JP2004093299A - Ultrasonic vibrator and ultrasonic flowmeter using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic vibrator capable of suppressing generation of an abnormal resonance mode, and acquiring an excellent frequency, and an ultrasonic flowmeter using it. <P>SOLUTION: Positions of the top face of a case 32 of this ultrasonic vibrator 1 and a piezoelectric body 6, positions of the top face of the case 32 and an acoustic matching layer 4, and a position of the center of the acoustic matching layer 4 to the center of the piezoelectric body 6 are aligned on proper positions respectively. <P>COPYRIGHT: (C)2004,JPO

Description

となる。
【００６８】
ただし、ｎ＝１、２、３・・・・であり、Ｃｉｊは弾性定数であり、ρは密度である。ここで、厚み振動を用いている理由は、使用周波数（共振周波数）を圧電体６のＴ（厚み）で制御可能なため、厚みＴを変えるだけで周波数を変えることが可能であり、広帯域に対応可能で、超音波流量計を小径にできるためである。
【００６９】
また、ケース（振動板）３２の厚み範囲としては、ｔ＝０．１〜０．５ｍｍが好ましい。図７に示すように、ケース（振動板）３２の厚みが薄いと超音波流量計の超音波の送受信の感度が増加し、ケース（振動板）３２の厚みが厚いと超音波流量計の超音波の送受信の感度が低下する。ケース（振動板）３２の厚みが薄いと共振周波数は低下し、ケース（振動板）３２の厚みが厚いと共振周波数は増加する。その理由は、超音波流量計の超音波の送受信感度とケース（振動板）３２の厚みのトレードオフのためである。
【００７０】
超音波流量計の流量算出システム側から考慮すると、超音波の送受信感度においては２５％以内の低下ならば補正可能である。従って、ケース厚みｔは０．１〜０．５ｍｍまでである。
【００７１】
また、ケース（振動板）３２の厚みと超音波流量計を構成する部品間の位置ずれとの関係について説明する。
【００７２】
▲１▼位置ずれは、ベクトル量ではなく絶対値に依存する（ずれ方向による依存無し：図８参照）。ただし、圧電体のずれ量と相関係数との関係を示す図８において、中心側の円は相関係数が０．９９０、最も外側の円は相関係数が０．９６０、中心から上向き及び右向きには、正方向のずれ量、中心から下向き及び左向きには、負方向のずれ量とする。
【００７３】
▲２▼ケース（振動板）３２の厚みｔが厚くなるに従い、相関係数は位置ずれ量に鈍感になる傾向にある（図９〜図１１参照）。図９では、ケース３２の天面の中心に対する圧電体６の中心の位置ずれ量Δα（ｍｍ）が大きくなればなるほど相関係数は低下し、ケース（振動板）３２の厚みｔが厚くなるに従い、相関係数は位置ずれ量の低下度合いが小さくなる。また、図１０では、ケース３２の天面の中心に対する音響整合層４の中心の位置ずれ量Δβ（ｍｍ）が大きくなればなるほど相関係数は低下し、ケース（振動板）３２の厚みｔが厚くなるに従い、相関係数は位置ずれ量の低下度合いが小さくなる。さらに、図１１では、圧電体６の中心に対する音響整合層４の中心の位置ずれ量Δγ（ｍｍ）が大きくなればなるほど相関係数は低下し、ケース（振動板）３２の厚みｔが厚くなるに従い、相関係数は位置ずれ量の低下度合いが小さくなる。
【００７４】
計測回路１０１の計測精度を実現できる超音波流量計の相関係数は０．９６０以上である。そのため、上記グラフ２〜４の相関係数が０．９６０以上を実現できる範囲は、ケース（振動板）３２の厚みｔでずれ量を割ると、夫々、
（Δα／ｔ）＜２、（Δβ／ｔ）＜３、Δγ＜（５／２）　である。
【００７５】
また、計測精度と使用周波数帯域に関して説明する。
【００７６】
要求計測精度としては、都市ガス（１３Ａ）は、３リットル／ｈであり、ＬＰガスは、１リットル／ｈであり、時間分解能で、０．０１ｎｓｅｃ（使用周波数：５２０ＫＨｚ）、０．０２ｎｓｅｃ（使用周波数：２６０ＫＨｚ）が実現可能である。
【００７７】
高周波数を使用するほど高分解能になるため高周波数を用いたいが、計測回路１０１上、高周波数になればなるほどノイズなどに弱くなるため、通常２００ＫＨｚ〜８００ＫＨｚの周波数が用いられる。
【００７８】
計測回路１０１としては、電流型回路を用いているが、理想的な電流型回路であれば２次側を短絡することにより、流路、超音波流量計のインピーダンスによらず、出力電流は受信と送信を入れ替えても同じである。ただし、１次側と２次側の超音波流量計としてはできるだけインピーダンスの似たものが必要である。
【００７９】
上記実施形態によれば、超音波振動子１の各部品（例えば、ケース３２、圧電体６、音響整合層４）のそれぞれの位置を適正な位置に合わせ込むことにより、異常共振モードの発生を抑制し、周波数的に良好とすることができ、計測精度の向上を図ることができる。ここで、お互いの超音波流量計のインピーダンスの周波数特性がどのくらい似ているかを示す指標として相関係数がある。流量算出システムとの兼ね合いから相関係数が０．９６０までの範囲の超音波流量計なら一般的に合格とされることから、上記適正な範囲内の位置ズレ量になるように合わせ込むことにより、相関係数を０．９６０までの範囲に確実に収めることができて、信頼性の高い超音波流量計を提供することができる。
【００８０】
【実施例】
以下、具体的な実施例により、上記第１実施形態の実験的考察並びに本発明の効果の説明を行う。
【００８１】
（実施例１）
ケース材料に使用されるステンレスの厚みをｔ＝０．２ｍｍにおいてプレス加工を施し、φ１１．８ｍｍ、高さ５．６ｍｍのケース状にした。このとき、ケース天面はφ１１ｍｍである。圧電体の大きさは７．４ｍｍ×７．４ｍｍで高さ２．６５ｍｍ、整合層はφ１０ｍｍ、高さ１．１５ｍｍである。このとき、整合層とケース天面はお互いの中心を一致させるように接合し、圧電体のケースとの接合面の中心をケース天面の中心と少しずつずらして何種類かの超音波流量計を作成した。基準となる超音波流量計は整合層、ケース天面、圧電体のケース接合面の中心を合わせて作成している。それぞれの超音波流量計に±５Ｖの電圧を印加して、周波数を１００ＫＨｚ〜１ＭＨｚまで変化させてインピーダンスの周波数特性を測定した。超音波流量計として使用する周波数帯である３５０ＫＨｚ〜７５０ＫＨｚを基準超音波流量計と比較して相関係数を求めた。ここで、相関係数とは、お互いの超音波流量計のインピーダンスの周波数特性がどのくらい似ているかを示すものである。その結果を図８に示す。ずれ量とその方向によって相関係数が異なるかどうか、すなわちベクトル量として見なければならないかどうかを判断するためにそれぞれの相関係数を計算した。図８に示されるように、中心からずれる方向によらず、ずれの絶対量に依存することが判明した。
【００８２】
（実施例２）
ケース（振動板）の厚みによってどのように超音波流量計の超音波の送受信感度が変化するかを調べた。ケース（振動板）の厚みが０．１ｍｍのときを基準として、厚みを０．２ｍｍ、０．３ｍｍ、０．８ｍｍ、１．０ｍｍと変化させて検討した結果を図７に示す。ケースはプレス加工を施し、φ１１．８ｍｍ、高さ５．６ｍｍのケース状にした。このとき、ケース天面はφ１１ｍｍである。圧電体の大きさは７．４ｍｍ×７．４ｍｍで高さ２．６５ｍｍ、整合層はφ１０ｍｍ高さ１．１５ｍｍである。結果から、ケース（振動板）の厚みが厚くなるに従い、超音波の送受信感度が比例して低下することがわかった。
【００８３】
（実施例３）
ケース材料に使われるステンレスの厚みをｔ＝０．１〜０．５ｍｍまで変化させてプレス加工を施し、φ１１．８ｍｍ、高さ５．６ｍｍのケース状にした。このとき、ケース天面はφ１１ｍｍである。圧電体の大きさは７．４ｍｍ×７．４ｍｍで高さ２．６５ｍｍ、整合層はφ１０ｍｍ、高さ１．１５ｍｍである。このとき、整合層とケース天面はお互いの中心を一致させるように接合し、圧電体のケースとの接合面の中心をケース天面の中心と少しずつずらして何種類かの超音波流量計を作成した。基準となる超音波流量計は整合層、ケース天面、圧電体のケース接合面の中心を合わせて作成している。それぞれの超音波流量計に±５Ｖの電圧を印加して、周波数を１００ＫＨｚ〜１ＭＨｚまで変化させてインピーダンスの周波数特性を測定した。超音波流量計として使用する周波数帯である３５０ＫＨｚ〜７５０ＫＨｚをお互いに比較して相関係数を求めた。ここで、相関係数とは、お互いの超音波流量計のインピーダンスの周波数特性がどのくらい似ているかを示すものである。その結果を図９に示す。ずれ量をΔαとすると圧電体のケース天面の中心からのずれ量が増加すると相関係数の値が比例的に低下することがわかる。ただし、ケース天面（振動板）の厚みを変化させるとその傾きは厚みが薄いほど急になる傾向が見られた。流量算出システムとの兼ね合いから相関係数の値としては０．９６０までの範囲の超音波流量計なら合格とされることから、相関係数０．９６０以上の相関係数の値に注目するとケース天面の厚みに関わらず、（Δα／ｔ）≦２の関係があることがわかった。以上より、（Δα／ｔ）≦２を満たす超音波流量計であれば、超音波流量計の特性として、流量算出システム上、同じ特性を満たす超音波流量計として用いることが可能である。
【００８４】
（実施例４）
ケース材料に使われるステンレスの厚みをｔ＝０．１〜０．５ｍｍまで変化させてプレス加工を施し、φ１１．８ｍｍ、高さ５．６ｍｍのケース状にした。このときケース天面はφ１１ｍｍである。圧電体の大きさは７．４ｍｍ×７．４ｍｍで高さ２．６５ｍｍ、整合層はφ９．５ｍｍ、高さ１．１５ｍｍである。このとき、圧電体とケース天面はお互いの中心を一致させるように接合し、整合層のケースとの接合面の中心をケース天面の中心と少しずつずらして何種類かの超音波流量計を作成した。基準となる超音波流量計は整合層、ケース天面、圧電体のケース接合面の中心を合わせて作成している。それぞれの超音波流量計に±５Ｖの電圧を印加して、周波数をＩ００ＫＨｚ〜１ＭＨｚまで変化させてインピーダンスの周波数特性を測定した。超音波流量計として使用する周波数帯である３５０ＫＨｚ〜７５０ＫＨｚをお互いに比較して相関係数を求めた。ここで、相関係数とは、お互いの超音波流量計のインピーダンスの周波数特性がどのくらい似ているかを示すものである。その結果を図１０に示す。ずれ量をΔβとすると実施例３の場合と同様に、整合層のケース天面の中心からのずれ量が増加すると相関係数の値が比例的に低下することがわかる。ただし、ケース天面（振動板）の厚みを変化させるとその傾きは厚みが薄いほど急になる傾向が見られた。流量算出システムとの兼ね合いから相関係数の値としては０．９６０までの範囲の超音波流量計なら合格とされることから、相関係数０．９６０以上の相関係数の値に注目するとケース天面の厚みに関わらず、（Δβ／ｔ）≦３の関係があることがわかった。以上より、（Δβ／ｔ）≦３を満たす超音波流量計であれば、超音波流量計の特性として、流量算出システム上、同じ特性を満たす超音波流量計として用いることが可能である。
【００８５】
（実施例５）
ケース材料に使われるステンレスの厚みをｔ＝０．１〜０．５ｍｍまで変化させて、プレス加工を施し、φ１１．８ｍｍ、高さ５．６ｍｍのケース状にした。このときケース天面はφ１１ｍｍである。圧電体の大きさは７．４ｍｍ×７．４ｍｍで高さ２．６５ｍｍ、整合層はφ１０ｍｍ、高さ１．１５ｍｍである。このとき、圧電体と音響整合層をケース天面の中心を軸としてお互いに反対方向に少しずつずらして何種類かの超音波流量計を作成した。基準となる超音波流量計は整合層、ケース天面、圧電体のケース接合面の中心を合わせて作成している。それぞれの超音波流量計に±５Ｖの電圧を印加して、周波数を１００ＫＨｚ〜１ＭＨｚまで変化させてインピーダンスの周波数特性を測定した。超音波流量計として使用する周波数帯である３５０ＫＨｚ〜７５０ＫＨｚをお互いに比較して相関係数を求めた。ここで、相関係数とは、お互いの超音波流量計のインピーダンスの周波数特性がどのくらい似ているかを示すものである。その結果を図１１に示す。圧電体の中心に対する音響整合層の中心のずれ量をΔγとすると実施例２，４と同様に上記圧電体の中心に対する上記音響整合層の中心ののずれ量Δγが増加するに従い比例的に相関係数が低下することが判明した。実施例３および実施例４のように流量算出システムとの兼ね合いから相関係数０．９６０以上の範囲でステンレス（振動板）の厚みに関わらず（Δγ／ｔ）≦（５／２）を満たすことがわかった。以上より、（Δγ／ｔ）≦（５／２）を満たす超音波流量計であれば、超音波流量計の特性として、流量算出システム上、同じ特性を満たす超音波流量計として用いることが可能である。
【００８６】
（実施例６）
実施例３の結果をもとに、送受信を交互に繰り返す流量算出システムにおいて超音波流量計を１対で使用する場合に、圧電体が中心からある量だけずれた超音波流量計を基準として、その超音波流量計ともう一方の超音波流量計の圧電体のずれ量をΔχとして相関係数を計算した。また、流量算出システム上、計測精度が保証できるかどうかで合否を判定した。条件は実施例３と同様に、ケース材料に使われるステンレスの厚みをｔ＝０．１〜０．５ｍｍまで変化させて、プレス加工を施し、φ１１．８ｍｍ、高さ５．６ｍｍのケース状にした。このときケース天面はφ１１ｍｍである。圧電体の大きさは７．４ｍｍ×７．４ｍｍで高さ２．６５ｍｍ、整合層はφ１０ｍｍ、高さ１．１５ｍｍである。それぞれの超音波流量計に±５Ｖの電圧を印加して、周波数を１００ＫＨｚ〜１ＭＨｚまで変化させてインピーダンスの周波数特性を測定した。超音波流量計として使用する周波数帯である３５０ＫＨｚ〜７５０ＫＨｚをお互いに比較して相関係数を求めた。ここで、相関係数とは、お互いの超音波流量計のインピーダンスの周波数特性がどのくらい似ているかを示すものである。その結果を表１に示す。表１の結果、ケースの中心を基準として、ケースの中心から０．５ｍｍ以内のずれ量内であれば、それぞれの超音波流量計のずれ量の差がケース（振動板）の厚みｔで割った値、すなわち（Δχ／ｔ）≦２となることがわかった。
【００８７】
【表１】

【００８８】
（実施例７）
実施例２の結果をもとに、超音波の送受信を交互に繰り返す流量算出システムにおいて超音波流量計を１対で使用する場合に、音響整合層が中心からある量だけずれた超音波流量計を基準として、その超音波流量計ともう一方の超音波流量計の音響整合層のずれ量をΔφとして相関係数を計算した。また、流量算出システム上、計測精度が保証できるかどうかで合否を判定した。条件は実施例２と同様に、ケース材料に使われるステンレスの厚みをｔ＝０．１〜０．５ｍｍまで変化させて、プレス加工を施し、φ１１．８ｍｍ、高さ５．６ｍｍのケース状にした。このときケース天面はφ１１ｍｍである。圧電体の大きさは７．４ｍｍ×７．４ｍｍで高さ２．６５ｍｍ、整合層はφ９．５ｍｍ、高さ１．１５ｍｍである。それぞれの超音波流量計に±５Ｖの電圧を印加して、周波数を１００ＫＨｚ〜１ＭＨｚまで変化させてインピーダンスの周波数特性を測定した。超音波流量計として使用する周波数帯である３５０ＫＨｚ〜７５０ＫＨｚをお互いに比較して相関係数を求めた。ここで、相関係数とは、お互いの超音波流量計のインピーダンスの周波数特性がどのくらい似ているかを示すものである。その結果を表２に示す。表２の結果、ケースの中心を基準として、ケースの中心から０．５ｍｍ以内のずれ量内であればそれぞれの超音波流量計のずれ量の差がケース（振動板）の厚みｔで割った値、すなわち（Δφ／ｔ）≦３となることがわかった。
【００８９】
【表２】

なお、上記様々な実施形態のうちの任意の実施形態を適宜組み合わせることにより、それぞれの有する効果を奏するようにすることができる。
【００９０】
【発明の効果】
この発明によれば、超音波振動子の各部品（例えば、ケース、圧電体、音響整合層）のそれぞれの位置を適正な範囲内の位置ズレ量になるように合わせ込むことにより、異常共振モードの発生を抑制し、周波数的に良好とすることができ、計測精度の向上を図ることができる。すなわち、お互いの超音波流量計のインピーダンスの周波数特性がどのくらい似ているかを示す、相関係数は、流量算出システムとの兼ね合いから０．９６０までの範囲の超音波流量計なら一般的に合格とされることから、上記適正な範囲内の位置ズレ量になるように合わせ込むことにより、相関係数を０．９６０までの範囲に確実に収めることができて、信頼性の高い超音波流量計を提供することができる。
【００９１】
より具体的には、本発明の第１態様にかかる超音波振動子において、上記音響整合層が設けられた面の反対側の面に圧電体が設けられた超音波振動子であって、振動板を兼ねる上記ケースの天面の中心に対して、上記圧電体が上記ケースと接合される接合面の中心のずれ量をΔα、上記振動板の厚みをｔとしたとき、（Δα／ｔ）≦２を満たすように上記ケースの天面の中心と上記圧電体が上記ケースの天面と接合される接合面の中心を合わせるようにすれば、異常共振モードの発生を防ぐことができる。
【００９２】
また、本発明の第２態様にかかる超音波振動子において、上記音響整合層が設けられた面の反対側の面に圧電体が設けられた超音波振動子であって、振動板を兼ねる上記ケースの天面の中心に対して、上記音響整合層が上記ケースと接合される接合面の中心のずれ量をΔβ、上記振動板の厚みをｔとしたとき、（Δβ／ｔ）≦３を満たすように上記ケースの天面の中心と上記音響整合層が上記ケースの天面と接合される接合面の中心を合わせるようにすれば、対向する２つの超音波振動子の軸ズレを防ぎ、感度低下を抑えることができる。
【００９３】
また、本発明の第３態様にかかる超音波振動子において、上記圧電体の中心に対する上記音響整合層の中心のずれ量をΔγ、上記振動板の厚みをｔとしたとき、（Δγ／ｔ）≦（５／２）を満たすように上記圧電体が上記ケースの天面と接合される接合面の中心と上記音響整合層が上記ケースの天面と接合される接合面の中心とを合わせるようにすれば、感度低下を抑えることができる。
【００９４】
また、本発明の第４態様にかかる超音波振動子において、上記音響整合層が設けられた面の反対側の面に圧電体が設けられた超音波振動子であって、１対の超音波振動子で交互に超音波の送受信を繰り返して測定を行う超音波振動子において、振動板を兼ねる上記ケースの天面の中心に対して圧電体のずれ量Δα≦０．５ｍｍである超音波振動子ならば、各々超音波振動子に用いられる圧電体のずれ量をΔχ、上記振動板の厚みをｔとしたとき、（Δχ／ｔ）≦２を満たすようにすれば、感度及びインピーダンスの周波数特性で位相ずれ及び異常共振などを最小限に抑えることができる、高い計測精度を実現することができる。
【００９５】
また、本発明の第５態様にかかる超音波振動子において、上記音響整合層が設けられた面の反対側の面に圧電体が設けられた超音波振動子であって、１対の超音波振動子で交互に超音波の送受信を繰り返して測定を行う超音波振動子において、振動板を兼ねる上記ケースの天面の中心に対して音響整合層のずれ量Δβ≦０．５ｍｍである超音波振動子ならば、各々超音波振動子に用いられる音響整合層のずれ量をΔφ、上記振動板の厚みをｔとしたとき、（Δφ／ｔ）≦３を満たすようにすれば、感度及びインピーダンスの周波数特性で位相ずれ及び異常共振などを最小限に抑えることができる、高い計測精度を実現することができる。
【００９６】
さらに、超音波流量計として、被測定流体が流れる流路を有する流量測定部と、この流量測定部に設けられた上記第１〜５いずれか１つの態様に記載の超音波振動子を１対対向して上記流路を挟んで配置された超音波振動子と、上記超音波振動子間で上記流路を通する超音波の伝搬時間を計測する計測回路と、上記計測回路で計測された結果情報を示す信号に基づいて上記被測定流体の流量を算出する流量演算手段とを備えるようにすれば、上記した超音波振動子の種々の作用効果を奏することができる。
【図面の簡単な説明】
【図１】本発明の第１実施形態における超音波振動子の外観図である。
【図２】上記第１実施形態における超音波振動子の断面図である。
【図３】上記第１実施形態における超音波振動子を利用する超音波流量計の断面図である。
【図４】上記第１超音波流量計の断面図である。
【図５】本発明の第２実施形態における超音波振動子の断面図である。
【図６】本発明の第３実施形態における超音波振動子の断面図である。
【図７】ケース（振動板）の厚みに対する感度低下率を示すグラフである。
【図８】圧電体のずれ量と相関係数との関係を示すグラフである。
【図９】ケース（振動板）の天面の中心に対する圧電体の位置ずれ量分布を示すグラフである。
【図１０】ケース（振動板）の天面の中心に対する音響整合層の位置ずれ量分布を示すグラフである。
【図１１】圧電体の中心に対する音響整合層の位置ずれ量分布を示すグラフである。
【符号の説明】
１…超音波振動子、２…支持体、３…板状部材、４…音響整合層、５…フランジ部、６…圧電体、７…端子板、８ａ，８ｂ…端子、９…絶縁物、１０…導電性ゴム、１１…流量測定部、１２…側壁部、１３…側壁部、１４…シール材、１５…上板部、１６…流路断面、１７…超音波振動子、１８…超音波振動子、１９…振動子取り付け穴、２０…振動子取り付け穴、２１…シール材、２２…シール材、３０…接着層、３１…接着層、３２…有底状ケース、１００…超音波流量計、１００ａ…入口路、１００ｂ…出口路、１０１…計測回路、１０２…流量演算手段。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic vibrator for measuring a flow rate and a flow velocity of a gas or a liquid by ultrasonic waves, and an ultrasonic flowmeter using the same.
[0002]
[Prior art]
Conventionally, as an ultrasonic transducer used for this type of ultrasonic flow measuring device, for example, Japanese Patent Application Laid-Open No. H11-325992 is known. A piezoelectric body is provided on an inner surface of a top of a case, and an acoustic matching layer is provided on the top. Is provided.
[0003]
[Problems to be solved by the invention]
However, in the conventional configuration, only the acoustic matching layer is provided, and no consideration is given to an appropriate acoustic matching layer, a piezoelectric body, and a case.
[0004]
In particular, from the viewpoint of mutual positional deviation, there is no method that considers the optimal combination of the acoustic matching layer, the piezoelectric body, and the case, and this is not described from the viewpoint of efficiency and reliability. In other words, if the displacement becomes large, an abnormal resonance mode may occur, which causes a decrease in the function of the ultrasonic transducer.
[0005]
In recent gas flow meters, the type and measurement accuracy of the gas used (for example, the accuracy required for the flow measurement device for city gas is 0.5 nsec or more, and the ultrasonic vibrator has higher accuracy than this. (Required), there is a demand for improved functions of the ultrasonic vibrator, and from such industrial needs, there is a demand for improved functions of the ultrasonic vibrator.
[0006]
In particular, the ultrasonic vibrator performs its function by receiving the ultrasonic signal transmitted from one ultrasonic vibrator by the other ultrasonic vibrator. Become. If the displacement is large, an abnormal resonance mode is generated, and the frequency cannot be maintained satisfactorily, resulting in deterioration of measurement accuracy.
[0007]
An object of the present invention is to solve the above-described problems, and to provide an ultrasonic vibrator capable of suppressing occurrence of an abnormal resonance mode and improving the frequency, and an ultrasonic flowmeter using the same.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0009]
According to a first aspect of the present invention, there is provided a bottomed cylindrical case, and an acoustic matching layer provided on at least one surface of the case,
An ultrasonic vibrator in which a piezoelectric body is provided on a surface opposite to a surface on which the acoustic matching layer is provided, wherein the piezoelectric body is provided on the case with respect to a center of a top surface of the case also serving as a diaphragm. The center of the top surface of the case and the piezoelectric body are aligned with the case so that (Δα / t) ≦ 2, where Δα is the amount of deviation of the center of the bonding surface to be bonded to the substrate and t is the thickness of the diaphragm. An ultrasonic vibrator characterized in that a center of a joint surface to be joined to a top surface of the ultrasonic transducer is aligned.
[0010]
According to a second aspect of the present invention, there is provided a bottomed cylindrical case, and an acoustic matching layer provided on at least one surface of the case,
An ultrasonic vibrator in which a piezoelectric body is provided on a surface opposite to a surface on which the acoustic matching layer is provided, wherein the acoustic matching layer has the acoustic matching layer with respect to a center of a top surface of the case also serving as a diaphragm. When the amount of deviation of the center of the joining surface joined to the case is Δβ and the thickness of the diaphragm is t, the center of the top surface of the case and the acoustic matching layer are adjusted so that (Δβ / t) ≦ 3. An ultrasonic vibrator characterized in that a center of a joint surface to be joined to a top surface of the case is aligned.
[0011]
According to a third aspect of the present invention, there is provided a bottomed cylindrical case, and an acoustic matching layer provided on at least one surface of the case, and a piezoelectric layer on a surface opposite to the surface provided with the acoustic matching layer. In the ultrasonic vibrator provided with a body, when the amount of deviation of the center of the acoustic matching layer from the center of the piezoelectric body is Δγ and the thickness of the diaphragm is t, (Δγ / t) ≦ (5 / 2) the center of the bonding surface where the piezoelectric body is bonded to the top surface of the case and the center of the bonding surface where the acoustic matching layer is bonded to the top surface of the case so as to satisfy (2). An ultrasonic transducer characterized by the following.
[0012]
According to a fourth aspect of the present invention, there is provided a bottomed cylindrical case, and an acoustic matching layer provided on at least one surface of the case,
An ultrasonic vibrator in which a piezoelectric body is provided on a surface opposite to the surface on which the acoustic matching layer is provided, wherein a pair of ultrasonic vibrators alternately transmits and receives ultrasonic waves to perform measurement. In the case of an ultrasonic vibrator in which the displacement of the piezoelectric body is Δα ≦ 0.5 mm with respect to the center of the top surface of the case, which also functions as the vibration plate, the displacement of the piezoelectric body used for each ultrasonic transducer Provided is an ultrasonic vibrator characterized by satisfying (Δχ / t) ≦ 2 when the amount is Δχ and the thickness of the diaphragm is t.
[0013]
According to a fifth aspect of the present invention, there is provided a bottomed cylindrical case, and an acoustic matching layer provided on at least one surface of the case,
An ultrasonic vibrator in which a piezoelectric body is provided on a surface opposite to the surface on which the acoustic matching layer is provided, wherein a pair of ultrasonic vibrators alternately transmits and receives ultrasonic waves to perform measurement. In the case of the ultrasonic vibrator, if the ultrasonic matching element has a displacement amount Δβ ≦ 0.5 mm of the acoustic matching layer with respect to the center of the top surface of the case also serving as the vibration plate, the acoustic matching layer used for each ultrasonic vibrator An ultrasonic vibrator characterized by satisfying (Δφ / t) ≦ 3, where Δφ is a shift amount and t is a thickness of the diaphragm.
[0014]
According to the sixth aspect of the present invention, a flow rate measurement unit having a flow path through which the fluid to be measured flows,
An ultrasonic vibrator disposed opposite to the ultrasonic vibrator according to any one of the first to fifth aspects provided in the flow rate measuring unit and disposed across the flow path;
A measurement circuit that measures the propagation time of ultrasonic waves passing through the flow path between the ultrasonic transducers,
An ultrasonic flowmeter comprising: a flow rate calculating means for calculating a flow rate of the fluid to be measured based on a signal indicating result information measured by the measurement circuit.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
In the specification of the present application, the facing area indicates an area where the piezoelectric body, the plate-like member, and the acoustic matching layer directly or indirectly face and overlap.
[0017]
Hereinafter, an ultrasonic transducer according to a first embodiment of the present invention and an ultrasonic flowmeter using the same will be described with reference to FIGS. In addition, the same reference numerals are given to those having the same functions as the conventional ones.
[0018]
FIG. 1 is an external view of an ultrasonic oscillator according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view of the embodiment, and FIGS. 3 and 4 show an ultrasonic flowmeter using the ultrasonic oscillator according to the embodiment. FIG.
[0019]
In FIG. 1, reference numeral 1 denotes an ultrasonic vibrator, 6 denotes a piezoelectric body serving as a driving source, 4 denotes an acoustic matching layer for transmitting ultrasonic waves to a transmission medium such as gas or liquid, and 3 denotes one surface (outer wall surface). This is a plate-like member provided with the acoustic matching layer 4 on the side 3a and the piezoelectric body 6 on the opposite side (inner wall surface) 3b. More specifically, the acoustic matching layer 4 and the piezoelectric body 6 are bonded via the adhesive layers 30 and 31. Provide. The plate member 3 is a vibration propagation member that transmits vibration of the piezoelectric body 6 to the acoustic matching layer 4, and acoustically connects the piezoelectric body 6 and the acoustic matching layer 4.
[0020]
Reference numeral 2 denotes a support for supporting the plate-shaped member 3, and more specifically, an outer peripheral portion of the plate-shaped member 3 is engaged with and joined to an inner peripheral portion of a cylindrical shape. In the first embodiment, the plate-like member 3 and the support 2 constitute a bottomed case 32 having a ceiling 32a, a side wall 32b, and an opening 32c. Reference numeral 5 denotes a flange portion for joining the ultrasonic vibrator 1 to a side wall forming an attachment hole of the ultrasonic vibrator 1 connected to the flow path of the ultrasonic flowmeter as described later.
[0021]
In FIG. 2, reference numeral 6 denotes a piezoelectric member arranged on the inner wall surface of the plate member 3, reference numeral 7 denotes a terminal plate fixed to the flange portion 5, reference numerals 8a and 8b denote terminals provided on the terminal plate 7, and reference numeral 9 denotes a terminal. An insulator 10 that insulates 8a and 8b is a conductive rubber for electrically connecting the piezoelectric body 6 and the terminal 8a. The piezoelectric body 6 is closed by the bottomed case 32 and the terminal plate 7 and sealed with an inert gas.
[0022]
FIG. 3 is a cross-sectional view of an ultrasonic flowmeter 100 including the ultrasonic vibrator 1.
[0023]
The schematic configuration of the ultrasonic flowmeter 100 is as follows. A flow rate measuring unit 11 that measures the flow rate of a fluid to be measured flowing from an inlet passage 100a connected to a supply pipe to which a fluid to be measured such as a gas is supplied, An outlet path 100b communicating with the section 11 and guiding the fluid to be measured to the outside, and a pair of ultrasonic transducers 17 and 18 provided in the flow rate measuring section 11 for transmitting and receiving ultrasonic waves (each of which is connected to the ultrasonic transducer 1). And a measuring circuit 101 for measuring a propagation time between the ultrasonic transducers 17 and 18 and a flow rate calculating means 102 for calculating a flow rate based on a signal from the measuring circuit 101. Here, the measurement circuit 101 and the flow rate calculation means 102 constitute a flow rate calculation system.
[0024]
As a practical example, the flow rate measuring unit 11 is assumed to be a household gas meter for measuring the flow rate of LP gas or natural gas as a material, and uses aluminum alloy die casting. Then, as shown in FIG. 4, the upper plate 15 is screwed to the end surfaces of the side walls 12 and 13 constituting the gas flow path via a sealing material 14 made of, for example, cork material, so that the flow path cross section 16 is rectangular. Make up things. Further, as shown in FIG. 3, the ultrasonic transducers 17 and 18 are provided obliquely on the side walls 12 and 13 such that the transmitting and receiving surfaces for transmitting and receiving the ultrasonic waves are opposed to each other. Specifically, it is fixed to the mounting holes 19 and 20 of the ultrasonic vibrators 17 and 18 provided on the side wall parts 12 and 13 via sealing materials 21 and 22 made of, for example, O-rings. This is one example, and the present invention is not limited to this.
[0025]
On the other hand, the plate-shaped member 3 is located between the acoustic matching layer 4 and the piezoelectric body 6 and plays a role of a joining portion or a fixing portion between the acoustic matching layer 4 and the piezoelectric body 6 from a physical viewpoint. In addition, from an acoustic point of view, the connector is a connector for transmitting an ultrasonic signal (or sound pressure) from the acoustic matching layer 4 to the piezoelectric body 6 and from the piezoelectric body 6 to the acoustic matching layer 4. Fulfill. Therefore, the physical bonding area of the acoustic matching layer 4, the plate-like member 3, and the piezoelectric body 6 is very important.
[0026]
Next, the operation of the ultrasonic transducer 1 will be described, and the transmission efficiency of transmission will be considered.
[0027]
The ultrasonic signal transmitted from the piezoelectric body 6 is transmitted to the acoustic matching layer 4 via the adhesive layer 31, the plate-like member (vibration propagation member) 3, and the adhesive layer 30.
[0028]
(Consideration of propagation efficiency of transmission between piezoelectric body and plate member)
When the ultrasonic signal transmitted from the piezoelectric body 6 is propagated to the plate-shaped member 3, the propagation efficiency from the piezoelectric body 6 to the plate-shaped member 3 is determined by the fact that the piezoelectric body 6, which is a driving source, is acoustically connected to the plate-shaped member 3. It depends on the size of the bonding area to be bonded. This bonding area substantially coincides with the bonding area where the plate member 3, the piezoelectric body 6, and the bonding layer 31 overlap when the piezoelectric body 6 is bonded to the plate member 3 using the bonding layer 31. Therefore, in order to efficiently transmit an ultrasonic signal from the piezoelectric body 6 to the plate-like member 3, the plate-like member 3 needs to be larger than the bonding area between the plate-like member 3 and the piezoelectric body 6 (the plate-like member 3 and the piezoelectric body 3). 6 or more).
[0029]
Further, the ultrasonic signal transmitted to the plate-shaped member 3 is transmitted to the acoustic matching layer 4 via the adhesive layer 30 that joins the plate-shaped member 3 and the acoustic matching layer 4.
[0030]
(Consideration of propagation efficiency of transmission between plate-like member and acoustic matching layer)
The acoustic coupling area between the plate member 3 and the acoustic matching layer 4 matches the area where the plate member 3, the acoustic matching layer 4, and the adhesive layer 30 overlap. Therefore, in order to efficiently transmit an ultrasonic signal from the plate-shaped member 3 to the acoustic matching layer 4, the plate-shaped member 3 needs to be larger than the bonding area between the plate-shaped member 3 and the acoustic matching layer 4 (when the acoustic matching layer 4 is (The area facing the plate member 3 or more) is desirable.
[0031]
From the above, the area where the acoustic coupling area of the piezoelectric body 6, the plate-shaped member 3, and the acoustic matching layer 4 overlaps is the effective coupling area, and substantially coincides with the joint area for joining the respective members. Therefore, the acoustic matching layer 4 needs to have a larger area than the bonding area between the piezoelectric body 6 and the plate-shaped member 3 or a larger area than the facing area where the piezoelectric body 6 faces the acoustic matching layer 4. Since the ultrasonic signal generated by the piezoelectric body 6 propagates only in the ratio of the coupling area, the transmission efficiency is reduced and the transmission sensitivity of the ultrasonic wave is also reduced. Therefore, the area where the coupling area of the piezoelectric body 4, the plate member 3, and the acoustic matching layer 6 overlaps is the acoustically effective coupling area, and is the physical effective joining area.
[0032]
Next, a case where an ultrasonic signal is received will be considered.
[0033]
In the case of reception, the propagation process is the reverse of that in the case of transmission. That is, the ultrasonic signal received from the acoustic matching layer 4 is transmitted to the piezoelectric body 6 via the adhesive layer 30, the plate-like member 3, and the adhesive layer 31.
[0034]
(Consideration of propagation efficiency of reception between plate member and acoustic matching layer)
The ultrasonic signal received by the acoustic matching layer 4 is propagated to the plate-like member 3 via the adhesive layer 30 that joins the acoustic matching layer 4 and the plate-like member 3, so that the ultrasonic signal is transmitted to the plate-like member 3 as in the case of transmission. The joint area between the acoustic matching layer 3 and the acoustic matching layer 4 is equal to the area where the plate member 3 overlaps the acoustic matching layer 4 and the adhesive layer 30. Therefore, in order to efficiently transmit an ultrasonic signal from the acoustic matching layer 4 to the plate-like member 3, the plate-like member 3 needs to be larger than the bonding area of the plate-like member 3 and the acoustic matching layer 4 (the acoustic matching layer 4 has a plate-like shape). (The area facing the member 3 or more) is desirable.
[0035]
Further, the ultrasonic signal propagated to the plate member 3 is propagated to the piezoelectric body 6 via an adhesive layer 31 joining the plate member 3 and the piezoelectric body 6.
[0036]
(Consideration of the propagation efficiency of reception between the plate member and the piezoelectric body)
The bonding area between the plate member 3 and the piezoelectric body 6 matches the area where the plate member 3, the piezoelectric body 6, and the adhesive layer 31 overlap. Therefore, in order to efficiently transmit an ultrasonic signal from the plate-shaped member 3 to the piezoelectric body 6, the plate-shaped member 3 needs to be larger than the bonding area of the plate-shaped member 3 and the piezoelectric body 6 (the plate-shaped member 3 and the piezoelectric body 6). Is larger than the facing area of the facing).
[0037]
From the above, as in the case of transmission, the area where the bonding area of the piezoelectric body 6, the plate-shaped member 3, and the acoustic matching layer 4 overlaps is the acoustically effective coupling area or the physically effective coupling area.
[0038]
Therefore, the acoustic matching layer 4 needs to have a larger area than the bonding area between the piezoelectric body 6 and the plate-shaped member 3 or more than the area where the piezoelectric body 6 faces the acoustic matching layer 4 in the same manner as in the transmission. When the condition is smaller than the above condition, the ultrasonic signal generated by the piezoelectric body 6 propagates only in the ratio of the bonding area, so that the propagation efficiency is reduced and the receiving sensitivity of the ultrasonic wave is also reduced.
[0039]
Next, the adhesive layer 31 will be considered.
[0040]
The adhesive layer 31 that joins the piezoelectric body 6 and the plate-shaped member 3 has a role of not only physically joining the piezoelectric body 6 and the plate-shaped member 3 but also acoustically coupling them. The adhesive 31 is, for example, an epoxy-based thermosetting adhesive, and temporarily joins the piezoelectric body 6 and the plate-shaped member 3 in a viscous state, and is hardened by heat or the like, and is permanently joined. Then, after the adhesive layer 31 is cured for bonding, if the facing area facing the piezoelectric body 6 and the plate member 3 is smaller than the piezoelectric body 6, the ultrasonic signal generated from the piezoelectric body 6 is applied to the plate member 3. At the time of propagation, the bonding area between the piezoelectric body 6 and the plate-shaped member 3 is reduced, and the propagation efficiency is reduced. Therefore, the transmission sensitivity of the ultrasonic wave decreases.
[0041]
The adhesive of the adhesive layer 31 includes urethane-based, cyano-based, and silicone-based resin adhesives.
[0042]
On the other hand, in the reception in which the ultrasonic signal propagated from the acoustic matching layer 4 is propagated to the plate member 3 and propagated to the piezoelectric body 6 via the adhesive layer 31, the facing area facing the plate member 3 is the piezoelectric body. If it is smaller than 6, when the ultrasonic signal propagated to the plate-shaped member 3 is propagated to the piezoelectric body 6, the bonding area between the piezoelectric body 6 and the plate-shaped member 3 becomes small, and the propagation efficiency is reduced. As a result, the receiving sensitivity of the ultrasonic wave decreases.
[0043]
Therefore, the adhesive layer 31 that joins the plate member 3 and the piezoelectric body 6 has an area after curing of the adhesive layer 31 equal to or larger than the joint area between the piezoelectric body 6 and the plate member 3 (the piezoelectric body 6 faces the adhesive layer 31). ), It is possible to minimize the reduction in propagation efficiency.
[0044]
In addition, in terms of physical bonding, that is, from the viewpoint of adhesive strength, the area after curing of the adhesive layer 31 needs to be equal to or larger than the facing area where the piezoelectric body 6 faces the plate member 3. If the area of the adhesive layer 31 after curing is smaller than the area of the piezoelectric body 6 facing the plate-like member 3, the adhesive layer 31 does not wrap around the piezoelectric body 6 so as to wrap the piezoelectric body 6 outside. And the anchoring effect can hardly be expected, so that the adhesive strength decreases. Therefore, even after physical bonding, the area after curing of the adhesive layer 31 needs to be equal to or larger than the bonding area between the piezoelectric body 6 and the plate-shaped member 3 or equal to or larger than the facing area where the piezoelectric body 6 faces the adhesive layer 31. Therefore, the adhesive strength can be improved and the reliability can be improved.
[0045]
Similarly, the adhesive layer 30 that joins the acoustic matching layer 4 and the plate member 3 is also a thermosetting adhesive, and not only physically joins the acoustic matching layer 4 and the plate member 3 but also acoustically. Has the role of joining. Therefore, when the cured adhesive layer 30 has a smaller area facing the acoustic matching layer 4 and the plate-shaped member 3 than the acoustic matching layer 4 after the curing, the ultrasonic signal generated from the piezoelectric body 6 is converted to the plate-shaped member. 3. When transmitting from the plate-shaped member 3 to the acoustic matching layer 4, the bonding area between the plate-shaped member 3 and the acoustic matching layer 4 is reduced, so that the propagation efficiency is reduced and the transmission sensitivity of ultrasonic waves is reduced.
[0046]
On the other hand, when the ultrasonic signal is received by the acoustic matching layer 4 and then propagated from the acoustic matching layer 4 to the plate-like member 3, the reception transmitted to the plate-like member 3 through the adhesive layer 30 is performed by the adhesive layer 30. If the facing area facing the plate member 3 and the acoustic matching layer 4 is smaller than the acoustic matching layer 4 after curing, the ultrasonic signal propagated to the acoustic matching layer 4 The joint area between the matching layer 4 and the plate-shaped member 3 is reduced, and the propagation efficiency is reduced, so that the receiving sensitivity of the ultrasonic wave is reduced.
[0047]
Therefore, the area after curing of the adhesive layer 30 that joins the acoustic matching layer 4 and the plate-shaped member 3 is equal to or greater than the bonding area of the acoustic matching layer 4 or equal to or greater than the area where the acoustic matching layer 4 faces the adhesive layer 30. This makes it possible to minimize the reduction in propagation efficiency. Further, in terms of physical bonding, that is, in terms of the adhesive strength, the area after curing of the adhesive layer 30 needs to be equal to or larger than the facing area where the acoustic matching layer 4 faces the plate member 3. If the area after curing of the adhesive layer 30 is smaller than the area of the acoustic matching layer 4 facing the plate-like member 3, the adhesive layer 30 does not wrap around the acoustic matching layer 4 so as to be wrapped outside, so that it is substantially Since the bonding area is small and the anchor effect can hardly be expected, the adhesive strength is reduced. Therefore, even from physical bonding, the area after curing of the adhesive layer 30 needs to be equal to or greater than the bonding area of the acoustic matching layer 4 or equal to or greater than the area where the acoustic matching layer 4 faces the adhesive layer 30. Thus, the bonding strength can be improved and the reliability can be improved.
[0048]
Note that the relationship described in the first embodiment always holds regardless of the shape and size of the acoustic matching layer 4, the plate member 3, and the piezoelectric body 6.
[0049]
Also, as shown in FIGS. 5 and 6, the plate-shaped member 3 and the support 2 are not separately formed, but as shown in FIG. 5, the plate-shaped member and the support are integrally formed (for example, press molding). The same effect can be obtained in the second embodiment using the bottomed case 33 provided integrally (integrally formed) and the third embodiment in which the adhesive layer 31 is not present as shown in FIG.
[0050]
In the first embodiment, the occurrence of the abnormal resonance mode is suppressed by adjusting the position of each component of the ultrasonic transducer to an appropriate position, thereby improving the frequency.
[0051]
Specifically, the center between the case 32 and the piezoelectric body 6 is adjusted to an appropriate range, the center between the case 32 and the acoustic matching layer 4 is adjusted to an appropriate range, and the center between the piezoelectric body 6 and the acoustic matching layer 4 is adjusted appropriately. Adjusting the relationship between the amount of displacement of the piezoelectric body 4 and the thickness of the diaphragm, and the relationship between the amount of displacement of the acoustic matching layer 4 and the thickness of the diaphragm. There are two forms. These correspond to Examples 3 to 7 described later, respectively.
[0052]
First, the first mode includes a bottomed cylindrical case 32 and an acoustic matching layer 4 provided on at least one surface of the case 32, and is opposite to the surface 3a on which the acoustic matching layer 4 is provided. The ultrasonic vibrator 1 in which the piezoelectric body 6 is provided on the side surface 3b, wherein the piezoelectric body 6 is bonded to the case 32 with respect to the center of the top surface of the case 32 also serving as a diaphragm. When the amount of deviation of the center of the surface is Δα and the thickness of the diaphragm is t, the center of the top surface of the case 32 and the top of the piezoelectric body 6 are adjusted so that (Δα / t) ≦ 2. The center of the joining surface to be joined with the surface is aligned.
[0053]
According to the first aspect, the occurrence of the abnormal resonance mode can be prevented.
[0054]
Next, in the second mode, the amount of deviation of the center of the bonding surface where the acoustic matching layer 4 is bonded to the case 32 with respect to the center of the top surface of the case 32 also serving as a diaphragm is Δβ. When the thickness of the diaphragm is t, the center of the top surface of the case 32 and the center of the joining surface where the acoustic matching layer 4 is joined to the top surface of the case 32 so that (Δβ / t) ≦ 3 is satisfied. It is to match.
[0055]
According to the second aspect, it is possible to prevent the two ultrasonic transducers facing each other from being displaced in the axis, and to suppress a decrease in sensitivity.
[0056]
Next, the third mode satisfies (Δγ / t) ≦ (5/2), where Δγ is the amount of displacement between the piezoelectric body 6 and the acoustic matching layer 4 and t is the thickness of the diaphragm. As described above, the center of the bonding surface where the piezoelectric body 6 is bonded to the top surface of the case 32 and the center of the bonding surface where the acoustic matching layer 4 is bonded to the top surface of the case 32 are aligned.
[0057]
According to the third embodiment, it is possible to suppress a decrease in sensitivity.
[0058]
Next, in a fourth embodiment, in the ultrasonic vibrator 1 for performing measurement by repeating transmission and reception of ultrasonic waves alternately by the pair of ultrasonic vibrators 17 and 18, the top surface of the case 32 serving also as a diaphragm If the ultrasonic vibrators 17 and 18 have a displacement amount Δα ≦ 0.5 mm of the piezoelectric body 6 with respect to the center of the piezoelectric vibrator 6, the displacement amount of the piezoelectric body 4 used for the ultrasonic vibrators 17 and 18 is Δχ, respectively. When the thickness of the plate is t, it is configured to satisfy (Δ よ う / t) ≦ 2.
[0059]
According to the fourth aspect, it is possible to realize high measurement accuracy in which the phase shift and the abnormal resonance can be minimized by the frequency characteristics of the sensitivity and the impedance.
[0060]
Finally, the fifth mode is a top surface of the case 32, which also functions as a diaphragm, in the ultrasonic vibrator 1 that performs measurement by repeatedly transmitting and receiving ultrasonic waves alternately by the pair of ultrasonic vibrators 17, 18. Of the acoustic matching layer 4 with respect to the center of the ultrasonic transducers 17 and 18, the displacement of the acoustic matching layer 4 used for the ultrasonic transducers 17 and 18 is Δφ, When the thickness of the diaphragm is t, the diaphragm is configured to satisfy (Δφ / t) ≦ 3.
[0061]
According to the fifth aspect, it is possible to realize high measurement accuracy in which phase shift and abnormal resonance can be minimized by the frequency characteristics of sensitivity and impedance.
[0062]
Also, the flow rate measuring unit 11 having a flow path through which the fluid to be measured flows, and the ultrasonic vibrators 17 and 18 provided in the flow rate measuring unit 11 in any one of the above-described five forms are opposed to each other. The ultrasonic transducers 17 and 18 arranged with the flow path interposed therebetween, a measuring circuit 101 for measuring the propagation time of the ultrasonic wave passing through the flow path between the ultrasonic transducers 17 and 18, An ultrasonic flowmeter may be configured to include flow rate calculating means for calculating the flow rate of the fluid to be measured based on a signal indicating the result information measured by the measurement circuit 101.
[0063]
According to this ultrasonic flowmeter, various functions and effects of the above-described ultrasonic vibrator can be obtained.
[0064]
Here, as the material of the bottomed case 32, a metal material (stainless steel, aluminum, titanium, and an alloy containing them) is preferable. As a material of the acoustic matching layer 4, a combination of epoxy and hollow glass or an inorganic material (metal foam, nanoporous material) is preferable. Further, as a material of the piezoelectric body 6, PZT (piezo piezoelectric element) is preferable.
[0065]
When the bottomed case 32 is cylindrical, the size of the bottomed case 32 is preferably a diameter (φ5 mm to φ14 mm) × a height (5 mm to 14 mm). In the case where the bottomed case 32 is in the shape of a square tube, one side (5 mm to 14 mm) × height (5 mm to 14 mm) is preferable. However, the size of the flow path of the ultrasonic flow meter is 14.8 mm in height, 22 mm in width, and 31.4 mm in length, and the size is as described above in consideration of the used frequency band.
[0066]
The vibration mode of the piezoelectric body 6 utilizes thickness vibration, and when the thickness of the piezoelectric body 6 is T, the resonance frequency f is
[0067]
(Equation 1)

It becomes.
[0068]
Here, n = 1, 2, 3,..., Cij is an elastic constant, and ρ is density. Here, the reason why the thickness vibration is used is that the operating frequency (resonance frequency) can be controlled by the T (thickness) of the piezoelectric body 6, so that the frequency can be changed only by changing the thickness T, and the frequency can be widened. This is because the diameter of the ultrasonic flowmeter can be reduced and the diameter can be reduced.
[0069]
The thickness range of the case (diaphragm) 32 is preferably t = 0.1 to 0.5 mm. As shown in FIG. 7, if the thickness of the case (diaphragm) 32 is thin, the sensitivity of the ultrasonic flowmeter for transmitting and receiving ultrasonic waves increases, and if the thickness of the case (diaphragm) 32 is thick, the superposition of the ultrasonic flowmeter is increased. The sensitivity of transmission and reception of sound waves is reduced. When the thickness of the case (diaphragm) 32 is thin, the resonance frequency decreases, and when the thickness of the case (diaphragm) 32 is thick, the resonance frequency increases. The reason is that there is a trade-off between the transmission / reception sensitivity of the ultrasonic wave of the ultrasonic flowmeter and the thickness of the case (diaphragm) 32.
[0070]
Considering from the flow rate calculation system side of the ultrasonic flow meter, it is possible to correct the ultrasonic transmission / reception sensitivity as long as it falls within 25%. Therefore, the case thickness t is from 0.1 to 0.5 mm.
[0071]
The relationship between the thickness of the case (diaphragm) 32 and the misalignment between components constituting the ultrasonic flowmeter will be described.
[0072]
{Circle around (1)} The displacement depends not on the vector amount but on the absolute value (no dependence on the displacement direction: see FIG. 8). However, in FIG. 8 showing the relationship between the amount of displacement of the piezoelectric body and the correlation coefficient, the circle on the center has a correlation coefficient of 0.990, the outermost circle has a correlation coefficient of 0.960, The shift amount in the positive direction is rightward, and the shift amount in the negative direction is downward and leftward from the center.
[0073]
{Circle around (2)} As the thickness t of the case (diaphragm) 32 increases, the correlation coefficient tends to become less sensitive to the amount of displacement (see FIGS. 9 to 11). In FIG. 9, the correlation coefficient decreases as the positional shift amount Δα (mm) of the center of the piezoelectric body 6 with respect to the center of the top surface of the case 32 increases, and as the thickness t of the case (diaphragm) 32 increases. In the correlation coefficient, the degree of decrease in the amount of displacement is small. In FIG. 10, the correlation coefficient decreases as the positional deviation amount Δβ (mm) of the center of the acoustic matching layer 4 with respect to the center of the top surface of the case 32 increases, and the thickness t of the case (diaphragm) 32 decreases. As the thickness increases, the degree of decrease in the displacement amount of the correlation coefficient decreases. Further, in FIG. 11, the correlation coefficient decreases as the positional deviation amount Δγ (mm) of the center of the acoustic matching layer 4 with respect to the center of the piezoelectric body 6 increases, and the thickness t of the case (diaphragm) 32 increases. Accordingly, the degree of decrease in the amount of displacement of the correlation coefficient decreases.
[0074]
The correlation coefficient of the ultrasonic flowmeter capable of realizing the measurement accuracy of the measurement circuit 101 is 0.960 or more. Therefore, the range in which the correlation coefficient of the above graphs 2 to 4 can realize 0.960 or more is obtained by dividing the shift amount by the thickness t of the case (diaphragm) 32,
(Δα / t) <2, (Δβ / t) <3, Δγ <(5/2).
[0075]
The measurement accuracy and the frequency band used will be described.
[0076]
The required measurement accuracy is 3 liters / h for city gas (13A), 1 liter / h for LP gas, and 0.01 nsec (use frequency: 520 KHz) and 0.02 nsec (use (Frequency: 260 KHz) is feasible.
[0077]
Since the higher the frequency, the higher the resolution, the higher the resolution, the higher the frequency, the higher the frequency. However, the higher the frequency, the weaker the noise and the like. Therefore, a frequency of 200 kHz to 800 kHz is usually used.
[0078]
Although a current-type circuit is used as the measuring circuit 101, in the case of an ideal current-type circuit, the output current is received regardless of the impedance of the flow path and the ultrasonic flowmeter by short-circuiting the secondary side. It is the same even if the transmission is exchanged. However, it is necessary that the primary and secondary ultrasonic flowmeters have impedances as similar as possible.
[0079]
According to the above-described embodiment, the occurrence of the abnormal resonance mode is prevented by adjusting the position of each component (for example, the case 32, the piezoelectric body 6, and the acoustic matching layer 4) of the ultrasonic transducer 1 to an appropriate position. The frequency can be suppressed, and the frequency can be improved, and the measurement accuracy can be improved. Here, there is a correlation coefficient as an index indicating how similar the frequency characteristics of the impedance of the ultrasonic flowmeters are similar to each other. An ultrasonic flowmeter having a correlation coefficient in the range up to 0.960 is generally considered to be acceptable from the viewpoint of the flow rate calculation system. , The correlation coefficient can be reliably set in the range up to 0.960, and a highly reliable ultrasonic flowmeter can be provided.
[0080]
【Example】
Hereinafter, experimental considerations of the first embodiment and effects of the present invention will be described with reference to specific examples.
[0081]
(Example 1)
The stainless steel used for the case material was pressed at a thickness of t = 0.2 mm to form a case with a diameter of 11.8 mm and a height of 5.6 mm. At this time, the case top surface is φ11 mm. The size of the piezoelectric body is 7.4 mm × 7.4 mm, the height is 2.65 mm, the matching layer is φ10 mm, and the height is 1.15 mm. At this time, the matching layer and the top of the case are joined so that their centers match each other, and the center of the joining surface between the piezoelectric body and the case is slightly shifted from the center of the top of the case, and several types of ultrasonic flowmeters are used. It was created. The ultrasonic flowmeter serving as a reference is created by matching the centers of the matching layer, the case top surface, and the case joining surface of the piezoelectric body. A voltage of ± 5 V was applied to each ultrasonic flowmeter, and the frequency was changed from 100 KHz to 1 MHz, and the frequency characteristics of the impedance were measured. The correlation coefficient was determined by comparing the frequency band of 350 KHz to 750 KHz used as the ultrasonic flow meter with the reference ultrasonic flow meter. Here, the correlation coefficient indicates how similar the frequency characteristics of the impedance of the ultrasonic flowmeters are similar to each other. FIG. 8 shows the result. Each correlation coefficient was calculated in order to determine whether the correlation coefficient differs depending on the amount of displacement and its direction, that is, whether it should be viewed as a vector amount. As shown in FIG. 8, it has been found that it depends on the absolute amount of shift regardless of the direction of shift from the center.
[0082]
(Example 2)
It was examined how the transmission / reception sensitivity of the ultrasonic flowmeter changes with the thickness of the case (diaphragm). FIG. 7 shows the results of the study in which the thickness of the case (diaphragm) was changed to 0.2 mm, 0.3 mm, 0.8 mm, and 1.0 mm based on the case where the thickness of the case (diaphragm) was 0.1 mm. The case was pressed to form a case having a diameter of 11.8 mm and a height of 5.6 mm. At this time, the case top surface is φ11 mm. The size of the piezoelectric body is 7.4 mm × 7.4 mm and the height is 2.65 mm, and the matching layer is φ10 mm and the height is 1.15 mm. From the results, it was found that as the thickness of the case (diaphragm) increases, the transmission / reception sensitivity of the ultrasonic wave decreases in proportion.
[0083]
(Example 3)
The thickness of the stainless steel used for the case material was changed from t = 0.1 to 0.5 mm and pressed to form a case with a diameter of 11.8 mm and a height of 5.6 mm. At this time, the case top surface is φ11 mm. The size of the piezoelectric body is 7.4 mm × 7.4 mm, the height is 2.65 mm, the matching layer is φ10 mm, and the height is 1.15 mm. At this time, the matching layer and the top of the case are joined so that their centers match each other, and the center of the joining surface between the piezoelectric body and the case is slightly shifted from the center of the top of the case, and several types of ultrasonic flowmeters are used. It was created. The ultrasonic flowmeter serving as a reference is created by matching the centers of the matching layer, the case top surface, and the case joining surface of the piezoelectric body. A voltage of ± 5 V was applied to each ultrasonic flowmeter, and the frequency was changed from 100 KHz to 1 MHz, and the frequency characteristics of the impedance were measured. The correlation coefficient was determined by comparing 350 KHz to 750 KHz, which are frequency bands used as an ultrasonic flowmeter, with each other. Here, the correlation coefficient indicates how similar the frequency characteristics of the impedance of the ultrasonic flowmeters are similar to each other. The result is shown in FIG. Assuming that the shift amount is Δα, the value of the correlation coefficient decreases proportionally as the shift amount of the piezoelectric body from the center of the top surface of the case increases. However, when the thickness of the case top surface (diaphragm) was changed, the inclination tended to be steeper as the thickness was smaller. Since the ultrasonic flowmeter in the range up to 0.960 is accepted as the value of the correlation coefficient due to the balance with the flow rate calculation system, the case of focusing on the value of the correlation coefficient of 0.960 or more is considered as a case. It was found that there was a relationship of (Δα / t) ≦ 2 regardless of the thickness of the top surface. As described above, any ultrasonic flow meter that satisfies (Δα / t) ≦ 2 can be used as an ultrasonic flow meter that satisfies the same characteristics on the flow rate calculation system as the characteristics of the ultrasonic flow meter.
[0084]
(Example 4)
The thickness of the stainless steel used for the case material was changed from t = 0.1 to 0.5 mm and pressed to form a case with a diameter of 11.8 mm and a height of 5.6 mm. At this time, the case top surface is φ11 mm. The size of the piezoelectric body is 7.4 mm × 7.4 mm, the height is 2.65 mm, the matching layer is φ9.5 mm, and the height is 1.15 mm. At this time, the piezoelectric body and the top of the case are joined so that their centers coincide with each other, and the center of the joining surface between the matching layer and the case is slightly shifted from the center of the top of the case. It was created. The ultrasonic flowmeter serving as a reference is created by matching the centers of the matching layer, the case top surface, and the case joining surface of the piezoelectric body. A voltage of ± 5 V was applied to each ultrasonic flow meter, and the frequency was changed from 100 KHz to 1 MHz to measure the frequency characteristics of impedance. The correlation coefficient was determined by comparing 350 KHz to 750 KHz, which are frequency bands used as an ultrasonic flowmeter, with each other. Here, the correlation coefficient indicates how similar the frequency characteristics of the impedance of the ultrasonic flowmeters are similar to each other. The result is shown in FIG. Assuming that the shift amount is Δβ, as in the third embodiment, it can be seen that as the shift amount from the center of the case top surface of the matching layer increases, the value of the correlation coefficient decreases proportionally. However, when the thickness of the case top surface (diaphragm) was changed, the inclination tended to be steeper as the thickness was smaller. Since the ultrasonic flowmeter in the range up to 0.960 is accepted as the value of the correlation coefficient due to the balance with the flow rate calculation system, the case of focusing on the value of the correlation coefficient of 0.960 or more is considered as a case. It was found that there was a relationship of (Δβ / t) ≦ 3 regardless of the thickness of the top surface. As described above, any ultrasonic flow meter that satisfies (Δβ / t) ≦ 3 can be used as an ultrasonic flow meter that satisfies the same characteristics on the flow rate calculation system as the characteristics of the ultrasonic flow meter.
[0085]
(Example 5)
The thickness of the stainless steel used for the case material was changed from t = 0.1 to 0.5 mm, and the stainless steel was pressed to form a case having a diameter of 11.8 mm and a height of 5.6 mm. At this time, the case top surface is φ11 mm. The size of the piezoelectric body is 7.4 mm × 7.4 mm, the height is 2.65 mm, the matching layer is φ10 mm, and the height is 1.15 mm. At this time, several kinds of ultrasonic flowmeters were prepared by slightly shifting the piezoelectric body and the acoustic matching layer in directions opposite to each other with the center of the top surface of the case as an axis. The ultrasonic flowmeter serving as a reference is created by matching the centers of the matching layer, the case top surface, and the case joining surface of the piezoelectric body. A voltage of ± 5 V was applied to each ultrasonic flowmeter, and the frequency was changed from 100 KHz to 1 MHz, and the frequency characteristics of the impedance were measured. The correlation coefficient was determined by comparing 350 KHz to 750 KHz, which are frequency bands used as an ultrasonic flowmeter, with each other. Here, the correlation coefficient indicates how similar the frequency characteristics of the impedance of the ultrasonic flowmeters are similar to each other. The result is shown in FIG. Assuming that the shift amount of the center of the acoustic matching layer with respect to the center of the piezoelectric body is Δγ, the phase shift proportionally increases as the shift amount Δγ of the center of the acoustic matching layer with respect to the center of the piezoelectric body increases, as in the second and fourth embodiments. It was found that the number of relations decreased. As in the third and fourth embodiments, (Δγ / t) ≦ (5/2) is satisfied regardless of the thickness of the stainless steel (diaphragm) within the range of the correlation coefficient of 0.960 or more due to the balance with the flow rate calculation system. I understand. As described above, any ultrasonic flow meter that satisfies (Δγ / t) ≦ (5/2) can be used as an ultrasonic flow meter that satisfies the same characteristics on the flow rate calculation system as a characteristic of the ultrasonic flow meter. It is.
[0086]
(Example 6)
Based on the results of the third embodiment, when a pair of ultrasonic flowmeters is used in a flow calculation system that alternately repeats transmission and reception, based on the ultrasonic flowmeter in which the piezoelectric body is shifted from the center by a certain amount, The correlation coefficient was calculated by setting the displacement between the piezoelectric bodies of the ultrasonic flow meter and the other ultrasonic flow meter as Δχ. In addition, the pass / fail was determined based on whether the measurement accuracy could be guaranteed on the flow rate calculation system. The conditions were the same as in Example 3, where the thickness of the stainless steel used for the case material was changed from t = 0.1 to 0.5 mm and pressed to form a case with a diameter of φ11.8 mm and a height of 5.6 mm. did. At this time, the case top surface is φ11 mm. The size of the piezoelectric body is 7.4 mm × 7.4 mm, the height is 2.65 mm, the matching layer is φ10 mm, and the height is 1.15 mm. A voltage of ± 5 V was applied to each ultrasonic flowmeter, and the frequency was changed from 100 KHz to 1 MHz, and the frequency characteristics of the impedance were measured. The correlation coefficient was determined by comparing 350 KHz to 750 KHz, which are frequency bands used as an ultrasonic flowmeter, with each other. Here, the correlation coefficient indicates how similar the frequency characteristics of the impedance of the ultrasonic flowmeters are similar to each other. Table 1 shows the results. As a result of Table 1, if the deviation is within 0.5 mm from the center of the case with respect to the center of the case, the difference between the deviations of the respective ultrasonic flow meters is divided by the thickness t of the case (diaphragm). That is, it was found that (Δχ / t) ≦ 2.
[0087]
[Table 1]

[0088]
(Example 7)
When a pair of ultrasonic flowmeters are used in a flow calculation system that alternately transmits and receives ultrasonic waves based on the results of the second embodiment, the ultrasonic flowmeters whose acoustic matching layers are shifted from the center by a certain amount The correlation coefficient was calculated with Δ と し て as the deviation amount of the acoustic matching layer between the ultrasonic flowmeter and the other ultrasonic flowmeter based on the above. In addition, the pass / fail was determined based on whether the measurement accuracy could be guaranteed on the flow rate calculation system. The conditions were the same as in Example 2, except that the thickness of the stainless steel used for the case material was changed from t = 0.1 to 0.5 mm, and press working was performed to form a case with a diameter of 11.8 mm and a height of 5.6 mm. did. At this time, the case top surface is φ11 mm. The size of the piezoelectric body is 7.4 mm × 7.4 mm, the height is 2.65 mm, the matching layer is φ9.5 mm, and the height is 1.15 mm. A voltage of ± 5 V was applied to each ultrasonic flowmeter, and the frequency was changed from 100 KHz to 1 MHz, and the frequency characteristics of the impedance were measured. The correlation coefficient was determined by comparing 350 KHz to 750 KHz, which are frequency bands used as an ultrasonic flowmeter, with each other. Here, the correlation coefficient indicates how similar the frequency characteristics of the impedance of the ultrasonic flowmeters are similar to each other. Table 2 shows the results. As a result of Table 2, the difference between the displacements of the respective ultrasonic flowmeters was divided by the thickness t of the case (diaphragm) if the displacement was within 0.5 mm from the center of the case with respect to the center of the case. Value, that is, (Δφ / t) ≦ 3.
[0089]
[Table 2]

Note that by appropriately combining any of the various embodiments described above, the effects of the respective embodiments can be achieved.
[0090]
【The invention's effect】
According to the present invention, the position of each component (for example, the case, the piezoelectric body, and the acoustic matching layer) of the ultrasonic vibrator is adjusted so as to have a positional deviation amount within an appropriate range, whereby the abnormal resonance mode is achieved. Can be suppressed, the frequency can be improved, and the measurement accuracy can be improved. That is, the correlation coefficient, which indicates how similar the frequency characteristics of the impedance of the ultrasonic flowmeters are to each other, is generally acceptable if the ultrasonic flowmeter is in the range of 0.960 from the balance with the flow rate calculation system. Therefore, by adjusting the amount of misalignment so as to be within the above-described appropriate range, the correlation coefficient can be reliably set in the range up to 0.960, and a highly reliable ultrasonic flowmeter can be obtained. Can be provided.
[0091]
More specifically, in the ultrasonic vibrator according to the first aspect of the present invention, the ultrasonic vibrator has a piezoelectric body provided on a surface opposite to a surface provided with the acoustic matching layer, With respect to the center of the top surface of the case that also serves as the plate, the amount of deviation of the center of the joint surface where the piezoelectric body is joined to the case is Δα, and the thickness of the diaphragm is t, (Δα / t) If the center of the top surface of the case and the center of the joint surface where the piezoelectric body is joined to the top surface of the case are set to satisfy ≦ 2, occurrence of the abnormal resonance mode can be prevented.
[0092]
Further, in the ultrasonic vibrator according to the second aspect of the present invention, the ultrasonic vibrator in which a piezoelectric body is provided on a surface opposite to a surface on which the acoustic matching layer is provided, wherein the ultrasonic vibrator also serves as a diaphragm With respect to the center of the top surface of the case, when the amount of deviation of the center of the joining surface where the acoustic matching layer is joined to the case is Δβ, and when the thickness of the diaphragm is t, (Δβ / t) ≦ 3 If the center of the top surface of the case and the center of the joining surface where the acoustic matching layer is joined to the top surface of the case are aligned so as to satisfy, the axial displacement of the two facing ultrasonic transducers is prevented, Sensitivity reduction can be suppressed.
[0093]
In the ultrasonic vibrator according to the third aspect of the present invention, when a deviation amount of a center of the acoustic matching layer from a center of the piezoelectric body is Δγ and a thickness of the diaphragm is t, (Δγ / t) The center of the joining surface where the piezoelectric body is joined to the top surface of the case and the center of the joining surface where the acoustic matching layer is joined to the top surface of the case so as to satisfy ≦ (5/2). By doing so, it is possible to suppress a decrease in sensitivity.
[0094]
Further, in the ultrasonic vibrator according to the fourth aspect of the present invention, the ultrasonic vibrator has a piezoelectric body provided on a surface opposite to a surface provided with the acoustic matching layer, and comprises a pair of ultrasonic vibrators. In an ultrasonic vibrator that performs measurement by repeating transmission and reception of ultrasonic waves alternately with a vibrator, the ultrasonic vibration having a displacement Δα ≦ 0.5 mm of a piezoelectric body with respect to a center of a top surface of the case also serving as a vibration plate. If the piezoelectric element used in the ultrasonic vibrator is Δχ and the thickness of the vibrating plate is t, (Δχ / t) ≦ 2, sensitivity and impedance frequency It is possible to realize high measurement accuracy, which can minimize phase shift and abnormal resonance in characteristics.
[0095]
Further, in the ultrasonic vibrator according to the fifth aspect of the present invention, the ultrasonic vibrator has a piezoelectric body provided on a surface opposite to the surface provided with the acoustic matching layer. In an ultrasonic vibrator that performs measurement by repeating transmission and reception of ultrasonic waves alternately with a vibrator, an ultrasonic wave having a displacement Δβ ≦ 0.5 mm of an acoustic matching layer with respect to a center of a top surface of the case also serving as a diaphragm. In the case of a vibrator, sensitivity and impedance can be obtained by satisfying (Δφ / t) ≦ 3, where Δφ is the amount of displacement of the acoustic matching layer used in the ultrasonic vibrator and t is the thickness of the diaphragm. With the frequency characteristics described above, it is possible to minimize the phase shift and abnormal resonance, and realize high measurement accuracy.
[0096]
Further, as an ultrasonic flowmeter, a pair of a flow measurement unit having a flow path through which a fluid to be measured flows and the ultrasonic transducer according to any one of the first to fifth aspects provided in the flow measurement unit is provided as a pair. Ultrasonic transducers arranged opposite to each other with the flow path interposed therebetween, a measurement circuit for measuring the propagation time of the ultrasonic wave passing through the flow path between the ultrasonic transducers, and a measurement circuit By providing a flow rate calculating means for calculating the flow rate of the fluid to be measured based on the signal indicating the result information, it is possible to achieve the various effects of the ultrasonic transducer described above.
[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 according to the first embodiment.
FIG. 3 is a cross-sectional view of an ultrasonic flowmeter using the ultrasonic transducer according to the first embodiment.
FIG. 4 is a sectional view of the first ultrasonic flowmeter.
FIG. 5 is a sectional view of an ultrasonic transducer according to a second embodiment of the present invention.
FIG. 6 is a sectional view of an ultrasonic transducer according to a third embodiment of the present invention.
FIG. 7 is a graph showing a sensitivity reduction rate with respect to a thickness of a case (diaphragm).
FIG. 8 is a graph showing a relationship between a displacement amount of a piezoelectric body and a correlation coefficient.
FIG. 9 is a graph showing a displacement distribution of a piezoelectric body with respect to a center of a top surface of a case (diaphragm).
FIG. 10 is a graph showing a positional deviation amount distribution of an acoustic matching layer with respect to a center of a top surface of a case (diaphragm).
FIG. 11 is a graph showing a positional deviation amount distribution of the acoustic matching layer with respect to the center of the piezoelectric body.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ultrasonic vibrator, 2 ... Support body, 3 ... Plate member, 4 ... Sound matching layer, 5 ... Flange part, 6 ... Piezoelectric body, 7 ... Terminal plate, 8a, 8b ... Terminal, 9 ... Insulator, DESCRIPTION OF SYMBOLS 10 ... Conductive rubber, 11 ... Flow measurement part, 12 ... Side wall part, 13 ... Side wall part, 14 ... Sealing material, 15 ... Upper plate part, 16 ... Cross section of a flow path, 17 ... Ultrasonic vibrator, 18 ... Ultrasonic wave Vibrator, 19: vibrator mounting hole, 20: vibrator mounting hole, 21: sealing material, 22: sealing material, 30: adhesive layer, 31: adhesive layer, 32: bottomed case, 100: ultrasonic flow meter .., 100a entrance path, 100b exit path, 101 measurement circuit, 102 flow rate calculation means.

Claims (6)

A bottomed cylindrical case (32), and an acoustic matching layer (4) provided on at least one surface of the case;
An ultrasonic vibrator (1) in which a piezoelectric body (6) is provided on a surface opposite to a surface on which the acoustic matching layer is provided, wherein: When the amount of deviation of the center of the joint surface where the piezoelectric body is joined to the case is Δα, and the thickness of the diaphragm is t, the center of the top surface of the case is set to satisfy (Δα / t) ≦ 2. An ultrasonic vibrator wherein the center of a bonding surface where the piezoelectric body is bonded to a top surface of the case is aligned. A bottomed cylindrical case (32), and an acoustic matching layer (4) provided on at least one surface of the case;
An ultrasonic vibrator (1) in which a piezoelectric body (6) is provided on a surface opposite to a surface on which the acoustic matching layer is provided, wherein: When the shift amount of the center of the joining surface where the acoustic matching layer is joined to the case is Δβ, and the thickness of the diaphragm is t, the center of the top surface of the case satisfies (Δβ / t) ≦ 3. And a center of a joint surface where the acoustic matching layer is joined to a top surface of the case. A bottomed cylindrical case (32); and an acoustic matching layer (4) provided on at least one surface of the case, and a piezoelectric body (6) provided on a surface opposite to the surface provided with the acoustic matching layer. , Where Δγ is the amount of deviation of the center of the acoustic matching layer from the center of the piezoelectric body and t is the thickness of the diaphragm, and (Δγ / t) ≦ The center of the bonding surface where the piezoelectric body is bonded to the top surface of the case and the center of the bonding surface where the acoustic matching layer is bonded to the top surface of the case so as to satisfy (5/2). An ultrasonic vibrator characterized in that: A bottomed cylindrical case (32), and an acoustic matching layer (4) provided on at least one surface of the case;
An ultrasonic vibrator (1) in which a piezoelectric body (6) is provided on a surface opposite to a surface on which the acoustic matching layer is provided, and a pair of ultrasonic vibrators alternately transmits and receives ultrasonic waves. In an ultrasonic transducer that repeatedly performs measurement, if the ultrasonic transducer has a displacement amount Δα ≦ 0.5 mm of the piezoelectric body with respect to the center of the top surface of the case also serving as the vibration plate, each of the ultrasonic transducers An ultrasonic vibrator characterized by satisfying (Δχ / t) ≦ 2, where Δ ず れ is a displacement amount of a piezoelectric body used and t is a thickness of the diaphragm. A bottomed cylindrical case (32), and an acoustic matching layer (4) provided on at least one surface of the case;
An ultrasonic vibrator (1) in which a piezoelectric body (6) is provided on a surface opposite to a surface on which the acoustic matching layer is provided, and a pair of ultrasonic vibrators alternately transmits and receives ultrasonic waves. In the ultrasonic vibrator which repeatedly performs measurement, if the ultrasonic vibrator satisfies a deviation amount Δβ ≦ 0.5 mm of the acoustic matching layer with respect to the center of the top surface of the case also serving as the vibrating plate, each ultrasonic vibrator An ultrasonic vibrator characterized by satisfying (Δφ / t) ≦ 3, where Δφ is the amount of displacement of the acoustic matching layer used and Δ is the thickness of the diaphragm. A flow measuring unit (11) having a flow path through which the fluid to be measured flows;
An ultrasonic vibrator (17, 18), which is provided in the flow rate measuring unit, and which is disposed so as to oppose the ultrasonic vibrator according to any one of claims 1 to 5 with the flow path interposed therebetween.
A measuring circuit (101) for measuring a propagation time of an ultrasonic wave passing through the flow path between the ultrasonic transducers;
An ultrasonic flowmeter comprising: a flow rate calculating means (102) for calculating a flow rate of the fluid to be measured based on a signal indicating result information measured by the measurement circuit.

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