JP3732642B2 - Ultrasonic liquid level measuring device - Google Patents

Description

【００５２】
次に、振幅情報から、ｎ回多重反射のうち、液面下での反射回数ｉを算出する。超音波は液槽壁１ａの内側界面において反射するが、反射率は界面の接する内部の状態（液相、気相）により異なる。この性質を利用して、多数回の反射を繰り返した後で受信側の超音波探触子６（２２、２３）に入射した超音波の減衰率と時間情報とから求めた多重反射回数から算出した入射角で反射する超音波の反射率から液面下での反射回数ｉを算出する。
【００５３】
そして、液槽に液体が貯蔵され、液面が送受信探触子の間にあり、液面下での反射回数がｉ回になっているとすると、このときの受信超音波強度Ｉｎは（４）式で表現される。
【００５４】
【数２】

【００５５】
上記の（５）式において、液位の変化に応じて変化するのは、液相界面での反射回数ｉの値のみであり、α（θｎ）≠β（θｎ）であれば、ここで挙げた各因子について数値的に推定量を求め、多重反射の後に受信された電気信号強度と上記の数値の代入により、液相での反射回数を求めることができる。この反射回数ｉと、探触子設置位置情報から液面の位置ｌを（５）式の不等式にて換算できる。
【００５６】
【数３】

【００５７】
多重反射の回数が異なると超音波の反射する位置が異なることを利用し、複数の多重反射の結果の液位を総合することにより反射回数が異なる多重反射エコーパルス毎に求められる液位に比べてその精度が向上する。
【００５８】
全反射回数ｎと液相での反射回数ｉと、超音波探触子の設置位置情報ｄから液面の位置ｌを（６）式の不等式にて換算できる。
【００５９】
ｄ（２ｉ＋１）／２ｎ＜ｌ＜ｄ｛２（ｉ＋１）＋１｝／２ｎ …（６）
各多重反射回数ｎに対して、このような不等式により液位の高さ（液位の位置ｌ）を限定できる。
【００６０】
単一の反射回数ｎにより得られる液面の分解能はｄ／ｎであるが、複数の多重反射回数ｎに対して得られる液面不等式の情報の活用により、液面分解能は、各反射回数毎の反射位置の間隔の最小値により決定され、ｄ／２ｎ〜ｄ／２ｎ（ｎ−１）に向上できる。
【００６１】
ここで、液位換算手段１０は、超音波の波高変化測定のための基準値を超音波探触子間の内壁面がすべて液相に接しているときの測定結果のエコーパルス強度を基準した液位換算処理を行なう。これにより、超音波送受信における角度依存性などの補正量の影響を打ち消し合うようにする。これは、図４に示す特性曲線４５の波形（２個の超音波探触子間が完全に気相−壁材界面の時の包絡線波形）を基にして、残りの特性曲線４１〜４４を計算することに相当する。
【００６２】
【数４】

【００６３】
これにより、式中の細かいγ、σなどの係数の影響を打ち消し合うことができる。
【００６４】
また、液位換算手段１０は、超音波の波高変化測定のための基準値を超音波探触子間の内壁面がすべて気相に接しているときの測定結果のエコーパルス強度を基準にした液位換算処理を行なうことにより、超音波送受信における角度依存性などの補正量の影響を打ち消し合うようにする。これは、図４に示す特性曲線４１の波形（２個の超音波探触子間が完全に気相−壁材界面の時の包絡線波形）を基にして、残りの特性曲線４２〜４５を計算することに相当する。
【００６５】
【数５】

【００６６】
これにより、式中の細かいγ、σなどの係数の影響を打ち消し合うことができる。
【００６７】
また、液位換算手段１０は、各超音波探触子について波高変化測定の基準値を超音波探触子自身での超音波送受信の結果得られる受信強度に基づき補正する。ことにより、超音波探触子の劣化などによる変化の影響を打ち消す。
【００６８】
図７に示すように定期的に送信側の超音波探触子７１および受信側の超音波探触子７２から壁材方向に垂直に超音波７３、７４を送受信し、内部状態が同じときの受信信号強度を信号検出手段９に保持しておく。そして、液位換算手段１０での処理において、この情報を利用することにより、反射回数の評価精度を向上させる。
【００６９】
次に、図８に示すように、超音波の送受信を行う超音波探触子の接続を順次切り替えることができるように、送信側の超音波探触子８１と超音波発振手段７との間および受信側の超音波探触子８２と超音波受信手段８との間に、それぞれ送受信切替回路１２を設ける。
【００７０】
すなわち、多重反射の回数が異なると超音波の反射する位置が異なることを利用し、送信側の超音波探触子８１と受信側の超音波探触子８２とを切り替え、反射回数が異なる多重反射エコーパルス毎に求められる液位の相対位置の情報の組み合せにより推定される液位の区間を狭め、連続的な液位測定をできるようにする。
【００７１】
このように、超音波探触子の送信側と受信側とを順次切り替えることにより、発信側の超音波探触子が異なれば超音波多重反射位置が微妙に異なることを利用し、超音波探触子の配置は同じでも超音波が壁材中を伝播する経路を変えることが可能である。また、各送信毎に得られる波形情報を組み合わせることにより、液位の測定精度の向上および一部の超音波探触子の故障の発見の早期実現、故障した超音波探触子の存在条件下でも他の超音波探触子により、喪失された情報の補足ができる。
【００７２】
次に、図９に示すように、液槽壁１ａの内壁からのエコーパルス間のノイズ強度の変化に基づいて、信号検出手段９により液槽内部の気液二相混合部の有無および幅を推定するようにする。これは、液槽内部の液相に気泡が混入している状態を測定することにより行う。
【００７３】
図９において、送信側の超音波探触子９１から発信された超音波９３は、液槽壁１ａの壁材中を伝播し、液相−壁材界面において反射を起こすが、この場合、混合相中の超音波９４、９５のように一部の超音波が液相中に透過する。混合相中に透過した超音波の進行方向に、気泡９６が存在しない場合には、透過した超音波９５のように液相中をそのまま伝播していく。
【００７４】
一方、超音波の進行方向に気泡９６がある場合には、その超音波９４が混合相中の気泡９６の表面に到達すると気泡９６の表面で反射が起こり、その反射した超音波は、超音波９７のように液槽壁１ａの壁材中に伝播する。この伝播した超音波９７が受信側の超音波探触子９２に入射することで、混合相中の気泡９６の存在を示す超音波の反射波を検出できる。
【００７５】
この反射波９７は壁材中内部のみの反射により入射した超音波に比べて微弱であり、また伝播時間も気相液相中の音速の違いにより異なり、また気泡位置も液相中に広く分布するため、図３に示すエコーパルスにおいてはベースライン３０上の雑音成分に寄与する。すなわち、図４におけるエコーパルス間の平均強度の特性曲線４６の変化から、気泡９６による反射成分の強さを評価でき、気泡９６の存在の有無を測定できる。
【００７６】
このように、信号検出手段９は液槽壁１ａの内壁からのエコーパルス間のノイズ強度の変化を検出する。液槽壁１ａの壁材界面にて液相に透過し、液槽内部の気液二相混合部の気泡表面で反射後、受信側の超音波探触子９２に入射した超音波９７の有無から気液二相混合部の有無を測定する。
【００７７】
液相中に２相状態が形成されているときには、液面下で液相−壁材界面に入射した超音波９４の一部が液相中に透過する。この透過波９４が気泡９６表面において反射し、再び壁材方向に戻ってくる成分を生じる。壁材に液相方向から入射する超音波の一部は壁材中を伝播し、受信側の超音波探触子９２に入射するが、その際に液相での音波速度が壁材中に比べて低いこと、伝播経路が異なることから壁材内部を伝播してきた超音波と異なる遅れ時間を有し、かつ低い超音波強度であることから、これらの状態の有無は、超音波エコーパルスピークには寄与せず、反射回数の異なるエコーパルスの間の散乱超音波成分に寄与する。気泡９６が存在する場合には、この散乱成分が増大することを検出し、２相状態の有無が検出できる。
【００７８】
ここで、図９の条件において、実際の測定条件と同様の体系において気泡９６が液相中に含まれる割合すなわちボイド率を、気泡９６の流量を変化させることにより変化させ、同時に別な手法でボイド率を予め測定しておく。一方、得られた受信信号のノイズ強度を測定し、ノイズ強度−ボイド率の対応テーブルを作成し予め信号検出手段９に記憶しておく。そして、ノイズ強度が変化したときには、このノイズ強度−ボイド率対応テーブルを参照してボイド率を推定する。これにより、迅速にボイド率を推定することができる。
【００７９】
このように、気液二相混合部のボイド率の増大により気泡９６の表面積が増える結果、気泡表面での超音波の反射量が増え、液槽壁１ａの内壁からのエコーパルス間のノイズ強度が増大するという性質を利用して、予め作成したノイズ強度−ボイド率対応テーブルを参照してボイド率を推定する。
【００８０】
次に、図１０は液位換算手段１０にニューラルネットワークを導入したときのアルゴリズムの説明図である。液位換算手段１０は、レファレンスとなる参照強度変化を学習させたニューラルネットワークにより、反射エコーパルス強度の変化から液位を推定する。
【００８１】
図４に示したような液位をパラメータとしたエコーパルス包絡線の特性曲線４１〜４５のような波形が各液位に対応して予め得られているとすると、その波形情報を図１０のピーク形状１０１のように異なる液位に対応する波形形状を入力として、液位を出力とするような誤差逆伝播アルゴリズムに基づくフィードフォワード型人工神経回路網１０２により学習を行なう。そして、学習が終了した人工神経回路網１０４を液位換算手段１０の処理機構として組み込む。これにより、測定された波形形状１０３を入力として液位情報を推定する。
【００８２】
このように、液位換算手段１０としてレファレンスとなる参照強度変化を学習させたニューラルネットワークを採用し、反射エコーパルス強度の変化から液位を推定する。従って、液位をより精度良くかつ迅速に推定できるようになる。
【００８３】
図１１は、超音波探触子としてフェーズドアレイセンサを用いた場合の説明図である。図１１に示すように、小型超音波探触子を並べて構成したフェーズドアレイ超音波探触子１１１、１１２を設置する。これにより超音波１１３が液槽壁１ａの内壁面で反射する位置にフェーズドアレイによる焦点１１４を合わせ、その位置での反射率の相違から液相の有無を検出する。フェーズドアレイにおいて合成超音波発信方向はアレイを構成する超音波探触子の発信時刻の遅れ時間を制御することで実現されており、この遅れ時間を連続的に変化させることで、液槽内壁面での焦点位置１１４を連続的に移動させ、液面の位置を連続的に測定する。
【００８４】
このように、超音波探触子として、複数の小型超音波探触子を並べて構成するフェーズドアレイ型の超音波探触子を用いることにより、液槽壁内面の特定位置にフェーズドアレイから発信した超音波の焦点１１４をあわせ、その位置での液位の有無を高分解能で測定し、さらに焦点位置を連続的に変化させることにより液位の連続的測定を可能とする。
【００８５】
次に、本発明の第２の実施の形態を説明する。図１２は本発明の第２の実施の形態を示すブロック構成図である。この第２の実施の形態は連続しきい値判定方式で液位を計測するものである。すなわち、複数個の超音波探触子ＳＥ１〜ＳＥ９を多段に液槽外壁面に液槽内に向けて設置し、超音波送受信手段１３により、これら超音波探触子ＳＥ１〜ＳＥ９を順次切り替えて超音波の送信を行い液槽内面からの反射エコーパルスを超音波探触子の切り替え順序で受信する。そして、信号処理手段１４により超音波送受信手段ＳＥ１〜ＳＥ９からの反射エコーパルスの波高値に基づいて各々の超音波探触子ＳＥ１〜ＳＥ９の正面における液槽内包液の有無を確定して連続した液位を求めるようにしたものである。
【００８６】
超音波送受信手段１３は第１の実施の形態の超音波発信手段７および超音波受信手段８に相当し、複数個の超音波探触子ＳＥ１〜ＳＥ９を順次切り替えて受信する機能を有する。また、信号処理手段１４は第１の実施の形態の信号検出手段９および液位換算手段１０に相当し、順次受信した反射エコーパルスに基づき液位を連続的に求めるものである。
【００８７】
図１２において、液槽１の液槽壁１ａの外面に液槽１内に向けて多段の超音波探触子ＳＥ１、ＳＥ２、ＳＥ３、ＳＥ４、ＳＥ５、ＳＥ６、ＳＥ７、ＳＥ８、ＳＥ９を配置する。超音波送受信手段１３は、これら超音波探触子ＳＥ１〜ＳＥ９を切り替え駆動する切替駆動機能と、超音波探触子ＳＥ１〜ＳＥ９からの信号を受信する受信機能と、所定の周波数で発信される超音波の発信機能とを有する。
【００８８】
信号処理手段１４は、受信信号を所定のしきい値で２値化する検波機能と、２値化した信号に基づいて各々の超音波探触子ＳＥ１〜ＳＥ９の正面の液槽内包液の有無を判定する。そして、これら内包液の有無から液面を確定する機能と、連続した液位を信号処理し外部出力する出力機能を有する。
【００８９】
まず、信号処理手段１４からの駆動信号により超音波送受信手段１３は、超音波探触子ＳＥ１から順番に選択切替し、選択切り替えした超音波探触子から超音波を発信させる。そして、超音波送受信手段１３は、超音波を発信させた超音波探触子から反射波を受信する。
【００９０】
図１２では２番目の超音波探触子ＳＥ２から超音波Ｓ１が発信されたものを示しており、液槽壁１ａから発信された超音波Ｓ１は液槽壁１ａ内を伝播し、液槽１の内面が空気または蒸気相である場合には、発信信号とほぼ同じ波高値の反射波Ｓ２が超音波探触子ＳＥ２に戻ってくる。この反射波Ｓ２の波高値は所定のしきい値より大きいことから、液槽１内の超音波探触子ＳＥ２の正面は、空気または蒸気相であることを判定し記憶する。この液槽１の内包液の有無を判定し終わると、次段の超音波探触子ＳＥ３に切り替える。このようにして、各々の超音波探触子位置での液槽１の内包液の有無を判定する。例えば、超音波探触子ＳＥ６においては、入射波Ｓ３に対し、鉄鋼材と水の音響インピーダンスの差が空気と蒸気の場合と比較し小さいことから、超音波Ｓ３の漏洩波Ｓ５が発生し、超音波探触子ＳＥ６に戻ってくる反射波Ｓ４の波高値が内包液がない場合より小さくなる。このことから、受信した反射波Ｓ４の波高値は所定のしきい値より小さくなり、液槽１内の超音波探触子ＳＥ６の正面には内包液が存在すると判定し記憶する。
【００９１】
このようにして、超音波探触子ＳＥを順次切り替えて内包液の有無の境界点から確定された水面位置を、液位信号として信号処理手段１４から液位出力手段１１に出力する。
【００９２】
すなわち、複数個の超音波探触子ＳＥを多段に設置し、各段の測定（超音波送受信及び信号処理）が完了した後、次段の超音波探触子ＳＥの送受信を開始するタイムシェアリング方式により頂番に液位の有無を確認することで、各超音波探触子ＳＥの超音波干渉を防ぐ。また、測定精度は超音波探触子である圧電素子の構造寸法に依存することから、小型の圧電素子を用いることにより測定精度向上が図れ、多段、一列に超音波探触子を配列し高速スキャンすることで連続的な液位測定が可能となる。
【００９３】
ここで、超音波探触子ＳＥの正面における液槽内包液の有無判定のしきい値は、信号処理手段１４により、超音波の発信パルス波高値を基準として随時決定するようにしている。
【００９４】
図１３（ａ）および図１３（ｂ）に示すように、圧力容器又はタンク等の液槽内包液の有無を判定するしきい値ＥＰは、発信した超音波Ｓ１（Ｓ３）の波高値Ｅ１から減衰分ΔＥ１を減じた値として随時決定し更新する。
【００９５】
例えば、図１３（ａ）において、超音波入射波Ｓ１のパルス波高値Ｅ１に対し、ある一定の減衰分ΔＥ１（３％）を考慮した値をしきい値とする。つまり、しきい値ＥＰはＥ１−ΔＥ１となる。液槽内で超音波探触子正面に内包液が存在しない場合（空気や蒸気相の場合）、液槽の壁内面からの反射波Ｓ２は殆ど減衰しないパルス波高値Ｅ２で受信され、しきい値ＥＰを越えることから、内包液なしと判定する。
【００９６】
また、図１３（ｂ）において、超音波入射波Ｓ３のパルス波高値Ｅ３に対し、ある一定の減衰分ΔＥ３（３％）とすると、その場合のしきい値ＥＰはＥ３−ΔＥ３となる。液槽内で超音波探触子正面に内包液が存在する場合（液相の場合）、液槽１の壁内面からの反射波Ｓ４は液相側への超音波の漏洩分Ｓ５が反射しないことから、パルス波高値Ｅ４が受信され、しきい値ＥＰを下回ることから、内包液ありと判定する。これを全ての超音波探触子ＳＥについて、繰り返すことにより連続した液位を算出する。
【００９７】
以上のような処理を用いることにより、超音波探触子ＳＥの入射波のパルス波高値の経年変化や波高値の不安定性に対応することが可能となる。
【００９８】
また、液槽壁外面に容器内に向けて設置した多段の超音波探触子については、超音波探触子ＳＥの配置を図１４に示すように千鳥状に配置する。図１４（ａ）は液槽壁１ａの側面方向から見た図であり、図１４（ｂ）は液槽壁１ａの平面方向から見た図である。図１４に示すように超音波探触子ＳＥを千鳥状に配列し、このような配列の超音波探触子ＳＥの一列目の超音波探触子ＳＥ(2m-1)と二列目の超音波探触子ＳＥ(2m)とから交互に、つまり、ＳＥ１、ＳＥ２、ＳＥ３、ＳＥ４、ＳＥ５、…の順番にて液位の有無を計測する。これにより、連続的に液位計測を行うことができ、超音波探触子ＳＥの寸法以下の液位を測定することが可能となる。
【００９９】
以上のように、この第２の実施の形態では、多段の超音波探触子ＳＥを設け、連続的に液位計測を行う連続しきい値判定方式であるが、第１の実施の形態における多重反射エコーパルス方式を合わせて採用することも可能である。すなわち、第１の実施の形態における多重エコーパルス方式の機能を超音波送受信手段１３および信号処理手段１４に持たせ、第２の実施の形態における連続しきい値判定方式とを、信号処理手段１４にて切り替えて用いる。これにより、単一装置にて２種類の測定方式を実施できる。
【０１００】
連続的に液位測定する連続しきい値判定方式の構成は、図１２に示したものとと同様である。一方、超音波送受信手段１３は、超音波探触子ＳＥのいずれか１個から超音波を送信して残りの超音波探触子から液槽内壁面からの反射パルスを受信し、信号処理手段１４は、その反射パルスの減衰率と受信側の超音波探触子および送信側の超音波探触子との取り付け位置に基づいて液槽内の液位を求める。これにより、第１の実施の形態における多重反射エコーパルス方式が実現される。
【０１０１】
そして、多重反射エコーパルス方式と連続しきい値判定方式とをタイムシェアリング処理にて切り替えて用いる。従って、常時２種類の異なる測定方式による液位監視の多様化が可能となる。
【０１０２】
例えば、多重反射エコーパルス方式にて、第１回目のフルレンジスキャンが終了し液位が確定した後に、連続しきい値判定方式による液位計測を開始する。これを繰り返し、常時２種類の測定方式で液位を確認することとなる。
【０１０３】
また、通常時は一方の測定方式とし、ある一定期間毎に中央操作室や計器校正室等から遠隔操作により他の測定方式で１点校正や超音波探触子の健全性確認を行う方法として用いることができる。
【０１０４】
ここで、図１２に示したものでは、超音波探触子ＳＥと超音波送受信手段１３との間は駆動信号ケーブルで接続しているが、図１５に示すように、超音波探触子ＳＥの間に次段の超音波探触子ＳＥの駆動タイミング信号を出力するための駆動信号遅延回路１５を設け、１段目の超音波探触子ＳＥ１と超音波送受信手段１３との間は駆動信号ケーブル１６で接続し、残りの超音波探触子ＳＥと超音波送受信手段１３との間は受信専用ケーブル１７で接続し、駆動信号ケーブルを大幅に削減することも可能である。
【０１０５】
図１５において、多段の超音波探触子ＳＥ間に、駆動信号遅延回路１５を各々設け、超音波探触子ＳＥの駆動信号ケーブル１６を１段目の超音波探触子ＳＥ１への１ループとする。これにより、多段に設置された超音波探触子ＳＥ毎の駆動信号ケーブルを大幅に削減することが可能となる。信号処理手段１４から超音波送受信手段１３を介して、ある周波数で発信された超音波探触子ＳＥの駆動信号は超音波探触子ＳＥの駆動用と反射波受信側を一体化した駆動信号ケーブル１６を伝播し、超音波探触子ＳＥ１が駆動され、超音波入射波及び壁面からの反射波がその駆動信号ケーブル１６を伝播し、超音波送受信手段１３を介して信号処理手段１４に入力され、液位の有無を判定しその結果を記憶する。
【０１０６】
次に、最適な遅れ時間に調整された駆動信号遅延回路１５を介して、次段の超音波探触子ＳＥ２が駆動され、超音波入射波及び壁面からの反射波が受信専用ケーブル１７を伝搬し、超音波送受信手段１３を介して信号処理手段１４に入力され液位の有無を判定しその結果を記憶する。こうして、最終段の超音波探触子ＳＥまである最適な遅れ時間で順々に駆動し、その受信信号から信号処理手段１４にて液位を算出し液位出力手段１１に信号出力する。
【０１０７】
次に、本発明の第３の実施の形態を説明する。図１６は第３の実施の形態に係わる超音波液位計測装置の超音波探触子部分の説明図である。この第３の実施の形態は、第１の実施の形態または第２の実施の形態に対し、液槽と材質を同じくし超音波探触子と断面積を同じくした冷却部材を液槽と超音波探触子との間に設けたものである。
【０１０８】
図１６において、被測定対象である圧力容器やタンク（液槽）が高温となる場合を考慮して、超音波探触子ＳＥへの熱伝達を低減するために、冷却部材１８を液槽と超音波探触子との間に設ける。
【０１０９】
すなわち、超音波探触子ＳＥ１〜ＳＥ５を液槽である液槽壁１ａの外面に設置する際に、液槽１と材質を同じくし各超音波探触子ＳＥ１〜ＳＥ５と断面積を同じくした冷却部材１８を液槽壁１ａにロウ付けとし、その冷却部材１８に超音波探触子ＳＥを取り付ける。この冷却部材１８の熱は外気によるフィン効果で放熱される。このように冷却部材１８で液槽である液槽１からの熱を空冷することにより、超音波探触子ＳＥへの熱伝達を低減し、極度の高温状態で特性が劣化することを防ぐ。
【０１１０】
また、第２の実施の形態のように多段の超音波探触子ＳＥを設ける場合においては、図１７に示すように、液槽である液槽の壁１ａと多段の超音波探触子ＳＥとの間に、液槽と材質を同じくし多段の超音波探触子ＳＥに共通の一体型の冷却部材１８を設けるようにする。
【０１１１】
図１７において、各超音波探触子ＳＥの共通の一体型の冷却部材１８を超音波探触子ＳＥ１〜ＳＥ５とロウ付け一体とし、冷却部材１８の両端を液槽壁１ａに溶接した固定治具１９に締付ボルト２０にて取り付ける。これにより、超音波探触子ＳＥの裾付や取り外しを容易にする。また、上部の締付ボルト２０と冷却部村１８の接触面を滑らかにすることにより、液槽の温度状態により垂直方向に伸縮し、超音波液位計測装置事態が破損等に至ることを防止することが可能となる。
【０１１２】
ここで、第２の実施の形態または第３の実施の形態のように多段の超音波探触子ＳＥを設ける場合においては、図１８に示すように、連続的に液槽内の液位を計測する多段の超音波探触子ＳＥに対して、それらの背面にＬＥＤ表示回路２１を設置し、現場のタンクや圧力容器等の液槽の外壁面において液位指示することも可能である。
【０１１３】
図１８において、各々の超音波探触子ＳＥの背面には制御回路２２とＬＥＤ表示回路２１が設置されている。超音波探触子ＳＥが受信した反射波を制御回路２２にて、その超音波探触子ＳＥの正面における液槽内包液の有無判定のしきい値と比較し、その比較結果をＬＥＤ表示回路２１にて表示する。このように、液位の有無を各々出力することで、現場のタンクや圧力容器等の液槽の外壁面にて液位指示することが可能となる。なお、図１８では、図１５に示した超音波液位計測装置に対してＬＥＤ表示回路２１を設置したものを示しているが、図１２、図１４、図１６、図１７に示した超音波液位計測装置に対して、ＬＥＤ表示回路２１を設けるようにしても良いことは言うまでもない。
【０１１４】
次に、図１９に示すように、液槽１の胴部にレベルゲージ方式にて取り出された配管２３を設け、その配管２３の外壁面に超音波探触子ＳＥを設けるようにしても良い。
【０１１５】
例えば、沸騰水型原子力発電所における原子炉圧力容器の胴部より枝管にて取り出された配管２３に対して、その配管２３の外壁面に超音波探触子ＳＥを設ける。つまり、原子炉の圧力容器から超音波探触子ＳＥを離隔することにより、超音波探触子ＳＥの放射線劣化を軽減し、耐熱性を向上させる。
【０１１６】
【発明の効果】
以上に説明したように、本発明によれば、被測定対象と非接触で液相内の液位の測定が精度よく行え、しかも耐環境性を向上できる。すなわち、原理的にタンクや圧力容器等の液槽外からの非接触液位測定であるので、差圧計測方式の場合の導圧配管用タップは不要となり、また、液位を電気信号として出力することから、差圧式計測のように基準水柱や変動水柱の配管ルートが異なる温度雰囲気を通さず極力同一ルートを併走するようにできる。従って、液槽及び導圧配管の内包水の密度条件が計器校正条件と異なった場合の液位指示に対する密度補正を実施する必要もなくなる。
【０１１７】
また、液槽が沸騰水型原子力発電所の圧力容器である場合には、原子炉液位測定について、原子炉格納容器壁に導圧配管用貫通部を設ける必要もなくなり、その工事物量を削減できる。さらに、測定精度が測定スパンに依存しないことから、用途や仕様別の差圧伝送器を多数設置する必要がなくなり、設備要素の個数を削減することができる。
【０１１８】
また、原子炉圧力容器のような高温の圧力容器に対しては、その外壁に超音波探触子を設置する場合には冷却部材を介在させて設置し、またレベルゲージ方式にて取り出された配管を設けてその配管に超音波探触子を設置することができるので、高温環境における耐久性や又は耐放射線性が向上する。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係わる超音波液位計測装置のブロック構成図。
【図２】本発明の第１の実施の形態に係わる超音波液位計測装置で受信側の超音波探触子を複数個（２個）設けた場合のブロック構成図。
【図３】本発明の第１の実施の形態における超音波受信手段で受信された超音波のエコーパルスの波形図。
【図４】液位変化に対する図３のエコーパルス強度の変化を示す特性図。
【図５】図４のエコーパルス強度の変化から換算された各反射波毎の減衰率を示す特性図。
【図６】図５の減衰率の変化から換算された液面下での超音波反射回数を示す特性図。
【図７】本発明の第１の実施の形態における各超音波探触子について波高変化測定の基準値を超音波探触子自身での超音波送受信の結果得られる受信強度に基づき補正する場合の超音波の送受信の説明図。
【図８】本発明の第１の実施の形態における送信側と受信側の超音波探触子の接続を順次切り替えるための送受信切替回路の説明図。
【図９】本発明の第１の実施の形態におけるタンク内部の気液二相混合部の有無および幅を推定する場合の超音波の散乱の様子の説明図。
【図１０】本発明の第１の実施の形態における液位換算手段にニューラルネットワークを導入したときのアルゴリズムの説明図。
【図１１】本発明の第１の実施の形態における超音波探触子としてフェーズドアレイセンサを用いた場合の説明図。
【図１２】本発明の第２の実施の形態に係わる超音波液位計測装置のブロック構成図。
【図１３】本発明の第２の実施の形態における信号処理手段での超音波探触子の正面における液槽内包液の有無判定のしきい値の説明図。
【図１４】本発明の第２の実施の形態における複数個の超音波探触子を千鳥状に配置した場合の説明図。
【図１５】本発明の第２の実施の形態における多段の超音波探触子間に駆動信号遅延回路を設けた場合の超音波液位計測装置のブロック構成図。
【図１６】本発明の第３の実施の形態に係わる超音波液位計測装置の超音波探触子部分の説明図。
【図１７】図１６の冷却部材を各々の超音波探触子に共通の一体型の冷却部材とした場合の説明図。
【図１８】本発明の第２の実施の形態または第３の実施の形態に係わる超音波液位計測装置の液槽の外壁面において液位指示する場合の説明図。
【図１９】本発明の第１の実施の形態乃至第３の実施の形態のうちのいずれかに係わる超音波液位計測装置の液槽胴部にレベルゲージ方式にて取り出された配管を設けた場合の超音波探触子の取付の説明図。
【図２０】従来の差圧測定方式で液位を計測する場合の説明図。
【図２１】従来の超音波式のレベルスイッチ方式で液位を計測する場合の説明図。
【符号の説明】
１ 圧力容器
２ 導圧配管
３ 差圧伝送器
４ 液位指示計
５、６ 超音波探触子
７ 超音波発信手段
８ 超音波受信手段
９ 信号検出手段
１０ 液位換算手段
１１ 液位出力手段
１２ 送受信切替回路
１３ 超音波送受信手段
１４ 信号処理手段
１５ 駆動信号遅延回路
１６ 駆動信号ケーブル
１７ 受信専用ケーブル
１８ 冷却部材
１９ 固定金具
２０ 締付ボルト
２１ ＬＥＤ表示回路
２２ 制御回路
２３ 配管[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic liquid level measuring device that detects a liquid level and a liquid surface position in a liquid tank such as a tank or a pressure vessel using ultrasonic waves.
[0002]
[Prior art]
In general, the liquid level in a liquid tank such as a tank or pressure vessel is measured using a differential pressure measurement method that measures the converted liquid level by measuring the pressure difference between the liquid phase part and the gas phase part using a pressure guiding pipe. It has been.
[0003]
That is, in FIG. 20, the pressure difference between the pressure guiding pipe 2 a taken out from the gas phase part A and the pressure guiding pipe 2 b taken out from the liquid phase part B with the liquid level C of the liquid tank 1 as a boundary is represented by the differential pressure transmitter 3. The differential pressure is converted into a standard signal (4 to 20 mA DC) at, and the liquid level indicator 4 indicates the converted liquid level.
[0004]
Further, there is an ultrasonic liquid level measurement method that measures the liquid level in the liquid tank 1 such as a tank and a pressure vessel using ultrasonic waves. This ultrasonic liquid level measurement method introduces a probe into the liquid tank 1 and measures the reflection time of ultrasonic waves transmitted from the upper and lower probes of the liquid tank 1 to obtain the liquid level. There are a measurement method, an ultrasonic waveguide dedicated resonance frequency change measurement method for obtaining a liquid level by measuring a change in resonance frequency of an ultrasonic rod waveguide, and the like.
[0005]
On the other hand, as a liquid level measurement from the outside of the liquid tank 1 such as a tank or a pressure vessel, there is a level switch type liquid level measurement method for determining whether the liquid level is above or below a certain position. As a technique of this level switch method, there is a method of determining the presence or absence of a liquid phase in the liquid tank 1 by ultrasonic transmission and reception from a probe installed on the wall surface of the liquid tank (US Patent No. 4,934,191 of Siemens).
[0006]
This is because when there is no liquid to be measured in the liquid tank 1, the ultrasonic wave does not leak into the water, so the reflection echo level decreases little, but when there is a liquid, the ultrasonic wave leaks into the water. This is due to the fact that the reflected echo level decreases.
[0007]
That is, in FIG. 21A, when the inner surface of the liquid tank wall 1a is a gas phase, the ultrasonic incident wave S1 transmitted from the detector SE1 into the structural material of the liquid tank wall 1a is the structural material and the gas phase portion in the container. As shown in FIG. 21B, most of the ultrasonic waves are reflected and returned to the detector SE1 as a reflected wave S2. When the inner surface of the liquid tank wall 1a is in the liquid phase, the ultrasonic incident wave S3 transmitted from the detector SE2 in the structural village of the liquid tank wall 1a is an acoustic impedance between the structural material and the liquid phase portion in the liquid tank. Is smaller than that in the gas phase, and the ultrasonic wave partially leaks into the liquid phase as a leakage wave S5, so that the reflected wave S4 returns to the detector SE2 as a low peak value as shown in FIG. Come.
[0008]
The ultrasonic level switch system is a system for detecting the presence or absence of liquid contained in the liquid tank 1 in front of the ultrasonic probe from the difference in the reflected wave peak value of the ultrasonic wave between the gas phase part and the liquid phase part.
[0009]
[Problems to be solved by the invention]
However, in the conventional differential pressure measurement method, the pressure guiding pipe 2 on the reference water column (low pressure) side and the variable water column (high pressure) side has an error in measuring the water level when the water density in the water column is different. It is necessary to construct so that the same route runs as much as possible so that the pipe route does not pass through different temperature atmospheres. Therefore, when the density condition of the contained water in the liquid tank 1 and the pressure guiding pipe 2 is different from the instrument calibration condition, it is necessary to perform the density correction on the operator side to correct the water level instruction. In addition, for example, in boiling water nuclear power plants, it is necessary to provide a pressure guide hole for water level measurement in the reactor pressure vessel, and to prepare a through-hole for pressure guide piping in the reactor containment vessel wall. The quantity is not small. In addition, the differential pressure measurement method does not measure the water level directly, but measures it by an indirect method called differential pressure.
[0010]
Here, for example, in the measurement of the water level of a reactor pressure vessel, the differential pressure transmitters 3 are installed in multiple according to the application and required specifications such as narrow band, wide band, fuel area, stop area, etc. If it can be integrated with high accuracy, it is possible to greatly reduce the quantity.
[0011]
On the other hand, the conventional ultrasonic liquid level measurement method using ultrasonic waves requires the introduction of a probe into the liquid tank, and therefore the sensor installation requires processing to penetrate the liquid tank wall. In addition, the level switch type liquid level measurement method from the outside of the liquid tank can only obtain discrete liquid level information from the positional relationship between the probe mounting position and the liquid level, and cannot obtain continuous liquid level information. It was. Also, the presence or absence of a liquid phase due to reception of multiple reflections of ultrasonic waves transmitted in one direction from the transmission side probe is determined, and it is necessary to install the reception side probe at a position corresponding to the ultrasonic transmission direction. And was insufficient to provide liquid level information for use as a reactor control signal.
[0012]
In addition, when the ultrasonic transducer used in the ultrasonic threshold judgment type water level gauge is directly installed on the outer wall of a high-temperature liquid tank such as a reactor pressure vessel, there is a concern about the influence of the high-temperature environment for a long period of time. .
[0013]
An object of the present invention is to obtain an ultrasonic liquid level measuring apparatus that can accurately measure the liquid level in the liquid phase without contact with the object to be measured and that has improved environmental resistance.
[0014]
[Means for Solving the Problems]
The ultrasonic liquid level measuring apparatus according to the invention of claim 1 is connected to any one of a plurality of ultrasonic probes installed on the outer wall surface of the liquid tank toward the inside of the liquid tank and the ultrasonic probe. Ultrasonic transmission means for transmitting ultrasonic waves, and ultrasonic reception means for receiving reflected pulses from the inner wall surface of the liquid tank connected to the remaining ultrasonic probes and transmitted by the ultrasonic transmission means; A signal detecting means for calculating the signal level and propagation time of the reflected pulse received by the ultrasonic receiving means for each ultrasonic receiving means, the attenuation rate of the reflected pulse, the ultrasonic probe on the receiving side, and the transmitting side A liquid level conversion means for converting the liquid level in the liquid tank based on the attachment position with the ultrasonic probe, and a liquid level output means for outputting the liquid level converted by the liquid level conversion means The ultrasonic liquid level measuring device, wherein the liquid level conversion means includes a multiplexing for each number of reflections specified by a delay time from an ultrasonic pulse transmission time obtained from a propagation path length in the wall material and a sound velocity in the wall material. For reflected echo pulses, a reference value is set for each echo pulse in advance, and the reflectivity due to the difference between the attenuation rate obtained from the rate of change in the pulse height with respect to the reference value and the state of contact of the inner wall surface with the number of multiple reflections of the echo pulse Based on the difference between the reflection phase at the liquid phase-wall material interface and the number of reflections at the gas phase-inner wall interface, the transmission side probe is calculated from the number of reflections at the liquid phase-wall material interface with respect to the number of multiple reflections. The liquid level with respect to the attachment position of the probe and the receiving probe is determined as a relative position relative to the multiple reflection position, and information on the relative position of the liquid level obtained for each of the multiple reflection echo pulses having different numbers of reflections is combined. By and were adapted to convert the liquid level of the liquid bath It is characterized by that.
[0016]
Claim 2 An ultrasonic liquid level measuring apparatus according to the invention of claim 1's In the invention, the liquid level conversion means determines the reference value for measuring the ultrasonic wave height change based on the reflected echo pulse intensity when all the inner wall surfaces between the ultrasonic probes are in contact with the liquid phase. It is characterized by that.
[0017]
Claim 3 An ultrasonic liquid level measuring apparatus according to the invention of claim 1's In the invention, the liquid level conversion means determines the reference value for measuring the ultrasonic wave height change based on the reflected echo pulse intensity when all the inner wall surfaces between the ultrasonic probes are in contact with the gas phase. It is characterized by that.
[0018]
Claim 4 An ultrasonic liquid level measuring apparatus according to the invention of claim 1's In the present invention, the liquid level conversion means determines a reference value for measuring a change in ultrasonic wave height based on a reception intensity obtained as a result of ultrasonic transmission / reception by the ultrasonic probe itself.
[0019]
Claim 5 The ultrasonic liquid level measuring apparatus according to the invention of A plurality of ultrasonic probes installed on the outer wall surface of the liquid tank toward the inside of the liquid tank, an ultrasonic wave transmitting means connected to any one of the ultrasonic probes and transmitting ultrasonic waves, and the remaining An ultrasonic receiving means connected to an ultrasonic probe for receiving a reflected pulse from an inner wall surface of a liquid tank transmitted by the ultrasonic transmitting means, and a reflected pulse signal received by the ultrasonic receiving means Based on signal detection means for calculating the level and propagation time for each ultrasonic reception means, the attenuation rate of the reflected pulse, and the attachment positions of the reception-side ultrasonic probe and the transmission-side ultrasonic probe An ultrasonic liquid level measuring device comprising: a liquid level conversion means for converting the liquid level in the liquid tank; and a liquid level output means for outputting the liquid level converted by the liquid level conversion means, A transmission / reception switching circuit is provided between the transmission-side ultrasonic probe and the ultrasonic oscillation means and between the reception-side ultrasonic probe and the ultrasonic reception means, respectively, and the transmission-side ultrasonic probe is provided. And the ultrasonic probe on the receiving side are switched.
[0020]
Claim 6 An ultrasonic liquid level measuring apparatus according to the present invention is the first aspect. To claim 5 In the invention according to any one of the above, the signal detecting means estimates the presence / absence and width of the gas-liquid two-phase mixing portion inside the liquid tank from a change in noise intensity between echo pulses from the inner wall of the liquid tank wall. Features.
[0021]
Claim 7 An ultrasonic liquid level measuring apparatus according to the invention of claim 6 In the invention, the signal detecting means estimates the void ratio from the noise intensity between echo pulses from the inner surface of the liquid tank wall with reference to a noise intensity-void ratio correspondence table prepared in advance.
[0022]
Claim 8 An ultrasonic liquid level measuring device according to the invention of claim 1 to claim 1. 7 In any one of the inventions, the liquid level conversion means is characterized in that the liquid level is estimated from the change in the reflected echo pulse intensity by a neural network that has learned the reference intensity change as a reference.
[0023]
Claim 9 An ultrasonic liquid level measuring device according to the invention of claim 1 to claim 1. 8 In any one of the inventions, each ultrasonic probe is a phased array type in which a plurality of small ultrasonic probes are arranged side by side.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. FIG. 1 is a block diagram of an ultrasonic liquid level measuring apparatus according to the first embodiment of the present invention. In the first embodiment, the liquid level is measured by a multiple reflection echo pulse method.
[0034]
In FIG. 1, two ultrasonic probes 5, 6 are provided outside the liquid tank wall 1 a storing the liquid, and one of the ultrasonic probes 5 is connected to the ultrasonic transmission means 7. Has been. The electrical signal generated from the ultrasonic transmission means 7 is converted into ultrasonic waves and transmitted from the ultrasonic probe 5 toward the liquid tank wall 1a. The ultrasonic wave inside the liquid tank wall surface in FIG. 1 propagates as a sound ray in the direction indicated by the arrow. The transmitted ultrasonic wave is reflected on the inner wall surface of the liquid tank wall 1a, and the reflected wave reaches the outer wall surface with which the ultrasonic probes 5 and 6 are in contact again and is repeatedly reflected. This process is repeated in the wall.
[0035]
When the reflection surface is in contact with the liquid phase when reflection is repeated, the refractive index propagating in the liquid phase is larger than the refractive index to the gas phase, so that the reflectance of the ultrasonic wave is lowered. The ultrasonic waves are received by the other ultrasonic probe 6 installed at a location away from the side outer wall through multiple reflection at different positions on the side wall surface between the ultrasonic probes according to the transmission angle.
[0036]
The number of times of reflection at the surface in contact with the liquid phase and the number of reflections in the gas phase are determined from the degree of decrease in the intensity of the multiple reflection echo pulse at this time, and a different path for each multiple reflection is determined. Information on the number of reflections under the liquid phase obtained from a plurality of propagated ultrasonic echo pulses is integrated. This, as a result, enables continuous measurement of the liquid level with an accuracy that cannot be achieved with multiple reflections in a single direction.
[0037]
The ultrasonic wave received by the ultrasonic probe 6 is converted into an electric signal corresponding to the reception intensity by the ultrasonic wave receiving means 8 at the subsequent stage. This converted signal is sent to the signal detection means 9. The ultrasonic signals received at this time have different echo pulse intensities and time delays depending on the number of reflections and the propagation distance, as shown in FIG.
[0038]
In FIG. 3, the echo pulse changes with reference to the baseline 30. The characteristic curve 31 is an echo pulse of a one-time reflected wave, and similarly, the characteristic curve 32 is an echo pulse of a two-time reflected wave, the characteristic curve 33 is an echo pulse of a three-time reflected wave, and in FIG. Echo pulses are shown.
[0039]
The signal detection means 9 performs processing for detecting information on the signal level of the echo pulse and the ultrasonic arrival time obtained according to the number of reflections. Based on the ultrasonic propagation time information and amplitude information, and information on the installation positions and intervals of the ultrasonic probes 5 and 6, the liquid level conversion means 10 in the next stage performs a process of calculating the liquid level. The calculated liquid level result is output to the liquid level output means 11 as a numerical value or a relative liquid level with respect to the structure height.
[0040]
In the above description, the two ultrasonic probes 5 and 6 are used. However, ultrasonic reception using three ultrasonic probes will be described with reference to FIG. In FIG. 2, three ultrasonic probes 21, 22, and 23 are installed at a distance in the vertical direction, and ultrasonic waves are transmitted from a single ultrasonic probe 21. Then, the ultrasonic probes 22 and 23 on the receiving side are arranged so that the ultrasonic waves 24 and 25 propagated through the wall surface can be received at a plurality of positions (two locations). The ultrasonic waves incident on the individual ultrasonic probes 22 and 23 follow different paths in the wall material of the liquid tank wall 1a, and the reflection positions 26 and 27 of the respective ultrasonic sound rays on the inner wall surface of the liquid tank respectively. Since the number of reflections of the ultrasonic probes 22 and 23 differs, the information can be multiplexed as compared with the case where information transmitted and received by the pair of ultrasonic probes 5 and 6 is used. There is an effect of improving accuracy.
[0041]
FIG. 4 is a characteristic diagram showing a change of the echo pulse intensity in FIG. 3 with respect to a change in the liquid level. In the ultrasonic echo pulse shown as a vertical line in FIG. 3, the attenuation rate changes because the number of reflections at the interface between the liquid phase and the wall material changes according to the change in the liquid level, and each echo pulse intensity changes to the liquid level. Decreases accordingly.
[0042]
In FIG. 4, a characteristic curve 41 is an envelope waveform when two ultrasonic probes are completely at the gas phase-wall material interface, and a characteristic curve 42 is the upper 3 / b between the two ultrasonic probes. 4 is an envelope waveform when the gas phase-wall material interface is present, and the characteristic curve 43 is an envelope waveform and characteristic curve 44 when the upper half between the two ultrasonic probes is the gas phase-wall material interface. Is the envelope waveform when the upper third between the two ultrasonic probes is the gas phase-wall material interface, and the characteristic curve 45 is the gas phase-wall material between the two ultrasonic probes completely. It is an envelope waveform at the time of an interface. The characteristic curve 46 is an average signal intensity between echo pulses of a transmission / reception signal.
[0043]
That is, the echo pulse of FIG. 3 is measured under five different liquid level conditions of the characteristic curves 41 to 45, and changes in the echo pulse intensity are shown. The horizontal axis in FIG. 4 represents the number of reflections at the wall material inner wall interface converted from the time delay from the ultrasonic wave transmission time.
[0044]
Next, FIG. 5 shows how the attenuation rate changes according to the number of reflections when an ultrasonic probe is installed on the outer wall surface of the tank storing water based on the echo pulse intensity. The reflectivity of ultrasonic waves at the water-wall material interface is about 0.94, and the ultrasonic reflectivity at the gas phase (here, air at normal temperature and normal pressure) -wall material interface is approximately 1.0, which is equivalent to total reflection. . In FIG. 5, the attenuation rate corresponding to the characteristic curves 41 to 45 in FIG. 4 is plotted for the case where the liquid level is changed.
[0045]
FIG. 6 is a characteristic diagram showing the number of ultrasonic reflections below the liquid level converted from the change in attenuation rate of FIG. In FIG. 6, based on this data, the number of reflections at the water-wall material interface is obtained from the attenuation rate and the reflectance for each time, and the same plotting is performed when the liquid level is changed.
[0046]
Thus, in 1st Embodiment, it has the some ultrasonic probe 5 and 6 (21, 22, 23) attached to the outer wall surface of a liquid tank, Among them, one specific ultrasonic wave The ultrasonic wave transmitting means 7 is connected to the probe 5 (21), and the reflected wave from the inner wall surface of the transmitted ultrasonic wave is ultrasonicated via the other ultrasonic probe 6 (22, 23). The signal is received by the receiving means 8 and the output of the ultrasonic receiving means 8 is the input of the signal detecting means 9.
[0047]
Due to the separation of the ultrasonic wave transmitting means 7 and the ultrasonic wave receiving means 8, the air that exists at an intermediate position between the ultrasonic probe 5 (21) and the ultrasonic probe 6 (22, 23) connected to them. The arrangement is such that the position of the interface between the phase and the liquid phase results in a change in the intensity of ultrasonic wave reception that undergoes multiple reflections.
[0048]
Furthermore, the signal detection means 9 for detecting the arrival time and the signal intensity of the echo pulse signal, the liquid level conversion means 10 for converting the liquid level based on the output signal, and the liquid level output for outputting the converted liquid level The liquid level conversion means 10 has a function of converting the liquid level from the attenuation amount of the ultrasonic intensity and the installation positions of the ultrasonic probes 5 and 6.
[0049]
The liquid level conversion means 10 preliminarily echoes multiple reflection echo pulses for each number of reflections specified by the delay time from the pulse transmission time obtained from the propagation path length in the wall material of the liquid tank wall 1a and the sound speed in the wall material. A reference value is set for each pulse, and based on the difference in reflectance due to the difference between the attenuation rate obtained from the rate of change in the pulse height with respect to the reference value and the number of multiple reflections of the echo pulse, the contact state of the inner wall surface -Calculate the number of reflections at the wall material interface and the number of reflections at the gas phase-inner wall interface, and calculate the number of reflections at the interface between the liquid phase and the wall material against the number of multiple reflections. The liquid level with respect to the attachment position with the ultrasonic probe is determined as an interval relative position with respect to the multiple reflection position.
[0050]
Hereinafter, processing contents in the liquid level conversion means 10 will be described. First, the number of multiple reflections n corresponding to the path from pulse transmission to reception is calculated from the time information. The number of multiple reflections n can be obtained from the following equation (1) from the delay time τ of the pulse arrival time with respect to the pulse transmission time.
[0051]
[Expression 1]

[0052]
Next, the number of reflections i below the liquid level is calculated from the amplitude information among n multiple reflections. The ultrasonic waves are reflected at the inner interface of the liquid tank wall 1a, but the reflectivity varies depending on the internal state (liquid phase, gas phase) in contact with the interface. Utilizing this property, calculation is performed from the number of multiple reflections obtained from the attenuation rate of the ultrasonic wave incident on the receiving side ultrasonic probe 6 (22, 23) and the time information after repeating many reflections. The number of reflections i below the liquid surface is calculated from the reflectance of the ultrasonic wave reflected at the incident angle.
[0053]
Then, assuming that the liquid is stored in the liquid tank, the liquid level is between the transmitting and receiving probes, and the number of reflections below the liquid level is i, the received ultrasonic intensity In at this time is (4 ) Expression.
[0054]
[Expression 2]

[0055]
In the above equation (5), only the value of the number of reflections i at the liquid phase interface changes according to the change in the liquid level, and if α (θn) ≠ β (θn), it is listed here. The number of reflections in the liquid phase can be obtained by obtaining an estimated amount numerically for each factor and substituting the electric signal intensity received after multiple reflections and the above numerical values. From the number of reflections i and the probe installation position information, the liquid level position l can be converted by the inequality (5).
[0056]
[Equation 3]

[0057]
Compared to the liquid level required for each multiple reflection echo pulse with different number of reflections by combining the liquid levels of multiple multiple reflection results by utilizing the fact that the position where ultrasonic waves are reflected differs when the number of multiple reflections is different The accuracy is improved.
[0058]
The liquid surface position l can be converted from the total reflection number n, the liquid phase reflection number i, and the ultrasonic probe installation position information d by the inequality (6).
[0059]
d (2i + 1) / 2n <l <d {2 (i + 1) +1} / 2n (6)
For each multiple reflection n, the liquid level height (liquid level position l) can be limited by such an inequality.
[0060]
The resolution of the liquid level obtained by a single reflection number n is d / n. However, by utilizing the information of the liquid level inequality obtained for a plurality of multiple reflection times n, the liquid level resolution is It is determined by the minimum value of the interval between the reflection positions, and can be improved to d / 2n to d / 2n (n-1).
[0061]
Here, the liquid level conversion means 10 is based on the echo pulse intensity of the measurement result when the inner wall surface between the ultrasonic probes is in contact with the liquid phase as a reference value for ultrasonic wave height change measurement. Liquid level conversion processing is performed. Thereby, the influence of the correction amount such as the angle dependency in the ultrasonic transmission / reception is canceled out. This is based on the waveform of the characteristic curve 45 shown in FIG. 4 (the envelope waveform when the two ultrasonic probes are completely at the gas phase-wall material interface), and the remaining characteristic curves 41-44. Is equivalent to calculating
[0062]
[Expression 4]

[0063]
Thereby, it is possible to cancel the influences of the coefficients such as γ and σ in the formula.
[0064]
The liquid level conversion means 10 uses the reference value for measuring the ultrasonic wave height as a reference based on the echo pulse intensity of the measurement result when the inner wall surface between the ultrasonic probes is in contact with the gas phase. In By performing the liquid level conversion process, the influence of the correction amount such as angle dependency in ultrasonic transmission / reception is canceled out. This is based on the waveform of the characteristic curve 41 shown in FIG. 4 (envelope waveform when the two ultrasonic probes are completely at the gas phase-wall material interface), and the remaining characteristic curves 42-45. Is equivalent to calculating
[0065]
[Equation 5]

[0066]
Thereby, it is possible to cancel the influences of the coefficients such as γ and σ in the formula.
[0067]
Further, the liquid level conversion means 10 corrects the reference value of the measurement of the change in the pulse height for each ultrasonic probe based on the reception intensity obtained as a result of ultrasonic transmission / reception by the ultrasonic probe itself. This cancels the influence of changes caused by deterioration of the ultrasonic probe.
[0068]
As shown in FIG. 7, ultrasonic waves 73 and 74 are periodically transmitted and received perpendicularly to the wall material direction from the ultrasonic probe 71 on the transmission side and the ultrasonic probe 72 on the reception side, and the internal state is the same. The received signal strength is held in the signal detection means 9. And in the process in the liquid level conversion means 10, the evaluation precision of the frequency | count of reflection is improved by utilizing this information.
[0069]
Next, as shown in FIG. 8, between the ultrasonic probe 81 on the transmission side and the ultrasonic oscillation means 7 so that the connection of the ultrasonic probe for transmitting and receiving ultrasonic waves can be sequentially switched. A transmission / reception switching circuit 12 is provided between the ultrasonic probe 82 on the receiving side and the ultrasonic receiving means 8.
[0070]
In other words, by utilizing the fact that the position where ultrasonic waves are reflected differs when the number of multiple reflections is different, switching between the ultrasonic probe 81 on the transmission side and the ultrasonic probe 82 on the reception side is performed. The liquid level section estimated by the combination of the information on the relative position of the liquid level obtained for each reflected echo pulse is narrowed to enable continuous liquid level measurement.
[0071]
In this way, by sequentially switching between the transmitting side and the receiving side of the ultrasonic probe, the ultrasonic multiple reflection position is slightly different if the transmitting side ultrasonic probe is different. Even if the arrangement of the tentacles is the same, it is possible to change the path through which the ultrasonic waves propagate in the wall material. In addition, by combining the waveform information obtained for each transmission, the liquid level measurement accuracy is improved and early detection of failure of some ultrasonic probes, the existence conditions of faulty ultrasonic probes But other ultrasound probes can supplement the lost information.
[0072]
Next, as shown in FIG. 9, on the basis of the change in noise intensity between echo pulses from the inner wall of the liquid tank wall 1a, the presence and width of the gas-liquid two-phase mixing part inside the liquid tank is determined by the signal detection means 9. Try to estimate. This is performed by measuring a state in which bubbles are mixed in the liquid phase inside the liquid tank.
[0073]
In FIG. 9, the ultrasonic wave 93 transmitted from the ultrasonic probe 91 on the transmission side propagates through the wall material of the liquid tank wall 1 a and causes reflection at the liquid phase-wall material interface. Some ultrasonic waves penetrate into the liquid phase, such as ultrasonic waves 94 and 95 in the phase. When the bubble 96 does not exist in the traveling direction of the ultrasonic wave transmitted through the mixed phase, it propagates through the liquid phase as it is like the transmitted ultrasonic wave 95.
[0074]
On the other hand, when there is a bubble 96 in the traveling direction of the ultrasonic wave, when the ultrasonic wave 94 reaches the surface of the bubble 96 in the mixed phase, reflection occurs on the surface of the bubble 96, and the reflected ultrasonic wave is an ultrasonic wave. It propagates in the wall material of the liquid tank wall 1a as shown in 97. When the propagated ultrasonic wave 97 enters the ultrasonic probe 92 on the receiving side, it is possible to detect a reflected wave of the ultrasonic wave indicating the presence of the bubble 96 in the mixed phase.
[0075]
The reflected wave 97 is weaker than the incident ultrasonic wave due to reflection only inside the wall material, the propagation time varies depending on the difference in sound velocity in the gas phase liquid phase, and the bubble position is widely distributed in the liquid phase. Therefore, the echo pulse shown in FIG. 3 contributes to the noise component on the baseline 30. That is, from the change in the characteristic curve 46 of the average intensity between echo pulses in FIG. 4, the strength of the reflection component by the bubble 96 can be evaluated, and the presence or absence of the bubble 96 can be measured.
[0076]
Thus, the signal detection means 9 detects a change in noise intensity between echo pulses from the inner wall of the liquid tank wall 1a. Presence / absence of ultrasonic wave 97 that is transmitted to the liquid phase at the wall material interface of the liquid tank wall 1a and reflected on the bubble surface of the gas-liquid two-phase mixing part inside the liquid tank and then incident on the ultrasonic probe 92 on the receiving side. From this, the presence or absence of the gas-liquid two-phase mixing part is measured.
[0077]
When the two-phase state is formed in the liquid phase, a part of the ultrasonic wave 94 incident on the liquid phase-wall material interface below the liquid surface is transmitted into the liquid phase. This transmitted wave 94 is reflected on the surface of the bubble 96 to generate a component that returns to the wall material again. A part of the ultrasonic wave incident on the wall material from the liquid phase direction propagates in the wall material and enters the receiving side ultrasonic probe 92. At this time, the sound velocity in the liquid phase is increased in the wall material. Compared with the ultrasonic wave propagating through the wall material due to the low propagation path and the propagation path, it has a different delay time and low ultrasonic intensity. It contributes to the scattered ultrasonic component between echo pulses with different numbers of reflections. When the bubble 96 exists, it can be detected that the scattering component is increased and the presence or absence of the two-phase state can be detected.
[0078]
Here, under the conditions shown in FIG. 9, in the same system as the actual measurement conditions, the ratio of the bubbles 96 contained in the liquid phase, that is, the void ratio, is changed by changing the flow rate of the bubbles 96, and at the same time by another method. The void ratio is measured in advance. On the other hand, the noise intensity of the obtained reception signal is measured, a noise intensity / void ratio correspondence table is created and stored in the signal detection means 9 in advance. When the noise intensity changes, the void ratio is estimated with reference to this noise intensity-void ratio correspondence table. Thereby, a void ratio can be estimated quickly.
[0079]
As described above, as the void ratio of the gas-liquid two-phase mixing portion increases, the surface area of the bubble 96 increases. As a result, the amount of ultrasonic reflection on the bubble surface increases, and the noise intensity between echo pulses from the inner wall of the liquid tank wall 1a. The void ratio is estimated with reference to a noise intensity / void ratio correspondence table created in advance using the property that the increase of the noise ratio.
[0080]
Next, FIG. 10 is an explanatory diagram of an algorithm when a neural network is introduced into the liquid level conversion means 10. The liquid level conversion means 10 estimates the liquid level from the change in the reflected echo pulse intensity by a neural network that has learned the reference intensity change as a reference.
[0081]
Assuming that waveforms such as the characteristic curves 41 to 45 of the echo pulse envelope with the liquid level as a parameter shown in FIG. 4 are obtained in advance corresponding to each liquid level, the waveform information of FIG. Learning is performed by a feedforward artificial neural network 102 based on an error back-propagation algorithm in which waveform shapes corresponding to different liquid levels such as the peak shape 101 are input and the liquid level is output. Then, the artificial neural network 104 for which learning has been completed is incorporated as a processing mechanism of the liquid level conversion means 10. Thereby, the liquid level information is estimated by using the measured waveform shape 103 as an input.
[0082]
As described above, a neural network in which a reference intensity change as a reference is learned is adopted as the liquid level conversion means 10, and the liquid level is estimated from the change in the reflected echo pulse intensity. Accordingly, the liquid level can be estimated more accurately and quickly.
[0083]
FIG. 11 is an explanatory diagram when a phased array sensor is used as an ultrasonic probe. As shown in FIG. 11, phased array ultrasonic probes 111 and 112 each having a small ultrasonic probe arranged side by side are installed. Thereby, the focal point 114 by the phased array is set at a position where the ultrasonic wave 113 is reflected by the inner wall surface of the liquid tank wall 1a, and the presence or absence of the liquid phase is detected from the difference in reflectance at that position. In the phased array, the synthetic ultrasonic wave transmission direction is realized by controlling the delay time of the transmission time of the ultrasonic probe constituting the array, and by continuously changing this delay time, the inner wall surface of the liquid tank The focal position 114 is continuously moved, and the position of the liquid level is continuously measured.
[0084]
As described above, by using a phased array type ultrasonic probe configured by arranging a plurality of small ultrasonic probes as an ultrasonic probe, the phased array transmits a specific position on the inner surface of the liquid tank wall. The ultrasonic focus 114 is adjusted, the presence or absence of the liquid level at that position is measured with high resolution, and the liquid level can be continuously measured by continuously changing the focal position.
[0085]
Next, a second embodiment of the present invention will be described. FIG. 12 is a block diagram showing a second embodiment of the present invention. In the second embodiment, the liquid level is measured by a continuous threshold determination method. That is, a plurality of ultrasonic probes SE1 to SE9 are installed in multiple stages on the outer wall surface of the liquid tank toward the inside of the liquid tank, and these ultrasonic probes SE1 to SE9 are sequentially switched by the ultrasonic transmission / reception means 13. Ultrasonic waves are transmitted and reflected echo pulses from the inner surface of the liquid tank are received in the order of switching the ultrasonic probe. Then, based on the peak value of the reflected echo pulse from the ultrasonic transmission / reception means SE1 to SE9, the signal processing means 14 determines the presence / absence of the liquid contained in the liquid tank in front of each ultrasonic probe SE1 to SE9. The liquid level is determined.
[0086]
The ultrasonic transmission / reception unit 13 corresponds to the ultrasonic transmission unit 7 and the ultrasonic reception unit 8 of the first embodiment, and has a function of sequentially switching and receiving a plurality of ultrasonic probes SE1 to SE9. The signal processing means 14 corresponds to the signal detection means 9 and the liquid level conversion means 10 of the first embodiment, and continuously obtains the liquid level based on the sequentially received reflected echo pulses.
[0087]
In FIG. 12, multistage ultrasonic probes SE1, SE2, SE3, SE4, SE5, SE6, SE7, SE8, and SE9 are arranged on the outer surface of the liquid tank wall 1a of the liquid tank 1 toward the inside of the liquid tank 1. The ultrasonic transmission / reception means 13 is transmitted at a predetermined frequency, a switching drive function for switching and driving these ultrasonic probes SE1 to SE9, a reception function for receiving signals from the ultrasonic probes SE1 to SE9, and a predetermined frequency. It has an ultrasonic transmission function.
[0088]
The signal processing means 14 has a detection function for binarizing the received signal with a predetermined threshold, and the liquid contained in the liquid tank in front of each ultrasonic probe SE1 to SE9 based on the binarized signal. Determine presence or absence. And it has the function to determine a liquid level from the presence or absence of these inclusion liquids, and the output function which carries out the signal processing of the continuous liquid level, and outputs it externally.
[0089]
First, the ultrasonic transmission / reception means 13 selects and switches in order from the ultrasonic probe SE1 by the drive signal from the signal processing means 14, and transmits ultrasonic waves from the selected and switched ultrasonic probe. And the ultrasonic transmission / reception means 13 receives a reflected wave from the ultrasonic probe which sent the ultrasonic wave.
[0090]
FIG. 12 shows that the ultrasonic wave S1 is transmitted from the second ultrasonic probe SE2, and the ultrasonic wave S1 transmitted from the liquid tank wall 1a propagates through the liquid tank wall 1a, and the liquid tank 1 When the inner surface is in the air or vapor phase, the reflected wave S2 having the same peak value as the transmission signal returns to the ultrasonic probe SE2. Since the peak value of the reflected wave S2 is larger than a predetermined threshold value, it is determined and stored that the front surface of the ultrasonic probe SE2 in the liquid tank 1 is in the air or vapor phase. When the presence / absence of the inclusion liquid in the liquid tank 1 is determined, the ultrasonic probe SE3 is switched to the next stage. In this way, the presence or absence of the inclusion liquid in the liquid tank 1 at each ultrasonic probe position is determined. For example, in the ultrasonic probe SE6, since the difference in acoustic impedance between the steel material and water is smaller than that in the case of air and steam with respect to the incident wave S3, a leakage wave S5 of the ultrasonic wave S3 is generated. The peak value of the reflected wave S4 that returns to the ultrasonic probe SE6 is smaller than when there is no inclusion liquid. From this, the peak value of the received reflected wave S4 becomes smaller than a predetermined threshold value, and it is determined and stored that the contained liquid exists in front of the ultrasonic probe SE6 in the liquid tank 1.
[0091]
In this way, the ultrasonic probe SE is sequentially switched, and the water surface position determined from the boundary point of the presence or absence of the inclusion liquid is output from the signal processing means 14 to the liquid level output means 11 as a liquid level signal.
[0092]
That is, a plurality of ultrasonic probes SE are installed in multiple stages, and after each stage of measurement (ultrasonic transmission / reception and signal processing) is completed, transmission / reception of the next-stage ultrasonic probe SE starts. By confirming the presence or absence of the liquid level at the top by the ring method, ultrasonic interference of each ultrasonic probe SE is prevented. In addition, since measurement accuracy depends on the structural dimensions of the piezoelectric element, which is an ultrasonic probe, measurement accuracy can be improved by using small piezoelectric elements, and ultrasonic probes are arranged in multiple stages and in a single row. Continuous liquid level measurement is possible by scanning.
[0093]
Here, the threshold value for the presence / absence determination of the liquid contained in the liquid tank in front of the ultrasonic probe SE is determined by the signal processing means 14 at any time on the basis of the transmitted pulse peak value of the ultrasonic wave.
[0094]
As shown in FIGS. 13 (a) and 13 (b), the threshold value EP for determining the presence or absence of liquid contained in a liquid tank such as a pressure vessel or tank is the peak value E1 of the transmitted ultrasonic wave S1 (S3). Is determined and updated at any time as a value obtained by subtracting the attenuation ΔE1.
[0095]
For example, in FIG. 13A, the threshold value is a value that takes into account a certain amount of attenuation ΔE1 (3%) with respect to the pulse peak value E1 of the ultrasonic incident wave S1. That is, the threshold value EP is E1−ΔE1. When the inclusion liquid does not exist in front of the ultrasonic probe in the liquid tank (in the case of air or vapor phase), the reflected wave S2 from the inner wall surface of the liquid tank is received at the pulse peak value E2 that hardly attenuates, and the threshold value is reached. Since the value EP is exceeded, it is determined that there is no inclusion liquid.
[0096]
Further, in FIG. 13B, when the certain amount of attenuation ΔE3 (3%) is set with respect to the pulse peak value E3 of the ultrasonic incident wave S3, the threshold value EP in that case is E3−ΔE3. When the inclusion liquid is present in front of the ultrasonic probe in the liquid tank (in the case of liquid phase), the reflected wave S4 from the wall inner surface of the liquid tank 1 does not reflect the ultrasonic leakage S5 to the liquid phase side. Therefore, since the pulse peak value E4 is received and falls below the threshold value EP, it is determined that the inclusion liquid is present. A continuous liquid level is calculated by repeating this for all the ultrasonic probes SE.
[0097]
By using the processing as described above, it is possible to cope with the secular change of the pulse peak value of the incident wave of the ultrasonic probe SE and the instability of the peak value.
[0098]
For the multi-stage ultrasonic probe installed on the outer surface of the liquid tank wall toward the inside of the container, the ultrasonic probes SE are arranged in a staggered manner as shown in FIG. FIG. 14A is a view seen from the side surface direction of the liquid tank wall 1a, and FIG. 14B is a view seen from the plane direction of the liquid tank wall 1a. As shown in FIG. 14, the ultrasonic probes SE are arranged in a zigzag pattern, and the ultrasonic probe SE (2m-1) in the first row and the second row in the ultrasonic probe SE having such an arrangement are arranged. The presence or absence of the liquid level is measured alternately from the ultrasonic probe SE (2 m), that is, in the order of SE1, SE2, SE3, SE4, SE5,. Thereby, the liquid level can be continuously measured, and the liquid level below the dimension of the ultrasonic probe SE can be measured.
[0099]
As described above, in the second embodiment, the multi-stage ultrasonic probe SE is provided and the continuous threshold value determination method for continuously measuring the liquid level is used. However, in the first embodiment, It is also possible to adopt a multiple reflection echo pulse method. That is, the function of the multiple echo pulse method in the first embodiment is provided to the ultrasonic transmission / reception means 13 and the signal processing means 14, and the continuous threshold determination method in the second embodiment is changed to the signal processing means 14. Switch between and use. Thereby, two types of measurement methods can be implemented with a single device.
[0100]
The configuration of the continuous threshold value determination method for continuously measuring the liquid level is the same as that shown in FIG. On the other hand, the ultrasonic transmission / reception means 13 transmits ultrasonic waves from any one of the ultrasonic probes SE, receives reflected pulses from the inner wall surface of the liquid tank from the remaining ultrasonic probes, and performs signal processing. 14 obtains the liquid level in the liquid tank based on the attenuation rate of the reflected pulse and the attachment positions of the reception-side ultrasonic probe and the transmission-side ultrasonic probe. Thereby, the multiple reflection echo pulse system in the first embodiment is realized.
[0101]
Then, the multiple reflection echo pulse method and the continuous threshold value determination method are switched and used in the time sharing process. Therefore, it is possible to diversify the liquid level monitoring by always using two different measurement methods.
[0102]
For example, in the multiple reflection echo pulse method, after the first full-range scan is completed and the liquid level is determined, the liquid level measurement by the continuous threshold value determination method is started. This is repeated and the liquid level is always confirmed by two types of measurement methods.
[0103]
In addition, one measurement method is normally used, and as a method of performing one-point calibration and checking the soundness of the ultrasonic probe by remote measurement from a central operation room or an instrument calibration room at regular intervals. Can be used.
[0104]
In the example shown in FIG. 12, the ultrasonic probe SE and the ultrasonic transmission / reception means 13 are connected by a drive signal cable. However, as shown in FIG. 15, the ultrasonic probe SE is used. A drive signal delay circuit 15 for outputting a drive timing signal for the next-stage ultrasonic probe SE is provided between the first-stage ultrasonic probe SE1 and the ultrasonic transmission / reception means 13. It is also possible to connect the signal cable 16 and connect the remaining ultrasonic probe SE and the ultrasonic transmission / reception means 13 using the reception-only cable 17 to greatly reduce the drive signal cable.
[0105]
In FIG. 15, a drive signal delay circuit 15 is provided between the multi-stage ultrasonic probes SE, and the drive signal cable 16 of the ultrasonic probe SE is connected to one loop to the first-stage ultrasonic probe SE1. And As a result, it is possible to greatly reduce the drive signal cable for each of the ultrasonic probes SE installed in multiple stages. The drive signal of the ultrasound probe SE transmitted at a certain frequency from the signal processing means 14 via the ultrasound transmission / reception means 13 is a drive signal in which the drive for the ultrasound probe SE and the reflected wave receiving side are integrated. The ultrasonic probe SE 1 is driven through the cable 16, and the ultrasonic incident wave and the reflected wave from the wall surface propagate through the drive signal cable 16 and are input to the signal processing unit 14 through the ultrasonic transmission / reception unit 13. Then, the presence / absence of the liquid level is determined and the result is stored.
[0106]
Next, the ultrasonic probe SE2 at the next stage is driven through the drive signal delay circuit 15 adjusted to the optimum delay time, and the ultrasonic incident wave and the reflected wave from the wall surface propagate through the reception-only cable 17. Then, it is input to the signal processing means 14 via the ultrasonic transmission / reception means 13 and the presence / absence of the liquid level is determined and the result is stored. In this way, the ultrasonic probe SE of the final stage is sequentially driven with a certain optimum delay time, the liquid level is calculated by the signal processing means 14 from the received signal, and the signal is output to the liquid level output means 11.
[0107]
Next, a third embodiment of the present invention will be described. FIG. 16 is an explanatory diagram of an ultrasonic probe portion of the ultrasonic liquid level measuring apparatus according to the third embodiment. This third embodiment is different from the first embodiment or the second embodiment in that a cooling member having the same material as that of the liquid tank and the same cross-sectional area as that of the ultrasonic probe is used. It is provided between the acoustic probe.
[0108]
In FIG. 16, in consideration of the case where the pressure vessel or tank (liquid tank) that is the object to be measured becomes high temperature, the cooling member 18 is replaced with the liquid tank in order to reduce heat transfer to the ultrasonic probe SE. Provided between the ultrasonic probe.
[0109]
That is, when the ultrasonic probes SE1 to SE5 are installed on the outer surface of the liquid tank wall 1a, which is a liquid tank, the material is the same as that of the liquid tank 1 and the cross-sectional area is the same as that of the ultrasonic probes SE1 to SE5. The cooling member 18 is brazed to the liquid tank wall 1a, and the ultrasonic probe SE is attached to the cooling member 18. The heat of the cooling member 18 is radiated by the fin effect caused by the outside air. Thus, by cooling the heat from the liquid tank 1 which is the liquid tank by the cooling member 18, heat transfer to the ultrasonic probe SE is reduced, and the characteristics are prevented from being deteriorated at an extremely high temperature state.
[0110]
Further, when the multistage ultrasonic probe SE is provided as in the second embodiment, as shown in FIG. 17, the wall 1a of the liquid tank, which is a liquid tank, and the multistage ultrasonic probe SE are provided. Between the two, a common integrated cooling member 18 is provided for the multistage ultrasonic probe SE, using the same material as the liquid tank.
[0111]
In FIG. 17, a common integrated cooling member 18 of each ultrasonic probe SE is brazed integrally with the ultrasonic probes SE1 to SE5, and both ends of the cooling member 18 are welded to the liquid tank wall 1a. Attach to the tool 19 with fastening bolts 20. This facilitates the skirting and removal of the ultrasonic probe SE. In addition, by smoothing the contact surface between the upper clamping bolt 20 and the cooling unit village 18, it is possible to expand or contract in the vertical direction depending on the temperature state of the liquid tank, preventing the ultrasonic liquid level measuring device from being damaged. It becomes possible to do.
[0112]
Here, when the multi-stage ultrasonic probe SE is provided as in the second embodiment or the third embodiment, the liquid level in the liquid tank is continuously changed as shown in FIG. It is also possible to install an LED display circuit 21 on the back of the multi-stage ultrasonic probe SE to be measured and to instruct the liquid level on the outer wall surface of a liquid tank such as a tank or a pressure vessel in the field.
[0113]
In FIG. 18, a control circuit 22 and an LED display circuit 21 are installed on the back surface of each ultrasonic probe SE. The control circuit 22 compares the reflected wave received by the ultrasonic probe SE with a threshold value for determining the presence or absence of liquid contained in the liquid tank in front of the ultrasonic probe SE, and the comparison result is indicated by an LED. Displayed by the circuit 21. Thus, by outputting the presence / absence of the liquid level, it is possible to instruct the liquid level on the outer wall surface of the liquid tank such as a tank or a pressure vessel in the field. 18 shows the ultrasonic liquid level measuring device shown in FIG. 15 in which the LED display circuit 21 is installed. However, the ultrasonic waves shown in FIG. 12, FIG. 14, FIG. 16, and FIG. It goes without saying that the LED display circuit 21 may be provided for the liquid level measuring device.
[0114]
Next, as shown in FIG. 19, a pipe 23 taken out by a level gauge method may be provided in the body portion of the liquid tank 1, and an ultrasonic probe SE may be provided on the outer wall surface of the pipe 23. .
[0115]
For example, an ultrasonic probe SE is provided on the outer wall surface of the pipe 23 taken out from the trunk of the reactor pressure vessel in the boiling water nuclear power plant with a branch pipe. That is, by separating the ultrasonic probe SE from the reactor pressure vessel, radiation deterioration of the ultrasonic probe SE is reduced and heat resistance is improved.
[0116]
【The invention's effect】
As described above, according to the present invention, the liquid level in the liquid phase can be accurately measured without contact with the measurement target, and the environmental resistance can be improved. That is, in principle, it is a non-contact liquid level measurement from outside the liquid tank such as a tank or pressure vessel, so there is no need for a tap for pressure guiding piping in the case of the differential pressure measurement method, and the liquid level is output as an electrical signal Therefore, unlike the differential pressure type measurement, the piping route of the reference water column and the fluctuating water column can run along the same route as much as possible without passing through different temperature atmospheres. Therefore, it is not necessary to perform density correction for the liquid level indication when the density condition of the contained water in the liquid tank and the pressure guiding pipe is different from the instrument calibration condition.
[0117]
In addition, when the liquid tank is a boiling water nuclear power plant pressure vessel, it is no longer necessary to provide a penetration piping penetration on the reactor containment wall for reactor liquid level measurement, reducing the amount of construction work. it can. Furthermore, since the measurement accuracy does not depend on the measurement span, it is not necessary to install a large number of differential pressure transmitters according to applications and specifications, and the number of equipment elements can be reduced.
[0118]
In addition, for high-temperature pressure vessels such as reactor pressure vessels, when installing an ultrasonic probe on the outer wall, it was placed with a cooling member interposed, and was taken out by a level gauge method. Arrangement Tube Establish its arrangement On the tube Install an ultrasound probe be able to Therefore, durability in a high temperature environment or radiation resistance is improved.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram of an ultrasonic liquid level measuring apparatus according to a first embodiment of the present invention.
FIG. 2 is a block configuration diagram in the case where a plurality (two) of ultrasonic probes on the receiving side are provided in the ultrasonic liquid level measuring apparatus according to the first embodiment of the present invention.
FIG. 3 is a waveform diagram of ultrasonic echo pulses received by the ultrasonic wave receiving means according to the first embodiment of the present invention.
4 is a characteristic diagram showing a change in echo pulse intensity of FIG. 3 with respect to a change in liquid level.
5 is a characteristic diagram showing an attenuation factor for each reflected wave converted from a change in echo pulse intensity in FIG. 4;
FIG. 6 is a characteristic diagram showing the number of ultrasonic reflections below the liquid level converted from the change in the attenuation factor of FIG.
FIG. 7 shows a case in which the reference value of the wave height change measurement is corrected based on the reception intensity obtained as a result of ultrasonic transmission / reception by the ultrasonic probe itself for each ultrasonic probe according to the first embodiment of the present invention. Explanatory drawing of transmission / reception of an ultrasonic wave.
FIG. 8 is an explanatory diagram of a transmission / reception switching circuit for sequentially switching the connection between the transmitting side and the receiving side ultrasonic probes in the first embodiment of the present invention.
FIG. 9 is an explanatory diagram of the state of ultrasonic scattering when estimating the presence / absence and width of a gas-liquid two-phase mixing unit in the tank according to the first embodiment of the present invention.
FIG. 10 is an explanatory diagram of an algorithm when a neural network is introduced into the liquid level conversion means in the first embodiment of the present invention.
FIG. 11 is an explanatory diagram when a phased array sensor is used as the ultrasonic probe according to the first embodiment of the invention.
FIG. 12 is a block configuration diagram of an ultrasonic liquid level measuring apparatus according to a second embodiment of the present invention.
FIG. 13 is an explanatory diagram of a threshold value for determining presence / absence of liquid contained in a liquid tank in front of an ultrasonic probe in a signal processing unit according to a second embodiment of the present invention.
FIG. 14 is an explanatory diagram when a plurality of ultrasonic probes according to the second embodiment of the invention are arranged in a staggered manner.
FIG. 15 is a block configuration diagram of an ultrasonic liquid level measurement apparatus when a drive signal delay circuit is provided between multistage ultrasonic probes according to the second embodiment of the present invention.
FIG. 16 is an explanatory diagram of an ultrasonic probe portion of an ultrasonic liquid level measuring apparatus according to a third embodiment of the present invention.
FIG. 17 is an explanatory diagram in the case where the cooling member of FIG. 16 is an integrated cooling member common to each ultrasonic probe.
FIG. 18 is an explanatory diagram when the liquid level is instructed on the outer wall surface of the liquid tank of the ultrasonic liquid level measuring apparatus according to the second embodiment or the third embodiment of the present invention.
FIG. 19 is provided with a pipe taken out by a level gauge method in the liquid tank body of the ultrasonic liquid level measuring device according to any one of the first to third embodiments of the present invention. Explanatory drawing of attachment of the ultrasonic probe in the case of.
FIG. 20 is an explanatory diagram in the case of measuring a liquid level by a conventional differential pressure measurement method.
FIG. 21 is an explanatory diagram when the liquid level is measured by a conventional ultrasonic level switch method.
[Explanation of symbols]
1 Pressure vessel
2 Induction piping
3 Differential pressure transmitter
4 Level indicator
5, 6 Ultrasonic probe
7 Ultrasonic transmission means
8 Ultrasonic wave receiving means
9 Signal detection means
10 Liquid level conversion means
11 Liquid level output means
12 Transmission / reception switching circuit
13 Ultrasonic transmission / reception means
14 Signal processing means
15 Drive signal delay circuit
16 Drive signal cable
17 Receive-only cable
18 Cooling member
19 Fixing bracket
20 Tightening bolt
21 LED display circuit
22 Control circuit
23 Piping

Claims (9)

A plurality of ultrasonic probes installed on the outer wall surface of the liquid tank toward the inside of the liquid tank, an ultrasonic wave transmitting means connected to any one of the ultrasonic probes and transmitting ultrasonic waves, and the remaining An ultrasonic receiving means connected to an ultrasonic probe for receiving a reflected pulse from an inner wall surface of a liquid tank transmitted by the ultrasonic transmitting means, and a reflected pulse signal received by the ultrasonic receiving means Based on signal detection means for calculating the level and propagation time for each ultrasonic reception means, the attenuation rate of the reflected pulse, and the attachment positions of the reception-side ultrasonic probe and the transmission-side ultrasonic probe An ultrasonic liquid level measuring device comprising: a liquid level conversion means for converting the liquid level in the liquid tank; and a liquid level output means for outputting the liquid level converted by the liquid level conversion means ,
The liquid level conversion means, for each echo pulse in advance, for multiple reflection echo pulses for each number of reflections specified by the delay time from the ultrasonic pulse transmission time obtained from the propagation path length in the wall material and the sound speed in the wall material Set a reference value, and based on the difference in reflectivity due to the difference in the state of contact of the inner wall surface with the attenuation rate obtained from the rate of change in wave height with respect to the reference value and the number of multiple reflections of echo pulses, the liquid phase-wall material Calculate the reflection reflexes at the interface and the number of reflections at the gas phase-inner wall interface, and determine the mounting position of the transmitter and receiver probes from the number of reflections at the liquid phase-wall interface relative to the number of multiple reflections. The liquid level in the liquid tank is determined by combining the information on the relative position of the liquid level obtained for each of the multiple reflection echo pulses having different numbers of reflections. Ultrasonic liquid level measuring device which is characterized in that so as to calculate. In the invention of claim 1, the liquid level conversion means is a reflected echo pulse when the inner wall surface between the ultrasonic probes is in contact with the liquid phase with respect to a reference value for measuring a change in ultrasonic wave height. An ultrasonic liquid level measuring apparatus, characterized by being determined based on intensity . In the invention according to claim 1 , the liquid level conversion means is a reflected echo pulse when the inner wall surface between the ultrasonic probes is in contact with the gas phase with respect to a reference value for measuring the ultrasonic wave height change. An ultrasonic liquid level measuring apparatus, characterized by being determined based on intensity . In the invention of claim 1 , the liquid level conversion means determines a reference value for measuring a change in ultrasonic wave height based on a reception intensity obtained as a result of ultrasonic transmission / reception by the ultrasonic probe itself. Ultrasonic liquid level measuring device characterized by. A plurality of ultrasonic probes installed on the outer wall surface of the liquid tank toward the inside of the liquid tank, an ultrasonic wave transmitting means connected to any one of the ultrasonic probes and transmitting ultrasonic waves, and the remaining An ultrasonic receiving means connected to an ultrasonic probe for receiving a reflected pulse from an inner wall surface of a liquid tank transmitted by the ultrasonic transmitting means, and a reflected pulse signal received by the ultrasonic receiving means Based on signal detection means for calculating the level and propagation time for each ultrasonic reception means, the attenuation rate of the reflected pulse, and the attachment positions of the reception-side ultrasonic probe and the transmission-side ultrasonic probe An ultrasonic liquid level measuring device comprising: a liquid level conversion means for converting the liquid level in the liquid tank; and a liquid level output means for outputting the liquid level converted by the liquid level conversion means,
A transmission / reception switching circuit is provided between the transmission-side ultrasonic probe and the ultrasonic oscillation means and between the reception-side ultrasonic probe and the ultrasonic reception means, respectively, and the transmission-side ultrasonic probe is provided. And an ultrasonic probe on the receiving side are switched . 6. The gas-liquid two-phase mixing unit in the liquid tank according to any one of claims 1 to 5, wherein the signal detection means is a change in noise intensity between echo pulses from the inner wall of the liquid tank wall. An ultrasonic liquid level measuring apparatus for estimating presence / absence and width . The invention according to claim 6 is characterized in that the signal detecting means estimates the void ratio from a noise intensity between echo pulses from the inner surface of the liquid tank wall with reference to a noise intensity-void ratio correspondence table prepared in advance. An ultrasonic liquid level measuring device. 8. The liquid level conversion means according to claim 1 , wherein the liquid level conversion means estimates the liquid level from a change in reflected echo pulse intensity by a neural network that has learned a reference intensity change as a reference. An ultrasonic liquid level measuring device characterized by that. The ultrasonic liquid according to any one of claims 1 to 8, wherein each ultrasonic probe is a phased array type in which a plurality of small ultrasonic probes are arranged side by side. Position measuring device.

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