JP4087648B2

JP4087648B2 - Ultrasonic fluid measuring device

Info

Publication number: JP4087648B2
Application number: JP2002178503A
Authority: JP
Inventors: 輝彦友廣; 康裕梅景; 茂岩永
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2002-06-19
Filing date: 2002-06-19
Publication date: 2008-05-21
Anticipated expiration: 2022-06-19
Also published as: JP2004020480A

Description

【０００１】
【発明の属する技術分野】
本発明は、気体や液体などの流体の流速や流量を超音波を用いて計測する超音波流体計測装置に関するものである。
【０００２】
【従来の技術】
この種の従来の超音波流体計測装置としては、例えば、特開平９−１８９５９１号公報に開示されたものが知られている。この超音波流体計測装置は、図７に示すように、一端にフランジ２を有して流体を一方（図の左方）から他方（図の右方）に流す円筒状の測定管１と、その測定管１の中心線を挟み、且つその中心線に対して所定の角度で対向配置されて相互に超音波の授受を行う一対の超音波送受波器３，４と、測定管１に対し同一方向で、且つ平行の向きで測定管１の流体吸入口７に配列して設けられた複数本の細管９からなる整流体８と、上記一対の超音波送受波器３，４の検出データに基づき流体の流速および流量を測定する測定部（図示せず）とにより構成されている。
【０００３】
上記超音波流体計測装置は、測定管１の内部を流れる流体の流速を、一対の超音波送受波器３，４相互間で交互に発射されて受信される超音波の伝播時間差として検出し、この流体速度に測定管１の断面積を乗じて流量を算出している。この超音波流体計測装置では、流体吸入口７から測定管１へ流入する流体を、整流体８を構成する複数本の細管９によって流れ方向を測定管１と同一方向に規制していることにより、流体が流体吸入口７部分で様々な角度から吸い込まれたり、捩じれなどの乱れがあっても、細管９を通過する過程で整流することができる。これにより、流体吸入口７に近い位置に超音波送受波器３，４を設けた場合であっても、整流は安定した流線となり、正常な状態で伝播時間を測定することができ、流速の測定精度の悪化を防止できるとされている。
【０００４】
仮に、上記整流体８を設けない場合には、流体が流体吸入口７に対し様々な角度から吸い込まれる場合や、捩じれを伴って吸い込まれる際に、流体が渦を巻く状態で測定管１内を流下したりして、流体の乱れが顕著になる。このように流体が測定管１内を乱れた状態で流れた場合には、超音波送受波器３，４相互間で授受される超音波が流体中を伝播するとき、乱れの境界面で様々な反射や屈折を生じて、結果的に超音波の受信波のレベルが大きく変動して測定不能、あるいは内部流線の傾きによって測定精度が悪化することになる。このような不具合の発生を防止しようとすれば、測定管１における超音波送受波器３，４の取付位置を、流線が十分に安定する流体吸入口７から離れた下流側に設定することが必要となる。そのような構成とした場合には、測定管１が長くなって取付場所の制約を受けるという問題が発生する。上記超音波流体計測装置は、整流体８を設けることにより、上述した問題の解消を図ったものである。
【０００５】
【発明が解決しようとする課題】
しかしながら上記超音波流体計測装置では、超音波送受波器３，４間で計測した流速に、測定管１の断面積を乗じて流量を算出しているので、正確な流量を算出するためには、超音波送受波器３，４の取付位置と流量にそれぞれ対応した流速補正係数が必要となる。ところがこの流速補正係数は、流体の流れが定常である場合には主として流量に応じて変化するが、流体の流れが脈動流のように非定常な場合には流量の変化率によって流速分布が変化することから、常に流量に応じた流速補正係数を用いる場合には、流速および流量の測定精度が低下するという問題が生じることになる。
【０００６】
そこで、本発明は、上記従来の課題に鑑みてなされたもので、流体の流れが脈動流のような非定常なものである場合においても、流速および流量を高い測定精度で測定することのできる超音波流体計測装置を提供することを目的とするものである。
【０００７】
【課題を解決するための手段】
上記目的を達成するために、本発明に係る超音波流体計測装置は、被計測流体が流れる計測流路と、前記計測流路を超音波が斜めに横切って伝播するように前記計測流路の上流側および下流側に配設された一対の超音波送受信器と、前記超音波送受信器の送受信信号の伝播時間差に基づいて前記被計測流体の流速を求める流速計測制御部と、前記被計測流体の流速変化率を検知する流速変化率検知手段と、予め記憶されたデータベースを用いて、前記被計測流体の流速と前記流速変化率とに基づく流速補正係数を求め、前記流速補正係数で補正した前記被計測流体の流速に基づいて前記被計測流体の流量を算出する流量演算手段とを備えることを特徴としている。
【０００８】
この超音波流体計測装置では、流速変化率検知手段の検知結果に基づいて被計測流体の流れが定常流か非定常流かを判別することができるので、この判別結果に基づいて、超音波送受信器の送受信信号の伝播時間差から求めた被計測流体の流速を補正するための最適な流速補正係数を決定することができる。したがって、被計測流体の流れが脈動流などの非定常なものであっても、流速および流量の計測精度を高めることができる。
【００１１】
上記構成において、前記データベースは、流速と流速変化率と流速補正係数との関係を求めた表であることが好ましい。この構成によれば、瞬時の計測流速のデータと被計測流体の流れ状態の判別結果との両方を用いて最適な流速補正係数を一層簡単、且つ正確に設定することができ、被計測流体のより幅広い範囲の流れ状態に対して計測精度を一層高めることができる。
【００１４】
【発明の実施の形態】
以下、本発明の好ましい実施の形態について図面を参照しつつ詳細に説明する。
【００１５】
（第１の実施の形態）
図１および図２はそれぞれ本発明の第１の実施の形態に係る超音波流体計測装置の概略構成を示す横断面図および縦断面図である。この超音波流体計測装置は、流路壁１１に囲まれて被計測流体が流れる計測流路１０を有し、流路壁１１には、上流側および下流側の一対の超音波送受信器１２，１３が、計測流路１０の幅方向に対し超音波が図の左方から右方へ横切って伝播するように相対向する配置で配設されている。両超音波送受信器１２と１３は、図１に示すように、計測流路１０の幅方向を斜めに横切るように距離Ｌだけ隔てられ計測流路１０を流れる被計測流体の流動方向Ｆに対して所定の角度θだけ傾斜して配設され、且つ、図２に示すように計測流路１０の高さＨ方向に対しほぼ中央に位置している。
【００１６】
また、超音波送受信器１２，１３の取付箇所には、超音波の送受を可能とする超音波ガイド孔１４，１７がそれぞれ設けられている。更に両超音波ガイド孔１４，１７が相対向する箇所には、図１および図２に２点鎖線で示すように、相対向する一対の超音波送受信器１２，１３間で送信された超音波が流路壁１１の壁面に反射することなく相手側に直接的に伝播される超音波伝播路１８が形成されている。
【００１７】
また、計測流路１０の上流側（図の左側）は、上流側屈曲部１９を介して、被計測流体の入口となる流体導入部２０に連通されているとともに、計測流路１０の下流側（図の右側）は、下流側屈曲部２１を介して、被計測流体の出口となる流体導出部２２に連通されている。これにより、この超音波流体計測装置は、被計測流体の流路全体のコンパクト化が図られている。なお、上流側屈曲部１９には開閉弁（図示せず）が設けられている。
【００１８】
また、計測流路１０の入口側には整流体２３が配設されており、被計測流体の流れ方向を整える方向規制部２３ａと、流速分布の均一化または流れの変動を低減するための抵抗部２３ｂとを有している。方向規制部２３ａは、計測流路１０における被計測流体の流動方向Ｆと同一方向に、かつ互いに平行に配置された複数枚の板状の仕切壁からなり、計測流路１０の横断面を均一に分割している。抵抗部２３ｂは、被計測流体の流動方向Ｆに対する長さが短い多数の微細形状の連通路を計測流路１０の横断面に対して形成する形状を有している。なお、この整流体２３は、流路壁１１の内壁面に設けられた凹部２４に嵌め込まれて、流路壁１１に対し段差が生じない状態で取り付けられている。
【００１９】
流路壁１１における流体入口側の内壁面には、流速変化率検知手段２６が配設されている。この流速変化率検知手段２６は、被計測流体の流速の変化率（つまり流速の増大または減少の変化率）を検知するものであって、周知の流速センサ、あるいは被計測流体の流れの動圧を受ける抵抗体と周知の圧力センサとを組み合わせた構成からなる。
【００２０】
流速補正係数記憶部２７には、被計測流体の種々の流動状態に対応して実験的に予め求められた流速補正係数が記憶されている。流速補正係数設定部２８は、上記流速変化率検知手段２６から得られる変化率信号に基づいて被計測流体の流れの状態が定常流か非定常流かを判別して、その判別結果に対応する流速補正係数を流速補正係数記憶部２７から読み出しする。流速計測制御部２９は、一対の超音波送受信器１２，１３間での送受信を制御するとともに両超音波送受信器１２，１３の送受波信号の伝播時間を計測して、その伝播時間と後述の演算式とに基づき流速を算出するものである。流量演算部３０は、流速計測制御部２９から入力する流速のデータと流速補正係数設定部２８から入力する流速補正係数とに基づいて、被計測流体の流量を算出するものである。上記した流速補正係数記憶部２７、流速補正係数設定部２８、流速計測制御部２９および流量演算部３０は、流量演算手段３１を構成する。
【００２１】
つぎに、上記超音波流体計測装置における流量計測動作について説明する。計測流路１０における超音波伝播路１８では、被計測流体の流れに対して流速計測制御部２９の制御によって一対の超音波送受波器１２，１３間で計測流路１０を横切るように超音波の送受が行われる。このとき、流速計測制御部２９は、上流側超音波送受信器１２から発射された超音波が下流側超音波送受信器１３で受信されるまでの伝搬時間Ｔ₁を計測するとともに、下流側超音波送受信器１３から発射された超音波が上流側超音波送受信器１２で受信されるまでの伝搬時間Ｔ₂を計測して、その計測データと後述の演算式に基づき流速を算出する。
【００２２】
すなわち、計測流路１０内を流れる被計測流体の流速をＶ、被計測流体の流動方向Ｆと上記超音波伝播路１８とのなす角度をθ、両超音波送受信器１２，１３間の距離をＬ、被測定流体の音速をＣとそれぞれした場合に、Ｔ₁＝Ｌ／（Ｃ＋Ｖｃｏｓθ）、Ｔ₂＝Ｌ／（Ｃ−Ｖｃｏｓθ）となるから、Ｔ₁の逆数からＴ₂の逆数を減算して、上記各式から音速Ｃを消去して、Ｖ＝（Ｌ／２ｃｏｓθ）×〔（１／Ｔ₁）−（１／Ｔ₂）〕の式が導かれる。この式において、角度θおよび距離Ｌは既知であるから、流速計測制御部２９は、計測した伝搬時間Ｔ₁，Ｔ₂の値に基づいて流速Ｖを算出できる。
【００２３】
いま、空気の流量を計測することを仮定した場合は、角度θを４５°、距離ＬＡ７０ｍｍ、音速Ｃを３４０ｍ／ｓ、流速Ｖを８ｍ／ｓと想定すると、伝搬時間Ｔ₁は、２．０×１０^-4秒となり、伝搬時間Ｔ₂は、２．１×１０^-4秒となり、瞬時に計測ができる。
【００２４】
ところで、上述の式によって算出される流速Ｖは超音波伝播路１８で計測したものであり、この超音波伝播路１８は、計測流路１０内を斜めに横切るものであるから、上記の超音波伝播路１８内で計測した平均流速は、超音波伝播路１８の断面位置が異なる箇所毎に流れの状態が異なるとともに、高さＨ方向の断面における流路全体を計測したものでない。そのため計測流路１０に直交する横断面全域から算出した平均流速に対して差が生じることになる。しかも、超音波伝播路１８内の超音波の強度分布は、両超音波送受信器１２，１３の中心軸上である中央部において最も強くなる特性を有しているため、超音波伝播路１８内の高さＨ方向の中心部を主体的に計測することになる。
【００２５】
被計測流体の流量Ｑは、計測流路１０の被計測流体の流れ方向に直交する横断面積をＳ、流速補正係数をＫとすると、Ｑ＝ＫＶＳの式から算出することができる。ところで、上記流速補正係数Ｋは、横断面積Ｓにおける流速分布を考慮して求める必要がある。すなわち、流速補正係数Ｋは、両超音波送受信器１２，１３間の超音波の伝搬時間Ｔ₁，Ｔ₂に基づき算出した流速Ｖと計測流路１０内の被計測流体の総流量とを結びつける係数であるから、流量Ｑを精度良く算出するためには、流速補正係数Ｋを被計測流体の流動状態に応じた適切な値に設定する必要がある。
【００２６】
通常、流量が少ない定常な流れの場合における流速分布は、図２の被計測流体の速度分布Ｕに示すように、流路壁１１から遠ざかるに伴って速度が順次大きくなる放物線状の凸形となる。そのため、上記流速分布では、最大流速の発生位置が高さＨ方向のほぼ中央付近に存在し、中央部と周辺部との流速差が比較的大きい。これに対して、両超音波送受信器１２，１３によって流速を計測する箇所は主に計測流路１０の中央部であるから、算出される流速は、流速分布における最大流速に近い値となる。したがって、流速補正係数Ｋとしては、「１」より小さい値を用いる必要がある。一方、流量が多くなって、いわゆる乱流領域になると、速度分布は、上述の放物線状の凸形から、中央付近が平らなほぼ台形状に変化する。すなわち、中央部と周辺部とにおける流速の差が小さくなる。そのため、流速補正係数Ｋとしては、「１」に近い値を用いる必要がある。これに対して、上記超音波流体計測装置では、流速変化率検知手段２６に出力に基づいて最適な流速補正係数Ｋを設定する構成になっており、この点について、以下に詳述する。
【００２７】
図３は、流速が変化する非定常な流れの場合における計測流路１０内の流速の変化の一例を示す流速分布の説明図であり、図の左側から右方に流れる流量をプラス流量として示したものである。図４は非定常な流れの場合における流量の変化の一例を示す説明図である。図３の各流速分布Ｕ１〜Ｕ５は、流量が図４に示すように変化した場合における変化を示したものである。すなわち、図４のＰ１の区間に示すような定常流の状態では図３の流速分布Ｕ１のような流速の変化となる。図４に示すＰ２，Ｐ３，Ｐ４の各区間は、流量が減少してく途中の状態を示したものであり、図３の流速分布Ｕ２，Ｕ３，Ｕ４のような流速の変化となる。
【００２８】
Ｐ３は、プラス流量からマイナス流量への変化点であって、実流量が「０」の状態であり、そのときの流速分布Ｕ３は、図３に明示するように、非常に複雑な分布になっている。すなわち、流速分布Ｕ３は、計測流路１０の中央部において図の右向きの速度を有しているが、流路壁１１の近傍箇所において図の左向きの速度を有しており、全体としての流量が「０」になっている。
【００２９】
すなわち、中央部付近の流速が減少しつつある非定常な状態では、計測される流速が「０」となる時点よりも少し前の時点て流量が「０」になる状態が生じていることになるので、この実施の形態では、流速変化率検知手段２６の出力に基づいて流速補正係数設定部２８が適切な流速補正係数Ｋを算出する。なお、流速変化率検知手段２６が流路壁１１の近傍箇所の被計測流体の流れの変化を検知し、この流速変化率検知手段２６からの出力に基づいて流速補正係数設定部２８が流速補正係数Ｋを算出する構成とすることもできる。この場合、流路壁１１の近傍箇所の被計測流体の流速が「０」となった少し後で全体の流量が「０」となることは言うまでもない。
【００３０】
上記超音波流体計測装置では、計測流路１０内の流れの状態が定常流または非定常に流量変化する非定常流の各々に応じて生じる特徴的な流速分布を予め求めるとともに、その流速分布の特質に基づいて種々の流れ状態についての流速補正係数Ｋを実験的に求めて、このようにして求めた流速補正係数Ｋを数表の形でデータベース化して上記流速補正係数記憶部２７に予め記憶されている。したがって、流速補正係数設定部２８は、流速変化率検知手段２６から入力される信号、つまり計測流路１０内の被計測流体の流れ状態の変化に対応した信号に基づいて被検出流体の流れ状態を判別して、その判別結果に対応する流速補正係数Ｋを流速補正係数記憶部２７から読み出して流量演算部３０に対し出力する。流量演算部３０は、流速計測制御部２９で算出して入力される流速のデータと、流速補正係数記憶部２７から入力される流速補正係数Ｋに基づいて流速Ｖを算出した上で、流量Ｑを算出するので、流量Ｑを高精度に求めることができる。
【００３１】
（第２の実施の形態）
図５および図６は本発明の第２の実施の形態に係る超音波流体計測装置の概略構成を示す横断面図および縦断面図であり、これらの図において、図１および図２と同一若しくは同等のものには同一の符号を付して、重複する説明を省略する。この実施の形態が第１の実施の形態と相違するのは以下の構成のみである。すなわち、第１の実施の形態では、流速変化率検知手段２６から入力する流速変化率のデータのみに基づいて流速補正係数設定部２８が被計測流体の流れ状態を判別して、その判別結果に基づく最適の流速補正係数Ｋを流速補正係数記憶部２７から読み出すようにしていたが、この実施の形態では、流速補正係数設定部２８が、流速変化率検知手段２６から入力される流速変化率と、流速計測制御部２９から入力される流速との両方に基づいて計測流路１０内の被計測流体の流れ状態を特定して、その結果に基づき最適な流速補正係数Ｋを流速補正係数記憶部２７から読み出す構成になっている。
【００３２】
したがって、この実施の形態では、図６に矢印で示すように、被計測流体の順方向（図の左側から右方）の流れと逆方向（図の右側から左方）の流れとで流速分布が大きく異なる場合であっても、的確な流速補正係数Ｋを設定することが可能となる。すなわち、図６に示すように、計測流路１０内の流速分布Ｕは流路形状によって大きく異なり、この実施の形態では、計測流路１０に角部３２が存在することにより、この角部３２によって被計測流体のいわゆる剥離流れ３３が生じるために、最大流速Ｕ_maxの位置が流路の高さＨ方向の片側に偏位した流速分布Ｕとなる。したがって、このような場合には、第１の実施の形態の図２に示すような最大流速Ｕ_maxが高さＨ方向の中央部付近にある場合の流速補正係数Ｋとは異なる流速補正係数Ｋを設定しなければ、正確な流量を求めることができない。
【００３３】
そこで、この実施の形態では、計測流路１０が入口側と出口側とで異なる場合であっても、流速変化率検知手段２６からの流速変化率に基づき判別する被計測流体の流れ状態に加えて、流速計測制御部２９からの流速Ｖ、つまり被計測流体の流れの方向と大きさを考慮して、最適な流速補正係数Ｋを設定するので、やはり正確な流量Ｑを算出することができる。
【００３４】
なお、流速変化率は、一対の超音波送受信器１２，１３の送受信信号の時間変化から求めることもできるから、流速計測制御部２９に流速変化率を算出する機能を付加することが可能であり、その場合には、流速変化率検知手段２６が不要となり、コストの低減および装置全体の小型化を測ることができる。
【００３５】
また、流速補正係数Ｋは、被計測流体の流量の大小と、被計測流体の流動方向と、被計測流体の流速の変化率とによって大きく変化するので、これら３種類の流れ状態の要素を組み合わせた少なくとも８通りの値を使い分けることができる。すなわち、上記各実施の形態のように、種々の流れ状態に応じてその時々の最適な流速補正係数Ｋを流速補正係数記憶部２７からその都度読み出すのではなく、計測流路１０内の流速分布が大きく変化する少なくとも３種類の流れ状態のみに基づいて少なくとも８種類の流速補正係数Ｋを使い分けることにより、広範囲な流れ状態に対して効率良く高精度な測定をすることができる。流量の大小や変化率を２種類ではなく、より多くに分割することにより、さらに計測精度を高めることができるのは言うまでもない。
【００３６】
【発明の効果】
以上のように本発明の超音波流体計測装置よれば、流速変化率検知手段の検知結果に基づいて被計測流体の流れが定常流か非定常流かを判別することができるので、この判別結果に基づいて、超音波送受信器の送受信信号の伝播時間差から求めた被計測流体の流速を補正するための最適な流速補正係数を決定することができる。したがって、被計測流体の流れが脈動流などの非定常なものであっても、流速および流量の計測精度を高めることができる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係る超音波流体計測装置の概略構成を示す横断面図。
【図２】同上の超音波流体計測装置の概略構成を示す縦断面図。
【図３】同上の超音波流体計測装置における流速が変化する非定常な流れの場合における計測流路内の流速の変化を示す流速分布の説明図。
【図４】同上の非定常な流れの場合における流量の変化の一例を示す説明図。
【図５】本発明の第２の実施の形態に係る超音波流体計測装置の概略構成を示す横断面図。
【図６】同上の超音波流体計測装置の概略構成を示す縦断面図。
【図７】従来の超音波流体計測装置を示す側面図。
【符号の説明】
１０計測流路
１２，１３超音波送受信器
２６流速変化率検知手段
２７流速補正係数記憶部
２８流速補正係数設定部
２９流速計測制御部
３０流量演算部
３１流量演算手段
Ｆ流動方向[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic fluid measurement device that measures the flow velocity and flow rate of a fluid such as gas or liquid using ultrasonic waves.
[0002]
[Prior art]
As this type of conventional ultrasonic fluid measuring apparatus, for example, one disclosed in Japanese Patent Laid-Open No. 9-189591 is known. As shown in FIG. 7, this ultrasonic fluid measuring apparatus has a cylindrical measuring tube 1 having a flange 2 at one end and flowing fluid from one side (left side in the figure) to the other side (right side in the figure), A pair of ultrasonic transducers 3 and 4 that sandwich the center line of the measurement tube 1 and are opposed to the center line at a predetermined angle and exchange ultrasonic waves with each other, and the measurement tube 1 Detection data of the rectifier 8 composed of a plurality of thin tubes 9 arranged in the same direction and parallel to the fluid suction port 7 of the measuring tube 1 and the pair of ultrasonic transducers 3 and 4 And a measurement unit (not shown) for measuring the flow rate and flow rate of the fluid.
[0003]
The ultrasonic fluid measuring device detects the flow velocity of the fluid flowing in the measuring tube 1 as a difference in propagation time of ultrasonic waves that are alternately emitted and received between the pair of ultrasonic transducers 3 and 4, The flow rate is calculated by multiplying the fluid velocity by the cross-sectional area of the measuring tube 1. In this ultrasonic fluid measuring device, the flow direction of the fluid flowing into the measuring tube 1 from the fluid suction port 7 is regulated in the same direction as the measuring tube 1 by the plurality of thin tubes 9 constituting the rectifier 8. The fluid can be rectified in the process of passing through the thin tube 9 even if the fluid is sucked from various angles at the fluid suction port 7 portion or is disturbed such as twisting. Thereby, even when the ultrasonic transducers 3 and 4 are provided at positions close to the fluid suction port 7, the rectification becomes a stable streamline, and the propagation time can be measured in a normal state. It is said that the deterioration of measurement accuracy can be prevented.
[0004]
If the rectifying body 8 is not provided, when the fluid is sucked into the fluid suction port 7 from various angles, or when sucked with twisting, the fluid is swirled in the measurement tube 1. Or fluid flow becomes noticeable. When the fluid flows in a turbulent state in the measurement tube 1 as described above, when the ultrasonic wave transmitted and received between the ultrasonic transducers 3 and 4 propagates in the fluid, various changes occur at the turbulent boundary surface. As a result, the level of the received wave of the ultrasonic wave greatly fluctuates and measurement is impossible, or the measurement accuracy deteriorates due to the inclination of the internal streamline. If it is going to prevent generation | occurrence | production of such a malfunction, the attachment position of the ultrasonic transducers 3 and 4 in the measurement tube 1 should be set to the downstream side away from the fluid inlet 7 where a streamline is fully stabilized. Is required. In the case of such a configuration, there arises a problem that the measuring tube 1 becomes long and is restricted by the mounting location. The ultrasonic fluid measuring device is intended to solve the above-described problems by providing a rectifying body 8.
[0005]
[Problems to be solved by the invention]
However, in the above ultrasonic fluid measuring device, the flow rate is calculated by multiplying the flow velocity measured between the ultrasonic transducers 3 and 4 by the cross-sectional area of the measurement tube 1, so that an accurate flow rate can be calculated. The flow velocity correction coefficient corresponding to the mounting position and flow rate of the ultrasonic transducers 3 and 4 is required. However, this flow velocity correction coefficient changes mainly according to the flow rate when the fluid flow is steady, but when the fluid flow is unsteady like a pulsating flow, the flow velocity distribution changes depending on the rate of change of the flow rate. Therefore, when the flow velocity correction coefficient corresponding to the flow rate is always used, there arises a problem that the measurement accuracy of the flow velocity and the flow rate is lowered.
[0006]
Therefore, the present invention has been made in view of the above-described conventional problems, and even when the fluid flow is unsteady such as a pulsating flow, the flow velocity and the flow rate can be measured with high measurement accuracy. An object of the present invention is to provide an ultrasonic fluid measuring device.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an ultrasonic fluid measurement device according to the present invention includes a measurement channel through which a fluid to be measured flows, and the measurement channel so that ultrasonic waves propagate obliquely across the measurement channel. and upstream and one pair is disposed on the downstream side ultrasonic transducer, and the flow rate measurement control unit which on the basis of the propagation time difference between the transmission and reception signals of the ultrasonic transducer determining the flow velocity of the fluid to be measured, the object to be measured a flow rate change rate detecting means for detecting the flow rate change of the fluid, by using a pre-stored database, determine the flow rate correction coefficient based on the flow velocity and the flow rate change rate of the fluid to be measured, the flow rate correction factor in based on the flow rate of the corrected the fluid to be measured it is characterized by obtaining Bei and flow rate calculation means for calculating the flow rate of the fluid to be measured.
[0008]
In this ultrasonic fluid measuring device, it is possible to determine whether the flow of the fluid to be measured is a steady flow or an unsteady flow based on the detection result of the flow velocity change rate detection means. It is possible to determine an optimum flow velocity correction coefficient for correcting the flow velocity of the fluid to be measured obtained from the propagation time difference between the transmission and reception signals of the device. Therefore, even if the flow of the fluid to be measured is unsteady such as a pulsating flow, the measurement accuracy of the flow velocity and the flow rate can be improved.
[0011]
The said structure WHEREIN: It is preferable that the said database is the table | surface which calculated | required the relationship between the flow velocity, the flow velocity change rate, and the flow velocity correction coefficient . According to this configuration, the optimum flow velocity correction coefficient can be set more easily and accurately using both the instantaneous measurement flow velocity data and the determination result of the flow state of the fluid to be measured. Measurement accuracy can be further improved over a wider range of flow conditions.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0015]
(First embodiment)
FIG. 1 and FIG. 2 are a transverse sectional view and a longitudinal sectional view, respectively, showing a schematic configuration of the ultrasonic fluid measuring apparatus according to the first embodiment of the present invention. This ultrasonic fluid measuring device has a measurement channel 10 surrounded by a channel wall 11 and through which a fluid to be measured flows. The channel wall 11 includes a pair of ultrasonic transceivers 12 on the upstream side and the downstream side, 13 are arranged so as to face each other so that the ultrasonic waves propagate across the width direction of the measurement channel 10 from the left to the right in the figure. As shown in FIG. 1, the ultrasonic transmitters / receivers 12 and 13 are separated by a distance L so as to cross the width direction of the measurement flow path 10 diagonally, and with respect to the flow direction F of the fluid to be measured flowing through the measurement flow path 10. Are inclined at a predetermined angle θ, and are positioned substantially in the center with respect to the height H direction of the measurement channel 10 as shown in FIG.
[0016]
In addition, ultrasonic guide holes 14 and 17 that enable transmission / reception of ultrasonic waves are provided at locations where the ultrasonic transceivers 12 and 13 are attached. Furthermore, in the place where the ultrasonic guide holes 14 and 17 are opposed to each other, as shown by two-dot chain lines in FIGS. 1 and 2, ultrasonic waves transmitted between the pair of ultrasonic transmitters and receivers 12 and 13 facing each other. Is formed in the ultrasonic wave propagation path 18 that is directly propagated to the other side without being reflected by the wall surface of the flow path wall 11.
[0017]
Further, the upstream side (the left side in the figure) of the measurement channel 10 communicates with the fluid introduction unit 20 serving as the inlet of the fluid to be measured via the upstream bent portion 19, and the downstream side of the measurement channel 10. The right side of the figure is communicated with the fluid outlet 22 serving as the outlet of the fluid to be measured via the downstream bent portion 21. Thereby, in this ultrasonic fluid measuring device, the entire flow path of the fluid to be measured is made compact. The upstream bent portion 19 is provided with an on-off valve (not shown).
[0018]
Further, a rectifying body 23 is disposed on the inlet side of the measurement flow path 10, and a direction restricting portion 23 a that adjusts the flow direction of the fluid to be measured, and a resistance for equalizing the flow velocity distribution or reducing flow fluctuations. Part 23b. The direction restricting portion 23a includes a plurality of plate-like partition walls arranged in the same direction as the flow direction F of the fluid to be measured in the measurement channel 10 and parallel to each other, and has a uniform cross section of the measurement channel 10 It is divided into. The resistance portion 23 b has a shape that forms a large number of finely shaped communication passages having a short length in the flow direction F of the fluid to be measured with respect to the cross section of the measurement flow channel 10. The rectifying body 23 is fitted in a recess 24 provided on the inner wall surface of the flow path wall 11 and attached to the flow path wall 11 in a state where no step is generated.
[0019]
On the inner wall surface of the flow path wall 11 on the fluid inlet side, a flow rate change rate detecting means 26 is disposed. This flow rate change rate detection means 26 detects the change rate of the flow rate of the fluid to be measured (that is, the rate of change of increase or decrease of the flow rate), and is a known flow rate sensor or dynamic pressure of the flow of the fluid to be measured. It comprises a combination of a resistor that receives the pressure and a known pressure sensor.
[0020]
The flow velocity correction coefficient storage unit 27 stores a flow velocity correction coefficient that is experimentally obtained in advance corresponding to various flow states of the fluid to be measured. The flow velocity correction coefficient setting unit 28 determines whether the flow state of the fluid to be measured is a steady flow or an unsteady flow based on the change rate signal obtained from the flow rate change rate detection means 26, and corresponds to the determination result. The flow velocity correction coefficient is read from the flow velocity correction coefficient storage unit 27. The flow velocity measurement control unit 29 controls transmission / reception between the pair of ultrasonic transmitters / receivers 12 and 13 and measures the propagation time of the transmission / reception signals of both ultrasonic transmitters / receivers 12 and 13. The flow velocity is calculated based on the arithmetic expression. The flow rate calculation unit 30 calculates the flow rate of the fluid to be measured based on the flow rate data input from the flow rate measurement control unit 29 and the flow rate correction coefficient input from the flow rate correction coefficient setting unit 28. The flow velocity correction coefficient storage unit 27, the flow velocity correction coefficient setting unit 28, the flow velocity measurement control unit 29, and the flow rate calculation unit 30 constitute a flow rate calculation unit 31.
[0021]
Next, the flow measurement operation in the ultrasonic fluid measuring device will be described. In the ultrasonic wave propagation path 18 in the measurement flow path 10, the ultrasonic wave is passed across the measurement flow path 10 between the pair of ultrasonic transducers 12 and 13 by the control of the flow velocity measurement control unit 29 with respect to the flow of the fluid to be measured. Are sent and received. At this time, the flow velocity measurement control unit 29 measures the propagation time T ₁ until the ultrasonic wave emitted from the upstream ultrasonic transmitter / receiver 12 is received by the downstream ultrasonic transmitter / receiver 13 and the downstream ultrasonic wave. The propagation time T ₂ until the ultrasonic wave emitted from the transmitter / receiver 13 is received by the upstream ultrasonic transmitter / receiver 12 is measured, and the flow velocity is calculated based on the measurement data and an arithmetic expression described later.
[0022]
That is, the flow velocity of the fluid to be measured flowing in the measurement channel 10 is V, the angle between the flow direction F of the fluid to be measured and the ultrasonic wave propagation path 18 is θ, and the distance between the ultrasonic transceivers 12 and 13 is L, when the acoustic velocity of the fluid to be measured and respectively _{C, T 1 = L / (} C + Vcosθ), T 2 = L / because comprising (C-Vcosθ), subtracts the inverse of T ₂ from the reciprocal of T ₁ Thus, the sound velocity C is eliminated from the above equations, and an equation of V = (L / 2 cos θ) × [(1 / T ₁ ) − (1 / T ₂ )] is derived. In this equation, since the angle θ and the distance L are known, the flow velocity measurement controller 29 can calculate the flow velocity V based on the measured propagation times T ₁ and T ₂ .
[0023]
Assuming that the air flow rate is measured, assuming that the angle θ is 45 °, the distance LA is 70 mm, the sound velocity C is 340 m / s, and the flow velocity V is 8 m / s, the propagation time T ₁ is 2. It becomes 0 × 10 ⁻⁴ seconds, and the propagation time T ₂ becomes 2.1 × 10 ⁻⁴ seconds, which can be measured instantaneously.
[0024]
By the way, the flow velocity V calculated by the above equation is measured by the ultrasonic wave propagation path 18, and the ultrasonic wave propagation path 18 obliquely crosses the measurement flow path 10, so that the ultrasonic wave described above is used. The average flow velocity measured in the propagation path 18 is not a value obtained by measuring the entire flow path in the cross section in the height H direction while the flow state is different for each portion where the cross-sectional position of the ultrasonic propagation path 18 is different. Therefore, a difference is generated with respect to the average flow velocity calculated from the entire cross section orthogonal to the measurement flow path 10. In addition, since the intensity distribution of the ultrasonic wave in the ultrasonic wave propagation path 18 has the strongest characteristic in the central portion on the central axis of both the ultrasonic transmitters / receivers 12 and 13, The center part in the height H direction is measured mainly.
[0025]
The flow rate Q of the fluid to be measured can be calculated from the equation Q = KVS, where S is the cross-sectional area perpendicular to the flow direction of the fluid to be measured in the measurement channel 10 and K is the flow velocity correction coefficient. By the way, the flow velocity correction coefficient K needs to be obtained in consideration of the flow velocity distribution in the cross-sectional area S. That is, the flow velocity correction coefficient K combines the flow velocity V calculated based on the ultrasonic propagation times T ₁ and T ₂ between the ultrasonic transceivers 12 and 13 and the total flow rate of the fluid to be measured in the measurement channel 10. Since it is a coefficient, in order to calculate the flow rate Q with high accuracy, it is necessary to set the flow velocity correction coefficient K to an appropriate value according to the flow state of the fluid to be measured.
[0026]
Normally, the flow velocity distribution in the case of a steady flow with a low flow rate is a parabolic convex shape in which the velocity increases gradually with increasing distance from the channel wall 11 as shown in the velocity distribution U of the fluid to be measured in FIG. Become. For this reason, in the flow velocity distribution, the position where the maximum flow velocity is generated is present in the vicinity of the center in the height H direction, and the flow velocity difference between the central portion and the peripheral portion is relatively large. On the other hand, since the location where the flow velocity is measured by both ultrasonic transceivers 12 and 13 is mainly the central portion of the measurement flow path 10, the calculated flow velocity is close to the maximum flow velocity in the flow velocity distribution. Therefore, it is necessary to use a value smaller than “1” as the flow velocity correction coefficient K. On the other hand, when the flow rate increases and a so-called turbulent flow region is reached, the velocity distribution changes from the above-mentioned parabolic convex shape to a substantially trapezoidal shape in which the vicinity of the center is flat. That is, the difference in flow velocity between the central portion and the peripheral portion is reduced. Therefore, it is necessary to use a value close to “1” as the flow velocity correction coefficient K. On the other hand, the ultrasonic fluid measuring device has a configuration in which an optimum flow velocity correction coefficient K is set in the flow velocity change rate detection means 26 based on the output, which will be described in detail below.
[0027]
FIG. 3 is an explanatory diagram of a flow velocity distribution showing an example of a change in the flow velocity in the measurement flow path 10 in the case of an unsteady flow where the flow velocity changes. The flow rate flowing from the left side to the right side of the drawing is shown as a positive flow rate. It is a thing. FIG. 4 is an explanatory diagram showing an example of a change in flow rate in the case of an unsteady flow. Each flow velocity distribution U1-U5 of FIG. 3 shows the change when the flow rate changes as shown in FIG. That is, in a steady flow state as shown in the section P1 in FIG. 4, the flow velocity changes as in the flow velocity distribution U1 in FIG. Each section of P 2 , P 3, and P 4 shown in FIG. 4 shows a state where the flow rate is decreasing, and the flow rate changes like the flow rate distributions U 2, U 3, and U 4 of FIG.
[0028]
P3 is a change point from the positive flow rate to the negative flow rate, and the actual flow rate is "0". The flow velocity distribution U3 at that time is a very complicated distribution as clearly shown in FIG. ing. That is, the flow velocity distribution U3 has a rightward speed in the figure at the center of the measurement flow path 10, but has a leftward speed in the figure in the vicinity of the flow path wall 11, and the flow rate as a whole. Is “0”.
[0029]
That is, in the unsteady state where the flow velocity near the center is decreasing, a state where the flow rate becomes “0” occurs slightly before the time point when the measured flow velocity becomes “0”. Therefore, in this embodiment, the flow velocity correction coefficient setting unit 28 calculates an appropriate flow velocity correction coefficient K based on the output of the flow velocity change rate detection means 26. The flow rate change rate detection means 26 detects a change in the flow of the fluid to be measured in the vicinity of the flow path wall 11, and the flow rate correction coefficient setting unit 28 corrects the flow rate based on the output from the flow rate change rate detection means 26. A configuration for calculating the coefficient K may be employed. In this case, needless to say, the entire flow rate becomes “0” a little after the flow velocity of the fluid to be measured near the flow path wall 11 becomes “0”.
[0030]
In the ultrasonic fluid measuring apparatus, a characteristic flow velocity distribution generated according to each of the steady flow or the unsteady flow in which the flow rate changes unsteadily in the measurement flow path 10 is obtained in advance, and the flow velocity distribution Based on the characteristics, the flow velocity correction coefficient K for various flow states is experimentally obtained, and the flow velocity correction coefficient K thus obtained is databased in the form of a numerical table and stored in the flow velocity correction coefficient storage unit 27 in advance. Has been. Therefore, the flow velocity correction coefficient setting unit 28 is based on a signal input from the flow velocity change rate detection means 26, that is, a signal corresponding to a change in the flow state of the fluid to be measured in the measurement flow path 10. The flow velocity correction coefficient K corresponding to the determination result is read from the flow velocity correction coefficient storage unit 27 and output to the flow rate calculation unit 30. The flow rate calculation unit 30 calculates the flow rate V based on the flow rate data calculated and input by the flow rate measurement control unit 29 and the flow rate correction coefficient K input from the flow rate correction coefficient storage unit 27. Therefore, the flow rate Q can be obtained with high accuracy.
[0031]
(Second Embodiment)
5 and 6 are a transverse sectional view and a longitudinal sectional view showing a schematic configuration of the ultrasonic fluid measuring apparatus according to the second embodiment of the present invention. In these drawings, the same as FIG. 1 and FIG. Equivalent parts are denoted by the same reference numerals, and redundant description is omitted. This embodiment is different from the first embodiment only in the following configuration. That is, in the first embodiment, the flow velocity correction coefficient setting unit 28 determines the flow state of the fluid to be measured based only on the flow velocity change rate data input from the flow velocity change rate detector 26, and the determination result is based optimum flow rate correction is the coefficient K had to read out from the flow rate correction coefficient storage unit 27, in this embodiment, the flow rate correction coefficient setting unit 28, flow rate change rate inputted from the flow rate change rate detecting means 26 And the flow state of the fluid to be measured in the measurement flow path 10 based on both the flow velocity input from the flow velocity measurement control unit 29 and the optimum flow velocity correction coefficient K is stored in the flow velocity correction coefficient memory based on the result. The data is read from the unit 27.
[0032]
Therefore, in this embodiment, as indicated by an arrow in FIG. 6, the flow velocity distribution is represented by the flow of the fluid to be measured in the forward direction (from left to right in the figure) and in the reverse direction (from right to left in the figure). Even when the values are greatly different, it is possible to set an accurate flow velocity correction coefficient K. That is, as shown in FIG. 6, the flow velocity distribution U in the measurement channel 10 varies greatly depending on the channel shape. In this embodiment, the corner portion 32 exists in the measurement channel 10, and thus this corner portion 32. As a result, a so-called separation flow 33 of the fluid to be measured is generated, so that the flow velocity distribution U in which the position of the maximum flow velocity U _max is shifted to one side in the height H direction of the flow path is obtained. Therefore, in such a case, the flow velocity correction coefficient K different from the flow velocity correction coefficient K in the case where the maximum flow velocity U _max as shown in FIG. 2 of the first embodiment is near the center in the height H direction. If is not set, accurate flow rate cannot be obtained.
[0033]
Therefore, in this embodiment, even if the measurement channel 10 is different between the inlet side and the outlet side, in addition to the flow state of the fluid to be measured, which is discriminated based on the flow rate change rate from the flow rate change rate detection means 26. Thus, since the optimum flow velocity correction coefficient K is set in consideration of the flow velocity V from the flow velocity measurement control unit 29, that is, the direction and magnitude of the flow of the fluid to be measured, it is possible to calculate the accurate flow rate Q. .
[0034]
The flow rate change rate can also be obtained from the time change of the transmission / reception signals of the pair of ultrasonic transmitters / receivers 12 and 13, so that it is possible to add a function for calculating the flow rate change rate to the flow rate measurement control unit 29. In this case, the flow rate change rate detecting means 26 is not necessary, and it is possible to measure cost reduction and downsizing of the entire apparatus.
[0035]
The flow velocity correction coefficient K varies greatly depending on the flow rate of the fluid to be measured, the flow direction of the fluid to be measured, and the rate of change in the flow velocity of the fluid to be measured. At least 8 different values can be used properly. That is, as in each of the above embodiments, the optimum flow velocity correction coefficient K at each time is not read from the flow velocity correction coefficient storage unit 27 each time according to various flow conditions, but the flow velocity distribution in the measurement flow path 10 is read. By properly using at least eight types of flow velocity correction coefficients K based only on at least three types of flow states in which the change greatly changes, it is possible to efficiently and accurately measure a wide range of flow states. It goes without saying that the measurement accuracy can be further improved by dividing the flow rate magnitude and rate of change into more than two types.
[0036]
【The invention's effect】
As described above, according to the ultrasonic fluid measurement device of the present invention, it is possible to determine whether the flow of the fluid to be measured is a steady flow or an unsteady flow based on the detection result of the flow rate change rate detection means. Based on the above, it is possible to determine an optimum flow velocity correction coefficient for correcting the flow velocity of the fluid to be measured, which is obtained from the propagation time difference between the transmission and reception signals of the ultrasonic transceiver. Therefore, even if the flow of the fluid to be measured is unsteady such as a pulsating flow, the measurement accuracy of the flow velocity and the flow rate can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic configuration of an ultrasonic fluid measuring apparatus according to a first embodiment of the present invention.
FIG. 2 is a longitudinal sectional view showing a schematic configuration of the ultrasonic fluid measuring apparatus according to the first embodiment.
FIG. 3 is an explanatory diagram of a flow velocity distribution showing a change in the flow velocity in the measurement flow path in the case of an unsteady flow in which the flow velocity changes in the ultrasonic fluid measurement apparatus same as above.
FIG. 4 is an explanatory diagram showing an example of a change in flow rate in the case of the unsteady flow.
FIG. 5 is a cross-sectional view showing a schematic configuration of an ultrasonic fluid measuring apparatus according to a second embodiment of the present invention.
FIG. 6 is a longitudinal sectional view showing a schematic configuration of the above ultrasonic fluid measuring apparatus.
FIG. 7 is a side view showing a conventional ultrasonic fluid measuring device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Measurement flow path 12, 13 Ultrasonic transmitter / receiver 26 Flow velocity change rate detection means 27 Flow velocity correction coefficient memory | storage part 28 Flow velocity correction coefficient setting part 29 Flow velocity measurement control part 30 Flow rate calculation part 31 Flow rate calculation means F Flow direction

Claims

A measurement channel through which the fluid to be measured flows;
And the measuring flow path of the measurement flow path a pair that are arranged upstream and downstream of such ultrasonic wave propagates across diagonally ultrasonic transceivers,
A flow velocity measurement control unit for obtaining a flow velocity of the fluid to be measured based on a propagation time difference between transmission and reception signals of the ultrasonic transceiver; and
A flow rate change rate detecting means for detecting the flow rate change rate of the fluid to be measured,
Using a database stored in advance, a flow velocity correction coefficient based on the flow velocity of the fluid to be measured and the flow rate change rate is obtained, and the flow rate of the fluid to be measured is corrected based on the flow velocity of the fluid to be measured corrected by the flow velocity correction coefficient. ultrasonic fluid measurement apparatus characterized by obtaining Bei and flow rate calculation means for calculating the flow rate.

The ultrasonic fluid measurement device according to claim 1, wherein the database is a table in which a relationship among a flow velocity, a flow velocity change rate, and a flow velocity correction coefficient is obtained .