JP2004205475A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the impossibility of measuring due to the reason that ultrasonic waves do not adequately reach the other oscillator, when bubbles are contained in a fluid in an ultrasonic flowmeter. <P>SOLUTION: The flow rate v1 of a fluid which does not contain foreign substances such as bubbles is measured with a first oscillator and a second oscillator. The flow rate v2 of a fluid which contains foreign substances, such as bubbles is measured with the first oscillator and a third oscillator. In the ST08, it is decided which flow rate is selected. The ultrasonic flowmeter can measure the flow rate of a fluid, regardless of the presence or absence of the mixing of foreign substances, such as bubbles. While removing bubbles by temporarily performing deairing processing or removing foreign substances by filtration leads to increase in facility costs and operating costs, the present invention eliminates the need for such processings, thereby reducing the facility costs and operating costs. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００６】
すなわち、▲１▼式の逆数から▲２▼式の逆数を差引くことで▲３▼式を導き出し、この▲３▼式をｖ１について整理したものが▲４▼式である。この▲４▼式によれば、流体の流速ｖ１は距離Ｌ１、時間ｔ１及び時間ｔ２が定まれば求まる。このようにして求めた流速ｖ１に測定管１０１の内断面積を乗ずれば、流量が求まる。
【０００７】
【発明が解決しようとする課題】
図１１（ａ）、（ｂ）は従来の超音波流量計の課題を説明する図である。
（ａ）では、測定管１０１に純水１０４を流したところ、第２振動子１０３から発振した超音波１０５が高いレベルで第１振動子１０２に到達した様子を示す。
【０００８】
（ｂ）では、測定管１０１に気泡１０６・・・（・・・は複数個を示す。以下同様）が混じった水道水１０７を流した場合を示す。第２振動子１０３から発振した超音波１０８は、一部が気泡１０６・・・に衝突して乱反射するため減衰する。この結果、低レベルの超音波１０９が第１振動子１０２に到達することになる。
【０００９】
到達した超音波１０９が低レベルであれば、正確に流量を測ることができなくなる。そこで、従来は、計測対象の流体は気泡を含まぬものに限られていた。
しかし、工業プロセスではラインに複数の弁類や分岐が存在し、弁や分岐を通過する際に速度が急変するなどして、流体圧が局部的に低下することがある。圧力が下がると流体中に溶解していた成分が膨張して気泡になる。
【００１０】
上記理由やその他の要因で、測定対象の流体から完全に気泡を除去することは難しい。このことが、特許文献１に記載の超音波流量計の普及を妨げているとも言える。
そこで、本発明の目的は、気泡などの異物を含む可能性のある流体であっても流量を計測することのできる超音波流量計を提供することにある。
【００１１】
【課題を解決するための手段】
上記目的を達成するために請求項１は、計測すべき流体を流し、この流体の流れを妨げる障害物を管内に有していない測定管と、この測定管の外面に取付けた第１振動子と、この第１振動子から流体の流れに沿って所定の距離を置いて前記測定管の外面に取付けた第２振動子と、上流側の振動子から発した超音波が下流側の振動子に達するまでの時間と下流側の振動子から発した超音波が上流側の振動子に達するまでの時間との時間差に基づいて流体の流量を演算する第１演算部と、前記測定管の外面に且つ前記第１振動子の近傍に取付けた第３振動子と、前記第１振動子の発した超音波の周波数と前記第３振動子で受けた超音波の周波数との周波数の差に基づいて流体に含まれる気泡などの異物の流速を求め、この流速から流体の流量を演算する第２演算部とで超音波流量計を構成する。
【００１２】
第１振動子と第２振動子とにより、異物を含まぬ流体の流速を計測する。そして、第１振動子と第３振動子とにより、異物を含む流体の流速を計測する。
従って、気泡などの異物の混入の有無に関係なく流体の流量を計測することができる。
【００１３】
請求項２では、請求項１記載の超音波流量計は、第１振動子の発した超音波の周波数と第３振動子で受けた超音波の周波数との周波数の差が、ゼロ若しくはゼロに近似したときには前記第１演算部を選択し、それ以外のときには前記第２演算部を選択する選択部を備えることを特徴とする。
【００１４】
請求項１では２つの流速情報が発生する可能性がある。そこで、選択部で好適な一方を選択するようにした。
【００１５】
【発明の実施の形態】
本発明の実施の形態を添付図に基づいて以下に説明する。なお、図面は符号の向きに見るものとする。
図１は本発明に係る第１〜第３振動子の配置を示す斜視図であり、計測すべき流体を流し、この流体の流れを妨げる障害物を管内に有していない測定管１０と、この測定管１０の外面に取付けた第１振動子１１と、この第１振動子１１から流体の流れに沿って所定の距離を置いて測定管１０の外面に取付けた第２振動子１２と、測定管１０の外面に且つ第１振動子１１の近傍に取付けた第３振動子１３と、を示す。
【００１６】
図２は図１の２−２線断面図であり、管内に障害物を有していない測定管１０の外面に、円弧状の第１振動子１１を樹脂、グリースなどの音響結合材１４を介して取付ける。第１振動子１１の中心角θは任意に設定することができる。この設定については後述する。
【００１７】
図３は本発明に係る超音波流量計の原理図であり、超音波流量計２０は、測定管１０と、第１振動子１１と、第２振動子１２と、第３振動子１３と、第１振動子１１に第１スイッチ２１及び第２振動子１２に第２スイッチ２２を介して結合した電源２３及び第１増幅器２４と、この第１増幅器２４で増幅した情報を演算処理する第１演算部２５と、第３振動子１３に結合した第２増幅器２６と、この第２増幅器２６で増幅した情報を演算処理する第２演算部２７と、第１・第２演算部２５、２７の何れを選択するかを決める選択部２８と、選択した方の演算結果を表示する表示部２９とからなる。
【００１８】
第１・第２スイッチ２１、２２を図の様にＡ側に切換えることにより、第１振動子１１を発振器、第２振動子１２を受振器として、順流れの伝搬時間を計測し、また、第１・第２スイッチ２１、２２を図とは逆にＢ側に切換えることにより、第１振動子１１を受振器、第２振動子１２を発振器として、逆流れの伝搬時間を計測することができる。
【００１９】
第１振動子１１から第２振動子１１に超音波が到達するための時間ｔ１と、第２振動子１２から第１振動子１１に超音波が到達するための時間ｔ２との間に、差が生じる。流体における音速をｃ、流体の速度をｖ１とすれば次の計算式により流速ｖ１が求まる。詳細は従来の技術の項参照。
【００２０】
【数２】

【００２１】
一方、第３振動子１３は受振専用器である。第３受振器１３の作用は後述する。
第１振動子１１と第２振動子１２との距離をＬ１、第１振動子１１と第３振動子１３との距離をＬ２としたときに、Ｌ１：Ｌ２は、１０：（０．５〜８）、好ましくは１０：（１〜３）に設定する。従って、第３振動子１３は第１振動子１１の近傍に配置したと言える。
【００２２】
距離Ｌ２が０．５未満では、第３振動子１３が第１振動子１１に接近しすぎて製造が難しくなるとともに、第１振動子１１の振動が測定管１０を通じて直接第３振動子１３に伝わる虞がある。そこで、距離Ｌ２は０．５以上、好ましくは１．０以上とする。
また、距離Ｌ２が８を超えると、次図で述べる異物３１による反射成分（ｆｒ）が弱まり、第３振動子１３での受振レベルが低下し、ノイズとの識別が難しくなる。そこで、距離Ｌ２は８以下、好ましくは３以下にする。
【００２３】
図４は本発明の第３振動子の作用説明図であり、白抜き矢印が流体の流れ方向を示す。
第１振動子１１から周波数ｆｓの超音波が発せられると、超音波は第２振動子１２及び第３振動子１３に向かう。第３振動子１３に向かう成分は、流体中に気泡などの異物３１があると、異物３１に衝突せずに直接的に第３振動子１３に到達する「ａ」と、異物３１に衝突し、反転してから第３振動子１３に至る「ｂ」とに区分することができる。
【００２４】
図５は第１振動子で発する超音波の波形及び第３振動子で受ける超音波の波形を示す図であり、横軸は全て時間軸である。
（ａ）において、第１振動子で周波数ｆｓの超音波を発振したとする。
【００２５】
（ｂ）において、ある程度遅れて周波数ｆｓと周波数ｆｒとの混合波を第３振動子で受振したことを示す。周波数ｆｒは反射波であるため、周波数ｆｓの成分よりΔｔ時間だけ遅れて到達する。
遅れて到達する周波数ｆｓが安定した時間領域に「窓３２」を開けて、この窓３２から混合波を信号的に取出す。この取出した混合波を周波数分離手段により、周波数ｆｒの成分を取出す。
【００２６】
周波数分離手段は各種の原理の手段が適用できる。例えば、混合波から既知の周波数（発振周波数）ｆｓ成分を除去し、残った成分をｆｒと見なす方法もある。
【００２７】
（ｃ）は、取出された周波数ｆｒの波形を示す。これで、図４における周波数ｆｒを求めることができる。なお、この周波数ｆｒは向かってくる異物に対する反射波であるから、ドプラー効果により周波数が高まり、ｆｓ＜ｆｒとなる。
発射波の周波数をｆｓ、反射波の周波数をｆｒ、音速をｃ、異物の流速をｖ２とすれば次の計算式が成立する。
【００２８】
【数３】

【００２９】
▲５▼式をｖについて整理すると▲６▼式の通りに、ｖ２を求めることができる。このｖ２は異物の速度であるが、異物は流体と同一の速度で流れていると考えて差し支えないから、流体の速度と見なすことができる。
【００３０】
図６は本発明の超音波流量計の制御フロー図である。ＳＴ××はステップ番号を示す。
ＳＴ０１：第１振動子から周波数がｆｓの超音波を発振する。
ＳＴ０２：同超音波を、第２振動子で受振し、受振までの所要時間ｔ１を計測する。
【００３１】
ＳＴ０３：上記超音波を、第３振動子でも受振し、反射波の周波数ｆｒを計測する。
ＳＴ０４：第２振動子から周波数がｆｓの超音波を発振する。
ＳＴ０５：同超音波を、第１振動子で受振し、受振までの所要時間ｔ２を計測する。
【００３２】
ＳＴ０６：第１振動子−第２振動子間距離Ｌ１は既値であり、ＳＴ０２で時間ｔ１が求まり、ＳＴ０５で時間ｔ２が求まるので、これらを計算式に投入して、流速ｖ１を計算する。
ＳＴ０７：音速ｃ及び発振周波数ｆｓは既値であり、ＳＴ０３で周波数ｆｒが求まるので、これらを計算式に投入して流速ｖ２を計算する。
【００３３】
流速情報はｖ１、ｖ２の２つが存在するため、何れを選択するかが重要となる。
流体中に気泡などの異物が存在しないときには、第３振動子は反射波を受けることなく、直接波のみを受振することになる。本発明では周波数分析（分離）の結果、反射波が検出できないときには、周波数の差（ｆｒ−ｆｓ）はゼロと見なす。
【００３４】
ＳＴ０８：（ｆｒ−ｆｓ）がゼロであるか否かを調べる。
ＳＴ０９：（ｆｒ−ｆｓ）＝０であれば、異物なしの流体を計測していることになり、流速にｖ１を充てる。
ＳＴ１０：（ｆｒ−ｆｓ）が０でなければ、異物ありの流体を計測していることになり、流速にｖ２を充てる。
【００３５】
ＳＴ１１：選択した流速ｖ１又はｖ２に管内断面積を乗じることにより流量が求まる。求めた流量をディスプレイなどに表示する。
従って、図３の表示部２９に異物の有無に関係なく、そのときの流量を表示させることができる。表示は印字でもよく、形式は任意である。また、表示の他にアナログ信号やデジタル信号の形式で別の計測機器へ情報を提供させることは差し支えない。
【００３６】
なお、ＳＴ０８での判別式は、（ｆｒ−ｆｓ）＜（ｆｓ／１０００）の如く書き直すことができる。そうすれば、ノイズなどの影響でｆｒがｆｓから僅かに異なった場合でも、実質的（ｆｒ−ｆｓ）＝０と判別させることができるからである。
【００３７】
図７は本発明に係る超音波流量計の変更レイアウトを示す図である。横向き矢印は流れ方向を示す。
（ａ）では、第３振動子１３は第１振動子１１の近傍で且つ、第１振動子１１の下流側に配置した。
（ｂ）では、第３振動子１３は第２振動子１２の近傍で且つ、第２振動子１２の上流側に配置した。
【００３８】
（ｃ）では、第３振動子１３は第２振動子１２の近傍で且つ、第２振動子１２の下流側に配置した。
（ｄ）では、２個の第１振動子１１、１１Ａを配置し、一方の第１振動子１１から所定距離離れた位置に第２振動子１２を配置し、他方の第１振動子１１Ａの近傍に且つ第１振動子１１Ａの上流側に第３振動子１３を配置した。
このように、第３振動子１３は第１振動子１１、１１Ａ又は第２振動子１２の近傍に配置すればよく、レイアウトは自由である。
【００３９】
図８は本発明に係る振動子の変形例を示す図である。
（ａ）の振動子１１〜１３は、リング状センサである。
（ｂ）の振動子１１〜１３は、中心角θが１８０°である半割円筒状のセンサである。
【００４０】
（ｃ）の振動子１１〜１３は、中心角θが９０°である四分円筒状のセンサである。
（ｄ）の振動子１１〜１３は、中心角θが３０°である部分円筒状のセンサである。
【００４１】
（ａ）のリング状の振動子１１〜１３は、測定管１０の中心に向かって均等に超音波を発することができ、測定管１０の全周から満遍なく受振することができる。しかし、振動子１１〜１３は、測定管１０の一端から図面表裏方向に嵌合するため、造りにくく製造コストが嵩む。
【００４２】
この点、（ｂ）〜（ｄ）の振動子１１〜１３は、測定管１０の任意の位置に矢印▲１▼の要領で着脱できる。しかし、振動子１１〜１３の送受振能力は、測定管１０に接触している円弧の長さに比例する。そのため、（ａ）に対して、（ｂ）〜（ｄ）は送受振能力の点で問題が起こる可能性があり、従来は試みられていなかった。
【００４３】
本発明者らが試作し実測したところ、送受振能力は、（ｂ）〜（ｄ）であっても（ａ）に対してそれ程の遜色がないことが分かった。その理由を説明する。
（ａ）に示す振動子１１〜１３は、測定管１０に円滑に嵌合できるように、内径は測定管１０の外径より大きくする必要がある。大きくしないと、途中で測定管１０の外周面に引っかかるからである。そのために、音響結合材１４は厚くなる。音響結合材１４が厚い程超音波が減衰される。
【００４４】
（ｂ）に示す振動子１１〜１３は矢印▲１▼の如く取付けるために、その内周面は測定管１０の外周面に密着させることができ、音響結合材１４はごく薄くすることができる。この結果、（ｂ）は（ａ）と同等の送受振能力が得られる。
【００４５】
（ｃ）は（ｂ）より送受振能力が低下し、（ｄ）は更に送受振能力が低下する。
そこで、取付けが容易で且つ高い送受振能力が得られる（ｂ）が好適であると言える。しかし、使用条件によっては、（ｃ）や（ｄ）でも使用可能である。
従って、振動子１１〜１３の形状は任意に決めることができる。
【００４６】
図９は本発明の振動子の更なる変更例を示す図である。
（ａ）は取付け状態を示す斜視図であり、測定管１０に音響結合材１４で棒状の振動子１１〜１３を取付けたことを示す。
（ｂ）は小径の測定管１０に棒状の振動子１１〜１３を取付け、（ｃ）は大径の測定管１０Ｂに振動子１１〜１３を取付けたことを示す断面図である。
【００４７】
振動子１１〜１３が棒形状であれば、測定管１０、１０Ｂの径に無関係に採用することができる。図８（ａ）〜（ｄ）であれば、測定管１０の曲率に振動子１１〜１３の曲率を合致させる必要があった。この点、図９の棒状の振動子１１〜１３であれば、測定管１０、１０Ｂの曲率に制限されることはない。
【００４８】
尚、本発明の超音波流量計は、流速を求め、この流速に管内断面積を乗じることで流量を求めることを原理とするから、流速計を兼ねさせることができる。すなわち、超音波流速計、超音波流速・流量計の全てを総称して超音波流量計と呼称した。
【００４９】
また、請求項１の測定管は、直管のほか、曲管であってもよい。
【００５０】
【発明の効果】
本発明は上記構成により次の効果を発揮する。
請求項１では第１振動子と第２振動子とにより、異物を含まぬ流体の流速を計測する。そして、第１振動子と第３振動子とにより、異物を含む流体の流速を計測する。
【００５１】
請求項１によれば、気泡などの異物の混入の有無に関係なく流体の流量を計測することができる。
仮に脱気処理などを施すことで気泡を除去したり、ろ過処理することで異物を除去すると設備費用及び運転費用が嵩むが、本発明によればそのような処理は不要であるために設備費用及び運転費用を低減することができる。
【００５２】
請求項１では２つの流速情報が発生する可能性がある。そこで、請求項２では選択部を付設し、この選択部で好適な一方を選択するようにした。
これにより、流速や流量の認識が容易となり、流量計の使い勝手が良くなる。
【図面の簡単な説明】
【図１】本発明に係る第１〜第３振動子の配置を示す斜視図
【図２】図１の２−２線断面図
【図３】本発明に係る超音波流量計の原理図
【図４】本発明の第３振動子の作用説明図
【図５】第１振動子で発する超音波の波形及び第３振動子で受ける超音波の波形を示す図
【図６】本発明の超音波流量計の制御フロー図
【図７】本発明に係る超音波流量計の変更レイアウトを示す図
【図８】本発明に係る振動子の変形例を示す図
【図９】本発明の振動子の更なる変更例を示す図
【図１０】超音波流量計の原理図
【図１１】従来の超音波流量計の課題を説明する図
【符号の説明】
１０…測定管、１１…第１振動子、１２…第２振動子、１３…第３振動子、１４…音響結合材、２０…超音波流量計、２５…第１演算部、２７…第２演算部、２８…選択部、２９…表示部、３１…異物。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic flowmeter suitable for small-diameter piping.
[0002]
[Prior art]
Various types of flow meters are practically used, and among them, an ultrasonic flow meter using ultrasonic waves is also known (for example, Patent Document 1).
[0003]
[Patent Document 1]
JP-A-10-122923 (FIG. 3)
[0004]
The operation principle of the ultrasonic flowmeter will be described with reference to the following diagram which is a simplified version of FIG.
FIG. 10 is a principle diagram of an ultrasonic flowmeter, in which a first vibrator 102 and a second vibrator 103 are attached to a measuring tube 101 at a predetermined distance L1, and ultrasonic waves are oscillated from one of the vibrators 102 or 103. Then, the time t1 for the ultrasonic wave to reach the second transducer 103 from the first transducer 102 when the other transducer 103 or 102 receives vibration, and the time from the second transducer 103 to the first transducer 102. There is a difference between the time t2 at which the ultrasonic wave arrives and the time t2. Assuming that the sound velocity in the fluid is c and the velocity of the fluid is v1, the following formula is established.
[0005]
(Equation 1)

[0006]
That is, equation (3) is derived by subtracting the reciprocal of equation (2) from the reciprocal of equation (1), and equation (4) is obtained by rearranging equation (3) for v1. According to the equation (4), the flow velocity v1 of the fluid can be obtained if the distance L1, the time t1, and the time t2 are determined. The flow rate is obtained by multiplying the flow velocity v1 thus obtained by the inner cross-sectional area of the measuring tube 101.
[0007]
[Problems to be solved by the invention]
FIGS. 11A and 11B are diagrams for explaining the problem of the conventional ultrasonic flowmeter.
3A shows a state in which pure water 104 flows through the measuring tube 101, and the ultrasonic waves 105 oscillated from the second vibrator 103 reach the first vibrator 102 at a high level.
[0008]
(B) shows a case where tap water 107 mixed with bubbles 106... The ultrasonic wave 108 oscillated from the second vibrator 103 attenuates because a part of the ultrasonic wave collides with the bubbles 106 and is irregularly reflected. As a result, the low-level ultrasonic waves 109 reach the first transducer 102.
[0009]
If the reached ultrasonic wave 109 is at a low level, the flow rate cannot be measured accurately. Therefore, conventionally, the fluid to be measured has been limited to a fluid that does not contain bubbles.
However, in an industrial process, a plurality of valves and branches exist in a line, and the fluid pressure may locally decrease due to a sudden change in speed when passing through the valves or branches. When the pressure drops, the components dissolved in the fluid expand and become bubbles.
[0010]
For the above reasons and other factors, it is difficult to completely remove bubbles from the fluid to be measured. It can be said that this has hindered the spread of the ultrasonic flowmeter described in Patent Document 1.
Therefore, an object of the present invention is to provide an ultrasonic flowmeter capable of measuring the flow rate of a fluid that may contain foreign matter such as air bubbles.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention is directed to a measuring pipe which flows a fluid to be measured and has no obstacle in the pipe for obstructing the flow of the fluid, and a first vibrator mounted on an outer surface of the measuring pipe. A second vibrator attached to the outer surface of the measurement tube at a predetermined distance from the first vibrator along the flow of the fluid, and an ultrasonic wave emitted from the upstream vibrator is connected to the downstream vibrator. A first calculation unit for calculating the flow rate of the fluid based on a time difference between a time required to reach the upstream transducer and a time required for the ultrasonic waves emitted from the downstream transducer to reach the upstream transducer, and an outer surface of the measurement tube. And a third vibrator attached near the first vibrator and a frequency difference between a frequency of an ultrasonic wave emitted from the first vibrator and a frequency of an ultrasonic wave received by the third vibrator. The flow rate of foreign matter such as air bubbles contained in the fluid, and calculate the flow rate of the fluid from this flow rate. In a second operation unit which constitutes the ultrasonic flow meter.
[0012]
The first oscillator and the second oscillator measure the flow velocity of the fluid containing no foreign matter. Then, the flow velocity of the fluid containing the foreign matter is measured by the first vibrator and the third vibrator.
Therefore, the flow rate of the fluid can be measured regardless of the presence or absence of foreign matter such as bubbles.
[0013]
According to a second aspect of the present invention, in the ultrasonic flowmeter according to the first aspect, the difference between the frequency of the ultrasonic wave emitted from the first vibrator and the frequency of the ultrasonic wave received by the third vibrator is zero or zero. It is characterized in that a selector is provided for selecting the first arithmetic unit when approximation is performed, and for selecting the second arithmetic unit otherwise.
[0014]
In claim 1, there is a possibility that two pieces of flow rate information are generated. Therefore, the selection unit selects the preferred one.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the accompanying drawings. The drawings should be viewed in the direction of reference numerals.
FIG. 1 is a perspective view showing the arrangement of the first to third vibrators according to the present invention, in which a fluid to be measured flows, and a measuring tube 10 having no obstacle in the tube to obstruct the flow of the fluid, A first vibrator 11 mounted on the outer surface of the measuring tube 10, a second vibrator 12 mounted on the outer surface of the measuring tube 10 at a predetermined distance from the first vibrator 11 along a flow of fluid, 3 shows a third vibrator 13 attached to the outer surface of the measuring tube 10 and near the first vibrator 11.
[0016]
FIG. 2 is a cross-sectional view taken along the line 2-2 in FIG. 1. The first vibrator 11 having an arc shape is provided with an acoustic coupling material 14 such as resin or grease on the outer surface of the measurement tube 10 having no obstacle in the tube. Installed via The center angle θ of the first vibrator 11 can be set arbitrarily. This setting will be described later.
[0017]
FIG. 3 is a principle diagram of the ultrasonic flow meter according to the present invention. The ultrasonic flow meter 20 includes a measuring tube 10, a first vibrator 11, a second vibrator 12, a third vibrator 13, A power supply 23 and a first amplifier 24 coupled to the first vibrator 11 via a first switch 21 and a second switch 22 via a second switch 22, and a first processing unit for processing information amplified by the first amplifier 24 A computing unit 25, a second amplifier 26 coupled to the third transducer 13, a second computing unit 27 for computing the information amplified by the second amplifier 26, and a first / second computing unit 25, 27. It comprises a selection unit 28 for deciding which one to select, and a display unit 29 for displaying the calculation result of the selected one.
[0018]
By switching the first and second switches 21 and 22 to the A side as shown in the figure, the propagation time of the forward flow is measured using the first vibrator 11 as an oscillator and the second vibrator 12 as a receiver. By switching the first and second switches 21 and 22 to the B side opposite to the figure, the propagation time of the reverse flow can be measured using the first vibrator 11 as a geophone and the second vibrator 12 as an oscillator. it can.
[0019]
The difference between the time t1 for the ultrasonic wave from the first vibrator 11 to reach the second vibrator 11 and the time t2 for the ultrasonic wave from the second vibrator 12 to the first vibrator 11 is different. Occurs. Assuming that the sound velocity in the fluid is c and the velocity of the fluid is v1, the flow velocity v1 is obtained by the following formula. Refer to the section on conventional technology for details.
[0020]
(Equation 2)

[0021]
On the other hand, the third vibrator 13 is a vibration receiving device. The operation of the third vibration receiver 13 will be described later.
When the distance between the first vibrator 11 and the second vibrator 12 is L1, and the distance between the first vibrator 11 and the third vibrator 13 is L2, L1: L2 is 10: (0.5 to 0.5). 8), preferably 10: (1-3). Therefore, it can be said that the third vibrator 13 is arranged near the first vibrator 11.
[0022]
If the distance L2 is less than 0.5, the third vibrator 13 is too close to the first vibrator 11 to make it difficult to manufacture, and the vibration of the first vibrator 11 is directly transmitted to the third vibrator 13 through the measurement tube 10. There is a risk of transmission. Therefore, the distance L2 is set to 0.5 or more, preferably 1.0 or more.
Further, when the distance L2 exceeds 8, the reflection component (fr) due to the foreign matter 31 described below will be weakened, the level of reception by the third vibrator 13 will be reduced, and it will be difficult to distinguish it from noise. Therefore, the distance L2 is set to 8 or less, preferably 3 or less.
[0023]
FIG. 4 is an explanatory view of the operation of the third vibrator of the present invention, and the white arrows indicate the flow direction of the fluid.
When the ultrasonic wave having the frequency fs is emitted from the first vibrator 11, the ultrasonic wave goes to the second vibrator 12 and the third vibrator 13. The component heading to the third vibrator 13, when there is a foreign substance 31 such as air bubbles in the fluid, directly reaches the third vibrator 13 without colliding with the foreign substance 31, and collides with the foreign substance 31. , And “b” that reaches the third vibrator 13 after being inverted.
[0024]
FIG. 5 is a diagram showing a waveform of an ultrasonic wave emitted from the first vibrator and a waveform of an ultrasonic wave received by the third vibrator, and the horizontal axis is a time axis.
In (a), it is assumed that an ultrasonic wave having a frequency fs is oscillated by the first vibrator.
[0025]
3B shows that the third vibrator receives a mixed wave of the frequency fs and the frequency fr with a certain delay. Since the frequency fr is a reflected wave, the frequency fr arrives later by the time Δt than the component of the frequency fs.
A "window 32" is opened in a time region where the frequency fs which arrives late is stable, and a mixed wave is extracted from this window 32 as a signal. The component of the frequency fr is extracted from the extracted mixed wave by the frequency separating means.
[0026]
As the frequency separating means, means based on various principles can be applied. For example, there is a method in which a known frequency (oscillation frequency) fs component is removed from the mixed wave, and the remaining component is regarded as fr.
[0027]
(C) shows a waveform of the extracted frequency fr. Thus, the frequency fr in FIG. 4 can be obtained. Since this frequency fr is a reflected wave toward the incoming foreign substance, the frequency increases due to the Doppler effect, and fs <fr.
If the frequency of the emitted wave is fs, the frequency of the reflected wave is fr, the speed of sound is c, and the flow velocity of the foreign matter is v2, the following formula is established.
[0028]
[Equation 3]

[0029]
By rearranging equation (5) with respect to v, v2 can be obtained as in equation (6). This v2 is the speed of the foreign matter, but it can be considered that the foreign matter is flowing at the same speed as the fluid, and can be regarded as the speed of the fluid.
[0030]
FIG. 6 is a control flow chart of the ultrasonic flowmeter of the present invention. STxx indicates a step number.
ST01: An ultrasonic wave having a frequency of fs is oscillated from the first vibrator.
ST02: The ultrasonic wave is received by the second vibrator, and a time t1 required for receiving the ultrasonic wave is measured.
[0031]
ST03: The ultrasonic wave is also received by the third transducer, and the frequency fr of the reflected wave is measured.
ST04: An ultrasonic wave having a frequency of fs is oscillated from the second vibrator.
ST05: The ultrasonic wave is received by the first vibrator, and the time t2 required for receiving the ultrasonic wave is measured.
[0032]
ST06: The distance L1 between the first vibrator and the second vibrator is a known value, and the time t1 is obtained in ST02 and the time t2 is obtained in ST05. Therefore, these are put into a calculation formula to calculate the flow velocity v1.
ST07: The sound velocity c and the oscillation frequency fs are already set values, and the frequency fr is obtained in ST03. Therefore, these are put into a calculation formula to calculate the flow velocity v2.
[0033]
Since there are two flow velocity information v1 and v2, it is important to select which one.
When no foreign matter such as air bubbles exists in the fluid, the third vibrator receives only the direct wave without receiving the reflected wave. In the present invention, when the reflected wave cannot be detected as a result of the frequency analysis (separation), the frequency difference (fr-fs) is regarded as zero.
[0034]
ST08: Check whether (fr-fs) is zero or not.
ST09: If (fr-fs) = 0, it means that the fluid without foreign matter is being measured, and v1 is assigned to the flow velocity.
ST10: If (fr-fs) is not 0, it means that the fluid with foreign matter is being measured, and v2 is assigned to the flow velocity.
[0035]
ST11: The flow rate is obtained by multiplying the selected flow velocity v1 or v2 by the cross-sectional area in the pipe. The obtained flow rate is displayed on a display or the like.
Therefore, the flow rate at that time can be displayed on the display unit 29 of FIG. 3 regardless of the presence or absence of foreign matter. The display may be printed, and the format is arbitrary. In addition to the display, information may be provided to another measuring device in the form of an analog signal or a digital signal.
[0036]
Note that the discriminant in ST08 can be rewritten as (fr-fs) <(fs / 1000). Then, even if fr is slightly different from fs due to the influence of noise or the like, it can be determined that substantially (fr−fs) = 0.
[0037]
FIG. 7 is a diagram showing a modified layout of the ultrasonic flowmeter according to the present invention. The horizontal arrow indicates the flow direction.
In (a), the third vibrator 13 is arranged near the first vibrator 11 and downstream of the first vibrator 11.
In (b), the third vibrator 13 is arranged near the second vibrator 12 and on the upstream side of the second vibrator 12.
[0038]
In (c), the third vibrator 13 is arranged near the second vibrator 12 and on the downstream side of the second vibrator 12.
In (d), two first vibrators 11 and 11A are arranged, a second vibrator 12 is arranged at a position separated by a predetermined distance from one first vibrator 11, and the other first vibrator 11A The third vibrator 13 is arranged near and upstream of the first vibrator 11A.
Thus, the third vibrator 13 may be arranged in the vicinity of the first vibrator 11, 11A or the second vibrator 12, and the layout is free.
[0039]
FIG. 8 is a view showing a modified example of the vibrator according to the present invention.
The vibrators 11 to 13 in (a) are ring-shaped sensors.
The transducers 11 to 13 in (b) are half-cylindrical sensors having a central angle θ of 180 °.
[0040]
The vibrators 11 to 13 in (c) are quadrant cylindrical sensors having a central angle θ of 90 °.
The vibrators 11 to 13 in (d) are partially cylindrical sensors having a central angle θ of 30 °.
[0041]
The ring-shaped vibrators 11 to 13 in (a) can emit ultrasonic waves uniformly toward the center of the measuring tube 10 and can receive the ultrasonic waves evenly from the entire circumference of the measuring tube 10. However, since the vibrators 11 to 13 are fitted from one end of the measuring tube 10 in the front and back directions in the drawing, it is difficult to manufacture the vibrators and the manufacturing cost increases.
[0042]
In this regard, the vibrators 11 to 13 of (b) to (d) can be attached to and detached from an arbitrary position of the measuring tube 10 in the manner of the arrow (1). However, the transmitting and receiving capabilities of the vibrators 11 to 13 are proportional to the length of the arc in contact with the measuring tube 10. Therefore, with respect to (a), (b) to (d) may have a problem in terms of transmission / reception capability, and so far no attempt has been made.
[0043]
As a result of trial production and actual measurement by the present inventors, it was found that the transmission / reception capability was not so inferior to (a) even in (b) to (d). The reason will be described.
The vibrators 11 to 13 shown in (a) need to have an inner diameter larger than the outer diameter of the measuring tube 10 so that they can be fitted smoothly into the measuring tube 10. This is because if not increased, it will be caught on the outer peripheral surface of the measuring tube 10 on the way. Therefore, the acoustic coupling material 14 becomes thick. Ultrasonic waves are attenuated as the acoustic coupling material 14 becomes thicker.
[0044]
Since the vibrators 11 to 13 shown in (b) are attached as shown by the arrow (1), the inner peripheral surface thereof can be in close contact with the outer peripheral surface of the measuring tube 10, and the acoustic coupling material 14 can be made extremely thin. . As a result, (b) obtains the same transmission and reception capability as (a).
[0045]
In (c), the transmission / reception capability is lower than in (b), and in (d), the transmission / reception capability is further reduced.
Therefore, it can be said that (b), which is easy to attach and obtains high transmission / reception capability, is preferable. However, depending on the use conditions, (c) and (d) can also be used.
Therefore, the shapes of the vibrators 11 to 13 can be arbitrarily determined.
[0046]
FIG. 9 is a view showing a further modified example of the vibrator of the present invention.
(A) is a perspective view showing an attached state, and shows that rod-shaped vibrators 11 to 13 are attached to the measurement tube 10 with the acoustic coupling material 14.
(B) is a sectional view showing that rod-shaped vibrators 11 to 13 are attached to the small-diameter measuring tube 10, and (c) is a sectional view showing that vibrators 11 to 13 are attached to the large-diameter measuring tube 10 </ b> B.
[0047]
If the vibrators 11 to 13 are rod-shaped, they can be adopted irrespective of the diameter of the measuring tubes 10 and 10B. 8A to 8D, it is necessary to match the curvatures of the vibrators 11 to 13 with the curvature of the measuring tube 10. In this regard, the curvature of the measuring tubes 10 and 10B is not limited in the case of the rod-shaped vibrators 11 to 13 in FIG.
[0048]
The ultrasonic flowmeter of the present invention is based on the principle that the flow rate is obtained by multiplying the flow velocity by the cross-sectional area of the inside of the pipe, so that the ultrasonic flowmeter can also serve as the flowmeter. That is, the ultrasonic flowmeter and the ultrasonic flowmeter / flowmeter were collectively referred to as an ultrasonic flowmeter.
[0049]
Further, the measuring pipe of claim 1 may be a curved pipe other than a straight pipe.
[0050]
【The invention's effect】
The present invention has the following effects by the above configuration.
In the first aspect, the flow velocity of the fluid containing no foreign matter is measured by the first vibrator and the second vibrator. Then, the flow velocity of the fluid containing the foreign matter is measured by the first vibrator and the third vibrator.
[0051]
According to the first aspect, the flow rate of the fluid can be measured regardless of the presence or absence of foreign matter such as air bubbles.
If air bubbles are removed by performing degassing or the like, and foreign matter is removed by filtration, equipment costs and operating costs increase, but according to the present invention, such processing is unnecessary, so equipment costs are increased. In addition, operating costs can be reduced.
[0052]
In claim 1, there is a possibility that two pieces of flow rate information are generated. In view of this, in claim 2, a selection unit is additionally provided, and a suitable one is selected by the selection unit.
This facilitates the recognition of the flow velocity and the flow rate, and improves the usability of the flow meter.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an arrangement of first to third transducers according to the present invention. FIG. 2 is a sectional view taken along line 2-2 of FIG. 1. FIG. 3 is a principle diagram of an ultrasonic flowmeter according to the present invention. FIG. 4 is a diagram for explaining the operation of the third vibrator of the present invention. FIG. 5 is a diagram showing a waveform of an ultrasonic wave emitted from the first vibrator and a waveform of an ultrasonic wave received by the third vibrator. FIG. FIG. 7 is a control flow diagram of the ultrasonic flow meter. FIG. 7 is a diagram showing a modified layout of the ultrasonic flow meter according to the present invention. FIG. 8 is a diagram showing a modified example of the vibrator according to the present invention. FIG. 10 is a diagram showing the principle of an ultrasonic flowmeter. FIG. 11 is a diagram illustrating problems of a conventional ultrasonic flowmeter.
DESCRIPTION OF SYMBOLS 10 ... Measurement pipe, 11 ... 1st vibrator, 12 ... 2nd vibrator, 13 ... 3rd vibrator, 14 ... Acoustic coupling material, 20 ... Ultrasonic flowmeter, 25 ... 1st arithmetic part, 27 ... 2nd Arithmetic unit, 28 selection unit, 29 display unit, 31 foreign matter.

Claims (2)

A measuring pipe which flows a fluid to be measured and has no obstacle in the pipe for obstructing the flow of the fluid, a first vibrator attached to an outer surface of the measuring pipe, and a flow from the first vibrator to a flow of the fluid. A second transducer attached to the outer surface of the measurement tube at a predetermined distance along the length of time between when the ultrasonic wave emitted from the upstream transducer reaches the downstream transducer and the downstream transducer. A first calculation unit for calculating a flow rate of the fluid based on a time difference from a time required for the emitted ultrasonic waves to reach the transducer on the upstream side, and attached to an outer surface of the measurement tube and near the first transducer. A third vibrator and a flow rate of a foreign substance such as a bubble included in a fluid based on a difference between a frequency of an ultrasonic wave emitted from the first vibrator and a frequency of an ultrasonic wave received by the third vibrator. And a second calculation unit for calculating the flow rate of the fluid from the flow velocity. Total. The ultrasonic flowmeter according to claim 1, wherein the difference between the frequency of the ultrasonic wave emitted by the first vibrator and the frequency of the ultrasonic wave received by the third vibrator is close to zero or zero. An ultrasonic flowmeter, comprising: a selection unit that selects the first calculation unit, and otherwise selects the second calculation unit.

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