JP3624743B2

JP3624743B2 - Ultrasonic flow meter

Info

Publication number: JP3624743B2
Application number: JP14283999A
Authority: JP
Inventors: 裕治中林; 晃一竹村
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1999-05-24
Filing date: 1999-05-24
Publication date: 2005-03-02
Anticipated expiration: 2019-05-24
Also published as: JP2000329597A

Description

【０００１】
【発明の属する技術分野】
本発明は、超音波流量計に関するものである。
【０００２】
【従来の技術】
従来の超音波流量計は、図５に示すようなものが一般的であった。この装置は流体の流れる測定流路１に設置した超音波振動子２と、超音波振動子２を駆動する駆動回路３と、駆動回路３にスタート信号を出力する制御部４と、超音波の伝播時間を測定する伝搬時間測定部５と、伝搬時間測定部５から測定データを受け取る演算部６と、超音波振動子２から送信した超音波を受ける超音波振動子７と、超音波振動子７の出力を増幅するアンプ８と、アンプ８の出力と基準電圧とを比較し大小関係が反転したときに伝搬時間測定部５を停止させる受信検知回路９とを有していた。
【０００３】
そして、上記超音波流量計は、制御部４からスタート信号を受けた駆動回路３が超音波振動子２を一定時間パルス駆動を行うと同時に伝搬時間測定部５は制御部４からの信号によってに時間計測始める。パルス駆動された超音波振動子２からは超音波が送信される。超音波振動子２から送信した超音波は被測定流体中を伝搬し超音波振動子６で受信される。超音波振動子７の受信出力は、アンプ８において制御部４が設定した増幅率によって増幅される。そしてアンプ８の出力を受けた受信検知回路９で超音波の受信を判定し伝搬時間測定部５を停止させる。そして制御部４では伝搬時間測定部５から得た時間情報ｔから（式１）によって流速を求める（但し、伝搬時間測定部５から得た測定時間をｔ、超音波振動子間の流れ方向の有効距離をＬ、音速をｃ、被測定流体の流速をｖとする）。
【０００４】
ｖ＝（Ｌ／ｔ）−ｃ・・・（式１）
受信信号は、緩やかに立ち上がる波形となっており、超音波振動子の温度特性や、流速によって受信信号のレベルは変化する。前記基準電圧と受信信号のレベルの関係が適正でないと受信検知回路９の動作は安定せず測定精度が悪くなる。
【０００５】
また、他の測定方法として受信検知回路９の判定結果を伝搬時間測定部５ではなく、帰還回路によって駆動回路３に返し、再度送信を行う場合もあった。このような繰り返し動作を予め設定した回数行いその時間を測定し、その測定時間を元に（式２）の計算によって流速を求める方法もあった（但し、繰り返しの回数をｎ、測定時間をｔｓ、超音波振動子間の流れ方向の有効距離をＬ，音速をｃ、被測定流体の流速をｖとする）。
【０００６】
ｖ＝Ｌ／（ｔｓ／ｎ）−ｃ・・・（式２）
この方法によれば（式１）の方法に比べｎ倍分解度を高くして測定することができる。
【０００７】
また、超音波振動子２と超音波振動子７とを切り替え、被測定流体の上流から下流と下流から上流へのそれぞれの伝搬時間を測定し、（式３）より速度ｖを求める方法もある（但し、上流から下流への測定時間時間をｔ１、下流から上流への測定時間時間をｔ２とする）。
【０００８】
ｖ＝Ｌ／２（（１／ｔ１）−（１／ｔ２））・・・（式３）
この方法によれば音速の変化の影響を受けずに流度を測定することが出来るので、流速・流量・距離などの測定に広く利用されている。
【０００９】
【発明が解決しようとする課題】
しかしながら従来の超音波流量計では、流量変動による波形や振幅の変化、あるいはノイズなどの影響によって受信検知しているタイミングがずれるため、正確な流量計測ができない場合があった。また測定流量が多くなると超音波の伝播経路に渦などの乱れが発生し、受信信号が短い時間で大きく変動するようになる。この場合受信タイミングがずれ誤測定をしてしまうが、それを誤測定と判定することができなかった。
【００１０】
本発明は正常測定と誤測定とを判別し、誤測定による測定精度の低下を排除することを課題とするものである。
【００１１】
【課題を解決するための手段】
本発明は上記課題を解決するため誤測定判定手段が音速出力手段より得た被測定流体の音速と実際に流量測定のために測定した伝搬時間とを比較し、誤測定判定手段からの信号に基づいて流量を調節するとともに、誤測定判定手段が誤測定と判定したときに流量をより少なくなるように調節し、前記伝搬時間を再測定するようしたものである。
【００１２】
上記本発明によれば音速と伝搬時間は逆比例の関係にあるため、求めた伝搬時間を音速出力手段より得た音速で誤測定かどうか確認することができ、誤測定判定手段が誤測定と判定したときに流量調節手段を動作させ流量をより少なくなるように調節し伝搬時間を再測定するため、流量が大きくなったために発生した乱流や渦を押さえるので確実に正しい流量測定を行なうことができる。
【００１３】
【発明の実施の形態】
第１の発明は、超音波信号を送信する第１の超音波振動子と、前記第１の超音波振動子から送信され流体を伝搬した超音波信号を受信する第２の超音波振動子と、前記超音波の伝搬時間を計測する伝搬時間計測部と、前記伝搬時間から演算によって流量を求める演算部と、前記流体の音速を出力する音速出力手段と、前記音速と前記伝搬時間から求めた音速とを比較し正常な測定かどうかを判定する誤測定判定手段とを備えている。上記発明によれば音速と伝搬時間は逆比例の関係にあるため、求めた伝搬時間を音速出力手段より得た音速で誤測定かどうかを確認することができる。
【００１４】
第２の発明は、第１の発明において、誤測定判定手段が、超音波の流れ方向への伝搬時間と逆流方向への伝搬時間との逆数和から求めた音速と前記音速出力手段で出力した音速とを比較し正常な測定かどうかを判定する。超音波の流れ方向への伝搬時間と逆流方向への伝搬時間との逆数和は、流体の流速に関係なく被測定流体の流速０の時の音速に比例するので、２つの伝搬時間が正しければ前記逆数和に定数をかけることによって正確に音速を求めることができる。この演算によって求めた音速と音速出力手段によって求めた音速とを比較するので、正確に正常な伝搬時間の測定かどうかを確認することができる。
【００１５】
第３の発明は、第１の発明において、誤測定判定手段が超音波の流れ方向への伝搬時間と逆流方向への伝搬時間との平均値の逆数から求めた音速と前記音速出力手段で出力した音速とを比較し正常な測定かどうかを判定する。超音波の流れ方向への伝搬時間と逆流方向への伝搬時間との平均値は、流体の流速が音速に比べて十分小さい範囲では被測定流体の流速０の時の音速の逆数に比例するので、逆数に定数をかけることによって２つの伝搬時間から音速を求めることができる。逆数和を求めるに比べ平均を求めることは容易であり、演算処理の負荷を低減しつつ正常な伝搬時間の測定かどうかを確認することができる。
【００１６】
第４の発明は、前記第１の発明乃至第３の発明において、前記音速出力手段が、前記流体に接し流量の影響を受けない状況下において超音波を送受信する超音波振動子と、前記超音波の伝搬時間を測定するタイマを含み、前記流体に接し流量の影響を受けない状況下での伝搬時間から求めた音速を出力する。音速出力手段では流体の流速に影響しない音速を出力できるので、安定した音速を得ることができ、流量測定が誤計測か否かを判定することができる。
【００１７】
第５の発明は、前記第１の発明乃至第３の発明において、前記音速出力手段は、被測定流体の温度を検知する温度センサと、前記温度センサにより検知された温度における音速を演算する音速変換部とを備え、前記演算された音速を出力する。被測定流体が決まっている場合、その流体の温度が決まれば流速０の時の音速は求まるので、温度センサが被測定流体の温度を測定し、測定した温度から被測定流体の流速０の時の音速を演算により求める。音波を伝搬させずに音速を測定するため超音波による流量計測が音波の干渉の影響を受けず音速測定を任意のタイミングで行なうことができる。また、流量測定と音速測定を同時に行なうことができるので、流量測定が正常な測定であったかどうかの判定基準の精度が向上し測定の正誤判定を精度よくできる。
【００１８】
第６の発明は、第１の発明乃至第３の発明において、前記音速出力手段は、以前に測定した超音波の伝搬時間を記憶する伝搬時間記憶部を備え、前記伝搬時間記憶部に記憶された伝搬時間から求めた音速を出力する。伝播時間記憶部に記憶している超音波の伝搬時間から求めた音速と、新たに測定した伝搬時間から求めた音速とを比較し、大きく異なっていた場合この測定結果を誤測定と判定する。２つの音速がほぼ同じ値であれば正常な伝搬時間であったと判断すると同時に、記憶部に記憶している値を更新し次の判定に使用する。このため、音速測定のためのセンサを新たに付加する必要がないので流量計の構成を簡単にすることができる。
【００１９】
第７の発明は、第１の発明乃至第６の発明において、前記誤測定判定手段からの信号に基づいて流量を調節する流量調節手段をさらに備え、前記誤測定判定手段が誤測定と判定したときに流量をより少なくなるように調節し、前記伝搬時間を再測定する。前記誤測定判定手段が誤測定と判定したときに前記流量調節手段を動作させ流量をより少なくなるように調節し伝搬時間を再測定するため、流量が大きくなったために発生した乱流や渦を押さえるので確実に正しい流量測定を行なうことができる。
【００２０】
第８の発明は、第１の発明乃至第７の発明において、予め設定した回数前記第２の超音波振動子の出力を前記第１の超音波振動子に帰還し再度超音波信号を出力させる帰還回路をさらに備え、前記誤測定判定手段が誤測定と判定したときには前記帰還回路の帰還回数を少なくなるように設定し伝搬時間を再測定する。つまり測定に誤りが発生する機会を少なくして再測定するので、より正しい流量を求めることができる。
【００２１】
第９の発明は、超音波信号を送信し、流体を伝搬した前記超音波信号を受信し、前記超音波の伝搬時間を計測し、前記伝搬時間から演算によって流量を求め、前記流体の音速と前記伝搬時間から求めた音速とを比較し正常な測定かどうかを判定する。
【００２２】
【実施例】
以下、本発明の実施例について図面を用いて説明する。
【００２３】
（実施例１）
図１は本発明の実施例１の超音波流量計を示すブロック図である。
【００２４】
図１において、１０は被測定流体が流れる流路、流路１０に設置した超音波振動子１１と１６、超音波振動子１１を駆動する駆動回路１２と、駆動回路１２にスタート信号を出力する制御部１３と、超音波の伝播時間を測定する伝搬時間測定部１４と、伝搬時間測定部１４から測定データを受け取る演算部１５と、超音波振動子１１から送信した超音波を受ける超音波振動子１６と、超音波振動子１６の出力を増幅するアンプ１７と、アンプ１７の出力波形から受信を検知し伝搬時間測定部１４を停止させる受信検知回路１８と、流量の影響を受けない同一流体に接した超音波振動子２０と送受信回路２１と超音波振動子２０が超音波を送信してから受信するまでの時間を測定するタイマからなる音速出力手段１９と、音速出力手段１９によって求めた音速と伝搬時間とを比較し正常な測定かどうか判定する誤測定判定手段２２と、超音波振動子１１と１６の接続を制御部１３の出力によって入れ替える切替スイッチ２３とを有している。
【００２５】
次に動作、作用について説明すると、制御部１３からスタート信号を受けた駆動回路１２が超音波振動子１１を駆動すると同時に伝搬時間測定部１４は制御部１３は時間計測を始める。また駆動回路１２によって駆動された超音波振動子１１は超音波を送信する。超音波振動子１１が送信した超音波は被測定流体中を伝搬し超音波振動子１６で受信される。超音波振動子１６で受信した超音波信号を受けたアンプ１７は増幅し受信検知回路１８に出力する。受信検知回路１８は超音波の受信を判定し伝搬時間測定部１４を停止させる。この時の伝播時間をｔ１とする。次に制御回路は切替スイッチ２３を動作させ駆動回路１２と超音波振動子１６、超音波振動子１１とアンプ１７をそれぞれ接続させる。その後上記と同様の動作を行いｔ１と逆方向の伝搬時間、つまり超音波センサ１６から送信し超音波センサ１１で受信した場合の超音波の伝搬時間ｔ２を測定する。演算部１３はｔ１、ｔ２より（式３）によって流速を求めさらに流量を演算によって求める。
【００２６】
音速出力手段１９では、送受信回路２１が超音波振動子２０から超音波を送信し壁で反射した超音波を超音波振動子２０で受信するまでの時間を誤測定判定手段２２に出力する。誤測定判定手段２２は音速出力手段によって求めた音速に流体の流速の最大値に相当する幅を持たせ、ｔ１、ｔ２より求めた音速と比較する。ｔ１、ｔ２が幅の中にあれば正しい測定結果と判断し、測定結果を採用する。ｔ１、ｔ２が幅の外にあれば異常測定と判断し測定結果を破棄する。
【００２７】
この実施例の構成によれば、流体の流速による影響を受けずに音速出力手段１９が音速を検知できるので、安定した音速を得ることができ、正しい測定が異常測定かを判断することができる。
【００２８】
また、上記方法と別に、ｔ１、ｔ２の逆数和と音速出力手段１９によって求めた音速とを比較することによって正常測定か異常測定かを判定することもできる。逆数和は（式４）のようになる。
【００２９】

となりｔ１、ｔ２の逆数和に定数をかけたものが音速なので、音速出力手段によって求めた音速と比較する場合流速を考慮する必要がなく、考慮する場合であってもわずかの流量相当であるので、より正確に異常測定を判断することができる。
【００３０】
また、上記方法とは別に、ｔ１、ｔ２の平均値の逆数と音速出力手段１９によって求めた音速とを比較することによって異常測定を判定することもできる。平均値の逆数は（式６）のようになる。
【００３１】

となりｔ１、ｔ２の平均の逆数に定数をかけたものがほぼ音速となる。このとき音速出力手段によって求めた音速と比較する場合に流速を考慮する必要がなく、考慮する場合であってもわずかの流量相当であるので、より確実に異常測定か否かを判断することができると同時に、逆数和を求める場合の計算と比較し、計算量を低減することができる。
【００３２】
（実施例２）
図２は本発明の実施例２の超音波流量計を示す図である。
【００３３】
本実施例２において、実施例１と異なる点は音速出力手段１９が温度センサ２４と音速変換部２５で構成している点である。
【００３４】
なお、実施例１と同一符号のものは同一構成要素とし、説明は省略する。
【００３５】
次に動作、作用を説明する。被測定流体が決まっている場合、その流体の温度が決まれば流速０の時の音速は求まる。温度センサが被測定流体の温度を測定し、音速変換部２５が被測定流体の温度から流速０の音速を演算により求める。この方法によれば音波を伝搬させずに音速を測定するため、音速測定は流量計測に音波の干渉を与えることなく任意のタイミングでできる。また、流量測定と音速測定を同時に行なうことができ、流量測定が正常な測定であったかどうかの判定基準の精度をよくすることができる。
【００３６】
（実施例３）
図３は本発明の実施例３の超音波流量計を示す図である。
【００３７】
本実施例３において、実施例１と異なる点は音速出力手段１９が以前に測定した超音波の伝搬時間を記憶する伝搬時間記憶部２６で構成している点である。
【００３８】
なお、実施例１と同一符号のものは同一構成要素とし、説明は省略する。
【００３９】
次に動作、作用を説明すると、伝搬時間記憶部２６に記憶している超音波の伝搬時間から求めた音速と、新たに測定した伝搬時間から式（５）あるいは式（７）によって求めた音速とを比較し、あらかじめ設定した値以上異なっていた場合この測定結果を誤測定と判定する。２つの音速がほぼ同じ値であれば正常な伝搬時間であったと判断すると同時に、記憶部に記憶している値を更新し次の判定に使用する。
【００４０】
一定条件のもとで音速は大きく変化することはないので、測定間隔の間に予測される音速変化を見込んだ値を音速変化の許容値として設定し、その範囲内であれば正しい測定であると判断することができる。
【００４１】
このため、音速測定のためのセンサを新たに付加する必要がないので流量計の構成を簡単にすることができる。
【００４２】
（実施例４）
図４は本発明の実施例３の超音波流量計を示す図である。
【００４３】
なお、実施例１と同一符号のものは同一構成要素とし、説明は省略する。
【００４４】
本実施例４において、実施例１と異なる点は誤測定判定手段２２が設定した回数受信検知回路１８の出力を駆動回路１２に帰還し再度超音波信号を出力させる帰還回路２８と、誤測定判定手段２２からの指令信号によって流量を調節する流量調節手段２７とを有する点である。
【００４５】
次に動作、作用を説明すると、誤測定判定手段が誤測定と判定したときに流量調節手段２７を動作させ流量をより少なくなるように調節し伝搬時間を再測定するため、流量が大きくなったために発生した乱流や渦を押さえるので確実に正しい流量測定を行なうことができる。
【００４６】
このため、回路やその他の機能異常のため流量測定ができなくなったのか、過大流量のため超音波の伝搬が乱れ流量測定ができなくなったのかを判断することができる。
【００４７】
また、誤測定判定手段２２が誤測定と判定したときに帰還回路２８の帰還回数を少なく設定し伝搬時間を再測定する。つまり測定に誤りが発生する機会を少なくして再測定するので、より正しい流量を求めることができる。
【００４８】
以上の説明から明らかのように、本発明の各実施の形態における超音波流量計によれば次の効果を奏する。
【００４９】
（１）誤測定判定手段が音速出力手段より得た被測定流体の音速と実際に流量測定のために測定した伝搬時間から求めた音速とを比較する。音速と伝搬時間は逆比例の関係にあるため、求めた伝搬時間を音速出力手段より得た音速で誤測定かどうか確認することができ、誤測定を測定結果に反映することがなく、正確な流量計を実現することができる。
【００５０】
（２）超音波の流れ方向への伝搬時間と逆流方向への伝搬時間との逆数和から求めた音速と音速出力手段から出力された音速とを比較し判定するので、２つの伝搬時間から容易に正確な音速を求め誤測定かどうかを判断するとができる。
【００５１】
（３）超音波の流れ方向への伝搬時間と逆流方向への伝搬時間との平均値の逆数から求めた音速と音速出力手段から出力された音速とを比較し判定する。超音波の流れ方向への伝搬時間と逆流方向への伝搬時間との平均値は、流体の流速が音速に比べて十分小さい範囲では被測定流体の流速０の時の音速の逆数に比例するので、逆数に定数をかけることによって２つの伝搬時間から音速を求めることができる。よって逆数和を求めのるに比べ平均を求めることは容易であり、演算処理の負荷を低減しつつ正常な伝搬時間の測定かどうかを確認することができる。
【００５２】
（４）前記流体に接し流量の影響を受けない状況下での超音波の伝搬時間から求めた音速を出力し、この音速と流量測定のために測定した伝搬時間から求めた音速とを比較する。このため、流体の流速に影響しない安定した音速と流量測定のために測定した伝搬時間から求めた音速とを比較することができ、流量測定が誤計測か否かを判定することができる。
【００５３】
（５）被測定流体の温度を検知する温度センサと音速変換部よりなる音速出力手段を有している。被測定流体が決まっている場合、その流体の温度が決まれば流速０の時の音速は求まるので、温度センサが被測定流体の温度を測定し、測定した温度から被測定流体の流速０の時の音速を演算により求める。よって音波を伝搬させずに音速を測定するため超音波による流量計測が音波の干渉の影響を受けず音速測定を任意のタイミングで行なうことができると共に、流量測定と音速測定を同時に行なうことができるので、流量測定が正常な測定であったかどうかの判定基準の精度が向上し、その結果測定の正誤判定を精度よく行うことができる。
【００５４】
（６）音速出力手段が以前に測定した超音波の伝搬時間を記憶する伝搬時間記憶部を有し、伝搬時間記憶部に記憶している超音波の伝搬時間から求めた音速と、新たに測定した伝搬時間から求めた音速とを比較し、大きく異なっていた場合この測定結果を誤測定と判定する。２つの音速がほぼ同じ値であれば正常な伝搬時間であったと判断すると同時に、記憶部に記憶している値を更新し次の判定に使用する。このため、音速測定のためのセンサを新たに付加する必要がないので流量計の構成を簡単にすることができる。
【００５５】
（７）誤測定判定手段が誤測定と判定したときに流量調節手段を動作させ流量をより少なくなるように調節し伝搬時間を再測定するため、流量が大きくなったために発生した乱流や渦を押さえるので確実に正しい流量測定を行なうことができる。このため、回路やその他の機能異常のため流量測定ができなくなったのか、過大流量のため超音波の伝搬が乱れ流量測定ができなくなったのかを判断することができる。
【００５６】
（８）予め設定した回数超音波振動子の出力を第１の超音波振動子に帰還し再度超音波信号を出力させる帰還回路と、計測した伝搬時間が適正かどうかを判定する誤測定判定手段とを有し、誤測定判定手段が誤測定と判定したときに帰還回路の帰還回数を少なく設定し伝搬時間を再測定する。このため測定に誤りが発生する機会を少なくして再測定するので、より正しい流量測定を行うことができる。
【００５７】
（９）超音波信号を送信し、流体を伝搬した前記超音波信号を受信し、前記超音波の伝搬時間を計測し、前記伝搬時間から演算によって流量を求め、前記流体の音速と前記伝搬時間から求めた音速とを比較し正常な測定かどうかを判定する。音速と伝搬時間は逆比例の関係にあるため、求めた伝搬時間を音速出力手段より得た音速で誤測定かどうかを確認することができる。
【００５８】
【発明の効果】
本発明の超音波流量計によれば、誤測定判定手段が音速出力手段より得た被測定流体の音速と実際に流量測定のために測定した伝搬時間から求めた音速とを比較する。音速と伝搬時間は逆比例の関係にあるため、求めた伝搬時間を音速出力手段より得た音速で誤測定かどうか確認することができ、誤測定判定手段が誤測定と判定したときに流量調節手段を動作させ流量をより少なくなるように調節し伝搬時間を再測定するため、流量が大きくなったために発生した乱流や渦を押さえるので確実に正しい流量測定を行なうことができる。
【図面の簡単な説明】
【図１】本発明の実施例１における超音波流量計のブロック図
【図２】本発明の実施例２における超音波流量計のブロック図
【図３】本発明の実施例３における超音波流量計のブロック図
【図４】本発明の実施例４における超音波流量計のブロック図
【図５】従来の超音波流量計のブロック図
【符号の説明】
１１超音波振動子
１５演算部
１６超音波振動子
１９音速出力手段
２２誤測定判定手段
２４温度センサ
２６伝搬時間記憶部
２７流量調節手段
２８帰還回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic flowmeter.
[0002]
[Prior art]
Conventional ultrasonic flowmeters are generally as shown in FIG. This apparatus includes an ultrasonic transducer 2 installed in a measurement flow path 1 through which a fluid flows, a drive circuit 3 that drives the ultrasonic transducer 2, a control unit 4 that outputs a start signal to the drive circuit 3, an ultrasonic wave Propagation time measurement unit 5 that measures propagation time, calculation unit 6 that receives measurement data from propagation time measurement unit 5, ultrasonic transducer 7 that receives ultrasonic waves transmitted from ultrasonic transducer 2, and ultrasonic transducer 7 and the reception detection circuit 9 that compares the output of the amplifier 8 with the reference voltage and stops the propagation time measurement unit 5 when the magnitude relationship is inverted.
[0003]
In the ultrasonic flow meter, the drive circuit 3 that has received the start signal from the control unit 4 performs pulse driving of the ultrasonic transducer 2 for a predetermined time, and at the same time, the propagation time measurement unit 5 receives the signal from the control unit 4. Start measuring time. Ultrasound is transmitted from the pulse-driven ultrasonic transducer 2. The ultrasonic wave transmitted from the ultrasonic transducer 2 propagates through the fluid to be measured and is received by the ultrasonic transducer 6. The reception output of the ultrasonic transducer 7 is amplified by the amplification factor set by the control unit 4 in the amplifier 8. Then, the reception detection circuit 9 receiving the output of the amplifier 8 determines reception of the ultrasonic wave and stops the propagation time measuring unit 5. Then, the control unit 4 obtains the flow velocity from the time information t obtained from the propagation time measuring unit 5 by (Equation 1) (however, the measurement time obtained from the propagation time measuring unit 5 is t and the flow direction between the ultrasonic transducers is determined. The effective distance is L, the speed of sound is c, and the flow velocity of the fluid to be measured is v).
[0004]
v = (L / t) -c (Formula 1)
The received signal has a waveform that rises gently, and the level of the received signal changes depending on the temperature characteristics of the ultrasonic transducer and the flow velocity. If the relationship between the reference voltage and the level of the received signal is not appropriate, the operation of the reception detection circuit 9 is not stable and the measurement accuracy is deteriorated.
[0005]
As another measurement method, the determination result of the reception detection circuit 9 may be returned to the drive circuit 3 by the feedback circuit instead of the propagation time measurement unit 5 and transmitted again. There is a method in which such a repeated operation is performed a predetermined number of times and the time is measured, and the flow velocity is obtained by calculation of (Equation 2) based on the measurement time (however, the number of repetitions is n and the measurement time is ts). The effective distance in the flow direction between the ultrasonic transducers is L, the speed of sound is c, and the flow velocity of the fluid to be measured is v).
[0006]
v = L / (ts / n) -c (Formula 2)
According to this method, it is possible to measure with a higher n-fold resolution than the method of (Equation 1).
[0007]
There is also a method of switching the ultrasonic transducer 2 and the ultrasonic transducer 7 and measuring the respective propagation times from upstream to downstream and downstream to upstream of the fluid to be measured, and obtaining the velocity v from (Equation 3). (However, the measurement time from upstream to downstream is t1, and the measurement time from downstream to upstream is t2.)
[0008]
v = L / 2 ((1 / t1)-(1 / t2)) (Formula 3)
According to this method, the flow rate can be measured without being affected by the change in the sound speed, and thus it is widely used for measuring the flow velocity, the flow rate, the distance, and the like.
[0009]
[Problems to be solved by the invention]
However, in the conventional ultrasonic flowmeter, since the timing of reception detection is shifted due to a change in waveform or amplitude due to flow rate fluctuation or noise, there are cases where accurate flow rate measurement cannot be performed. In addition, when the measurement flow rate increases, turbulence such as vortices occurs in the propagation path of the ultrasonic wave, and the received signal greatly fluctuates in a short time. In this case, the reception timing is shifted and erroneous measurement is performed, but it cannot be determined as erroneous measurement.
[0010]
An object of the present invention is to discriminate between normal measurement and erroneous measurement and to eliminate a decrease in measurement accuracy due to erroneous measurement.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention compares the sound speed of the fluid to be measured obtained by the erroneous measurement determination means from the sound speed output means with the propagation time actually measured for measuring the flow rate, and generates a signal from the erroneous measurement determination means. The flow rate is adjusted based on this, and the flow rate is adjusted to be smaller when the erroneous measurement determination means determines that the measurement is erroneous, and the propagation time is remeasured .
[0012]
According to the present invention, since the sound speed and the propagation time are in an inversely proportional relationship, it is possible to confirm whether the obtained propagation time is an erroneous measurement with the sound speed obtained from the sound speed output means , and the erroneous measurement determination means is an erroneous measurement. When the judgment is made, the flow rate adjustment means is operated to adjust the flow rate to be smaller and the propagation time is re-measured, so that the turbulent flow and vortex generated due to the increased flow rate are suppressed so that the correct flow rate can be measured. It is Ru can.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The first invention includes a first ultrasonic transducer that transmits an ultrasonic signal, a second ultrasonic transducer that receives an ultrasonic signal transmitted from the first ultrasonic transducer and propagated through a fluid, and A propagation time measurement unit that measures the propagation time of the ultrasonic wave, a calculation unit that obtains a flow rate by calculation from the propagation time, a sonic speed output means that outputs a sound speed of the fluid, and a speed of sound obtained from the sound speed and the propagation time. Erroneous measurement determination means for comparing the speed of sound and determining whether or not the measurement is normal. According to the above invention, since the sound speed and the propagation time are in an inversely proportional relationship, it is possible to confirm whether the obtained propagation time is erroneously measured with the sound speed obtained from the sound speed output means.
[0014]
According to a second invention, in the first invention , the erroneous measurement determination means outputs the sound speed obtained from the reciprocal sum of the propagation time in the ultrasonic flow direction and the propagation time in the backward flow direction and the sound speed output means. Compare with the speed of sound to determine whether the measurement is normal. The reciprocal sum of the propagation time in the ultrasonic flow direction and the propagation time in the reverse flow direction is proportional to the speed of sound when the flow velocity of the fluid to be measured is 0 regardless of the flow velocity of the fluid. By multiplying the reciprocal sum by a constant, the speed of sound can be obtained accurately. Since the sound speed obtained by this calculation is compared with the sound speed obtained by the sound speed output means, it can be confirmed whether or not the normal propagation time is correctly measured.
[0015]
According to a third invention, in the first invention , the erroneous measurement determining means outputs the sound speed obtained from the reciprocal of the average value of the propagation time in the ultrasonic flow direction and the propagation time in the reverse flow direction and the sound speed output means. The sound speed is compared to determine whether the measurement is normal. Since the average value of the propagation time in the ultrasonic flow direction and the propagation time in the reverse flow direction is proportional to the reciprocal of the sound speed when the fluid flow velocity is sufficiently smaller than the sound velocity, the flow velocity of the fluid to be measured is zero. By multiplying the reciprocal by a constant, the sound speed can be obtained from the two propagation times. It is easier to obtain the average than to obtain the reciprocal sum, and it is possible to confirm whether or not the normal propagation time is measured while reducing the processing load.
[0016]
According to a fourth aspect of the present invention, in the first to third aspects of the invention , the sonic velocity output means transmits and receives an ultrasonic wave in a state where it is in contact with the fluid and is not affected by the flow rate, and the supersonic wave It includes a timer for measuring the propagation time of the sound wave, and outputs the speed of sound obtained from the propagation time in a state where it is in contact with the fluid and is not affected by the flow rate. Since the sonic velocity output means can output a sonic velocity that does not affect the flow velocity of the fluid, a stable sonic velocity can be obtained, and it can be determined whether or not the flow measurement is an erroneous measurement.
[0017]
According to a fifth invention, in the first to third inventions , the sound velocity output means is a temperature sensor that detects a temperature of a fluid to be measured, and a sound velocity that calculates a sound velocity at a temperature detected by the temperature sensor. A converter, and outputs the calculated sound speed. If the fluid to be measured is determined, the sound velocity at the flow velocity of 0 can be obtained if the temperature of the fluid is determined. Therefore, the temperature sensor measures the temperature of the fluid to be measured, and when the flow velocity of the fluid to be measured is 0 from the measured temperature. Is obtained by calculation. Since the sound velocity is measured without propagating the sound wave, the flow rate measurement by the ultrasonic wave is not affected by the interference of the sound wave, and the sound velocity measurement can be performed at an arbitrary timing. Further, since the flow rate measurement and the sound velocity measurement can be performed at the same time, the accuracy of the determination criterion as to whether or not the flow rate measurement is normal is improved, and the correctness / incorrectness of the measurement can be accurately determined.
[0018]
According to a sixth invention, in the first to third inventions , the sound velocity output means includes a propagation time storage unit that stores a previously measured ultrasonic propagation time, and is stored in the propagation time storage unit. The speed of sound obtained from the propagation time is output. The speed of sound obtained from the propagation time of the ultrasonic wave stored in the propagation time storage unit is compared with the speed of sound obtained from the newly measured propagation time, and if there is a large difference, the measurement result is determined as an erroneous measurement. If the two sound velocities are approximately the same value, it is determined that the propagation time is normal, and at the same time, the value stored in the storage unit is updated and used for the next determination. For this reason, since it is not necessary to newly add a sensor for measuring the speed of sound, the configuration of the flow meter can be simplified.
[0019]
According to a seventh invention, in the first invention to the sixth invention , further comprising a flow rate adjusting means for adjusting a flow rate based on a signal from the erroneous measurement determination means, wherein the erroneous measurement determination means has determined an erroneous measurement. Sometimes the flow rate is adjusted to be lower and the propagation time is re-measured. When the erroneous measurement determination means determines that the measurement is incorrect, the flow rate adjusting means is operated to adjust the flow rate to be smaller and re-measure the propagation time. Since it is held down, the correct flow rate can be measured reliably.
[0020]
In an eighth aspect based on the first to seventh aspects, the output of the second ultrasonic transducer is fed back to the first ultrasonic transducer a predetermined number of times and an ultrasonic signal is output again. A feedback circuit is further provided, and when the erroneous measurement determination means determines that an erroneous measurement is made, the number of feedbacks of the feedback circuit is set to be reduced, and the propagation time is measured again. In other words, since the measurement is performed again with fewer opportunities for error, a more accurate flow rate can be obtained.
[0021]
The ninth invention transmits an ultrasonic signal, receives the ultrasonic signal propagated through the fluid, measures the propagation time of the ultrasonic wave, obtains a flow rate by calculation from the propagation time, The sound speed obtained from the propagation time is compared to determine whether the measurement is normal.
[0022]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0023]
(Example 1)
FIG. 1 is a block diagram showing an ultrasonic flowmeter according to a first embodiment of the present invention.
[0024]
In FIG. 1, reference numeral 10 denotes a flow path through which a fluid to be measured flows, ultrasonic vibrators 11 and 16 installed in the flow path 10, a drive circuit 12 that drives the ultrasonic vibrator 11, and a start signal to the drive circuit 12. The control unit 13, the propagation time measurement unit 14 that measures the propagation time of the ultrasonic wave, the calculation unit 15 that receives the measurement data from the propagation time measurement unit 14, and the ultrasonic vibration that receives the ultrasonic wave transmitted from the ultrasonic transducer 11 A receiver 16, an amplifier 17 for amplifying the output of the ultrasonic transducer 16, a reception detection circuit 18 for detecting reception from the output waveform of the amplifier 17 and stopping the propagation time measuring unit 14, and the same fluid not affected by the flow rate A sound velocity output means 19 comprising a timer for measuring a time from when the ultrasonic transducer 20 in contact with the transmitter / receiver circuit 21 and the ultrasonic transducer 20 transmit an ultrasonic wave to receiving the ultrasonic wave; Erroneous measurement determination means 22 that compares the speed of sound and propagation time obtained in this way to determine whether the measurement is normal, and a selector switch 23 that switches the connection of the ultrasonic transducers 11 and 16 with the output of the control unit 13. Yes.
[0025]
Next, the operation and action will be described. At the same time as the drive circuit 12 receiving the start signal from the control unit 13 drives the ultrasonic transducer 11, the propagation time measurement unit 14 starts the time measurement by the control unit 13. The ultrasonic transducer 11 driven by the drive circuit 12 transmits ultrasonic waves. The ultrasonic wave transmitted by the ultrasonic transducer 11 propagates through the fluid to be measured and is received by the ultrasonic transducer 16. Upon receiving the ultrasonic signal received by the ultrasonic transducer 16, the amplifier 17 amplifies and outputs the amplified signal to the reception detection circuit 18. The reception detection circuit 18 determines reception of the ultrasonic wave and stops the propagation time measurement unit 14. The propagation time at this time is assumed to be t1. Next, the control circuit operates the changeover switch 23 to connect the drive circuit 12 and the ultrasonic transducer 16, and the ultrasonic transducer 11 and the amplifier 17, respectively. Thereafter, the same operation as described above is performed to measure the propagation time in the direction opposite to t1, that is, the propagation time t2 of the ultrasonic wave transmitted from the ultrasonic sensor 16 and received by the ultrasonic sensor 11. The calculation unit 13 obtains the flow rate from (Equation 3) from t1 and t2, and further obtains the flow rate by calculation.
[0026]
In the sonic output means 19, the transmission / reception circuit 21 transmits the ultrasonic wave from the ultrasonic vibrator 20 and outputs the ultrasonic wave reflected by the wall to the erroneous measurement determining means 22. The erroneous measurement determination means 22 gives a width corresponding to the maximum value of the fluid flow velocity to the sound speed obtained by the sound speed output means, and compares it with the sound speed obtained from t1 and t2. If t1 and t2 are within the width, it is determined that the measurement result is correct, and the measurement result is adopted. If t1 and t2 are outside the width, it is determined that the measurement is abnormal, and the measurement result is discarded.
[0027]
According to the configuration of this embodiment, since the sound speed output means 19 can detect the sound speed without being affected by the flow velocity of the fluid, a stable sound speed can be obtained, and it can be determined whether the correct measurement is an abnormal measurement. .
[0028]
In addition to the above method, it is also possible to determine whether the measurement is normal or abnormal by comparing the reciprocal sum of t1 and t2 with the sound speed obtained by the sound speed output means 19. The reciprocal sum is as shown in (Formula 4).
[0029]

Since the sound speed is obtained by multiplying the reciprocal sum of t1 and t2 by a constant, it is not necessary to consider the flow velocity when compared with the sound velocity obtained by the sound velocity output means, and even if it is considered, it corresponds to a slight flow rate. Therefore, it is possible to determine an abnormal measurement more accurately.
[0030]
In addition to the above method, the abnormal measurement can be determined by comparing the reciprocal of the average value of t1 and t2 with the sound speed obtained by the sound speed output means 19. The reciprocal of the average value is as shown in (Equation 6).
[0031]

The sound speed is almost equal to the average reciprocal of t1 and t2 multiplied by a constant. At this time, it is not necessary to consider the flow velocity when comparing with the sound velocity obtained by the sound velocity output means, and even if it is considered, it corresponds to a slight flow rate, so it is possible to more reliably determine whether or not abnormal measurement is performed. At the same time, the amount of calculation can be reduced compared with the calculation for obtaining the reciprocal sum.
[0032]
(Example 2)
FIG. 2 is a diagram showing an ultrasonic flowmeter according to a second embodiment of the present invention.
[0033]
The second embodiment is different from the first embodiment in that the sound speed output means 19 includes a temperature sensor 24 and a sound speed conversion unit 25.
[0034]
In addition, the thing of the same code | symbol as Example 1 is made into the same component, and description is abbreviate | omitted.
[0035]
Next, the operation and action will be described. If the fluid to be measured is determined, the sound velocity at a flow velocity of 0 can be obtained if the temperature of the fluid is determined. The temperature sensor measures the temperature of the fluid to be measured, and the sound velocity conversion unit 25 obtains the sound velocity at a flow velocity of 0 from the temperature of the fluid to be measured by calculation. According to this method, since the sound speed is measured without propagating the sound wave, the sound speed measurement can be performed at an arbitrary timing without giving the sound wave interference to the flow rate measurement. Further, the flow rate measurement and the sound velocity measurement can be performed at the same time, and the accuracy of the criterion for determining whether or not the flow rate measurement is a normal measurement can be improved.
[0036]
(Example 3)
FIG. 3 is a diagram showing an ultrasonic flowmeter according to a third embodiment of the present invention.
[0037]
The third embodiment is different from the first embodiment in that the sound speed output unit 19 is configured by a propagation time storage unit 26 that stores the propagation time of the ultrasonic wave measured previously.
[0038]
In addition, the thing of the same code | symbol as Example 1 is made into the same component, and description is abbreviate | omitted.
[0039]
Next, the operation and action will be described. The sound speed obtained from the propagation time of the ultrasonic wave stored in the propagation time storage unit 26 and the sound speed obtained from the newly measured propagation time by the equation (5) or the equation (7). And if the difference is more than a preset value, this measurement result is determined to be erroneous measurement. If the two sound velocities are approximately the same value, it is determined that the propagation time is normal, and at the same time, the value stored in the storage unit is updated and used for the next determination.
[0040]
Since the sound speed does not change significantly under certain conditions, a value that allows for the expected change in sound speed during the measurement interval is set as an allowable value for the sound speed change, and if it is within that range, the sound is measured correctly. It can be judged.
[0041]
For this reason, since it is not necessary to newly add a sensor for measuring the speed of sound, the configuration of the flow meter can be simplified.
[0042]
(Example 4)
FIG. 4 is a diagram showing an ultrasonic flowmeter according to the third embodiment of the present invention.
[0043]
In addition, the thing of the same code | symbol as Example 1 is made into the same component, and description is abbreviate | omitted.
[0044]
The fourth embodiment is different from the first embodiment in that a feedback circuit 28 that feeds back the output of the number of times reception detection circuit 18 set by the erroneous measurement determination means 22 to the drive circuit 12 and outputs an ultrasonic signal again, and erroneous measurement determination The flow rate adjusting means 27 for adjusting the flow rate according to a command signal from the means 22 is provided.
[0045]
Next, the operation and action will be described. Since the flow rate adjustment means 27 is operated to adjust the flow rate to be smaller and the propagation time is remeasured when the erroneous measurement determination unit determines that the measurement is erroneous, the flow rate is increased. Since the turbulent flow and vortices generated in the chamber are suppressed, the correct flow rate can be measured reliably.
[0046]
For this reason, it is possible to determine whether the flow measurement cannot be performed due to an abnormal circuit or other function, or whether the ultrasonic wave propagation is disturbed due to the excessive flow and the flow measurement cannot be performed.
[0047]
Further, when the erroneous measurement determination means 22 determines that there is an erroneous measurement, the number of feedbacks of the feedback circuit 28 is set to be small and the propagation time is remeasured. In other words, since the measurement is performed again with fewer opportunities for error, a more accurate flow rate can be obtained.
[0048]
As is apparent from the above description, the ultrasonic flowmeter according to each embodiment of the present invention has the following effects.
[0049]
(1) The erroneous measurement determination means compares the sound speed of the fluid to be measured obtained from the sound speed output means with the sound speed obtained from the propagation time actually measured for flow rate measurement. Since the speed of sound and the propagation time are inversely proportional, it is possible to check whether the obtained propagation time is an erroneous measurement using the sound speed obtained from the sound speed output means. A flow meter can be realized.
[0050]
(2) Since the sound speed obtained from the reciprocal sum of the propagation time in the flow direction of the ultrasonic wave and the propagation time in the backward flow direction is compared with the sound speed output from the sound speed output means, determination is made easily from the two propagation times. It is possible to determine whether it is an erroneous measurement by obtaining an accurate sound speed.
[0051]
(3) The sound speed obtained from the reciprocal of the average value of the propagation time in the ultrasonic flow direction and the propagation time in the reverse flow direction is compared with the sound speed output from the sound speed output means. Since the average value of the propagation time in the ultrasonic flow direction and the propagation time in the reverse flow direction is proportional to the reciprocal of the sound speed when the fluid flow velocity is sufficiently smaller than the sound velocity, the flow velocity of the fluid to be measured is zero. By multiplying the reciprocal by a constant, the sound speed can be obtained from the two propagation times. Accordingly, it is easier to obtain the average than to obtain the reciprocal sum, and it is possible to confirm whether or not the normal propagation time is measured while reducing the processing load.
[0052]
(4) Outputs the speed of sound obtained from the propagation time of the ultrasonic wave in a state where it is in contact with the fluid and is not affected by the flow rate, and compares this sound speed with the speed of sound obtained from the propagation time measured for measuring the flow rate. . For this reason, it is possible to compare a stable sound velocity that does not affect the flow velocity of the fluid and a sound velocity obtained from the propagation time measured for the flow rate measurement, and to determine whether or not the flow rate measurement is an erroneous measurement.
[0053]
(5) It has a sonic velocity output means comprising a temperature sensor for detecting the temperature of the fluid to be measured and a sonic velocity conversion unit. If the fluid to be measured is determined, the sound velocity at the flow velocity of 0 can be obtained if the temperature of the fluid is determined. Therefore, the temperature sensor measures the temperature of the fluid to be measured, and when the flow velocity of the fluid to be measured is 0 from the measured temperature. Is obtained by calculation. Therefore, since the sound velocity is measured without propagating the sound wave, the flow rate measurement by the ultrasonic wave is not affected by the interference of the sound wave, and the sound velocity measurement can be performed at an arbitrary timing, and the flow rate measurement and the sound velocity measurement can be simultaneously performed. Therefore, the accuracy of the criterion for determining whether or not the flow rate measurement is normal is improved, and as a result, whether the measurement is correct or incorrect can be accurately performed.
[0054]
(6) The sound speed output means has a propagation time storage unit for storing the propagation time of the ultrasonic wave measured previously, and the sound speed obtained from the propagation time of the ultrasonic wave stored in the propagation time storage unit is newly measured. The sound speed obtained from the propagation time measured is compared, and if there is a large difference, this measurement result is determined as an erroneous measurement. If the two sound velocities are approximately the same value, it is determined that the propagation time is normal, and at the same time, the value stored in the storage unit is updated and used for the next determination. For this reason, since it is not necessary to newly add a sensor for measuring the speed of sound, the configuration of the flow meter can be simplified.
[0055]
(7) When the erroneous measurement determination means determines that there is an erroneous measurement, the flow rate adjustment means is operated to adjust the flow rate to be smaller and the propagation time is remeasured. Therefore, the correct flow rate can be measured reliably. For this reason, it is possible to determine whether the flow measurement cannot be performed due to an abnormal circuit or other function, or whether the ultrasonic wave propagation is disturbed due to the excessive flow and the flow measurement cannot be performed.
[0056]
(8) A feedback circuit for returning the output of the ultrasonic transducer to the first ultrasonic transducer for a preset number of times and outputting the ultrasonic signal again, and erroneous measurement determination means for determining whether the measured propagation time is appropriate When the erroneous measurement determination means determines that the measurement is incorrect, the number of feedbacks of the feedback circuit is set to be small and the propagation time is remeasured. For this reason, since the measurement is performed again with fewer opportunities for error, more accurate flow rate measurement can be performed.
[0057]
(9) An ultrasonic signal is transmitted, the ultrasonic signal propagated through the fluid is received, a propagation time of the ultrasonic wave is measured, a flow rate is obtained by calculation from the propagation time, and a sound speed and the propagation time of the fluid are calculated. The sound speed obtained from the above is compared to determine whether the measurement is normal. Since the sound speed and the propagation time are in an inversely proportional relationship, it is possible to confirm whether the obtained propagation time is erroneously measured with the sound speed obtained from the sound speed output means.
[0058]
【The invention's effect】
According to the ultrasonic flowmeter of the present invention, the erroneous measurement determination means compares the sound speed of the fluid to be measured obtained from the sound speed output means with the sound speed obtained from the propagation time actually measured for flow measurement. Since the acoustic velocity and the propagation time in inverse proportion relationship, determined propagation time to be able to determine whether erroneous measurement at the speed of sound obtained from the sound velocity output means is, flow rate control when the erroneous measurement determining means determines that erroneous measurement Since the means is operated to adjust the flow rate to be smaller and the propagation time is measured again, the turbulent flow and vortex generated due to the increased flow rate are suppressed, so that the correct flow rate can be measured reliably .
[Brief description of the drawings]
FIG. 1 is a block diagram of an ultrasonic flowmeter according to Embodiment 1 of the present invention. FIG. 2 is a block diagram of an ultrasonic flowmeter according to Embodiment 2 of the present invention. FIG. 4 is a block diagram of an ultrasonic flowmeter in Embodiment 4 of the present invention. FIG. 5 is a block diagram of a conventional ultrasonic flowmeter.
DESCRIPTION OF SYMBOLS 11 Ultrasonic vibrator 15 Calculation part 16 Ultrasonic vibrator 19 Sonic output means 22 Error measurement judgment means 24 Temperature sensor 26 Propagation time memory | storage part 27 Flow volume adjustment means 28 Feedback circuit

Claims

A first ultrasonic transducer for transmitting an ultrasonic signal, a second ultrasonic transducer for receiving an ultrasonic signal transmitted from the first ultrasonic transducer and propagated through a fluid, and propagation of the ultrasonic wave Comparison is normally made between the propagation time measurement unit that measures time, the calculation unit that calculates the flow rate from the propagation time, the sound speed output means that outputs the sound speed of the fluid, and the sound speed and the sound speed determined from the propagation time. An erroneous measurement determination means for determining whether or not the measurement is incorrect, and a flow rate adjustment means for adjusting a flow rate based on a signal from the erroneous measurement determination means, and the flow rate when the erroneous measurement determination means determines that the measurement is erroneous. The ultrasonic flowmeter which adjusts so that it may become less, and re-measures the said propagation time .

A first ultrasonic transducer for transmitting an ultrasonic signal, a second ultrasonic transducer for receiving an ultrasonic signal transmitted from the first ultrasonic transducer and propagated through a fluid, and propagation of the ultrasonic wave Comparison is normally made between the propagation time measurement unit that measures time, the calculation unit that calculates the flow rate from the propagation time, the sound speed output means that outputs the sound speed of the fluid, and the sound speed and the sound speed determined from the propagation time. An erroneous measurement determination means for determining whether or not the measurement is performed, a feedback circuit for returning the output of the second ultrasonic transducer to the first ultrasonic transducer a predetermined number of times and outputting an ultrasonic signal again; An ultrasonic flowmeter that sets the number of feedbacks of the feedback circuit to be reduced and re-measures the propagation time when the erroneous measurement determination means determines that there is an erroneous measurement .

The erroneous measurement determination means compares the sound speed obtained from the reciprocal sum of the propagation time in the ultrasonic flow direction and the propagation time in the reverse flow direction with the sound speed output from the sound speed output means to determine whether the measurement is normal. The ultrasonic flowmeter according to claim 1 or 2 .

Whether the erroneous measurement determination means is a normal measurement by comparing the sound speed obtained from the reciprocal of the average value of the propagation time in the ultrasonic flow direction and the propagation time in the reverse flow direction with the sound speed output by the sound speed output means. The ultrasonic flowmeter according to claim 1 or 2, wherein:

The sonic output means includes an ultrasonic transducer that transmits and receives ultrasonic waves under a condition that is in contact with the fluid and is not affected by the flow rate, and a timer that measures the propagation time of the ultrasonic wave, and is in contact with the fluid and is affected by the flow rate. The ultrasonic flowmeter according to any one of claims 1 to 4 , wherein a sound velocity obtained from a propagation time under a condition where no vibration is received is output.

The sound speed output means includes a temperature sensor that detects a temperature of a fluid to be measured, and a sound speed converter that calculates a sound speed at a temperature detected by the temperature sensor, and outputs the calculated sound speed. The ultrasonic flowmeter according to claim 4 .

The speed of sound output means, according to claim 1 to claim 4 previously provided with a propagation time storage unit for storing a propagation time of the ultrasonic wave is measured, and outputs a sound velocity obtained from the propagation propagation time stored in the time storage unit The ultrasonic flowmeter according to any one of the above.