JP5372831B2

JP5372831B2 - Ultrasonic densitometer

Info

Publication number: JP5372831B2
Application number: JP2010094973A
Authority: JP
Inventors: 英一村上; 敬章鶴見; 雅之柳橋
Original assignee: Atsuden Co Ltd
Current assignee: Atsuden Co Ltd
Priority date: 2010-04-16
Filing date: 2010-04-16
Publication date: 2013-12-18
Anticipated expiration: 2030-04-16
Also published as: JP2011226844A

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic concentration meter capable of measuring a concentration of a fluid accurately without using a temperature sensor by using the principle of a time difference type ultrasonic flowmeter. <P>SOLUTION: An average period of vibration is calculated from zero-cross points in a free vibration part Wb of a reception waveform W with respect to a water solution having certain temperature and concentration. This average period depends only on temperature. By emitting an ultrasonic beam from upstream and from downstream into a water solution that is a fluid, acoustic velocity of the water solution is obtained. Because the acoustic velocity is proportional to the concentration and varies by the temperature of the water solution, a temperature-corrected concentration can be calculated from the obtained acoustic velocity and temperature. <P>COPYRIGHT: (C)2012,JPO&INPIT

Description

本発明は、時間差式の超音波流量計の原理を利用して、流体の濃度を測定する超音波式濃度計に関するものである。 The present invention relates to an ultrasonic densitometer that measures the concentration of a fluid using the principle of a time difference type ultrasonic flowmeter.

時間差式の超音波流量計は図９に示すように、例えば流体が矢印方向に流れるコ字型の管路１の両側に、超音波振動子である圧電素子２、３を取り付けた構造とされている。一方の圧電素子２に電圧を印加して発振させることにより、流体中に超音波ビームを伝播させることができる。他方の圧電素子３はこの超音波ビームを受信すると、その応力から圧電効果を生じ、誘起された電荷を読み取ることで、超音波ビームの受信信号を得ることができる。圧電素子２、３による超音波ビームの送信、受信を交互に行って、流体中の超音波ビームの上流から下流へ、下流から上流への伝播時間をそれぞれ検出する。 As shown in FIG. 9, the time difference type ultrasonic flowmeter has a structure in which, for example, piezoelectric elements 2 and 3 that are ultrasonic vibrators are attached to both sides of a U-shaped pipe 1 in which a fluid flows in the direction of an arrow. ing. By applying a voltage to one piezoelectric element 2 and oscillating it, an ultrasonic beam can be propagated in the fluid. When the other piezoelectric element 3 receives this ultrasonic beam, a piezoelectric effect is generated from the stress, and a received signal of the ultrasonic beam can be obtained by reading the induced charge. Transmission and reception of the ultrasonic beam by the piezoelectric elements 2 and 3 are alternately performed to detect the propagation time of the ultrasonic beam in the fluid from upstream to downstream and from downstream to upstream.

このようにして、超音波ビームを上流の圧電素子２から流体を経て下流の圧電素子３に伝播させたときの伝播時間Ｔｄと、下流の圧電素子３から上流の圧電素子２に伝播させたときの伝播時間Ｔｕの時間差を基に、流量を測定することは例えば特許文献１等において公知である。 In this way, when the ultrasonic beam is propagated from the upstream piezoelectric element 2 to the downstream piezoelectric element 3 via the fluid and to the downstream piezoelectric element 3, the propagation time Td is propagated from the downstream piezoelectric element 3 to the upstream piezoelectric element 2. The measurement of the flow rate based on the time difference of the propagation time Tu is known in, for example, Patent Document 1.

即ち、管路１の長さをＬ、流体の音速をＣ、管路１内の流体の流速をＶとすると、伝播時間Ｔｄ、Ｔｕは次式のようになる。
Ｔｄ＝Ｌ／（Ｃ＋Ｖ）・・・（１）
Ｔｕ＝Ｌ／（Ｃ−Ｖ）・・・（２） That is, if the length of the pipe line 1 is L, the sound velocity of the fluid is C, and the flow velocity of the fluid in the pipe line 1 is V, the propagation times Td and Tu are as follows.
Td = L / (C + V) (1)
Tu = L / (C−V) (2)

これらの式（１）、（２）から音速Ｃを消去すると、流速Ｖに関する式（３）が得られる。逆に、流速Ｖを消去することで、音速Ｃに関する式（４）を得ることができる。これらの式（３）、（４）は超音波ビームの伝播時間Ｔｕ、Ｔｄを求めれば、流速Ｖ、音速Ｃを得ることができることを示している。
Ｖ＝Ｌ（Ｔｕ−Ｔｄ）／（２・Ｔｄ・Ｔｕ）・・・（３）
Ｃ＝（Ｌ／２）（１／Ｔｄ＋１／Ｔｕ）・・・（４） When the sound velocity C is eliminated from these equations (1) and (2), equation (3) relating to the flow velocity V is obtained. Conversely, by eliminating the flow velocity V, the equation (4) relating to the sound velocity C can be obtained. These equations (3) and (4) indicate that the flow velocity V and the sound velocity C can be obtained by obtaining the ultrasonic beam propagation times Tu and Td.
V = L (Tu−Td) / (2 · Td · Tu) (3)
C = (L / 2) (1 / Td + 1 / Tu) (4)

超音波流量計では、式（３）を用いて流速Ｖを求め、これに次式（５）のように、管路１の断面積Ｓを乗ずることにより流体の流量Ｆを算出できる。
Ｆ＝Ｖ・Ｓ・・・（５） In the ultrasonic flowmeter, the flow rate F of the fluid can be calculated by obtaining the flow velocity V using the equation (3) and multiplying this by the cross-sectional area S of the pipe line 1 as in the following equation (5).
F = V · S (5)

特開２０１０−２５６８０号公報JP 2010-25680 A 特開２００４−３０９４５０号公報JP 2004-309450 A

液体の濃度と音速は相関関係があり、超音波ビームによる反射時間等を用いて流体の濃度を測定することは、例えば特許文献２等で知られている。予め、液体の濃度と音速の関係をテーブルとして記憶しておくことで、液体内の超音波ビームの音速を測定し濃度に換算することができる。 There is a correlation between the concentration of the liquid and the speed of sound, and measuring the concentration of the fluid using the reflection time by an ultrasonic beam or the like is known from Patent Document 2, for example. By storing the relationship between the liquid concentration and the sound velocity in advance as a table, the sound velocity of the ultrasonic beam in the liquid can be measured and converted into a concentration.

しかし、音速は液体の温度により変動するので、濃度測定中に温度を計測し、得られた濃度を温度により補正する必要がある。また、従来の超音波ビームを利用した濃度計は、所定の容器等に液体を充填して測定するものであり、配管中を流れる流体を対象としたものは少ない。 However, since the speed of sound varies depending on the temperature of the liquid, it is necessary to measure the temperature during the concentration measurement and to correct the obtained concentration based on the temperature. Further, a conventional densitometer using an ultrasonic beam is to measure a predetermined container filled with a liquid, and few are intended for a fluid flowing in a pipe.

本発明の目的は、上述の課題を解決し、従来の超音波流量計の原理を利用して、温度センサを用いることなく、流体の濃度を精度良く測定可能な超音波式濃度計を提供することにある。 An object of the present invention is to provide an ultrasonic densitometer that can accurately measure the concentration of a fluid without using a temperature sensor by using the principle of a conventional ultrasonic flowmeter, solving the above-described problems. There is.

上記目的を達成するための本発明に係る超音波式濃度計は、流体が流れる管体に距離を隔てて一対の超音波送受信素子を配置し、これらの超音波送受信素子間で前記管体中の流体に対し超音波ビームをそれぞれ送信、受信し、前記超音波ビームの上流から下流へ、下流から上流への伝播時間をそれぞれ検出する伝播時間検出手段と、超音波ビームの受信波形の前半の強制振動部分と後半の自由振動部分のうち、前記後半の自由振動部分の受信パルスの周期を基に流体の温度を算出する温度算出手段と、前記伝播時間検出手段で得られた前記２つの伝播時間から流体の音速を算出する音速算出手段と、該音速算出手段により得られた音速から流体の濃度を算出する濃度算出手段と、前記音速又は前記濃度を前記温度算出手段で得られた温度により補正する温度補正手段とを有することを特徴とする。 In order to achieve the above object, an ultrasonic densitometer according to the present invention has a pair of ultrasonic transmission / reception elements arranged at a distance from a pipe through which a fluid flows, and the ultrasonic transmission / reception elements are disposed in the pipe between the ultrasonic transmission / reception elements. An ultrasonic beam is transmitted to and received from the fluid, and a propagation time detecting means for detecting the propagation time from the upstream to the downstream and from the downstream to the upstream of the ultrasonic beam, and the first half of the received waveform of the ultrasonic beam of forced oscillation portion and the free vibration portion of the second half, the temperature calculation means for calculating the temperature of the fluid based on the period of the received pulse of the free vibration portion of the second half, the propagation time detecting means obtained in the two propagation A sound speed calculating means for calculating the sound speed of the fluid from the time, a concentration calculating means for calculating the concentration of the fluid from the sound speed obtained by the sound speed calculating means, and the sound speed or the concentration to the temperature obtained by the temperature calculating means. Yo And having a correction to the temperature compensation means.

本発明に係る超音波式濃度計によれば、流体の温度補正がなされた濃度を求めることができる。 According to the ultrasonic densitometer according to the present invention, it is possible to obtain the concentration of the fluid subjected to temperature correction.

実施例の超音波式濃度計のブロック回路構成図である。It is a block circuit block diagram of the ultrasonic concentration meter of an Example. 超音波ビームの発信及び受信波形図である。It is a transmission and reception waveform diagram of an ultrasonic beam. ゼロクロス法による伝播時間の求め方の説明図である。It is explanatory drawing of how to obtain | require propagation time by the zero cross method. 強制振動部分から立ち上り点の時間ｔ０を算出する説明図である。It is explanatory drawing which calculates time t0 of a rising point from a forced vibration part. ゼロクロス法による時間と最初の立ち上がり点の時間の温度に対する流速の関係のグラフ図である。It is a graph of the relationship of the flow velocity with respect to the temperature of the time by the zero cross method and the time of the first rising point. 自由振動部分における温度と平均周期のグラフ図である。It is a graph of the temperature and average period in a free vibration part. 自由振動部分の平均周期を求める説明図である。It is explanatory drawing which calculates | requires the average period of a free vibration part. 水溶液の濃度と音速の関係のグラフ図である。It is a graph of the relationship between the density | concentration of aqueous solution and a sound speed. 超音波流量計の構成図である。It is a block diagram of an ultrasonic flowmeter.

本発明を図１〜図８に図示の実施例に基づいて詳細に説明する。
図１は実施例の超音波式濃度計のブロック回路構成図である。例えば、合成樹脂製の円管から成る管体１１に対して、上流及び下流の２個所の所定位置に、超音波送受信素子として超音波ビームを送信、受信するための圧電素子１２、１３が固定されている。圧電素子１２、１３は管体１１と一体に射出成型された合成樹脂製の取付ベース１４、１５に固定されている。 The present invention will be described in detail based on the embodiment shown in FIGS.
FIG. 1 is a block circuit diagram of an ultrasonic densitometer of the embodiment. For example, piezoelectric elements 12 and 13 for transmitting and receiving ultrasonic beams as ultrasonic transmission / reception elements are fixed at two predetermined positions upstream and downstream of a tubular body 11 made of a synthetic resin circular pipe. Has been. The piezoelectric elements 12 and 13 are fixed to synthetic resin mounting bases 14 and 15 which are integrally molded with the tube body 11.

圧電素子１２、１３には送受信切換スイッチ１６を介して、送信部１７、受信部１８がそれぞれ択一的に接続されている。送信部１７、受信部１８は制御演算部１９に接続され、更に制御演算部１９にはメモリ部２０、表示部２１が接続されている。制御演算部１９は例えばＣＰＵであり、送受信切換スイッチ１６、送信部１７、受信部１８、メモリ部２０、表示部２１を制御すると共に、内蔵のメモリに記憶したプログラムに従って所定の演算を行う。 A transmission unit 17 and a reception unit 18 are alternatively connected to the piezoelectric elements 12 and 13 via a transmission / reception selector switch 16. The transmission unit 17 and the reception unit 18 are connected to a control calculation unit 19, and a memory unit 20 and a display unit 21 are further connected to the control calculation unit 19. The control calculation unit 19 is, for example, a CPU, and controls the transmission / reception changeover switch 16, the transmission unit 17, the reception unit 18, the memory unit 20, and the display unit 21, and performs a predetermined calculation according to a program stored in a built-in memory.

測定に際しては、制御演算部１９の指令で送受信切換スイッチ１６により送信部１７に圧電素子１２を切換え、受信部１８を圧電素子１３に切換える。図２に示すように、送信部１７から圧電素子１２に駆動用のパルス電圧を加え、圧電素子１２から発生した超音波ビームを流体中に伝達する。超音波ビームは流体中を伝播し、圧電素子１３において受信波形Ｗが得られ、この受信波形Ｗは受信部１８、制御演算部１９を経てメモリ部２０に記憶される。制御演算部１９はメモリ部２０に記憶した受信波形Ｗから超音波ビームの伝播時間Ｔｄを検出する。 At the time of measurement, the piezoelectric element 12 is switched to the transmission unit 17 by the transmission / reception changeover switch 16 and the reception unit 18 is switched to the piezoelectric element 13 by the command of the control calculation unit 19. As shown in FIG. 2, a pulse voltage for driving is applied from the transmitter 17 to the piezoelectric element 12, and the ultrasonic beam generated from the piezoelectric element 12 is transmitted into the fluid. The ultrasonic beam propagates in the fluid, and a received waveform W is obtained in the piezoelectric element 13, and this received waveform W is stored in the memory unit 20 through the receiving unit 18 and the control calculation unit 19. The control calculation unit 19 detects the propagation time Td of the ultrasonic beam from the received waveform W stored in the memory unit 20.

次に、送受信切換スイッチ１６を切換えて、圧電素子１３から超音波ビームを送信し、圧電素子１２で得られた受信波形Ｗから同様にして伝播速度Ｔｕを検出する。本実施例においては、これらの伝播速度Ｔｄ、Ｔｕを基に、前述の式（４）により濃度と相関のある音速Ｃを求める。 Next, the transmission / reception selector switch 16 is switched to transmit an ultrasonic beam from the piezoelectric element 13, and the propagation velocity Tu is detected in the same manner from the received waveform W obtained by the piezoelectric element 12. In the present embodiment, based on these propagation velocities Td and Tu, the sound velocity C having a correlation with the density is obtained by the above-described equation (4).

本来、超音波ビームの伝播時間とは、図２に示すように正確には送信側の圧電素子にパルスを印加した時間から、受信側の圧電素子による超音波ビームの受信波形の最初の受信パルスが０Ｖから正の電圧に変わる立ち上がり点の時間ｔ０までのことである。しかし、この立ち上がり点はそれ以前の必要な負の波形データが得られないことから検出が困難であり、一般に近似的な方法としてゼロクロス法が用いられている。 Originally, the propagation time of the ultrasonic beam is, as shown in FIG. 2, precisely the first received pulse of the received waveform of the ultrasonic beam by the receiving piezoelectric element from the time when the pulse is applied to the transmitting piezoelectric element. Is the rising point time t0 when the voltage changes from 0V to a positive voltage. However, this rising point is difficult to detect because the necessary negative waveform data before that cannot be obtained, and the zero cross method is generally used as an approximate method.

ゼロクロス法とは受信波形Ｗの測定できる部分のうち、受信波形Ｗの電圧レベルが０Ｖとなる点であり、パルス印加時間から例えば特定の何番目かの受信パルスのゼロクロス点までの時間、或いは幾つか受信パルスのゼロクロス点の平均時間を求め、超音波ビームの伝播時間としている。 The zero-cross method is a point at which the voltage level of the received waveform W becomes 0 V among the measurable part of the received waveform W, and the time from the pulse application time to the zero-cross point of a certain number of received pulses, for example, Or the average time of the zero-cross point of the received pulse is obtained as the propagation time of the ultrasonic beam.

本実施例における音速Ｃの測定においては、制御演算部１９によってこのような従来のゼロクロス法によって伝播時間を求めることができる。例えば図３に示すように、１受信波形ごとにドット間隔５０ｎｓ（クロック周波数２０ＭＨｚ）で１００点の波形データを取り込む。各波形について取り込んだデータの中で、最も大きい電圧の点を１００ｍＶとし、最も小さい電圧の点を−１００ｍＶとして規格化し、０Ｖ近傍の４点（正の点２、負の点２）を最小二乗法で線形近似し、その直線と時間軸の交点を求めるべきゼロクロス点とする。 In the measurement of the sound speed C in the present embodiment, the propagation time can be obtained by the control arithmetic unit 19 by such a conventional zero cross method. For example, as shown in FIG. 3, 100 points of waveform data are captured at a dot interval of 50 ns (clock frequency 20 MHz) for each received waveform. Among the data acquired for each waveform, the highest voltage point is normalized to 100 mV, the lowest voltage point is normalized to -100 mV, and four points near 0 V (positive point 2, negative point 2) are minimum two. A linear approximation is performed by multiplication, and the intersection of the straight line and the time axis is set as a zero cross point to be obtained.

一定の流速で、１５、２０、２５、３０℃の水の超音波ビームの受信波形を各１６０波形ずつ、つまり圧電素子１２から圧電素子１３に伝播させた８０個の受信波形、圧電素子１３から圧電素子１２に伝播させた８０個の受信波形を使用した。このようなゼロクロス法から求めた伝播時間Ｔｄ、Ｔｕを８０波形分平均し、制御演算部１９によって式（３）から流速Ｖを求めると、温度の順に０．６４７、０．６５４、０．６３１、０．６２４（ｍ／ｓ）となった。 From the piezoelectric element 13, the received waveform of the ultrasonic beam of water at 15, 20, 25, and 30 ° C. at a constant flow rate is 160 waveforms each, that is, 80 received waveforms propagated from the piezoelectric element 12 to the piezoelectric element 13. 80 received waveforms propagated to the piezoelectric element 12 were used. When the propagation times Td and Tu obtained from the zero cross method are averaged for 80 waveforms, and the flow velocity V is obtained from the equation (3) by the control calculation unit 19, 0.647, 0.654, 0.631 in order of temperature. 0.624 (m / s).

ゼロクロス法以外にも伝播時間を検出するには相関法が知られているが、更に正確な伝播時間を得るためには、次に説明するように受信波形から最初の立ち上がりの時間ｔ０を推定して使用することが好ましい。 In addition to the zero cross method, the correlation method is known for detecting the propagation time. However, in order to obtain a more accurate propagation time, the first rise time t0 is estimated from the received waveform as described below. Are preferably used.

復元力のあるばねモデルとして運動方程式を解くと、得られた変位は圧電素子による超音波ビームの受信波形Ｗと考えられる。図２の受信波形Ｗのうち、前半の４周期は入力パルス由来の力による強制振動部分Ｗａで、後半は外力が働かない周波数の復元力による自由振動部分Ｗｂである。 When the equation of motion is solved as a spring model having a restoring force, the obtained displacement is considered to be the received waveform W of the ultrasonic beam by the piezoelectric element. In the received waveform W of FIG. 2, the first four periods are the forced vibration portions Wa due to the force derived from the input pulse, and the second half are the free vibration portions Wb due to the restoring force of the frequency at which no external force works.

受信波形Ｗの前半の強制振動部分Ｗａの周波数は、入力された超音波ビームの共振周波数に支配されているため温度依存性が少なく、超音波ビームの伝播時間の検出に適している。一方、５周期目以降は自由振動部分Ｗｂであり、その共振周波数は弾性スティフネスの影響を受けるため温度変化によって変化する。 Since the frequency of the forced vibration portion Wa in the first half of the received waveform W is governed by the resonance frequency of the input ultrasonic beam, it has little temperature dependence and is suitable for detecting the propagation time of the ultrasonic beam. On the other hand, the fifth and subsequent cycles are free vibration portions Wb, and the resonance frequency thereof is affected by the elastic stiffness, and therefore changes with temperature.

そこで本実施例においては、音速Ｃを求めるための伝播時間Ｔｄ、Ｔｕの検出は、温度依存性が少ない前半の強制振動部分Ｗａから求めることが好ましく、温度情報を後半の自由振動部分Ｗｂから求める。 Therefore, in the present embodiment, the detection of the propagation times Td and Tu for obtaining the sound velocity C is preferably obtained from the first-half forced vibration part Wa having low temperature dependence, and the temperature information is obtained from the second-half free vibration part Wb. .

図４に示すように、制御演算部１９によって強制振動部分Ｗａのゼロクロス点の位置と時間の例えば４つのプロット点に対し最小二乗法を用いて直線を引くと、その時間軸に対して交叉する切片は最初の立ち上がり点の時間ｔ０を示すことになる。このように、強制振動部分Ｗａから求めた最初の立ち上がり点の時間ｔ０を基に超音波ビームの伝播時間が得られる。 As shown in FIG. 4, when a straight line is drawn using the least square method for the position and time of the zero-crossing point of the forced vibration portion Wa and, for example, four plot points, the control operation unit 19 crosses the time axis. The intercept indicates the time t0 of the first rising point. As described above, the propagation time of the ultrasonic beam is obtained based on the time t0 of the first rising point obtained from the forced vibration portion Wa.

強制振動部分Ｗａからの時間ｔ０により、先のゼロクロス法と同じ条件で制御演算部１９によって伝播時間Ｔｄ、Ｔｕを求めて、式（３）から流速Ｖを算出すると、温度の順に０．６４７、０．６５０、０．６５０、０．６４９（ｍ／ｓ）となった。 Based on the time t0 from the forced vibration portion Wa, the control calculation unit 19 obtains the propagation times Td and Tu under the same conditions as in the previous zero cross method, and the flow velocity V is calculated from the equation (3). It became 0.650, 0.650, 0.649 (m / s).

図５はゼロクロス法と立ち上り点の時間ｔ０による流速の関係をグラフ図としたものである。従来のゼロクロス法による普遍分散は１．９０×１０^-4で、最初の立ち上がり点を算出して用いる場合には１．７８×１０^-6である。 FIG. 5 is a graph showing the relationship between the zero cross method and the flow velocity according to the rise time t0. The universal dispersion according to the conventional zero-cross method is 1.90 × 10 ⁻⁴ , and 1.78 × 10 ⁻⁶ when the first rising point is calculated and used.

この結果から、ゼロクロス法を用いるよりも、強制振動部分Ｗａにより最初の受信パルスの立ち上がり点を求めた伝播時間の検出は、温度に対する影響が少ないことが確認できた。 From this result, it was confirmed that the detection of the propagation time in which the rising point of the first received pulse was obtained by the forced vibration portion Wa had less influence on the temperature than using the zero cross method.

超音波ビームの受信波形Ｗの自由振動部分Ｗｂは、流体の温度変化の影響を受け、例えば温度が上昇すると共振周波数が下がるため、自由振動部分Ｗｂの周期が長くなる。制御演算部１９によってこの自由振動部分Ｗｂの周波数を算出し、その変化から流体の温度情報を得ることができる。 The free vibration portion Wb of the received waveform W of the ultrasonic beam is affected by the temperature change of the fluid. For example, when the temperature rises, the resonance frequency decreases, so the period of the free vibration portion Wb becomes longer. The frequency of the free vibration part Wb can be calculated by the control calculation unit 19, and the temperature information of the fluid can be obtained from the change.

メタノールを水で希釈して作製した濃度０、５、１０、１５、２０％の水溶液について、温度を１５、２０、２５、３０℃と変化させ、自由振動部分Ｗｂの平均周期を求めたところ、表１のデータが得られた。 For an aqueous solution having a concentration of 0, 5, 10, 15, 20% prepared by diluting methanol with water, the temperature was changed to 15, 20, 25, 30 ° C., and the average period of the free vibration part Wb was determined. The data in Table 1 was obtained.

表１自由振動部分の平均周期（ｎｓ）
０％５％１０％１５％２０％
１５℃ ４７２．９４７２．９４７２．９４７２．９４７３．０
２０℃ ４７３．６４７３．６４７３．６４７３．６４７３．５
２５℃ ４７４．２４７４．３４７４．３４７４．３４７４．２
３０℃ ４７４．８４７４．７４７４．７４７４．８４７４．８ Table 1 Average period of free vibration part (ns)
0% 5% 10% 15% 20%
15 ° C 472.9 472.9 472.9 472.9 473.0
20 ° C 473.6 473.6 473.6 473.6 473.5
25 ° C 474.2 474.3 474.3 474.3 474.2
30 ° C 474.8 474.7 474.7 474.8 474.8

表１は所定の濃度、温度の水溶液に関し、自由振動部分Ｗｂの１１番目〜１９番目までのゼロクロス点から求めた振動の平均周期を示している。これを図６に示すと、何れの濃度においても平均周期は温度に対しほぼ一定値であり、自由振動部分Ｗｂの平均周期は濃度によらず温度によって定まるパラメータであることが分かる。このように、超音波ビームの自由振動部分Ｗｂの平均周期は、メタノール水溶液濃度０〜２０％の間では、温度変化のみに依存することが実験により確認できた。従って、平均周期が得られれば図６から温度を求めることができる。 Table 1 shows the average period of vibration obtained from the eleventh to nineteenth zero cross points of the free vibration portion Wb for the aqueous solution having a predetermined concentration and temperature. FIG. 6 shows that the average period is almost constant with respect to the temperature at any concentration, and the average period of the free vibration portion Wb is a parameter determined by the temperature regardless of the concentration. Thus, it has been confirmed by experiments that the average period of the free vibration portion Wb of the ultrasonic beam depends only on the temperature change when the methanol aqueous solution concentration is 0 to 20%. Therefore, if the average period is obtained, the temperature can be obtained from FIG.

自由振動部分Ｗｂの平均周期を得るためには、制御演算部１９は自由振動部分Ｗｂのゼロクロス点を適当に２つ選択し、その差から求めればよい。しかし本実施例では、約２ＭＨｚの受信波形Ｗに対し５０ｎｓの間隔で波形を取り込んでいるため、単純に差を求めると分散が大きく、明確な温度依存性が得られない。 In order to obtain the average period of the free vibration portion Wb, the control calculation unit 19 may appropriately select two zero cross points of the free vibration portion Wb and obtain the difference from the two. However, in this embodiment, since the waveform is captured at an interval of 50 ns with respect to the received waveform W of about 2 MHz, if the difference is simply obtained, the dispersion is large and a clear temperature dependency cannot be obtained.

そこで、本実施例では図７に示すように、各受信パルスのゼロクロス点を番号順にプロットし、自由振動部分Ｗｂの平均周期を求めている。この方法はゼロクロス点まで時間をプロットしているので、その直線の傾きが用いたゼロクロス点に関する平均周期となっており、直線の傾きが大きいほど温度が高くなっている。 Therefore, in this embodiment, as shown in FIG. 7, the zero-cross points of the respective reception pulses are plotted in numerical order to obtain the average period of the free vibration portion Wb. Since this method plots the time to the zero cross point, the slope of the straight line is the average period for the zero cross point used, and the temperature increases as the slope of the straight line increases.

また、メタノールを水で希釈して作製した濃度０、５、１０、１５、２０％の水溶液について、温度を１５、２０、２５、３０℃と変化させ、各音速Ｃを求めたところ、表２のデータが得られた。 Further, regarding the aqueous solutions having concentrations of 0, 5, 10, 15, and 20% prepared by diluting methanol with water, the temperatures were changed to 15, 20, 25, and 30 ° C., and the respective sound speeds C were obtained. Data was obtained.

表２メタノール水溶液の音速（ｍ／ｓ）
０％５％１０％１５％２０％
１５℃ １５５５１５７３１５９４１６１４１６３１
２０℃ １５６６１５８２１６００１６１８１６３３
２５℃ １５７７１５９０１６０６１６２１１６３３
３０℃ １５８６１５９７１６１０１６２２１６３２ Table 2 Sound velocity of aqueous methanol solution (m / s)
0% 5% 10% 15% 20%
15 ° C 1555 1573 1594 1614 1631
20 ° C 1566 1582 1600 1618 1633
25 ° C 1577 1590 1606 1621 1633
30 ° C 1586 1597 1610 1622 1632

流体の濃度が変化すると音速Ｃが変化し、また温度が変化すると音速Ｃが変化し、温度が一定の条件であれば、音速Ｃと濃度は比例関係にあることが実験により確められた。この表２をグラフ化すると図８に示すようになり、予めテーブルとしてメモリ部２０に記憶しておけば、制御演算部１９は表１で得られた温度を基に、音速Ｃを濃度に換算することができる。 When the fluid concentration changes, the sound speed C changes, and when the temperature changes, the sound speed C changes. If the temperature is constant, it has been experimentally confirmed that the sound speed C and the density are in a proportional relationship. When this Table 2 is graphed, it becomes as shown in FIG. 8, and if it is stored in the memory unit 20 as a table in advance, the control calculation unit 19 converts the sound speed C into a concentration based on the temperature obtained in Table 1. can do.

このように、本実施例では超音波ビームの伝播速度から音速Ｃを求めることができ、先の算出した自由振動部分Ｗｂから得られた平均周期から求めた温度により温度補正を行って、制御演算部１９は水溶液の濃度を算出し、表示部２１に表示することができる。なお、演算の過程で音速に対し温度補正を行っても濃度に対し温度補正を行っても何れでもよい。 As described above, in this embodiment, the sound speed C can be obtained from the propagation speed of the ultrasonic beam, and the temperature is corrected by the temperature obtained from the average period obtained from the previously calculated free vibration portion Wb, and the control calculation is performed. The unit 19 can calculate the concentration of the aqueous solution and display it on the display unit 21. It should be noted that either the temperature correction for the sound velocity or the temperature correction for the density may be performed during the calculation process.

１１管体
１２、１３圧電素子
１６送受信切換スイッチ
１７送信部
１８受信部
１９制御演算部
２０メモリ部
２１表示部 DESCRIPTION OF SYMBOLS 11 Tube 12, 13 Piezoelectric element 16 Transmission / reception changeover switch 17 Transmission part 18 Reception part 19 Control operation part 20 Memory part 21 Display part

Claims

流体が流れる管体に距離を隔てて一対の超音波送受信素子を配置し、これらの超音波送受信素子間で前記管体中の流体に対し超音波ビームをそれぞれ送信、受信し、前記超音波ビームの上流から下流へ、下流から上流への伝播時間をそれぞれ検出する伝播時間検出手段と、超音波ビームの受信波形の前半の強制振動部分と後半の自由振動部分のうち、前記後半の自由振動部分の受信パルスの周期を基に流体の温度を算出する温度算出手段と、前記伝播時間検出手段で得られた前記２つの伝播時間から流体の音速を算出する音速算出手段と、該音速算出手段により得られた音速から流体の濃度を算出する濃度算出手段と、前記音速又は前記濃度を前記温度算出手段で得られた温度により補正する温度補正手段とを有することを特徴とする超音波式濃度計。 A pair of ultrasonic transmission / reception elements are arranged at a distance from a tubular body through which the fluid flows, and an ultrasonic beam is transmitted and received between the ultrasonic transmission / reception elements with respect to the fluid in the tubular body. free vibration portion of the second half of the forced oscillation portion and the free vibration portion of the second half of the first half of the received waveform from upstream to downstream, a propagation time detecting means for detecting respective travel times from the downstream to the upstream, the ultrasonic beam Temperature calculating means for calculating the temperature of the fluid based on the period of the received pulse, sound speed calculating means for calculating the sound speed of the fluid from the two propagation times obtained by the propagation time detecting means, and the sound speed calculating means Ultrasound, comprising: concentration calculating means for calculating the concentration of fluid from the obtained sound speed; and temperature correcting means for correcting the sound speed or the concentration with the temperature obtained by the temperature calculating means. Densitometer.

前記伝播時間検出手段は前記強制振動部分の波形から前記受信波形の最初の立ち上がり点の時間を算出して前記伝播時間を検出することを特徴とする請求項１に記載の超音波式濃度計。 2. The ultrasonic densitometer according to claim 1, wherein the propagation time detecting means detects the propagation time by calculating a time of an initial rising point of the received waveform from a waveform of the forced vibration portion.

前記伝播時間検出手段は前記受信波形のゼロクロス点の時間を基に前記伝播時間を検出することを特徴とする請求項１又は２に記載の超音波式濃度計。 The ultrasonic densitometer according to claim 1 or 2, wherein the propagation time detecting means detects the propagation time based on a time of a zero cross point of the received waveform.

前記温度算出手段は前記自由振動部分の複数のゼロクロス点の時間間隔から周期を算出することを特徴とする請求項１〜３の何れか１つの請求項に記載の超音波式濃度計。 The ultrasonic densitometer according to any one of claims 1 to 3, wherein the temperature calculation means calculates a period from time intervals of a plurality of zero cross points of the free vibration portion.