなったときにポート＃Ｑ出力ＶｄはＬとなる。
【００３５】
ゼロクロスポイントパルス発生回路５４は、ＲＳＦＦ回路５３のポート＃Ｑ出力Ｖｄの立ち下がりエッジを検出し、ゼロクロス点に対応してＨとなるパルスをゼロクロスポイント検出信号Ｖｅとして出力する。パルスカウンタ回路６１は、ゼロクロスポイント検出パルス信号（Ｖｅ）と送信側振動子２１（図１参照）の超音波送信パルス信号との間のクロックパルス数をカウントして、到達時間検出信号Ｖｆを出力する。このようにして到達時間検出信号Ｖｆで得られた直接到達時間Ｔｕ（逆方向到達時間）は、実際の（真の）到達時間より長くなっている。つまり、受信開始からトリガー波（第▲３▼波）のゼロクロス点までの間（第▲１▼波〜第▲３▼波の１．５周期分）の経過時間を補正値として、検出到達時間から差し引くと実際の到達時間が得られる。
【００３６】
（２）反射到達時間Ｔｄ（順方向到達時間）の計測
図３において、受信手段３２では受信信号切替手段７１により、受信側振動子出力（図２参照）として、次に送受信振動子２１の出力Ｖ0d（反射受信信号）が選択される。そして、上述の直接到達時間Ｔｕ（逆方向到達時間）の計測と同様にして、反射到達時間Ｔｄ（順方向到達時間）の計測が行われる。このようにして到達時間検出信号Ｖｆで得られた反射到達時間Ｔｄ（順方向到達時間）は、実際の（真の）到達時間と等価なものとなっている。つまり、ここでは受信開始からゼロクロス点までの経過時間を補正値として差し引かなくてもよいので、超音波振動子の温度依存性を排除することができる。
【００３７】
（実施例２）
次に、図４は図１（実施例１）と同様に用いられる超音波流量計の他の実施例の基本構成を示す。この超音波流量計２００では、送受信振動子２１と受信反射振動子３１とが流路１を挟んで対向配置された透過型Ｚ配列に構成されている。すなわち、送受信振動子２１は、流路１の壁１０に固定され、流体の流れ方向上手側（超音波受信反射部３側）に向けて超音波を発振した後、後述する受信反射振動子３１で反射され流れ方向上手側から到来する超音波を受信する。
【００３８】
一方、受信反射振動子３１は、超音波送受信部２（送受信振動子２１）よりも流れ方向上手側の、超音波送受信部２（送受信振動子２１）の設置側と対向する流路１の壁１０に固定される。この受信反射振動子３１は、送受信振動子２１から発振された超音波を受信し、かつ少なくともその超音波の一部を送受信振動子２１に向けて反射する。受信反射振動子３１で反射された超音波は測線Ｍに沿ってもと来た径路を逆戻りし、送受信振動子２１で受信される。
【００３９】
そして、図４に示す超音波流量計２００においても、図２及び図３（実施例１）と同様に作動する。なお、図４において図１と共通する機能を有する部分には同一符号を付して説明を省略する。
【００４０】
（実施例３）
次に、図５は図１（実施例１）と同様に用いられる超音波流量計のさらに他の実施例の基本構成を示す。この超音波流量計３００では、図３（実施例１）において、順方向到達時間として反射到達時間Ｔｄが実際の（真の）到達時間と等価なものとして計測できることに着目し、さらに逆方向に超音波を発振させて、逆方向到達時間として反射到達時間Ｔｕについても、同様に実際の到達時間と等価なものとして計測しようとするものである（図７参照）。
【００４１】
図５において、計測部を図１と同様に反射型Ｖ字配列に配置している。具体的には、相互に超音波の発振・受信・反射が行えるように、流路１の流れ方向下手側と上手側とに一対の超音波送受信反射部１２，１３を配置している。流れ方向下手側に配置する超音波送受信反射部１２は、流れ方向上手側に向けて超音波を発振する機能と、流れ方向上手側から到来する超音波を受信する機能と、少なくとも到来した超音波の一部を流れ方向上手側に向けて反射する機能とを有する送受信反射振動子１２１を具備している。一方、流れ方向上手側に配置する超音波送受信反射部１３は、流れ方向下手側に向けて超音波を発振する機能と、流れ方向下手側から到来する超音波を受信する機能と、少なくとも到来した超音波の一部を流れ方向下手側に向けて反射する機能とを有する送受信反射振動子１３１を具備している。なお、図５において図１と共通する機能を有する部分には同一符号を付して説明を省略する。
【００４２】
切替手段７には、受信信号切替手段７１（図１参照）の他に、計測切替手段７２が備えられている。計測切替手段７２は、一対の送受信反射振動子１２１，１３１を用いた第一回計測と第二回計測とを切り替える機能を有する。具体的には、一対の送受信反射振動子１２１，１３１のうち一方を第一振動子１２１、他方を第二振動子１３１としたとき、
・第一回計測：第一振動子１２１を発振・受信側とし、第二振動子１３１を受信・反射側とする；
・第二回計測：第二振動子１３１を発振・受信側とし、第一振動子１２１を受信・反射側とする；
【００４３】
時間計測手段６により、第一回計測において第一回反射到達時間Ｔｄを計測し、第二回計測において第二回反射到達時間Ｔｕを計測する。ただし、第一回反射到達時間Ｔｄとは、第二振動子１３１に超音波が到達した時点から第二振動子１３１で反射された超音波を第一振動子１２１が受信するまでの時間であり、第二回反射到達時間Ｔｕとは、第一振動子１２１に超音波が到達した時点から第一振動子１２１で反射された超音波を第二振動子１３１が受信するまでの時間である。
【００４４】
次に、図６及び図７のフローチャートについて概要を説明する。まず、第一回計測において、第一振動子１２１を発振・受信側とし、第二振動子１３１を受信・反射側とすれば、図３（実施例１）と同様にして第一回反射到達時間Ｔｄが実際の（真の）到達時間と等価なものとして計測できる（図６参照）。続いて、第二回計測において、第二振動子１３１を発振・受信側とし、第一振動子１２１を受信・反射側とすれば、図３（実施例１）と同様にして第二回反射到達時間Ｔｕが実際の（真の）到達時間と等価なものとして計測できる（図７参照）。これによって、順方向到達時間と逆方向到達時間とに第一回反射到達時間Ｔｄ及び第二回反射到達時間Ｔｕを当てはめれば、順方向到達時間と逆方向到達時間の計測値のいずれにおいても、受信開始からトリガー波までに経過した時間を減算補正する必要がなくなり、測定精度が大幅に向上する。
【００４５】
実施例１において、送受信振動子２１で発振された超音波が流路の内壁面で１回反射して受信反射振動子３１に到達する場合についてのみ説明したが、内壁面での反射回数は任意に設定できる。実施例３において、計測部を反射型Ｖ字配列に配置した場合についてのみ説明したが、透過型Ｚ配列等の配置にも適用できる。
【図面の簡単な説明】
【図１】本発明に係る超音波流量計の一実施例の基本構成を示す説明図。
【図２】計測部のブロック図。
【図３】図２のタイミングチャート。
【図４】本発明に係る超音波流量計の他の実施例の基本構成を示す説明図。
【図５】本発明に係る超音波流量計のさらに他の実施例の基本構成を示す説明図。
【図６】図５において時間ｔまでのタイミングチャート。
【図７】図６に続いて時間ｔ以降のタイミングチャート。
【符号の説明】
１流路
１０壁
２超音波送受信部
２１送受信振動子
３超音波受信反射部
３１受信反射振動子
４増幅手段
６時間計測手段
７１受信信号切替手段（切替手段）
１００，２００超音波流量計
１２，１３超音波送受信反射部
１２１第一振動子
１３１第二振動子
７２計測切替手段（切替手段）
３００超音波流量計[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic flow meter.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an ultrasonic flowmeter that measures flow velocity using ultrasonic waves is known as a flow measurement device that measures the flow rate of a fluid such as city gas or water. In general, a “propagation time difference method” is used as a measurement principle at that time. This is provided with a pair of ultrasonic transmission / reception units on the upper and lower sides of the fluid flow direction of the flow path, and alternately switching the transmission / reception of ultrasonic signals, and the ultrasonic transmission unit (transmission-side transducer) on the upper side in the flow direction To the ultrasonic wave receiving unit (reception-side transducer) on the lower side in the flow direction (hereinafter referred to as the forward arrival time) and the flow from the ultrasonic transmission unit (transmission-side transducer) on the lower side in the flow direction Measure the time to reach the ultrasonic receiver (reception-side transducer) on the upper side of the direction (hereinafter referred to as reverse direction arrival time), and calculate the average flow velocity and flow rate of the fluid flowing through the flow path from the time difference between the two. It is a method to seek.
[0003]
In addition, since the ultrasonic reception signal waveform has an irregular waveform portion that does not have a sufficient amplitude level due to the influence of noise or the like in the initial reception, it is a trigger for measuring the forward arrival time (or reverse arrival time). Various attempts have been made to appropriately determine a wave (for example, the third wave) and improve measurement accuracy. For example, Patent Document 1 discloses a technique for improving measurement accuracy by optimizing a trigger level (comparison level).
[0004]
[Patent Document 1]
JP 2002-13958 A
[0005]
[Problems to be solved by the invention]
However, the improvement disclosed in Patent Document 1 and the like is limited to the signal processing for the given ultrasonic reception signal waveform, and the time elapsed from the start of reception to the trigger wave (1.5 when the trigger wave is the third wave). The period) must be subtracted from the forward arrival time (or reverse arrival time) measured as before. However, since the oscillation frequency (natural frequency) of an ultrasonic transducer is temperature-dependent, it is necessary to re-correct the correction value as the ambient temperature changes, leading to a fundamental improvement in measurement accuracy. It wasn't. Further, as the signal processing becomes complicated, there is a risk that the measurement speed becomes slow and the consumption of the measurement battery becomes intense.
[0006]
Accordingly, an object of the present invention is to provide an ultrasonic flowmeter that can greatly improve the measurement accuracy without reducing the measurement speed or significantly consuming the measurement battery.
[0007]
[Means for Solving the Problems and Effects of the Invention]
In order to solve the above problems, an ultrasonic flowmeter according to the present invention is:
A flow path for passing fluid;
An ultrasonic transmission / reception unit in which a transmission / reception transducer for receiving ultrasonic waves arriving from the upper side or lower side of the flow direction is attached to the flow path after oscillating ultrasonic waves toward the upper side or lower side of the fluid flow direction When,
The ultrasonic wave oscillated from the transmission / reception transducer is received in the flow path on the upper side or the lower side in the flow direction of the ultrasonic transmission / reception unit, and at least a part of the ultrasonic wave is reflected toward the transmission / reception transducer. An ultrasonic wave receiving / reflecting unit to which a receiving / reflecting vibrator is attached;
Measures the direct arrival time from when the transmitting / receiving transducer oscillates the ultrasonic wave until the receiving / reflecting transducer receives the ultrasonic wave, and receives and reflects the ultrasonic wave when the ultrasonic wave reaches the receiving / reflecting transducer. A time measuring means for measuring a reflection arrival time until the transmission / reception vibrator receives the ultrasonic wave reflected by the vibrator;
It is characterized by providing.
[0008]
According to this ultrasonic flowmeter, the reflection arrival time is the time from when the ultrasonic wave arrives at the reception reflective vibrator and received until the transmission / reception vibrator receives the ultrasonic wave reflected by the reception reflective vibrator. Therefore, it is not necessary to subtract and correct the time elapsed from the start of reception until the trigger wave, and the measurement accuracy can be greatly improved. In addition, since complicated signal processing is not required for the ultrasonic wave reception signal waveform, it is possible to prevent the measurement speed from being slow and the measurement battery from being consumed.
[0009]
Note that even in a conventional ultrasonic flowmeter (see, for example, Patent Document 1 above), when receiving an ultrasonic wave in the ultrasonic receiving unit, the receiving-side transducer is directed toward the ultrasonic transmitting unit (transmitting-side transducer). Acoustic reflections are inevitably generated. However, the reflected wave has been treated as a noise component so far, and it has generally been considered that it should be excluded in order to improve the measurement accuracy. On the other hand, in the present invention, in order to remove the error / correction element from the ultrasonic reception signal waveform itself and improve the measurement accuracy of the reflection arrival time by the time measuring means, the reflected ultrasonic waves are detected in the ultrasonic flowmeter. We are going to use it actively.
[0010]
In addition, when the ultrasonic flowmeter according to the present invention is applied to a reflective V-shaped array in order to solve the above problem,
A flow path for passing fluid;
Ultrasound with a transmission / reception transducer attached to the flow path wall that receives ultrasonic waves coming from the upper side or lower side in the flow direction after oscillating ultrasonic waves toward the upper or lower side in the fluid flow direction A transceiver unit;
In the cross section of the flow path including the fluid flow direction axis and the transmission / reception vibrator, the wall of the flow path on the upper or lower side in the flow direction is oscillated from the transmission / reception vibrator at least once on the inner wall surface of the flow path. An ultrasonic wave receiving / reflecting unit to which a reception reflection vibrator that receives reflected ultrasonic waves and reflects at least a part of the ultrasonic waves toward the transmission / reception vibrator is attached;
Measures the direct arrival time from when the transmitting / receiving transducer oscillates the ultrasonic wave until the receiving / reflecting transducer receives the ultrasonic wave, and receives and reflects the ultrasonic wave when the ultrasonic wave reaches the receiving / reflecting transducer. A time measuring means for measuring a reflection arrival time until the transmission / reception vibrator receives the ultrasonic wave reflected by the vibrator;
It is characterized by providing.
[0011]
Even when used in a reflection type V-shaped ultrasonic flowmeter, it is not necessary to perform subtraction correction on the reflection arrival time in the same manner as described above, so that the measurement accuracy can be greatly improved. In addition, since only the ultrasonic wave is oscillated from the transmission / reception vibrator and the ultrasonic wave is not oscillated from the reception reflection vibrator, the complicated signal processing is not required for the ultrasonic reception signal waveform. It is effective in reducing costs, improving measurement speed, and preventing battery consumption. In addition, since the propagation distance can be relatively increased in the reflective V-shaped arrangement, the measurement accuracy of the reflection arrival time by the time measuring means can be further improved.
[0012]
Therefore, the flow path is formed in a rectangular shape in a cross section perpendicular to the fluid flow direction, and the transmission / reception vibrator and the reception reflection vibrator flow on the wall surface forming one of the short sides of the cross section perpendicular to the flow direction of the flow path. The ultrasonic survey lines arranged in the flow path are configured in a reflective V-shaped array by using a wall surface that is attached at a predetermined distance in the direction and that forms the other short side as a reflection surface. Thus, by forming the short side wall surface of the rectangular cross-section flow path on the vibrator mounting surface and the reflection surface, an ultrasonic flowmeter having a thin, small and compact measuring unit can be obtained.
[0013]
Furthermore, when the ultrasonic flowmeter according to the present invention is applied to a transmissive Z array in order to solve the above problem,
A flow path for passing fluid;
Ultrasound with a transmission / reception transducer attached to the flow path wall that receives ultrasonic waves coming from the upper side or lower side in the flow direction after oscillating ultrasonic waves toward the upper or lower side in the fluid flow direction A transceiver unit;
In the cross section of the flow path including the flow direction axis of the fluid and the transmission / reception transducer, the ultrasonic transmission / reception unit is connected to the wall of the flow path facing the installation side of the ultrasonic transmission / reception unit on the upper side or lower side in the flow direction. An ultrasonic wave receiving / reflecting unit to which a receiving reflection vibrator that receives the oscillated ultrasonic wave and reflects at least a part of the ultrasonic wave toward the transmitting / receiving vibrator is attached;
Measures the direct arrival time from when the transmitting / receiving transducer oscillates the ultrasonic wave until the receiving / reflecting transducer receives the ultrasonic wave, and receives and reflects the ultrasonic wave when the ultrasonic wave reaches the receiving / reflecting transducer. A time measuring means for measuring a reflection arrival time until the transmission / reception vibrator receives the ultrasonic wave reflected by the vibrator;
It is characterized by providing.
[0014]
Even when used in an ultrasonic flowmeter with a transmissive Z array, it is not necessary to perform subtraction correction on the reflection arrival time as in the reflective V-shaped array, so that the measurement accuracy can be greatly improved. In addition, since only the ultrasonic wave is oscillated from the transmission / reception vibrator and the ultrasonic wave is not oscillated from the reception reflection vibrator, the complicated signal processing is not required for the ultrasonic reception signal waveform. It is effective in reducing costs, improving measurement speed, and preventing battery consumption. In addition, since the propagation distance can be relatively shortened in the transmission type Z array, the transmission can be carried out without worrying about attenuation by the reflected wave.
[0015]
In these ultrasonic flowmeters, the ultrasonic transmission / reception unit is arranged on the lower side in the flow direction than the ultrasonic reception reflection unit, and the transmission / reception transducer is ultrasonic waves toward the reception reflection transducer arranged on the upper side in the flow direction. Is preferably configured to oscillate. In general, when there is a fluid flow in the flow path, if ultrasonic waves are oscillated in the direction along the flow (lower side in the flow direction), the ultrasonic output decreases, and in the direction against the flow (upper side in the flow direction). It is known that the ultrasonic output increases when ultrasonic waves are oscillated. Therefore, as described above, the transmission / reception vibrator oscillates the ultrasonic wave toward the reception reflection vibrator to increase the ultrasonic output, so that the output decrease of the reflected wave from the reception reflection vibrator toward the transmission / reception vibrator is compensated. A decrease in reception level and a decrease in measurement accuracy can be suppressed.
[0016]
Further, in these ultrasonic flow meters, in order to measure the direct arrival time and the reflection arrival time by the time measuring means, the direct reception signal oscillated from the transmission / reception vibrator and received by the reception reflection vibrator, and the reception reflection vibrator Amplifying means for amplifying the reflected reception signal reflected by the transmitter / receiver transducer is provided, and the amplification means may set the amplification factor of the reflected reception signal to be larger than the amplification factor of the direct reception signal. Even when the transmission / reception transducer is disposed on the lower side in the flow direction and the reception reflection transducer is disposed on the upper side in the flow direction, the level of the reflected reception signal generally tends to be lower than the level of the direct reception signal. Therefore, by performing signal amplification of the reflected reception signal with a relatively large amplification factor before the arrival time is measured, it is possible to further suppress a decrease in the level of the reflected reception signal and a decrease in measurement accuracy.
[0017]
For this purpose, a reception signal switching means for switching and supplying a reception signal or a reflection reception signal directly to the amplification means is provided between the ultrasonic transmission / reception section and the ultrasonic reception reflection section and the amplification means. The switching means can be configured to issue an amplification factor change command to the amplifying means in accordance with signal switching between the direct reception signal and the reflected reception signal. Thereby, stable signal amplification is executed with a relatively large amplification factor with respect to the reflected reception signal.
[0018]
In addition, a flow detection means for detecting the flow direction of the fluid flowing through the flow path is provided, and when the flow detection means detects a change in the fluid flow direction, a direct reception signal and a reflected reception signal are transmitted to the reception signal switching means. A signal switching timing change command may be issued. As a result, even when a situation occurs in which the fluid flows backward in the flow path, the detection is quickly performed and the reception signal level is adjusted, so that it is possible to prevent the signal level and the measurement accuracy from being lowered. In addition, as the flow detection means, the time measurement means (measurement data) which is a constituent element of the present invention is used, or a well-known flowmeter (or differential pressure type, area type, vortex type, etc.) separately from the ultrasonic flowmeter (or An anemometer) may be used. Further, instead of or in addition to the method (first method) for switching the reception signal and the reflected reception signal directly using the reception signal switching means when the backflow is detected, the ultrasonic transmission / reception unit using the measurement switching means You may employ | adopt the method (2nd method) which switches an ultrasonic wave reception reflection part. At that time, when the back flow rate is small, the first method can be used for warning display, when the back flow rate is large, the second method can be used first, and the shutoff valve can be operated when the flow rate is increased.
[0019]
Next, in order to solve the above problems, an ultrasonic flowmeter according to the present invention is:
A flow path for passing fluid;
A function of oscillating ultrasonic waves toward the upper side or lower side of the flow direction, a function of receiving ultrasonic waves arriving from the upper side or lower side of the flow direction, and at least a part of the incoming ultrasonic waves A transmission / reception reflection vibrator having a function of reflecting toward the lower side is provided, and disposed on the upper and lower sides in the flow direction of the flow path so that ultrasonic waves can be oscillated, received, and reflected from each other. A pair of ultrasonic transmission / reception reflectors;
Of the pair of transmission / reception reflection vibrators, one of the transmission / reception reflection vibrators (hereinafter referred to as a first vibrator) is an oscillation / reception side, and the other transmission / reception reflection vibrator (hereinafter referred to as a second vibrator) is received / received. A measurement switching means for switching between the first measurement on the reflection side and the second measurement on the second transducer as the oscillation / reception side and the first transducer as the reception / reflection side;
In the first measurement, the first reflection arrival time from when the ultrasonic wave reaches the second vibrator until the first vibrator receives the ultrasonic wave reflected by the second vibrator is measured. In addition, in the second measurement, the second reflected arrival from the time when the ultrasonic wave reaches the first vibrator until the second vibrator receives the ultrasonic wave reflected by the first vibrator. A time measuring means for measuring time;
It is characterized by providing.
[0020]
According to this ultrasonic flowmeter, the first reflection arrival time in the first measurement is that the ultrasonic wave reflected by the second vibrator from the time when the ultrasonic wave reaches the second vibrator and is received is first. This is the time until the transducer receives. On the other hand, in the second measurement, the second reflection arrival time is the time from when the ultrasonic wave reaches the first transducer and is received until the second transducer receives the ultrasonic wave reflected by the first transducer. It's time. Therefore, if the first reflection arrival time and the second reflection arrival time are applied to the forward arrival time and the reverse arrival time, reception starts in both the forward arrival time and the backward arrival time measurement value. It is no longer necessary to subtract and correct the time elapsed from to the trigger wave, and the measurement accuracy is further greatly improved. In addition, since complicated signal processing is not required for the ultrasonic wave reception signal waveform, it is possible to prevent the measurement speed from being slow and the measurement battery from being consumed.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a basic configuration of an embodiment of an ultrasonic flow meter used as a general residential gas meter or the like. A flow measurement gas (fluid) flows along the flow direction axis O in the illustrated flow direction (average flow velocity v) in the flow rate measurement flow path 1 of the ultrasonic flowmeter 100. An ultrasonic transmission / reception unit 2 on the lower side in the flow direction and an ultrasonic wave receiving / reflecting unit 3 on the upper side in the flow direction are attached to the wall 10 of the flow path 1, and as shown in FIG. In the cross section of the flow path including the transmission / reception unit 2, the ultrasonic reception reflection unit 3 is located on the wall 10 on the ultrasonic transmission unit 2 installation side.
[0022]
The flow channel 1 for measurement has a flow direction axis O that is linear between at least the ultrasonic transmission / reception unit 2 and the ultrasonic reception / reflection unit 3, and the shape and cross-sectional area of the axial cross section are the same in the flow direction. . When the measurement target is a gas, the axial cross-sectional shape of the measurement channel 1 may be any shape that forms a space closed by the wall 10. For example, any of a circular shape, an elliptical shape, a square shape, a rectangular shape, etc. It may be adopted. The flow path 1 shown in FIG. 1 is formed in a rectangular shape, and the transmission / reception vibrator 21 and the reception reflection vibrator 31 flow on the wall surface (attachment surface) forming one short side 11a of the cross section orthogonal to the flow direction of the flow path 1. The ultrasonic measurement lines M arranged in the flow path 1 are configured in a reflective V-shaped arrangement by using the wall surface that is attached at a predetermined distance in the direction and that forms the other short side 11b as a reflection surface. If the measurement target is a liquid such as water, an open shape (for example, a semicircular shape) in which the zenith portion of the wall 10 is open to the atmosphere may be employed as the axial cross-sectional shape of the measurement channel 1. .
[0023]
The ultrasonic transmission / reception unit 2 is fixed to the wall 10 of the flow path 1, and includes a transmission / reception vibrator 21 including a piezoelectric element, a diaphragm, an electrode plate, and the like, a drive voltage circuit for causing the transmission / reception vibrator 21 to oscillate, and the like. The transmission means 22 comprised from these. The transmission / reception vibrator 21 oscillates an ultrasonic wave toward the upper side of the fluid flow direction (the ultrasonic wave receiving / reflecting unit 3 side), and then is reflected by a reception reflection vibrator 31 described later and arrives from the upper side of the flow direction. Receive.
[0024]
The ultrasonic wave receiving / reflecting unit 3 is fixed to the wall 10 on the upper side in the flow direction than the ultrasonic wave transmitting / receiving unit 2 (the transmitting / receiving transducer 21), and is a receiving reflective transducer 31 composed of a piezoelectric element, a diaphragm, an electrode plate, and the like. And a receiving means 32 including a voltage detection circuit for detecting a voltage generated by the reception reflection vibrator 31 or the transmission / reception vibrator 21. The reception reflection vibrator 31 receives the ultrasonic wave oscillated from the transmission / reception vibrator 21 and reflected once by the inner wall surface (reflection surface 12) of the flow channel 1, and at least a part of the ultrasonic wave is received by the transmission / reception vibrator 21. Reflect towards The ultrasonic wave reflected by the reception reflection vibrator 31 returns to the original path along the measurement line M and is received by the transmission / reception vibrator 21.
[0025]
In FIG. 1, the average flow velocity of gas is v, the speed of sound propagating in the gas is c, and the angle between the ultrasonic traveling direction (measurement line M) and the gas flow direction (flow direction axis O) is θ (hereinafter referred to as a measurement line). If the ultrasonic propagation distance is L (= D / cos θ), the forward arrival time Td and the reverse arrival time Tu are respectively expressed as follows.
Td = L / (c + v · cos θ) (1)
Tu = L / (cv · cos θ) (2)
Taking the reciprocal of equations (1) and (2) and taking the difference, the following equation is obtained.
1 / Td−1 / Tu = 2v · cos θ / L (3)
Therefore, from the measurement of the forward arrival time Td and the reverse arrival time Tu, the average gas flow velocity v and flow rate Q are obtained by the following equations. However, A is a cross-sectional area of the flow path 1.
v = (1 / Td−1 / Tu) L / 2 cos θ (4)
Q = v · A (5)
In this way, by eliminating the sound velocity c depending on the gas temperature, the contained component, etc. from the equation (4), from the measured values (arrival times Td, Tu) and the constant values (propagation distance L, line angle θ). There is an advantage that the flow velocity v can be obtained.
[0026]
Therefore, as shown in FIG. 1, the ultrasonic flowmeter 100 includes an amplification unit 4 that amplifies the reception-side transducer output obtained by the reception reflection transducer 31 or the transmission / reception transducer 21 as a measurement unit, and “ Zero cross point detecting means 5 for detecting the ultrasonic arrival time from the output waveform by the “zero cross method”, time measuring means 6 for measuring the ultrasonic arrival time, and reception signal switching means 71 (for switching signals to be processed by the receiving means 32) Switching means 7).
[0027]
The amplifying unit 4 amplifies the direct reception signal oscillated from the transmission / reception transducer 21 and received by the reception / reflection transducer 31 and the reflection reception signal reflected by the reception / reflection transducer 31 and received by the transmission / reception transducer 21. The amplification factor of the reflected reception signal is set to be larger than the amplification factor of the direct reception signal (see FIG. 3).
[0028]
The reception signal switching unit 71 (switching unit 7) is provided between the ultrasonic transmission / reception unit 2, the ultrasonic reception reflection unit 3, and the amplification unit 4, and is received by the reception reflection vibrator 31 with respect to the amplification unit 4. The direct reception signal or the reflection reception signal received by the transmission / reception transducer 21 is switched by the reception means 32 and supplied. The received signal switching means 71 issues an amplification factor change command to the amplifying means 4 in accordance with the signal switching between the direct received signal and the reflected received signal.
[0029]
The time measuring means 6 has a direct arrival time from when the transmission / reception transducer 21 oscillates an ultrasonic wave until the reception reflection transducer 31 receives the ultrasonic wave (reverse direction arrival time Tu in the above equation (2) in FIG. 1). Is equivalent). Further, the time measuring means 6 is the reflection arrival time from when the ultrasonic wave reaches the reception reflection vibrator 31 until the transmission / reception vibrator 21 receives the ultrasonic wave reflected by the reception reflection vibrator 31 (in FIG. (Corresponding to the forward direction arrival time Td in equation (1)).
[0030]
By the way, as is clear from the above formulas (1) and (2), the forward arrival time Td measured by the time measuring means 6 is smaller than the backward arrival time Tu. Therefore, the time measuring means 6 can also have a function as a flow detecting means for detecting the flow direction of the fluid flowing through the flow path 1. That is, the flow detection unit 6 issues a signal switching timing change command between the reception signal and the reflection reception signal directly to the reception signal switching unit 71 when detecting a change in the fluid flow direction, thereby performing subsequent signal processing. Is performed along the fluid flow direction.
[0031]
Next, the operation of the ultrasonic flowmeter 100 will be described based on the block diagram of the measurement unit shown as an example in FIG. 2 and the timing chart shown in FIG. As shown in FIG. 2, the receiving-side vibrator output (here, the transmitting / receiving vibrator 21 output V0d or the receiving reflection vibrator 31 output V0u) is amplified by an amplifier 41 (for example, an operational amplifier) constituting the amplifying means 4 (for example, an operational amplifier). Amplified signal Va is input to zero cross point detecting means 5. In the zero cross point detection means 5, the amplified signal Va is input (for example, non-inverted input) to the zero cross type comparator 51 (first comparator) and input (for example, inverted input) to the differential type comparator 52 (second comparator). The comparator outputs Vb and Vc are input to ports #S and #R of an RS flip-flop circuit (hereinafter referred to as RSFF circuit) 53, respectively. By the port #Q output Vd of the RSFF circuit 53, the zero cross point pulse generation circuit 54 constituted by a monostable multivibrator or the like detects the ultrasonic arrival time in the output waveform Va, and the zero cross point detection signal Ve is sent to the time measuring means 6. Output. Based on the zero cross point detection signal Ve, the time measuring means 6 counts the number of clock pulses from the clock pulse generation circuit 62 (for example, a crystal oscillator or an astable multivibrator) by a pulse counter circuit 61 (for example, a JK flip-flop circuit). The arrival time detection signal Vf is output. Each output of the differential comparator 52 output Vc, the port #Q output Vd of the RSFF circuit 53, and the zero cross point detection signal Ve is controlled by the reception signal switching output Vg so as to be terminated only once. (See FIG. 3).
[0032]
(1) Measurement of direct arrival time Tu (reverse direction arrival time)
In FIG. 3, in the receiving means 32, the output V0u of the reception reflecting vibrator 31 is first selected as the receiving-side vibrator output (see FIG. 2) by the reception signal switching means 71.
The amplified signal Va (direct reception signal of the reception reflection vibrator 31) is an irregular waveform signal that does not have a sufficient amplitude (generated voltage) level due to the influence of noise or the like in the initial reception, and is the nth ( In the figure, it is normal that the amplitude level finally reaches a stable measurement finally in the (3) waveform portion. Therefore, in order to enable accurate time measurement in the amplified signal Va of the ultrasonic reception output, the zero cross method described below is generally employed. That is, “the waveform portion (the third wave in the figure) that reaches (or falls below) the threshold value VS input and set in the differential comparator 52 (see FIG. 2) is set as the trigger wave, and the amplitude ( Alternatively, the zero cross point at which the phase) becomes zero is detected by the zero cross point pulse generation circuit 54 (see FIG. 2) on the waveform of the amplified signal Va (or a derivative signal thereof).
[0033]
Specifically, the zero cross method is applied to the waveform of the amplified signal Va as follows. In the zero cross type comparator 51 to which the amplified signal Va is input non-inverted, the amplitude (generated voltage) of the waveform of the amplified signal Va has a positive waveform portion (the first wave, the third wave, the fifth wave). ... Is intermittently output as the first comparator output Vb. On the other hand, in the differential comparator 52 to which the negative polarity amplification signal Va and the positive polarity threshold value VS are input, it corresponds to a waveform portion exceeding the threshold value VS (the third wave, the top of the fifth wave). Then, the pulse that becomes L is intermittently output as the second comparator output Vc.
[0034]
Until the pulse signal of the trigger wave ((3) wave) exceeding the threshold value VS is first input at the second comparator output Vc, H is continuously input to the port #R of the RSFF circuit 53. The port #Q output Vd of the circuit 53 is maintained at L. In the state where the waveform detection pulse signal of the third wave from the first comparator output Vb is input (H) to the port #S of the RSFF circuit 53, the trigger wave (third wave) is output from the second comparator output Vc. When the threshold VS detection pulse signal is input (L) to the port #R, the port #Q output Vd changes to H. The port #Q output Vd is maintained at H and the input to the port #S is L until the waveform detection pulse signal of the third wave from the first comparator output Vb is not input to the port #S of the RSFF circuit 53. The port #Q output Vd becomes L.
[0035]
The zero cross point pulse generation circuit 54 detects the falling edge of the port #Q output Vd of the RSFF circuit 53 and outputs a pulse that becomes H corresponding to the zero cross point as the zero cross point detection signal Ve. The pulse counter circuit 61 counts the number of clock pulses between the zero cross point detection pulse signal (Ve) and the ultrasonic transmission pulse signal of the transmission-side transducer 21 (see FIG. 1), and outputs the arrival time detection signal Vf. To do. The direct arrival time Tu (reverse arrival time) obtained by the arrival time detection signal Vf in this way is longer than the actual (true) arrival time. That is, the detection arrival time with the elapsed time from the start of reception to the zero cross point of the trigger wave ((3) wave) (1.5 cycles of (1) wave to (3) wave) as a correction value Subtract from to get the actual arrival time.
[0036]
(2) Measurement of reflection arrival time Td (forward arrival time)
In FIG. 3, in the receiving means 32, the output V0d (reflected received signal) of the transmitting / receiving vibrator 21 is next selected as the receiving-side vibrator output (see FIG. 2) by the received signal switching means 71. Then, the reflection arrival time Td (forward arrival time) is measured in the same manner as the measurement of the direct arrival time Tu (reverse arrival time). The reflection arrival time Td (forward arrival time) obtained by the arrival time detection signal Vf in this way is equivalent to the actual (true) arrival time. That is, here, since it is not necessary to subtract the elapsed time from the start of reception to the zero cross point as a correction value, it is possible to eliminate the temperature dependence of the ultrasonic transducer.
[0037]
(Example 2)
Next, FIG. 4 shows a basic configuration of another embodiment of the ultrasonic flowmeter used in the same manner as FIG. 1 (Embodiment 1). In the ultrasonic flowmeter 200, the transmission / reception vibrator 21 and the reception reflection vibrator 31 are configured in a transmission type Z array in which the flow path 1 is opposed to each other. That is, the transmission / reception vibrator 21 is fixed to the wall 10 of the flow path 1, oscillates an ultrasonic wave toward the upper side in the fluid flow direction (the ultrasonic wave reception / reflection part 3 side), and then a reception reflection vibrator 31 described later. The ultrasonic waves that are reflected by the light and arrive from the upper side in the flow direction are received.
[0038]
On the other hand, the reception reflection vibrator 31 is a wall of the flow path 1 facing the installation side of the ultrasonic transmission / reception unit 2 (transmission / reception transducer 21) on the upper side in the flow direction than the ultrasonic transmission / reception unit 2 (transmission / reception transducer 21). 10 is fixed. The reception reflection vibrator 31 receives the ultrasonic wave oscillated from the transmission / reception vibrator 21 and reflects at least a part of the ultrasonic wave toward the transmission / reception vibrator 21. The ultrasonic wave reflected by the reception reflection vibrator 31 returns to the original path along the measurement line M and is received by the transmission / reception vibrator 21.
[0039]
The ultrasonic flow meter 200 shown in FIG. 4 operates in the same manner as in FIGS. 2 and 3 (Example 1). In FIG. 4, parts having the same functions as those in FIG.
[0040]
(Example 3)
Next, FIG. 5 shows a basic configuration of still another embodiment of the ultrasonic flowmeter used in the same manner as FIG. 1 (Embodiment 1). In this ultrasonic flowmeter 300, in FIG. 3 (Example 1), attention is paid to the fact that the reflection arrival time Td can be measured as the forward arrival time equivalent to the actual (true) arrival time. The ultrasonic wave is oscillated, and the reflection arrival time Tu as the reverse arrival time is similarly measured as equivalent to the actual arrival time (see FIG. 7).
[0041]
In FIG. 5, the measurement units are arranged in a reflective V-shaped arrangement as in FIG. 1. Specifically, a pair of ultrasonic transmission / reception reflectors 12 and 13 are arranged on the lower side and the upper side in the flow direction of the flow path 1 so that ultrasonic waves can be oscillated, received, and reflected from each other. The ultrasonic transmission / reception reflection unit 12 disposed on the lower side in the flow direction has a function of oscillating ultrasonic waves toward the upper side in the flow direction, a function of receiving ultrasonic waves coming from the upper side in the flow direction, and at least an incoming ultrasonic wave. The transmission / reception reflection vibrator 121 having a function of reflecting a part of the sway toward the upper side in the flow direction is provided. On the other hand, the ultrasonic wave transmitting / receiving reflector 13 arranged on the upper side in the flow direction has at least a function of oscillating ultrasonic waves toward the lower side in the flow direction and a function of receiving ultrasonic waves coming from the lower side in the flow direction. A transmission / reception reflection vibrator 131 having a function of reflecting a part of ultrasonic waves toward the lower side in the flow direction is provided. In FIG. 5, parts having the same functions as those in FIG.
[0042]
The switching unit 7 includes a measurement switching unit 72 in addition to the reception signal switching unit 71 (see FIG. 1). The measurement switching means 72 has a function of switching between the first measurement and the second measurement using the pair of transmission / reception reflection vibrators 121 and 131. Specifically, when one of the pair of transmission / reception reflection vibrators 121 and 131 is the first vibrator 121 and the other is the second vibrator 131,
First measurement: the first vibrator 121 is on the oscillation / reception side, and the second vibrator 131 is on the reception / reflection side;
Second measurement: the second vibrator 131 is the oscillation / reception side, and the first vibrator 121 is the reception / reflection side;
[0043]
The time measurement means 6 measures the first reflection arrival time Td in the first measurement, and measures the second reflection arrival time Tu in the second measurement. However, the first reflection arrival time Td is the time from when the ultrasonic wave reaches the second vibrator 131 until the first vibrator 121 receives the ultrasonic wave reflected by the second vibrator 131. The second reflection arrival time Tu is the time from when the ultrasonic wave reaches the first vibrator 121 until the second vibrator 131 receives the ultrasonic wave reflected by the first vibrator 121.
[0044]
Next, an outline of the flowcharts of FIGS. 6 and 7 will be described. First, in the first measurement, if the first vibrator 121 is on the oscillation / reception side and the second vibrator 131 is on the reception / reflection side, the first reflection arrival is performed in the same manner as in FIG. 3 (Example 1). The time Td can be measured as equivalent to the actual (true) arrival time (see FIG. 6). Subsequently, in the second measurement, if the second vibrator 131 is set to the oscillation / reception side and the first vibrator 121 is set to the reception / reflection side, the second reflection is performed in the same manner as in FIG. 3 (Example 1). The arrival time Tu can be measured as equivalent to the actual (true) arrival time (see FIG. 7). Thus, if the first reflection arrival time Td and the second reflection arrival time Tu are applied to the forward arrival time and the reverse arrival time, both the forward arrival time and the reverse arrival time are measured. This eliminates the need to subtract and correct the time elapsed from the start of reception until the trigger wave, greatly improving measurement accuracy.
[0045]
In the first embodiment, only the case where the ultrasonic wave oscillated by the transmission / reception vibrator 21 is reflected once by the inner wall surface of the flow path and reaches the reception reflection vibrator 31 is described, but the number of reflections on the inner wall surface is arbitrary. Can be set. In the third embodiment, only the case where the measurement units are arranged in the reflective V-shaped array has been described, but the present invention can also be applied to an arrangement such as a transmissive Z array.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a basic configuration of an embodiment of an ultrasonic flowmeter according to the present invention.
FIG. 2 is a block diagram of a measurement unit.
3 is a timing chart of FIG.
FIG. 4 is an explanatory diagram showing a basic configuration of another embodiment of the ultrasonic flowmeter according to the present invention.
FIG. 5 is an explanatory diagram showing a basic configuration of still another embodiment of the ultrasonic flowmeter according to the present invention.
6 is a timing chart up to time t in FIG.
FIG. 7 is a timing chart after time t following FIG. 6;
[Explanation of symbols]
1 channel
10 walls
2 Ultrasonic transceiver
21 Transceiver
3 Ultrasonic wave reception reflector
31 Reception reflector
4 Amplification means
6 Time measurement means
71 Received signal switching means (switching means)
100,200 Ultrasonic flow meter
12, 13 Ultrasonic wave transmission / reception reflector
121 First vibrator
131 Second vibrator
72 Measurement switching means (switching means)
300 Ultrasonic flow meter

Claims

A flow path for passing fluid;
An ultrasonic transmission / reception unit in which a transmission / reception transducer for receiving ultrasonic waves arriving from the upper side or lower side of the flow direction is attached to the flow path after oscillating ultrasonic waves toward the upper side or lower side of the fluid flow direction When,
The ultrasonic wave oscillated from the transmission / reception transducer is received in the flow path on the upper side or the lower side in the flow direction of the ultrasonic transmission / reception unit, and at least a part of the ultrasonic wave is reflected toward the transmission / reception transducer. An ultrasonic wave receiving / reflecting unit to which a receiving / reflecting vibrator is attached;
Measures the direct arrival time from when the transmitting / receiving transducer oscillates the ultrasonic wave until the receiving / reflecting transducer receives the ultrasonic wave, and receives and reflects the ultrasonic wave when the ultrasonic wave reaches the receiving / reflecting transducer. A time measuring means for measuring a reflection arrival time until the transmission / reception vibrator receives the ultrasonic wave reflected by the vibrator;
An ultrasonic flowmeter comprising:

A flow path for passing fluid;
Ultrasound with a transmission / reception transducer attached to the flow path wall that receives ultrasonic waves coming from the upper side or lower side in the flow direction after oscillating ultrasonic waves toward the upper or lower side in the fluid flow direction A transceiver unit;
In the cross section of the flow path including the fluid flow direction axis and the transmission / reception vibrator, the wall of the flow path on the upper or lower side in the flow direction is oscillated from the transmission / reception vibrator at least once on the inner wall surface of the flow path. An ultrasonic wave receiving / reflecting unit to which a reception reflection vibrator that receives reflected ultrasonic waves and reflects at least a part of the ultrasonic waves toward the transmission / reception vibrator is attached;
Measures the direct arrival time from when the transmitting / receiving transducer oscillates the ultrasonic wave until the receiving / reflecting transducer receives the ultrasonic wave, and receives and reflects the ultrasonic wave when the ultrasonic wave reaches the receiving / reflecting transducer. A time measuring means for measuring a reflection arrival time until the transmission / reception vibrator receives the ultrasonic wave reflected by the vibrator;
An ultrasonic flowmeter comprising:

The flow path is formed in a rectangular shape in a cross section orthogonal to the fluid flow direction,
A wall surface on which the transmitting / receiving vibrator and the receiving reflection vibrator are attached to a wall surface forming one of the short sides of the cross section perpendicular to the flow direction of the flow path at a predetermined distance in the flow direction and forming the other short side The ultrasonic flowmeter according to claim 1 or 2, wherein an ultrasonic survey line arranged in the flow path is configured in a reflective V-shaped array by using a reflection surface.

A flow path for passing fluid;
Ultrasound with a transmission / reception transducer attached to the flow path wall that receives ultrasonic waves coming from the upper side or lower side in the flow direction after oscillating ultrasonic waves toward the upper or lower side in the fluid flow direction A transceiver unit;
In the cross section of the flow path including the flow direction axis of the fluid and the transmission / reception transducer, the ultrasonic transmission / reception unit is connected to the wall of the flow path facing the installation side of the ultrasonic transmission / reception unit on the upper side or lower side in the flow direction. An ultrasonic wave receiving / reflecting unit to which a receiving reflection vibrator that receives the oscillated ultrasonic wave and reflects at least a part of the ultrasonic wave toward the transmitting / receiving vibrator is attached;
Measures the direct arrival time from when the transmitting / receiving transducer oscillates the ultrasonic wave until the receiving / reflecting transducer receives the ultrasonic wave, and receives and reflects the ultrasonic wave when the ultrasonic wave reaches the receiving / reflecting transducer. A time measuring means for measuring a reflection arrival time until the transmission / reception vibrator receives the ultrasonic wave reflected by the vibrator;
An ultrasonic flowmeter comprising:

The ultrasonic transmission / reception unit is arranged on the lower side in the flow direction than the ultrasonic reception / reflection unit, and the transmission / reception transducer oscillates an ultrasonic wave toward the reception / reflection transducer arranged on the upper side in the flow direction. 5. The ultrasonic flowmeter according to any one of items 4 to 4.

In order to measure the direct arrival time and the reflection arrival time by the time measuring means, a direct reception signal oscillated from the transmission / reception vibrator and received by the reception reflection vibrator, and reflected by the reception reflection vibrator, Amplifying means for amplifying the reflected reception signal received by the transmission / reception vibrator is provided,
6. The ultrasonic flowmeter according to claim 1, wherein the amplification means sets the amplification factor of the reflected reception signal to be larger than the amplification factor of the direct reception signal.

A reception signal switching means for switching and supplying the direct reception signal or the reflection reception signal to the amplification means is provided between the ultrasonic transmission / reception section and the ultrasonic reception reflection section and the amplification means. ,
The ultrasonic flowmeter according to claim 6, wherein the reception signal switching unit issues an amplification factor change command to the amplification unit in accordance with signal switching between the direct reception signal and the reflected reception signal.

A flow detecting means for detecting a flow direction of the fluid flowing through the flow path is provided;
8. The ultrasonic wave according to claim 7, wherein the flow detection means issues a signal change timing change command between the direct reception signal and the reflected reception signal to the reception signal switching means when detecting a change in a fluid flow direction. Flowmeter.

A flow path for passing fluid;
A function of oscillating ultrasonic waves toward the upper side or lower side of the flow direction, a function of receiving ultrasonic waves arriving from the upper side or lower side of the flow direction, and at least a part of the incoming ultrasonic waves A transmission / reception reflection vibrator having a function of reflecting toward the lower side is provided, and disposed on the upper and lower sides in the flow direction of the flow path so that ultrasonic waves can be oscillated, received, and reflected from each other. A pair of ultrasonic transmission / reception reflectors;
Of the pair of transmission / reception reflection vibrators, one of the transmission / reception reflection vibrators (hereinafter referred to as a first vibrator) is an oscillation / reception side, and the other transmission / reception reflection vibrator (hereinafter referred to as a second vibrator) is received / received. A measurement switching means for switching between the first measurement on the reflection side and the second measurement on the second transducer as the oscillation / reception side and the first transducer as the reception / reflection side;
In the first measurement, the first reflection arrival time from when the ultrasonic wave reaches the second vibrator until the first vibrator receives the ultrasonic wave reflected by the second vibrator is measured. In addition, in the second measurement, the second reflected arrival from the time when the ultrasonic wave reaches the first vibrator until the second vibrator receives the ultrasonic wave reflected by the first vibrator. A time measuring means for measuring time;
An ultrasonic flowmeter comprising: