JP3562261B2

JP3562261B2 - Ultrasonic transducer and ultrasonic flowmeter using the same

Info

Publication number: JP3562261B2
Application number: JP28170897A
Authority: JP
Inventors: 明久足立; 茂岩永; 雅彦橋本; 利春佐藤
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1997-10-15
Filing date: 1997-10-15
Publication date: 2004-09-08
Anticipated expiration: 2017-10-15
Also published as: JPH11118550A

Description

【０００１】
【発明の属する技術分野】
本発明は、超音波により気体や液体の流量や流速の計測を行う超音波流量計に関するものである。
【０００２】
【従来の技術】
従来この種の超音波流量計に用いる超音波振動子を図１８、図１９に示す。例えば特開平４−３０９８１７号公報が知られており、図１８に示すように圧電セラミック１を金属振動板２にロー付けし、この金属振動板２を金属ハウジング３に溶接していた。また特表平６−５００３８９号公報が知られており、エポキシ樹脂と微小ガラス球からなる壷形整合層５が圧電セラミック４を内包するケースとして共用されていた。
【０００３】
【発明が解決しようとする課題】
しかしながら上記の従来の構成では金属ハウジングに防振対策がなされていないため、圧電セラミックの振動が金属振動板を通じて金属ハウジングに伝わる。金属ケースでは振動が減衰されにくいため、金属ハウジングの振動が再び圧電セラミックに戻る。このため圧電セラミックの振動がなかなかおさまらず、残響の長い超音波パルスになる。この残響がノイズ要因の一つとなるため、Ｓ／Ｎが劣化し流量や流速の計測精度が低下するという課題を有していた。またエポキシ樹脂と微小ガラス球からなる材料をケースとして利用すると、ケースは振動しにくくなり残響は短くなる。しかしこのような材料は一般的に微多孔性を有すためケースの中に被測定流体が浸入し、被測定流体の成分によっては圧電体の電極等を腐食させ特性を劣化させるという課題を有していた。
【０００４】
本発明では上記課題を解決するもので、残響の短い超音波パルスの送受波が可能で、信頼性の高い超音波振動子を実現し、超音波流量計の計測精度を向上させることを目的とする。
【０００５】
【課題を解決するための手段】
本発明は、上記課題を解決するために、天部と側壁部とを有する有天筒状のケースと、前記天部の内壁面に固定された圧電体と、前記天部の外壁面に設けられた音響整合層と、前記側壁部の外壁に設けた支持部とを備え、前記圧電体の振動が前記側壁部へ伝搬することを防止するように側壁部に天部と同心状の折り曲げ部を設ける超音波振動子である。
また、天部と側壁部とを有する有天筒状のケースと、前記天部の内壁面に固定された圧電体と、前記天部の外壁面に設けられた音響整合層と、前記側壁部の外壁に設けた支持部とを備え、前記圧電体の振動が前記側壁部へ伝搬することを防止するように側壁部の軸方向に複数の凸部または凹部を備えた超音波振動子である。
また、天部と側壁部とを有する有天筒状のケースと、前記天部の内壁面に固定された圧電体と、前記天部の外壁面に設けられた音響整合層と、前記側壁部の外壁に設けた支持部とを備え、前記圧電体の振動が前記側壁部へ伝搬することを防止するように側壁部を多角形の筒状とした超音波振動子である。
【０００６】
【発明の実施の形態】
本発明の一実施形態は、超音波振動子を構成する圧電体は被測定流体から遮断する金属製ケースで内包し、この金属製ケースに折り曲げ部を設けることにより剛性を高め、振動の伝搬を低減させたものである。上記実施形態によれば、圧電体の振動が金属製ケースに伝わり難くすることができ、残響の短い超音波パルスの送受信が可能な超音波振動子を得ることができる。この結果残響によるノイズの発生を低減でき、Ｓ／Ｎが改善されて被測定流体の流量、流速の計測精度が向上できる。また被測定流体が圧電体に接触することを防止できるので、超音波振動子の信頼性も向上できる。
【０００７】
本発明の第１の形態の超音波振動子は、天部と側壁部を有す有天筒状のケースと、前記天部の内壁面に固定された圧電体と、前記天部の外壁面に設けられた音響整合層と、前記側壁部の外壁に設けた支持部とを備え、前記ケースが防振構造を有し圧電体の振動が前記ケースへ伝搬することを防止しており、残響の短い超音波パルスの送受信が可能な超音波振動子を得ることができる。
【０００８】
本発明は第２の形態の超音波振動子は、第１の形態の超音波振動子において、側壁部の剛性が増大する形状としたため、圧電体の振動が側壁部へ伝搬することが防止され、残響の短い超音波パルスの送受信が可能な超音波振動子を得ることができる。
【０００９】
本発明は第３の形態の超音波振動子は、第２の形態の超音波振動子において、側壁部に天部と同心状の折り曲げ部を設けたため、側壁部の剛性が増大し圧電体の振動が側壁部へ伝搬することが防止され、残響の短い超音波パルスの送受信が可能な超音波振動子を得ることができる。
【００１０】
本発明は第４の形態の超音波振動子は、第２の形態の超音波振動子において、側壁部の軸方向に複数の凸部または凹部を備えたため、側壁部の剛性が増大し圧電体の振動が側壁部へ伝搬することが防止され、残響の短い超音波パルスの送受信が可能な超音波振動子を得ることができる。
【００１１】
本発明は第５の形態の超音波振動子は、第２の形態の超音波振動子において、側壁部を多角形の筒状としたため、側壁部の剛性が増大し圧電体の振動が側壁部へ伝搬することが防止され、残響の短い超音波パルスの送受信が可能な超音波振動子を得ることができる。
【００１２】
本発明は第６の形態の超音波振動子は、第１の形態の超音波振動子において、天部の外周部に凸部または凹部を備えたため、天部の外周部の剛性が増大し圧電体の振動が側壁部へ伝搬することが防止され、残響の短い超音波パルスの送受信が可能な超音波振動子を得ることができる。
【００１３】
本発明は第７の形態の超音波振動子は、第１の形態の超音波振動子において、天部の外周部に薄肉部を備えたため、天部のうち圧電体を固定した部分が振動しやすくなるため圧電体の振動が側壁部へ伝搬することが防止され、残響の短い超音波パルスの送受信が可能な超音波振動子を得ることができる。
【００１４】
本発明は第８の形態の超音波流量計は、被測定流体が流れる流量測定部と、この流量測定部に設けられ超音波を送受信する第１ないし第７のいずれかの形態の１対の超音波振動子と、前記超音波振動子間の伝搬時間を計測する計測回路と、前記計測回路からの信号に基づいて流量を算出する流量演算手段とを備えたため、残響によるノイズの影響を低減できるためＳ／Ｎが改善でき、被測定流体の流量、流速の計測精度が高い超音波流量計を得ることができる。
【００１５】
本発明は第９の形態の超音波流量計は、第８の形態の超音波流量計において、支持部に固定される端子板にシール部を有す超音波振動子を備えたため、被測定流体が流量測定部から外部に漏れることが防止でき、信頼性の高い超音波流量計を得ることができる。
【００１６】
【実施例】
以下、本発明の実施例について図面を用いて説明する。なお図面中で同一符号を付しているものは同一なものであり、詳細な説明は省略する。
【００１７】
（実施例１）
図１は本発明の実施例１の超音波振動子の外観図である。図２は図１の超音波振動子の断面図である。図３は図１の超音波振動子に用いる圧電体の外観図である。図１において、６は超音波振動子、７はケース、８はケース７の天部、９は天部８の外壁面に固定された音響整合層、１０はケース７の側壁部、１１は側壁部１０に固定された折り曲げ部、１２はケース７を固定するための支持部である。図２において、１３は天部８の内壁面に配置された圧電体、１４は支持部１２に固定された端子板、１５ａ、１５ｂは端子板１４に設けられた端子、１６は端子１５ａと端子１５ｂを絶縁するための絶縁部、１７は圧電体１３と端子１５ａを電気的に接続するためのリード線である。図３において、１８は圧電体１３の電極、１９は圧電体１３に設けられた溝である。
【００１８】
以上のように構成さた超音波振動子の作成方法の一例について図１、図２、図３を用いて説明する。超音波振動子６はＬＰガスや天然ガス中で使用することを想定して、ケース７にはステンレス、音響整合層９にはエポキシ樹脂と中空ガラス球の混合体からなる材料を選択する。ケース７の加工方法には量産性を考え、切削加工でなく絞り加工のような成型加工を選択する。またステンレスの厚みは、ケース７の成型加工の容易さ、構造的強度、超音波振動子６の感度への影響から０．１から０．５ｍｍ程度、波長の１０分の１以下程度の厚みを選択する。次に圧電体１３はステンレスからなる天部８に接着固定されるため、広がり方向の振動が阻害される。超音波振動子６の高感度化を図るためには広がり振動よりも厚み縦振動を主モードを利用するほうが有利である。しかし圧電体１３は形状により振動の主モードが決定されてしまい、圧電体１３の形状と使用周波数に対しする許容範囲が狭い。そこで図３に示したように直方体の圧電体１３に溝１９を２本設けた構造を選択した。溝１９を設けたことにより、横２０、縦２１が８ｍｍ、厚み２２が４ｍｍの直方体の圧電体１３は約４００ＫＨｚにおいて厚み振動が主モードとすることが可能となる。ただし溝１９の本数、深さ、方向は圧電体１３の形状、不要モードの影響、取り扱いの容易性から判断する。
【００１９】
まず厚み０．２ｍｍのステンレス板から直径１３ｍｍ程度の円板状の天部８を有す有天円筒状のケース７を成型加工する。このとき側壁部１０には天部８と同心円状の折り曲げ部１１を１個同時に成型加工する。次に天部８の外壁面に直径１２．５ｍｍの円板状の音響整合層９、内壁面には圧電体１３をエポキシ系接着剤を用いて接着固定する。このとき溝１９により分割された電極１８と天部８を１０μｍ以下の薄い接着層を介して接着固定することにより、分割された電極１８と天部８の電気的導通も取ることができる。リード線１７は図示されていない圧電体１３の電極と端子ａにそれぞれハンダ付けする。最後に直径１６ｍｍ程度、厚み０．８ｍｍ程度のステンレス板からなる端子板１４を支持部１２に電気溶接により固定し、封止と電気的導通を同時に行う。圧電体１３はケース７をグランドとして共用し、さらにケース７および端子板１４で覆われるためノイズの影響を低減できる。また封止するとき、ケース７内部に乾燥した窒素や不活性ガスで置換すると、圧電体１３の電極、圧電体１３とケース７の接着層等の長期間使用による劣化の防止も可能となる。
【００２０】
以上のように作成された超音波振動子を用いた超音波流量計の作製方法について図４、図５を用いて説明する。流量測定部２３を構成する材料はＬＰガスや天然ガスの流量計測する家庭用ガスメータを想定しアルミニウム合金ダイカストとした。側壁部２４、２５の端面に例えばコルク材からなるシール材３５を介して上板部３６をネジどめして、流路断面３７が矩形の流量測定部２３を構成する。また超音波振動子２７、２８は送受波面が相対するよう側壁部２４、２５に斜めに設けられた振動子取付穴２９、３０に例えばＯリングからなるシール材３１、３２を介して固定する。
【００２１】
以上のように構成された流量測定部２３を用いた超音波流量計についてその動作を説明する。超音波振動子２７と超音波振動子２８の中心を結ぶ距離をＬとし、この直線と流れの方向である流路２６の長手方向となす角をθとする。またＬＰガスの無風状態での音速をＣ、流路２６内でのＬＰガスの流速をＶとする。流量測定部２３の上流側に配置された超音波振動子２７から送信された超音波は流路２６を斜めに横断し、下流側に配置された超音波振動子２８で受信する。
【００２２】
このときの伝搬時間ｔ１は、
【００２３】
【数１】

【００２４】
で示される。次に送信・受信する超音波振動子を切り替え、超音波振動子２８から超音波を送信し、超音波振動子２７で受信する。このときの伝搬時間ｔ２は、
【００２５】
【数２】

【００２６】
で示される。ｔ１とｔ２の式からＬＰガスの音速Ｃを消去すると、
【００２７】
【数３】

【００２８】
の式が得られる。Ｌとθが既知ならば、計測回路３３にてｔ１とｔ２を測定すれば流速Ｖが求められる。この流速Ｖから流量Ｑは、断面３７の面積をＳ、補正係数をＫとすれば、流量演算回路３４で、
Ｑ＝ＫＳＶ
を演算し、流量を求めることができる。
【００２９】
超音波流量計では時間ｔ１、ｔ２を高精度に計測することが高精度な流量計測にとって重要となる。そこで、ケース７の振動の計測への影響について考える。送信側では、駆動信号により生じた圧電体１３の振動が音響整合層９を介してＬＰガスに超音波パルスとして放射されるだけなく、ケース７も振動させる。また受信側では、受信した超音波パルスは圧電体１３で電気信号に変換されるのと同時にケース７も振動させる。ここでケース７が振動してしまうと、ケース７では振動をほとんど減衰できないため、圧電体１３の長い残響として送信側、受信側ともに観測されてしまう。送信側の残響は計測回路３３に対し電気的ノイズとなり、受信した超音波パルスのＳ／Ｎを劣化させ測定精度を低下させる要因となる。また受信側の残響は受信した超音波パルスと合成されるため振幅、位相に影響を与え、時間ｔ１、ｔ２の計測に誤差を与える要因となる。本実施例ではケース７は折り曲げ部１１により側壁部１０の剛性が増加されているため、側壁部１０は振動しにくくなっている。このためケース７の振動を抑えることができ、超音波振動子６の残響を低減することが可能となる。このため超音波流量計の計測精度を高めることができる。
【００３０】
以上のように、本実施例によれば直方体の圧電体１３に２本の溝を設けることにより厚み縦振動を主モードとして利用することが可能となる。また圧電体１３と天部８を１０μｍ以下のエポキシ系接着剤で接着固定することにより、接着強度と同時に導通もとることができる。また圧電体１３の溝１９により分割された電極１８を天部８に接着固定することにより、分割された電極１８の接続が容易となるうえ、分割された圧電体１３が横方向へたわむような振動をすることを防止できる。圧電体１３をステンレス製ケース７と端子板１４でシールドされているため、外部からのノイズの影響を低減できる。
【００３１】
なお実施例１では折り曲げ部１１を１個設けるとしたが、２個以上の複数でも良く、また図６に示すように側壁部１０にビート３８を設けた構造としても良い。また天部８を円板状としたが、楕円径でも良い。
【００３２】
（実施例２）
以下、本発明の実施例２について、図面を参照しながら説明する。
【００３３】
図７は超音波振動子３９の上面図、図８は超音波振動子３９の側面図である。８は天部、９は音響整合層、１０は側壁部、１２は支持部、１４は端子板、１５は端子で、以上は図１、図２の構成と同様なものである。図１、図２の構成とことなるのは、側壁部１０に軸方向に８個の凸部を設けた点である。
【００３４】
以上のように構成さた超音波振動子の作成方法の一例について図４、図５を用いて説明する。超音波振動子３９はＬＰガスや天然ガス中で使用することを想定して、ケース７にはステンレス、音響整合層９にはエポキシ樹脂と中空ガラス球の混合体からなる材料を選択する。また量産性を考えケース７の加工方法には、切削加工でなく絞り加工のような成型加工を選択する。
【００３５】
まず厚み０．２ｍｍのステンレス板から直径１３ｍｍ程度の円板状の天部８を有す有天円筒状のケース７を成型加工する。このとき側壁部１０には軸方向に凸部４０を８個成型し、上方から見ると側壁部１０が花びら状に見える。次に天部８の外壁面に直径１２．５ｍｍの円板状の音響整合層９をエポキシ系接着剤を用いて接着固定する。これ以後の超音波振動子３９の作製方法、超音波流量計の作製方法、動作原理は実施例１と同様になるため省略する。
【００３６】
側壁部１０の剛性が高ければ高いほどケース７は振動しにくくなるため、残響を抑えることができる。薄い金属板から作られたケース７の剛性を高めるためには、凸部や凹部を設ければ良く、成型加工も容易にできる。本実施例では側壁部１０の軸方向に８個の凸部４０を設けることにより剛性を高め超音波振動子３９の残響を低減することができる。
【００３７】
なお実施例２では８個の凸部４０を側壁部１０に設けるとしたが、１個以上なら何個でも構わない。また図９に示すように側壁部１０に凹部４１を設け王冠状にしても良いし、凸部と凹部を組み合わせても良い。
【００３８】
（実施例３）
以下、本発明の実施例３について、図面を参照しながら説明する。
【００３９】
図１０は超音波振動子４２の外観図である。７はケース、１０は側壁部、１２は支持部で、以上は図１の構成と同様なものである。図１の構成とことなるのは、天部４３が四角形、音響整合層４４が直方体、折り曲げ部４５が側壁部１０の軸方向に設けたれた点である。
【００４０】
以上のように構成さた超音波振動子の作成方法の一例について図１０を用いて説明する。超音波振動子４２はＬＰガスや天然ガス中で使用することを想定して、ケース７にはステンレス、音響整合層４４にはエポキシ樹脂と中空ガラス球の混合体からなる材料を選択する。また量産性を考えケース７の加工方法には、切削加工でなく絞り加工のような成型加工を選択する。
【００４１】
まず厚み０．２ｍｍのステンレス板から１辺が９ｍｍの正方形の天部４３を有す有天角筒状のケース７を成型加工する。このとき側壁部１０はほぼ四角柱となるよう側壁部１０に折り曲げ部４５を成型加工する。次に天部４３に１辺８ｍｍの正方形の面を有す直方体の音響整合層４４をエポキシ系接着剤を用いて接着固定する。これ以後の超音波振動子４２の作製方法、超音波流量計の作製方法、動作原理は実施例１と同様になるため省略する。
【００４２】
側壁部１０の剛性が高ければ高いほどケース７は振動しにくくなるため、残響を抑えることができる。ここで薄い金属板から作られたケース７の剛性を高めるためには、側壁部を多角形の柱状にすれば良く、側壁部１０を多角形に成型加工することは容易である。本実施例では側壁部１０を四角柱とすることにより剛性を高められ超音波振動子４２の残響を低減することができる。
【００４３】
なお実施例３では天部４３は正方形、側壁部１０は四角柱としたが、四角形以外の多角形でも構わない。また支持部１２を円板形状としたが、天板８と同様に正方形でも、それ以外の多角形でも良い。
【００４４】
（実施例４）
以下、本発明の実施例４について、図面を参照しながら説明する。
【００４５】
図１１は超音波振動子４６の断面図、図１２は超音波振動子４６の上面図である。７はケース、８は天部、９は音響整合層、１０は側壁部、１２は支持部、１３は圧電体、１４は端子板、１５ａ、１５ｂは端子、１６は端子１５ａと端子１５ｂを絶縁するための絶縁部、１７は圧電体１３と端子１５ａを電気的に接続するためのリード線で、以上は図１の構成と同様なものである。図１の構成とことなるのは、天部８の外周部４９の４ケ所に凸部４７ａ〜４７ｄ、凸部４７と音響整合層９の間に空隙部４８を設けた点である。
【００４６】
以上のように構成さた超音波振動子４６の作成方法の一例について図１１、図１２を用いて説明する。超音波振動子４６はＬＰガスや天然ガス中で使用することを想定して、ケース７にはステンレス、音響整合層９にはエポキシ樹脂と中空ガラス球の混合体からなる材料を選択する。また量産性を考えケース７の加工方法には、切削加工でなく絞り加工のような成型加工を選択する。まず厚み０．２ｍｍのステンレス板から直径１５ｍｍ程度の円板状の天部８を有す有天円筒状のケース７を成型加工する。このとき天部８の外周部４９に高さが音響整合層９の厚みより薄い、０．８ｍｍ程度の凸部４７ａ〜４７ｄを同心円状に構成する。次に天部８の外壁面で凸部４７ａ〜４７ｄの内側に直径１２．５ｍｍの円板状の音響整合層９をエポキシ系接着剤を用いて接着固定する。このとき音響整合層９と凸部４７ａ〜４７ｄの間に、空隙部４８が形成される。これ以後の超音波振動子４６の作製方法、超音波流量計の作製方法、動作原理は実施例１と同様になるため省略する。
【００４７】
天部８の外周部４９の剛性が高くなると、振動は側壁部１０に伝わりにくくなりケース７は振動しにくくなる。このため超音波振動子４６の残響を抑えることができる。ここで薄い金属板から作られたケース７の剛性を高めるためには、外周部４９に凸部あるいは凹部を設ければよく、外周部４９に凸部あるいは凸部を成型加工することは容易である。本実施例では外周部４９に４ケ所凸部４７ａ〜４７ｄを設けることによりケース７の剛性を高められ超音波振動子３９の残響を低減することができる。
【００４８】
なお実施例４では外周部４９に凸部４７を４ケ所設けるとしたが、１ケ所以上ならいくつでも構わないし、図１３に示したように凸部５０を円環状に設けても良い。また外周部４９に凸部を設けるとしたが、図１４に示すように複数の凹部５１あるいは円環状の凹部５１を設けても良い。また音響整合層９と凸部４７の間に空隙部４８を設けるとしたが、音響整合層９の接着強度を増加させるために空隙部４８にエポキシ系接着剤を充填しても構わないし、音響整合層９の振動の減衰をはやめるためシリコンゴムなどの弾性体を充填しても構わない。
【００４９】
（実施例５）
以下、本発明の実施例５について、図面を参照しながら説明する。
【００５０】
図１５は超音波振動子５２の断面図である。７はケース、８は天部、９は音響整合層、１０は側壁部、１２は支持部、１３は圧電体、１４は端子板、１５ａ、１５ｂは端子、１６は端子１５ａと端子１５ｂを絶縁するための絶縁部、１７は圧電体１３と端子１５ａを電気的に接続するためのリード線で、以上は図１の構成と同様なものである。図１の構成とことなるのは、天部８の外周部５３に肉薄部５４を設けた点である。
【００５１】
以上のように構成さた超音波振動子５２の作成方法の一例について図１５を用いて説明する。超音波振動子５２はＬＰガスや天然ガス中で使用することを想定して、ケース７にはステンレス、音響整合層９にはエポキシ樹脂と中空ガラス球の混合体からなる材料を選択する。また量産性を考えケース７の加工方法には、切削加工でなく絞り加工のような成型加工を選択する。
【００５２】
まず厚み０．３ｍｍのステンレス板から直径１４ｍｍ程度の円板状の天部８を有す有天円筒状のケース７を成型加工する。このとき天部８の内壁面と外壁面の外周部５３には、天部８と同心円状で厚みが０．１ｍｍ程度となる肉薄部５４を１本構成する。次に天部８の外壁面で肉薄部５４の内側に直径１２．５ｍｍの円板状の音響整合層９をエポキシ系接着剤を用いて接着固定する。天部８の内壁面には圧電体１３をエポキシ系接着剤で接着固定する。これ以後の超音波振動子４６の作製方法、超音波流量計の作製方法、動作原理は実施例１と同様になるため省略する。
【００５３】
ケース７の振動を抑えるためには、ケース７の剛性を高める以外に天部８を振動しやすくする方法がある。天部８と側壁部１０の振動的つながりを弱めることにより可能となる。そこで肉薄部５４により、天部８の肉薄部５４の内側は振動しやすく、その外側には振動が伝わりにくくする。このためケース７は振動しにくくなり、超音波振動子５２の残響を抑えられる。
【００５４】
なお実施例５では外周部５４の内壁面と外壁面に肉薄部５４を設けるとしたが、内壁面だけでも外壁面だけでも良い。また同心円状の肉薄部５４を１本設けるとしたが、２本以上でも構わないし、円環状に連続していなくても良い。
【００５５】
（実施例６）
以下、本発明の実施例６について、図面を参照しながら説明する。
【００５６】
図１６は超音波振動子５５の断面図、図１７は超音波流量計の流量測定部２３の超音波振動子取付部分の断面図である。７はケース、８は天部、９は音響整合層、１０は側壁部、１１は折り曲げ部、１２は支持部、１３は圧電体、１５ａ、１５ｂは端子、１６は端子１５ａと端子１５ｂを絶縁するための絶縁部、１７は圧電体１３と端子１５ａを電気的に接続するためのリード線で、以上は図１の構成と同様なものである。図１の構成と異なるのは、端子板５６の直径が支持部１２より大きいことと、端子板５６の外周にシール部５７をを設けた点である。以上のように構成さた超音波振動子５５の作成方法、超音波流量計の作製方法、動作原理は実施例１と同様になるため省略する。
【００５７】
超音波振動子５５を流量測定部２３に取り付ける方法を説明する。側壁部２４に設けられた振動子取付穴２９に超音波振動子５５を挿入する。超音波振動子５５の端子板５６は厚みが１ｍｍ、直径が２０ｍｍとする。端子板５６は支持部１２の直径１６ｍｍに対し４ｍｍ大きく構成されており、この部分にシール部５７を設けてある。シール部５７と側壁部２４に設けられた流路シール面５８の間にＯリングからなるシール材５７を挟む。次にドーナツ型の固定体と図示されていないネジにより端子板５６を背面から加圧しながら固定する。
【００５８】
超音波振動子５５では支持部１２と端子板５６を電気溶接した際、支持部１２の表面に凹凸ができることがある。支持部１２の表面に凹凸ができると、シール材５９を用いても振動子取付穴２９からガスが漏れることを防げないことも考えられる。本実施例では支持部１２より外形寸法の大きい端子板５６を用いることにより、端子板５６の外周に電気溶接の影響を受けない表面が滑らかなシール部５７を持つことが可能となる。このため超音波流量計のガス漏れに対する安全性が向上できる。
【００５９】
なお実施例６では、端子板５６とシール部５９の厚みは同一としたが、端子板５６とシール部５９の厚みを等しくする必要はなく、例えば端子板５６の厚みよりシール部５９の厚みを厚くしても良い。また端子板５６は円板状としたが、シール部５９を折り曲げて構成しても良い。また端子板５６の直径を支持部１２より大きいとしたが、支持部１２の直径を端子板５６より大きくし、支持部１２にシール部を設けても良い。
【００６０】
なお、実施例１〜６では、圧電体１３を圧電セラミック、周波数を４００ＫＨｚ、形状を縦８ｍｍ、横８ｍｍ、厚み４ｍｍの直方体、溝を２本設けるとしたが、上記条件に限定されるわけでなく、材料、周波数、形状、寸法、溝の本数を適宜変えて構成することができ、例えば薄い円板の厚み振動、円柱や角柱の厚み縦振動でも構わない。また流量測定部２３の材料をアルミニウム合金ダイカストとしたが、上記条件に限定されるわけでなく、被測定流体により材料を適宜変えて構成することができる。また流路断面３７を矩形、超音波振動子２７、２８、５５を流路２６に対し斜めに配置したが、上記条件に限定されるわけでなく、流路形状、超音波振動子の配置を適宜変えて構成することができ、流路形状は円筒形でも構わないし、超音波振動子を流れに対して平行に配置しても構わない。またシール材３１、３２、５９をＯリングとしたが、上記条件に限定されるわけでなく、可燃性被測定流体をシールできるのであれば材料、形状を適宜変えて構成することができる。
【００６１】
また被測定流体をＬＰガス、天然ガスとしたが、それ以外の液化天然ガス、石油、灯油等の気体、液体でも構わない。また超音波流量計として家庭用ガスメータを想定したが、それ以外の超音波流量計あるいは超音波流速計でも構わず、給湯器のガスの流量制御用流速計、自動車の空気や燃料の流量計でも構わない。またケース７、端子板１４、５６をステンレスとしたが、上記条件に限定されるわけでなく、材料は適宜変えて構成することができる。また支持部１２を側壁部の端面に設けたが、それ以外の場所に設けても良い。また整合層９、４４はエポキシ樹脂と微小ガラス球からなるの材料を１層のみ用いたが、被測定流体に適した形状の材料を１層以上、あるいは被測定流体によっては設ける必要がない場合もある。また複数の実施例の構成を組み合わせて実施しても良い。また超音波振動子を超音波流量計に用いるとしてが、距離センサ等の超音波センサとして用いても良い。またケース７と端子板１４で囲まれた空間を乾燥した窒素や不活性ガスで置換するとしたが、真空にしても良いし、空気でも良い。
【００６２】
以上の説明から明らかなように本発明の実施形態の超音波振動子及びこれを用いた流量計によれば次の効果が得られる。
【００６３】
本発明の実施形態における第１の超音波振動子は、天部と側壁部を有す有天筒状のケースと、前記天部の内壁面に固定された圧電体と、前記天部の外壁面に設けられた音響整合層と、前記側壁部の外壁に設けた支持部とを備え、前記ケースが防振構造を有し圧電体の振動が前記ケースへ伝搬することを防止したため、残響の短い超音波パルスの送受信が可能となり、残響によるノイズの影響を低減した高Ｓ／Ｎの計測ができる超音波振動子を得られる。
【００６４】
本発明の実施形態における第２の超音波振動子は、側壁部の剛性が増大する形状としたため、圧電体の振動が側壁部へ伝搬することが防止され、残響の短い超音波パルスの送受信が可能となり、残響によるノイズの影響を低減した高Ｓ／Ｎの計測ができる超音波振動子を得られる。
【００６５】
本発明の実施形態における第３の超音波振動子は、側壁部に天部と同心状の折り曲げ部を設けたため、側壁部の剛性が増大し圧電体の振動が側壁部へ伝搬することが防止され、残響の短い超音波パルスの送受信が可能となり、残響によるノイズの影響を低減した高Ｓ／Ｎの計測ができる超音波振動子を得られる。
【００６６】
本発明の実施形態における第４の超音波振動子は、側壁部の軸方向に複数の凸部または凹部を備えたため、側壁部の剛性が増大し圧電体の振動が側壁部へ伝搬することが防止され、残響の短い超音波パルスの送受信が可能となり、残響によるノイズの影響を低減した高Ｓ／Ｎの計測ができる超音波振動子を得られる。
【００６７】
本発明の実施形態における第５の超音波振動子は、側壁部を多角形の筒状としたため、側壁部の剛性が増大し圧電体の振動が側壁部へ伝搬することを防止したため、残響の短い超音波パルスの送受信が可能となり、残響によるノイズの影響を低減した高Ｓ／Ｎの計測ができる超音波振動子を得られる。
【００６８】
本発明の実施形態における第６の超音波振動子は、天部の外周部に凸部または凹部を備えたため、天部の外周部の剛性が増大し圧電体の振動が側壁部へ伝搬することを防止したため、残響の短い超音波パルスの送受信が可能となり、残響によるノイズの影響を低減した高Ｓ／Ｎの計測ができる超音波振動子を得られる。
【００６９】
本発明の実施形態における第７の超音波振動子は、天部の外周部に薄肉部を備えたため、天部のうち圧電体を固定した部分が振動しやすくなり圧電体の振動が側壁部へ伝搬することが防止したため、残響の短い超音波パルスの送受信が可能となり、残響によるノイズの影響を低減した高Ｓ／Ｎの計測ができる超音波振動子を得られる。
【００７０】
本発明の実施形態における超音波流量計は、被測定流体が流れる流量測定部と、この流量測定部に設けられ超音波を送受信する第１ないし第７のいずれかの１対の超音波振動子と、前記超音波振動子間の伝搬時間を計測する計測回路と、前記計測回路からの信号に基づいて流量を算出する流量演算手段とを備えたため、残響によるノイズの影響を低減できＳ／Ｎが改善され、被測定流体の流量、流速の計測精度が高い超音波流量計を得ることができる。
本発明の実施形態における超音波流量計は、支持部に固定される端子板にシール部を有す超音波振動子を備えたため、被測定流体が流量測定部から外部に漏れることが防止でき、信頼性の高い超音波流量計を得ることができる。
【００７１】
【発明の効果】
以上の説明から明らかなように本発明の超音波振動子及びこれを用いた流量計によれば、ケースが防振構造を有し圧電体の振動が側壁部へ伝搬することを防止したため、残響の短い超音波パルスの送受信が可能となり、残響によるノイズの影響を低減した高Ｓ／Ｎの計測ができる超音波振動子を得られる。
【図面の簡単な説明】
【図１】本発明の実施例１の超音波振動子の外観図
【図２】同超音波振動子の断面図
【図３】同超音波振動子に用いる圧電体の外観図
【図４】同超音波振動子に用いる超音波流量計の一部断面図を含む構成図
【図５】同流量計の断面ａーａ’線の横断面図
【図６】同超音波振動子の変形例の断面図
【図７】本発明の実施例２における超音波振動子の上面図
【図８】同超音波振動子の側面図
【図９】同超音波振動子の変形例の外観図
【図１０】本発明の実施例３における超音波振動子の外観図
【図１１】本発明の実施例４における超音波振動子の断面図
【図１２】同超音波振動子の上面図
【図１３】同超音波振動子の変形例の上面図
【図１４】同超音波振動子の変形例の断面図
【図１５】本発明の実施例５における超音波振動子の断面図
【図１６】本発明の実施例６における超音波振動子の断面図
【図１７】超音波流量計の流量測定部の超音波振動子取付部分の断面図
【図１８】従来の超音波流量計用超音波振動子の断面図
【図１９】従来の他の超音波流量計用超音波振動子の断面図
【符号の説明】
６超音波振動子
７ケース
８天部
９音響整合層
１０側壁部
１１折り曲げ部
１２支持部
１３圧電体
２７，２８超音波振動子
２３流量測定部
３３計測回路
３４流量演算手段
４０，４７凸部
４１，５１凹部
５４肉薄部
５７シール部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic flowmeter that measures the flow and flow velocity of a gas or liquid using ultrasonic waves.
[0002]
[Prior art]
FIGS. 18 and 19 show an ultrasonic transducer conventionally used for this type of ultrasonic flowmeter. For example, Japanese Patent Application Laid-Open No. 4-309817 is known, in which a piezoelectric ceramic 1 is brazed to a metal vibration plate 2 and this metal vibration plate 2 is welded to a metal housing 3 as shown in FIG. Japanese Patent Publication No. 6-500389 is also known, in which a pot-shaped matching layer 5 made of epoxy resin and fine glass spheres is commonly used as a case containing the piezoelectric ceramic 4.
[0003]
[Problems to be solved by the invention]
However, in the above-described conventional configuration, since the metal housing is not provided with an anti-vibration measure, the vibration of the piezoelectric ceramic is transmitted to the metal housing through the metal diaphragm. Since the vibration is hardly attenuated in the metal case, the vibration of the metal housing returns to the piezoelectric ceramic again. Therefore, the vibration of the piezoelectric ceramic is not easily suppressed, and the ultrasonic pulse has a long reverberation. Since this reverberation is one of the noise factors, there is a problem that the S / N is deteriorated and the measurement accuracy of the flow rate and the flow velocity is reduced. When a material made of epoxy resin and fine glass spheres is used as the case, the case is less likely to vibrate and the reverberation is reduced. However, since such a material generally has microporosity, the fluid to be measured infiltrates into the case, and depending on the components of the fluid to be measured, there is a problem that the electrodes of the piezoelectric body are corroded and the characteristics are deteriorated. Was.
[0004]
The present invention solves the above-mentioned problems, and it is possible to transmit and receive an ultrasonic pulse having a short reverberation, realize a highly reliable ultrasonic transducer, and improve the measurement accuracy of an ultrasonic flowmeter. I do.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a cylindrical case having a ceiling portion and a side wall portion, a piezoelectric body fixed to an inner wall surface of the ceiling portion, and an outer wall surface of the ceiling portion. And a support portion provided on the outer wall of the side wall portion, and a bent portion concentric with the top portion on the side wall portion so as to prevent the vibration of the piezoelectric body from propagating to the side wall portion. The ultrasonic vibrator provided with.
A cylindrical case having a top portion and a side wall portion; a piezoelectric body fixed to an inner wall surface of the top portion; an acoustic matching layer provided on an outer wall surface of the top portion; And a support portion provided on an outer wall of the ultrasonic transducer, wherein a plurality of convex portions or concave portions are provided in an axial direction of the side wall portion so as to prevent the vibration of the piezoelectric body from propagating to the side wall portion. .
A cylindrical case having a top portion and a side wall portion; a piezoelectric body fixed to an inner wall surface of the top portion; an acoustic matching layer provided on an outer wall surface of the top portion; An ultrasonic vibrator having a side wall portion having a polygonal cylindrical shape so as to prevent the vibration of the piezoelectric body from propagating to the side wall portion.It is.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
In one embodiment of the present invention, the piezoelectric body constituting the ultrasonic vibrator is enclosed in a metal case that blocks from the fluid to be measured, and the metal case is provided with a bent portion to increase rigidity and increase the propagation of vibration. It has been reduced.According to the above embodiment, it is possible to make it difficult for the vibration of the piezoelectric body to be transmitted to the metal case, and it is possible to obtain an ultrasonic transducer capable of transmitting and receiving an ultrasonic pulse having a short reverberation. As a result, generation of noise due to reverberation can be reduced, S / N is improved, and measurement accuracy of the flow rate and flow velocity of the fluid to be measured can be improved. Further, since the fluid to be measured can be prevented from contacting the piezoelectric body, the reliability of the ultrasonic vibrator can be improved.
[0007]
The present inventionofThe ultrasonic vibrator of the first mode is provided on a cylindrical case having a top portion and a side wall portion, a piezoelectric body fixed to an inner wall surface of the top portion, and an outer wall surface of the top portion. An acoustic matching layer, and a supporting portion provided on an outer wall of the side wall portion, wherein the case has an anti-vibration structure to prevent vibration of the piezoelectric body from propagating to the case, and has a short reverberation. An ultrasonic transducer capable of transmitting and receiving a sound pulse can be obtained.
[0008]
According to the second aspect of the present invention, the ultrasonic vibrator of the first embodiment has a shape in which the rigidity of the side wall is increased in the ultrasonic vibrator of the first embodiment, so that the vibration of the piezoelectric body is prevented from propagating to the side wall. Thus, it is possible to obtain an ultrasonic transducer capable of transmitting and receiving an ultrasonic pulse having a short reverberation.
[0009]
The ultrasonic transducer according to the third aspect of the present invention is the ultrasonic transducer according to the second aspect, in which the side wall is provided with a bent portion concentric with the ceiling, so that the rigidity of the side wall is increased, and Vibration is prevented from propagating to the side wall, and an ultrasonic transducer capable of transmitting and receiving an ultrasonic pulse having a short reverberation can be obtained.
[0010]
According to a fourth aspect of the present invention, there is provided an ultrasonic vibrator according to the second aspect, wherein the ultrasonic vibrator according to the second mode includes a plurality of convex portions or concave portions in the axial direction of the side wall portion, so that the rigidity of the side wall portion increases and Is prevented from propagating to the side wall, and an ultrasonic transducer capable of transmitting and receiving an ultrasonic pulse having a short reverberation can be obtained.
[0011]
The ultrasonic transducer according to the fifth aspect of the present invention is the ultrasonic transducer according to the second aspect, wherein the side walls are formed in a polygonal cylindrical shape, so that the rigidity of the side walls is increased and the vibration of the piezoelectric body is reduced. Therefore, it is possible to obtain an ultrasonic vibrator which is prevented from propagating to the ultrasonic wave and capable of transmitting and receiving an ultrasonic pulse having a short reverberation.
[0012]
According to a sixth aspect of the present invention, there is provided an ultrasonic vibrator according to the first aspect, wherein the ultrasonic vibrator according to the first aspect includes a convex portion or a concave portion on the outer peripheral portion of the top portion, so that the rigidity of the outer peripheral portion of the top portion increases, and It is possible to prevent the vibration of the body from being propagated to the side wall, and to obtain an ultrasonic transducer capable of transmitting and receiving an ultrasonic pulse having a short reverberation.
[0013]
The ultrasonic transducer according to the seventh aspect of the present invention is the ultrasonic transducer according to the first aspect, in which the thin portion is provided on the outer peripheral portion of the top portion, so that the portion of the top portion to which the piezoelectric body is fixed vibrates. As a result, the vibration of the piezoelectric body is prevented from propagating to the side wall, and an ultrasonic vibrator capable of transmitting and receiving ultrasonic pulses having short reverberation can be obtained.
[0014]
According to an eighth aspect of the present invention, there is provided an ultrasonic flowmeter according to the eighth aspect, comprising: a flow rate measuring unit through which a fluid to be measured flows; Ultrasonic vibrator, a measuring circuit for measuring the propagation time between the ultrasonic vibrators, and a flow rate calculating means for calculating a flow rate based on a signal from the measuring circuit, thereby reducing the influence of noise due to reverberation. Therefore, the S / N can be improved, and an ultrasonic flowmeter having high measurement accuracy of the flow rate and the flow velocity of the fluid to be measured can be obtained.
[0015]
The ultrasonic flowmeter according to the ninth aspect of the present invention is the ultrasonic flowmeter according to the eighth aspect, wherein an ultrasonic vibrator having a seal portion is provided on a terminal plate fixed to the support portion. Can be prevented from leaking to the outside from the flow measurement unit, and a highly reliable ultrasonic flow meter can be obtained.
[0016]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, components denoted by the same reference numerals are the same components, and a detailed description thereof will be omitted.
[0017]
(Example 1)
FIG. 1 is an external view of an ultrasonic transducer according to a first embodiment of the present invention. FIG. 2 is a sectional view of the ultrasonic transducer shown in FIG. FIG. 3 is an external view of a piezoelectric body used in the ultrasonic transducer of FIG. In FIG. 1, reference numeral 6 denotes an ultrasonic transducer, 7 denotes a case, 8 denotes a top portion of the

case

7, 9 denotes an acoustic matching layer fixed to an outer wall surface of the

top portion

8, 10 denotes a side wall portion of the case 7, and 11 denotes a side wall. A bent portion 12 fixed to the portion 10 is a support portion for fixing the case 7. In FIG. 2, reference numeral 13 denotes a piezoelectric body disposed on the inner wall surface of the top portion 8, 14 denotes a terminal plate fixed to the support portion 12, 15a and 15b denote terminals provided on the terminal plate 14, and 16 denotes a terminal 15a and a terminal. An insulating portion for insulating 15b and a lead wire 17 for electrically connecting the piezoelectric body 13 and the terminal 15a are provided. In FIG. 3, reference numeral 18 denotes an electrode of the piezoelectric body 13 and 19 denotes a groove provided in the piezoelectric body 13.
[0018]
An example of a method for producing the ultrasonic transducer configured as described above will be described with reference to FIGS. 1, 2, and 3. FIG. Assuming that the ultrasonic vibrator 6 is used in LP gas or natural gas, a material made of stainless steel for the case 7 and a mixture of epoxy resin and hollow glass spheres for the acoustic matching layer 9 is selected. In consideration of mass productivity, the forming method of the case 7 is not a cutting but a forming such as drawing. The thickness of the stainless steel should be about 0.1 to 0.5 mm and about one-tenth or less of the wavelength because of the influence on the ease of molding the case 7, the structural strength, and the sensitivity of the ultrasonic vibrator 6. select. Next, since the piezoelectric body 13 is bonded and fixed to the ceiling portion 8 made of stainless steel, vibration in the spreading direction is inhibited. In order to increase the sensitivity of the ultrasonic vibrator 6, it is more advantageous to use the thickness longitudinal vibration in the main mode rather than the spread vibration. However, the main mode of vibration of the piezoelectric body 13 is determined by the shape thereof, and the allowable range for the shape and use frequency of the piezoelectric body 13 is narrow. Therefore, a structure in which two grooves 19 are provided in the rectangular parallelepiped piezoelectric body 13 as shown in FIG. 3 was selected. The provision of the groove 19 enables the thickness mode of the piezoelectric body 13 having a width of 20 mm, a height of 8 mm and a thickness 22 of 4 mm to be the main mode at about 400 KHz. However, the number, depth, and direction of the grooves 19 are determined based on the shape of the piezoelectric body 13, the influence of the unnecessary mode, and the ease of handling.
[0019]
First, a cylindrical case 7 having a disk-shaped top portion 8 having a diameter of about 13 mm is formed from a stainless steel plate having a thickness of 0.2 mm. At this time, one bent portion 11 concentric with the top portion 8 is formed on the side wall portion 10 at the same time. Next, a disc-shaped acoustic matching layer 9 having a diameter of 12.5 mm is fixed to the outer wall surface of the top portion 8 and the piezoelectric body 13 is fixed to the inner wall surface by using an epoxy-based adhesive. At this time, by bonding and fixing the electrode 18 and the top portion 8 divided by the groove 19 via a thin adhesive layer of 10 μm or less, electrical conduction between the divided electrode 18 and the top portion 8 can also be obtained. The lead wire 17 is soldered to the electrode of the piezoelectric body 13 not shown and the terminal a, respectively. Finally, a terminal plate 14 made of a stainless steel plate having a diameter of about 16 mm and a thickness of about 0.8 mm is fixed to the support portion 12 by electric welding, and sealing and electrical conduction are simultaneously performed. The piezoelectric body 13 uses the case 7 as a ground and is covered with the case 7 and the terminal plate 14, so that the effect of noise can be reduced. Further, when the inside of the case 7 is replaced with dry nitrogen or an inert gas, the deterioration of the electrodes of the piezoelectric body 13 and the adhesive layer between the piezoelectric body 13 and the case 7 due to long-term use can be prevented.
[0020]
A method of manufacturing an ultrasonic flowmeter using the ultrasonic vibrator prepared as described above will be described with reference to FIGS. The material constituting the flow rate measuring unit 23 was an aluminum alloy die cast assuming a household gas meter for measuring the flow rate of LP gas or natural gas. The upper plate portion 36 is screwed onto the end surfaces of the

side wall portions

24 and 25 via a sealing material 35 made of, for example, cork material, so that the flow path measuring section 23 having a rectangular channel cross section 37 is formed. The

ultrasonic vibrators

27 and 28 are fixed to

vibrator mounting holes

29 and 30 provided obliquely on the

side walls

24 and 25 so that the transmitting and receiving surfaces face each other via sealing

materials

31 and 32 made of, for example, O-rings.
[0021]
The operation of the ultrasonic flowmeter using the flow measurement unit 23 configured as described above will be described. Let L be the distance connecting the centers of the

ultrasonic transducers

27 and 28, and let θ be the angle between this straight line and the longitudinal direction of the flow path 26, which is the direction of flow. The sound speed of the LP gas in a windless state is C, and the flow velocity of the LP gas in the flow path 26 is V. The ultrasonic waves transmitted from the ultrasonic transducer 27 arranged on the upstream side of the flow measuring unit 23 obliquely cross the flow path 26 and are received by the ultrasonic transducer 28 arranged on the downstream side.
[0022]
The propagation time t1 at this time is
[0023]
(Equation 1)

[0024]
Indicated by Next, the ultrasonic transducer to be transmitted / received is switched, an ultrasonic wave is transmitted from the ultrasonic transducer 28, and the ultrasonic transducer 27 receives the ultrasonic wave. The propagation time t2 at this time is
[0025]
(Equation 2)

[0026]
Indicated by Eliminating the sound velocity C of LP gas from the equations of t1 and t2,
[0027]
(Equation 3)

[0028]
Is obtained. If L and θ are known, the flow velocity V can be obtained by measuring t1 and t2 in the measurement circuit 33. From the flow velocity V, the flow rate Q can be calculated by the flow rate calculation circuit 34 if the area of the cross section 37 is S and the correction coefficient is K.
Q = KSV
To calculate the flow rate.
[0029]
It is important for the ultrasonic flowmeter to measure the times t1 and t2 with high accuracy for high-accuracy flow measurement. Therefore, the influence of the vibration of the case 7 on the measurement will be considered. On the transmitting side, the vibration of the piezoelectric body 13 generated by the drive signal is not only emitted as an ultrasonic pulse to the LP gas through the acoustic matching layer 9 but also causes the case 7 to vibrate. On the receiving side, the case 7 is vibrated at the same time as the received ultrasonic pulse is converted into an electric signal by the piezoelectric body 13. Here, if the case 7 vibrates, the vibration can hardly be attenuated in the case 7, so that a long reverberation of the piezoelectric body 13 is observed on both the transmitting side and the receiving side. The reverberation on the transmission side becomes electrical noise to the measurement circuit 33, which degrades the S / N of the received ultrasonic pulse and causes a reduction in measurement accuracy. Also, the reverberation on the receiving side is combined with the received ultrasonic pulse, so that it affects the amplitude and phase and causes an error in the measurement of the times t1 and t2. In the present embodiment, since the rigidity of the side wall 10 is increased by the bent portion 11 of the case 7, the side wall 10 is less likely to vibrate. Therefore, the vibration of the case 7 can be suppressed, and the reverberation of the ultrasonic vibrator 6 can be reduced. Therefore, the measurement accuracy of the ultrasonic flowmeter can be improved.
[0030]
As described above, according to this embodiment, the thickness longitudinal vibration can be used as the main mode by providing two grooves in the rectangular parallelepiped piezoelectric body 13. Further, by bonding and fixing the piezoelectric body 13 and the top portion 8 with an epoxy-based adhesive having a thickness of 10 μm or less, conduction can be achieved simultaneously with the adhesive strength. In addition, by bonding and fixing the electrode 18 divided by the groove 19 of the piezoelectric body 13 to the top portion 8, the connection of the divided electrode 18 becomes easy, and the divided piezoelectric body 13 bends in the horizontal direction. Vibration can be prevented. Since the piezoelectric body 13 is shielded by the stainless steel case 7 and the terminal plate 14, the influence of external noise can be reduced.
[0031]
In the first embodiment, one bent portion 11 is provided. However, two or more bent portions may be provided, and a structure in which a beat 38 is provided on the side wall portion 10 as shown in FIG. Further, although the top portion 8 has a disk shape, it may have an elliptical diameter.
[0032]
(Example 2)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.
[0033]
7 is a top view of the ultrasonic vibrator 39, and FIG. 8 is a side view of the ultrasonic vibrator 39. 8 is a top part, 9 is an acoustic matching layer, 10 is a side wall part, 12 is a support part, 14 is a terminal plate, 15 is a terminal, and the above is the same as the structure of FIG. 1 and 2 is that the side wall portion 10 is provided with eight convex portions in the axial direction.
[0034]
An example of a method for producing the ultrasonic transducer configured as described above will be described with reference to FIGS. Assuming that the ultrasonic vibrator 39 is used in LP gas or natural gas, a material made of stainless steel for the case 7 and a mixture of epoxy resin and hollow glass spheres for the acoustic matching layer 9 is selected. In consideration of mass productivity, the forming method of the case 7 is not a cutting but a forming such as drawing.
[0035]
First, a cylindrical case 7 having a disk-shaped top portion 8 having a diameter of about 13 mm is formed from a stainless steel plate having a thickness of 0.2 mm. At this time, eight convex portions 40 are formed in the side wall portion 10 in the axial direction, and when viewed from above, the side wall portion 10 looks like a petal. Next, a disc-shaped acoustic matching layer 9 having a diameter of 12.5 mm is bonded and fixed to the outer wall surface of the top section 8 using an epoxy-based adhesive. The method of manufacturing the ultrasonic vibrator 39, the method of manufacturing the ultrasonic flowmeter, and the operation principle thereafter are the same as those in the first embodiment, and thus description thereof is omitted.
[0036]
The case 7 is more difficult to vibrate as the rigidity of the side wall portion 10 is higher, so that reverberation can be suppressed. In order to increase the rigidity of the case 7 made of a thin metal plate, a convex portion or a concave portion may be provided, and the molding process can be facilitated. In this embodiment, by providing eight convex portions 40 in the axial direction of the side wall portion 10, rigidity can be increased and reverberation of the ultrasonic transducer 39 can be reduced.
[0037]
In the second embodiment, eight convex portions 40 are provided on the side wall portion 10. However, any number of one or more convex portions may be used. Further, as shown in FIG. 9, a concave portion 41 may be provided in the side wall portion 10 to form a crown, or a convex portion and a concave portion may be combined.
[0038]
(Example 3)
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.
[0039]
FIG. 10 is an external view of the ultrasonic transducer 42. Reference numeral 7 denotes a case, 10 denotes a side wall portion, and 12 denotes a support portion. The above is the same as the configuration in FIG. The difference from the configuration of FIG. 1 is that the top 43 is rectangular, the acoustic matching layer 44 is a rectangular parallelepiped, and the bent portion 45 is provided in the axial direction of the side wall 10.
[0040]
An example of a method for producing the ultrasonic transducer configured as described above will be described with reference to FIG. Assuming that the ultrasonic vibrator 42 is used in LP gas or natural gas, the case 7 is made of stainless steel, and the acoustic matching layer 44 is made of a material made of a mixture of epoxy resin and hollow glass spheres. In consideration of mass productivity, the forming method of the case 7 is not a cutting but a forming such as drawing.
[0041]
First, a case 7 in the shape of a square with a square head having a square top 43 with a side of 9 mm is formed from a stainless steel plate having a thickness of 0.2 mm. At this time, the bent portion 45 is formed on the side wall portion 10 so that the side wall portion 10 becomes substantially a square pillar. Next, a rectangular parallelepiped acoustic matching layer 44 having a square surface of 8 mm on a side is bonded and fixed to the top portion 43 using an epoxy-based adhesive. The method of manufacturing the ultrasonic transducer 42, the method of manufacturing the ultrasonic flowmeter, and the operation principle thereafter are the same as those in the first embodiment, and thus description thereof is omitted.
[0042]
The case 7 is more difficult to vibrate as the rigidity of the side wall portion 10 is higher, so that reverberation can be suppressed. Here, in order to increase the rigidity of the case 7 made of a thin metal plate, the side wall may be formed in a polygonal column shape, and it is easy to mold the side wall 10 into a polygon. In the present embodiment, by forming the side wall portion 10 as a square pole, rigidity can be increased and reverberation of the ultrasonic transducer 42 can be reduced.
[0043]
In the third embodiment, the top portion 43 is a square, and the side wall portion 10 is a quadratic prism, but may be a polygon other than a quadrangle. Further, although the support portion 12 has a disk shape, the support portion 12 may have a square shape similarly to the top plate 8, or may have another polygonal shape.
[0044]
(Example 4)
Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings.
[0045]
FIG. 11 is a sectional view of the ultrasonic vibrator 46, and FIG. 12 is a top view of the ultrasonic vibrator 46. 7 is a case, 8 is a top, 9 is an acoustic matching layer, 10 is a side wall, 12 is a support, 13 is a piezoelectric body, 14 is a terminal plate, 15a and 15b are terminals, and 16 is a terminal 15a and a terminal 15b are insulated. Insulating portion 17 is a lead wire for electrically connecting the piezoelectric body 13 and the terminal 15a, and has the same configuration as that of FIG. The configuration shown in FIG. 1 is different from the configuration in that convex portions 47 a to 47 d are provided at four positions on an outer peripheral portion 49 of the top portion 8, and a gap portion 48 is provided between the convex portion 47 and the acoustic matching layer 9.
[0046]
An example of a method for producing the ultrasonic transducer 46 configured as described above will be described with reference to FIGS. Assuming that the ultrasonic vibrator 46 is used in LP gas or natural gas, a material made of stainless steel for the case 7 and a mixture of epoxy resin and hollow glass spheres for the acoustic matching layer 9 is selected. In consideration of mass productivity, the forming method of the case 7 is not a cutting but a forming such as drawing. First, a cylindrical case 7 having a disk-shaped top portion 8 having a diameter of about 15 mm is formed from a stainless steel plate having a thickness of 0.2 mm. At this time, on the outer peripheral portion 49 of the top portion 8, convex portions 47a to 47d whose height is smaller than the thickness of the acoustic matching layer 9 and are approximately 0.8 mm are formed concentrically. Next, a disc-shaped acoustic matching layer 9 having a diameter of 12.5 mm is bonded and fixed on the outer wall surface of the top portion 8 inside the convex portions 47a to 47d using an epoxy-based adhesive. At this time, a gap 48 is formed between the acoustic matching layer 9 and the protrusions 47a to 47d. The method of manufacturing the ultrasonic transducer 46, the method of manufacturing the ultrasonic flow meter, and the operation principle thereafter are the same as those in the first embodiment, and thus description thereof is omitted.
[0047]
When the rigidity of the outer peripheral portion 49 of the top portion 8 is increased, the vibration is less likely to be transmitted to the side wall portion 10, and the case 7 is less likely to vibrate. Therefore, reverberation of the ultrasonic transducer 46 can be suppressed. Here, in order to increase the rigidity of the case 7 made of a thin metal plate, a convex portion or a concave portion may be provided on the outer peripheral portion 49, and it is easy to mold the convex portion or the convex portion on the outer peripheral portion 49. is there. In this embodiment, by providing four convex portions 47a to 47d on the outer peripheral portion 49, the rigidity of the case 7 can be increased and the reverberation of the ultrasonic transducer 39 can be reduced.
[0048]
In the fourth embodiment, four convex portions 47 are provided on the outer peripheral portion 49. However, any number of one or more convex portions may be provided, and the convex portions 50 may be provided in an annular shape as shown in FIG. Further, although the convex portion is provided on the outer peripheral portion 49, a plurality of concave portions 51 or an annular concave portion 51 may be provided as shown in FIG. Although the gap 48 is provided between the acoustic matching layer 9 and the projection 47, the gap 48 may be filled with an epoxy-based adhesive in order to increase the adhesive strength of the acoustic matching layer 9; An elastic body such as silicon rubber may be filled to stop the attenuation of the vibration of the matching layer 9.
[0049]
(Example 5)
Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings.
[0050]
FIG. 15 is a cross-sectional view of the ultrasonic transducer 52. 7 is a case, 8 is a top, 9 is an acoustic matching layer, 10 is a side wall, 12 is a support, 13 is a piezoelectric body, 14 is a terminal plate, 15a and 15b are terminals, and 16 is a terminal 15a and a terminal 15b are insulated. Insulating portion 17 is a lead wire for electrically connecting the piezoelectric body 13 and the terminal 15a, and has the same configuration as that of FIG. 1 in that a thin portion 54 is provided on the outer peripheral portion 53 of the top portion 8.
[0051]
An example of a method for producing the ultrasonic transducer 52 configured as described above will be described with reference to FIG. Assuming that the ultrasonic vibrator 52 is used in LP gas or natural gas, stainless steel is used for the case 7 and a material made of a mixture of epoxy resin and hollow glass spheres is selected for the acoustic matching layer 9. In consideration of mass productivity, the forming method of the case 7 is not a cutting but a forming such as drawing.
[0052]
First, a cylindrical case 7 having a disk-shaped top portion 8 having a diameter of about 14 mm is formed from a stainless steel plate having a thickness of 0.3 mm. At this time, a single thin portion 54 having a thickness of about 0.1 mm, which is concentric with the top portion 8, is formed on the outer peripheral portion 53 of the inner wall surface and the outer wall surface of the top portion 8. Next, a disk-shaped acoustic matching layer 9 having a diameter of 12.5 mm is bonded and fixed to the outer wall surface of the top portion 8 inside the thin portion 54 using an epoxy-based adhesive. The piezoelectric body 13 is bonded and fixed to the inner wall surface of the top section 8 with an epoxy adhesive. The method of manufacturing the ultrasonic transducer 46, the method of manufacturing the ultrasonic flowmeter, and the operation principle thereafter are the same as those in the first embodiment, and thus description thereof is omitted.
[0053]
In order to suppress the vibration of the case 7, there is a method of easily vibrating the ceiling portion 8 in addition to increasing the rigidity of the case 7. This is made possible by weakening the vibrational connection between the top section 8 and the side wall section 10. Therefore, the thin portion 54 makes it easy for the inside of the thin portion 54 of the top portion 8 to vibrate, and makes it difficult for the vibration to be transmitted to the outside. For this reason, the case 7 does not easily vibrate, and the reverberation of the ultrasonic transducer 52 can be suppressed.
[0054]
In the fifth embodiment, the thin portion 54 is provided on the inner wall surface and the outer wall surface of the outer peripheral portion 54. However, only the inner wall surface or only the outer wall surface may be provided. In addition, although one concentric thin portion 54 is provided, two or more concentric thin portions may be provided, and the concentric thin portions 54 may not be continuous in an annular shape.
[0055]
(Example 6)
Hereinafter, a sixth embodiment of the present invention will be described with reference to the drawings.
[0056]
FIG. 16 is a cross-sectional view of the ultrasonic vibrator 55, and FIG. 17 is a cross-sectional view of an ultrasonic vibrator mounting portion of the flow measuring unit 23 of the ultrasonic flowmeter. 7 is a case, 8 is a top portion, 9 is an acoustic matching layer, 10 is a side wall portion, 11 is a bent portion, 12 is a support portion, 13 is a piezoelectric body, 15a and 15b are terminals, and 16 is an insulating terminal 15a and a terminal 15b. Insulating portions 17 are lead wires for electrically connecting the piezoelectric body 13 and the terminals 15a, and have the same configuration as that of FIG. The difference from the configuration of FIG. 1 is that the diameter of the terminal plate 56 is larger than the support portion 12 and that a seal portion 57 is provided on the outer periphery of the terminal plate 56. The method for producing the ultrasonic transducer 55 having the above-described structure, the method for producing the ultrasonic flowmeter, and the operating principle are the same as those in the first embodiment, and a description thereof will be omitted.
[0057]
A method of attaching the ultrasonic vibrator 55 to the flow measuring unit 23 will be described. The ultrasonic transducer 55 is inserted into the transducer mounting hole 29 provided in the side wall part 24. The terminal plate 56 of the ultrasonic transducer 55 has a thickness of 1 mm and a diameter of 20 mm. The terminal plate 56 is configured to be 4 mm larger than the 16 mm diameter of the support portion 12, and a seal portion 57 is provided in this portion. A seal member 57 made of an O-ring is interposed between the seal portion 57 and a flow path seal surface 58 provided on the side wall portion 24. Next, the terminal plate 56 is fixed by applying pressure from the back surface with a donut-shaped fixing body and a screw (not shown).
[0058]
In the ultrasonic transducer 55, when the support portion 12 and the terminal plate 56 are electrically welded, irregularities may be formed on the surface of the support portion 12. If the surface of the support portion 12 has irregularities, it is conceivable that even if the seal material 59 is used, it is not possible to prevent gas from leaking from the vibrator mounting hole 29. In the present embodiment, by using the terminal plate 56 having a larger outer dimension than the support portion 12, it is possible to have a smooth seal portion 57 on the outer periphery of the terminal plate 56 which is not affected by electric welding. Therefore, the safety of the ultrasonic flowmeter against gas leakage can be improved.
[0059]
In the sixth embodiment, the terminal plate 56 and the seal portion 59 have the same thickness. However, the terminal plate 56 and the seal portion 59 do not have to have the same thickness. It may be thick. Further, although the terminal plate 56 has a disk shape, the terminal portion 56 may be configured by bending the seal portion 59. In addition, although the diameter of the terminal plate 56 is larger than that of the support portion 12, the diameter of the support portion 12 may be larger than that of the terminal plate 56, and the support portion 12 may be provided with a seal portion.
[0060]
In the first to sixth embodiments, the piezoelectric body 13 is a piezoelectric ceramic, the frequency is 400 KHz, the shape is a rectangular parallelepiped having a length of 8 mm, a width of 8 mm, and a thickness of 4 mm, and two grooves are provided. However, the present invention is not limited to the above conditions. Instead, the material, frequency, shape, dimensions, and number of grooves can be changed as appropriate, and for example, thickness vibration of a thin disk, or thickness vibration of a cylinder or prism can be used. Although the material of the flow rate measuring unit 23 is an aluminum alloy die-cast, the present invention is not limited to the above conditions, and the material can be appropriately changed depending on the fluid to be measured. Further, the cross section 37 of the flow path is rectangular, and the

ultrasonic transducers

27, 28, and 55 are arranged obliquely with respect to the flow path 26. However, the present invention is not limited to the above conditions. The flow path shape may be cylindrical, or the ultrasonic vibrator may be arranged in parallel to the flow. Although the

seal members

31, 32, and 59 are O-rings, the present invention is not limited to the above conditions, and the material and shape can be appropriately changed as long as the flammable fluid to be measured can be sealed.
[0061]
Although the fluid to be measured is LP gas and natural gas, other gases and liquids such as liquefied natural gas, petroleum, and kerosene may be used. A household gas meter is assumed as the ultrasonic flow meter, but other ultrasonic flow meters or ultrasonic flow meters may be used, and a flow meter for controlling the flow rate of gas in a water heater, or a flow meter for air or fuel in an automobile. I do not care. Although the case 7 and the terminal plates 14 and 56 are made of stainless steel, the present invention is not limited to the above conditions, and the materials can be appropriately changed. Further, although the support portion 12 is provided on the end face of the side wall portion, it may be provided in other places. The matching layers 9 and 44 use only one layer of a material made of epoxy resin and micro glass spheres, but there is no need to provide one or more layers of a material having a shape suitable for the fluid to be measured or depending on the fluid to be measured. There is also. Moreover, you may implement combining the structure of several Example. Although the ultrasonic transducer is used for the ultrasonic flow meter, it may be used as an ultrasonic sensor such as a distance sensor. Although the space surrounded by the case 7 and the terminal plate 14 is replaced by dry nitrogen or an inert gas, the space may be evacuated or air.
[0062]
More thanAs apparent from the description, the present inventionOf the embodiment ofAccording to the ultrasonic transducer and the flow meter using the same, the following effects can be obtained.
[0063]
In the embodiment of the present inventionThe first ultrasonic vibrator includes a cylindrical case having a ceiling portion and a side wall portion, a piezoelectric body fixed to an inner wall surface of the ceiling portion, and an acoustic member provided on an outer wall surface of the ceiling portion. A matching layer, and a supporting portion provided on the outer wall of the side wall portion, wherein the case has an anti-vibration structure and prevents the vibration of the piezoelectric body from propagating to the case, so that transmission and reception of an ultrasonic pulse having a short reverberation can be achieved. And an ultrasonic transducer capable of measuring high S / N with reduced influence of noise due to reverberation can be obtained.
[0064]
In the embodiment of the present inventionSince the second ultrasonic vibrator has a shape in which the rigidity of the side wall portion is increased, the vibration of the piezoelectric body is prevented from propagating to the side wall portion, and an ultrasonic pulse having a short reverberation can be transmitted and received. Thus, an ultrasonic vibrator capable of measuring a high S / N with reduced influence of the vibration can be obtained.
[0065]
In the embodiment of the present inventionSince the third ultrasonic vibrator has a bent portion concentric with the top portion on the side wall portion, the rigidity of the side wall portion is increased, and the vibration of the piezoelectric body is prevented from being propagated to the side wall portion. It is possible to transmit and receive a sound wave pulse, and to obtain an ultrasonic transducer capable of measuring high S / N with reduced influence of noise due to reverberation.
[0066]
In the embodiment of the present inventionSince the fourth ultrasonic vibrator has a plurality of convex portions or concave portions in the axial direction of the side wall portion, the rigidity of the side wall portion is increased, and the vibration of the piezoelectric body is prevented from propagating to the side wall portion, and the reverberation is short. It is possible to transmit and receive ultrasonic pulses and obtain an ultrasonic transducer capable of measuring high S / N with reduced influence of noise due to reverberation.
[0067]
In the embodiment of the present inventionSince the fifth ultrasonic transducer has a polygonal cylindrical side wall, the rigidity of the side wall is increased, and the vibration of the piezoelectric body is prevented from propagating to the side wall. And an ultrasonic transducer capable of measuring high S / N with reduced influence of noise due to reverberation can be obtained.
[0068]
In the embodiment of the present inventionSince the sixth ultrasonic vibrator has a convex portion or a concave portion on the outer peripheral portion of the top portion, the rigidity of the outer peripheral portion of the top portion is increased, and the vibration of the piezoelectric body is prevented from propagating to the side wall portion. It is possible to transmit and receive short ultrasonic pulses and obtain an ultrasonic transducer capable of measuring high S / N with reduced influence of noise due to reverberation.
[0069]
In the embodiment of the present inventionSince the seventh ultrasonic vibrator has a thin portion on the outer peripheral portion of the top portion, the portion of the top portion to which the piezoelectric body is fixed easily vibrates, and the vibration of the piezoelectric body is prevented from propagating to the side wall portion. Thus, it is possible to transmit and receive an ultrasonic pulse having a short reverberation, and obtain an ultrasonic transducer capable of measuring a high S / N with reduced influence of noise due to the reverberation.
[0070]
In the embodiment of the present inventionThe ultrasonic flowmeter includes a flow measurement unit through which the fluid to be measured flows, a pair of first to seventh ultrasonic transducers provided in the flow measurement unit for transmitting and receiving ultrasonic waves, and the ultrasonic vibration Since the measurement circuit for measuring the propagation time between the slaves and the flow rate calculation means for calculating the flow rate based on the signal from the measurement circuit are provided, the influence of noise due to reverberation can be reduced, the S / N is improved, and the measured It is possible to obtain an ultrasonic flowmeter having high measurement accuracy of the flow rate and the flow velocity of the fluid.
The ultrasonic flowmeter according to the embodiment of the present invention includes the ultrasonic vibrator having the seal portion on the terminal plate fixed to the support portion, so that the fluid to be measured can be prevented from leaking from the flow measurement portion to the outside, A highly reliable ultrasonic flow meter can be obtained.
[0071]
【The invention's effect】
As is apparent from the above description, according to the ultrasonic vibrator of the present invention and the flow meter using the same, the case has a vibration-proof structure and prevents the vibration of the piezoelectric body from propagating to the side wall, so that the reverberation It is possible to transmit and receive an ultrasonic pulse having a short length and obtain an ultrasonic transducer capable of measuring a high S / N with reduced influence of noise due to reverberation..
[Brief description of the drawings]
FIG. 1 is an external view of an ultrasonic transducer according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of the ultrasonic transducer.
FIG. 3 is an external view of a piezoelectric body used in the ultrasonic transducer.
FIG. 4 is a configuration diagram including a partial cross-sectional view of an ultrasonic flowmeter used for the ultrasonic transducer.
FIG. 5 is a cross-sectional view taken along line aa ′ of the flow meter.
FIG. 6 is a sectional view of a modified example of the ultrasonic transducer.
FIG. 7 is a top view of an ultrasonic transducer according to a second embodiment of the present invention.
FIG. 8 is a side view of the ultrasonic transducer.
FIG. 9 is an external view of a modified example of the ultrasonic transducer.
FIG. 10 is an external view of an ultrasonic transducer according to a third embodiment of the present invention.
FIG. 11 is a sectional view of an ultrasonic transducer according to a fourth embodiment of the present invention.
FIG. 12 is a top view of the ultrasonic transducer.
FIG. 13 is a top view of a modified example of the ultrasonic transducer.
FIG. 14 is a sectional view of a modified example of the ultrasonic transducer.
FIG. 15 is a sectional view of an ultrasonic transducer according to a fifth embodiment of the present invention.
FIG. 16 is a sectional view of an ultrasonic transducer according to a sixth embodiment of the present invention.
FIG. 17 is a sectional view of an ultrasonic vibrator mounting portion of a flow measuring unit of the ultrasonic flow meter.
FIG. 18 is a cross-sectional view of a conventional ultrasonic transducer for an ultrasonic flowmeter.
FIG. 19 is a sectional view of another conventional ultrasonic transducer for an ultrasonic flowmeter.
[Explanation of symbols]
6 Ultrasonic transducer
7 cases
8 Tenbu
9 Acoustic matching layer
10 Side wall
11 bending part
12 Support
13 Piezoelectric body
27,28 Ultrasonic transducer
23 Flow rate measurement unit
33 Measurement circuit
34 Flow rate calculation means
40, 47 convex part
41, 51 recess
54 Thin part
57 Seal part

Claims

A cylindrical case having a top portion and a side wall portion, a piezoelectric body fixed to an inner wall surface of the top portion, an acoustic matching layer provided on an outer wall surface of the top portion, and an outer wall of the side wall portion An ultrasonic vibrator having a bent portion concentric with the top portion on the side wall portion to prevent the vibration of the piezoelectric body from propagating to the side wall portion.

A cylindrical case having a top portion and a side wall portion, a piezoelectric body fixed to an inner wall surface of the top portion, an acoustic matching layer provided on an outer wall surface of the top portion, and an outer wall of the side wall portion An ultrasonic vibrator comprising: a plurality of convex portions or concave portions in an axial direction of the side wall portion so as to prevent the vibration of the piezoelectric body from propagating to the side wall portion.

A cylindrical case having a top portion and a side wall portion, a piezoelectric body fixed to an inner wall surface of the top portion, an acoustic matching layer provided on an outer wall surface of the top portion, and an outer wall of the side wall portion An ultrasonic vibrator having a side wall portion having a polygonal cylindrical shape so as to prevent the vibration of the piezoelectric body from propagating to the side wall portion.

The flow rate measuring unit through which the fluid to be measured flows, and a pair of the ultrasonic vibrator according to any one of claims 1 to 3 , which are provided in the flow rate measuring unit and transmit and receive an ultrasonic wave. A measuring circuit for measuring a propagation time, and a flow rate calculating means for calculating a flow rate based on a signal from the measuring circuit, and the ultrasonic vibrator has a seal portion on a terminal plate fixed to a support portion. Ultrasonic flow meter.

Ultrasonic transducer of the piezoelectric body according to any one of claims 1 having a groove in the axial direction 3.

The ultrasonic transducer according to any one of claims 1 to 3 , wherein a terminal plate is fixed to the support portion to seal the inside of the case.

The ultrasonic vibrator according to claim 6 , wherein the inside of the case is sealed with an inert gas.