JP3759988B2 - Ultrasonic flow meter - Google Patents

Description

【００４４】
このようにして〔表１〕のデータテーブルを作成してマイクロコンピュータのメモリに格納するとデータの数は前記３００００個の１／１０の３０００個になる。
【００４５】
第２のカウンタ９の測定値Ｔ₁ −ｎτ，Ｔ₂ −ｎτの最下位桁が０の値の上位桁の数値の逆数の有効数字８桁の集合で表１のデータテーブルを作成したわけである。
【００４６】
こうして〔表１〕のデータテーブルでは、メモリ容量が小さくて済むが、第２のカウンタ９の測定値Ｔ₁ −ｎτ，Ｔ₂ −ｎτの最下位桁が０以外の数値のときの値を直接テーブルから読み出すことができない。
【００４７】
例えば第２のカウンタ９の測定値Ｔ₁ 又はＴ₂ が１７９４３の場合、この測定値１７９４３に対応するアドレスは一定値ｎτを６００とすると１７９４３−６００＝１７３４３となる。これに対応する逆数のデータをずばり〔表１〕のデータテーブルからは読み出せない。そこで測定値１７３４３に対応する時間逆数値を〔表１〕のデータテーブルから読み出したデータを活用して直線近似で求める。
【００４８】
第２のカウンタ９の測定値が１７９４３であるので、この測定値の数値から一定値ｎτ＝６００を引いた前述のように１７３４３である。そこで、その上位の４桁の数値１７３４に相当するアドレスと、この上位桁の数値１７３４に１を加算した１７３５に相当するアドレスより、１／（１０×１７３４）と１／（１０×１７３５）に相当する二つの格納データを〔表１〕のデータテーブルから読み出す。実際にはコントローラ部７を構成するマイクロコンピュータのメモリに格納したデータから読み出す。
【００４９】
アドレス データ
１７３４ ５７６７０１２７
１７３５ ５７６３６８８８
そして、これらの二つのデータから測定値１７９４３に対応するデータを次の（５）式で直線近似を使って導く。
【００５０】
測定値１７９４３に対応するデータ＝５７６７０１２７−（５７６７０１２７
−５７６３６８８８）×（３／１０） ・・・（５）
（５）式の演算をマイクロコンピュータでする場合、（５７６７０１２７−５７６３６８８８）×（３／１０）の計算に多少の時間がかかるものの、テーブルが小さくなり、実現可能となる。
このようにして、小さいテーブルから読み出したデータを用いて、直線近似でテーブルの中間のデータを演算することで、テーブルを格納するメモリが小さくてすみ、しかも全体として割算に長時間をかけなくてすむ。
【００５１】
（５）式の演算以後の流速、流量、積算流量等の演算は周知の方法でできるので詳細な説明を省略する。
なお、データテーブルのデータは、〔表１〕の値から一定値を減じた値として記憶格納するようにしてもよい。この場合のオフセット分は、その後の演算｛１／（Ｔ₁ −ｎτ）｝−｛１／（Ｔ₂ −ｎτ）｝で差し引かれて相殺されるので問題にはならない。また流量等の演算を考慮して、データを流管の断面積等の定数を乗じた値として記憶格納することで、後の演算時間を小さくすることができる。
【００５２】
上記第１の実施の形態では、発明の考え方の基本を説明するための第１の実施態様を述べたが、次の第２の実施態様のように流量計を構成してもコントローラでの演算時間を小さくできる。
【００５３】
図１のブロック図で、コントローラ部７を構成するマイクロコンピュータの作用だけが前記第１の実施態様と相違するので、以下、この相違点を主体にして第２の実施態様を説明する。
【００５４】
第２のカウンタ９から読み取るべき測定値Ｔ₁ 又はＴ₂ を最下位１桁の数値Ｂとその他の上位桁の数値Ａに分けて、該その他の上位桁の数値Ａに相当するアドレスと、該アドレスに対応する前記第２のカウンタ９から読み取った測定値Ｔ₁又はＴ₂ より遅れ時間に相当する一定値ｎτを減じた時間Ｔ₁ −ｎτ又はＴ₂ −ｎτの逆数１／（Ｔ₁ −ｎτ）又は１／（Ｔ₂ −ｎτ）に対応するデータ１／（１０Ａ−ｎτ）との集合からなるデータテーブル（表２）をマイクロコンピュータのメモリに格納し、
順方向又は逆方向の計測に当たって第２のカウンタ９から読み取った測定値Ｔ₁ 又はＴ₂ に対応する前記上位桁の数値Ａに相当するアドレスと、この上位桁Ａに１を加算した数値Ａ＋１に相当するアドレスより両アドレスに対応する二つの時間逆数の数値１／（１０Ａ−ｎτ）と１／（１０（Ａ＋１）−ｎτ）に相当する二つの格納データを前記データテーブル（表２）から読み出し、これらのデータと前記測定値Ｔ₁ 又はＴ₂ の最下位１桁の数値Ｂとから時間逆数１／（Ｔ₁ −ｎτ）又は１／（Ｔ₂ −ｎτ）に相当する値１／（１０Ａ＋Ｂ−ｎτ）を直線近似によって導き、流速や流量の演算に使用する。
【００５５】
前記第１の実施態様では、第２のカウンタ９から読み取るべき測定値Ｔ₁ ，Ｔ₂ から遅れ時間に相当する一定値ｎτを減じた値、Ｔ₁ −ｎτ，Ｔ₂ −ｎτがとり得る範囲が１５００１から４５０００の場合について、最下位の桁を除くその他の上位桁の数値１５００〜４５００をアドレスとして、各アドレスに対応するデータ１／（１０×１５００）〜１／（１０×４５００）を〔表１〕のようなデータテーブルとしてメモリに格納した。
【００５６】
従って、メモリに格納した〔表１〕のデータテーブルのアドレスにアクセスするには、第２のカウンタ９から読み取った測定値Ｔ₁ ，Ｔ₂ から遅れ時間に相当する一定値ｎτを減算してＴ₁ −ｎτやＴ₂ −ｎτを得てから、その最下位の桁を除いたその他の上位桁の数値をアドレスとしてアクセスしていた。
【００５７】
ところが、第２の実施態様では、前記〔表１〕に対応する数値を使って〔表２〕のデータテーブルを作成すると、次のようになる。
基準クロック等の条件が前記第１の実施態様と同じで、一定値ｎτが６００カウントとすると、第２のカウンタ９から読み取るべき測定値Ｔ₁ ，Ｔ₂ の範囲は１５００１＋６００〜４５０００＋６００、つまり１５６０１〜４５６００となる。
【００５８】
この１５６０１〜４５６００という測定値が第２のカウンタ９の測定値として直接コントローラ部７のマイクロコンピュータで読み取られる。この測定値は１ＭＨｚの基準クロックのカウント値である。
【００５９】
測定値１５６０１に対応するアドレスは最下位桁の１を除いた１５６０となり、該アドレス１５６０に対応するデータ１／（１０Ａ−ｎτ）は、Ａ＝１５６０、ｎτ＝６００であるから、
アドレス１５６０に対応するデータ＝１／（１５６００−６００）
＝１／１５０００＝６．６６６６６６７×１０^-5 ・・・（６）
となる。
【００６０】
この（６）式の右辺のデータは前記第１の実施態様で説明した（４）式のデータと全く同じである。
そこで、〔表２〕のデータテーブルを次のように作成して、コントローラ部７のマイクロコンピュータに記憶格納する。
【００６１】
【表２】

【００６２】
この第２の実施態様の場合も、データの数は前記第１の実施態様のときと同じ３０００個という小さな数であり、かつ各データの数値は〔表１〕の場合のデータの数値と同じである。
【００６３】
ところで、この第２の実施態様で、第２のカウンタ９で測定した見掛け上の伝搬時間の総和Ｔ₁ 又はＴ₂ が前記第１の実施態様の場合に使用した測定値１７９４３であったとする。
【００６４】
この場合のアドレスは１７９４３の最下位の１桁の数値３を除いた他の上位桁の数値であるから、Ｂ＝３，Ａ＝１７９４となる。従ってアドレスＡは１７９４となり、このときの時間逆数は〔表２〕のデータテーブルからのデータとして、５７６７０１２７を読み出すことができる。
【００６５】
またＡ＋１のアドレスは１７９４＋１＝１７９５となり、このアドレス１７９５に対応する時間逆数は〔表２〕のデータテーブルからのデータとして５７６３６８８８を読み出すことができる。
【００６６】
従って、第２のカウンタ９の測定値１７９４３に対する時間逆数のデータは、上記二つのデータから直線近似で次のように求めることができる。
測定値１７９４３に対応するデータ＝５７６７０１２７−
（５７６７０１２７−５７６３６８８８）×（３／１０）・・・（７）
上記（７）式は、前記第１の実施態様の場合の（５）式と同じであり、流速、流量、積算流量等を求めるその後の演算は、当然第１の実施態様と同様にして行うことができる。
【００６７】
この第２実施態様は、前記第１の実施態様と比較して、データテーブルにアクセスしてデータを読み出すときに、第２のカウンタ９の測定値から一定の遅れ時間に相当する値ｎτ＝６００カウントを減算した値からアドレスを決める必要がないので、順方向や逆方向の測定の都度、ｎτ＝６００カウントの値を測定値Ｔ₁ 又はＴ₂ から引き算する操作が不要となり、その分演算速度や消費電流の面でより有利となる。
【００６８】
この第２の実施態様の場合でも、データテーブルのデータは、〔表２〕の値から一定値を減じた値として記憶格納するようにしてもよい。また流量等の演算を考慮して、データを流管の断面積等の定数を乗じた値として記憶格納することで後の演算時間を小さくすることができる。
【００６９】
【実施例】
次に請求項１の発明に対応する実施例について説明する。この実施例では、図１のブロック図に示す第２のカウンタ９の構成が図４のように変わっており、かつコントローラ部７を構成するマイクロコンピュータの作用が前記実施態様と相違するので、以下この相違点を主体にして説明する。
【００７０】
図４において、９は第２のカウンタで、９１は第２の実施態様の基準カウンタ９１と同じ１ＭＨｚの基準クロックを発振する基準クロック発生器、９２は第２の実施態様のゲート９２と同じように基準クロック発生器９１からの１ＭＨｚの基準クロックを第１送信指令信号と第ｎ受信波検知信号に応じて開閉するゲート、９３は第２の実施態様の１０進１桁のカウンタ９３と同様に、ゲート９２が開いている間の１ＭＨｚの基準クロックを計数する１桁の１０進カウンタで構成され、１０進カウンタ９３より上位が２進カウンタ９８で構成されて図示のように接続されている。
【００７１】
１０進カウンタ９３と２進カウンタ９８は第１送信指令信号が各リセット端子Ｒに入力されるとその内容が零にリセットされる。また１０進カウンタ９３の１，２，４，８出力と２進カウンタ９８の出力Ｑ₁ ，Ｑ₂ ，Ｑ₃ ，…はコントローラ部７へ接続されている。
【００７２】
この実施例ではコントローラ部７を構成するマイクロコンピュータが第２のカウンタ（９）の測定値（Ｔ₁ 又はＴ₂ ）として読み取るべき数値を、その上位桁を２進数（ａ′）で、最下位桁を１０進数（ｂ）で読み取り、別途、前記２進数の上位桁（ａ′）を１０進変換した値（ｃ）の逆数に１／１０を乗じたデータ１／（１０ｃ）を上位桁（ａ′）をアドレスとするデータテーブル〔表３〕として前記マイクロコンピュータのメモリに格納し、
上位桁（ａ′）に相当するアドレスと、これに１を加算した数値（ａ′＋１）に相当するアドレスより両アドレスに対応する時間逆数の数値１／（１０ｃ）と１／｛１０（ｃ＋１）｝に相当する二つのデータを読み出し、これらのデータと前記下位桁の数値（ｂ）とから直線近似によって時間逆数｛１／（Ｔ₁ −ｎτ）又は１／（Ｔ₂ −ｎτ）｝に相当する値１／（１０ｃ＋ｂ）を導き、以後の流速又は流量等の演算に使用するようにしている。
【００７３】
この実施例では、マイクロコンピュータのデータテーブルのアドレスは２進数である。
前述の実施態様の数値例のように、アドレス１７３４から、対応するデータ５７６７０１２７を得る場合、実際には１０進数１７３４を１６進化２進表現であらわした２進数に変換して６Ｃ６Ｈとし、これを加工して得たデータの格納アドレスを求めることを行っている。
【００７４】
マイクロコンピュータを８ビットのマイクロコンピュータとすると、４個のアドレス分のエリアがメモリに割り当てられていて、下記〔表３〕のデータテーブルを記憶格納しておく。
【００７５】
※を付けた行のアドレスを出すには６Ｃ６を４倍して、更にオフセット分の一定値αを加算して、この計算で格納アドレスを出す。
【００７６】
【表３】

【００７７】
この実施例ではマイクロコンピュータの負担を小さくするため第２のカウンタ９における最下位の１０進１桁のカウンタ９３より上位の桁には２進カウンタ（バイナリカウンタ）９８を使い、１０進から２進への煩わしい変換を不要としている。
【００７８】
なお、遅れ時間ｎτに相当する一定値の引き算は、１０進数と２進数が混在した数値でも全１０進数や全２進数の時と同様に可能である。
また、この実施例の場合でも、データテーブルのデータは、［表３］の値から一定値を減じた値として記憶格納するようにしてもよい。また流量等の演算を考慮して、データを流管の断面積等の定数を乗じた値として記憶格納することで後の演算時間を小さくすることができる。
【００７９】
【発明の効果】
本発明の超音波流量計は、上述のように構成されているので、従来技術で行っていた有効数字が６桁程度の割算を順方向や逆方向の測定値Ｔ₁ ，Ｔ₂ から行うことが不必要となり、予めメモリに記憶格納してあるデータテーブルのアドレスをアクセスして時間逆数値に相当するデータを読み出して、流速、流量や積算流量の演算に活用できる。
【００８０】
その結果、高速動作のマイクロコンピュータが不要で、演算時間が短くて済むため、低消費電流でかつ低電圧で作動する超音波流量計が実用化できるという効果を奏する。
【００８１】
また、データテーブルの大きさが小さくて済みメモリ容量が小さくても良く、この点においても効果的である。
【図面の簡単な説明】
【図１】 本発明の好ましい実施形態のブロック図である。
【図２】 図１の実施形態のタイムチャートである。
【図３】 本発明の実施形態に用いる第２のカウンタの電気回路図である。
【図４】 本発明の実施例に用いる第２のカウンタの電気回路図である。
【図５】 超音波流量計の原理を説明する略図である。
【図６】 従来技術の受信波検知部の動作を説明するための電気信号波形を示す線図である。
【符号の説明】
１ 流管
２ 上流側の送受波器
３ 下流側の送受波器
４ 受信波検知部
５ 切替部を構成する信号切替器
６ 送波器駆動部
７ コントローラ部
８ 第１のカウンタ
９ 第２のカウンタ
１０ 切替部を構成する切替スイッチ
９１ 基準クロック発生器
９２ ゲート
９３ 最下位の１桁の１０進カウンタ
９４ １０¹ 位の１桁の１０進カウンタ
９７ １０⁴ 位の１桁の１０進カウンタ
９８ ２進カウンタ
ａ 数値ｂの桁以外の上位桁の数値
ｂ 最下位１桁の数値
ａ ２進数の上位桁の数値ａ′を１０進数に変換した数値
ａ′ ２進数の上位桁の数値
Ａ 数値Ｂの桁以外の上位桁の数値
Ｂ 最下位１桁の数値
Ｔ₁ 順方向計測時の測定値、時間
Ｔ₂ 逆方向計測時の測定値、時間
ｎ 順方向又は逆方向計測時の繰り返し回数
ｎτ 遅れ時間[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an improvement in an ultrasonic flow meter.
[0002]
[Prior art]
  An ultrasonic flowmeter using the time reciprocal difference method is known.
  In FIG. 5, assuming that the sound velocity in the static fluid is C and the fluid flow velocity is V, if the propagation direction of the sound wave coincides with the direction along the flow (hereinafter referred to as the forward direction), the propagation velocity is (C + V In the case of the direction against the flow (hereinafter referred to as the reverse direction), (CV).
[0003]
  When a pair of transducers 2 and 3 are spaced apart from each other by a distance L and arranged upstream and downstream of the flow tube 1 and ultrasonic waves are emitted in the forward direction from the transducer 2, The time required for the sound wave to reach t₁When the ultrasonic wave is emitted from the transmitter 3 in the reverse direction, the time required for the ultrasonic wave to reach the wave receiver 2 is t₂given that,
          t₁= L / (C + V) (1)
          t₂= L / (C-V) (2)
It becomes.
[0004]
  The above propagation time t of ultrasonic waves in the forward and reverse directions₁, T₂The flow velocity V was calculated from this, and the flow rate was further obtained or the integrated flow rate was obtained.
  The flow velocity V is independent of the speed of sound C from the above equations (1) and (2).
          V = (L / 2) [(1 / t₁)-(1 / t₂]] ... (3)
As time and t₁, T₂Reciprocal of 1 / t₁, 1 / t₂This is called the time reciprocal difference method.
[0005]
  Drive pulse P to transmitter 2 (or 3)₁When excitation is applied, propagation time t₁(Or t₂) Later, the ultrasonic wave reaches the receiver 3 (or 2), but the received wave (electrical signal) received by the receiver 3 (or 2) gradually grows from zero at the top value as shown in FIG. However, the first wave, the second wave, the third wave, the fourth wave, and the fifth wave become large values in order, and the waveform gradually attenuates after the peak value is passed.
[0006]
  Propagation time t₁(Or t₂) Is the beginning of the waveform indicated by the symbol “A”, but since this point cannot be detected, the zero cross point after the third or fifth wave is actually set to the receiver 3 ( Or it is detected by the received wave detector connected to 2). In FIG. 6, the drive pulse P₁To the zero cross point “b” immediately after the third wave of the received wave is detected by the received wave detecting unit, and the propagation time t is subtracted from the delay time τ previously obtained and stored in another experiment.₁(Or t₂)
[0007]
  In order to increase the resolution of the propagation time and improve the measurement accuracy of the flow meter, the next transmission in the same direction is performed simultaneously with reception instead of the transmission / reception of one ultrasonic wave, and transmission / reception in the same direction multiple times (n times) Continuously and repeatedly, the time from the first (first) transmission to the last nth reception is measured, and the time t from the first transmission to reception is determined from that value.₁(Or t₂).
[0008]
  First transmission or drive pulse P₁6 to the n-th reception, since the reception wave detection unit directly detects the arrival of the ultrasonic wave is the zero cross point “b” in FIG. 6 as described above, the measurement is being performed n times in the same direction. If the flow velocity V is constant, nt in the forward direction₁+ Nτ, nt in the reverse direction₂+ Nτ.
[0009]
  Therefore, the time nt from the first transmission to the nth reception₁+ Nτ and nt₂The flow rate and the flow rate were obtained by using the time reciprocal difference method using + nτ, and the integrated flow rate (volume) was further obtained.
[0010]
  The time from the first transmission to the nth reception in the forward measurement is T₁, The time from the first transmission to the nth reception in the reverse measurement is T₂Then, as an expression corresponding to the expressions (1) and (2),
          T₁-Nτ = nL / (C + V) (1A)
          T₂−nτ = nL / (C−V) (2A)
Is obtained.
[0011]
  The flow velocity V is independent of the sound velocity C from the above equations (1A) and (2A).
  V = (nL / 2) [{1 / (T₁-Nτ)}-{1 / (T₂−nτ)}] (3A)
As required.
[0012]
  In this type of ultrasonic flowmeter, the switching control between the forward direction measurement and the reverse direction measurement is performed by a controller unit configured by a microcomputer, and the calculation of the mathematical expression (3A) is also performed using this microcomputer. ing.
[0013]
[Problems to be solved by the invention]
  In the prior art, 1 / (T₁-Nτ) or 1 / (T₂-Nτ) is divided by a microcomputer.
[0014]
  In general, microcomputers take time to divide, and this type of flowmeter requires a lot of time for calculation, so it takes much more time and requires a high-speed microcomputer, which is expensive and requires high power. There was a problem.
[0015]
  For example, the speed of sound is 440 m / sec, the distance L is 0.2 m, the number of repetitions n is 200 times, the time T₁Or T₂1 MHz (= 10⁶Hz), when the fluid flow velocity V is zero, T₁= T₂If this is expressed as T,
          T-nτ = 200 × 0.2 × 10⁶/ 440 count
                  = 90909 count = 90909 × 10^-6s
It becomes.
[0016]
  Therefore, it is necessary to divide the effective number of 1 ÷ 90909 by about 6 digits according to the equation (3A).
  Actually, it depends on the difference in fluid flow velocity V and the forward or reverse measurement.₁, T₂Becomes a different value, or delay time nτ is time T₁, T₂The subtraction is the denominator of the division. When the ultrasonic frequency is 500 KHz, nτ is the reference clock of 1 MHz when the zero cross point “b” of the third wave of the received wave is detected as shown in FIG. The count value of
          200 x 1.5 x 2 = 600 counts
Therefore, it is about 0.66% of the 90909 count, and the number of digits for division is about 6 digits.
[0017]
  In order to perform normal division with a microcomputer, calculation is performed while performing subtraction many times, and the number of subtractions is determined by actually subtracting. Therefore, if division with a large number of digits is performed, the calculation may not end at the flow rate or flow rate measurement interval.
[0018]
  Even if the flow meter system is designed to be in time, there is a problem in that the microcomputer keeps moving and low power consumption cannot be realized.
  Accordingly, an object of the present invention is to provide an ultrasonic flowmeter using the time reciprocal difference method that can eliminate such problems.
[0019]
[Means for Solving the Problems]
  To achieve the above purpose,Claim1The invention of
  A pair of ultrasonic transducers (2) and (3) acting both on the transmitting side and on the receiving side for transmitting and receiving ultrasonic waves in the same or oblique direction as the flow in the fluid flow;
  A reception wave detector (4) that outputs a reception wave detection signal when a reception wave transmitter (3 or 2) is connected and a reception wave is detected;
  When the first transmission command signal is input, the transmitter / receiver (2 or 3) is driven, and thereafter an n-th received wave detection signal to be described later is received for each received wave detection signal from the received wave detector (4). A transmitter driver (6) for driving the transmitter / receiver (2 or 3) on the transmitting side until input,
  When measuring in the forward direction, connect the upstream transducer (2) to the transducer driver (6) and connect the downstream transducer (3) to the received wave detector (4). When measuring in the reverse direction, the downstream transducer (3) is connected to the transducer driver (6) and the upstream transducer (2) is connected to the received wave detector (4). A switching unit (5, 10) to perform,
  The first transmission command signal is output each time while the switching unit (5, 10) is alternately switched at a fixed timing to output a transmission / reception switching signal for switching between the forward measurement and the reverse measurement to alternately switch transmission / reception. A controller unit (7) for outputting
  The received wave detection signal is received from the received wave detection unit (4), and the nth received wave detection signal is detected and output at the nth received wave detection signal every time the forward measurement and the reverse measurement are performed. 1 counter (8),
  Time from the first transmission command signal to the nth received wave detection signal at the time of forward measurement (T₁) And the time from the first transmission command signal to the n-th received wave detection signal (T₂A second counter (9) for measuring)
  When the nth received wave detection signal is received, the measured value (T₁Or T₂), And an ultrasonic flowmeter that performs calculations such as a flow rate and a flow rate using the inverse time difference method in the controller unit (7),
  The time measuring unit constituting the second counter (9) is a counter that counts the reference clock, the lowest order is a decimal counter (93) with one digit, and the higher order is a binary counter (98),
  The controller unit (7) is composed of a micro computer,
  The microcomputer measures the value (T) of the second counter (9).₁Or T₂) Is read as a binary number (a ′) and the least significant digit as a decimal number (b).
  Separately, data 1 / (10c) obtained by multiplying the reciprocal of the value (c) obtained by decimal conversion of the upper digit (a ′) of the binary number by 1/10 is used as a data table having the upper digit (a ′) as an address. Stored in the memory of the microcomputer;
  From the address corresponding to the upper digit (a ′) and the address corresponding to the numerical value (a ′ + 1) obtained by adding 1 to this, the numerical values 1 / (10c) and 1 / {10 (c + 1) of the time reciprocal corresponding to both addresses )} Is read out, and the reciprocal time {1 / (T₁-Nτ) or 1 / (T₂-Nτ)} is an ultrasonic flowmeter characterized by deriving a value 1 / (10c + b) corresponding to −nτ)} and using it for subsequent calculations such as flow velocity or flow rate.
[0020]
  Claim2The present invention comprises a pair of ultrasonic transducers (2) and (3) that act both on the transmitting side and on the receiving side for transmitting and receiving ultrasonic waves in the same or oblique direction as the flow in the fluid flow,
  A reception wave detector (4) that outputs a reception wave detection signal when a reception wave transmitter (3 or 2) is connected and a reception wave is detected;
  When the first transmission command signal is input, the transmitter / receiver (2 or 3) is driven, and thereafter an n-th received wave detection signal to be described later is received for each received wave detection signal from the received wave detector (4). A transmitter driver (6) for driving the transmitter / receiver (2 or 3) on the transmitting side until input,
  When measuring in the forward direction, connect the upstream transducer (2) to the transducer driver (6) and connect the downstream transducer (3) to the received wave detector (4). When measuring in the reverse direction, the downstream transducer (3) is connected to the transducer driver (6) and the upstream transducer (2) is connected to the received wave detector (4). A switching unit (5, 10) to perform,
  The first transmission command signal is output each time while the switching unit (5, 10) is alternately switched at a fixed timing to output a transmission / reception switching signal for switching between the forward measurement and the reverse measurement to alternately switch transmission / reception. A controller unit (7) for outputting
  The received wave detection unit (4) receives the received wave detection signal, detects the nth received wave detection signal and outputs the nth received wave detection signal for each measurement in the forward direction and in the reverse direction. 1 counter (8),
  Time from the first transmission command signal to the nth received wave detection signal at the time of forward measurement (T₁) And the time from the first transmission command signal to the n-th received wave detection signal (T₂A second counter (9) for measuring)
  When the nth received wave detection signal is received, the measured value (T₁Or T₂), And an ultrasonic flowmeter that performs calculations such as a flow rate and a flow rate using the inverse time difference method in the controller unit (7),
  The time measuring unit constituting the second counter (9) is a counter that counts the reference clock, the lowest order is a decimal counter (93) with one digit, and the higher order is a binary counter (98),
  The controller unit (7) is composed of a micro computer,
  The microcomputer measures the value (T) of the second counter (9).₁Or T₂) Is read as a binary number (a ′) and the least significant digit as a decimal number (b).
  Separately, the reciprocal data of the value (c) obtained by decimal conversion of the upper digit (a ′) of the binary number is stored in the memory of the microcomputer as a data table having the upper digit (a ′) as an address,
  Two data of the reciprocal time corresponding to both addresses are read out from the address corresponding to the upper digit (a ′) and the address corresponding to the numerical value obtained by adding 1 to these, and these data and the numerical value (b) of the lower digit To the inverse of time {1 / (T₁-Nτ) or 1 / (T₂-Nτ)}, and is used for subsequent calculation of flow velocity or flow rate.
  Claim3The invention of claim2In the ultrasonic flowmeter, the data stored in the data table is claimed in claim2The data table is configured by using as a data a value obtained by subtracting a constant value from the data described in the above or a value obtained by multiplying the constant value.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
  FIG. 1 illustrates the present invention.First to explain the basics of thinkingFIG. 2 is a time chart in the embodiment. In the figure, reference numerals 2 and 3 denote a pair of ultrasonic transducers, which transmit and receive ultrasonic waves in the same direction as the flow or in an oblique direction in the fluid flow, as in the prior art.
[0022]
  Reference numeral 4 denotes a received wave detection unit, which is connected to the input of the receiving side transmitter / receiver 3 or 2 selected by the signal switch 5, and converts the received wave to the zero cross point of the predetermined wave, for example, as shown in FIG. When detected at the zero crossing point “B” immediately after the wave, a received wave detection signal (see FIG. 2) is output.
[0023]
  In FIG. 2, the first, second, third,..., And nth received wave detection signals are respectively labeled 1, 2, 3,.
  6 excites the transmitter / receiver 2 or 3 when a first transmission command signal is input from the controller unit 7 which will be described later, and thereafter, for each received wave detection signal from the receiver detection unit 4 It is a transmitter driver that excites the transmitter / receiver 2 or 3 on the transmission side until an n received wave detection signal is input.
[0024]
  Reference numeral 7 denotes a controller unit composed of a microcomputer that outputs a transmission / reception switching signal for alternately switching between forward measurement and reverse measurement by switching the signal switch 5 and the changeover switch 10 synchronously at a fixed timing. Thus, each time the transmission / reception is switched alternately, the first transmission command signal is output to the transmitter driving unit 6, the first counter 8 and the second counter 9, which will be described later.
[0025]
  The signal selector 5 and the selector switch 10 together constitute a selector, and when performing forward measurement, the selector switch 10 is in the state shown in the figure and the upstream transducer 2 is connected to the transmitter driver 6. At the same time, the signal switch 5 is placed in the state shown in the figure, and the downstream transducer 3 is connected to the received wave detector 4.
[0026]
  When measuring in the reverse direction, the selector switch 10 is switched from the illustrated state to connect the downstream transmitter / receiver 3 to the transmitter driver 6, and the signal switch 5 is switched from the illustrated state. The upstream transducer 2 is connected to the received wave detector 4.
[0027]
  8 is a first counter that receives a received wave detection signal from the received wave detection unit 4 and counts the received wave detection signal for each measurement in the forward direction and in the reverse direction, and the count value becomes n. That is, the nth received wave detection signal is detected and the nth received wave detection signal is output. Note that the count value of the first counter 8 is reset to zero by the first transmission command signal from the controller unit 7.
[0028]
  A second counter 9 is a time T from the first transmission command signal P from the controller unit 7 to the nth received wave detection signal from the first counter 8 at the time of forward measurement.₁(See FIG. 2) and time T from the first transmission command signal to the n-th received wave detection signal at the time of reverse direction measurement₂Measure each.
[0029]
  As shown in FIG. 2, the apparent propagation time of each time in the forward direction is the net propagation time t.₁T added to each time delay time τ₁+ Τ, the time from the first transmission command signal P to the n-th received wave detection signal, that is, the measured value T of the second counter 9 at the time of forward measurement₁Is
          T₁= Nt₁+ Nτ
It is expressed.
[0030]
  Similarly, the measured value T of the second counter 9 at the time of backward measurement₂Is
          T₂= Nt₂+ Nτ
It is expressed.
[0031]
  The time measuring unit constituting the second counter 9 is composed of a decimal counter, counts a 1 MHz reference clock, and from the first transmission command signal P to the nth received wave detection signal at the time of forward measurement shown in FIG. Time T₁And a time T from the first transmission command signal to the nth received wave detection signal at the time of reverse direction measurement.₂Is counted as the count value of the reference clock.
[0032]
  FIG. 3 shows the configuration of the second counter 9. 91 is a clock generator that oscillates a 1 MHz reference clock, and 92 is a gate that passes or stops the reference clock from the clock generator 91. When the first transmission command signal is received, the gate 92 opens and passes the reference clock. Thus, when the nth received wave detection signal from the first counter 8 is received, the gate 92 which has been opened so far is closed.
[0033]
  93, 94,..., 97 are decimal one digit counters, 93 is the first digit, 94 is the second digit,. Counter 93 counts the reference clock that has passed through gate 92 and inputs the carry to counter 94 of the second digit. In this way, the carry of each counter 93, 94,... Is input to the next higher digit counter 94,.₁, T₂Count.
[0034]
  The first transmission command signal opens the gate 92 and resets the contents of the counters 93, 94,.
  Each of the decimal counters 93, 94,..., 97 has 1, 2, 4, 8 output terminals, and 1, 2, 4, 8 outputs from these terminals are input to the controller unit 7. It has become so.
[0035]
  Each of the decimal counters 93, 94,.⁰, 10¹, ..., 10^FourThe counters of 5 decimal digits are configured in total, and the number of these counters is prepared according to the number of decimal digits of the second counter 9 required.
[0036]
  The controller unit 7 measures the measured value T of the second counter 9 each time it receives the nth received wave detection signal from the first counter 8 during forward measurement and reverse measurement.₁, T₂And calculate the flow velocity, flow rate, integrated flow rate, etc. using the time reciprocal difference method.But the reverseIn order to calculate the number, the data table stored in the memory of the microcomputer is avoided, avoiding the calculation of about 6 digits by the microcomputer as described in the above section [Problems to be solved by the invention]. It is used to derive the inverse time value in a short time.
[0037]
  In the embodiment of FIG. 1, the measured value T to be read from the second counter 9₁, T₂, ... This is the time T with a decimal counter of 1MHz reference clock₁, T₂Is expressed as a count value counted during the period ... A value T obtained by subtracting a value obtained by converting a constant value nτ corresponding to a delay time into a count value of a reference clock of 1 MHz.₁-Nτ, T₂-Nτ is divided into the lowest 1 digit and other upper digits, the lowest 1 digit numerical value is b, the other higher digit numerical value is a, and the address corresponding to the other higher digit numerical value a and the address A data table of [Table 1] consisting of a set of data 1 / (10a) corresponding to is stored in the memory of the microcomputer.
[0038]
  The measurement value T of the second counter 9 expressed by the count value of the reference clock of 1 MHz.₁, T₂The delay time nτ is determined by the distance L, the fluid flow speed V, the number of repetitions n in the forward and reverse directions, the cycle of the ultrasonic wave, the angle formed by the fluid flow and the ultrasonic wave emission direction, and the like. , T₁-Nτ, T₂If the range that can be taken by the value of −nτ is expressed by a count value of a reference clock of 1 MHz, for example, a range from 15001 to 45000, these count values are composed of a set of 45000-15000 = 30000 count values. A data table will be provided.
[0039]
  In the embodiment of FIG. 1, it is not necessary to divide by about 6 digits by preparing a data table consisting of a smaller number of sets and reading the reciprocal time value from this data table, and a small data table. I am trying to do it.
[0040]
  That is, each count value constituting a set of 30000 count values consisting of 15001, 15002,..., 44999, 45000, that is, a measurement value T to be read from the second counter 9.₁-Nτ, T₂-Nτ is divided into the lowest 1 digit and other upper digits, the lowest 1 digit numerical value is b, the other higher digit numerical value is a, and the address corresponding to the other higher digit numerical value a and the address A data table consisting of a set of data 1 / (10a) corresponding to the reciprocal of is stored in the memory of the microcomputer.
[0041]
  This data table contains measured values T₁When −nτ is 15001, the lowest-order numerical value b is 1. The numerical value of the other upper digits is 1500. Therefore, the address corresponding to the measured value 15001 is 1500, and the data 1 / (10a) corresponding to the address 1500 is
  1 / (10 × 1500) = 6.6666667 × 10^-Five... (4)
It becomes. The least significant digit 6 of the eight significant digits on the right side of the above expression is expressed by rounding the least significant digit 6 to 7.
[0042]
  In this way, the data table of the data corresponding to the address is as shown in [Table 1]. Note that the data in Table 1 is obtained by removing the decimal point of the same numerical value as the 8-digit significant number on the right side of the above equation (4).
[0043]
[Table 1]

[0044]
  When the data table of [Table 1] is created in this way and stored in the memory of the microcomputer, the number of data becomes 3000, which is 1/10 of the above 30000.
[0045]
  Measurement value T of second counter 9₁-Nτ, T₂The data table of Table 1 was created with a set of 8 significant digits that are the reciprocal of the numerical value of the upper digit of the value with the lowest digit of -nτ being 0.
[0046]
  Thus, in the data table of [Table 1], the memory capacity may be small, but the measured value T of the second counter 9₁-Nτ, T₂The value when the least significant digit of −nτ is a numerical value other than 0 cannot be directly read from the table.
[0047]
  For example, the measured value T of the second counter 9₁Or T₂17943, the address corresponding to the measured value 17943 is 17943-600 = 17343 when the constant value nτ is 600. The reciprocal data corresponding to this cannot be read from the data table of [Table 1]. Therefore, an inverse time value corresponding to the measured value 17343 is obtained by linear approximation using data read from the data table of [Table 1].
[0048]
  Since the measured value of the second counter 9 is 17943, it is 17343 as described above, which is obtained by subtracting the constant value nτ = 600 from the numerical value of this measured value. Therefore, the address corresponding to the upper four-digit value 1734 and the address corresponding to 1735 obtained by adding 1 to the upper-digit value 1734 are 1 / (10 × 1734) and 1 / (10 × 1735). Two corresponding stored data are read from the data table of [Table 1]. Actually, the data is read from the data stored in the memory of the microcomputer constituting the controller unit 7.
[0049]
        Address data
        1734 5770127
        1735 576368888
Then, from these two data, data corresponding to the measured value 17943 is derived using linear approximation in the following equation (5).
[0050]
  Data corresponding to measured value 17943 = 5770127- (5767127
                                -57636888) × (3/10) (5)
When the calculation of equation (5) is performed by a microcomputer, the calculation of (5760127127-5766888) × (3/10) takes some time, but the table becomes small and can be realized.
  In this way, by using the data read from the small table and calculating the intermediate data of the table by linear approximation, the memory for storing the table can be reduced, and the division as a whole does not take a long time. Tesumu.
[0051]
  Since the calculation of the flow velocity, the flow rate, the integrated flow rate, etc. after the calculation of the equation (5) can be performed by a well-known method, the detailed description is omitted.
  The data in the data table may be stored and stored as a value obtained by subtracting a certain value from the value in [Table 1]. In this case, the offset is calculated by a subsequent calculation {1 / (T₁-Nτ)}-{1 / (T₂−nτ)} is subtracted and canceled out, so there is no problem. In addition, taking into account calculations such as flow rate, data can be stored and stored as a value multiplied by a constant such as the cross-sectional area of the flow tube, thereby reducing the subsequent calculation time.The
[0052]
  UpFirstImplementation formIn stateOf the inventionFirst to explain the basics of thinkingDescribe the embodimentSolidBut,Next second embodimentEven if the flow meter is configured likeThe computation time in the controller can be reduced.The
[0053]
  FigureIn the block diagram of FIG. 1, only the operation of the microcomputer constituting the controller unit 7 isFirstSince it is different from the embodiment, the following will focus on this difference.Second embodimentWill be explained.
[0054]
  FirstMeasured value T to be read from the counter 9 of 2₁Or T₂Is divided into the lowest one digit B and the other higher digit A, the address corresponding to the other higher digit A, and the measured value read from the second counter 9 corresponding to the address. T₁Or T₂A time T obtained by subtracting a constant value nτ corresponding to the delay time.₁-Nτ or T₂Reciprocal of -nτ 1 / (T₁-Nτ) or 1 / (T₂A data table (Table 2) consisting of a set of data 1 / (10A-nτ) corresponding to -nτ) is stored in the memory of the microcomputer;
  The measured value T read from the second counter 9 in the forward or reverse measurement₁Or T₂And an address corresponding to the numerical value A of the upper digit corresponding to 1 and a numerical value 1 / (10A-nτ) of two time reciprocals corresponding to both addresses from an address corresponding to the numerical value A + 1 obtained by adding 1 to the upper digit A Two stored data corresponding to 1 / (10 (A + 1) -nτ) are read from the data table (Table 2), and these data and the measured value T₁Or T₂Time reciprocal 1 / (T₁-Nτ) or 1 / (T₂A value 1 / (10A + B−nτ) corresponding to −nτ) is derived by linear approximation and used for calculation of flow velocity and flow rate.
[0055]
  SaidFirstIn an embodiment, the measured value T to be read from the second counter 9.₁, T₂A value obtained by subtracting a constant value nτ corresponding to the delay time from T₁-Nτ, T₂When the range that −nτ can take is 15001 to 45000, data 1 / (10 × 1500) to 1 / (1) corresponding to each address is obtained by using numerical values 1500 to 4500 of other upper digits excluding the lowest digit as addresses. 10 × 4500) was stored in the memory as a data table as shown in [Table 1].
[0056]
  Therefore, to access the address of the data table of [Table 1] stored in the memory, the measured value T read from the second counter 9 is used.₁, T₂A constant value nτ corresponding to the delay time is subtracted from T₁-Nτ and T₂After obtaining -nτ, the numerical value of the other upper digits except the lowest digit was accessed as an address.
[0057]
  However, the secondEmbodiment ofThen, when the data table of [Table 2] is created using the numerical values corresponding to [Table 1], it becomes as follows.
  The conditions such as the reference clockFirstAs in the embodiment, when the constant value nτ is 600 counts, the measured value T to be read from the second counter 9 is as follows.₁, T₂The range is 15001 + 600-45000 + 600, that is, 15601-45600.
[0058]
  The measurement values 15601 to 45600 are directly read by the microcomputer of the controller unit 7 as the measurement values of the second counter 9. This measured value is a count value of a reference clock of 1 MHz.
[0059]
  Since the address corresponding to the measurement value 15601 is 1560 excluding the least significant digit 1 and the data 1 / (10A−nτ) corresponding to the address 1560 is A = 1560 and nτ = 600,
Data corresponding to address 1560 = 1 / (15600-600)
          = 1/15000 = 6.6666667 × 10^-Five ... (6)
It becomes.
[0060]
  The data on the right side of the equation (6)FirstThis is exactly the same as the data of equation (4) described in the embodiment.
  Therefore, the data table of [Table 2] is created as follows and stored in the microcomputer of the controller unit 7.
[0061]
[Table 2]

[0062]
  This secondEmbodiment ofIn the case ofFirstThe number is as small as 3000 as in the embodiment, and the numerical value of each data is the same as the numerical value of data in the case of [Table 1].
[0063]
  By the way, this second implementationAspectThe total apparent propagation time T measured by the second counter 9₁Or T₂SaidFirstIt is assumed that the measurement value used in the embodiment is 17943.
[0064]
  In this case, since the address is a numerical value of the other high-order digits excluding the lowest-order numerical value 3 of 17943, B = 3 and A = 1794. Therefore, the address A is 1794, and the time reciprocal at this time can read 5770127 as the data from the data table of [Table 2].
[0065]
  Further, the address of A + 1 is 1794 + 1 = 1799, and the time reciprocal corresponding to this address 1795 can read 5766688 as data from the data table of [Table 2].
[0066]
  Therefore, the data of the reciprocal time with respect to the measured value 17943 of the second counter 9 can be obtained from the above two data by linear approximation as follows.
    Data corresponding to measured value 17943 = 5770127−
       (5770127-57636888) × (3/10) (7)
  The above equation (7)FirstIt is the same as the equation (5) in the case of the embodiment, and the subsequent calculation for obtaining the flow velocity, flow rate, integrated flow rate, etc. is naturallyFirstIt can be performed in the same manner as in the embodiment.
[0067]
  This second implementationAspectIsThe firstCompared with the embodiment, when reading data by accessing the data table, it is necessary to determine the address from the value obtained by subtracting the value nτ = 600 counts corresponding to a certain delay time from the measured value of the second counter 9. Therefore, every time measurement in the forward or reverse direction, the value of nτ = 600 counts is taken as the measured value T₁Or T₂This eliminates the need for subtracting from, making it more advantageous in terms of calculation speed and current consumption.The
[0068]
  This secondofImplementationAspectEven in this case, the data in the data table may be stored and stored as a value obtained by subtracting a certain value from the value in [Table 2]. In consideration of calculation such as flow rate, later calculation time can be shortened by storing and storing data as a value multiplied by a constant such as the cross-sectional area of the flow tube.The
[0069]
【Example】
  Next claim1Corresponding to the inventionFruitExamples will be described. In this embodiment, the configuration of the second counter 9 shown in the block diagram of FIG. 1 is changed as shown in FIG. 4 and the operation of the microcomputer constituting the controller unit 7 is different from that of the above embodiment. Based on this differenceTheoryLight up.
[0070]
  In FIG. 4, 9 is the second counter and 91 is the second counter.ofImplementationAspectThe reference clock generator for oscillating the same 1 MHz reference clock as the reference counter 91 of FIG.ofImplementationAspectSimilarly to the gate 92, the gate for opening and closing the 1 MHz reference clock from the reference clock generator 91 according to the first transmission command signal and the nth received wave detection signal,ofImplementationAspectIn the same way as the decimal one-digit counter 93, a one-digit decimal counter that counts a 1 MHz reference clock while the gate 92 is open is configured, and a binary counter 98 is configured above the decimal counter 93. And connected as shown.
[0071]
  When the first transmission command signal is input to each reset terminal R, the contents of the decimal counter 93 and the binary counter 98 are reset to zero. In addition, the output 1, 2, 4, 8 of the decimal counter 93 and the output Q of the binary counter 98₁, Q₂, Q_Three,... Are connected to the controller unit 7.
[0072]
  ThisThe fruitIn the embodiment, the microcomputer constituting the controller unit 7 measures the measured value (T of the second counter (9)).₁Or T₂), The upper digit (a ') of the numerical value to be read as a binary number (a'), the least significant digit as a decimal number (b), and the upper digit (a ') of the binary number converted to decimal ( data 1 / (10c) obtained by multiplying the reciprocal of c) by 1/10 as a data table [Table 3] with the upper digit (a ′) as an address and stored in the memory of the microcomputer;
  From the address corresponding to the upper digit (a ′) and the address corresponding to the numerical value (a ′ + 1) obtained by adding 1 to this, the numerical values 1 / (10c) and 1 / {10 (c + 1) of the time reciprocal corresponding to both addresses )} Is read out, and the reciprocal time {1 / (T₁-Nτ) or 1 / (T₂Value 1 / (10c + b) corresponding to −nτ)} is derived and used for the subsequent calculation of flow velocity or flow rate.
[0073]
  ThisThe fruitIn the embodiment, the address of the microcomputer data table is a binary number.
  As in the numerical example of the above embodiment, when the corresponding data 5770127 is obtained from the address 1734, the decimal number 1734 is actually converted into a binary number represented by the hexadecimal representation of binary 6C6H, which is processed. The storage address of the data obtained in this way is obtained.
[0074]
  If the microcomputer is an 8-bit microcomputer, four address areas are allocated to the memory, and the data table shown in Table 3 below is stored and stored.
[0075]
  To obtain the address of the line marked with *, 6C6 is multiplied by 4, and a fixed value α for the offset is added, and the storage address is obtained by this calculation.
[0076]
[Table 3]

[0077]
  ThisThe fruitIn this embodiment, in order to reduce the burden on the microcomputer, a binary counter (binary counter) 98 is used for the digit higher than the least significant decimal one digit counter 93 in the second counter 9 from decimal to binary. The troublesome conversion is unnecessary.
[0078]
  Note that subtraction of a constant value corresponding to the delay time nτ can be performed in the same manner as in the case of all decimal numbers and all binary numbers even in a numerical value in which decimal numbers and binary numbers are mixed.
  Also thisThe fruitEven in the embodiment, the data in the data table may be stored and stored as a value obtained by subtracting a certain value from the value in [Table 3]. In consideration of calculation such as flow rate, later calculation time can be shortened by storing and storing data as a value multiplied by a constant such as the cross-sectional area of the flow tube.The
[0079]
【The invention's effect】
  Since the ultrasonic flowmeter of the present invention is configured as described above, the division of a significant number of about six digits, which has been performed in the prior art, is a measurement value T in the forward direction or the reverse direction.₁, T₂The data table address stored in the memory in advance is accessed to read the data corresponding to the reciprocal value of the time, and can be used for the calculation of the flow rate, the flow rate and the integrated flow rate.
[0080]
  As a result, there is no need for a microcomputer that operates at high speed, and the calculation time is short, so that an ultrasonic flowmeter that operates with low current consumption and low voltage can be put into practical use.
[0081]
  Further, the size of the data table may be small, the memory capacity may be small, and this point is also effective.
[Brief description of the drawings]
FIG. 1 is a block diagram of a preferred embodiment of the present invention.
FIG. 2 is a time chart of the embodiment of FIG.
FIG. 3 is an electric circuit diagram of a second counter used in the embodiment of the present invention.
FIG. 4 The present inventionThe fruitIt is an electric circuit diagram of the 2nd counter used for an Example.
FIG. 5 is a schematic diagram illustrating the principle of an ultrasonic flow meter.
FIG. 6 is a diagram showing electrical signal waveforms for explaining the operation of the reception wave detection unit of the prior art.
[Explanation of symbols]
  1 Flow pipe
  2 Upstream transducer
  3 Downstream transducer
  4 Received wave detector
  5 Signal switching unit that constitutes the switching unit
  6 Transmitter drive
  7 Controller
  8 First counter
  9 Second counter
  10 Changeover switch constituting the changeover unit
  91 Reference clock generator
  92 gate
  93 Decimal counter with 1 digit at the bottom
  94 10¹1-digit decimal counter
  97 10^Four1-digit decimal counter
  98 binary counter
  a Numeric value of upper digit other than numeric digit b
  b The lowest digit
  a Numeric value of upper digit a 'converted to decimal number
  a 'Numeric value of upper digit of binary number
  A Numeric value of upper digit other than digit B
  B The numerical value of the least significant digit
  T₁ Measurement value and time during forward measurement
  T₂ Measured value and time during reverse measurement
  n Number of repetitions during forward or reverse measurement
  nτ delay time

Claims (3)

A pair of ultrasonic transducers (2) and (3) acting both on the transmitting side and on the receiving side for transmitting and receiving ultrasonic waves in the same or oblique direction as the flow in the fluid flow;
A reception wave detector (4) that outputs a reception wave detection signal when a reception-side transducer (3 or 2) is connected and a reception wave is detected;
When the first transmission command signal is input, the transmitter / receiver (2 or 3) is driven, and thereafter an n-th received wave detection signal to be described later is received for each received wave detection signal from the received wave detector (4). A transmitter driver (6) for driving the transmitter / receiver (2 or 3) on the transmitting side until input,
When measuring in the forward direction, connect the upstream transducer (2) to the transducer driver (6) and connect the downstream transducer (3) to the received wave detector (4). When measuring in the reverse direction, the downstream transducer (3) is connected to the transducer driver (6) and the upstream transducer (2) is connected to the received wave detector (4). A switching unit (5, 10) to perform,
The first transmission command signal is output each time while the switching unit (5, 10) is alternately switched at a fixed timing to output a transmission / reception switching signal for switching between the forward measurement and the reverse measurement to alternately switch transmission / reception. A controller unit (7) for outputting
The received wave detection signal is received from the received wave detection unit (4), and the nth received wave detection signal is detected and output at the nth received wave detection signal every time the forward measurement and the reverse measurement are performed. 1 counter (8),
Time (T ₁ ) from the first transmission command signal to the nth received wave detection signal at the time of forward measurement, and time (T ₂ ) from the first transmission command signal to the nth received wave detection signal at the time of backward measurement. A second counter (9) for measuring
When the nth received wave detection signal is received, the measurement value (T ₁ or T ₂ ) of the second counter (9) is read and the flow rate, flow rate, etc. are calculated by the controller unit (7) using the time reciprocal difference method. An ultrasonic flow meter,
The time measuring unit constituting the second counter (9) is a counter for counting a reference clock, the lowest order is a decimal counter (93) having one digit, and the higher order is a binary counter (98),
The controller unit (7) is composed of a micro computer,
The microcomputer reads the numerical value to be read as the measurement value (T ₁ or T ₂ ) of the second counter (9), with the upper digit as binary number (a ′) and the least significant digit as decimal number (b). ,
Separately, data 1 / (10c) obtained by multiplying the reciprocal of the value (c) obtained by decimal conversion of the upper digit (a ′) of the binary number by 1/10 is used as a data table having the upper digit (a ′) as an address. Stored in the memory of the microcomputer;
From the address corresponding to the upper digit (a ′) and the address corresponding to the numerical value (a ′ + 1) obtained by adding 1 to this, the numerical values 1 / (10c) and 1 / {10 (c + 1) of the time reciprocal corresponding to both addresses )} Is read out, and the time inverse {1 / (T ₁ −nτ) or 1 / (T ₂ −nτ)} is obtained by linear approximation from these data and the numerical value (b) of the lower digit. An ultrasonic flowmeter, wherein a corresponding value 1 / (10c + b) is derived and used for subsequent calculations of flow velocity or flow rate. A pair of ultrasonic transducers (2) and (3) acting both on the transmitting side and on the receiving side for transmitting and receiving ultrasonic waves in the same or oblique direction as the flow in the fluid flow;
A reception wave detector (4) that outputs a reception wave detection signal when a reception-side transducer (3 or 2) is connected and a reception wave is detected;
When the first transmission command signal is input, the transmitter / receiver (2 or 3) is driven, and thereafter an n-th received wave detection signal to be described later is received for each received wave detection signal from the received wave detector (4). A transmitter driver (6) for driving the transmitter / receiver (2 or 3) on the transmitting side until input,
When measuring in the forward direction, connect the upstream transducer (2) to the transducer driver (6) and connect the downstream transducer (3) to the received wave detector (4). When measuring in the reverse direction, the downstream transducer (3) is connected to the transducer driver (6) and the upstream transducer (2) is connected to the received wave detector (4). A switching unit (5, 10) to perform,
The first transmission command signal is output each time while the switching unit (5, 10) is alternately switched at a fixed timing to output a transmission / reception switching signal for switching between the forward measurement and the reverse measurement to alternately switch transmission / reception. A controller unit (7) for outputting
The received wave detection signal is received from the received wave detection unit (4), and the nth received wave detection signal is detected and output at the nth received wave detection signal every time the forward measurement and the reverse measurement are performed. 1 counter (8),
Time (T ₁ ) from the first transmission command signal to the nth received wave detection signal at the time of forward measurement, and time (T ₂ ) from the first transmission command signal to the nth received wave detection signal at the time of backward measurement. A second counter (9) for measuring
When the nth received wave detection signal is received, the measurement value (T ₁ or T ₂ ) of the second counter (9) is read and the flow rate, flow rate, etc. are calculated by the controller unit (7) using the time reciprocal difference method. An ultrasonic flow meter,
The time measuring unit constituting the second counter (9) is a counter for counting a reference clock, the lowest order is a decimal counter (93) having one digit, and the higher order is a binary counter (98),
The controller unit (7) is composed of a micro computer,
The microcomputer reads the numerical value to be read as the measurement value (T ₁ or T ₂ ) of the second counter (9), with the upper digit as binary number (a ′) and the least significant digit as decimal number (b). ,
Separately, the reciprocal data of the value (c) obtained by decimal conversion of the upper digit (a ′) of the binary number is stored in the microcomputer memory as a data table having the upper digit (a ′) as an address,
From the address corresponding to the upper digit (a ′) and the address corresponding to the numerical value obtained by adding 1 to this, two data of the time reciprocal corresponding to both addresses are read, and these data and the numerical value (b) of the lower digit An ultrasonic flow rate characterized in that a reciprocal time {1 / (T ₁ −nτ) or 1 / (T ₂ −nτ)} is derived from the above by linear approximation and used for subsequent calculations such as flow velocity or flow rate. Total. 3. The ultrasonic wave according to claim 2 , wherein the data stored in the data table is configured by using a value obtained by subtracting a constant value from the data described in claim 2 or a value obtained by multiplying the data by a constant value. Flowmeter.

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