JP4249546B2 - Ultrasonic flow meter and control method thereof - Google Patents

Description

【００１７】
これらの式から流速Ｖは以下の式で表される。
【００１８】
【数２】

【００１９】
流体の流速Ｖが求まれば、流路１３における流体の進行方向に垂直な断面積と流速Ｖとの積から流量Ｑが求まる。
【００２０】
流体の流れが理想的である場合、上述した方法により、流体の流量を正しく求めることができる。しかし、実際の流量計測において、流体は粘性を有するため、流体の壁面近傍では流速が小さくなり、流路を流れる流体の流速は流路１３の断面において一定ではなくなる。
【００２１】
図１８は、超音波振動子１および超音波振動子２間を伝播する超音波の伝播方向（以下超音波伝播方向と呼ぶ）および流体の移動方向（以下、流体移動方向と呼ぶ）に対して平行な面（ｙ-ｚ面）における流路１３を流れる流体の速度分布を模式的に示している。流路１３に一様の速度で流体３５が流入する場合、流路１３の壁面において流体３５の速度はゼロとなるが、壁面から離れると、速度は著しく大きくなる。このため、速度勾配の非常に大きな境界層と呼ばれる領域が壁面に沿って形成される。流入直後では、境界層は壁面近傍にのみ存在するため、流体は矢印で表される速度分布３６を持つ。境界層は流体の移動に伴って流路１３の中心に向かって発達する。境界層が流路１３の中心まで達すると、流体は矢印３７で示される速度分布を持ち、速度分布３７は一定となる。流体の速度分布が一定となるまでの距離は助走距離と呼ばれ、流体の速度分布が安定した位置において超音波振動子１および２の伝播経路が形成されるよう、超音波振動子１および２は配置される。
【００２２】
このとき、図１８に示すように、超音波の伝播経路は流路１３の全体を横切る。このため、超音波振動子１および２によって計測される流速は、矢印で表される速度分布３７の平均の値となり、流体の速度分布の全体を反映し、ほぼ正確な流速が求めることができる。
【００２３】
図１８の矢印で示される速度分布３７は、図１９（ａ）に示すように、流体移動方向に平行であり、図１８に示す面と直行する面（ｘ−ｙ面）においても同様に生じている。図に示すように超音波伝播方向と直交する方向（ｘ方向）において、超音波の伝播路の幅Ｌ１より流路１３の幅Ｌ２のほうが大きい場合、計測のための超音波が伝播しない領域１３ａが生じる。つまり、領域１３ａを流れる流体は流量の計測に寄与しない。このような場合には、速度分布３７を仮定し、速度分布３７に基づいて、計測により求められる流速から領域１３ａの流速を推定して、流路１３を移動する流体の流量を求める。具体的には、計測値と実際の流量とを整合させるための補正係数を導入し、計測値に補正係数をかけ合わせたものを用いて流量を求める。
【００２４】
補正係数は、速度分布３７に依存する。このため、流量によって速度分布３７が変化する場合には、流量ごとに補正係数を求めておく必要がある。また、補正係数は流路１３の形状に依存するため、器差をなくすために、流路１３ごとに補正係数を用意する必要がある。
【００２５】
このような問題を解決するため、特許文献１は、図１９（ｂ）に示すように、超音波伝播方向と直交する方向（ｘ方向）において、超音波の伝播路の幅Ｌ１を流路１３の幅Ｌ２と等しくした流路１３’を用いることを開示している。この流路１３’はｘ方向の幅がｚ方向の幅に比べて小さくなった扁平形状を備える。流路１３’によれば、超音波振動子１および２の間に形成される超音波の伝播経路はｚ−ｙ平面においてもｘ−ｙ平面においても流路１３を完全に横切るため、流体に流速分布がある場合でも、流速分布の全体を反映した計測が可能となる。このため、流速分布が変化しても、正しく流量を求めることが可能となる。また助走期間を短くすることができ、また、超音波流量計の外形を小さくすることが可能となる。
【００２６】
【特許文献１】
特開平８−２３３６２８号公報
【非特許文献１】
日本電気計測器工業会規格、ＪＥＭＩＳ ５０３２「超音波による流量測定法」（社）日本電気計測工業会、１９８７年
【００２７】
【発明が解決しようとする課題】
しかしながら、特許文献１に示す流路１３’を用いても、なお、超音波流量計により計測した流量と実際に流路１３’を移動する流体の流量は完全には一致しない。本願発明者の検討によれば、超音波振動子１、２の送受波面における受信感度はその位置により変化し、送受波面の周辺部に比べて中心部における受信感度が高くなっている。図１９（ｂ）に示すように、流速分布３７をもつ流体が流れる場合、中央付近の流速３７ａを持つ部分が、壁面に近い流速３７ｂの流速を持つ部分に比べて高い感度で計測される。このため、超音波の伝播経路が流路１３を完全に横切っていても流速分布３７の真の平均流速を求めることができず、計測誤差が生じでしまう。
【００２８】
本発明はこのような従来の超音波流量計の問題を解決し、精度の高い計測を行うことができる超音波流量計およびガスメータを提供することを目的とする。また、本発明は、そのような超音波流量計を制御する方法を提供することを目的とする。
【００２９】
【課題を解決するための手段】
本発明の超音波流量計は、超音波を送信し、流体の流路中に前記超音波が伝播する経路を形成するよう配置される第１の超音波振動子と、対向する第１および第２の主面を有する圧電体、前記第１の主面にそれぞれ設けられた複数の分割電極、ならびに、前記第２の主面に設けられた共通電極を有する圧電素子を含み、前記第１の超音波振動子から送信される超音波を受信するように配置される第２の超音波振動子と、前記共通電極と前記複数の分割電極とによってそれぞれ受信した複数の受信信号を異なる割合で増幅または減衰させる信号強度変換部と、前記信号強度変換部により変換された複数の受信信号を加算する加算部とを備え、前記加算部で得られた信号に基づいて流路を移動する流体の流量を計測する。
【００３０】
ある好ましい実施形態において、前記複数の分割電極は、前記第１の主面の中心からの距離に対応して規定される複数の領域にそれぞれ設けられている。
【００３１】
ある好ましい実施形態において、前記信号強度変換部は、前記複数の受信信号をそれぞれ異なる増幅率で増幅する複数の増幅部を含む。
【００３２】
ある好ましい実施形態において、前記信号強度変換部は、前記複数の受信信号をそれぞれ異なる増幅率で増幅する複数の増幅部を含み、前記分割電極の位置が前記第１の主面の中心から離れるにつれて、前記分割電極から得られる受信信号を増幅する増幅率が大きくなっている。
【００３３】
ある好ましい実施形態において、前記複数の増幅部は、オートゲインコントロールを備える。
【００３４】
ある好ましい実施形態において、前記信号強度変換部は、前記複数の受信信号のうち少なくとも１つを減衰させる減衰部を含む。
【００３５】
ある好ましい実施形態において、前記信号強度変換部は、前記複数の受信信号を異なる減衰率で減衰させる少なくとも２つの減衰部を含み、前記分割電極の位置が前記第１の主面の中心から離れるにつれて、前記分割電極から得られる受信信号を減衰させる減衰率が小さくなっている。
【００３６】
ある好ましい実施形態において、超音波流量計は、前記加算部で得られた信号を増幅する増幅部をさらに備える。
【００３７】
ある好ましい実施形態において、前記超音波の伝播経路における前記超音波の伝播方向と直交する方向の流路の最大幅は、その方向における前記第１または第２の超音波振動子の送受波面の幅より小さいかまたはほぼ等しくなっている。
【００３８】
ある好ましい実施形態において、前記信号強度変換部は、前記複数の分割電極の単位面積あたりの受信信号の強度が互いに等しくなるよう前記複数の受信信号を増幅または減衰する。
【００３９】
また、本発明の超音波流量計は、対向する第１および第２の主面を有する圧電体、前記第１の主面に設けられた複数の分割電極、ならびに、前記第２の主面に設けられた共通電極を有する圧電素子をそれぞれ含む第１および第２の超音波振動子と、前記第１または第２の超音波振動子の前記共通電極と前記複数の分割電極とによってそれぞれ受信した複数の受信信号を異なる割合で増幅または減衰させる信号強度変換部と、前記第１または第２の超音波振動子の前記共通電極と前記複数の分割電極との間にそれぞれ駆動電圧を印加する送信部と、前記第１の超音波振動子および前記第２の超音波振動子を前記信号強度変換部および前記送信部と選択的に接続する切り替え部と、前記信号強度変換部により変換された複数の受信信号を加算する加算部とを備え、前記第１および第２の超音波振動子間で超音波が双方向に伝播する経路を流体の流路中に形成するように配置し、前記加算部で得られた信号に基づいて超音波の双方向の伝播時間を求め、前記伝播時間の差に基づいて前記流体の流量を求める。
【００４０】
ある好ましい実施形態において、前記送信部は、前記第１または第２の超音波振動子の前記圧電体に均一な駆動電圧が印加されるよう、前記共通電極と前記複数の分割電極との間に駆動信号を印加する。
【００４１】
本発明のガスメータは、ガスが流れる流路に設けられた上記いずれかの超音波流量計と、前記流路を流れるガスを遮断する遮断弁とを備える。
【００４２】
本発明の超音波流量計の制御方法は、第１の超音波振動子と、対向する第１および第２の主面を有する圧電体、前記第１の主面にそれぞれ設けられた複数の分割電極、ならびに、前記第２の主面に設けられた共通電極を有する圧電素子を含む第２の超音波振動子とを用いて流体の流量を計測する、超音波流量計の制御方法であって、流体の流路中に超音波が伝播する経路を形成するよう第１の超音波振動子から第２の超音波振動子に向けて超音波を送信するステップ（Ａ）と、前記第２の超音波振動子の前記共通電極と前記複数の分割電極とによってそれぞれ受信される複数の受信信号を異なる割合で増幅または減衰させるステップ（Ｂ）と、前記複数の受信信号を加算するステップ（Ｃ）と、前記加算により得られた信号に基づいて前記流路を移動する流体の流量を求めるステップ（Ｄ）とを包含する。
【００４３】
ある好ましい実施形態において、前記複数の分割電極は、前記第１の主面の中心からの距離に対応して規定される複数の領域にそれぞれ設けられており、前記ステップ（Ｂ）において、前記分割電極の位置が前記第１の主面の中心から離れるにつれて、前記分割電極から得られる受信信号を増幅する増幅率が大きくなるよう、前記複数の信号を増幅する。
【００４４】
ある好ましい実施形態において、前記複数の分割電極は、前記第１の主面の中心からの距離に対応して規定される複数の領域にそれぞれ設けられており、前記ステップ（Ｂ）において、前記分割電極の位置が前記第１の主面の中心から離れるにつれて、前記分割電極から得られる受信信号を減衰させる減衰率が小さくなるよう、前記複数の受信信号を減衰させる。
【００４５】
ある好ましい実施形態において、前記ステップ（Ｂ）において、前記複数の分割電極の単位面積あたりの受信信号の強度が互いに等しくなるよう前記複数の受信信号を増幅または減衰する。
【００４６】
また本発明の超音波流量計の制御方法は、対向する第１および第２の主面を有する圧電体、前記第１の主面に設けられた複数の分割電極、ならびに、前記第２の主面に設けられた共通電極を有する圧電素子をそれぞれ含む第１および第２の超音波振動子を用いて流体の流量を計測する超音波流量計の制御方法であって、前記第１または第２の超音波振動子の前記圧電体に均一な駆動電圧が印加されるよう、前記共通電極と前記複数の分割電極との間にそれぞれ駆動信号を印加することにより、流体の流路中に超音波が伝播する経路を形成するよう第１または第２の超音波振動子から第２または第１の超音波振動子に向けて超音波を送信するステップ（Ａ）と、前記第２または第２の超音波振動子の前記共通電極と前記複数の分割電極とによってそれぞれ受信される複数の受信信号を異なる割合で増幅または減衰させるステップ（Ｂ）と、前記複数の受信信号を加算するステップ（Ｃ）と、前記加算により得られた信号に基づいて前記流路を移動する流体の流量を求めるステップ（Ｄ）とを包含する。
【００４７】
また、本発明のコンピュータ読み取り可能な記録媒体は、上記いずれかの超音波流量計の制御方法に規定した各ステップをコンピュータに実行させるためのプログラムを記録している。
【００４８】
【発明の実施の形態】
（第１の実施形態）
まず、図１および図２を参照しながら、本発明による超音波流量計の第１の実施形態で用いる超音波振動子４１を説明する。超音波振動子４１は、圧電素子４２と圧電素子４２を収納するケース４３を含む。図２に示すように、圧電素子４２は、対向する第１の主面４４ａおよび第２の主面４４ｂを備えた圧電体４４と、共通電極４５と、分割電極４６、４７、４８とを有する。本実施形態では、第１の主面４４ａおよび第２の主面４４ｂはたとえば、円形を有しており、共通電極４５は、第２の主面４４ｂのほぼ全体を覆うように形成されている。一方、分割電極４６、４７、４８は、第１の主面の中心４４ｃからの距離に応じて確定された３つの領域にそれぞれ形成されている。具体的には、分割電極４６は３つの分割電極４６、４７、４８のうち、最も中心に近い領域に形成されており、分割電極４８は最も外周側に形成されている。図２に示すように本実施形態では、分割電極４６は円形を有し、分割電極４７、４８はリング状に形成されている。これらの分割電極の中心は中心４４ｃと一致する。
【００４９】
図１に示すように、圧電素子４２は、共通電極４５がケース４３の面４３ａの内側に接触するようにケース４３に収納されており、ケース４３が作る空間４３ｃは封止されている。共通電極４５および分割電極４６、４７、４８には配線４９、５０、５１、５２が接続され、ケース４３の外部へ引き出されている。空間４３ｃには窒素などの不活性ガスが充填されている。
【００５０】
面４３ａを介して流体と圧電素子４２との間で効率よく超音波の伝達が行えるよう、一層もしくは二層以上の複合層からなる音響整合層５３を面４３ａの外側に設けてもよい。また、ケース４３が導電性を備えている場合には、共通電極４５を省略し、圧電体４４の第２の主面４４ｂを直接ケース４３の面４３ａに接合し、ケース４３に配線４９を接続してもよい。
【００５１】
以下において詳述するように、圧電素子４２において、第２の主面４４ｂに形成される電極は３つの分割電極４６、４７、４８に分割されている。これは、超音波振動子４１を用いて超音波を受信する際、超音波を受ける領域を複数に分割し、分割した領域ごとに受信した信号の増幅率を異ならせるためである。一方、超音波振動子４１を用いて超音波を送信する場合には、圧電体４４に均一な駆動電圧が印加されるよう共通電極４５と分割電極４６、４７、４８との間に駆動信号を印加する。これにより、圧電体４４の形状で定まる振動モードで圧電素子４２を振動させることができる。
【００５２】
次に、本発明による超音波流量計の第１の実施形態の構造を説明する。図３は流路７３に設けられた超音波流量計６１の構成を示すブロック図である。図４は、流路７３近傍の断面を拡大して示している。超音波流量計６１は、流体の流路７３中に超音波が双方向に伝搬する経路を形成するように配置される第１の超音波振動子７１および第２の超音波振動子７２を備えている。第１の超音波振動子７１および第２の超音波振動子７２はそれぞれの送受波面が互いに平行となり、送受波面の中心が同一線上に位置するよう配置されている。
【００５３】
第１の超音波振動子７１および第２の超音波振動子７２は、それぞれが送信器および受信器として機能する。第１の超音波振動子７１から送信された超音波は第２の超音波振動子６２により受信され、第２の超音波振動子７２から送信された超音波は第１の超音波振動子７１により受信する。これら双方向の伝搬路は、流路７３を流れる流体の流れる方向３５に対して角度θをなしている。角度θの大きさは、１０〜４０度の範囲内から選択される。
【００５４】
図４に示すように、超音波の伝播経路における前記超音波の伝播方向と直交する方向（ｘ方向）の流路の最大幅Ｌ２は、その方向における前記第１または第２の超音波振動子の送受波面の幅Ｌ１より小さいかまたはほぼ等しくなっている。このため、超音波の伝播経路はｚ−ｙ平面においてもｘ−ｙ平面においても流路７３を完全に横切る。
【００５５】
第１の超音波振動子７１および第２の超音波振動子７２には、図１および図２に示した超音波振動子４１を用いる。たとえば、第１の超音波振動子７１および第２の超音波振動子７２は、厚み振動モード、横すべり振動モード、縦振動モード等の振動モードにより、おおよそ２０ｋＨｚ以上の周波数で駆動される。測定すべき流体の状態や種類、また予想される流速に応じて最適な周波数が適宜選択される。本実施形態では、たとえば、厚み振動モードで振動し、５００ｋＨｚの共振周波数をもつ超音波振動子が用いられる。
【００５６】
超音波流量計６１は、切り替え部７４、送信部３、信号強度変換部７５、および加算部７６をさらに備える。切り替え部７４は、送信部３および信号強度変換部７５を選択的に第１の超音波振動子７１および第２の超音波振動子７２に接続する。送信部３と第１の超音波振動子７１とが接続される場合には、信号強度変換部７５と第２の超音波振動子７２とが接続され、送信部３と第２の超音波振動子７２とが接続される場合には、信号強度変換部７５と第１の超音波振動子７１とが接続される。
【００５７】
送信部３は、第１の超音波振動子７１および第２の超音波振動子７２の３つの分割電極４６、４７、４８へそれぞれ独立した信号を印加することができるよう、３本の配線により切り替え部７４と接続される。信号強度変換部７５も３つの分割電極４６、４７、４８からそれぞれ独立した信号を受け取ることができるよう、３本の配線により切り替え部７４と接続される。送信部３から分割電極４６、４７、４８に印加される駆動信号は、圧電体４４に印加される駆動電圧が均一になるよう設定されている。
【００５８】
切り替え部７４が、送信部３と第１の超音波振動子７１および第２の超音波振動子７２の分割電極４６、４７、４８のそれぞれと共通に接続するように構成されている場合には、送信部３と切り替え部７４とは１本の配線により接続されていてもよい。この場合には、送信部３から出力される駆動信号が、分割電極４６、４７、４８に共通に印加される。
【００５９】
信号強度変換部７５は、第１の増幅部７５ａ、第２の増幅部７５ｂおよび第３の増幅部７５ｃを含み、切り替え部７４を介して、第１の増幅部７５ａ、第２の増幅部７５ｂおよび第３の増幅部７５ｃは、分割電極４６、４７、４８にそれぞれ接続される。第１の増幅部７５ａ、第２の増幅部７５ｂおよび第３の増幅部７５ｃは、分割電極４６、４７、４８と共通電極４５とによってそれぞれ受信した受信信号を異なる割合で増幅する。具体的には、第３の増幅部７５ｃの増幅率が一番大きく、第１の増幅部７５ａが一番小さくなっている。第２の増幅部７５ｂの増幅率は、第３の増幅部７５ｃの増幅率と第１の増幅部５３ａの増幅率との間の値になっている。つまり、分割電極の位置が第１の主面の中心から離れるにつれて分割電極から得られる受信信号を増幅する増幅率は大きくなっている。増幅率の具体的な設定値については以下において詳述する。第１の増幅部７５ａ、第２の増幅部７５ｂおよび第３の増幅部７５ｃにおいて増幅された受信信号は加算部７６において加算される。
【００６０】
超音波流量計６１は、加算部７６で得られた受信信号に基づいて流体の流量を求める。たとえば、従来と同様、受信信号をゼロクロス検知法により検知し、シングアラウンド法によって超音波の伝播時間を累積することによって計測精度を向上させて超音波の伝播時間を計測する。具体的には、超音波流量計６１は、ピークホールド部６、レベル検知部７、ゼロクロス検知部８、遅延部９、繰り返し部１０、計時部１１、および流量算出部１２をさらに備える。図１７を参照して説明すると、加算部７６によって加算された受信信号３０は、ゼロクロス検知部８とピークホールド部６とへ送られる。ピークホールド部６は、受信信号３０のピーク値を保持しその値をピークホールド信号３１として出力を生成する。レベル検知部７は、ピークホールド信号３１が所定のレベル３２に達したことを検知し、ゼロクロス指令信号３３を生成する。ゼロクロス検知部７は、ゼロクロス指令信号３３が生成された直後におけるゼロクロスポイントを検知し、ゼロクロス検知信号３４を遅延部９へ出力する。このゼロクロスポイントを受信信号の伝播時間とし、この時点で受信信号を検知したとする。ゼロクロス検知信号３４はピークホールド部６にも入力される。ピークホールド部６は、ゼロクロス検知信号に基づいてピークホールド信号３１をリセットする。
【００６１】
遅延部９は、ゼロクロス検知信号３４に基づいて、所定の時間遅らせたタイミングで出力信号を生成する。繰り返し部１０は、遅延部９の出力信号をカウントし、所定回数以下であれば遅延部９の出力信号をトリガ信号として送信部３へ出力する。送信部３は、トリガ信号に基づいて、第１の超音波振動子７１または第２の超音波振動子７２を駆動する。
【００６２】
計時部１１は、所定の回数だけシングアラウンドを繰り返すのに要した時間を計測し、測定結果を流量算出部１２へ送る。流量算出部１２は、計時部１１から出力されるシングアラウンドを繰り返すのに要した時間に関するデータ、遅延時間およびシングアラウンド回数から、流速および流量を求める。
【００６３】
上述の各部は、電子部品等を用いたハードウエアにより構成することもソフトウエアにより構成することもできる。超音波流量計６１は、これら各部を制御するマイコン７７を備えている。
【００６４】
次に、信号強度変換部７５の各増幅部における増幅率について説明する。
【００６５】
図５は、超音波流量計６１の第１の超音波振動子７１および第２の超音波振動子７２間に形成される超音波の伝播経路付近における流体の流速分布と、超音波の信号強度分布を模式的に示している。図５に示すように、流路７３を流れる流体のｘ−ｙ平面における流量の分布は矢印３７で示すようになっており、流路７３を構成する壁面近傍３７ａ、３７ｃの流速は中央近傍３７ｂに比べて小さくなっている。
【００６６】
一方、一般に超音波が圧電素子から送信される場合、送信位置に近い近距離音場では、その信号は周波数に依存する複雑な強度分布を示すが、所定距離を伝播すると、強度分布が一定となる。流体の流量を測定する場合には、誤差が少なく、安定して計測を行うことができるように、伝播する超音波の強度分布が一定となる距離を隔てて超音波の送受信が行われる。たとえば第１の超音波振動子７１から送信した超音波が第２の超音波振動子７２に到達する際には、図５中、Ｉで示される強度分布を持つ。このため、第２の超音波振動子７２が受信する超音波のうち、流体３７の流速が大きい中央部近傍３７ｃを通過した成分は信号強度が強く、流体３７の流速が小さい壁面近傍３７ａおよび３７ｂを通過した成分は信号強度が弱い。このような受信信号を超音波の信号強度Ｉを考慮せずに増幅した場合、相対的に信号強度が強い流体３７の流速が大きい中央部近傍３７ｃの影響がより大きくなり、相対的に信号強度が弱い流体３７の流速が小さい壁面近傍３７ａ、３７ｂの影響がより小さくなる。つまり、流体３７の流速が大きい中央部近傍３７ｃの影響を過大に評価することとなり、平均の流量あるいは流路７３を移動する流量が真の値よりも大きくなってしまう。
【００６７】
超音波流量計６１はこの問題を解決するため、受信した超音波信号の強度分布を補正するように受信信号を増幅する。図６は、第１の超音波振動子７１および第２の超音波振動子７２の圧電振動子の半径方向の位置に対する、受信信号の強度、信号強度変換部７３の各増幅部の増幅率および増幅後の受信信号の強度を示している。図６において、横軸は、圧電振動子の第１の主面の一端から半径方向における距離を示している。第１の主面の中心４４ｃは横軸の中央に位置している。図に示すように、横軸中央付近に分割電極４６が形成されて領域が位置し、分割電極４６の外側に分割電極４７および分割電極４８が形成された領域がそれぞれ位置する。
【００６８】
図６の上部に示すように、受信する超音波の信号は第１の主面の中心４４ｃを通り第１の主面に対して垂直な線に対して回転対称となる強度分布を持つのに対して、分割電極４６、４７、４８は、第１の主面の中心４４ｃを中心として同心円状に配置されている。このため、各分割電極で受ける超音波の信号の強度分布は全体を１つの電極で受信する場合に比べて小さくなっている。
【００６９】
各分割電極で受信した信号を増幅する場合の増幅率は、図６の中央部に示すように設定する。具体的には、受信信号の信号強度がもっとも強い成分を受ける分割電極４６による受信信号を増幅する増幅率ａ１を小さくし、受信信号の信号強度がもっとも弱い成分を受ける分割電極４８による受信信号を増幅する増幅率ａ３を大きくする。分割電極４７による受信信号を増幅する増幅率はａ１とａ３の間の値に設定する。
【００７０】
このように、１つの電極で受ける受信信号の信号強度の分布を小さくし、電極ごとに増幅率を変化させることによって、図６の下部に示すように、増幅後の受信信号の強度分布は増幅前に比べて小さくなる。増幅前の受信信号の最大および最小の強度をそれぞれＩ_maxおよびＩ_minとし、増幅後の受信信号の最大および最小の強度をそれぞれＩ’_maxおよびＩ’_minとした場合、少なくともＩ_max／Ｉ_min＞Ｉ’_max／Ｉ’_minであり、好ましくは、１≦Ｉ’_max／Ｉ’_min≦２を満たすことが好ましい。より好ましくは、図６の下部において、破線で示すように各分割電極による受信信号の平均の信号強度がおおよそ一致するよう、増幅率ａ１、ａ２、ａ３が定められている。受信信号の強度分布は送信部３から出力する駆動信号が一定である限り、ほとんど変化しないため、一度、増幅率ａ１、ａ２、ａ３を決定すれば、測定ごとにこれらの値を調整する必要はない。しかし、超音波流量計７１を設置する環境（温度など）が大きく変化し、受信信号の強度分布に変化が生じる場合には、第１の増幅部７５ａ、第２の増幅部７５ｂおよび第３の増幅部７５ｃにそれぞれオートゲインコントロールを設け、増幅後の受信信号が上述の関係を満たすように増幅率ａ１、ａ２、ａ３を自動調整してもよい。
【００７１】
このように、受信した超音波の信号強度の分布が小さくなるよう信号強度変換部７５における各増幅部の増幅率を分割電極ごとに異ならせることにより、流体中の流速が遅い部分の流速を正しく評価することができる。このため、流路７３を移動する流体に速度分布が生じている場合や、速度分布が流量によって変化する場合でも、速度分布を反映した正確な平均の流速を求めることが可能となる。
【００７２】
本実施形態で用いる第１の超音波振動子７１および第２の超音波振動子７２の圧電素子は３つの分割電極を備えているが、図６の上部に示すように、受信する超音波信号の強度分布が大きい場合には、３つ以上に分割された電極を用いて信号を検出し、それぞれ異なる増幅率で信号を増幅してもよい。
【００７３】
各増幅部において異なる増幅率で増幅された信号は加算部７６において加算される。加算部７６から出力される受信信号は、従来の超音波流量計における受信信号と同様に扱うことができる。
【００７４】
次に、超音波流量計６１を用いて流体の流量を計測する手順を説明する。以下に説明する手順はマイコン７７により、各構成要素を順次制御することによって行われ、その手順をコンピュータに実行させるためのプログラムが、ＲＯＭやＲＡＭ、ハードディスク、磁気記録媒体などの情報記録媒体に保存されている。
【００７５】
図３に示すように、切り替え部７４を用いて、送信部３を第１の超音波振動子７１へ接続し、信号強度変換部３５を第２の超音波振動子７２に接続する。
【００７６】
図７に示すように、トリガ信号７８を送信部３に入力し、駆動信号を生成させ、第１の超音波振動子７１から超音波を発生させる。このとき、第１の超音波振動子７１の圧電体全体に均一な電圧が印加されるよう分割電極４６、４７、４８に印加する駆動信号が設定される。上述したように、分割電極４６、４７、４８が共通に送信部３と接続されるようにしてもよい。
【００７７】
流路７３を横切って第２の超音波振動子７２に到達した超音波は、共通電極４５と分割電極４６、４７、４８とを用いてそれぞれ受信され、信号強度変換部７５によって上述したように分割電極ごとに異なる増幅率で増幅される。信号強度変換部７５から出力される増幅された各受信信号は、加算部７６によって加算され、図７に示す受信信号７９となる。
【００７８】
加算部７６の出力である受信信号７９は、ピークホールド部６およびゼロクロス検知部８へ入力され、受信信号７９が所定のレベルを超えた直後のゼロクロスポイントがゼロクロス検知部８で検知される。遅延部９は、ゼロクロス検知部８から出力されるゼロクロス検知信号に基づいて、所定の遅延時間８０を経た後に、送信部３へトリガ信号７８’を出力する。これにより、シングアラウンドの１ループを構成する。所定の回数（例えば５０〜１０００回）、シングアラウンドを繰り返した後、計時部１１は、ループを繰り返すのに要した全時間８１を計測し、測定結果を流量算出部１２へ送る。流量算出部において、全時間８１をシングアラウンド回数で除し、その値から遅延時間８０を引いた値が、式（１）に示すｔ１となる。
【００７９】
次に、切り替え部７４を用いて、送信部３を第２の超音波振動子７２へ接続し、信号強度変換部７５を第１の超音波振動子７１へ接続する。そして上述の手順と同様の手順により、第２の超音波振動子７２から超音波を発生させ、第１の超音波振動子７１で超音波を受信する。所定の回数、シングアラウンドを繰り返した後、計時部１１では、ループを繰り返すのに要した全時間８１を計測し、測定結果を流量算出部１２へ送る。流量算出部において、全時間８１をシングアラウンド回数で除し、その値から遅延時間８０を引いた値が、式（１）に示すｔ２となる。
【００８０】
式（２）に、ｔ１およびｔ２の値と角度θを代入することによって、流体の流速Ｖが求まる。さらに流路７３の断面積をＳとすれば、流量ＱはＶ×Ｓによって求めることができる。この流量Ｑは、単位時間あたりに流量が移動する量であり、流量Ｑを積分することによって流体の量を求めることができる。
【００８１】
このように本実施形態によれば、受信側超音波振動子の圧電振動子の電極を分割し、到達する超音波信号のうち信号強度が弱くなる部分に対応する電極によって検出される信号をより大きな増幅度で増幅する。このため、受信信号の強度分布が小さくなるよう補償して受信信号を増幅することができ、流体に流速分布が生じている場合でも、分布が生じている流速のいずれの成分の寄与も正しく評価した真の平均流速を求めることが可能となる。したがって、流体の流速分布がある場合でも、正確に流量を計測できる超音波流量計が実現する。
【００８２】
また、本実施形態の超音波流量計によれば、流体に流速分布があっても、真の平均流速を求めることができるため、流量を補正するための流量係数を用いる必要がなく、さらに、流量の変動により、流速分布が変化しても、流量係数を用いることなく正確な平均流速および流量を求めることができる。
【００８３】
（第２の実施形態）
本発明による超音波流量計の第２の実施形態の構造を説明する。図８は流路７３に設けられた超音波流量計６２の構成を示すブロック図である。図８において第１の実施形態と同じ構成要素には同じ参照符号を付している。超音波流量計６２は、第１の実施形態の信号強度変換部７５に換えて信号強度変換部８２を備え、信号強度変換部８２によって強度が変換された各受信信号を加算部７６で加算した後、増幅部８３において加算された受信信号を増幅する点で、第１の実施形態の超音波流量計６１とは異なる。
【００８４】
図８に示すように、信号強度変換部８２は、第１の減衰部８２ａおよび第２の減衰部８２ｂを含む。切り替え部７２によって信号強度変換部８２が受信側の超音波振動子として用いられる第１の超音波振動子７１または第２の超音波振動子７２と接続された場合、第１の減衰部８２ａおよび第２の減衰部８２ｂは図１および図２に示す圧電素子４１の分割電極４６および分割電極４７とそれぞれ電気的に接続される。第１の減衰部８２ａおよび第２の減衰部８２ｂは、分割電極４６、４７と共通電極４５とによってそれぞれ受信した受信信号を異なる割合で減衰させる。具体的には、第１の減衰部８２ａの減衰率は第２の減衰部８２ｂの減衰率より大きくなっている。分割電極４８と共通電極４５とによって受信した受信信号は減衰されることなく加算部７６へ入力される。このため、分割電極の位置が第１の主面の中心から離れるにつれて分割電極から得られる受信信号を減衰させる減衰率は小さくなっている。
【００８５】
信号強度変換部８２は、受信した超音波信号の強度分布を補正するように受信信号を減衰させる。図９は、第１の実施形態と同様、第１の超音波振動子７１および第２の超音波振動子７２の圧電振動子の半径方向の位置に対する、受信信号の強度、信号強度変換部７３の各増幅部の増幅率および増幅後の受信信号の強度を示している。
【００８６】
図９の上部に示すように、受信する超音波の信号強度が分布している場合、図９の中央部に示すように、分割電極によって受信信号を減衰させる減衰部の減衰率を変化させる。受信信号の信号強度がもっとも強い成分を受ける分割電極４６による受信信号を減衰させる減衰率ｄ１を大きくし、次に受信信号の信号強度が強い部分を受ける分割電極４７による受信信号を減衰させる減衰率ｄ２を小さくする。受信信号の信号強度がもっとも弱い部分を受ける分割電極４８による受信信号は減衰させない。
【００８７】
このように減衰率を変化させることによって、図９の下部に示すように、減衰後の受信信号の強度分布は減衰前に比べて小さくなる。第１の実施形態と同様、減衰前の受信信号の最大および最小の強度をそれぞれＩｍａｘおよびＩｍｉｎとし、減衰後の受信信号の最大および最小の強度をそれぞれＩ’ｍａｘおよびＩ’ｍｉｎとした場合、少なくともＩｍａｘ／Ｉｍｉｎ＞Ｉ’ｍａｘ／Ｉ’ｍｉｎであり、好ましくは、１≦Ｉ’ｍａｘ／Ｉ’ｍｉｎ≦２を満たすことが好ましい。より好ましくは、図９の下部において、破線で示すように各分割電極による受信信号の平均の信号強度がおおよそ一致するよう、減衰率ｄ１、ｄ２が定められている。受信信号の強度分布は送信部３から出力する駆動信号が一定である限り、ほとんど変化しないため、一度、減衰率ｄ１、ｄ２、ａ３を決定すれば、測定ごとにこれらの値を調整する必要はない。しかし、第１の実施形態で説明したように、第１の減衰部８２ａおよび第２の増幅部８２ｂにそれぞれオートアッテネートコントロールを設け、減衰後の受信信号が上述の関係を満たすように減衰率ｄ１、ｄ２、を自動調整してもよい。
【００８８】
信号強度変換部８２によって強度が変換された各受信信号を加算部７６で加算した後、増幅部８３において加算された受信信号は、第１の実施形態と同様にしてゼロクロス検知部８により検知され、流速が求められる。
【００８９】
本実施形態によれば、受信側超音波振動子の圧電振動子の電極を分割し、到達する超音波信号のうち信号強度が大きくなる部分に対応する電極によって検出される信号をより大きな減衰率でいったん減衰させる。その後、分割した電極によりそれぞれ受信された信号を加算することにより、信号強度の分布が小さくなるよう信号の強度分布が補償された受信信号が得られる。この受信信号を増幅して、超音波の伝播時間を求めることにより、受信信号を増幅することができ、流体に流速分布が生じている場合でも、分布が生じている流速のいずれの成分の寄与も正しく評価した真の平均流速を求めることが可能となる。したがって、流体の流速分布がある場合でも、正確に流量を計測できる超音波流量計が実現する。
（第５の実施形態）
以下、本発明の超音波流量計を備えたガスメータを説明する。
【００９０】
図１０は、配管９０内を流れるガスの流量を計測するためのガスメータ６３のブロック図を示している。配管９０内を流れるガスは、天然ガスやプロパンガスなど一般家庭で用いられるもののほか、水素や酸素等、その他の気体であってもよい。
【００９１】
ガスメータ６３は、配管９０内を流れるガスの流量を計測するための超音波流量計９１と、緊急時に配管９０を流れるガスを遮断する遮断弁９２と、超音波流量計９１および遮断弁９２を制御するマイコン９３と、超音波流量計６３を用いて計測した流量や流量の積算値およびその他の情報を表示する表示部９４とを備える。超音波流量計９１には、第１および第２の実施形態の超音波流量計を用いることができる。マイコン９３は超音波流量計９１のマイコン（図３等のマイコン７７）を用いてもよい。図に示すように、ガスメータ６３は、ガス会社などへ計測した流量に関するデータを送信したり、ガス会社からガスメータ６３を制御するための通信ユニット９５を備えていてもよい。
【００９２】
マイコン９３は超音波流量計６３によって計測される流量に関するデータを表示部９４に表示するとともに、計測する流量に異常がないかを監視する。例えば、突然、大流量のガスが流れ始めた場合には、ガス漏れが生じていると判断して、遮断弁９２を動作させ、ガスの供給を停止する。
【００９３】
第１のおよび第２の実施形態で説明したように超音波流量計６３は、流体に流速分布が生じている場合でも、分布が生じている流速のいずれの成分の寄与も正しく評価した真の平均流速を求めることができる。このため、ガスメータ６３によれば、気温の変化等によって配管９０を流れるガスの流速分布が大きく変化することがあっても、高い精度で流量を計測することが可能である。
【００９４】
本発明は上記各実施形態で説明した超音波流量計およびガスメータに限定されるものではなく、各実施形態で説明した超音波流量計およびガスメータに種々の改変を加えてもよい。具体的には上記各実施形態で用いる超音波振動子の圧電素子は円柱状の圧電体と同心円により分割される分割電極を備えていたが圧電素子は他の構造を備えていてもよい。たとえば図１１に示す圧電素子１４２は、正方形の共通電極１４５と、圧電体１４４と、分割電極１４６、１４７とを備える。圧電体１４４は、複数の溝１４４ｅおよび溝１４４ｄによって分割され、マトリクス状に配置された複数の圧電部１４４ａを含む。各圧電部１４４ａの第１の主面１４４ａ側に分割電極１４４、１４７が設けられ、第２の主面１４４ｂ側には共通電極１４５が設けられている。溝１４４ｅおよび溝１４４ｄの位置および数は圧電体１４４の振動モード、不要な振動モードの影響、取り扱いの容易性などを考慮して決定される。
【００９５】
分割電極１４６は中央の４つの圧電部１４４ａの第１の主面１４４ａを覆うように設けられ、分割電極１４７は、その周囲に設けられた圧電部１４４ａの第１の主面１４４ａを覆うように設けられている。
【００９６】
圧電素子１４２を有する超音波振動子を用いて超音波の送受信を行う場合、分割電極１４７の領域の受信信号の強度は分割電極１４６の領域の受信信号の強度に比べて小さくなる。このため、分割電極１４７による受信信号を増幅する場合の増幅度を分割電極１４６の場合に比べて大きくすることによって、受信信号の強度分布を小さくすることができる。圧電素子１４２によれば、外形が正方形であるため、複数の圧電素子１４２を母基板から一度に複数製造することが可能となる。このため圧電素子１４２は量産性に優れ、製造コストを低減することができる。また、溝１４４ｅおよび溝１４４ｄによって圧電体１４４を分割することにより、不要な振動モードを減少させることができる。
【００９７】
また、図１２に示す圧電体素子１４２’を有する超音波振動子を本発明の超音波流量計に採用してもよい。圧電素子１４２’の圧電体１４４’は、図１１に示す圧電素子１４２の圧電体１４４において、矢印Ｄで示す四隅の圧電部１４４ａが取り去られている。四隅に圧電部が形成されていないため、分割電極１４６の外側には４つに分断された分割電極１４７ａが形成される。圧電体素子１４２’を有する超音波振動子を用いる場合には、４つの分割電極１４７ａを他の配線などにおり共通に接続することが好ましい。
【００９８】
また、図１３に示す圧電体素子２４２を有する超音波振動子を本発明の超音波流量計に採用してもよい。圧電体素子２４２は、正方形の共通電極２４５と、圧電体２４４と、分割電極２４６、２４７とを備える。圧電体２４４の第１の主面２４４ａには互いに平行な複数の溝２４４ｄが設けられており、溝２４４ｄは第２の主面２４４ｂには達していない。このため、圧電体２４４をひとつの部品として取り扱うことが可能であり、圧電体２４４の取り扱いが容易になる。第１の主面２４４ａには分割電極分割電極２４６、２４７が設けられており、第２の主面２４４ｂには共通電極２４５が設けられている。
【００９９】
また、図１４に示すように、上記各実施形態において、超音波流量計を設ける流路７３を規定する壁面に拡散板９６を設けてもよい。拡散板９６は、送信側の超音波振動子から送信された超音波が壁面にあたる場合に、壁面で反射した超音波が受信側の超音波振動子に入射しないよう、超音波を拡散させる。このような拡散板を設けることにより、送信側の超音波振動子から受信側の超音波振動子へ到達する超音波は壁面において反射せず、直接流路を横切って伝播するものだけとなり、より高い精度で流体の流速および流量を計測することが可能となる。
【０１００】
第１の実施形態の信号強度変換部は、増幅部のみを含み、第２の実施形態の信号強度変換部は減衰部のみを含んでいたが、超音波振動子に到達する超音波の信号強度分布が小さくなるよう、信号を変換することができる限り、信号強度変換部は増幅部および減衰部を含んでいてもよい。
【０１０１】
上記第１から第３の実施形態では第１の超音波振動子および第２の超音波振動子を用いて双方向に超音波を伝播させ、その伝播時間差により、流体の流速および流量を求めていた。しかし、式（１）から明らかなように、流体中の超音波の音速Ｃがわかっている場合には、第１の超音波振動子から第２の超音波振動子への伝播時間ｔ１または第２の超音波振動子から第１の超音波振動子への伝播時間ｔ２を計測することにより、流体の流速Ｖを求めることができる。つまり、第１から第５の実施形態において、第１の超音波振動子および第２の超音波振動子間の一方向の超音波の伝播時間を計測することにより、流体の流速および流量を求めもよい。
【０１０２】
また、本発明によれば、流路に生じた流速分布全体を正しく評価した平均流速および流量を求めることができるため、計測値と真の値との差異を補正するための流量係数を用いる必要はない。しかし、流路が特殊な形状をしていたり、流速が著しく変化する場合には、本発明の流量計を用いた上で、必要に応じて流量係数を設定してもよい。
【０１０３】
また、上記各実施形態では、流路を移動する流体が層流となっている場合を例示しているが、流体が乱流となっていても、同様に高い精度で流速および流量を求めることができる。流体が乱流になっている場合、流体中の速度分布は均一となる。このため、分割電極の１つで検出した受信信号のみを用いても、流体の流速および流量を正確に求めることができる。たとえば、図１および図２に示す分割電極４６と共通電極４５とを用いて検出される受信信号のみを用い、流体の流速および流量を求めてもよい。
【０１０４】
【発明の効果】
本発明によれば、受信した超音波の信号強度の分布が小さくなるよう信号強度変換部における各増幅部の増幅率を分割電極ごとに異ならせることにより、流体中の流速が遅い部分の流速を正しく評価することができる。このため、流路を移動する流体に速度分布が生じている場合や、速度分布が流量によって変化する場合でも、速度分布を反映した正確な平均の流速を求めることが可能となる。
【０１０５】
したがって、流体に速度分布が生じていたり、速度分布が変化する場合であっても高い制度で流量を求めることのできる超音波流量計およびガスメータが得られる。
【図面の簡単な説明】
【図１】本発明による超音波流量計の第１の実施形態で用いる超音波振動子４１の断面図である。
【図２】図１に示す超音波振動子の圧電素子を示す斜視図である。
【図３】本発明による超音波流量計の第１の実施形態を示すブロック図である。
【図４】図３に示す超音波流量計が設けられる流路の断面を示す模式図である。
【図５】図４に示す領域における流体の流速分布と超音波の信号強度分布との関係を示す図である。
【図６】図３に示す超音波流量計において、受信信号の強度分布、各分割電極で受信した信号を増幅するときの増幅率および増幅後の受信信号を説明する図である。
【図７】シングアラウンド法による流量の計測を説明する図である。
【図８】本発明による超音波流量計の第２の実施形態を示すブロック図である。
【図９】図８に示す超音波流量計において、受信信号の強度分布、各分割電極で受信した信号を増幅するときの増幅率および増幅後の受信信号を説明する図である。
【図１０】本発明によるガスメータの実施形態を示すブロック図である。
【図１１】本発明で用いる超音波振動子に用いられる圧電素子の他の形態を示す斜視図である。
【図１２】本発明で用いる超音波振動子に用いられる圧電素子の他の形態を示す斜視図である。
【図１３】本発明で用いる超音波振動子に用いられる圧電素子の他の形態を示す斜視図である。
【図１４】本発明の超音波流量計を設置する流路に拡散板を設ける例を示す図である。
【図１５】従来の超音波流量計を示すブロック図である。
【図１６】従来の超音波流量計に用いられる超音波振動子の構造を示す断面図である。
【図１７】ゼロクロス検知法による受信信号の検知を説明する図である。
【図１８】流路を移動する流体の流速分布を説明する図である。
【図１９】（ａ）および（ｂ）は、従来の超音波流量計が設けられた流路の断面を示す模式図である。
【符号の説明】
１、２、４１ 超音波振動子
３ 送信部
４ 受信部
５、７４ 切り替え部
６ ピークホールド部
７ レベル検知部
８ ゼロクロス検知部
９ 遅延部
１０ 繰り返し部
１１ 計時部
１２ 流量算出部
１３、７３ 流路
４２ 圧電振動子
４３ ケース
４４ 圧電体
４５ 共通電極
４６、４７、４８ 分割電極
６１、６２ 超音波流量計
６３ ガスメータ
７１ 第１の超音波振動子
７２ 第２の超音波振動子
７５、８２ 信号強度変換部
７６ 加算部
７７ マイコン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic flowmeter and a gas meter that measure the flow rate of a fluid using ultrasonic waves.
[0002]
[Prior art]
The ultrasonic flow meter has features such as a simple structure, a small number of mechanically movable parts, a wide range in which the flow rate can be measured, and no pressure loss due to the flow meter. In addition, recent advances in electronics technology have made it possible to improve the measurement accuracy of ultrasonic flowmeters. For this reason, studies using ultrasonic flowmeters have been made in various fields that require measurement of gas and liquid flow rates, including gas meters.
[0003]
Hereinafter, the structure and measurement principle of a conventional ultrasonic flowmeter will be described. FIG. 15 is a block diagram showing an example of a conventional ultrasonic flowmeter. The ultrasonic flow meter shown in FIG. 15 is disclosed in Non-Patent Document 1, for example. As shown in FIG. 15, the ultrasonic transducers 1 and 2 are arranged so as to sandwich the flow path 13 through which the fluid flows. The ultrasonic transducers 1 and 2 function as a transmitter and a receiver, respectively. Specifically, when the ultrasonic transducer 1 is used as a transmitter, the ultrasonic transducer 2 is used as a receiver, and when the ultrasonic transducer 2 is used as a transmitter, the ultrasonic transducer 1 is a receiver. Used as As shown in FIG. 15, the propagation path of the ultrasonic wave formed between the ultrasonic vibrators 1 and 2 is inclined by an angle θ with respect to the fluid flow direction.
[0004]
FIG. 16 schematically shows the structure of the ultrasonic transducer 20 used for the ultrasonic transducers 1 and 2. The ultrasonic transducer 20 includes a piezoelectric element 21 and a case 25, and the piezoelectric element 21 is accommodated in the case 25. An inert gas is sealed in the case 25. The piezoelectric element 21 has a piezoelectric body 26 having first and second main surfaces and a pair of electrodes 22 and 23 provided on the entire first and second main surfaces, respectively. Wirings 27 and 28 are connected to the electrodes 22 and 23, respectively, and are drawn out of the case 25. The piezoelectric element 21 is attached to the surface 25 a of the case 25 so that the electrode 22 contacts the inner surface of the case 25.
[0005]
By applying a voltage to the piezoelectric body 26 through the wirings 27 and 28 and the electrodes 22 and 23, the piezoelectric body 26 vibrates at a wavelength in the ultrasonic region, and ultrasonic waves are emitted through the case 25. When the surface 25 a of the case 25 receives ultrasonic waves, the piezoelectric body 26 vibrates, and an electromotive force corresponding to the vibration is generated between the electrodes 22 and 23.
[0006]
An acoustic matching layer 24 composed of one layer or two or more composite layers may be provided so that ultrasonic waves can be efficiently transmitted between the surface 25a and the fluid.
[0007]
When the ultrasonic wave is propagated from the ultrasonic vibrator 1 to the ultrasonic vibrator 2, the ultrasonic wave travels in the forward direction with respect to the fluid flow, and thus the speed is increased. On the other hand, when an ultrasonic wave is propagated from the ultrasonic transducer 2 to the ultrasonic transducer 1, the ultrasonic wave travels in the opposite direction to the fluid flow, and therefore the velocity is slow. Accordingly, the velocity of the fluid is obtained from the difference between the time for the ultrasonic wave to propagate from the ultrasonic vibrator 1 to the ultrasonic vibrator 2 and the time for the ultrasonic wave to propagate from the ultrasonic vibrator 2 to the ultrasonic vibrator 1. Can do. Further, the flow rate can be obtained from the product of the cross-sectional area of the flow path 13 and the flow velocity.
[0008]
As a specific method for obtaining the fluid flow rate in accordance with this principle, a measurement method based on the single-around method will be specifically described.
[0009]
As shown in FIG. 15, the ultrasonic flowmeter includes a transmission unit 3 and a reception unit 4, and the ultrasonic transducer 1 is selectively connected to one of the transmission unit 3 or the reception unit 4 by a switching unit 5. At this time, the ultrasonic transducer 2 is connected to the other of the transmission unit 3 or the reception unit 4 to which the ultrasonic transducer 1 is not connected.
[0010]
When the transmission unit 3 and the ultrasonic transducer 1 are connected, the transmission unit 3 drives the ultrasonic transducer 1, and the generated ultrasonic wave reaches the ultrasonic transducer 2 across the flow of the fluid. The ultrasonic wave received by the ultrasonic transducer 2 is converted into an electric signal, and the received signal is amplified by the receiving unit 4.
[0011]
FIG. 17 shows an example of zero cross detection in a conventional ultrasonic flowmeter. The peak hold unit 6 generates a peak hold signal 31 from the received signal 30. The level detection unit 7 detects that the peak hold signal 31 has reached a predetermined level 32 and generates a detection signal 33. The zero cross detection unit 8 detects a zero cross point immediately after the detection signal 33 is generated, and generates a zero cross detection signal 34. The zero cross point is a point where the amplitude of the received signal changes from positive to negative or from negative to positive. This zero cross point is the time when the ultrasonic wave reaches the ultrasonic vibrator 2. Based on the zero-crossing detection signal 34, a trigger signal is generated at a timing delayed by a predetermined time by the delay unit 9, and it is determined whether or not to repeat the signal by the repetition unit 10. If it is repeated, it is input to the transmission unit 3. The time from the generation of the zero cross detection signal 34 to the generation of the trigger signal is called a delay time.
[0012]
The transmission unit 3 drives the ultrasonic transducer 1 based on the trigger signal to generate the next ultrasonic wave. Repeating the ultrasonic transmission-reception-amplification / delay-transmission loop in this manner is called sing around, and the number of loops is called the number of sing around.
[0013]
The timer 11 measures the time required to repeat the loop a predetermined number of times, and sends the measurement result to the flow rate calculator 12. Next, the switching unit 5 is switched to perform measurement in the same manner using the ultrasonic transducer 2 as a transmitter and the ultrasonic transducer 1 as a receiver.
[0014]
A value obtained by subtracting a value obtained by multiplying the delay time and the number of sing-around times from the time measured by the above-described method, and further dividing the value by the number of sing-around times is the ultrasonic wave propagation time.
[0015]
The propagation time when the ultrasonic transducer 1 is on the transmission side is t1, and the propagation time when the ultrasonic transducer 2 is on the transmission side is t2. Further, as shown in FIG. 15, the distance between the ultrasonic transducer 1 and the ultrasonic transducer 2 is L, and the fluid flow velocity and the ultrasonic sound velocity are V and C, respectively. At this time, t1 and t2 are expressed by the following equations.
[0016]
[Expression 1]

[0017]
From these equations, the flow velocity V is expressed by the following equation.
[0018]
[Expression 2]

[0019]
If the flow velocity V of the fluid is obtained, the flow rate Q is obtained from the product of the cross-sectional area perpendicular to the fluid traveling direction in the flow path 13 and the flow velocity V.
[0020]
When the flow of the fluid is ideal, the flow rate of the fluid can be correctly obtained by the method described above. However, in actual flow measurement, since the fluid has viscosity, the flow velocity decreases near the wall surface of the fluid, and the flow velocity of the fluid flowing through the flow path is not constant in the cross section of the flow path 13.
[0021]
FIG. 18 shows the propagation direction of ultrasonic waves (hereinafter referred to as ultrasonic propagation direction) and the movement direction of fluid (hereinafter referred to as fluid movement direction) propagating between the ultrasonic transducer 1 and the ultrasonic transducer 2. The velocity distribution of the fluid which flows through the flow path 13 in a parallel surface (yz plane) is typically shown. When the fluid 35 flows into the flow path 13 at a uniform speed, the speed of the fluid 35 becomes zero on the wall surface of the flow path 13, but the speed increases remarkably as it moves away from the wall surface. For this reason, a region called a boundary layer having a very large velocity gradient is formed along the wall surface. Immediately after the inflow, since the boundary layer exists only in the vicinity of the wall surface, the fluid has a velocity distribution 36 represented by an arrow. The boundary layer develops toward the center of the flow path 13 as the fluid moves. When the boundary layer reaches the center of the flow path 13, the fluid has a velocity distribution indicated by an arrow 37, and the velocity distribution 37 becomes constant. The distance until the fluid velocity distribution becomes constant is called the run-up distance, and the ultrasound transducers 1 and 2 are formed so that the propagation paths of the ultrasound transducers 1 and 2 are formed at positions where the fluid velocity distribution is stable. Is placed.
[0022]
At this time, as shown in FIG. 18, the propagation path of the ultrasonic wave crosses the entire flow path 13. For this reason, the flow velocity measured by the ultrasonic transducers 1 and 2 is an average value of the velocity distribution 37 represented by the arrow, and reflects the entire velocity distribution of the fluid, and an almost accurate flow velocity can be obtained. .
[0023]
As shown in FIG. 19A, the velocity distribution 37 indicated by the arrow in FIG. 18 is parallel to the fluid movement direction, and similarly occurs on the plane (xy plane) perpendicular to the plane shown in FIG. ing. As shown in the figure, in the direction orthogonal to the ultrasonic propagation direction (x direction), when the width L2 of the flow path 13 is larger than the width L1 of the ultrasonic propagation path, the ultrasonic wave for measurement does not propagate in the region 13a. Occurs. That is, the fluid flowing through the region 13a does not contribute to the flow rate measurement. In such a case, the velocity distribution 37 is assumed, and based on the velocity distribution 37, the flow velocity of the region 13a is estimated from the flow velocity obtained by measurement, and the flow rate of the fluid moving through the flow path 13 is obtained. Specifically, a correction coefficient for matching the measured value with the actual flow rate is introduced, and the flow rate is obtained using a product obtained by multiplying the measured value by the correction coefficient.
[0024]
The correction coefficient depends on the speed distribution 37. For this reason, when the speed distribution 37 changes according to the flow rate, it is necessary to obtain a correction coefficient for each flow rate. Further, since the correction coefficient depends on the shape of the flow path 13, it is necessary to prepare a correction coefficient for each flow path 13 in order to eliminate instrumental errors.
[0025]
In order to solve such a problem, as shown in FIG. 19 (b), Patent Document 1 sets the width L1 of the ultrasonic propagation path to the flow path 13 in the direction orthogonal to the ultrasonic propagation direction (x direction). The use of a flow path 13 ′ that is equal to the width L 2 is disclosed. This flow path 13 ′ has a flat shape in which the width in the x direction is smaller than the width in the z direction. According to the flow path 13 ′, the propagation path of the ultrasonic wave formed between the ultrasonic transducers 1 and 2 completely crosses the flow path 13 in both the yz plane and the xy plane. Even when there is a flow velocity distribution, measurement reflecting the entire flow velocity distribution is possible. For this reason, even if the flow velocity distribution changes, the flow rate can be obtained correctly. Moreover, the run-up period can be shortened, and the outer shape of the ultrasonic flowmeter can be reduced.
[0026]
[Patent Document 1]
JP-A-8-233628
[Non-Patent Document 1]
Japan Electrical Measuring Instruments Manufacturers Association Standard, JEMIS 5032 "Flow Measurement Method Using Ultrasonic Wave" (Nippon Electric Measuring Manufacturers Association, 1987)
[0027]
[Problems to be solved by the invention]
However, even when the flow path 13 ′ shown in Patent Document 1 is used, the flow rate measured by the ultrasonic flowmeter does not completely match the flow rate of the fluid that actually moves through the flow path 13 ′. According to the inventor's investigation, the reception sensitivity of the ultrasonic transducers 1 and 2 on the transmission / reception surface varies depending on the position, and the reception sensitivity at the central portion is higher than that at the periphery of the transmission / reception surface. As shown in FIG. 19B, when a fluid having a flow velocity distribution 37 flows, a portion having a flow velocity 37a near the center is measured with higher sensitivity than a portion having a flow velocity 37b near the wall surface. For this reason, even if the ultrasonic propagation path completely crosses the flow path 13, the true average flow velocity of the flow velocity distribution 37 cannot be obtained, resulting in a measurement error.
[0028]
An object of the present invention is to provide an ultrasonic flowmeter and a gas meter that can solve the problems of the conventional ultrasonic flowmeter and can perform highly accurate measurement. It is another object of the present invention to provide a method for controlling such an ultrasonic flow meter.
[0029]
[Means for Solving the Problems]
The ultrasonic flowmeter of the present invention transmits first ultrasonic waves and is opposed to a first ultrasonic transducer disposed so as to form a path through which the ultrasonic waves propagate in a fluid flow path. A piezoelectric element having a piezoelectric body having two main surfaces, a plurality of divided electrodes provided on the first main surface, and a common electrode provided on the second main surface, Amplifying a plurality of reception signals respectively received by the second ultrasonic transducer arranged to receive ultrasonic waves transmitted from the ultrasonic transducer, and the common electrode and the plurality of divided electrodes at different rates Alternatively, the flow rate of the fluid moving through the flow path based on the signal obtained by the addition unit, the signal strength conversion unit to be attenuated, and an addition unit that adds a plurality of reception signals converted by the signal strength conversion unit Measure.
[0030]
In a preferred embodiment, the plurality of divided electrodes are respectively provided in a plurality of regions defined corresponding to the distance from the center of the first main surface.
[0031]
In a preferred embodiment, the signal intensity conversion unit includes a plurality of amplification units that amplify the plurality of received signals at different amplification rates.
[0032]
In a preferred embodiment, the signal intensity converting unit includes a plurality of amplifying units for amplifying the plurality of received signals at different amplification rates, and the position of the divided electrode is separated from the center of the first main surface. The amplification factor for amplifying the reception signal obtained from the divided electrode is large.
[0033]
In a preferred embodiment, the plurality of amplifying units include auto gain control.
[0034]
In a preferred embodiment, the signal strength conversion unit includes an attenuation unit that attenuates at least one of the plurality of received signals.
[0035]
In a preferred embodiment, the signal strength conversion unit includes at least two attenuation units for attenuating the plurality of received signals at different attenuation rates, and the position of the divided electrode is separated from the center of the first main surface. The attenuation factor for attenuating the received signal obtained from the divided electrodes is small.
[0036]
In a preferred embodiment, the ultrasonic flowmeter further includes an amplifying unit that amplifies the signal obtained by the adding unit.
[0037]
In a preferred embodiment, the maximum width of the flow path in the direction orthogonal to the ultrasonic propagation direction in the ultrasonic propagation path is the width of the transmission / reception surface of the first or second ultrasonic transducer in that direction. Smaller or nearly equal.
[0038]
In a preferred embodiment, the signal intensity conversion unit amplifies or attenuates the plurality of reception signals so that the reception signals per unit area of the plurality of divided electrodes are equal to each other.
[0039]
The ultrasonic flowmeter of the present invention includes a piezoelectric body having first and second main surfaces facing each other, a plurality of divided electrodes provided on the first main surface, and a second main surface. Received by the first and second ultrasonic transducers each including a piezoelectric element having a common electrode provided, and by the common electrode and the plurality of divided electrodes of the first or second ultrasonic transducer, respectively. A signal intensity converter that amplifies or attenuates a plurality of received signals at different rates, and a transmission that applies a drive voltage between the common electrode and the plurality of divided electrodes of the first or second ultrasonic transducer, respectively. A switching unit that selectively connects the first ultrasonic transducer and the second ultrasonic transducer to the signal intensity conversion unit and the transmission unit, and a plurality of units converted by the signal intensity conversion unit. The received signals of A signal obtained by the adder, wherein the signal obtained by the adder is arranged so as to form a path in the fluid flow path between the first and second ultrasonic transducers. The two-way propagation time of the ultrasonic wave is obtained based on the above, and the flow rate of the fluid is obtained based on the difference in the propagation time.
[0040]
In a preferred embodiment, the transmitting unit is arranged between the common electrode and the plurality of divided electrodes so that a uniform drive voltage is applied to the piezoelectric body of the first or second ultrasonic transducer. Apply drive signal.
[0041]
A gas meter of the present invention includes any one of the above ultrasonic flow meters provided in a flow path through which a gas flows, and a shut-off valve that blocks the gas flowing through the flow path.
[0042]
The method for controlling an ultrasonic flowmeter according to the present invention includes a first ultrasonic transducer, a piezoelectric body having first and second main surfaces facing each other, and a plurality of divisions provided on the first main surface, respectively. An ultrasonic flowmeter control method for measuring a flow rate of a fluid using an electrode and a second ultrasonic transducer including a piezoelectric element having a common electrode provided on the second main surface. (A) transmitting ultrasonic waves from the first ultrasonic transducer toward the second ultrasonic transducer so as to form a path for ultrasonic waves to propagate in the fluid flow path; and A step (B) of amplifying or attenuating a plurality of received signals respectively received by the common electrode and the plurality of divided electrodes of the ultrasonic transducer at different rates; and a step (C) of adding the plurality of received signals And the flow based on the signal obtained by the addition. Comprising the steps (D) to obtain the flow rate of the fluid to move.
[0043]
In a preferred embodiment, the plurality of divided electrodes are respectively provided in a plurality of regions defined corresponding to the distance from the center of the first main surface. In the step (B), the divided electrodes are provided. The plurality of signals are amplified so that the amplification factor for amplifying the reception signal obtained from the divided electrode increases as the position of the electrode moves away from the center of the first main surface.
[0044]
In a preferred embodiment, the plurality of divided electrodes are respectively provided in a plurality of regions defined corresponding to the distance from the center of the first main surface. In the step (B), the divided electrodes are provided. The plurality of reception signals are attenuated so that the attenuation rate for attenuating the reception signals obtained from the divided electrodes decreases as the position of the electrode moves away from the center of the first main surface.
[0045]
In a preferred embodiment, in the step (B), the received signals are amplified or attenuated so that received signal strengths per unit area of the divided electrodes are equal to each other.
[0046]
The ultrasonic flowmeter control method of the present invention includes a piezoelectric body having first and second main surfaces facing each other, a plurality of divided electrodes provided on the first main surface, and the second main surface. A method for controlling an ultrasonic flowmeter that measures a flow rate of a fluid using first and second ultrasonic transducers each including a piezoelectric element having a common electrode provided on a surface, the first or second By applying a drive signal between the common electrode and the plurality of divided electrodes so that a uniform drive voltage is applied to the piezoelectric body of the ultrasonic transducer of (A) transmitting an ultrasonic wave from the first or second ultrasonic transducer toward the second or first ultrasonic transducer so as to form a path for propagation, and the second or second By the common electrode and the plurality of divided electrodes of the ultrasonic vibrator. A step (B) of amplifying or attenuating a plurality of received signals received at different rates; a step (C) of adding the plurality of received signals; and the flow path based on the signal obtained by the addition. And (D) determining the flow rate of the moving fluid.
[0047]
The computer-readable recording medium of the present invention records a program for causing a computer to execute each step defined in any of the above-described ultrasonic flowmeter control methods.
[0048]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
First, an ultrasonic transducer 41 used in the first embodiment of the ultrasonic flowmeter according to the present invention will be described with reference to FIGS. 1 and 2. The ultrasonic transducer 41 includes a piezoelectric element 42 and a case 43 that houses the piezoelectric element 42. As shown in FIG. 2, the piezoelectric element 42 includes a piezoelectric body 44 having a first main surface 44a and a second main surface 44b facing each other, a common electrode 45, and divided electrodes 46, 47, and 48. . In the present embodiment, the first main surface 44a and the second main surface 44b have, for example, a circular shape, and the common electrode 45 is formed so as to cover almost the entire second main surface 44b. . On the other hand, the divided electrodes 46, 47 and 48 are respectively formed in three regions determined according to the distance from the center 44c of the first main surface. Specifically, the divided electrode 46 is formed in a region closest to the center among the three divided electrodes 46, 47 and 48, and the divided electrode 48 is formed on the outermost peripheral side. As shown in FIG. 2, in this embodiment, the divided electrode 46 has a circular shape, and the divided electrodes 47 and 48 are formed in a ring shape. The centers of these divided electrodes coincide with the center 44c.
[0049]
As shown in FIG. 1, the piezoelectric element 42 is housed in the case 43 so that the common electrode 45 contacts the inside of the surface 43 a of the case 43, and a space 43 c created by the case 43 is sealed. Wirings 49, 50, 51, 52 are connected to the common electrode 45 and the divided electrodes 46, 47, 48 and are drawn out of the case 43. The space 43c is filled with an inert gas such as nitrogen.
[0050]
An acoustic matching layer 53 made of one layer or two or more composite layers may be provided outside the surface 43a so that ultrasonic waves can be efficiently transmitted between the fluid and the piezoelectric element 42 via the surface 43a. When the case 43 has conductivity, the common electrode 45 is omitted, the second main surface 44b of the piezoelectric body 44 is directly joined to the surface 43a of the case 43, and the wiring 49 is connected to the case 43. May be.
[0051]
As will be described in detail below, in the piezoelectric element 42, the electrode formed on the second main surface 44b is divided into three divided electrodes 46, 47, and 48. This is because, when receiving an ultrasonic wave using the ultrasonic transducer 41, the area that receives the ultrasonic wave is divided into a plurality of areas, and the amplification factor of the received signal is made different for each of the divided areas. On the other hand, when transmitting an ultrasonic wave using the ultrasonic transducer 41, a drive signal is sent between the common electrode 45 and the divided electrodes 46, 47, 48 so that a uniform drive voltage is applied to the piezoelectric body 44. Apply. Thereby, the piezoelectric element 42 can be vibrated in a vibration mode determined by the shape of the piezoelectric body 44.
[0052]
Next, the structure of the first embodiment of the ultrasonic flowmeter according to the present invention will be described. FIG. 3 is a block diagram showing a configuration of the ultrasonic flowmeter 61 provided in the flow path 73. FIG. 4 shows an enlarged cross section near the flow path 73. The ultrasonic flowmeter 61 includes a first ultrasonic transducer 71 and a second ultrasonic transducer 72 that are disposed in the fluid flow path 73 so as to form a path in which ultrasonic waves propagate in both directions. ing. The first ultrasonic transducer 71 and the second ultrasonic transducer 72 are arranged such that their transmission / reception surfaces are parallel to each other and the centers of the transmission / reception surfaces are located on the same line.
[0053]
The first ultrasonic transducer 71 and the second ultrasonic transducer 72 function as a transmitter and a receiver, respectively. The ultrasonic wave transmitted from the first ultrasonic transducer 71 is received by the second ultrasonic transducer 62, and the ultrasonic wave transmitted from the second ultrasonic transducer 72 is the first ultrasonic transducer 71. Receive by. These bidirectional propagation paths form an angle θ with respect to the flow direction 35 of the fluid flowing through the flow path 73. The magnitude of the angle θ is selected from the range of 10 to 40 degrees.
[0054]
As shown in FIG. 4, the maximum width L2 of the flow path in the direction (x direction) orthogonal to the ultrasonic propagation direction in the ultrasonic propagation path is the first or second ultrasonic transducer in that direction. Is smaller than or substantially equal to the width L1 of the transmission / reception wave surface. For this reason, the propagation path of the ultrasonic wave completely crosses the flow path 73 in both the yz plane and the xy plane.
[0055]
As the first ultrasonic transducer 71 and the second ultrasonic transducer 72, the ultrasonic transducer 41 shown in FIGS. 1 and 2 is used. For example, the first ultrasonic transducer 71 and the second ultrasonic transducer 72 are driven at a frequency of approximately 20 kHz or more by a vibration mode such as a thickness vibration mode, a side-slip vibration mode, and a longitudinal vibration mode. The optimum frequency is appropriately selected according to the state and type of the fluid to be measured and the expected flow rate. In the present embodiment, for example, an ultrasonic vibrator that vibrates in the thickness vibration mode and has a resonance frequency of 500 kHz is used.
[0056]
The ultrasonic flowmeter 61 further includes a switching unit 74, a transmission unit 3, a signal intensity conversion unit 75, and an addition unit 76. The switching unit 74 selectively connects the transmission unit 3 and the signal intensity conversion unit 75 to the first ultrasonic transducer 71 and the second ultrasonic transducer 72. When the transmission unit 3 and the first ultrasonic transducer 71 are connected, the signal intensity conversion unit 75 and the second ultrasonic transducer 72 are connected, and the transmission unit 3 and the second ultrasonic vibration are connected. When the child 72 is connected, the signal intensity conversion unit 75 and the first ultrasonic transducer 71 are connected.
[0057]
The transmitter 3 is configured with three wires so that independent signals can be applied to the three divided electrodes 46, 47, and 48 of the first ultrasonic transducer 71 and the second ultrasonic transducer 72. Connected to the switching unit 74. The signal intensity conversion unit 75 is also connected to the switching unit 74 by three wires so as to receive independent signals from the three divided electrodes 46, 47 and 48. The drive signals applied from the transmitter 3 to the divided electrodes 46, 47 and 48 are set so that the drive voltage applied to the piezoelectric body 44 is uniform.
[0058]
In the case where the switching unit 74 is configured to be connected in common with each of the divided electrodes 46, 47, 48 of the transmission unit 3 and the first ultrasonic transducer 71 and the second ultrasonic transducer 72. The transmission unit 3 and the switching unit 74 may be connected by a single wire. In this case, the drive signal output from the transmission unit 3 is commonly applied to the divided electrodes 46, 47 and 48.
[0059]
The signal strength conversion unit 75 includes a first amplification unit 75a, a second amplification unit 75b, and a third amplification unit 75c, and the first amplification unit 75a and the second amplification unit 75b are connected via the switching unit 74. The third amplification unit 75c is connected to the divided electrodes 46, 47, and 48, respectively. The first amplifying unit 75a, the second amplifying unit 75b, and the third amplifying unit 75c amplify the received signals received by the divided electrodes 46, 47, and 48 and the common electrode 45 at different rates. Specifically, the amplification factor of the third amplification unit 75c is the largest, and the first amplification unit 75a is the smallest. The amplification factor of the second amplification unit 75b is a value between the amplification factor of the third amplification unit 75c and the amplification factor of the first amplification unit 53a. That is, the amplification factor for amplifying the reception signal obtained from the divided electrode increases as the position of the divided electrode moves away from the center of the first main surface. A specific set value of the amplification factor will be described in detail below. The reception signals amplified by the first amplification unit 75a, the second amplification unit 75b, and the third amplification unit 75c are added by the addition unit 76.
[0060]
The ultrasonic flowmeter 61 obtains the fluid flow rate based on the received signal obtained by the adder 76. For example, as in the past, the received signal is detected by the zero cross detection method, and the ultrasonic propagation time is measured by improving the measurement accuracy by accumulating the ultrasonic propagation time by the sing-around method. Specifically, the ultrasonic flowmeter 61 further includes a peak hold unit 6, a level detection unit 7, a zero cross detection unit 8, a delay unit 9, a repetition unit 10, a time measurement unit 11, and a flow rate calculation unit 12. Referring to FIG. 17, the reception signal 30 added by the adding unit 76 is sent to the zero cross detection unit 8 and the peak hold unit 6. The peak hold unit 6 holds the peak value of the reception signal 30 and generates an output using the peak value as the peak hold signal 31. The level detection unit 7 detects that the peak hold signal 31 has reached a predetermined level 32 and generates a zero cross command signal 33. The zero cross detection unit 7 detects the zero cross point immediately after the zero cross command signal 33 is generated, and outputs the zero cross detection signal 34 to the delay unit 9. Assume that this zero cross point is the propagation time of the received signal, and the received signal is detected at this point. The zero cross detection signal 34 is also input to the peak hold unit 6. The peak hold unit 6 resets the peak hold signal 31 based on the zero cross detection signal.
[0061]
The delay unit 9 generates an output signal at a timing delayed by a predetermined time based on the zero-cross detection signal 34. The repetition unit 10 counts the output signal of the delay unit 9 and outputs the output signal of the delay unit 9 to the transmission unit 3 as a trigger signal if the number is less than a predetermined number. The transmission unit 3 drives the first ultrasonic transducer 71 or the second ultrasonic transducer 72 based on the trigger signal.
[0062]
The time measuring unit 11 measures the time required to repeat the sing around a predetermined number of times, and sends the measurement result to the flow rate calculating unit 12. The flow rate calculation unit 12 obtains the flow rate and the flow rate from the data regarding the time required to repeat the sing-around output from the time measuring unit 11, the delay time, and the number of sing-around times.
[0063]
Each unit described above can be configured by hardware using electronic components or the like, or can be configured by software. The ultrasonic flowmeter 61 includes a microcomputer 77 that controls these units.
[0064]
Next, the amplification factor in each amplification unit of the signal intensity conversion unit 75 will be described.
[0065]
FIG. 5 shows the flow velocity distribution of the fluid in the vicinity of the ultrasonic wave propagation path formed between the first ultrasonic transducer 71 and the second ultrasonic transducer 72 of the ultrasonic flow meter 61, and the ultrasonic signal intensity. The distribution is schematically shown. As shown in FIG. 5, the flow rate distribution in the xy plane of the fluid flowing through the flow path 73 is as indicated by an arrow 37, and the flow velocity of the wall surfaces 37a and 37c constituting the flow path 73 is near the center 37b. It is smaller than
[0066]
On the other hand, in general, when ultrasonic waves are transmitted from a piezoelectric element, in a short-distance sound field close to the transmission position, the signal shows a complex intensity distribution that depends on the frequency. Become. When measuring the flow rate of the fluid, ultrasonic waves are transmitted and received at a distance where the intensity distribution of the propagating ultrasonic waves is constant so that there is little error and measurement can be performed stably. For example, when the ultrasonic wave transmitted from the first ultrasonic transducer 71 reaches the second ultrasonic transducer 72, it has an intensity distribution indicated by I in FIG. For this reason, among the ultrasonic waves received by the second ultrasonic transducer 72, the component passing through the central portion 37c where the flow rate of the fluid 37 is large has a high signal strength, and the wall portions 37a and 37b where the flow rate of the fluid 37 is small. The component that has passed through has a low signal strength. When such a received signal is amplified without considering the signal intensity I of the ultrasonic wave, the influence of the central portion 37c where the flow velocity of the fluid 37 having a relatively strong signal intensity is large becomes larger, and the signal intensity is relatively increased. The influence of the vicinity of the wall surface 37a, 37b where the flow velocity of the weak fluid 37 is small becomes smaller. That is, the influence of the central portion 37c where the flow rate of the fluid 37 is large is overestimated, and the average flow rate or the flow rate moving through the flow path 73 becomes larger than the true value.
[0067]
In order to solve this problem, the ultrasonic flowmeter 61 amplifies the received signal so as to correct the intensity distribution of the received ultrasonic signal. FIG. 6 shows the received signal strength, the amplification factor of each amplification unit of the signal strength conversion unit 73 with respect to the radial position of the piezoelectric transducer of the first ultrasonic transducer 71 and the second ultrasonic transducer 72, and The intensity of the received signal after amplification is shown. In FIG. 6, the horizontal axis indicates the distance in the radial direction from one end of the first main surface of the piezoelectric vibrator. The center 44c of the first main surface is located at the center of the horizontal axis. As shown in the figure, the divided electrode 46 is formed near the center of the horizontal axis and the region is located, and the divided electrode 47 and the divided electrode 48 are located outside the divided electrode 46.
[0068]
As shown in the upper part of FIG. 6, the received ultrasonic signal has an intensity distribution that is rotationally symmetric with respect to a line that passes through the center 44c of the first main surface and is perpendicular to the first main surface. On the other hand, the divided electrodes 46, 47 and 48 are arranged concentrically around the center 44c of the first main surface. For this reason, the intensity distribution of the ultrasonic signal received by each divided electrode is smaller than when the entire signal is received by one electrode.
[0069]
The amplification factor when a signal received by each divided electrode is amplified is set as shown in the center portion of FIG. Specifically, the amplification factor a1 for amplifying the received signal by the divided electrode 46 that receives the component with the strongest signal strength of the received signal is reduced, and the received signal by the divided electrode 48 that receives the component with the weakest signal strength of the received signal. The amplification factor a3 to be amplified is increased. The amplification factor for amplifying the reception signal by the divided electrode 47 is set to a value between a1 and a3.
[0070]
Thus, by reducing the signal intensity distribution of the received signal received by one electrode and changing the amplification factor for each electrode, the intensity distribution of the amplified received signal is amplified as shown in the lower part of FIG. Smaller than before. The maximum and minimum strengths of the received signal before amplification are expressed as I _max And I _min And the maximum and minimum intensities of the amplified received signal are I ′ _max And I ' _min If at least I _max / I _min > I ' _max / I ' _min And preferably 1 ≦ I ′ _max / I ' _min It is preferable to satisfy ≦ 2. More preferably, in the lower part of FIG. 6, the amplification factors a1, a2, and a3 are determined so that the average signal intensities of the received signals from the respective divided electrodes substantially match as shown by the broken lines. Since the intensity distribution of the received signal hardly changes as long as the drive signal output from the transmitter 3 is constant, once the amplification factors a1, a2, and a3 are determined, it is necessary to adjust these values for each measurement. Absent. However, when the environment (temperature, etc.) in which the ultrasonic flowmeter 71 is installed changes greatly, and the intensity distribution of the received signal changes, the first amplifier 75a, the second amplifier 75b, and the third amplifier The amplification unit 75c may be provided with an auto gain control, and the amplification factors a1, a2, and a3 may be automatically adjusted so that the amplified received signal satisfies the above relationship.
[0071]
In this way, by changing the amplification factor of each amplification unit in the signal intensity conversion unit 75 for each divided electrode so that the distribution of the signal intensity of the received ultrasonic wave becomes small, the flow rate of the slow flow rate in the fluid is correctly set. Can be evaluated. For this reason, even when a velocity distribution is generated in the fluid moving in the flow path 73, or when the velocity distribution changes depending on the flow rate, an accurate average flow velocity reflecting the velocity distribution can be obtained.
[0072]
The piezoelectric elements of the first ultrasonic transducer 71 and the second ultrasonic transducer 72 used in the present embodiment have three divided electrodes. As shown in the upper part of FIG. When the intensity distribution is large, the signal may be detected using electrodes divided into three or more, and the signal may be amplified with different amplification factors.
[0073]
Signals amplified at different amplification factors in the respective amplification units are added in the addition unit 76. The reception signal output from the adder 76 can be handled in the same manner as the reception signal in the conventional ultrasonic flowmeter.
[0074]
Next, a procedure for measuring the fluid flow rate using the ultrasonic flowmeter 61 will be described. The procedure described below is performed by sequentially controlling each component by the microcomputer 77, and a program for causing the computer to execute the procedure is stored in an information recording medium such as a ROM, a RAM, a hard disk, or a magnetic recording medium. Has been.
[0075]
As shown in FIG. 3, using the switching unit 74, the transmission unit 3 is connected to the first ultrasonic transducer 71 and the signal intensity conversion unit 35 is connected to the second ultrasonic transducer 72.
[0076]
As shown in FIG. 7, a trigger signal 78 is input to the transmission unit 3 to generate a drive signal, and an ultrasonic wave is generated from the first ultrasonic transducer 71. At this time, drive signals to be applied to the divided electrodes 46, 47, and 48 are set so that a uniform voltage is applied to the entire piezoelectric body of the first ultrasonic transducer 71. As described above, the divided electrodes 46, 47, and 48 may be connected to the transmitter 3 in common.
[0077]
The ultrasonic waves that have crossed the flow path 73 and reached the second ultrasonic transducer 72 are received using the common electrode 45 and the divided electrodes 46, 47, and 48, respectively, and as described above by the signal intensity conversion unit 75. Amplification is performed at a different amplification factor for each divided electrode. The amplified received signals output from the signal strength converting unit 75 are added by the adding unit 76 to become a received signal 79 shown in FIG.
[0078]
The reception signal 79 that is the output of the addition unit 76 is input to the peak hold unit 6 and the zero cross detection unit 8, and the zero cross point immediately after the reception signal 79 exceeds a predetermined level is detected by the zero cross detection unit 8. The delay unit 9 outputs a trigger signal 78 ′ to the transmission unit 3 after a predetermined delay time 80 based on the zero cross detection signal output from the zero cross detection unit 8. Thus, one loop of single-around is configured. After repeating the sing-around for a predetermined number of times (for example, 50 to 1000 times), the time measuring unit 11 measures the total time 81 required to repeat the loop and sends the measurement result to the flow rate calculating unit 12. In the flow rate calculation unit, the total time 81 is divided by the number of times of sing-around, and a value obtained by subtracting the delay time 80 from the value is t1 shown in Expression (1).
[0079]
Next, using the switching unit 74, the transmission unit 3 is connected to the second ultrasonic transducer 72, and the signal intensity conversion unit 75 is connected to the first ultrasonic transducer 71. Then, ultrasonic waves are generated from the second ultrasonic transducer 72 by the same procedure as described above, and ultrasonic waves are received by the first ultrasonic transducer 71. After repeating the sing around a predetermined number of times, the time measuring unit 11 measures the total time 81 required to repeat the loop, and sends the measurement result to the flow rate calculating unit 12. In the flow rate calculation unit, the total time 81 is divided by the number of times of sing-around, and a value obtained by subtracting the delay time 80 from the value is t2 shown in Expression (1).
[0080]
By substituting the values of t1 and t2 and the angle θ into the equation (2), the flow velocity V of the fluid is obtained. Further, if the cross-sectional area of the flow path 73 is S, the flow rate Q can be obtained by V × S. The flow rate Q is an amount by which the flow rate moves per unit time, and the amount of fluid can be obtained by integrating the flow rate Q.
[0081]
As described above, according to the present embodiment, the electrodes of the piezoelectric transducer of the reception-side ultrasonic transducer are divided, and the signal detected by the electrode corresponding to the portion where the signal intensity becomes weaker among the reaching ultrasonic signals is further increased. Amplifies with large amplification. Therefore, it is possible to amplify the received signal by compensating so that the intensity distribution of the received signal becomes small, and even when the flow velocity distribution is generated in the fluid, the contribution of any component of the generated flow velocity is correctly evaluated. It is possible to determine the true average flow velocity. Therefore, an ultrasonic flowmeter capable of accurately measuring the flow rate even when there is a fluid flow velocity distribution is realized.
[0082]
Further, according to the ultrasonic flowmeter of the present embodiment, even if the fluid has a flow velocity distribution, the true average flow velocity can be obtained, so there is no need to use a flow coefficient for correcting the flow rate. Even if the flow velocity distribution changes due to fluctuations in the flow rate, an accurate average flow velocity and flow rate can be obtained without using a flow coefficient.
[0083]
(Second Embodiment)
The structure of the second embodiment of the ultrasonic flowmeter according to the present invention will be described. FIG. 8 is a block diagram showing the configuration of the ultrasonic flowmeter 62 provided in the flow path 73. In FIG. 8, the same components as those in the first embodiment are denoted by the same reference numerals. The ultrasonic flowmeter 62 includes a signal intensity converting unit 82 instead of the signal intensity converting unit 75 of the first embodiment, and the received signals whose intensity has been converted by the signal intensity converting unit 82 are added by the adding unit 76. Thereafter, the received signal added in the amplifying unit 83 is amplified, which is different from the ultrasonic flowmeter 61 of the first embodiment.
[0084]
As shown in FIG. 8, the signal intensity conversion unit 82 includes a first attenuation unit 82a and a second attenuation unit 82b. When the signal intensity conversion unit 82 is connected to the first ultrasonic transducer 71 or the second ultrasonic transducer 72 used as the reception-side ultrasonic transducer by the switching unit 72, the first attenuation unit 82a and The second attenuation portion 82b is electrically connected to the divided electrode 46 and the divided electrode 47 of the piezoelectric element 41 shown in FIGS. The first attenuation unit 82a and the second attenuation unit 82b attenuate the reception signals received by the divided electrodes 46 and 47 and the common electrode 45 at different rates. Specifically, the attenuation rate of the first attenuation unit 82a is larger than the attenuation rate of the second attenuation unit 82b. The reception signal received by the divided electrode 48 and the common electrode 45 is input to the adder 76 without being attenuated. For this reason, the attenuation rate for attenuating the received signal obtained from the divided electrode decreases as the position of the divided electrode moves away from the center of the first main surface.
[0085]
The signal intensity conversion unit 82 attenuates the received signal so as to correct the intensity distribution of the received ultrasonic signal. FIG. 9 shows the received signal strength and signal strength conversion unit 73 with respect to the radial positions of the piezoelectric transducers of the first ultrasonic transducer 71 and the second ultrasonic transducer 72 in the same manner as in the first embodiment. The amplification factor of each amplification part and the intensity of the received signal after amplification are shown.
[0086]
As shown in the upper part of FIG. 9, when the signal intensity of the received ultrasonic wave is distributed, the attenuation rate of the attenuation unit that attenuates the received signal is changed by the divided electrodes as shown in the central part of FIG. 9. The attenuation rate d1 for attenuating the received signal by the divided electrode 46 receiving the component with the strongest signal strength of the received signal is increased, and then the attenuation rate for attenuating the received signal by the divided electrode 47 receiving the portion with the strong signal strength of the received signal. Reduce d2. The reception signal by the divided electrode 48 that receives the portion having the weakest signal strength is not attenuated.
[0087]
By changing the attenuation rate in this way, the intensity distribution of the received signal after attenuation becomes smaller than that before attenuation, as shown in the lower part of FIG. As in the first embodiment, when the maximum and minimum strengths of the reception signal before attenuation are Imax and Imin, respectively, and the maximum and minimum strengths of the reception signal after attenuation are I′max and I′min, respectively, At least Imax / Imin> I′max / I′min, and preferably 1 ≦ I′max / I′min ≦ 2. More preferably, in the lower part of FIG. 9, the attenuation factors d1 and d2 are determined so that the average signal strengths of the received signals from the respective divided electrodes substantially coincide as indicated by broken lines. Since the intensity distribution of the received signal hardly changes as long as the drive signal output from the transmitter 3 is constant, once the attenuation rates d1, d2, and a3 are determined, it is necessary to adjust these values for each measurement. Absent. However, as described in the first embodiment, the first attenuation unit 82a and the second amplification unit 82b are each provided with auto-attenuation control, and the attenuation rate d1 so that the received signal after attenuation satisfies the above-described relationship. , D2 may be automatically adjusted.
[0088]
After the reception signals whose strengths have been converted by the signal strength conversion unit 82 are added by the addition unit 76, the reception signals added by the amplification unit 83 are detected by the zero-cross detection unit 8 in the same manner as in the first embodiment. The flow rate is determined.
[0089]
According to this embodiment, the piezoelectric transducer electrode of the reception-side ultrasonic transducer is divided, and the signal detected by the electrode corresponding to the portion of the reaching ultrasonic signal where the signal intensity is increased is greater in attenuation rate. To attenuate once. Thereafter, by adding the signals received by the divided electrodes, a received signal in which the signal intensity distribution is compensated so as to reduce the signal intensity distribution is obtained. The received signal can be amplified by amplifying the received signal to obtain the propagation time of the ultrasonic wave. Even when a flow velocity distribution is generated in the fluid, any component of the flow velocity at which the distribution is generated contributes. It is possible to obtain a true average flow velocity that is correctly evaluated. Therefore, an ultrasonic flowmeter capable of accurately measuring the flow rate even when there is a fluid flow velocity distribution is realized.
(Fifth embodiment)
Hereinafter, the gas meter provided with the ultrasonic flowmeter of the present invention will be described.
[0090]
FIG. 10 shows a block diagram of a gas meter 63 for measuring the flow rate of the gas flowing in the pipe 90. The gas flowing in the pipe 90 may be other gas such as hydrogen or oxygen in addition to those used in general households such as natural gas and propane gas.
[0091]
The gas meter 63 controls the ultrasonic flow meter 91 for measuring the flow rate of the gas flowing in the pipe 90, the cutoff valve 92 for shutting off the gas flowing in the pipe 90 in an emergency, the ultrasonic flow meter 91 and the cutoff valve 92. And a display unit 94 for displaying the flow rate measured using the ultrasonic flowmeter 63, the integrated value of the flow rate, and other information. As the ultrasonic flow meter 91, the ultrasonic flow meters of the first and second embodiments can be used. The microcomputer 93 may be the microcomputer of the ultrasonic flowmeter 91 (the microcomputer 77 in FIG. 3 and the like). As shown in the figure, the gas meter 63 may include a communication unit 95 for transmitting data related to the measured flow rate to a gas company or the like, or for controlling the gas meter 63 from the gas company.
[0092]
The microcomputer 93 displays data on the flow rate measured by the ultrasonic flowmeter 63 on the display unit 94 and monitors whether there is an abnormality in the measured flow rate. For example, when a large flow rate of gas suddenly starts to flow, it is determined that a gas leak has occurred, the shutoff valve 92 is operated, and the gas supply is stopped.
[0093]
As described in the first and second embodiments, the ultrasonic flowmeter 63 is a true detector that correctly evaluates the contribution of any component of the flow velocity at which the distribution is generated even when the flow velocity distribution is generated in the fluid. The average flow rate can be determined. For this reason, the gas meter 63 can measure the flow rate with high accuracy even if the flow velocity distribution of the gas flowing through the pipe 90 changes greatly due to a change in temperature or the like.
[0094]
The present invention is not limited to the ultrasonic flowmeters and gas meters described in the above embodiments, and various modifications may be made to the ultrasonic flowmeters and gas meters described in the embodiments. Specifically, the piezoelectric element of the ultrasonic transducer used in each of the above embodiments includes a divided electrode divided by a cylindrical piezoelectric body and a concentric circle, but the piezoelectric element may have another structure. For example, the piezoelectric element 142 shown in FIG. 11 includes a square common electrode 145, a piezoelectric body 144, and divided electrodes 146 and 147. The piezoelectric body 144 is divided by a plurality of grooves 144e and a groove 144d and includes a plurality of piezoelectric portions 144a arranged in a matrix. Divided electrodes 144 and 147 are provided on the first main surface 144a side of each piezoelectric portion 144a, and a common electrode 145 is provided on the second main surface 144b side. The positions and number of the grooves 144e and 144d are determined in consideration of the vibration mode of the piezoelectric body 144, the influence of unnecessary vibration modes, ease of handling, and the like.
[0095]
The divisional electrode 146 is provided so as to cover the first main surface 144a of the four central piezoelectric portions 144a, and the divisional electrode 147 is provided so as to cover the first main surface 144a of the piezoelectric portion 144a provided around the divisional electrode 146. Is provided.
[0096]
When ultrasonic waves are transmitted and received using an ultrasonic transducer having the piezoelectric element 142, the intensity of the received signal in the area of the divided electrode 147 is smaller than the intensity of the received signal in the area of the divided electrode 146. For this reason, the intensity distribution of the received signal can be reduced by increasing the degree of amplification when the received signal by the divided electrode 147 is amplified compared to the case of the divided electrode 146. According to the piezoelectric element 142, since the outer shape is square, it is possible to manufacture a plurality of piezoelectric elements 142 from the mother substrate at a time. For this reason, the piezoelectric element 142 is excellent in mass productivity and can reduce manufacturing cost. Further, by dividing the piezoelectric body 144 by the groove 144e and the groove 144d, unnecessary vibration modes can be reduced.
[0097]
Further, an ultrasonic vibrator having the piezoelectric element 142 ′ shown in FIG. 12 may be employed in the ultrasonic flowmeter of the present invention. The piezoelectric body 144 ′ of the piezoelectric element 142 ′ is obtained by removing the piezoelectric portions 144a at the four corners indicated by arrows D in the piezoelectric body 144 of the piezoelectric element 142 shown in FIG. Since the piezoelectric portions are not formed at the four corners, the divided electrode 147 a divided into four is formed outside the divided electrode 146. When an ultrasonic transducer having a piezoelectric element 142 ′ is used, it is preferable to connect the four divided electrodes 147a to other wirings in common.
[0098]
Moreover, you may employ | adopt the ultrasonic transducer | vibrator which has the piezoelectric material element 242 shown in FIG. 13 for the ultrasonic flowmeter of this invention. The piezoelectric element 242 includes a square common electrode 245, a piezoelectric body 244, and divided electrodes 246 and 247. A plurality of grooves 244d parallel to each other are provided on the first main surface 244a of the piezoelectric body 244, and the grooves 244d do not reach the second main surface 244b. For this reason, the piezoelectric body 244 can be handled as one component, and the handling of the piezoelectric body 244 becomes easy. Divided electrode divided electrodes 246 and 247 are provided on the first main surface 244a, and a common electrode 245 is provided on the second main surface 244b.
[0099]
Further, as shown in FIG. 14, in each of the above embodiments, a diffusion plate 96 may be provided on the wall surface that defines the flow path 73 in which the ultrasonic flowmeter is provided. The diffusing plate 96 diffuses the ultrasonic waves so that the ultrasonic waves reflected by the wall surfaces do not enter the ultrasonic transducers on the reception side when the ultrasonic waves transmitted from the ultrasonic transducers on the transmission side hit the wall surfaces. By providing such a diffusion plate, the ultrasonic waves that reach the ultrasonic transducer on the receiving side from the ultrasonic transducer on the transmitting side are not reflected on the wall surface, but only propagate directly across the flow path. It becomes possible to measure the flow velocity and flow rate of the fluid with high accuracy.
[0100]
The signal intensity conversion unit of the first embodiment includes only the amplification unit, and the signal intensity conversion unit of the second embodiment includes only the attenuation unit. However, the signal intensity of the ultrasonic wave reaching the ultrasonic transducer is not included. As long as the signal can be converted so as to reduce the distribution, the signal intensity conversion unit may include an amplification unit and an attenuation unit.
[0101]
In the first to third embodiments, ultrasonic waves are propagated in both directions using the first ultrasonic transducer and the second ultrasonic transducer, and the flow velocity and flow rate of the fluid are obtained from the propagation time difference. It was. However, as is clear from the equation (1), when the sound velocity C of the ultrasonic wave in the fluid is known, the propagation time t1 from the first ultrasonic vibrator to the second ultrasonic vibrator or the first By measuring the propagation time t2 from the second ultrasonic transducer to the first ultrasonic transducer, the flow velocity V of the fluid can be obtained. That is, in the first to fifth embodiments, the flow velocity and flow rate of the fluid are obtained by measuring the propagation time of the ultrasonic wave in one direction between the first ultrasonic transducer and the second ultrasonic transducer. Also good.
[0102]
Further, according to the present invention, it is possible to obtain the average flow velocity and flow rate that correctly evaluate the entire flow velocity distribution generated in the flow path, and therefore it is necessary to use a flow coefficient for correcting the difference between the measured value and the true value. There is no. However, when the flow path has a special shape or the flow velocity changes remarkably, the flow coefficient may be set as necessary after using the flowmeter of the present invention.
[0103]
Further, in each of the above embodiments, the case where the fluid moving in the flow path is a laminar flow is illustrated, but the flow velocity and flow rate are similarly determined with high accuracy even if the fluid is turbulent. Can do. When the fluid is turbulent, the velocity distribution in the fluid is uniform. For this reason, even if only the received signal detected by one of the divided electrodes is used, the flow velocity and flow rate of the fluid can be accurately obtained. For example, the flow velocity and flow rate of the fluid may be obtained using only the reception signal detected using the divided electrode 46 and the common electrode 45 shown in FIGS.
[0104]
【The invention's effect】
According to the present invention, by changing the amplification factor of each amplification unit in the signal intensity conversion unit for each divided electrode so that the distribution of the signal intensity of the received ultrasonic wave becomes small, the flow rate of the slow flow rate in the fluid is reduced. Can be evaluated correctly. For this reason, even when a velocity distribution is generated in the fluid moving in the flow path, or even when the velocity distribution changes depending on the flow rate, an accurate average flow velocity reflecting the velocity distribution can be obtained.
[0105]
Therefore, it is possible to obtain an ultrasonic flowmeter and a gas meter capable of obtaining a flow rate with a high system even when a velocity distribution occurs in the fluid or the velocity distribution changes.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an ultrasonic transducer 41 used in a first embodiment of an ultrasonic flowmeter according to the present invention.
2 is a perspective view showing a piezoelectric element of the ultrasonic transducer shown in FIG. 1. FIG.
FIG. 3 is a block diagram showing a first embodiment of an ultrasonic flowmeter according to the present invention.
4 is a schematic view showing a cross section of a flow path in which the ultrasonic flowmeter shown in FIG. 3 is provided.
5 is a diagram showing a relationship between a fluid flow velocity distribution and an ultrasonic signal intensity distribution in the region shown in FIG. 4; FIG.
6 is a diagram for explaining the intensity distribution of a received signal, the amplification factor when a signal received by each divided electrode is amplified, and the received signal after amplification in the ultrasonic flowmeter shown in FIG. 3; FIG.
FIG. 7 is a diagram illustrating flow rate measurement by a sing-around method.
FIG. 8 is a block diagram showing a second embodiment of the ultrasonic flowmeter according to the present invention.
9 is a diagram for explaining the intensity distribution of a received signal, the amplification factor when a signal received by each divided electrode is amplified, and the received signal after amplification in the ultrasonic flowmeter shown in FIG. 8. FIG.
FIG. 10 is a block diagram showing an embodiment of a gas meter according to the present invention.
FIG. 11 is a perspective view showing another embodiment of the piezoelectric element used in the ultrasonic transducer used in the present invention.
FIG. 12 is a perspective view showing another embodiment of the piezoelectric element used in the ultrasonic transducer used in the present invention.
FIG. 13 is a perspective view showing another embodiment of the piezoelectric element used in the ultrasonic transducer used in the present invention.
FIG. 14 is a diagram showing an example in which a diffusion plate is provided in a flow path in which the ultrasonic flowmeter of the present invention is installed.
FIG. 15 is a block diagram showing a conventional ultrasonic flowmeter.
FIG. 16 is a cross-sectional view showing the structure of an ultrasonic transducer used in a conventional ultrasonic flowmeter.
FIG. 17 is a diagram illustrating detection of a received signal by a zero cross detection method.
FIG. 18 is a diagram illustrating a flow velocity distribution of a fluid moving through a flow path.
FIGS. 19A and 19B are schematic views showing a cross section of a flow path provided with a conventional ultrasonic flow meter. FIGS.
[Explanation of symbols]
1, 2, 41 Ultrasonic transducer
3 Transmitter
4 receiver
5, 74 switching part
6 Peak hold section
7 Level detector
8 Zero cross detector
9 Delay part
10 Repeating part
11 Timekeeping Department
12 Flow rate calculation unit
13, 73 flow path
42 Piezoelectric vibrator
43 cases
44 Piezoelectric body
45 Common electrode
46, 47, 48 Split electrode
61, 62 Ultrasonic flow meter
63 Gas meter
71 First ultrasonic transducer
72 Second ultrasonic transducer
75, 82 Signal strength converter
76 Adder
77 Microcomputer

Claims (19)

A first ultrasonic transducer that transmits ultrasonic waves and is arranged to form a path through which the ultrasonic waves propagate in a fluid flow path;
A piezoelectric element having first and second main surfaces facing each other, a plurality of divided electrodes respectively provided on the first main surface, and a piezoelectric element having a common electrode provided on the second main surface A second ultrasonic transducer that is arranged to receive ultrasonic waves transmitted from the first ultrasonic transducer;
A signal intensity converter that amplifies or attenuates a plurality of received signals respectively received by the common electrode and the plurality of divided electrodes at different rates;
An adder for adding a plurality of received signals converted by the signal strength converter;
An ultrasonic flowmeter that measures the flow rate of the fluid that moves through the flow path based on the signal obtained by the adding unit. 2. The ultrasonic flowmeter according to claim 1, wherein the plurality of divided electrodes are respectively provided in a plurality of regions defined corresponding to distances from a center of the first main surface. The ultrasonic flowmeter according to claim 1, wherein the signal intensity conversion unit includes a plurality of amplification units that amplify the plurality of reception signals at different amplification rates. The signal intensity conversion unit includes a plurality of amplifying units that amplify the plurality of received signals at different amplification factors, and is obtained from the divided electrodes as the position of the divided electrodes is separated from the center of the first main surface. The ultrasonic flowmeter according to claim 2, wherein an amplification factor for amplifying the received signal is increased. The ultrasonic flowmeter according to claim 3 or 4, wherein the plurality of amplifying units includes an auto gain control. The ultrasonic flowmeter according to claim 1, wherein the signal intensity conversion unit includes an attenuation unit that attenuates at least one of the plurality of reception signals. The signal intensity conversion unit includes at least two attenuation units for attenuating the plurality of received signals with different attenuation rates, and is obtained from the divided electrode as the position of the divided electrode is separated from the center of the first main surface. The ultrasonic flowmeter according to claim 2, wherein an attenuation rate for attenuating the received signal is small. The ultrasonic flowmeter according to claim 6, further comprising an amplifying unit that amplifies the signal obtained by the adding unit. The maximum width of the flow path in the direction orthogonal to the ultrasonic wave propagation direction in the ultrasonic wave propagation path is smaller than or substantially equal to the width of the transmission / reception surface of the first or second ultrasonic transducer in that direction. The ultrasonic flowmeter according to claim 1. 2. The ultrasonic flowmeter according to claim 1, wherein the signal intensity conversion unit amplifies or attenuates the plurality of reception signals so that the reception signals per unit area of the plurality of divided electrodes are equal to each other. A piezoelectric element having first and second main surfaces facing each other, a plurality of divided electrodes provided on the first main surface, and a piezoelectric element having a common electrode provided on the second main surface, respectively Including first and second ultrasonic transducers;
A signal intensity converter that amplifies or attenuates a plurality of received signals respectively received by the common electrode and the plurality of divided electrodes of the first or second ultrasonic transducer at different rates;
A transmitter for applying a driving voltage between the common electrode and the plurality of divided electrodes of the first or second ultrasonic transducer;
A switching unit that selectively connects the first ultrasonic transducer and the second ultrasonic transducer to the signal intensity conversion unit and the transmission unit;
An adder for adding a plurality of received signals converted by the signal strength converter;
With
A path through which the ultrasonic wave propagates bidirectionally between the first and second ultrasonic transducers is formed in the fluid flow path, and the ultrasonic wave is generated based on the signal obtained by the adding unit. An ultrasonic flowmeter for obtaining a bidirectional propagation time and obtaining a flow rate of the fluid based on a difference in the propagation time. The transmission unit applies a drive signal between the common electrode and the plurality of divided electrodes so that a uniform drive voltage is applied to the piezoelectric body of the first or second ultrasonic transducer. Item 12. The ultrasonic flowmeter according to Item 11. The ultrasonic flowmeter according to any one of claims 1 to 12, which is provided in a flow path through which gas flows;
A shutoff valve for shutting off a gas flowing through the flow path;
Gas meter equipped with. A first ultrasonic transducer, a piezoelectric body having first and second main surfaces facing each other, a plurality of divided electrodes respectively provided on the first main surface, and provided on the second main surface A method for controlling an ultrasonic flowmeter that measures a flow rate of a fluid using a second ultrasonic transducer including a piezoelectric element having a common electrode formed,
Transmitting ultrasonic waves from the first ultrasonic transducer toward the second ultrasonic transducer so as to form a path for ultrasonic waves to propagate in the fluid flow path;
Amplifying or attenuating a plurality of received signals respectively received by the common electrode and the plurality of divided electrodes of the second ultrasonic transducer at different rates;
Adding the plurality of received signals (C);
A step (D) of obtaining a flow rate of the fluid moving through the flow path based on the signal obtained by the addition; and
A method for controlling an ultrasonic flowmeter including: The plurality of divided electrodes are respectively provided in a plurality of regions defined corresponding to the distance from the center of the first main surface,
In the step (B), the plurality of signals are amplified so that the amplification factor for amplifying the reception signal obtained from the division electrode increases as the position of the division electrode moves away from the center of the first main surface. The method for controlling an ultrasonic flowmeter according to claim 14. The plurality of divided electrodes are respectively provided in a plurality of regions defined corresponding to the distance from the center of the first main surface,
In the step (B), the plurality of received signals are attenuated so that the attenuation rate for attenuating the received signals obtained from the divided electrodes decreases as the position of the divided electrodes moves away from the center of the first main surface. The method for controlling an ultrasonic flowmeter according to claim 14. The method of controlling an ultrasonic flowmeter according to claim 14, wherein in the step (B), the plurality of reception signals are amplified or attenuated so that the reception signals per unit area of the plurality of divided electrodes are equal to each other. A piezoelectric element having first and second main surfaces facing each other, a plurality of divided electrodes provided on the first main surface, and a piezoelectric element having a common electrode provided on the second main surface, respectively A control method for an ultrasonic flowmeter that measures a flow rate of a fluid using first and second ultrasonic transducers including:
By applying a drive signal between the common electrode and the plurality of divided electrodes so that a uniform drive voltage is applied to the piezoelectric body of the first or second ultrasonic transducer, Transmitting ultrasonic waves from the first or second ultrasonic transducer toward the second or first ultrasonic transducer so as to form a path through which the ultrasonic waves propagate in the flow path;
Amplifying or attenuating a plurality of received signals respectively received by the common electrode and the plurality of divided electrodes of the second or second ultrasonic transducer at different rates;
Adding the plurality of received signals (C);
A step (D) of obtaining a flow rate of the fluid moving through the flow path based on the signal obtained by the addition; and
A method for controlling an ultrasonic flowmeter including: A computer-readable recording medium recording a program for causing a computer to execute each step defined in the control method for an ultrasonic flowmeter according to claim 14.

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