JP2004251653A

JP2004251653A - Ultrasonic flowmeter

Info

Publication number: JP2004251653A
Application number: JP2003039787A
Authority: JP
Inventors: Hiroyuki Horiguchi; 浩幸堀口; Yoshihiro Sekine; 良浩関根
Original assignee: Ricoh Elemex Corp
Current assignee: Ricoh Elemex Corp
Priority date: 2003-02-18
Filing date: 2003-02-18
Publication date: 2004-09-09
Anticipated expiration: 2023-02-18
Also published as: JP4368591B2

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter capable of being easily constituted of an ultrasonic transmitter provided with a single transmission-side oscillator and a pair of ultrasonic receivers separately provided with reception-side oscillators without reductions in measurement accuracy. SOLUTION: Both the upstream reception-side oscillator 31u and the downstream reception-side oscillator 31d receive ultrasonic waves (expressed by an upstream-side traverse line Mu and a downstream-side traverse line Md) reflected once at an inner wall surface of a channel 1 and oscillate. The upstream-side ultrasonic receiver 3u (the upstream reception-side oscillator 31u) and the downstream-side ultrasonic receiver 3d (downstream reception-side oscillator 31d) are symmetrically arranged in such a way as to sandwich the ultrasonic transmitter 2 (the transmission-side oscillator 21) and set the equal separation distances D between the transmitters and receivers. COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、超音波流量計に関する。
【０００２】
【従来の技術】
従来、都市ガス、水などの流体の流量を計測する流量計測装置として、超音波を利用して流速を測定する超音波流量計が知られている。例えば、非特許文献１には、流路の一側壁に設けられた超音波送信部を挟んで流体の流れ方向上手側及び下手側の流路の他側壁に、一対の超音波受信部を設けることにより、送信部から同時に発せられた超音波を一対の受信部でほぼ同時に受信して計測時間の短縮を可能にする技術が開示されている。
【０００３】
【非特許文献１】
名真英司著，「センサ活用図絵ブック」，株式会社オーム社，平成５年１月，ｐ．９８，図３（ｄ）
【０００４】
【発明が解決しようとする課題】
しかし、非特許文献１に示すように各受信部が送信部に対向して設けられる超音波センサの配置では、一対の受信部の設置間隔を狭めて超音波流量計のコンパクト化を図ろうとすると発信部から各受信部への伝搬距離（到達時間）が短くなって測定精度が低下するおそれがある。一方、一対の受信部の設置間隔を広げた場合には、単独の超音波振動子（送信側振動子）では一対の受信部に対して広角に超音波発振できなくなり、各受信部に対応させて送信側振動子を設けなければならなくなる。
【０００５】
そこで本発明の課題は、測定精度を低下させることなく、単独の送信側振動子を備える超音波送信部と各別に受信側振動子を備える一対の超音波受信部とによって簡素に構成できる超音波流量計を提供することにある。
【０００６】
【課題を解決するための手段及び発明の効果】
上記課題を解決するために本発明に係る超音波流量計の第一は、
流体を通過させるための流路と、
その流路の壁に、流体の流れ方向上手側及び下手側に向けて超音波を発振する送信側振動子が取り付けられた超音波送信部と、
その超音波送信部を挟んで流体の流れ方向上手側及び下手側の前記流路の壁に、前記超音波送信部から発振され当該流路の内壁面で少なくとも１回反射された超音波によって発振される受信側振動子がそれぞれ取り付けられた一対の超音波受信部と、
を備えることを特徴とする。
【０００７】
第一の超音波流量計によれば、受信側振動子は少なくとも１回反射後の超音波を検出するので、一対の超音波受信部の設置間隔を狭めても超音波発信部から各超音波受信部への伝搬距離（到達時間）が相対的に長くなって測定精度が確保される。また、送信側振動子から流れ方向上手側及び下手側に向けて超音波を広角に発振しなくてもすむため、各超音波受信部に対応させて送信側振動子を設けなくてもよい。したがって、単独の送信側振動子を備える超音波送信部と各別に受信側振動子を備える一対の超音波受信部とによって、超音波流量計の測定部（超音波センサ部）を簡素に構成できる。なお、周囲環境の温度変化に伴って送信側振動子の発振周波数が変化しても、単独の送信側振動子を用いているために温度依存性が解消され、到達時間の複雑な補正等を要しない。
【０００８】
また、上記課題を解決するために本発明に係る超音波流量計の第二は、
流体の流れ方向軸線と超音波を発振する送信側振動子とを含む流路断面において、その流れ方向軸線が前記送信側振動子の取付位置に対応して極点部を形成するように曲がった流路と、
その流路の壁に、前記送信側振動子が流体の流れ方向上手側及び下手側に向けて超音波を発振するように取り付けられた超音波送信部と、
その超音波送信部を挟んで流体の流れ方向上手側及び下手側の前記流路の壁に、前記超音波送信部から発振され当該流路の内壁面で少なくとも１回反射された超音波によって発振される受信側振動子がそれぞれ取り付けられた一対の超音波受信部と、
を備えることを特徴とする。
【０００９】
第二の超音波流量計では、第一の構成にさらに流れ方向軸線が送信側振動子の取付位置に対応して極点（極大点又は極小点）部を形成するように曲がった流路を有するため、流れ方向軸線は送信側振動子の取付側に向って凸となる山型状、台地状、湾曲状等を呈する。これにより、流れ方向軸線が直線状である場合に比べて伝搬距離（到達時間）を相対的に長くすることができるので、測定精度をさらに向上させることができる。このとき、伝搬距離（到達時間）は、流路の曲がりにより送信側振動子に対向する内壁面が遠ざかる分長くなるとともに、内壁面での反射波はさらに送信側振動子から（流れ方向上手側又は下手側に）遠ざかることによって長くなる。したがって、必要な測定精度を確保しつつ、相対的に一対の超音波受信部の設置間隔を狭めてさらに超音波流量計のコンパクト化を図ることができる。なお、山型状のように鋭く折れ曲がる場合、湾曲状のようになだらかに曲がる場合等には、極点部は極点を形成する。一方、台地状のように扁平部分を含む場合等には、極点部は極点領域を形成する。
【００１０】
その際、これらの超音波流量計において、流路は、軸断面の形状及び断面積のうち少なくとも一方が流れ方向に沿って変化する場合がある。例えば、断面円形状の流路の断面積（直径）が流れ方向上手側から徐々に減少し送信側振動子の取付位置に対応して最小となり（このとき流れ方向軸線が極点（極大点又は極小点）に達し）、その後再び流路の断面積が徐々に増加するように変化する。
また、流路は、軸断面の形状及び断面積が流れ方向において同一となる場合がある。例えば、断面円形状で断面積（直径）一定の流路の流れ方向軸線が送信側振動子の取付側に向って凸となる山型状又は湾曲状を呈し、その流れ方向軸線が送信側振動子の取付位置に対応して極点（極大点又は極小点）に達するように変化する。
【００１１】
そして、一対の超音波受信部を、流体の流れ方向軸線と送信側振動子とを含む流路断面において、超音波送信部からそれぞれほぼ等しい距離離間させるとともに、いずれも超音波送信部設置側の壁に取り付けることが望ましい。これによって、超音波送信部（送信側振動子）から流れ方向下手側の超音波受信部（受信側振動子）に到達するまでの時間（以下、順方向到達時間という）Ｔｄと、超音波送信部（送信側振動子）から流れ方向上手側の超音波受信部（受信側振動子）に到達するまでの時間（以下、逆方向到達時間という）Ｔｕとの差ΔＴ等の算出が迅速に行える。また、超音波送信部及び一対の超音波受信部が流路に対してすべて同じ側の壁に取り付けられるので、流路壁への超音波センサの組み付け及び取り外し・取り替えが流路の一側方側から集中的に行え、作業効率が高くなる。
【００１２】
また、流路のうち少なくとも送信側振動子に対向する内壁面を、多重反射抑制のための超音波反射抑制層に形成してもよい。流路のうち送信側振動子に対向する内壁面を超音波反射抑制層に形成することによって、送信側振動子の発振により発生する超音波のうち流れ方向軸線に対して直角に近い角度（例えば、９０°±１０°〜９０°±２５°）で交差する成分の流路内壁面での反射を抑制することができる。すなわち、超音波反射抑制層は、本来流量計測に用いることを意図していない不要超音波が流路内壁面で散乱反射を繰り返すことによって雑音成分が形成され、受信側振動子で信号成分とともに感知されるに至る現象（多重反射）の防止と測定精度の向上に役立つ。なお、超音波反射抑制層の形成は、このような不要超音波を減衰させる超音波吸収材（例えば、ガラスウール入りエポキシ樹脂、ガラスウール入りシリコン樹脂等）の流路内壁面への貼り付け等によってなされる。
【００１３】
さらに、流路には、送信側振動子により発振された超音波が受信側振動子に到達する前に、超音波のビーム径を絞るためのビーム調整部を設けてもよい。これによって超音波の広がりを抑制し、受信側振動子各部への到達時間のばらつきを排除して、測定精度を向上させることができる。なお、ビーム調整部として、例えば厚み方向に貫通孔が形成された制御板を流れ方向に沿って衝立状に配設すると、送信側振動子により発振された超音波のうち孔径に相当するビーム径部分のみ通過させることになる。この場合、広がり角を約０．５ｒａｄとする超音波ビーム伝搬路が形成されると、貫通孔を通過する超音波は平面波となって受信側振動子の各部にほぼ同時に到達し、単一の受信信号出力により分解能を高めることができる。
【００１４】
【発明の実施の形態】
（実施例１）
次に、本発明の実施の形態を図面を用いて説明する。図１は、一般住宅用ガスメータ等として用いられる超音波流量計の一実施例の基本構成を示す。この超音波流量計１００の流量測定用の流路１には、流量測定用ガス（流体）が流れ方向軸線Ｏに沿って図示の流れ方向に流通（平均流速ｖ）している。流路１の壁１０には、超音波送信部２と一対の超音波受信部３ｕ，３ｄとが取り付けられ、図１に示すように、流れ方向軸線Ｏと超音波送信部２とを含む流路断面において、超音波受信部３ｕ，３ｄはいずれも超音波送信部２設置側の壁１０に位置している。
【００１５】
測定用の流路１は、少なくとも一対の超音波受信部３ｕ，３ｄ間において流れ方向軸線Ｏが直線状であり、軸断面の形状及び断面積が流れ方向において同一に形成されている。測定対象がガスの場合、測定用流路１の軸断面形状は壁１０により閉鎖された空間を形成するものであればよく、例えば、円形状、楕円形状、正方形状、矩形状等のいずれを採用してもよい。なお、測定対象が水等の液体であれば、測定用流路１の軸断面形状として壁１０の天頂部が大気中に開放されたオープン形状（例えば半円形状等）を採用できる場合がある。
【００１６】
超音波送信部２は、流路１の壁１０に固定され、圧電素子、振動板、電極板等から構成される送信側振動子２１と、この送信側振動子２１を発振させるための駆動電圧回路等から構成される送信手段２２とを備えている。送信側振動子２１には、単独でガスの流れ方向上手側及び下手側に向けて超音波を発振することができるように、比較的指向性の広い（半減角の大きい）圧電素子等を選択する。図１では、送信側振動子２１を中心として上流側測線Ｍｕと下流側測線Ｍｄとで形成される超音波発射角２α＝７０°＝±３５°に設定してある。
【００１７】
上流側超音波受信部３ｕは、超音波送信部２（送信側振動子２１）よりも流れ方向上手側の壁１０に固定され、圧電素子、振動板、電極板等から構成される上流受信側振動子３１ｕと、この上流受信側振動子３１ｕの発生電圧を検出するための電圧検出回路等から構成される受信手段３２とを備えている。一方、下流側超音波受信部３ｄは、超音波送信部２（送信側振動子２１）よりも流れ方向下手側の壁１０に固定され、圧電素子、振動板、電極板等から構成される下流受信側振動子３１ｄと、この下流受信側振動子３１ｄの発生電圧を検出するための電圧検出回路等から構成される受信手段３２とを備えている。上流受信側振動子３１ｕと下流受信側振動子３１ｄとはともに、流路１の内壁面で１回反射された超音波（上流側測線Ｍｕと下流側測線Ｍｄとで表わされる）を受信して発振するので、比較的指向性の狭い（半減角の小さい）圧電素子等を選択する。上流側超音波受信部３ｕ（上流受信側振動子３１ｕ）と下流側超音波受信部３ｄ（下流受信側振動子３１ｄ）とは、超音波送信部２（送信側振動子２１）を挟んで対称に設置され、送受信部間の離間距離Ｄが等しく設定されている。なお、上流側超音波受信部３ｕの受信手段と下流側超音波受信部３ｄの受信手段とは兼用構成されている。
【００１８】
図１において、ガスの平均流速をｖ、ガス中を伝搬する音速をｃ、超音波の進行方向（測線Ｍｕ，Ｍｄ）とガスの流れ方向（流れ方向軸線Ｏ）とのなす角をθ（以下、測線角という）、超音波の伝搬距離をＬ（＝Ｄ／ｃｏｓθ）とすると、順方向到達時間Ｔｄ及び逆方向到達時間Ｔｕはそれぞれ次のように表わされる。
Ｔｄ＝Ｌ／（ｃ＋ｖ・ｃｏｓθ）（１）
Ｔｕ＝Ｌ／（ｃ−ｖ・ｃｏｓθ）（２）
（１）、（２）式の逆数をとり、その差をとれば次式が得られる。
１／Ｔｄ−１／Ｔｕ＝２ｖ・ｃｏｓθ／Ｌ（３）
したがって、順方向到達時間Ｔｄと逆方向到達時間Ｔｕの測定から、ガスの平均流速ｖと流量Ｑが次式により求められる。ただし、Ａは流路１の断面積である。
ｖ＝（１／Ｔｄ−１／Ｔｕ）Ｌ／２ｃｏｓθ （４）
Ｑ＝ｖ・Ａ（５）
このように、ガスの温度・含有成分等に依存する音速ｃを（４）式から消去することで、測定値（到達時間Ｔｄ，Ｔｕ）と一定値（伝搬距離Ｌ，測線角θ）とから流速ｖが得られる利点を有している。
【００１９】
そこで、超音波流量計１００には、計測部として、受信側振動子３１ｕ，３１ｄにより得られる受信側振動子出力を増幅する増幅手段４と、後述する「ゼロクロス法」により出力波形から超音波到達時点を検出するゼロクロスポイント検出手段５と、超音波到達時間を測定する時間計測手段６とが備えられている（図１参照）。
【００２０】
図１に戻り、流路１を構成する壁１０が、送信側振動子２１に対向する内壁面に超音波反射率が低い超音波反射抑制層１１に形成され、両測線Ｍｕ，Ｍｄの反射点間の内壁面で不要超音波が反射することを抑制して、多重反射を生じないようにしている。具体的には、超音波発射角２α（図では７０°＝±３５°）の内側領域（例えば±１０°〜±２５°）の内壁面に、超音波反射抑制層１１としてガラスウール入りエポキシ樹脂製の超音波吸収材が埋め込まれているので、超音波をよく吸収・減衰し、多重反射の発生とノイズの混入を防止している。なお、超音波反射抑制層１１の内面は壁１０の内壁面と面一になるように調整して、ガスの流れを乱さないようにしている。また、送信側振動子２１の周囲の内壁面にも別の超音波反射抑制層１２が同様に埋め込まれている。
【００２１】
さらに、流路１には、流れ方向軸線Ｏを挟み流れ方向に沿ってその両側に、一対のビーム絞り板１３，１４（ビーム調整部）が配置されている。各ビーム絞り板１３，１４には、測線Ｍｕ，Ｍｄの伝搬方向に沿って徐々に孔径を大とした絞り孔１３ａ，１３ｂ，１４ａ，１４ｂ（貫通孔）が各々貫通形成されている。絞り孔の孔径が１３ａ＜１４ａ＜１４ｂ＜１３ｂの順（伝搬方向の並び順）に大きく形成されているので、送信側振動子２１により発振された超音波のビーム径が伝搬方向下手側ほど広がるにつれて無理なく絞られるため測定分解能が向上する。
【００２２】
（実施例２）
次に、図２は図１（実施例１）と同様に用いられる超音波流量計の他の実施例の基本構成を示す。この超音波流量計２００の流量測定用の流路１０１は、少なくとも一対の超音波受信部３ｕ，３ｄ間の流れ方向軸線Ｏと送信側振動子２１とを含む流路断面（壁１１０の流路間隔Ｈ）において、流れ方向軸線Ｏが送信側振動子２１の取付位置に対応して極点部Ｐを形成するように曲がって形成されている。ただし、流路１０１の軸断面の形状及び断面積は、図１と同様に流れ方向において同一に形成されている。
【００２３】
具体的には、極点部Ｐは、流れ方向軸線Ｏが送信側振動子２１（超音波送信部２）設置側（外側）に向って扁平部分を含む台地状に突出することにより、極大点（頂点）領域を形成している（図３参照）。流れ方向軸線Ｏを台地状に突出させるために、送信側振動子２１に対向する側の壁１１０は、送信側振動子２１取付位置対応部分（直線部分）と流れ方向上手側及び下手側への延長部分（直線部分）とが、流路１０１の外側に中心を有する半径Ｒの円弧（円弧面）で接続されている。
【００２４】
この実施例では、超音波反射抑制層１１１は、流路１０１を構成する壁１１０において、超音波発射角２α（図では５０°＝±２５°）の内側領域（例えば±１０°〜±２０°）の内壁面に接着剤等によって貼り付け固定されている。送信側振動子２１の周囲の内壁面にも別の超音波反射抑制層１１２が同様に貼り付け固定されている。流れ方向軸線Ｏに沿って、流れ方向上手側のビーム絞り板１１３（ビーム調整部）と流れ方向下手側のビーム絞り板１１４（ビーム調整部）とが直列状に配置されている。ビーム絞り板１１３には、測線Ｍｕの伝搬方向に沿って徐々に孔径を大とした絞り孔１１３ａ，１１３ｂ，１１３ｃ，１１３ｄ（貫通孔）が各々貫通形成されている。一方、ビーム絞り板１１４には、測線Ｍｄの伝搬方向に沿って徐々に孔径を大とした絞り孔１１４ａ，１１４，１１４ｃ，１１４ｄ（貫通孔）が各々貫通形成されている。このように、図２の実施例では、上流受信側振動子３１ｕと下流受信側振動子３１ｄとはともに、流路１０１の内壁面で３回反射された超音波（上流側測線Ｍｕと下流側測線Ｍｄとで表わされる）を受信して発振する。なお、図２において図１と共通する機能を有する部分には同一符号を付して説明を省略する。
【００２５】
次に、図２の部分拡大図である図３を用いて、実施例２の伝搬距離Ｌ２を実施例１の伝搬距離Ｌ１と対比して説明する。図３では、実施例１（流れ方向軸線Ｏ１が直線状）を示す場合に符号１を付し、実施例２（流れ方向軸線Ｏ２が台地状極点部Ｐ）を示す場合に符号２を付してある。また、超音波の発射角が２α、流れ方向軸線Ｏ１に対する流れ方向軸線Ｏ２の傾斜角がβで表わされている。
流路１，１０１において、送信側振動子２１（超音波送信部２）から発振された超音波が流れ方向上手側（又は流れ方向下手側）の対向内壁面で最初に反射するまでの伝搬距離をＬ１，Ｌ２とすると、伝搬距離Ｌ１，Ｌ２の流れ方向の長さＬｖ１，Ｌｖ２は、それぞれ次式で与えられる。
Ｌｖ１＝Ｙ１・Ｚ１＝Ｌ１・ｓｉｎα （６）
Ｌｖ２＝Ｘ・Ｚ２＝Ｌ２・ｓｉｎ（α＋β）（７）
壁１０，１１０の流路間隔をＨとすると、伝搬距離Ｌ１，Ｌ２は、
Ｌ１＝Ｘ・Ｙ１＝Ｈ／ｃｏｓα （８）
Ｌ２＝Ｘ・Ｙ２＝Ｈ／ｃｏｓ（α＋β）（９）
流れ方向長さの比をとると、

【００２６】
実施例２の流れ方向長さＬｖ２は、実施例１の流れ方向長さＬｖ１に比して式（１０）に示す割合で長く形成されるので、実施例２の測線角θ２が実施例１の測線角θ１よりも小さくなり、測線Ｍｕ２は測線Ｍｕ１よりも送信側振動子２１から遠ざかる。例えば、超音波発射角２α＝５０°、傾斜角β＝１０°のとき、Ｌｖ２：Ｌｖ１＝１．５０となる。
【００２７】
（変形例）
図２の変形例を図４に示す。図４（ａ）は、流れ方向軸線Ｏが山型状に折れ曲がることにより、極点部Ｐが極大点（頂点）を形成する場合を表わしている。また、図４（ｂ）は、流れ方向軸線Ｏが円弧状に滑らかに曲がることにより、極点部Ｐが極大点（頂点）を形成する場合を表わしている。ただし、図４（ａ）及び図４（ｂ）において、流路１０１の軸断面の形状及び断面積は図２と同様に流れ方向において同一に形成されている。
【００２８】
さらに、図４（ｃ）〜図４（ｅ）は、流路１０１の軸断面の形状及び断面積のうち少なくとも一方が流れ方向に沿って変化する形態を例示している。図４（ｃ）は流れ方向軸線Ｏが台地状に突出する場合、図４（ｄ）は流れ方向軸線Ｏが山型状に折れ曲がる場合、図４（ｅ）は流れ方向軸線Ｏが円弧状に曲がる場合をそれぞれ示している。これらにおいて、送信側振動子２１設置側の壁１１０ａの傾斜角（β１）及びそれに対向する壁１１０ｂの傾斜角（β２）は、流れ方向軸線Ｏの傾斜角βと一致しなくなる（β１＜β＜β２）。
【００２９】
以上の実施例においては、送信側振動子２１で発振された超音波が流路の内壁面で１回又は３回反射して受信側振動子３１ｕ，３１ｄに到達する場合についてのみ説明したが、内壁面での反射回数は任意に設定できる。また、一対の超音波受信部３ｕ，３ｄ（受信側振動子３１ｕ，３１ｄ）は、超音波送信部２（送信側振動子２１）からの離間距離Ｄを異ならせて配置してもよい。この場合、伝搬距離Ｌも上流側と下流側とで一致しなくなるが、検査工程における検量線作成作業等において考慮すればよい。さらに、図２の天地を逆にしたときには、極点部Ｐは極小点又は極小点領域を形成することになる。なお、超音波反射抑制層１１，１２と超音波反射抑制層１１１，１１２とは実施例を入れ替えることができ、ビーム絞り板１３，１４とビーム絞り板１１３，１１４とは実施例を入れ替えることができる。また、図１又は図２において、ビーム絞り板１３，１４，１１３，１１４に超音波反射抑制層１１，１２，１１１，１１２を形成してもよい。
【図面の簡単な説明】
【図１】本発明に係る超音波流量計の一実施例の基本構成を示す説明図。
【図２】本発明に係る超音波流量計の他の実施例の基本構成を示す説明図。
【図３】図２の部分拡大図。
【図４】図２の変形例を示す説明図。
【符号の説明】
１，１０１流路
１０，１１０壁
１１，１１１超音波反射抑制層
１３，１４，１１３，１１４ビーム絞り板（ビーム調整部）
２超音波送信部
２１送信側振動子
３ｕ上流側超音波受信部
３１ｕ上流受信側振動子
３ｄ下流側超音波受信部
３１ｄ下流受信側振動子
１００，２００超音波流量計[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic flow meter.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a flow rate measuring device that measures the flow rate of a fluid such as city gas or water, an ultrasonic flow meter that measures a flow velocity using an ultrasonic wave is known. For example, in Non-Patent Document 1, a pair of ultrasonic receivers is provided on the other side wall of the flow path on the upper side and the lower side of the flow direction of the fluid with the ultrasonic transmission section provided on one side wall of the flow path interposed therebetween. Thus, a technique has been disclosed in which ultrasonic waves simultaneously emitted from a transmitting unit are received almost simultaneously by a pair of receiving units, and the measurement time can be reduced.
[0003]
[Non-patent document 1]
Written by Eiji Nashin, "Sensor Utilization Picture Book", Ohmsha, Ltd., January 1993, p. 98, FIG. 3 (d)
[0004]
[Problems to be solved by the invention]
However, as shown in Non-Patent Document 1, in the arrangement of the ultrasonic sensors in which each receiving unit is provided to face the transmitting unit, it is necessary to reduce the installation interval of the pair of receiving units to reduce the size of the ultrasonic flowmeter. There is a possibility that the propagation distance (arrival time) from the transmitting unit to each receiving unit is shortened, and the measurement accuracy is reduced. On the other hand, if the installation interval of the pair of receiving units is widened, a single ultrasonic transducer (transmitting transducer) cannot perform ultrasonic oscillation at a wide angle with respect to the pair of receiving units. Therefore, a transmitter-side vibrator must be provided.
[0005]
Therefore, an object of the present invention is to provide an ultrasonic wave that can be simply configured by an ultrasonic transmitting unit having a single transmitting-side vibrator and a pair of ultrasonic receiving units each having a receiving-side vibrator without reducing measurement accuracy. It is to provide a flow meter.
[0006]
Means for Solving the Problems and Effects of the Invention
The first of the ultrasonic flow meters according to the present invention to solve the above problems,
A flow path for passing a fluid;
On the wall of the flow path, an ultrasonic transmission unit attached with a transmission-side vibrator that oscillates ultrasonic waves toward the upper side and the lower side of the flow direction of the fluid,
Oscillated by the ultrasonic waves oscillated from the ultrasonic transmission unit and reflected at least once on the inner wall surface of the flow path on the walls of the flow path on the upper side and the lower side of the flow direction of the fluid with the ultrasonic transmission unit interposed therebetween. A pair of ultrasonic receiving units each having a receiving transducer attached thereto,
It is characterized by having.
[0007]
According to the first ultrasonic flow meter, since the receiving-side vibrator detects the ultrasonic waves after being reflected at least once, even if the interval between the pair of ultrasonic receiving units is narrowed, each ultrasonic wave is transmitted from the ultrasonic transmitting unit. The propagation distance (arrival time) to the receiving unit is relatively long, and measurement accuracy is ensured. In addition, since it is not necessary to oscillate the ultrasonic waves at a wide angle from the transmitting-side transducer toward the upstream side and the downstream side in the flow direction, it is not necessary to provide the transmitting-side transducer corresponding to each ultrasonic receiving unit. Therefore, the measuring unit (ultrasonic sensor unit) of the ultrasonic flowmeter can be simply configured by the ultrasonic transmitting unit having the single transmitting-side vibrator and the pair of ultrasonic receiving units each having the receiving-side vibrator separately. . In addition, even if the oscillation frequency of the transmitting-side vibrator changes due to the temperature change of the surrounding environment, the temperature dependency is eliminated because the single transmitting-side vibrator is used, and complicated correction of the arrival time and the like can be performed. No need.
[0008]
The second of the ultrasonic flow meter according to the present invention to solve the above problems,
In a cross section of a flow path including a flow direction axis of a fluid and a transmission-side vibrator that oscillates ultrasonic waves, the flow direction axis is bent so as to form a pole portion corresponding to the mounting position of the transmission-side vibrator. Road and
An ultrasonic transmission unit attached to a wall of the flow path so that the transmission-side vibrator oscillates ultrasonic waves toward the upper side and the lower side in the flow direction of the fluid,
Oscillated by the ultrasonic waves oscillated from the ultrasonic transmission unit and reflected at least once on the inner wall surface of the flow path on the walls of the flow path on the upper side and the lower side of the flow direction of the fluid with the ultrasonic transmission unit interposed therebetween. A pair of ultrasonic receiving units each having a receiving transducer attached thereto,
It is characterized by having.
[0009]
In the second ultrasonic flowmeter, the first configuration further has a curved flow path such that the flow direction axis forms an extreme point (maximum point or minimum point) corresponding to the mounting position of the transmitting-side vibrator. Therefore, the flow direction axis exhibits a mountain shape, a plateau shape, a curved shape, or the like that is convex toward the mounting side of the transmitting-side vibrator. Thereby, the propagation distance (arrival time) can be relatively increased as compared with the case where the flow direction axis is linear, so that the measurement accuracy can be further improved. At this time, the propagation distance (arrival time) becomes longer by the distance of the inner wall facing the transmitting-side vibrator due to the bending of the flow path, and the reflected wave on the inner wall further flows from the transmitting-side vibrator (on the upstream side in the flow direction). Or to the lower side). Therefore, while maintaining the required measurement accuracy, the installation interval of the pair of ultrasonic receiving units can be relatively narrowed to further reduce the size of the ultrasonic flowmeter. Note that the pole portion forms a pole in a case where the pole portion is sharply bent like a mountain shape, a case where it is bent gently like a curved shape, or the like. On the other hand, when a flat portion is included as in a plateau shape, the pole portion forms a pole region.
[0010]
At that time, in these ultrasonic flow meters, at least one of the shape and the cross-sectional area of the axial cross section of the flow path may change along the flow direction. For example, the cross-sectional area (diameter) of the flow path having a circular cross-section gradually decreases from the upstream side in the flow direction and becomes the minimum corresponding to the mounting position of the transmitting-side vibrator (at this time, the flow direction axis is at a pole (maximum point or minimum Point)), and then the flow path changes again so that the cross-sectional area of the flow path gradually increases.
In some cases, the flow path has the same axial cross-sectional shape and cross-sectional area in the flow direction. For example, the flow direction axis of the flow path having a circular cross-section and a constant cross-sectional area (diameter) is convex or curved toward the mounting side of the transmitter-side vibrator, and the flow direction axis is the transmission-side vibration. It changes so as to reach an extreme point (maximum point or minimum point) according to the mounting position of the child.
[0011]
Then, the pair of ultrasonic receiving units are separated from the ultrasonic transmitting units by a substantially equal distance in a flow path cross section including the flow direction axis of the fluid and the transmitting-side vibrator, and both are disposed on the ultrasonic transmitting unit installation side. It is desirable to mount it on a wall. Thereby, a time (hereinafter referred to as a forward arrival time) Td from the ultrasonic transmission unit (transmission-side transducer) to reach the ultrasonic reception unit (reception-side transducer) on the lower side in the flow direction, and ultrasonic transmission. The difference ΔT from the time (hereinafter referred to as the “reverse direction arrival time”) from the part (transmitting transducer) to the ultrasonic receiving part (receiving transducer) on the upstream side in the flow direction can be quickly calculated. . Also, since the ultrasonic transmission unit and the pair of ultrasonic reception units are all mounted on the same wall with respect to the flow channel, the assembly, removal, and replacement of the ultrasonic sensor on the flow channel wall can be performed on one side of the flow channel. Work can be performed intensively from the side, and work efficiency is increased.
[0012]
Further, at least the inner wall surface of the flow path facing the transmitting-side vibrator may be formed on an ultrasonic reflection suppressing layer for suppressing multiple reflection. By forming the inner wall surface of the flow path facing the transmitting-side vibrator in the ultrasonic reflection suppressing layer, the ultrasonic wave generated by the oscillation of the transmitting-side vibrator has an angle close to a right angle to the flow direction axis (eg, , 90 ° ± 10 ° to 90 ° ± 25 °), the reflection on the inner wall surface of the flow path can be suppressed. In other words, in the ultrasonic reflection suppression layer, noise components are formed by repeated scattering and reflection of unnecessary ultrasonic waves that are not originally intended for flow rate measurement on the inner wall of the flow path, and are sensed together with signal components by the receiving transducer. This is useful for preventing the phenomenon (multiple reflection) from occurring and improving the measurement accuracy. The formation of the ultrasonic reflection suppressing layer is performed by attaching an ultrasonic absorber (for example, epoxy resin containing glass wool, silicon resin containing glass wool, or the like) to attenuate such unnecessary ultrasonic waves to the inner wall surface of the flow path. Done by
[0013]
Further, the flow path may be provided with a beam adjusting unit for narrowing the beam diameter of the ultrasonic wave before the ultrasonic wave oscillated by the transmitting-side vibrator reaches the receiving-side vibrator. As a result, the spread of the ultrasonic wave can be suppressed, the variation in the arrival time at each part of the receiving-side vibrator can be eliminated, and the measurement accuracy can be improved. As a beam adjusting unit, for example, when a control plate having a through hole formed in the thickness direction is arranged in a screen shape along the flow direction, a beam diameter corresponding to the hole diameter of the ultrasonic wave oscillated by the transmitting-side vibrator is provided. Only the part will be passed. In this case, when an ultrasonic beam propagation path having a divergence angle of about 0.5 rad is formed, the ultrasonic wave passing through the through-hole becomes a plane wave and reaches each part of the receiving-side vibrator almost at the same time. The resolution can be increased by the reception signal output.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a basic configuration of an embodiment of an ultrasonic flowmeter used as a general residential gas meter or the like. In the flow path 1 for flow measurement of the ultrasonic flow meter 100, a flow measurement gas (fluid) flows along the flow direction axis O in the illustrated flow direction (average flow velocity v). An ultrasonic transmission unit 2 and a pair of ultrasonic reception units 3u and 3d are attached to a wall 10 of the flow path 1, and a flow including an flow direction axis O and the ultrasonic transmission unit 2 as shown in FIG. In the cross section of the road, the ultrasonic receiving units 3u and 3d are both located on the wall 10 on the installation side of the ultrasonic transmitting unit 2.
[0015]
In the flow path 1 for measurement, the flow direction axis O is linear between at least the pair of ultrasonic receiving units 3u and 3d, and the shape and the cross-sectional area of the axial cross section are the same in the flow direction. When the measurement object is a gas, the axial cross-sectional shape of the measurement flow path 1 may be any as long as it forms a space closed by the wall 10. For example, any one of a circular shape, an elliptical shape, a square shape, a rectangular shape, and the like can be used. May be adopted. If the measurement target is a liquid such as water, an open shape (for example, a semicircular shape) in which the zenith of the wall 10 is open to the atmosphere may be adopted as the axial cross-sectional shape of the measurement flow path 1. .
[0016]
The ultrasonic transmission unit 2 is fixed to the wall 10 of the flow path 1 and includes a transmission-side vibrator 21 including a piezoelectric element, a vibration plate, an electrode plate, and the like, and a driving voltage for causing the transmission-side vibrator 21 to oscillate. A transmission unit 22 including a circuit and the like. A piezoelectric element or the like having a relatively wide directivity (having a large half-angle) is selected as the transmitting-side vibrator 21 so that ultrasonic waves can be oscillated alone toward the upper side and the lower side in the gas flow direction. I do. In FIG. 1, the ultrasonic emission angle 2α formed by the upstream measurement line Mu and the downstream measurement line Md around the transmission-side transducer 21 is set to 2α = 70 ° = ± 35 °.
[0017]
The upstream ultrasonic receiving unit 3u is fixed to the wall 10 on the upstream side in the flow direction from the ultrasonic transmitting unit 2 (transmitting transducer 21), and includes an upstream receiving side composed of a piezoelectric element, a vibration plate, an electrode plate, and the like. It includes a vibrator 31u, and a receiving means 32 including a voltage detection circuit for detecting a voltage generated by the upstream receiving-side vibrator 31u. On the other hand, the downstream-side ultrasonic receiving unit 3d is fixed to the wall 10 on the downstream side in the flow direction from the ultrasonic transmitting unit 2 (the transmitting-side vibrator 21), and includes a downstream element including a piezoelectric element, a vibration plate, an electrode plate, and the like. The receiving side vibrator 31d includes a receiving unit 32 including a voltage detecting circuit for detecting a voltage generated by the downstream receiving side vibrator 31d. Both the upstream receiving transducer 31u and the downstream receiving transducer 31d receive the ultrasonic waves (represented by the upstream measurement line Mu and the downstream measurement line Md) reflected once on the inner wall surface of the flow path 1. Since oscillation occurs, a piezoelectric element or the like having relatively narrow directivity (small half-angle) is selected. The upstream ultrasonic receiving unit 3u (upstream receiving transducer 31u) and the downstream ultrasonic receiving unit 3d (downstream receiving transducer 31d) are symmetrical with respect to the ultrasonic transmitting unit 2 (transmitting transducer 21). And the separation distance D between the transmitting and receiving units is set to be equal. Note that the receiving means of the upstream ultrasonic receiving unit 3u and the receiving means of the downstream ultrasonic receiving unit 3d are configured to serve both purposes.
[0018]
In FIG. 1, the average flow velocity of the gas is v, the velocity of sound propagating in the gas is c, and the angle between the traveling direction of the ultrasonic wave (measurement lines Mu and Md) and the flow direction of the gas (flow direction axis O) is θ (hereinafter referred to as θ). , The propagation angle of the ultrasonic wave) and L (= D / cos θ), the forward arrival time Td and the backward arrival time Tu are expressed as follows, respectively.
Td = L / (c + v · cos θ) (1)
Tu = L / (cv · cos θ) (2)
By taking the reciprocal of equations (1) and (2) and taking the difference, the following equation is obtained.
1 / Td-1 / Tu = 2v · cos θ / L (3)
Therefore, from the measurement of the forward arrival time Td and the backward arrival time Tu, the average flow velocity v and the flow rate Q of the gas can be obtained by the following equations. Here, A is the cross-sectional area of the flow path 1.
v = (1 / Td-1 / Tu) L / 2 cos θ (4)
Q = v · A (5)
As described above, by eliminating the sound velocity c depending on the gas temperature, the contained components, and the like from the equation (4), the measured value (the arrival time Td, Tu) and the constant value (the propagation distance L, the measurement line angle θ) can be obtained. This has the advantage that a flow velocity v can be obtained.
[0019]
Therefore, the ultrasonic flowmeter 100 includes, as a measuring unit, an amplifying unit 4 for amplifying the output of the receiving-side vibrator obtained by the receiving-

side vibrators

31u and 31d, and the ultrasonic wave from the output waveform by the “zero-cross method” described later. A zero cross point detecting means 5 for detecting a time point and a time measuring means 6 for measuring an ultrasonic arrival time are provided (see FIG. 1).
[0020]
Returning to FIG. 1, a wall 10 constituting the flow path 1 is formed on an ultrasonic reflection suppressing layer 11 having a low ultrasonic reflectivity on an inner wall surface facing the transmitting-side vibrator 21, and the reflection points of the two measurement lines Mu and Md are formed. The reflection of unnecessary ultrasonic waves on the inner wall surface between them is suppressed to prevent multiple reflections. Specifically, an epoxy resin containing glass wool as an ultrasonic reflection suppressing layer 11 is formed on the inner wall surface of an inner region (for example, ± 10 ° to ± 25 °) having an ultrasonic emission angle 2α (70 ° = ± 35 ° in the figure). Since the ultrasonic absorber is embedded, the ultrasonic wave is well absorbed and attenuated to prevent the occurrence of multiple reflections and noise. The inner surface of the ultrasonic reflection suppressing layer 11 is adjusted so as to be flush with the inner wall surface of the wall 10 so as not to disturb the gas flow. Further, another ultrasonic reflection suppression layer 12 is similarly embedded in the inner wall surface around the transmission-side vibrator 21.
[0021]
Further, in the flow path 1, a pair of beam diaphragm plates 13 and 14 (beam adjustment units) are arranged on both sides of the flow direction axis O along the flow direction. In each of the

beam aperture plates

13 and 14,

aperture holes

13a, 13b, 14a and 14b (through holes) whose diameters gradually increase along the propagation directions of the measurement lines Mu and Md are formed to penetrate. Since the diameters of the apertures are formed larger in the order of 13a <14a <14b <13b (the order of propagation in the propagation direction), the beam diameter of the ultrasonic wave oscillated by the transmission-side vibrator 21 increases toward the lower side in the propagation direction. As a result, the measurement resolution is improved.
[0022]
(Example 2)
Next, FIG. 2 shows a basic configuration of another embodiment of the ultrasonic flowmeter used in the same manner as FIG. 1 (Embodiment 1). The flow path 101 for flow measurement of the ultrasonic flow meter 200 has a flow path cross section including at least the flow direction axis O between the pair of ultrasonic receiving units 3u and 3d and the transmission-side vibrator 21 (flow path of the wall 110). At the interval H), the flow direction axis O is bent so as to form the pole portion P corresponding to the mounting position of the transmitting-side vibrator 21. However, the shape and the cross-sectional area of the axial section of the flow path 101 are the same in the flow direction as in FIG.
[0023]
Specifically, the pole portion P is formed by projecting the flow direction axis O in a plateau shape including a flat portion toward the transmitting side transducer 21 (ultrasonic transmitting unit 2) installation side (outside), thereby forming a local maximum point ( (Vertex) region (see FIG. 3). In order for the flow direction axis O to protrude in a plateau shape, the wall 110 on the side facing the transmission-side vibrator 21 has a portion (straight line portion) corresponding to the mounting position of the transmission-side vibrator 21, and extends upward and downward in the flow direction. The extended portion (linear portion) is connected by an arc (arc surface) having a radius R having a center outside the flow path 101.
[0024]
In this embodiment, the ultrasonic reflection suppressing layer 111 forms an inner region (for example, ± 10 ° to ± 20 °) of the ultrasonic emission angle 2α (50 ° = ± 25 ° in the figure) on the wall 110 constituting the flow path 101. ) Is adhered and fixed to the inner wall surface with an adhesive or the like. Another ultrasonic reflection suppression layer 112 is similarly attached and fixed to the inner wall surface around the transmission-side transducer 21. Along the flow direction axis O, a beam stop plate 113 (beam adjustment unit) on the upstream side in the flow direction and a beam stop plate 114 (beam adjustment unit) on the downstream side in the flow direction are arranged in series. In the beam stop plate 113, stop

holes

113a, 113b, 113c, and 113d (through holes) whose diameters gradually increase along the propagation direction of the measurement line Mu are formed through the beam stop plate 113, respectively. On the other hand, in the beam stop plate 114, stop

holes

114a, 114, 114c, and 114d (through holes) whose diameters gradually increase along the propagation direction of the measurement line Md are formed to penetrate. As described above, in the embodiment of FIG. 2, both the upstream receiving side transducer 31u and the downstream receiving side transducer 31d are ultrasonic waves reflected three times on the inner wall surface of the flow path 101 (the upstream side measuring line Mu and the downstream side (Represented by a measurement line Md). In FIG. 2, portions having the same functions as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
[0025]
Next, the propagation distance L2 of the second embodiment will be described in comparison with the propagation distance L1 of the first embodiment with reference to FIG. 3, which is a partially enlarged view of FIG. In FIG. 3, reference numeral 1 is assigned to the case where the first embodiment (the flow direction axis O 1 is straight), and reference numeral 2 is assigned to the case where the second embodiment (the flow direction axis O 2 is the plateau-like pole portion P). It is. The launch angle of the ultrasonic wave is represented by 2α, and the inclination angle of the flow direction axis O2 with respect to the flow direction axis O1 is represented by β.
In the

flow paths

1 and 101, the propagation distance until the ultrasonic wave oscillated from the transmission-side vibrator 21 (ultrasonic wave transmission unit 2) first reflects on the facing inner wall surface on the upper side in the flow direction (or on the lower side in the flow direction). Are L1 and L2, the lengths Lv1 and Lv2 of the propagation distances L1 and L2 in the flow direction are respectively given by the following equations.
Lv1 = Y1 · Z1 = L1 · sinα (6)
Lv2 = X · Z2 = L2 · sin (α + β) (7)
Assuming that the flow path interval between the

walls

10 and 110 is H, the propagation distances L1 and L2 are
L1 = X · Y1 = H / cosα (8)
L2 = X · Y2 = H / cos (α + β) (9)
Taking the ratio of the length in the flow direction,

[0026]
Since the length Lv2 in the flow direction of the second embodiment is formed to be longer than the length Lv1 of the flow direction of the first embodiment at the ratio shown in the equation (10), the measurement angle θ2 of the second embodiment is It becomes smaller than the survey line angle θ1, and the survey line Mu2 is farther from the transmitting-side vibrator 21 than the survey line Mu1. For example, when the ultrasonic emission angle 2α = 50 ° and the inclination angle β = 10 °, Lv2: Lv1 = 1.50.
[0027]
(Modification)
FIG. 4 shows a modification of FIG. FIG. 4A shows a case where the pole portion P forms a local maximum point (apex) by bending the flow direction axis O into a mountain shape. FIG. 4B shows a case where the pole portion P forms a maximum point (apex) by smoothly bending the flow direction axis O in an arc shape. However, in FIGS. 4A and 4B, the shape and the cross-sectional area of the axial section of the flow path 101 are the same in the flow direction as in FIG.
[0028]
Further, FIGS. 4C to 4E illustrate a mode in which at least one of the axial cross-sectional shape and the cross-sectional area of the flow path 101 changes along the flow direction. 4C shows the case where the flow direction axis O protrudes in a plateau shape, FIG. 4D shows the case where the flow direction axis O is bent in a mountain shape, and FIG. 4E shows the case where the flow direction axis O has an arc shape. Each case of turning is shown. In these cases, the inclination angle (β1) of the wall 110a on the transmitting-side vibrator 21 installation side and the inclination angle (β2) of the wall 110b opposed thereto do not match the inclination angle β of the flow direction axis O (β1 <β <). β2).
[0029]
In the above embodiment, only the case where the ultrasonic wave oscillated by the transmission-side vibrator 21 is reflected once or three times by the inner wall surface of the flow path and reaches the reception-

side vibrators

31u and 31d has been described. The number of reflections on the inner wall surface can be set arbitrarily. Further, the pair of ultrasonic receiving units 3u and 3d (receiving-

side transducers

31u and 31d) may be arranged with different distances D from the ultrasonic transmitting unit 2 (the transmitting-side transducer 21). In this case, the propagation distance L also does not match between the upstream side and the downstream side, but may be considered in the calibration curve creation work or the like in the inspection process. Further, when the top and bottom of FIG. 2 are reversed, the pole part P forms a minimum point or a minimum point area. Note that the ultrasonic

reflection suppressing layers

11 and 12 and the ultrasonic reflection suppressing layers 111 and 112 can exchange the embodiments, and the

beam stop plates

13 and 14 and the beam stop plates 113 and 114 can interchange the embodiments. it can. In addition, in FIG. 1 or FIG. 2, the ultrasonic

reflection suppressing layers

11, 12, 111, 112 may be formed on the

beam stop plates

13, 14, 113, 114.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a basic configuration of one embodiment of an ultrasonic flowmeter according to the present invention.
FIG. 2 is an explanatory view showing a basic configuration of another embodiment of the ultrasonic flowmeter according to the present invention.
FIG. 3 is a partially enlarged view of FIG. 2;
FIG. 4 is an explanatory view showing a modification of FIG. 2;
[Explanation of symbols]
1,101 Flow path 10,110 Wall 11,111 Ultrasonic reflection suppression layer 13,14,113,114 Beam stop plate (beam adjustment unit)
2 Ultrasonic transmitter 21 Transmitter transducer 3u Upstream ultrasonic receiver 31u Upstream receiver 3d Downstream ultrasonic receiver

31d Downstream receiver

100, 200 Ultrasonic flow meter

Claims

A flow path for passing a fluid;
On the wall of the flow path, an ultrasonic transmission unit attached with a transmission-side vibrator that oscillates ultrasonic waves toward the upper side and the lower side of the flow direction of the fluid,
Oscillated by the ultrasonic waves oscillated from the ultrasonic transmission unit and reflected at least once on the inner wall surface of the flow path on the walls of the flow path on the upper side and the lower side of the flow direction of the fluid with the ultrasonic transmission unit interposed therebetween. A pair of ultrasonic receiving units each having a receiving transducer attached thereto,
An ultrasonic flowmeter comprising:

In a cross section of a flow path including a flow direction axis of a fluid and a transmission-side vibrator that oscillates ultrasonic waves, the flow direction axis is bent so as to form a pole portion corresponding to the mounting position of the transmission-side vibrator. Road and
An ultrasonic transmission unit attached to a wall of the flow path so that the transmission-side vibrator oscillates ultrasonic waves toward the upper side and the lower side in the flow direction of the fluid,
Oscillated by the ultrasonic waves oscillated from the ultrasonic transmission unit and reflected at least once on the inner wall surface of the flow path on the walls of the flow path on the upper side and the lower side of the flow direction of the fluid with the ultrasonic transmission unit interposed therebetween. A pair of ultrasonic receiving units each having a receiving transducer attached thereto,
An ultrasonic flowmeter comprising:

The ultrasonic flowmeter according to claim 1, wherein at least one of a shape and a sectional area of an axial cross section of the flow path changes along a flow direction.

The ultrasonic flowmeter according to claim 1, wherein the flow path has the same axial cross-sectional shape and cross-sectional area in the flow direction.

The pair of ultrasonic receiving units are separated from the ultrasonic transmitting unit by substantially equal distances in a flow path cross section including the fluid flow direction axis and the transmitting-side vibrator, and both of the ultrasonic transmitting units are installed. The ultrasonic flowmeter according to any one of claims 1 to 4, which is attached to a side wall.

The ultrasonic wave according to any one of claims 1 to 5, wherein at least an inner wall surface of the flow path facing the transmitting-side vibrator is formed on an ultrasonic reflection suppression layer for suppressing multiple reflection. Flowmeter.

2. A beam adjusting unit for narrowing a beam diameter of an ultrasonic wave oscillated by the transmitting-side vibrator before the ultrasonic wave reaches the receiving-side vibrator. The ultrasonic flowmeter according to any one of claims 6 to 6.