JP2004361167A

JP2004361167A - Ultrasonic flowmeter

Info

Publication number: JP2004361167A
Application number: JP2003158057A
Authority: JP
Inventors: Yukio Kodama; 幸生小玉
Original assignee: Ricoh Elemex Corp
Current assignee: Ricoh Elemex Corp
Priority date: 2003-06-03
Filing date: 2003-06-03
Publication date: 2004-12-24

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter having low current consumption and capable of transmitting and receiving ultrasonic wave signals. <P>SOLUTION: The ultrasonic flowmeter is provided with an ultrasonic transmitter/receiver 3a and an ultrasonic transmitter/receiver 3b opposed to each other upstream and downstream of a fluid channel and an impressing voltage control part 4 for controlling an impressing voltage to be impressed on the ultrasonic transmitters at the transmission of ultrasonic waves according to the time of forward measurement and the time of backward measurement. The impressing voltage is lowered at the backward measurement than at the forward measurement. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、超音波を利用してガス、水道等の流体の流速、流量を計測する超音波流量計に関する。
【０００２】
【従来の技術】
この種の超音波流量計、例えば、超音波ガス流量計では、流体の流れる流路の上流側と下流側に超音波素子を配置し、上流側の超音波素子を駆動して超音波を送信し、下流側の超音波素子でその出力を受信し、送信開始から受信するまでの時間を計測する。同じく、下流側から超音波素子を駆動して超音波を送信し、上流側の超音波素子でその出力を受信し、送信開始から受信するまでの時間を計測する。この両時間より流速が求まり、流速に流路の断面積を乗じて流量を求めている。
【０００３】
超音波の到達時間検出方法として、予め定めた第何波かの波形の振幅がゼロとなるゼロクロス点までの時間を受信時間とする方法がある。図８は、超音波受信信号を表すもので、第１波を検出しようとすると振幅が小さく、十分なＳ／Ｎ比が確保できないため、例えば、第３波の立下がりゼロクロス点ｃの時間を検出しようとする場合、あるしきい値電圧ＶＴＨを設けて、そのしきい値電圧ＶＴＨを超えた次のゼロクロス点までの時間を計測する方法がある。ゼロクロス点ｃの前のピークとなる波形の部分、この例では、第３波をゼロクロストリガ波という。
【０００４】
上記の説明における、ゼロクロストリガ波でのピークの電圧値（最大振幅）を以下の説明ではピーク電圧という。ところが、このピーク電圧は、流体、流量、圧力、温度などにより、その最大振幅が大きく変化するものである。超音波流量計では、そうした変化に対応することが要求される。
【０００５】
【発明が解決しようとする課題】
従来の超音波流量計は、超音波素子を駆動するために常に一定の印加電圧を印加して超音波を発信している。この種の超音波ガス流量計では、例えば、電池駆動で約１０年の間、メンテナンスフリーで稼動することが要求され、従来の方法では、その消費電流が低いとはいえなかった。
【０００６】
本発明は上記した点に鑑みなされたものであって、低消費電流で超音波信号の送信、受信が可能な超音波流量計を提供することを課題とする。
【０００７】
【課題を解決するための手段及び発明の効果】
上記課題を解決するために本発明超音波流量計は、送受信を行うための少なくとも一対の超音波送受波器を設け、流体の流れの中を順方向と逆方向にそれぞれ超音波の送受を行い、その各向きの到達時間から流速さらに流量を求める超音波流量計であって、順方向計測時と逆方向計測時とに応じて超音波送波時の超音波送受波器に印加する印加電圧を制御する送波時印加電圧制御手段を設けたことを特徴とする。
【０００８】
本発明者が検討した過程で、超音波送受波器への電圧印加により送波された超音波が相手方の超音波送受波器で受波される際の受波電圧のピークは、順方向計測（送波）時と逆方向（送波）時で相当異なること、例えば、同じ印加電圧で送波しても、逆方向送波時には順方向送波時より高い受波電圧ピークを生じる傾向があり、順方向計測時の受波電圧で測定可能とすれば、逆方向送波計測時に得られる受波電圧は測定可能な程度より高い場合が多いことを検証し、この発明に至ったものである。
【０００９】
具体的には、例えば、送波時印加電圧制御手段は、順方向計測時と逆方向計測時に応じて超音波送波時の超音波送受波器に印加する印加電圧を、逆方向計測時には順方向計測時より低く制御する。
【００１０】
上記のように送波時印加電圧制御手段により、順方向計測時と逆方向計測時とで送波時の印加電圧を変えて、送波時における電圧印加を測定が許容される範囲内で送波時印加電圧を選択的に下げることにより、少ない電力消費で流量測定が可能となり、例えば、電源に簡易な電池を使用の場合でも、長期間のメンテナンスフリーを実現できる。
【００１１】
なお、上記において、流れ方向が一定に決まっている場合は、予め決められた順序（順方向計測、その後に逆方向計測、この順序を繰り返す、又は順方向計測を数回繰り返した後に逆方向計測を数回繰り返す、この計測順序を繰り返す）によったり、下流側の超音波送受波器に電圧を印加することを検知すれば、それが逆方向計測判別となり、流れ方向が順方向と逆方向との間で変わる場合には、流れ方向が反転したことを検知して、流れが変わった後において、下流に位置する超音波送受波器に対する電圧印加時を逆方向計測時と判定することができる。
【００１２】
さらに、本発明は、送受信を行うための少なくとも一対の超音波送受波器を設け、流体の流れの中を順方向と逆方向にそれぞれ超音波の送受を行い、その各向きの到達時間から流速さらに流量を求める超音波流量計であって、流速判定部を設けて、求めた流速に応じて超音波送波時の超音波送受波器に印加する印加電圧を制御する送波時印加電圧制御手段を設けたことを特徴とする。
【００１３】
超音波送受波器への電圧印加により送波された超音波が相手方の超音波送受波器で受波される際の受波電圧のピークは、流体の速度の大小により相当異なること、例えば順方向計測時には、同じ印加電圧で送波しても、流体の速度が遅いときには速いときより高い受波電圧ピークを生じる傾向があり、逆方向計測時には、同じ印加電圧で送波しても、流体の速度が遅いときには速いときより低い受波電圧ピークを生じる傾向があり、例えば順方向計測時に流速が速い場合の受波電圧で測定可能とすれば、流速が遅い場合の受波電圧は測定可能な程度より高い場合が多く、例えば逆方向計測時に流速が遅い場合の受波電圧で測定可能とすれば、流速が速い場合の受波電圧は測定可能な程度より高い場合が多いことを検証し、それが発明の基礎にある。
【００１４】
具体的には、例えば、送波時印加電圧制御手段は、求めた流速に応じて超音波送波時の超音波送受波器に印加する順方向計測時の印加電圧を、流体の流速が小さい場合は大きい場合に比べて印加電圧が低くなるようにし、逆方向計測時の印加電圧を、流体の流速が大きい場合は小さい場合に比べて印加電圧が低くなるように制御する。
【００１５】
上記のように送波時印加電圧制御手段により、流速が速い場合と遅い場合とで送波時の印加電圧を変えて、送波時における電圧印加を測定が許容される範囲内で選択的に下げることにより、少ない電力消費で流量測定が可能となり、例えば、電源に簡易な電池を使用の場合でも、長期間のメンテナンスフリーを実現できる。
【００１６】
さらに、本発明は、送受信を行うための少なくとも一対の超音波送受波器を設け、流体の流れの中を順方向と逆方向にそれぞれ超音波の送受を行い、その各向きの到達時間から流速さらに流量を求める超音波流量計であって、温度判定部を設けて、計測温度に応じて超音波送波時の超音波送受波器に印加する印加電圧を制御する送波時印加電圧制御手段を設けたことを特徴とする。
【００１７】
超音波送受波器への電圧印加により送波された超音波が相手方の超音波送受波器で受波される際の受波電圧のピークは、温度の高低で相当異なること、例えば、同じ印加電圧で送波しても、流体の温度が低いときには高いときより高い受波電圧ピークを生じる傾向があり、例えば、高い温度の場合の受波電圧で測定可能とすれば、温度が低い場合の受波電圧は測定可能な程度より高い場合が多い。
【００１８】
具体的には、例えば、送波時印加電圧制御手段は、計測温度に応じて超音波送波時の超音波送受波器に印加する順方向計測時および逆方向計測時の印加電圧を、流体の温度が低い場合は高い場合に比べて印加電圧が低くなるように制御する。
【００１９】
上記のように送波時印加電圧制御手段により、温度が高い場合と低い場合とで送波時の印加電圧を変えて、送波時における電圧印加を測定が許容される範囲内で選択的に下げることにより、測定に要する消費電力が節約され、電源を電池とする場合の長期間の電源保証が可能となる。
【００２０】
さらに、本発明は、送受信を行うための少なくとも一対の超音波送受波器を設け、流体の流れの中を順方向と逆方向にそれぞれ超音波の送受を行い、その各向きの到達時間から流速さらに流量を求める超音波流量計であって、計測体判定部を設けて、検知した計測流体に応じて超音波送波時の超音波送受波器に印加する印加電圧を制御する送波時印加電圧制御手段を設けたことを特徴とする。
【００２１】
具体的には、例えば、送波時印加電圧制御手段は、計測流体に応じて超音波送波時の超音波送受波器に印加する順方向計測時および逆方向計測時の印加電圧を、超音波の減衰が小さい計測流体の場合は超音波の減衰が大きい計測流体の場合に比べて印加電圧が低くなるように制御する。
【００２２】
上記のように送波時印加電圧制御手段により、被計測対象である流体の種別に応じて送波時の印加電圧を変えることにより、測定に要する消費電力が節約され、電源を電池とする場合の長期間の電源保証が可能となる。
【００２３】
さらに、本発明は、請求項１または２に記載の送波時印加電圧制御と、請求項３または４に記載の送波時印加電圧制御と、請求項５または６に記載の送波時印加電圧制御との、任意の２以上の結合による送波時印加電圧制御を実行する送波時印加電圧制御手段を含むことを特徴とする。
【００２４】
上記構成により、流体の流れ方向や流速および温度に応じて、これを任意に組み合わせて送波時の印加電圧を変えて計測が行なわれることにより、測定に要する消費電力が節約され、その効果は相乗的に高められ、例えば、電源に簡易な電池を使用の場合でも、長期間のメンテナンスフリーを実現できる。
【００２５】
【発明の実施の形態】
以下、本発明の実施の形態につき図面に示す実施例を参照して説明する。図１は、本発明の超音波流量計の概念を示す全体構成図であり、超音波流量計１は、流体の流路２に対向して配置され、圧電素子を含み構成される一対の超音波送受波器３ａと超音波送受波器３ｂと（これら総称して超音波送受波器３という場合がある）、超音波送受波器３の圧電素子を駆動し超音波を発信する駆動用の印加電圧を制御する印加電圧制御部４と、超音波送受波器３の圧電素子が駆動されたことにより送信された超音波信号を受信する超音波受信部５と、流路２の流れに対し順方向に超音波を送信したり、あるいは逆方向に超音波を送信したり、その方向を切替えるために超音波送受波器３と印加電圧制御部４との間、および超音波送受波器３と超音波受信部５の間に接続された送受切替部６と、超音波受信部５に接続され超音波の到達時間から流速を計算する処理を行う演算処理部７とを含み構成される。印加電圧制御部４の入力側に、流速判定部８と、順逆計測判定部９と、温度判定部１０と、流体判定部１１とが接続され印加電圧の制御をする信号が送信される。印加電圧制御部４は、送受切替部６を介し超音波送受波器３ａと３ｂとの印加電圧の制御（印加電圧の高低や印加時間の制御）を行う。なお、超音波受信部５は、流れに対し順方向と逆方向に送信された超音波の受信手段として兼用される。
【００２６】
次に、流量の計測方法について説明する。流体の流れは図１に示す矢印の方向（流体の流速をＶ）とする。先ず、流れに沿った方向（順方向）に超音波を送信した場合の到達時間を計測する。送受切替部６により、超音波送受波器３ａを送信側とし、一方、超音波送受波器３ｂを受信側とする。印加電圧制御部４により超音波送受波器３ａの圧電素子が駆動され超音波が送信され、流路２内を横切って、超音波送受波器３ｂまで到達する。超音波送受波器３ｂから超音波受信信号が超音波受信部５に入力される。
【００２７】
次に、図２に一例として示す計測部のブロック図と図３に示すタイミングチャートとに基づいて超音波受信部５で行われる動作について説明する。図２に示すように、受信側超音波素子（圧電素子）出力は、増幅器２０（例えばオペアンプ）で電圧増幅（例えば非反転増幅）され、増幅信号Ｖａがゼロクロス型コンパレータ２１（第一コンパレータ）に入力（例えば非反転入力）され、差動型コンパレータ２２（第二コンパレータ）に入力（例えば反転入力）される。コンパレータ出力Ｖｂ，Ｖｃは、ＲＳフリップフロップ回路（以下、ＲＳＦＦ回路という）２３のポート＃Ｓ，＃Ｒへ各々入力される。ＲＳＦＦ回路２３のポート＃Ｑ出力Ｖｄにより、単安定マルチバイブレータ等で構成されるゼロクロスポイントパルス発生回路２４が出力波形Ｖａにおける超音波到達時点を検出し、ゼロクロスポイント検出信号Ｖｅを出力する。ゼロクロスポイント検出信号Ｖｅに基づき、クロックパルス発生回路２５（例えば水晶発振子、無安定マルチバイブレータ）からのクロックパルス数をパルスカウンタ回路２６（例えばＪＫフリップフロップ回路）でカウントして到達時間検出信号Ｖｆが出力される。なお、ゼロクロスポイント検出信号Ｖｅは１回のみの出力で終了するように制御されている（図示せず）。
【００２８】
増幅信号Ｖａ（超音波受信出力）は、図３に示すように受信初期においてはノイズ混入等の影響により十分な振幅（発生電圧）レベルを有しない不規則波形信号であり、先頭から第ｎ番目（図では第▲３▼番目）の波形部分においてようやく安定して測定可能な振幅レベルに達するのが通常である。そこで、超音波受信出力の増幅信号Ｖａにおいて精度のよい時間測定を可能にするために、以下に述べるゼロクロス法が一般に採用されている。つまり、差動型コンパレータ２２（図２参照）に入力設定されたしきい値ＶＴＨを超える（又は下回る）に至る波形部分（図では第▲３▼波）をトリガ波とし、このトリガ波の振幅（又は位相）がゼロとなるゼロクロス点を、増幅信号Ｖａ（又はその派生信号）の波形上でゼロクロスポイントパルス発生回路２４（図２参照）により検出する方法である。
【００２９】
具体的には、増幅信号Ｖａの波形に対してゼロクロス法は次のように適用される。増幅信号Ｖａが非反転入力されたゼロクロス型コンパレータ２１では、増幅信号Ｖａの波形のうち振幅（発生電圧）が正の波形部分（第▲１▼波，第▲３▼波，第▲５▼波…）に対応してＨとなるパルスが、第一コンパレータ出力Ｖｂとして断続的に出力される。一方、負極性の増幅信号Ｖａと正極性のしきい値ＶＴＨとが入力された差動型コンパレータ２２では、しきい値ＶＴＨを超える波形部分（第▲３▼波，第▲５▼波…の頂部）に対応してＬとなるパルスが、第二コンパレータ出力Ｖｃとして断続的に出力される。
【００３０】
第二コンパレータ出力Ｖｃで最初にしきい値ＶＴＨを超えるトリガ波（第▲３▼波）のパルス信号が入力されるまではＲＳＦＦ回路２３のポート＃ＲにはＨが継続して入力されるので、ＲＳＦＦ回路２３のポート＃Ｑ出力ＶｄはＬに維持される。第一コンパレータ出力Ｖｂから第▲３▼波の波形検出パルス信号がＲＳＦＦ回路２３のポート＃Ｓに入力（Ｈ）されている状態において、第二コンパレータ出力Ｖｃからトリガ波（第▲３▼波）のしきい値ＶＴＨ検出パルス信号がポート＃Ｒに入力（Ｌ）されたとき、ポート＃Ｑ出力ＶｄはＨに変化する。そして、第一コンパレータ出力Ｖｂから第▲３▼波の波形検出パルス信号がＲＳＦＦ回路２３のポート＃Ｓに入力されなくなるまでポート＃Ｑ出力ＶｄはＨに維持され、ポート＃Ｓへの入力がＬとなったときにポート＃Ｑ出力ＶｄはＬとなる。
【００３１】
ゼロクロスポイントパルス発生回路２４は、ＲＳＦＦ回路２３のポート＃Ｑ出力Ｖｄの立ち下がりエッジを検出し、ゼロクロス点に対応してＨとなるパルスをゼロクロスポイント検出信号Ｖｅとして出力する。パルスカウンタ回路２６は、ゼロクロスポイント検出パルス信号（Ｖｅ）と送信側超音波素子（圧電素子）の超音波送信パルス信号との間のクロックパルス数をカウントして、到達時間検出信号Ｖｆを出力する。このようにして到達時間検出信号Ｖｆで得られた検出到達時間（順方向の到達時間Ｔｄ）は、実際の（真の）到達時間より長くなっている。つまり、受信開始からトリガ波（第▲３▼波）のゼロクロス点までの間（第▲１▼波〜第▲３▼波の１．５周期分）の経過時間を補正値として、検出到達時間から差し引くと実際の到達時間が得られる。
【００３２】
次に、流れに逆らう方向（逆方向）に超音波を送信した場合の到達時間を計測する。送受切替部６により、超音波送受波器３ｂを送信側とし、一方、超音波送受波器３ａを受信側とする。印加電圧制御部４により超音波送受波器３ｂの圧電素子が駆動され超音波が送信され、流路２内を横切って、超音波送受波器３ａまで到達する。同様にして、逆方向の到達時間Ｔｕが計測される。
【００３３】
超音波受信部５において、到達時間を計測したデータは、印加電圧制御部４からのタイミング信号を受けて、演算処理部７に送信される。演算処理部７は到達時間から流速を計算する。
【００３４】
上記で計測された順方向の到達時間Ｔｄと逆方向の到達時間Ｔｕから流速Ｖ（ｍ／ｓ）と流量Ｑ（ｍ^３／ｓ）が次の式から求められる。図１において、流体の流速をＶ、流体を伝播する音速をＣ、超音波の伝播距離をＬ、流路２の断面積をＡとする。
Ｔｄ＝Ｌ／（Ｃ＋Ｖ）（１）
Ｔｕ＝Ｌ／（Ｃ−Ｖ）（２）
Ｖ＝（１／Ｔｄ−１／Ｔｕ）Ｌ／２（３）
Ｑ＝Ｖ・Ａ（４）
【００３５】
次に、本発明の超音波送受波器３の印加電圧の制御について説明する。図４は、超音波送受波器３への電圧印加により送波された超音波が相手方の超音波送受波器３で受波される際の受波電圧のピーク電圧（最大振幅電圧）との関係を示す特性図である。圧電素子に印加される電圧と圧電素子の振動は比例する。印加電圧を高くするほどピーク電圧は高くなる。従って、図４のＡの印加電圧における受波電圧で測定が可能であれば、例えば、図４のＢの印加電圧にすることは、超音波流量計において、電圧過多となり消費電流を無駄に消費することになる。
【００３６】
図５は、一定の印加電圧を超音波送受波器３に印加し、順方向で計測のときと、逆方向で計測のときとにおけるピーク電圧と流路を通過する計測体の流速との関係を示す特性図である。順方向で計測（送波）のときと、逆方向で計測（送波）のときでピーク電圧は相当異なり、逆方向計測のときは、順方向計測のときより高くなる傾向にある。順方向計測のときの受波電圧で測定可能であれば、逆方向計測のときに得られる受波電圧は測定可能な程度より高い場合が多い。順逆計測判定部９により、これから計測する計測方向が順方向か逆方向かを判定する。順逆計測判定部９からの信号を受けて、印加電圧制御部４により逆方向に超音波を送信して計測する場合、図５の破線で示すように、順方向に計測（送波）する場合より低い電圧を印加する。このように、順方向計測時と逆方向計測時とで送波時の印加電圧を変えて、送波時における電圧印加を測定が許容される範囲内で選択的に下げることにより、少ない電力消費で流量測定が可能となり、例えば、電源に簡易な電池を使用の場合でも、長期間のメンテナンスフリーを実現できる。
【００３７】
順逆計測判定方法としては、流れ方向が一定に決まっている場合は、予め決められた順序（順方向計測、その後に逆方向計測、この順序を繰り返す、又は順方向計測を数回繰り返した後に逆方向計測を数回繰り返す、この計測順序を繰り返す）によったり、下流側の超音波送受波器３に電圧を印加することを検知すれば、それが逆方向計測判別となる。流れ方向が順方向と逆方向との間で変わる場合には、流れ方向が反転したことを検知して、流れが変わった後において、下流に位置する超音波送受波器に対する電圧印加時を逆方向計測時と判定することができる。そして、順方向を数回計測した後、逆方向を計測して、前記ピーク電圧が変わる傾向をとらえ、順逆の判定をする方法がある。また、順方向、逆方向のその到達時間差から順逆の判定をする方法もある。
【００３８】
また、流速が速くなるほど、逆方向計測のときのピーク電圧は高くなり、順方向計測のときのピーク電圧は低くなる傾向にある。順方向計測のとき、図５に示すＣ点における受波電圧で測定可能であれば、流速が遅い場合の受波電圧は測定可能な電圧よりも高い場合が多い。流速判定部８により、これから計測する流体の流速を判定する。流速判定部８からの信号を受けて、印加電圧制御部４により順方向計測の場合に、図５に示す１点鎖線ｖ１のように、流速がＤになるまでは低い印加電圧を印加する。Ｄ以上の流速を検知したときにｖ２のように高くする（元の電圧に戻す）。逆方向計測時には、流速が速い場合は遅い場合より低い印加電圧を印加する。このように、流速が速い場合と遅い場合とで送波時の印加電圧を変えて、送波時における電圧印加を測定が許容される範囲内で選択的に下げることにより、少ない電力消費で流量測定が可能となり、例えば、電源に簡易な電池を使用の場合でも、長期間のメンテナンスフリーを実現できる。
【００３９】
流速判定方法としては、計測する流体の流速が、予め設定されている複数の流速判定値に対して、その判定値に達したかどうかを判定する方法がある。この判定に基づき、印加電圧制御部４に対して複数の段階的な印加電圧の変更ができるようにする。つまり、流速判定部８は、演算処理部７から送信されてくる流速データから低い印加電圧を印加させるか否かを判定し印加電圧制御部４に対して出力する。
【００４０】
図６は、一定の印加電圧を印加したときの、ピーク電圧と計測体（流体）の温度との関係を示す特性図である。計測体の温度が低くなるほど、ピーク電圧は高くなる傾向にある。図６に示すＥ点における受波電圧で測定可能であれば、それより低い温度で計測した時の受波電圧は測定可能な程度よりも高い場合が多い。順方向と逆方向とに関係なく、全体的に温度が低いと減衰が小さく受波電圧は高い。温度判定部１０により、計測時の温度が、例えば、図６におけるＦ点以下の温度と判定した場合、温度判定部１０からの信号を受けて、印加電圧制御部４により、低い印加電圧を印加する。このように、温度が高い場合と低い場合とで送波時の印加電圧を変えて、送波時における電圧印加を測定が許容される範囲内で選択的に下げることにより、測定に要する消費電力が節約され、電源を電池とする場合の長期間の電源保証が可能となる。
【００４１】
温度判定方法としては、サーミスタ等のＩＣによって温度計測を行い、計測した温度が予め定められた温度以下に達したかどうか判定する方法がある。この判定に基づき、印加電圧制御部４に対して複数の段階的な印加電圧の変更ができるようにする。つまり、温度判定部１０は、設定した温度に達しているかどうかを判定し低い印加電圧を印加させるか否かの信号を印加電圧制御部４に対して出力する
【００４２】
なお、温度は、実施例のように計測体の温度とするのが好ましいが、超音波流量計が設置される場所の温度（周囲環境温度）に置き換えることができる。
【００４３】
図７は、一定の印加電圧を印加したときの、ピーク電圧と計測体の種類との関係を示す特性図である。計測体の種類としては、例えば、計測体Ａは空気、計測体Ｂは天然ガスがあげられる。計測体の種類によって、ピーク電圧の高さが変化する。空気の方が超音波の減衰が小さく超音波が伝わり易く、天然ガスの方が超音波の減衰が大きく超音波が伝わり難いといえる。図７に示す計測体Ｂ（天然ガス）の受波電圧で測定可能であれば、計測体Ａ（空気）の計測時に得られる受波電圧は測定可能な程度より高い場合が多い。順方向と逆方向とに関係なく、超音波の減衰の小さい計測体であれば受波電圧は高い。初めに異なる複数の種類の流体の流速を計測した後、流体判定部１１により、これから計測する流体の種類を判定して、例えば、計測体Ａを計測する場合、流体判定部１１からの信号を受けて、印加電圧制御部４により、送波時に低い印加電圧を印加する。これにより、測定に要する消費電力が節約され、電源を電池とする場合の長時間の電源保証が可能になる。
【００４４】
流体判定方法としては、超音波密度検出器があげられる。流路の壁に流体に接して密度検出用の超音波発信器を取りつけ、それに一定の電圧を与えて共振振動をさせ、その出力を検出する。計測した密度から流体の種類を判定する方法がある。この判定に基づき、印加電圧制御部４に対して複数の段階的な印加電圧の変更ができるようにする。つまり、異なる種類の流体の流速を計測した後、流体の種類毎の受信波の電圧波形のピーク電圧のデータに基づき、最も低い流体の種類を抽出し、その流体とは異なる他の種類の流体と決定したとき、流体判定部１１は、印加電圧を低くする信号を印加電圧制御部４に対して出力する。
【００４５】
なお、流体判定の手段として、超音波受信部５の到達時間のデータを用いて到達時間差から流体の種別を判定してもよい。また、音響インピーダンスの測定により流体の種別を判定してもよい。
【００４６】
図９は、送波印加電圧制御のフローチャートで超音波ガス流量計を例に説明する。Ｓ１において、流体の流れに対し逆方向で計測かどうかを判定する。ＹＥＳの場合（逆方向計測）、Ｓ２において、送波印加電圧を低く設定する。Ｓ３おいて、流速が予め設定したしきい値より小さいかどうかを判定する。ＹＥＳの場合（流速が遅い）、Ｓ４において、送波印加電圧を低く設定する。Ｓ５において、流体の温度が予め設定したしきい値より小さいかどうかを判定する。ＹＥＳの場合（温度が低い）、Ｓ６において、送波印加電圧を低く設定する。Ｓ７において、種別が計測体Ａかどうかを判定する。ＹＥＳの場合、Ｓ８において、送波印加電圧を低く設定する。Ｓ９において、超音波の計測のステップにおける超音波の送波のタイミングかどうかを判定する。ＹＥＳの場合、Ｓ１０において、上記で設定された送波電圧が印加される。このように、流体の流れ方向や流速および温度、流体の種別に応じて、送波時の印加電圧を変えて計測が行なわれることにより、測定に要する消費電力が節約される。上記条件は、いずれかを使いそれに応じて送波時の印加電圧を変えて計測を行ってもよく、または、これを任意に組み合わせて送波時の印加電圧を変えて計測を行ってもよい。これにより、測定に要する消費電力が節約され、その効果は相乗的に高められ、例えば、電源に簡易な電池を使用の場合でも、長期間のメンテナンスフリーを実現できる。なお、上記におけるＳ７およびＳ８の流体の種別を判定するステップは省略化してもよい。
【図面の簡単な説明】
【図１】本発明の超音波流量計の概念を示す全体構成図。
【図２】本発明に係る計測部のブロック図。
【図３】図２のタイミングチャート。
【図４】本発明に係る超音波送受波器に印加する印加電圧とゼロクロストリガ波のピーク電圧との関係を示す特性図。
【図５】本発明に係る順方向で計測のときおよび逆方向で計測のときの、ピーク電圧と流路を通過する計測体の流速との関係を示す特性図。
【図６】本発明に係るピーク電圧と環境温度との関係を示す特性図。
【図７】ピーク電圧と計測体の種類との関係を示す特性図。
【図８】ゼロクロス点の説明のための超音波信号波形図。
【図９】本発明に係る送波印加電圧制御のフローチャート。
【符号の説明】
２流路
３ａ，３ｂ超音波送受波器
４印加電圧制御部
５超音波受信部
６送受切替部
７演算処理部
８流速判定部
９順逆計測判定部
１０温度判定部
１１流体判定部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic flowmeter that measures the flow velocity and flow rate of a fluid such as gas or water using ultrasonic waves.
[0002]
[Prior art]
In this type of ultrasonic flow meter, for example, an ultrasonic gas flow meter, ultrasonic elements are arranged on the upstream side and the downstream side of a flow path through which a fluid flows, and ultrasonic waves are transmitted by driving the ultrasonic elements on the upstream side. Then, the output is received by the ultrasonic element on the downstream side, and the time from the start of transmission to the reception is measured. Similarly, the ultrasonic element is driven from the downstream side to transmit ultrasonic waves, the output is received by the upstream ultrasonic element, and the time from the start of transmission to reception is measured. The flow velocity is determined from these two times, and the flow rate is determined by multiplying the flow velocity by the cross-sectional area of the flow path.
[0003]
As a method of detecting the arrival time of the ultrasonic wave, there is a method in which a time until a zero cross point at which the amplitude of a predetermined number of waveforms becomes zero is set as the reception time. FIG. 8 shows an ultrasonic reception signal. When the first wave is detected, the amplitude is small and a sufficient S / N ratio cannot be secured. When the detection is to be performed, there is a method of providing a certain threshold voltage VTH and measuring the time until the next zero-cross point exceeding the threshold voltage VTH. The portion of the waveform that becomes the peak before the zero-cross point c, in this example, the third wave is called a zero-cross trigger wave.
[0004]
In the above description, the peak voltage value (maximum amplitude) in the zero cross trigger wave is referred to as a peak voltage in the following description. However, the maximum amplitude of the peak voltage greatly changes depending on fluid, flow rate, pressure, temperature, and the like. Ultrasonic flow meters are required to respond to such changes.
[0005]
[Problems to be solved by the invention]
A conventional ultrasonic flowmeter transmits an ultrasonic wave by constantly applying a constant applied voltage to drive an ultrasonic element. This type of ultrasonic gas flow meter is required to operate, for example, on a battery for about 10 years without maintenance, and the current consumption cannot be said to be low by the conventional method.
[0006]
The present invention has been made in view of the above points, and has as its object to provide an ultrasonic flowmeter capable of transmitting and receiving an ultrasonic signal with low current consumption.
[0007]
Means for Solving the Problems and Effects of the Invention
In order to solve the above problems, the ultrasonic flow meter of the present invention is provided with at least a pair of ultrasonic transducers for transmitting and receiving, transmitting and receiving ultrasonic waves in the forward and reverse directions in the flow of the fluid respectively. , An ultrasonic flowmeter for obtaining a flow velocity and a flow rate from the arrival time in each direction, and an applied voltage applied to an ultrasonic transducer during ultrasonic transmission according to forward measurement and reverse measurement , A transmission-time applied voltage control means for controlling the power supply.
[0008]
In the process studied by the present inventor, the peak of the received voltage when the ultrasonic wave transmitted by applying voltage to the ultrasonic transducer is received by the other ultrasonic transducer is measured in the forward direction. There is a considerable difference between (transmitting) and reverse (transmitting) times. For example, even when transmitting at the same applied voltage, there is a tendency that a higher receiving voltage peak occurs during reverse transmitting than during forward transmitting. Yes, if it is possible to measure with the received voltage at the time of forward measurement, it has been verified that the received voltage obtained at the time of backward transmission measurement is often higher than measurable, and has reached the present invention. is there.
[0009]
Specifically, for example, the applied voltage control unit at the time of transmission transmits the applied voltage applied to the ultrasonic transducer at the time of ultrasonic transmission according to the forward measurement and the backward measurement, and forward voltage during the backward measurement. Control lower than during direction measurement.
[0010]
As described above, the applied voltage at the time of transmission is changed by the applied voltage control means at the time of forward transmission and the backward measurement, and the applied voltage at the time of transmission is transmitted within a range in which measurement is allowed. By selectively lowering the wave application voltage, flow measurement can be performed with low power consumption. For example, even when a simple battery is used as a power supply, long-term maintenance-free operation can be realized.
[0011]
In the above description, if the flow direction is fixed, a predetermined order (forward measurement, then reverse measurement, repeat this order, or repeat forward measurement several times, then reverse measurement Is repeated several times, this measurement order is repeated), or when it is detected that a voltage is applied to the ultrasonic transducer on the downstream side, it is determined to be a backward measurement, and the flow direction is the forward direction and the reverse direction. If the flow direction changes, the flow direction is detected to be reversed, and after the flow direction changes, it is possible to determine that the time of voltage application to the ultrasonic transducer located downstream is the time of the reverse direction measurement. it can.
[0012]
Furthermore, the present invention provides at least a pair of ultrasonic transducers for transmitting and receiving, transmitting and receiving ultrasonic waves in the forward and reverse directions in the flow of the fluid, and determining the flow rate from the arrival time in each direction. Further, an ultrasonic flowmeter for obtaining a flow rate, provided with a flow velocity determining unit, for controlling an applied voltage to be applied to the ultrasonic transducer when transmitting the ultrasonic wave according to the determined flow velocity. Means are provided.
[0013]
The peak of the received voltage when the ultrasonic wave transmitted by the application of the voltage to the ultrasonic transducer is received by the other ultrasonic transducer is considerably different depending on the speed of the fluid, for example, At the time of direction measurement, even if the fluid is transmitted at the same applied voltage, when the velocity of the fluid is low, there is a tendency that the received voltage peak will be higher than when the fluid is fast. When the speed is slow, the receiving voltage peak tends to be lower than when the speed is high.For example, if it is possible to measure the receiving voltage when the flow velocity is high during forward measurement, the receiving voltage when the flow velocity is slow can be measured In many cases, if it is possible to measure with the received voltage when the flow velocity is slow when measuring in the reverse direction, the received voltage when the flow velocity is fast is often higher than measurable. That is the basis of the invention That.
[0014]
Specifically, for example, the applied voltage control unit at the time of transmission transmits the applied voltage at the time of forward measurement to be applied to the ultrasonic transducer at the time of ultrasonic transmission according to the determined flow velocity, and the flow velocity of the fluid is small. In this case, the applied voltage is made lower than when it is large, and the applied voltage at the time of reverse measurement is controlled so that the applied voltage is lower when the flow velocity of the fluid is large than when it is small.
[0015]
As described above, the transmission voltage applied voltage control means changes the applied voltage at the time of transmission between the case where the flow velocity is high and the case where the flow velocity is low, and selectively applies the voltage application at the time of transmission within a range where measurement is allowed. By lowering the flow rate, the flow rate can be measured with low power consumption. For example, even when a simple battery is used as the power supply, long-term maintenance-free operation can be realized.
[0016]
Furthermore, the present invention provides at least a pair of ultrasonic transducers for transmitting and receiving, transmitting and receiving ultrasonic waves in the forward and reverse directions in the flow of the fluid, and determining the flow rate from the arrival time in each direction. Further, an ultrasonic flowmeter for obtaining a flow rate, provided with a temperature determination unit, and an applied voltage control unit during transmission which controls an applied voltage applied to the ultrasonic transducer during ultrasonic transmission according to the measured temperature. Is provided.
[0017]
The peak of the received voltage when the ultrasonic wave transmitted by the application of the voltage to the ultrasonic transducer is received by the other ultrasonic transducer is considerably different depending on the temperature, for example, the same application. Even when transmitting at a voltage, when the temperature of the fluid is low, there is a tendency to generate a higher received voltage peak than when the fluid is high.For example, if it is possible to measure with the received voltage at a high temperature, if the temperature is low, The received voltage is often higher than measurable.
[0018]
Specifically, for example, the applied voltage control unit at the time of transmission transmits the applied voltage at the time of forward measurement and at the time of reverse measurement to be applied to the ultrasonic transducer at the time of ultrasonic transmission according to the measured temperature, Is controlled so that the applied voltage is lower when the temperature is low than when it is high.
[0019]
As described above, the applied voltage control unit at the time of transmission changes the applied voltage at the time of transmission between the case where the temperature is high and the case where the temperature is low, and selectively controls the voltage application at the time of transmission within a range where measurement is allowed. By lowering the power, the power consumption required for the measurement is saved, and a long-term power supply guarantee when using a battery as the power supply becomes possible.
[0020]
Furthermore, the present invention provides at least a pair of ultrasonic transducers for transmitting and receiving, transmitting and receiving ultrasonic waves in the forward and reverse directions in the flow of the fluid, and determining the flow rate from the arrival time in each direction. An ultrasonic flowmeter for further obtaining a flow rate, provided with a measurement object determining unit, for controlling an applied voltage to be applied to an ultrasonic transducer when transmitting an ultrasonic wave according to a detected measurement fluid, an application during transmission. A voltage control means is provided.
[0021]
Specifically, for example, the applied voltage control means at the time of transmission transmits the applied voltage at the time of forward measurement and reverse measurement applied to the ultrasonic transducer at the time of ultrasonic transmission according to the measurement fluid, The control is performed such that the applied voltage is lower in the case of the measurement fluid having a small attenuation of the sound wave than in the case of the measurement fluid having a large attenuation of the ultrasonic wave.
[0022]
When the applied voltage at the time of transmission is changed by the applied voltage control unit at the time of transmission according to the type of the fluid to be measured as described above, power consumption required for measurement is saved, and the battery is used as a power supply. For a long period of time.
[0023]
Furthermore, the present invention provides an applied voltage control at the time of transmission according to claim 1 or 2, an applied voltage control at the time of transmission according to claim 3 or 4, and an applied voltage at the time of transmission according to claim 5 or 6. The present invention is characterized in that it includes a transmission-time applied voltage control means for executing the transmission-time applied voltage control by arbitrary two or more combinations with the voltage control.
[0024]
According to the above configuration, according to the flow direction, the flow velocity, and the temperature of the fluid, the measurement is performed by changing the applied voltage at the time of transmitting by arbitrarily combining them, thereby saving power consumption required for the measurement. Synergistically, for example, even if a simple battery is used for the power supply, long-term maintenance-free operation can be realized.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to examples shown in the drawings. FIG. 1 is an overall configuration diagram showing the concept of an ultrasonic flow meter according to the present invention. An ultrasonic flow meter 1 is arranged to face a fluid flow path 2 and includes a pair of ultrasonic flow meters including a piezoelectric element. The ultrasonic wave transmitter / receiver 3a and the ultrasonic wave transmitter / receiver 3b (these are sometimes collectively referred to as an ultrasonic wave transmitter / receiver 3), and a driving element for driving a piezoelectric element of the ultrasonic wave transmitter / receiver 3 to transmit ultrasonic waves. An applied voltage control unit 4 for controlling an applied voltage; an ultrasonic receiving unit 5 for receiving an ultrasonic signal transmitted by driving a piezoelectric element of the ultrasonic transducer 3; In order to transmit an ultrasonic wave in a forward direction, or to transmit an ultrasonic wave in a reverse direction, and to switch the direction, between the ultrasonic transducer 3 and the applied voltage control unit 4 and between the ultrasonic transducer 3 And a transmission / reception switching unit 6 connected between the ultrasonic receiving unit 5 and the ultrasonic receiving unit 5. Constructed and a processing unit 7 for processing of calculating the flow rate from the wave arrival time. A signal for controlling the applied voltage is transmitted to the input side of the applied voltage control unit 4, to which the flow velocity determining unit 8, the forward / reverse measurement determining unit 9, the temperature determining unit 10, and the fluid determining unit 11 are connected. The applied voltage control unit 4 controls the applied voltage of the ultrasonic transducers 3a and 3b (controls the applied voltage level and application time) via the transmission / reception switching unit 6. The ultrasonic receiving unit 5 is also used as a receiving unit of the ultrasonic waves transmitted in the forward direction and the reverse direction with respect to the flow.
[0026]
Next, a method of measuring the flow rate will be described. The flow of the fluid is in the direction of the arrow shown in FIG. 1 (the flow velocity of the fluid is V). First, the arrival time when an ultrasonic wave is transmitted in a direction along the flow (forward direction) is measured. The transmission / reception switching unit 6 sets the ultrasonic transducer 3a as a transmitting side, and the ultrasonic transducer 3b as a receiving side. The piezoelectric element of the ultrasonic transducer 3a is driven by the applied voltage control unit 4, and the ultrasonic wave is transmitted. The ultrasonic wave is traversed in the flow path 2 and reaches the ultrasonic transducer 3b. An ultrasonic reception signal is input from the ultrasonic transducer 3b to the ultrasonic receiver 5.
[0027]
Next, an operation performed by the ultrasonic receiving unit 5 will be described based on a block diagram of a measuring unit illustrated as an example in FIG. 2 and a timing chart illustrated in FIG. As shown in FIG. 2, the output of the receiving-side ultrasonic element (piezoelectric element) is voltage-amplified (for example, non-inverted) by an amplifier 20 (for example, an operational amplifier), and the amplified signal Va is supplied to a zero-cross type comparator 21 (first comparator). An input (for example, a non-inverting input) is input to the differential comparator 22 (second comparator) (for example, an inverting input). The comparator outputs Vb and Vc are input to ports #S and #R of an RS flip-flop circuit (hereinafter, referred to as RSFF circuit) 23, respectively. The zero cross point pulse generation circuit 24 composed of a monostable multivibrator or the like detects the arrival time of the ultrasonic wave in the output waveform Va and outputs the zero cross point detection signal Ve from the port #Q output Vd of the RSFF circuit 23. Based on the zero cross point detection signal Ve, the number of clock pulses from the clock pulse generation circuit 25 (for example, a crystal oscillator or an astable multivibrator) is counted by a pulse counter circuit 26 (for example, a JK flip-flop circuit), and an arrival time detection signal Vf Is output. The zero cross point detection signal Ve is controlled so as to end with only one output (not shown).
[0028]
As shown in FIG. 3, the amplified signal Va (ultrasonic reception output) is an irregular waveform signal that does not have a sufficient amplitude (generated voltage) level due to the influence of noise and the like at the beginning of reception, and is the n-th signal from the top. It is usual that the amplitude level at which the measurable amplitude level finally reaches the measurable level in the (third) waveform portion. Therefore, in order to enable accurate time measurement of the amplified signal Va of the ultrasonic reception output, a zero-cross method described below is generally adopted. In other words, a waveform portion (the third wave in the figure) that exceeds (or falls below) the threshold value VTH input to the differential comparator 22 (see FIG. 2) is used as a trigger wave, and the amplitude of this trigger wave is used. This is a method in which a zero-crossing point at which (or phase) becomes zero is detected by the zero-crossing point pulse generation circuit 24 (see FIG. 2) on the waveform of the amplified signal Va (or a derivative thereof).
[0029]
Specifically, the zero-cross method is applied to the waveform of the amplified signal Va as follows. In the zero-crossing type comparator 21 to which the amplified signal Va is non-inverted, the amplitude (generated voltage) of the waveform of the amplified signal Va has a positive waveform portion (the first wave, the third wave, and the fifth wave). ..) Are output intermittently as the first comparator output Vb. On the other hand, in the differential comparator 22 to which the amplified signal Va of the negative polarity and the threshold value VTH of the positive polarity are inputted, the waveform portions exceeding the threshold value VTH (waves (3), (5)...) The pulse which becomes L corresponding to the top) is output intermittently as the second comparator output Vc.
[0030]
Since H is continuously input to the port #R of the RSFF circuit 23 until a pulse signal of a trigger wave (third wave) exceeding the threshold value VTH is first input at the second comparator output Vc. The port #Q output Vd of the RSFF circuit 23 is maintained at L. In a state where the waveform detection pulse signal of the third wave from the first comparator output Vb is input (H) to the port #S of the RSFF circuit 23, a trigger wave (third wave) is output from the second comparator output Vc. Is input (L) to the port #R, the output Vd of the port #Q changes to H. Then, the port #Q output Vd is maintained at H until the waveform detection pulse signal of the third wave from the first comparator output Vb is not input to the port #S of the RSFF circuit 23, and the input to the port #S is at L. , The port #Q output Vd becomes L.
[0031]
The zero cross point pulse generation circuit 24 detects the falling edge of the port #Q output Vd of the RSFF circuit 23, and outputs a pulse which becomes H corresponding to the zero cross point as a zero cross point detection signal Ve. The pulse counter circuit 26 counts the number of clock pulses between the zero cross point detection pulse signal (Ve) and the ultrasonic transmission pulse signal of the transmission-side ultrasonic element (piezoelectric element), and outputs the arrival time detection signal Vf. . The detection arrival time (forward arrival time Td) obtained by the arrival time detection signal Vf in this way is longer than the actual (true) arrival time. In other words, the detection arrival time is determined by using the elapsed time from the start of reception to the zero-cross point of the trigger wave (the third wave) (for 1.5 cycles of the first to third waves) as a correction value. Subtract from to get the actual arrival time.
[0032]
Next, the arrival time when the ultrasonic wave is transmitted in a direction opposite to the flow (reverse direction) is measured. The transmission / reception switching unit 6 sets the ultrasonic transducer 3b as a transmitting side, and the ultrasonic transducer 3a as a receiving side. The piezoelectric element of the ultrasonic transducer 3b is driven by the applied voltage controller 4 to transmit the ultrasonic wave, and the ultrasonic wave is traversed in the flow path 2 and reaches the ultrasonic transducer 3a. Similarly, the arrival time Tu in the reverse direction is measured.
[0033]
The data obtained by measuring the arrival time in the ultrasonic receiving unit 5 is transmitted to the arithmetic processing unit 7 upon receiving a timing signal from the applied voltage control unit 4. The arithmetic processing unit 7 calculates the flow velocity from the arrival time.
[0034]
The flow velocity V (m / s) and the flow rate Q (m) are calculated from the forward arrival time Td and the reverse arrival time Tu measured above. ³ / S) is obtained from the following equation. In FIG. 1, the flow velocity of the fluid is V, the speed of sound propagating through the fluid is C, the propagation distance of the ultrasonic wave is L, and the cross-sectional area of the flow path 2 is A.
Td = L / (C + V) (1)
Tu = L / (C−V) (2)
V = (1 / Td-1 / Tu) L / 2 (3)
Q = VA (4)
[0035]
Next, control of the applied voltage of the ultrasonic transducer 3 of the present invention will be described. FIG. 4 shows the relationship between the peak voltage (maximum amplitude voltage) of the received voltage when the ultrasonic wave transmitted by applying a voltage to the ultrasonic transducer 3 is received by the ultrasonic transducer 3 of the other party. FIG. 4 is a characteristic diagram showing a relationship. The voltage applied to the piezoelectric element is proportional to the vibration of the piezoelectric element. The higher the applied voltage, the higher the peak voltage. Therefore, if the measurement can be performed with the received voltage at the applied voltage of FIG. 4A, for example, setting the applied voltage of FIG. 4B to an excessively high voltage in the ultrasonic flowmeter results in wasteful consumption of current consumption. Will do.
[0036]
FIG. 5 shows the relationship between the peak voltage and the flow velocity of the measurement object passing through the flow path when a constant applied voltage is applied to the ultrasonic transducer 3 and measurement is performed in the forward direction and when measurement is performed in the reverse direction. FIG. The peak voltage is considerably different between when measuring (transmitting) in the forward direction and when measuring (transmitting) in the reverse direction, and tends to be higher in backward measurement than in forward measurement. If it can be measured with the received voltage at the time of forward measurement, the received voltage obtained at the time of reverse measurement is often higher than it can be measured. The forward / reverse measurement determination unit 9 determines whether the measurement direction to be measured from now on is forward or backward. In the case where the signal is received from the forward / reverse measurement determining unit 9 and the applied voltage control unit 4 transmits and measures the ultrasonic wave in the reverse direction, the measurement is performed in the forward direction as shown by the broken line in FIG. Apply lower voltage. As described above, the applied voltage at the time of transmission is changed between the forward measurement and the reverse measurement, and the voltage application at the time of transmission is selectively reduced within a range in which the measurement is allowed, thereby reducing power consumption. Thus, for example, even if a simple battery is used as a power supply, long-term maintenance-free operation can be realized.
[0037]
As the forward / reverse measurement determination method, if the flow direction is fixed, a predetermined order (forward direction measurement, then reverse direction measurement, repeat this order, or repeat forward direction measurement several times, then reverse If the direction measurement is repeated several times, and the measurement order is repeated), or if it is detected that a voltage is applied to the ultrasonic transducer 3 on the downstream side, the measurement becomes the reverse direction measurement determination. When the flow direction changes between the forward direction and the reverse direction, it is detected that the flow direction has been reversed, and after the flow has changed, the time of voltage application to the ultrasonic transducer located downstream is reversed. It can be determined that the direction is being measured. Then, there is a method of measuring the forward direction several times and then measuring the reverse direction to grasp the tendency of the peak voltage to change, thereby making a forward / reverse determination. There is also a method of determining forward / reverse from the difference in arrival time between the forward and reverse directions.
[0038]
Also, as the flow velocity increases, the peak voltage in the backward measurement tends to increase, and the peak voltage in the forward measurement tends to decrease. At the time of forward measurement, if the measurement can be performed at the reception voltage at the point C shown in FIG. 5, the reception voltage when the flow velocity is slow is often higher than the measurable voltage. The flow velocity determination unit 8 determines the flow velocity of the fluid to be measured. In the case of receiving a signal from the flow velocity determining unit 8 and performing forward measurement by the applied voltage control unit 4, a low applied voltage is applied until the flow velocity becomes D as indicated by a dashed line v1 in FIG. When a flow rate equal to or greater than D is detected, the flow rate is increased to v2 (return to the original voltage). At the time of measurement in the reverse direction, a lower applied voltage is applied when the flow velocity is high than when the flow velocity is low. As described above, the applied voltage at the time of transmission is changed between a case where the flow velocity is high and a case where the flow velocity is low, and the voltage application during the transmission is selectively reduced within a range in which measurement is allowed. Measurement becomes possible, and for example, even when a simple battery is used as a power supply, long-term maintenance-free operation can be realized.
[0039]
As a flow velocity determining method, there is a method of determining whether or not the flow velocity of the fluid to be measured has reached a predetermined plurality of flow velocity determination values. Based on this determination, the application voltage control unit 4 can change the application voltage in a plurality of steps. That is, the flow velocity determining unit 8 determines whether to apply a low applied voltage from the flow velocity data transmitted from the arithmetic processing unit 7 and outputs the result to the applied voltage control unit 4.
[0040]
FIG. 6 is a characteristic diagram showing the relationship between the peak voltage and the temperature of the measurement object (fluid) when a constant applied voltage is applied. The peak voltage tends to increase as the temperature of the measurement body decreases. If it can be measured at the receiving voltage at point E shown in FIG. 6, the receiving voltage measured at a lower temperature is often higher than the measurable level. Regardless of the forward direction and the reverse direction, when the temperature is low as a whole, the attenuation is small and the receiving voltage is high. When the temperature at the time of measurement is determined by the temperature determination unit 10 to be, for example, a temperature equal to or lower than the point F in FIG. 6, a signal from the temperature determination unit 10 is received, and the applied voltage control unit 4 applies a low applied voltage. I do. As described above, by changing the applied voltage at the time of transmission between the case where the temperature is high and the case where the temperature is low, the voltage application during the transmission is selectively lowered within a range in which the measurement is allowed, so that the power consumption required for the measurement is obtained. Is saved, and a long-term power supply can be guaranteed when the power supply is a battery.
[0041]
As a temperature determination method, there is a method of performing temperature measurement by an IC such as a thermistor and determining whether the measured temperature has reached a predetermined temperature or less. Based on this determination, the application voltage control unit 4 can change the application voltage in a plurality of steps. That is, the temperature determination unit 10 determines whether the temperature has reached the set temperature and outputs a signal indicating whether to apply a low applied voltage to the applied voltage control unit 4.
[0042]
The temperature is preferably the temperature of the measuring body as in the embodiment, but can be replaced by the temperature of the place where the ultrasonic flowmeter is installed (ambient environmental temperature).
[0043]
FIG. 7 is a characteristic diagram showing the relationship between the peak voltage and the type of the measuring object when a constant applied voltage is applied. Examples of the type of the measurement body include air for the measurement body A and natural gas for the measurement body B. The height of the peak voltage changes depending on the type of the measurement object. It can be said that air has a smaller attenuation of the ultrasonic wave and the ultrasonic wave is easily transmitted, and natural gas has a larger attenuation of the ultrasonic wave and the ultrasonic wave is hardly transmitted. If it is possible to measure with the receiving voltage of the measuring object B (natural gas) shown in FIG. 7, the receiving voltage obtained at the time of measuring the measuring object A (air) is often higher than the measurable degree. Regardless of the forward direction and the reverse direction, if the measurement object has a small attenuation of the ultrasonic wave, the reception voltage is high. First, after measuring the flow velocities of a plurality of different types of fluids, the fluid determination unit 11 determines the type of fluid to be measured from now on. For example, when measuring the measurement body A, a signal from the fluid determination unit 11 is output. In response, the applied voltage control unit 4 applies a low applied voltage during transmission. Thereby, the power consumption required for the measurement is saved, and a long-term power supply guarantee when the power supply is a battery can be provided.
[0044]
An example of the fluid determination method is an ultrasonic density detector. An ultrasonic transmitter for density detection is attached to the wall of the flow channel in contact with the fluid, and a constant voltage is applied to the ultrasonic transmitter to cause resonance vibration, and the output is detected. There is a method of determining the type of fluid from the measured density. Based on this determination, the application voltage control unit 4 can change the application voltage in a plurality of steps. That is, after measuring the flow velocities of different types of fluids, the lowest fluid type is extracted based on the peak voltage data of the voltage waveform of the received wave for each type of fluid, and another type of fluid different from that fluid is extracted. When determined, the fluid determination unit 11 outputs a signal for reducing the applied voltage to the applied voltage control unit 4.
[0045]
In addition, as a means for determining the fluid, the type of the fluid may be determined from the difference in the arrival time using the data of the arrival time of the ultrasonic receiving unit 5. Further, the type of the fluid may be determined by measuring the acoustic impedance.
[0046]
FIG. 9 is a flowchart of the control of the applied voltage of the transmitted wave, and the ultrasonic gas flow meter will be described as an example. In S1, it is determined whether the measurement is performed in the reverse direction to the flow of the fluid. In the case of YES (reverse direction measurement), in S2, the transmission wave applied voltage is set low. In S3, it is determined whether or not the flow velocity is smaller than a preset threshold value. In the case of YES (the flow velocity is low), in S4, the transmission voltage is set low. In S5, it is determined whether the temperature of the fluid is lower than a preset threshold value. If YES (the temperature is low), in S6, the transmission wave application voltage is set low. In S7, it is determined whether the type is the measurement object A. In the case of YES, in S8, the transmission wave application voltage is set low. In S9, it is determined whether or not it is the timing of transmitting the ultrasonic wave in the ultrasonic measurement step. In the case of YES, in S10, the transmission voltage set above is applied. As described above, the measurement is performed by changing the applied voltage at the time of transmission according to the flow direction, the flow velocity and the temperature of the fluid, and the type of the fluid, thereby saving power consumption required for the measurement. The above conditions may be used to perform measurement by changing the applied voltage at the time of transmission according to any of them, or may be measured by changing the applied voltage at the time of transmission by arbitrarily combining them. . As a result, the power consumption required for the measurement is saved, and the effect is synergistically enhanced. For example, even when a simple battery is used for the power supply, long-term maintenance-free operation can be realized. The step of determining the type of fluid in S7 and S8 in the above may be omitted.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing the concept of an ultrasonic flowmeter of the present invention.
FIG. 2 is a block diagram of a measuring unit according to the present invention.
FIG. 3 is a timing chart of FIG. 2;
FIG. 4 is a characteristic diagram showing a relationship between an applied voltage applied to the ultrasonic transducer according to the present invention and a peak voltage of a zero-cross trigger wave.
FIG. 5 is a characteristic diagram showing a relationship between a peak voltage and a flow velocity of a measurement object passing through a flow path when measurement is performed in a forward direction and when measurement is performed in a reverse direction according to the present invention.
FIG. 6 is a characteristic diagram showing a relationship between a peak voltage and an environmental temperature according to the present invention.
FIG. 7 is a characteristic diagram showing a relationship between a peak voltage and a type of a measurement object.
FIG. 8 is an ultrasonic signal waveform diagram for explaining a zero-cross point.
FIG. 9 is a flowchart of transmission wave application voltage control according to the present invention.
[Explanation of symbols]
2 Channel
3a, 3b Ultrasonic transducer
4 Applied voltage control unit
5 Ultrasonic receiver
6 Transmission / reception switching unit
7 arithmetic processing unit
8 Flow velocity judgment unit
9 Forward / reverse measurement judgment unit
10 Temperature judgment unit
11 Fluid judgment unit

Claims

At least a pair of ultrasonic transducers for transmitting and receiving are provided, ultrasonic waves are transmitted and received in the forward and reverse directions in the fluid flow, and the flow velocity and the flow rate are obtained from the arrival time in each direction. A flowmeter, wherein transmission-wave applied voltage control means for controlling an applied voltage to be applied to the ultrasonic transducer during ultrasonic transmission according to forward measurement and reverse measurement is provided. Characteristic ultrasonic flow meter.

The transmission voltage applied voltage control means controls the applied voltage applied to the ultrasonic transducer during ultrasonic transmission according to the forward measurement and the reverse measurement, to be lower than the forward measurement during the backward measurement. The ultrasonic flowmeter according to claim 1, wherein

At least a pair of ultrasonic transducers for transmitting and receiving are provided, ultrasonic waves are transmitted and received in the forward and reverse directions in the fluid flow, and the flow velocity and the flow rate are obtained from the arrival time in each direction. A flowmeter, provided with a flow velocity determination unit, and provided with a transmission time applied voltage control means for controlling an applied voltage applied to the ultrasonic transducer during ultrasonic transmission according to the obtained flow velocity. Characteristic ultrasonic flow meter.

The transmission-time applied voltage control means, the applied voltage at the time of forward measurement applied to the ultrasonic transducer during ultrasonic transmission according to the determined flow velocity, when the flow velocity of the fluid is small compared to when the flow velocity is large 4. The ultrasonic flowmeter according to claim 3, wherein the applied voltage is low, and the applied voltage at the time of reverse measurement is controlled such that the applied voltage is lower when the flow velocity of the fluid is higher than when the flow velocity of the fluid is lower.

At least a pair of ultrasonic transducers for transmitting and receiving are provided, ultrasonic waves are transmitted and received in the forward and reverse directions in the fluid flow, and the flow velocity and the flow rate are obtained from the arrival time in each direction. A flowmeter, wherein a temperature determination unit is provided, and transmission-time applied voltage control means for controlling an applied voltage applied to an ultrasonic transducer during ultrasonic transmission according to a measured temperature is provided. And ultrasonic flow meter.

The applied voltage control means at the time of transmission transmits the applied voltage at the time of forward measurement and reverse measurement applied to the ultrasonic transducer at the time of ultrasonic transmission according to the measured temperature, when the temperature of the fluid is low. The ultrasonic flowmeter according to claim 5, wherein the control is performed such that the applied voltage is lower than when the applied voltage is high.

At least a pair of ultrasonic transducers for transmitting and receiving are provided, ultrasonic waves are transmitted and received in the forward and reverse directions in the fluid flow, and the flow velocity and the flow rate are obtained from the arrival time in each direction. A flow meter, provided with a measurement object determination unit, and provided with a transmission time applied voltage control means for controlling an applied voltage applied to the ultrasonic transducer during ultrasonic transmission in accordance with the detected measurement fluid. An ultrasonic flowmeter, characterized in that:

The applied voltage control means at the time of transmission transmits an applied voltage at the time of forward measurement and reverse measurement applied to the ultrasonic transducer at the time of ultrasonic transmission in accordance with the fluid to be measured, and measures the attenuation of the ultrasonic wave with a small attenuation. The ultrasonic flowmeter according to claim 7, wherein the control is performed such that the applied voltage is lower in the case of a fluid than in the case of a measurement fluid in which ultrasonic attenuation is large.

Any of the applied voltage control at the time of transmission according to claim 1 or 2, the applied voltage control at the time of transmission according to claim 3 or 4, and the applied voltage control at the time of transmission according to claim 5 or 6. An ultrasonic flowmeter comprising: a transmission-time applied voltage control unit that executes a transmission-time applied voltage control by combining two or more of the above.