JP5092413B2 - Flow velocity or flow rate measuring device - Google Patents

Description

  The present invention relates to a flow velocity or flow rate measuring device that uses a vibrator or the like and measures a flow rate of gas or liquid using ultrasonic waves.

  Conventionally, as this type of flow rate measurement device, a vibrator is provided in a flow path in the flow direction, and the velocity of the fluid is calculated from the difference in ultrasonic propagation time (see, for example, Patent Document 1).

  FIG. 10 is a block diagram showing a configuration of a conventional ultrasonic flowmeter. In FIG. 10, a first vibrator 5 that transmits ultrasonic waves and a second vibrator 6 that receives ultrasonic waves are arranged in the flow direction in the middle of the fluid conduit 4. 7 is a transmission circuit to the first vibrator 5, and 8 is an amplification circuit for the signal received by the second vibrator 6. The amplified signal is compared with the reference signal by the comparison circuit 9, and is equal to or higher than the reference signal. When the signal is detected, the repeating unit 11 activates the trigger circuit 12 by the number of times set by the number setting circuit 10, and after delaying the signal by the delay unit 13, the ultrasonic signal is repeatedly transmitted.

When the repetition starts, the timer counter of the time measuring means 14 is started. When the number of repetitions set by the number setting circuit 10 is completed, the timer counter of the time measuring means 14 is stopped and the time is measured. Next, transmission / reception between the first vibrator 5 and the second vibrator 6 is switched by the switching means 15, and an ultrasonic signal is transmitted from the second vibrator 6 to the first vibrator 5, that is, from downstream to upstream. Is repeated as described above, and the time is counted. From the time difference, the flow rate calculation means 16 determines the flow rate value in consideration of the size of the pipe line and the flow state.
Japanese Patent Laid-Open No. 9-280917

  However, in the conventional flow rate measuring apparatus, an operation for switching between the transmitting-side vibrator and the receiving-side vibrator is entered, and a time lag occurs between the measurements, such as measurement-switching-measurement.

  The present invention solves the above-described problem. The ultrasonic wave reflected at least twice between the first time measuring means for measuring the time directly propagating between the vibrators and the vibrator so as not to cause a large time lag. The object is to calculate the flow rate based on the time measured with the second time measuring means for measuring the signal propagation time.

In order to solve the conventional problem, a flow rate measuring device according to the present invention includes a pair of transducers arranged in a flow path through which a fluid to be measured flows and transmits / receives ultrasonic waves, and the transducer output from the transducer on the transmission side. a first counting means for counting a first time until the ultrasonic waves are propagated to the vibrator recipient, at least 2 times for output said ultrasound said vibrator from said oscillator on the transmission side Second time measuring means for measuring a second time from reflection to propagation to the transducer on the receiving side, and flow rate calculating means for calculating a flow rate based on the first time and the second time with the door, the flow rate calculating unit, said a first time to calculate the flow rate of the fluid to be measured from the time obtained by subtracting the first time 2-fold from the second time, calculating the flow rate To do.

The flow rate measuring device of the present invention calculates a flow rate using a direct wave propagating between a pair of transducers arranged in a flow path and transmitting and receiving ultrasonic waves and a propagation time of an ultrasonic signal reflected at least twice.

  For this reason, there is no need to perform transmission / reception operations by switching the vibrator, so that measurement can be performed without causing a time lag.

According to a first aspect of the present invention, a pair of transducers arranged in a flow path through which a fluid to be measured flows and transmits / receives ultrasonic waves, and the ultrasonic waves output from the transducers on the transmission side are propagated to the transducers on the reception side And the ultrasonic wave output from the transducer on the transmission side propagates to the transducer on the reception side after reflecting between the transducers at least twice. comprises a second counting means for counting a second time to, and flow rate calculation means for calculating a flow rate based on the second time and the first time, the flow rate calculating means, said first And a flow rate measuring device that calculates the flow rate by calculating the flow velocity of the fluid to be measured from the time obtained by subtracting the first time that is twice the first time from the second time .

  And the time value of the 1st time measuring means which time-measures the time which propagated directly between the vibrators without reflecting, and the 2nd time-keeping means which time the propagation time of the ultrasonic signal reflected between the vibrator at least twice The flow rate is calculated based on the above. As a result, there is no need to perform transmission / reception operations by switching the vibrator, and therefore measurement can be performed without causing a time lag.

According to a second aspect of the present invention, there is provided a calculation correction unit that corrects a calculation coefficient of the flow rate calculation unit by using output signals of the first time measurement unit and the second time measurement unit when there is no flow rate. It is possible to adjust the error due to the reflected wave when there is no flow rate.

In the third aspect of the invention, the transmission-side vibrator is installed on the upstream side of the flow path, so that the propagation time can be shortened and power-saving measurement can be performed.

According to a fourth aspect of the present invention, the transmission-side vibrator is installed on the downstream side of the flow path, so that it is strongly excited by the transmission signal, so that adhesion of dust and the like around the transmission-side vibrator can be removed. Become.

  The seventh aspect of the invention has a configuration having a program for causing a computer to function as the control means in any one of the first to sixth aspects of the invention. It can be done easily, and it can flexibly cope with aging, etc., so the measurement accuracy can be improved more flexibly.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the present embodiment.

(Embodiment 1)
The flow velocity or flow rate measuring device of the present invention relating to Embodiment 1 will be described.

  FIG. 1 is a block diagram of a flow velocity or flow rate measuring apparatus showing the configuration of the present embodiment. In FIG. 1, an ultrasonic flowmeter of the present invention includes a flow path 31 through which a fluid to be measured flows, a first vibrator 32 and a second vibrator 33 that transmit and receive ultrasonic waves arranged in the flow path 31. The transmitter 34 for installing and driving the first vibrator 32, the receiver 35 for receiving the reception signal of the second vibrator 33 and determining the reception timing, and the first vibrator 32 by the transmitter 34 From the start of driving of the first ultrasonic wave, the first ultrasonic wave reaches the second vibrator 33 and the first time measuring means 36 for measuring the propagation time via the receiving means 35, and the direct ultrasonic wave the second vibrator 33. The second time measuring means 37 for measuring the propagation time via the receiving means 35 after reaching the second vibrator 33 after being reflected again by the first vibration 32 and the first time measuring means 36. And the pair of vibrators based on the time value of the second time measuring means 37 Flow rate calculated to the, then those having a flow rate calculating unit 38 for determining the flow rate.

  Further, a control unit 39 is provided to control at least one of the transmission unit 34, the reception unit 35, the first timing unit 36, the second timing unit 37, and the flow rate calculation unit 38.

  A normal flow rate or flow rate measurement operation will be described. Upon receiving the start signal from the control means 39, the transmission means 34 pulse-drives the first vibrator 32 for a certain time, and at the same time, the first time measuring means 36 and the second time measuring means 37 start measuring time. An ultrasonic wave is transmitted from the pulse-driven first vibrator 32. The ultrasonic wave transmitted from the first vibrator 32 propagates through the fluid to be measured and is received by the second vibrator 33. The reception output of the second vibrator 33 amplifies the signal by the receiving means 35 and then determines the reception of the ultrasonic wave at the signal level at a predetermined reception timing.

  When the reception of this ultrasonic wave is determined, the operation of the first time measuring unit 36 is stopped, and the flow velocity is obtained from the time information t according to (Equation 1).

Here, t is the measurement time obtained from the first time measuring means 36, L is the effective distance in the flow direction between the ultrasonic transducers, φ is the accuracy, c is the speed of sound, and v is the flow velocity of the fluid to be measured.
v = (1 / cosφ) * (L / t) −c (Equation 1)
The receiving means 35 is usually configured to compare the reference voltage and the received signal by a comparator.

  Further, the transmission and reception directions of the first vibrator 32 and the second vibrator 33 are switched, and the respective propagation times of the fluid under measurement from upstream to downstream and from downstream to upstream are measured. 3, the speed v can be obtained from Equation 4).

Here, the measurement time from the upstream to the downstream is t1, and the measurement time from the downstream to the upstream is t2. t1 = L / (c + v * cosφ) (Equation 2)
t2 = L / (c−v * cos φ) (Equation 3)
v = (L / 2 * cosφ) * ((1 / t1) − (1 / t2)) (Expression 4)
According to this method, the flow rate can be measured without being affected by the change in the sound speed, and thus it is widely used for measuring the flow velocity, the flow rate, the distance, and the like. When the flow velocity v is obtained, the flow rate can be derived by multiplying it by the cross-sectional area of the flow path 31.

  Although the flow velocity and flow rate can be obtained in this way, if an operation for switching the ultrasonic wave propagation direction from upstream to downstream and from downstream to upstream occurs, there will be a time lag between measurements such as measurement-switching-measurement. To do. In addition, the switching configuration becomes complicated, and adjustment to equalize the path length becomes difficult.

  Therefore, a method for obtaining the propagation time in which the propagation directions are paired without switching the transmission and reception directions will be described.

  Normal operation is as shown in the timing diagram of FIG. That is, measurement is started from the start signal at time t 0 by the control means 39 and the first vibrator 32 is driven via the transmission means 34. The ultrasonic signal generated there propagates through the flow path 31 and reaches the second transducer 33 at time t1, and when the reception means 35 detects the reception point, the signal is amplified and then received in advance. The reception of the ultrasonic wave is determined at the signal level. The first time measuring means 36 measures the propagation time of the propagation wave of the ultrasonic wave directly reaching the second vibrator 33 from the start of driving of the first vibrator 32 by the transmission means 34 via the receiving means 35. Thus, the propagation time from upstream to downstream can be obtained.

  When the ultrasonic wave reaches the second vibrator 33, it is reflected and propagates in the direction of the first vibrator 32. This is propagation from downstream to upstream. Similarly, the propagation signal reaching the first vibrator 32 is reflected there and propagates in the direction of the second vibrator 33. This is the same direction as the first direct propagation. FIG. 3 shows the process of propagation with the horizontal axis time and the vertical axis as the channel width. This will be described together with the timing chart of FIG. When there is no flow, the propagation time is the same regardless of the propagation direction. In FIG. 3, an ultrasonic signal is transmitted from the first transducer (transmission-side transducer) 32 at t0.

  The ultrasonic signal propagated through the flow path 31 reaches the second transducer (receiving transducer) 33 at time t1. The reflected ultrasonic signal returns to the first transducer 32 at time t2, is reflected there again, and reaches the second transducer 33 at time t3.

  At this time, since the output of the second vibrator 33 on the receiving side is connected to the receiving means 35, signals at time t1 and time t3 can be captured, but time t2 cannot be directly obtained.

  However, if the velocity of the fluid flowing through the flow path 31 from FIG. 3 does not change so fast that the ultrasonic wave propagation from t0 to t1 and the reflected wave propagation time in the same direction from t2 to t3 change, These two propagation times can be assumed to be equal as T1. By subtracting twice the amount of T1 from the total time T3, it is possible to obtain the propagation time T2 from the downstream to the upstream that is the opposite wave.

  The case where there is a flow will be described with reference to FIG. In FIG. 4, the direction of fluid flow is from left to right.

  Measurement is started from the start signal at time t 0 by the control means 39 and the first vibrator 32 is driven via the transmission means 34. The ultrasonic signal generated there propagates through the flow path 31 and reaches the second transducer 33 at time t1 ′. When the reception point is detected by the receiving means 35, the signal is amplified and then received in advance. The reception of the ultrasonic wave is determined based on the timing signal level. In this case, since the ultrasonic signal is along the flow of the fluid, it reaches the second vibrator earlier than time t1 in FIG. The first time measuring means 36 transmits a direct ultrasonic wave propagating directly from the start of driving of the first vibrator 32 by the transmitting means 34 to the second vibrator 33 and via the receiving means 35. The propagation time T1a is measured. Thus, the propagation time from upstream to downstream can be obtained.

Next, at time t2 ′, the propagation of the ultrasonic wave reaches the second vibrator 33, but this propagation time is longer than the time from t1 to t2 in FIG. This is the propagation time from downstream to upstream, but this time cannot be measured directly. Similarly, the ultrasonic wave reflected by the first vibrator 32 propagates in the direction of the second vibrator 32. This is in the same direction as the first direct propagation, and the entire propagation time T3a is measured by the second time measuring means 37 via the receiving means 35. By sending T1a obtained by the first time measuring means 36 and T3a obtained by the second time measuring means 37 to the flow rate calculating means 38, T2a can be obtained from Expression 5.
T2a = T3a-2 * T1a (Equation 5)
By setting T1a to t1, T2a to t2, and substituting Equation (4), the flow velocity can be obtained.

  When the flow velocity v is obtained, the flow rate can be derived by multiplying it by the cross-sectional area of the flow path 31.

  In the description of the present embodiment, the reflected wave is based on two-time reflection. However, the present invention is not limited to this, and the same relationship can be derived even when four or six times of reflected waves are used.

  As described above, the first time measuring means 36 for measuring the time directly propagating between the transducers 32 and 33 and the second time for measuring the propagation time of the ultrasonic signal reflected between the transducers 32 and 33 at least twice. By calculating the flow rate based on the time measured with the time measuring means 37, it is possible to obtain the relative propagation time without the need to perform transmission / reception operation by switching the vibrator, thereby making it possible to obtain the flow velocity. Become. As a result, measurement can be performed without causing a time lag such as switching between transmission and reception directions.

  Further, when determining the propagation arrival time, the zero cross point ta of a waveform exceeding a certain reference voltage Vref is often used as the arrival position of the received wave, for example, as shown in FIG. It is also possible to use an average of four points ta, tb, tc, and td instead of using one point ta. The ultrasonic waveform directly propagating from the first transducer 32 to the second transducer 33 is reflected twice to the second transducer 33 when the amplitude is A1 as shown in FIG. Since the arriving signal is attenuated, the amplitude is as small as A0 as shown in FIG. In this case, there is a possibility that the receiving point ta cannot be obtained by the receiving means 35. A method for avoiding this will be described with reference to FIG.

  When the control unit 39 detects that the first time measuring unit 36 has directly received the propagation wave, the control unit 39 increases the gain of the amplifying unit 43 in the preceding stage of the receiving unit 35 via the gain changing unit 42. For example, the amplitude A0 of the reflected wave in FIG. 6B is increased to A1. By doing so, the reflection that is otherwise attenuated and difficult to capture is amplified and the second time measuring means 37 can measure the propagation time by the reflected wave as a reception point. When the control means 39 detects that the reflected wave has arrived by the signal from the second time measuring means 37 or the flow rate calculating means 38, the gain changing means 42 returns the gain to the initial state in order to receive the next direct wave. The state of the amplification means 43 is adjusted via

  By having the gain changing means 42 in this way, it becomes possible to correctly capture a propagation signal having a small amplitude due to reflection.

  Further, even when the amplitude of the reflected wave is increased by the amplifying means 43 when obtaining the propagation arrival time of the reflected wave, it cannot be expected to be exactly the same as the direct wave waveform. Therefore, it is necessary to adjust the reference voltage Vref even with the same amplitude A1.

When the control means 39 detects that the first time measuring means 36 has directly received the propagation wave, the control means 39 increases the gain of the amplifying means 43 in the preceding stage of the receiving means 35 via the gain changing means 42 and sets the reference voltage changing means 44. Thus, the comparison voltage of the comparison means 45 in the subsequent stage of the amplification means 43 of the reception means 35 is adjusted. This adjustment can be performed by predicting the time for the reflected wave to arrive and automatically obtaining it by the control means 39 or by storing the value obtained in advance through experiments and replacing the value.

  By amplifying the reflection that would otherwise be attenuated and captured, and adjusting the reference voltage, the second time measuring means 37 can measure the propagation time by the reflected wave as a reception point even if the waveform shape changes. to enable. When the control means 39 detects the arrival of the reflected wave by the signal from the second time measuring means 37 or the flow rate calculating means 38, the reference voltage is changed so that the reference voltage is returned to the initial state in order to receive the next direct wave. The state of the comparison means 45 is adjusted via the means 44.

  As described above, by including the reference voltage changing unit 44 that changes the reference voltage of the receiving unit 35 in order to receive the reflected wave, it is possible to correctly capture the reception point of the propagation signal whose amplitude is reduced by reflection. Become.

  Further, the method of obtaining T2 from T1 and T3 in FIG. 3 assumes that the propagation times from reflected wave times t2 to t3 are equal from times t0 to t1. However, if the gain of the receiving means 35 is changed or the waveform of the reflected wave itself is deformed, this premise needs to be corrected.

  Therefore, when T2 obtained from the calculation is close to T1 (when the flow velocity becomes almost zero), the flow rate calculation means 38 sends a signal to the control means 39, and the control means 39 sets the flow rate when the flow velocity almost disappears. By correcting the coefficient L / 2 * cosφ of Equation 4 used in the calculation means 38, adjustment is performed so that calculation that reduces the error is possible. This adjustment can be realized automatically or by storing a value obtained in advance and adjusting the value while exchanging the value. It is also possible to adjust the flow rate to zero by closing the flow channel 31 from the outside. In that case, it is possible to further improve the accuracy by inputting that the flow rate is zero to the control means 39 by a communication means or the like.

  As described above, when there is no flow rate due to the output of the flow rate calculation means 38 or an external signal, the calculation coefficient of the flow rate calculation means 38 is corrected using the output signals of the first time measurement means 36 and the second time measurement means 37. By having the calculation correction means to perform, it becomes possible to adjust the error due to the direct wave and the reflected wave when there is no flow rate.

  Further, as shown in FIG. 1, it is possible to obtain the advantage of electric power by always installing the first vibrator 32 which is a transmission-side vibrator upstream. As shown in FIG. 4, the propagation time is shorter along the fluid flow direction.

  In FIG. 4, the total time T3a of the propagation time T1a along the flow being twice and the propagation time T2a facing the flow being one is measured. Here, T1a is shorter than T2a. If the transmission side is installed downstream, the propagation time opposite to the flow occurs twice, and the total time becomes longer than T3a. Since the second time measuring means 37 measures the propagation time, the shorter the operation time, the less power is required to operate this system.

  By installing the transmitting-side vibrator in the upstream side in this way, the propagation time can be shortened and power saving measurement can be performed.

Further, as shown in FIG. 1, it is possible to increase the reliability of the system by always installing the transmission-side transducer downstream. As shown in FIG. 1, the vibrator on the downstream side is opposed to the flow direction, so that, for example, if impurities are mixed in the fluid, there is a possibility that the vibrator will be in front of the vibrator. In such a case, if a passive movement is performed only to receive a signal, sensitivity is required, but the movement may be deteriorated due to impurity deposition. Therefore, by operating strongly by inputting a transmission signal, even if impurities or dust adhere to the front surface of the vibrator, reliability can be improved by removing it by the physical vibration operation of the vibrator. The upstream vibrator is structurally resistant to dust, so it seems that there is no problem even if the receiving operation is continued.

  By installing the transmission-side vibrator on the downstream side in this way, it is possible to remove adhesion of dust and the like around the transmission-side vibrator because the transmission signal is strongly excited.

  Further, as shown in FIG. 8, after receiving the direct wave and the reflected wave by the receiving means 35, it is possible to drive the first vibrator 32 again by the transmitting means 34 via the repeating means 40 and repeat the transmission and reception. is there. Then, after repeating a predetermined number of times, it is possible to perform a more accurate flow velocity calculation by obtaining the average of the obtained direct wave propagation time and reflected wave propagation time.

  Further, when the delay means 41 is used as shown in FIG. 9, transmission / reception can be repeated at a time when there is no influence even when reflection n times remains as reverberation.

(Embodiment 2)
The flow velocity or flow rate measuring apparatus of the present invention relating to the second embodiment will be described. The difference from the first embodiment is that control is performed to control at least one of the vibrators 32 and 33, the transmission means 34, the reception means 35, the first time measurement means 36, the second time measurement means 37, and the flow rate calculation means 38. The storage medium 46 having a program for causing a computer to function to ensure the operation of the means 39 is used.

  In order to perform the operation of the control means 39 shown in FIG. 4 in the first embodiment, the correction coefficient of Expression 4 is obtained in advance through experiments or the like, and correlations such as operation timing with respect to aging, temperature change, and system stability are correlated. The software is stored in the storage medium 46 as a program. Usually, it is convenient to use an electrically writable memory such as a microcomputer memory or a flash memory.

  As described above, when the operation of the control means 39 can be performed by a program, it is possible to easily set, change and adjust the measurement interval of the correction coefficient for the flow rate calculation, and to flexibly cope with aging. The accuracy of flow velocity or flow rate measurement can be improved more flexibly. In this embodiment, operations other than the control means 39 may be performed by a program using a microcomputer or the like.

  As a result, it has a configuration that has a program for causing the computer to function as a control means, making it easy to set and change the operation of the measurement method and flexibly respond to secular changes, etc. It can be performed.

  As described above, the flow velocity or flow rate measuring device according to the present invention does not need to perform transmission / reception operations by switching the vibrator, so that it is possible to measure the propagation time without causing a time lag and to accurately calculate the flow velocity and flow rate. Obtaining the results can be applied to uses such as household and industrial gas meters as gas flow meters and water meters as liquid flow meters.

Overall block diagram of the flow velocity or flow rate measuring device of the present invention (A) Timing diagram showing the operation of the measurement control means in the measuring device (b) Timing diagram showing the operation of the transmitted wave in the measuring device (c) Timing diagram showing the operation of the received wave and the reflected wave in the measuring device Timing chart showing propagation operation in the same measuring device Timing chart showing propagation operation in the same measuring device Timing chart showing received waves in the same measuring device (A) Timing diagram showing a received wave in the measuring device (b) Timing diagram showing a reflected wave in the measuring device Block diagram showing the periphery of the control means in the same measuring device Overall block diagram of a measuring apparatus showing another operation of the present invention Overall block diagram of a measuring apparatus showing another operation of the present invention Overall block diagram of a conventional flow measurement device

Explanation of symbols

31 Flow path 32 First vibrator 33 Second vibrator 34 Transmitting means 35 Receiving means 36 First timing means 37 Second timing means 38 Flow rate calculating means 39 Control means 42 Gain changing means 43 Amplifying means 44 Reference voltage Changing means 45 Comparison means 46 Storage medium

Claims (4)

A pair of transducers arranged in the flow path of the fluid to be measured and transmitting and receiving ultrasonic waves;
First time measuring means for measuring a first time until the ultrasonic wave output from the transmitting-side vibrator propagates to the receiving-side vibrator;
Second time measuring means for measuring a second time from when the ultrasonic wave output from the transmitting-side transducer is reflected at least twice between the transducers to propagate to the receiving-side transducer; ,
Flow rate calculating means for calculating a flow rate based on the first time and the second time,
The flow rate calculating means calculates the flow rate of the fluid to be measured from the first time and a third time obtained by subtracting the first time that is twice the second time. Flow measurement device. 2. The flow rate measuring apparatus according to claim 1, further comprising a calculation correction unit that corrects a calculation coefficient of the flow rate calculation unit by using output signals of the first time measurement unit and the second time measurement unit when there is no flow rate. The flow rate measuring device according to claim 1, wherein the transducer on the transmission side is installed upstream of the flow path. The flow rate measuring device according to claim 1, wherein the transducer on the transmission side is installed on the downstream side of the flow path.

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