JP2006162458A - Ultrasonic-type flow measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein a conventional ultrasonic flowmeter requires a reception waveform having a steep rising edge, and it is necessary to increase the number of measurements, in order to reduce variations in measurements. <P>SOLUTION: An ultrasonic type flow measuring apparatus is provided, which uses a first ultrasonic sensor 2 and a second ultrasonic sensor 3, operating at a period TS longer than a time difference ΔT (ΔT=T1-T2) with the maximum flow rate state; and a transmission means 4 giving a signal having the period TS, thereby carrying out exact measurements, regardless of the reception waveforms and increasing the number of measurement data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic flow measuring device that measures the flow velocity and / or flow rate of a fluid using ultrasonic waves.

  A conventional ultrasonic flow measuring device, more specifically, an ultrasonic flow meter is described in Patent Document 1.

  FIG. 8 is shown as one embodiment of this patent document 1, and the first vibrator 52 for transmitting ultrasonic waves and the second vibrator 53 for receiving are obliquely arranged in the flow direction in the flow path 51. It arrange | positions so that it may oppose.

  54 is a transmission circuit for the first vibrator 52, 55 is an amplification circuit for the signal received by the second vibrator 53, and the amplified signal is compared with the reference signal by the comparison circuit 56, and from the transmission to the reception. The time, so-called ultrasonic propagation time, is obtained by time measuring means 57 such as a timer counter.

  In accordance with the ultrasonic propagation time, the flow rate calculation unit 58 obtains the flow rate value in consideration of the size of the flow path 51 and the flow state, and the measurement interval changing unit 59 determines whether the flow rate calculation unit 58 The timing of signal transmission to the trigger means 60 is adjusted.

  Next, the operation will be described. A burst signal is transmitted from the trigger means 59 via the transmission circuit 54. As a result, the ultrasonic signal transmitted by the first vibrator 52 is transmitted through the flow and received by the second vibrator 53. . The received signal is processed by the amplifier circuit 55 and the comparison circuit 56, and the time from transmission to reception is measured by the time measuring means 57.

Now, assuming that the speed of sound in a static fluid is c and the speed of fluid flow is v, the propagation speed of ultrasonic waves in the forward direction of the flow is (c + v). When the distance between the transducers 52 and 53 is L, and the angle between the ultrasonic transmission axis and the central axis of the flow path 51 is φ, the time T that the ultrasonic wave reaches is:
T = L / (c + vcosφ) (1)
From the equation (1), v = (L / Tc) / cosφ (2)
If L and φ are known, the flow velocity v can be obtained by measuring T. If the passage area in the channel 51 is S and the correction count is K, the flow rate Q is
Q = KSv (3)
It becomes.

  FIG. 9 is introduced as another embodiment of the above-mentioned Patent Document 1. The transmission and reception are repeated by the repetition means 62 by the number of times set by the repetition setting means 61, and switching between oscillation and reception is further switched by the switching means 63. After that, repeat in the same way.

  That is, an ultrasonic wave is generated from the first vibrator 52 by the oscillation circuit 54, and this ultrasonic wave is received by the second vibrator 53 and reaches the comparison circuit 56 via the amplifier circuit 55. To trigger the transmission circuit 54.

  This repetition is performed the number of times set by the repetition setting means 61. When the set number of times is reached, the time required for the repetition is measured by the time measuring means 57. Thereafter, transmission and reception of the first vibrator 52 and the second vibrator 53 are reversely connected by the switching means 63, and this time, an ultrasonic wave is transmitted from the second vibrator 53 to the first vibrator 52, and Similarly, the arrival time is obtained, and this difference is input to the flow rate calculation means 58 to calculate the flow rate value.

Assuming that the speed of sound in a static fluid is c and the speed of fluid flow is v, the propagation speed of ultrasonic waves in the forward direction of the flow is (c + v), and the propagation speed of the reverse direction is (cv). When the distance between the transducers 52 and 53 is L, the angle between the ultrasonic transmission axis and the central axis of the pipe is φ, and the number of repetitions is n, the repetition times T1 and T2 in the forward direction and the reverse direction are respectively ,
T1 = n × L / (c + v cos φ) (4)
T2 = n × L / (c−v cos φ) (5)
From these equations (4) and (5), v = n × L / 2 cos φ × (1 / T1-1 / T2) (6)
If L and φ are known, the flow velocity v can be obtained by measuring T1 and T2.

  However, the difference between T1 and T2 is very small when the flow rate is small and the number of repetitions is small, and it is difficult to measure accurately. Therefore, the number of measurements is set large so that the error is relatively small.

  On the contrary, since the difference between T1 and T2 increases as the flow rate increases, measurement becomes easy, and in this case, the number of repeated settings is reduced to increase the sampling interval, thereby reducing the error. That is, the number of repetition setting means 61 is changed by the flow rate calculation means 58.

  Another Patent Document 2 discloses a measurement method in which ultrasonic wave propagation time is measured with high precision using ultrasonic waves in a short time and with low power consumption.

  As shown in FIG. 10, this is a transducer 65 that transmits an ultrasonic signal to the flow path wall 64 and receives the reflected wave, and a comparison means that compares the AC received signal of the transducer 65 with a threshold over a plurality of periods. 66, time measuring means 67 for measuring a plurality of propagation times for each detection by the comparison means 66 from transmission of the vibrator 65, and time calculating means 68 for calculating the propagation time from the average value of the time measured values of the time measuring means 67. It is provided.

  Reference numeral 69 denotes an amplifier circuit similar to that described above, a 70 switching circuit, and 71 a transmission circuit that operates in response to a signal from the start means 72.

  As a result, a measurement value obtained by comparing with the comparison means 66 many times can be obtained by one ultrasonic transmission / reception, and by obtaining the average value, a highly accurate measurement value of the propagation time can be obtained in a short time. Measurement can be performed with power consumption.

  Those described in Patent Documents 1 and 2 both use two vibrators to switch between transmission and reception, determine the flow velocity from the propagation time of the ultrasonic wave determined from each received waveform, This is a calculation method.

  Since the received waveform of the transducer has multiple periods, it is necessary to determine which period of the received waveform this time is to be obtained and to be able to obtain the propagation time for calculation in that period to ensure measurement accuracy It is necessary for that.

  If the propagation time is detected at a period other than the period determined due to a change in the received waveform due to fluid flow or noise, there is a problem that a large measurement error occurs.

  Furthermore, Patent Document 3 describes an ultrasonic transducer used for an ultrasonic flowmeter and a method for manufacturing the same. This relates to an acoustic matching layer for an ultrasonic transmitter / receiver that has a sufficiently small acoustic impedance and can be matched to a gas, which is an ultrasonic radiation medium, and can perform highly sensitive ultrasonic transmission / reception and can improve the rise response of the signal. Therefore, the configuration is as shown in FIG.

  The figure shows an ultrasonic wave transmission / reception constructed using an acoustic matching member 75 in which a first acoustic matching layer 73 having a low density and a slow sound speed and a second acoustic matching layer 74 having a higher density and a higher speed of sound are laminated. An effect can be obtained by a configuration in which a first acoustic matching layer 73 that shows a waver and is acoustic impedance matched with an ultrasonic radiation medium is arranged on the radiation medium side.

  In FIG. 11, the conductive case 76 in which the acoustic matching member 75 is fixed to the outer wall of the top surface by means such as adhesion is closed at the lower open portion by the terminal plate 77, and the piezoelectric vibrator 78 is formed on the inner wall of the top surface. Is fixed by means such as adhesion.

  One electrode of the piezoelectric vibrator 78 is connected to one terminal 79 via the case 76 and the terminal plate 77, and the other electrode is connected to the other terminal 81 attached to the terminal plate 77 via the electric insulating material 80. It is.

  With this configuration, the acoustic impedance is sufficiently small to match the gas that is the ultrasonic radiation medium, and high-sensitivity ultrasonic transmission / reception can be achieved. It is obtained.

  FIG. 12 shows the difference in the received output waveform of the ultrasonic wave due to the difference in the acoustic matching layer structure of the ultrasonic transducer of Patent Document 3, and FIGS. 12A and 12B show that the acoustic matching layer is a single layer. FIG. 6C shows an ultrasonic transducer that uses an acoustic matching member 75 having a two-layer structure of a first acoustic matching layer 73 and a second acoustic matching layer 74.

  As shown in FIG. 12b, the amplitude maximum width (peak-to-peak voltage) of the received output voltage is reduced by using a low-density dry gel as the acoustic matching layer, and the generally used glass balloon of FIG. Compared to the case where a cured acoustic matching layer (glass epoxy) is used, the peak-to-peak voltage is increased and the sensitivity is improved, but the rise of the received signal is slow.

  Furthermore, since the difference in output value between each wavefront of the 500 kHz ultrasonic signal at the rising edge and the wavefronts before and after the wavefront is small, the permissible width of the propagation time detection based on the arrival detection level is small, and error detection is likely to occur and detection is possible. It is described that it becomes difficult.

  Therefore, an ultrasonic transducer using silica dry gel as the acoustic matching layer has high sensitivity, but it is necessary to improve the rising characteristics. As shown in FIG. 12c, the silica dry gel and silicon oxide are fired. It is stated that the acoustic matching member tp made of a porous silica material produced in this manner has a large peak-to-peak voltage and a high sensitivity, and a good rise characteristic can be obtained.

The reason for this will be described with reference to FIG. 13 showing the vibration displacement frequency characteristics of the ultrasonic transducer. The figure a is a characteristic diagram when a single acoustic matching layer (glass epoxy) is used, b is a characteristic chart when a single acoustic matching layer (silica dry gel) is used, and c is a two-layer acoustic matching layer (silica). (Dry gel, porous silica) is a characteristic diagram. In FIG. A and FIG. B, the resonance has two poles, the frequency of the pole is about 480 kilohertz, and the difference Δf is about 120 kilohertz. Kilohertz. Thus, even if there is one or more resonance poles, if the frequency difference is small, the rising of the received waveform becomes gentle. In such a case, there is a problem that error detection is likely to occur.
JP-A-8-122117 (FIGS. 1 and 7) Japanese Patent Laid-Open No. 10-30947 (FIG. 1) JP 2002-018047 A (FIGS. 3 and 7)

  However, two ultrasonic sensors (represented as ultrasonic transducers or vibrators in the patent document of “Prior Art”) are alternately switched to transmission and reception, and each ultrasonic wave propagates. The conventional ultrasonic flowmeter that calculates the flow rate from the difference between these times, calculates the flow velocity from the difference, and further considers the cross-sectional area of the pipeline (also referred to as the flow path) that passes through the fluid. It has a big impact. For this reason, there is a problem that the reception waveform of the ultrasonic sensor is required to have a sharp rise.

  This point will be described in detail with reference to the drawings. Now, the measurement system is arranged in the flow path 82 as shown in FIG. 14 so that the first and second ultrasonic sensors 83 and 84 are diagonally opposed to each other, and is transmitted to the first ultrasonic sensor 83 by the switching circuit 85. The reception circuit 87 is connected to the circuit 86 and the second ultrasonic sensor 84 to measure the propagation time T1 of the ultrasonic wave in the gas, and then the transmission circuit 86 to the first ultrasonic sensor 83 by the switching circuit 85, A receiving circuit 87 is connected to the second ultrasonic sensor 84 to measure the propagation time T2 of the ultrasonic wave in the gas, and the flow velocity is obtained from the time difference between the two.

  FIG. 15 is a timing chart showing the transmission signal to the ultrasonic sensor, the received signal and the clock operation for measuring the time. (A-1), (a-2), and (a-3) are the cases where the first acoustic wave sensor 83 is on the transmitting side and the second ultrasonic sensor 84 is on the receiving side, and FIG. ), (B-2), and (b-3) are cases where the first ultrasonic sensor 83 is on the receiving side and the second ultrasonic sensor 84 is on the transmitting side.

  Since there is a fluid flow in the direction shown in FIG. 14, the ultrasonic wave propagation time T1 is shorter than T2. The detection of the received waveform will be described in detail with reference to FIG. This figure shows the received waveform, and there is a threshold value that is set to be approximately halfway between the peak values of the second and third waves of the received waveform, and there is a signal that exceeds this threshold value. Therefore, it is regarded as a received signal. The threshold value can be set, for example, between the reference value and the first wave, or between the second wave and the third wave. However, since the threshold value is low, there is a probability that noise superimposed on the reference value is erroneously determined as a received wave. It will increase, which is not desirable.

  When a waveform exceeding the threshold value is received, it is determined as a received waveform, and a point P1 at which the received waveform becomes a reference value is set as a detection point. The ultrasonic wave propagation time is measured by counting the clock from the transmission signal to the detection point. Since the actual reception point is PT, the time from PT to the third wave is treated as a fixed value, and the ultrasonic propagation time is obtained by subtracting this fixed value from the time to detection point P1.

  In such a detection method, when the rising edge has a gentle waveform as shown in FIG. 12a, the difference between the second wave and the third wave can be obtained even if the threshold is set between the second wave and the third wave. The following problems arise due to the small number. When the ultrasonic wave propagates and hits the wall surface that constitutes the flow path, the received waveform becomes the synthetic wave of the ultrasonic wave that enters through various paths, so the state of the synthetic wave may change depending on the gas flow velocity. . If there is such a change in waveform, the second wave and the third wave cannot be distinguished with the set threshold value. For this reason, the fourth wave is erroneously detected as the third wave. On the other hand, the uniformity of the gas flow in the channel tends to be obtained as the channel is flatter.

  For this reason, since many flow paths are formed flat, reflection of ultrasonic waves on the wall surface cannot be avoided. Even if the flow path is not flat and there is no reflection, if there is noise superimposition, it is easy to erroneously detect that the difference between the second wave and the third wave is small.

  Returning to FIG. 15, the measuring method by sing-around will be described. When the first transmission signal is given to the first ultrasonic sensor 83 in FIG. 11A-1, the second ultrasonic wave is transmitted after the ultrasonic propagation time T1 as shown in FIG. Sensor 84 receives. A point (detection point) that intersects the reference value immediately after detection of reception is detected using a threshold value set between the second wave and the third wave of the received wave.

After the delay time TD, which is a known time determined from the detection point, the second transmission signal is given to the first ultrasonic sensor 83 again. Such an operation is repeated n times. This is called that the number of times of single-around is n times. Counting the number of clocks N _C contained until detection point after n times from the first transmission. If one period of the clock is T (seconds) and the time from the actual reception point PT to the third wave is treated as a fixed value TH, the total measurement time is as shown in Equation (7).

N _C · T = T ₁ + T ₂ ... + T _n + n · T _H + (n−1) · T _D (7)
Accordingly, the average ultrasonic wave propagation time _TAVG is expressed by the following equation.

T _AVG = (T ₁ + T ₂ ... + T _n + n · T _H ) / n
_{= (N C · T-n} · T H - (n-1) · T D) / n
_{= N C · T / n-} T H - (n-1) · T D / n (8)
T / n in the first term on the right side of Equation (8) is that the counter period is divided by the number of times of sing-around n, so the counter of period T is apparently the period T / n, so the time resolution is fine. It has become. In this way, a measuring technique that uses a counter with a period T to set the time resolution to T / n is single-around.

  As described above, the sing-around measurement has an effect of increasing the time resolution, but is considered to have the following effect. Even if noise is superimposed on the first received wave and the detection point is judged to deviate from the true detection point, if the second, third, and subsequent detection points can be accurately detected, the first error is averaged. The effect is reduced by making it. That is, sing-around also has an averaging effect.

  Such a measurement by sing-around requires that the first wave, the second wave, the third wave,.

  Patent Document 2 describes a method for increasing averaging, but even with this method, it is required to accurately determine the first wave, the second wave, the third wave, etc. of the received wave, For this purpose, it is required that the received waveform of the ultrasonic sensor is easy to identify the first wave, the second wave, the third wave, etc., and the structure of the ultrasonic sensor has a two-layer structure, etc. There is a problem that it tends to be complicated.

  In order to solve the above-described conventional problems, an ultrasonic flowmeter of the present invention includes a flow path through which a fluid flows, at least a pair of ultrasonic sensors disposed in the flow path, and a transmission that provides a drive signal to the ultrasonic sensor. Means, a receiving means for receiving a signal from the ultrasonic sensor, and a timing means, the ultrasonic wave transmitted from the first ultrasonic sensor is received by the second ultrasonic sensor, and the propagation required for it is received. The time T1 is measured by the time measuring means, the ultrasonic wave transmitted from the second ultrasonic sensor is received by the first ultrasonic sensor, and the propagation time T2 required for the time T1 is measured by the time measuring means. The transmission means generates a signal having a period TS larger than the time difference ΔT (ΔT = T1-T2) at the maximum flow rate.

  As a result, it is not necessary to clearly determine the first wave, the second wave, the third wave,... In the received waveform consisting of a plurality of periods, and to obtain the propagation times T1 and T2 in each case, thereby simplifying the receiving means. In addition, the ultrasonic sensor structure can be simplified.

  The ultrasonic flowmeter of the present invention has the effect that accurate measurement can be performed even if the received waveform of ultrasonic waves has a steep rising characteristic or does not have a steep rising characteristic. There is.

  In a first aspect of the present invention, a flow path through which a fluid passes, at least a pair of ultrasonic sensors arranged in the flow path, transmission means for supplying a drive signal to the ultrasonic sensor, and a signal from the ultrasonic sensor are received. Receiving means and timing means, receiving the ultrasonic wave transmitted from the first ultrasonic sensor by the second ultrasonic sensor, measuring the propagation time T1 required for the ultrasonic wave by the timing means, The ultrasonic wave transmitted from the ultrasonic sensor 2 is received by the first ultrasonic sensor, the propagation time T2 required for the ultrasonic wave is measured by the time measuring means, and the transmission means measures the time difference ΔT (ΔT = By generating a signal having a period TS larger than (T1-T2), the first wave, the second wave, the third wave, etc. are clearly detected even for a reception signal having a plurality of periods. Thus, there is no need to obtain propagation times T1 and T2. , There is an effect that the ultrasonic reception waveform can be those having a steep rise characteristic, also a suitable probability be those that do not have a steep rise characteristic measurement.

  According to a second aspect of the present invention, there is provided an ultrasonic sensor that transmits and receives an ultrasonic signal, a comparison unit that compares an AC reception signal of the ultrasonic sensor with a reference value over a plurality of periods, and a plurality of propagations for each detection by the comparison unit. By providing time measuring means for measuring time and calculating means for calculating data of the time measuring means, the first wave, the second wave, the third wave,... Are clearly detected in the received waveform having a plurality of periods. Therefore, since it is not necessary to obtain the propagation time in each case, the measurement averaging effect can be improved by using a simple receiving means or an ultrasonic sensor having a simple structure.

  According to a third aspect of the present invention, there is provided a detection means for comparing the detection data of the comparison means for comparing the AC reception signals from the first and second ultrasonic sensors, whose transmission and reception are alternately switched, with a reference value over a plurality of periods. The time difference ΔT is obtained from each cycle. As a result, the detection point of the reception signal at the first ultrasonic sensor is a reception signal having a plurality of periods of the first wave, the second wave, the third wave,..., For example, the first wave, the second wave, etc. For example, when the detection points of the received signal at the second ultrasonic sensor are the second wave, the third wave, and the fourth wave at the wave 3rd and the 3rd wave, the first ultrasonic wave By removing the first wave at the sensor and the fourth wave at the second ultrasonic sensor, the time difference can be obtained between the corresponding waves.

  The fourth invention has a plurality of main resonance frequencies, but those resonance frequencies are close to each other, or by using an ultrasonic sensor having only one main resonance frequency, the sound constituting the ultrasonic sensor is used. When a matching layer having a low acoustic impedance that can improve acoustic matching with gas is used, the structure can be a simple structure of a single layer.

  According to a fifth aspect of the present invention, the ultrasonic wave propagating in the flow path hits the wall surface constituting the flow path and forms a complex synthetic wave, thereby improving the uniformity of the gas flow in the flow path. A flat flow path can be used, and in this case, the reception waveforms of the ultrasonic sensor A and the ultrasonic sensor B have different shapes, but the first wave, the second wave of the ultrasonic sensor A, It is possible to accurately detect the third wave, and the first wave, the second wave, the third wave,... Of the ultrasonic sensor B, and obtain a time difference between the corresponding waves.

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

  FIG. 1 shows the structure of an ultrasonic flowmeter according to the first embodiment of the present invention, in which a first ultrasonic sensor 2 and a second ultrasonic sensor 3 are diagonally opposed to a flow path 1 through which a gas flows. It is arranged as it is.

  A transmission signal is sent from the transmission means 4 to the first and second ultrasonic sensors 2 and 3. Further, the reception signal of the ultrasonic sensor is transmitted to the receiving means 5. Transmission and reception are selected by the switching means 7. If the first ultrasonic sensor 2 is selected to connect to the transmission means 4, the second ultrasonic sensor 3 is selected to connect to the reception means 5.

  Now, as shown in the figure, when the flow of fluid is from left to right, the ultrasonic wave transmitted by the first ultrasonic sensor 2 reaches the second ultrasonic sensor 3 after the propagation time T1. On the contrary, the ultrasonic wave transmitted by the second ultrasonic sensor 3 reaches the first ultrasonic sensor 2 after the propagation time T2, but T1 <T2 from the fluid flow direction. These times T1 and T2 are measured by the time measuring means 6. The calculating means 8 obtains the flow velocity and / or flow rate based on the data from the time measuring means 6.

  FIG. 2 is a waveform diagram showing waveforms of a transmission signal and a reception signal of the ultrasonic sensor. The first ultrasonic sensor in the case where the first ultrasonic sensor 2 transmits and the second ultrasonic sensor 3 receives. The transmission signal to 2 is represented by (a-1) in the figure, and the reception signal of the second ultrasonic sensor 3 is represented by (a-2) in the figure.

  On the other hand, the transmission signal to the second ultrasonic sensor 3 when the second ultrasonic sensor 3 transmits and the first ultrasonic sensor 2 receives is represented by (b-1) in FIG. The reception signal of the ultrasonic sensor 2 is shown in FIG.

  The transmission signal waveform is three rectangular waves with a period TS, and the reception waveform is a sine wave with multiple periods due to the characteristics of the ultrasonic sensor. The period is almost the same as TS, but the piezoelectric transducer that constitutes the ultrasonic sensor The characteristics may vary slightly. The period TS is set to be larger than the time difference ΔT (ΔT = T2−T1) of the propagation time of the ultrasonic wave.

FIG. 3 shows the relationship between the maximum flow rate handled by the ultrasonic flowmeter (maximum flow rate to be measured by the ultrasonic flowmeter) and the time difference ΔT.
1. Channel cross-sectional area S 1.2 × 10-3 square meters Distance L between ultrasonic sensor A and ultrasonic sensor B
Approximately 6.22 x 10-2 meters 3. Angle Φ 40 degrees between ultrasonic sensor and flow path This is a characteristic for the case where the sound velocity of gas is 450 meters per second.

A value larger than ΔT is selected for the period TS of the transmission signal. For example, when an ultrasonic flowmeter having a maximum flow rate of 1 cubic meter per hour is considered, the time difference ΔT is about 1 × 10 ⁻⁷ seconds, and therefore the period TS is set to a larger value of 2 × 10 ⁻⁶ seconds (500 kHz). ) Is selected.

  FIG. 4 is a waveform diagram showing the transmission signal of the ultrasonic sensor, the waveform of the reception signal, and the clock for counting the propagation time of the ultrasonic wave in this ultrasonic flow meter. A transmission signal to the first ultrasonic sensor 2 in the case of transmission and reception by the second ultrasonic sensor 3 is represented by (a-1) in the figure, and a reception signal of the second ultrasonic sensor 3 is represented in the figure. It is represented by (a-2) and the clock is represented by (a-3). On the other hand, the transmission signal to the second ultrasonic sensor 3 when the second ultrasonic sensor 3 transmits and the first ultrasonic sensor 2 receives is represented by (b-1) in FIG. The reception signal of the ultrasonic sensor 2 is represented by (b-2) in the figure, and the clock is represented by (b-3) in the figure.

  The receiving means sets a threshold for the received waveform of the ultrasonic sensor, determines reception when a received waveform exceeding the threshold is detected, and then detects a point where the waveform crosses the reference value. In FIG. 9A-2, since the third wave exceeds the threshold value, detection points are points where the subsequent waveforms intersect with the reference value, TA5, TA6, TA7, TA8, TA9, TA10, and TA11.

  The waveform of (b-2) in the figure is different in peak value from the waveform of (a-2) in the same figure. Since the ultrasonic wave propagating through the flow path 1 has a certain extent, there is an ultrasonic wave reflected on the wall, and a synthesized wave thereof becomes a received waveform. When there is a gas flow, the state of the individual waves to be synthesized changes, so that there may be a difference between the waveform in FIG. 2B-2 and the waveform in FIG.

  For this reason, even if the threshold value is set to the same value, in the case of (b-2) in the figure, reception is determined by the fourth wave, and detection points are TB7, TB8, TB9, TB10, TB11, TB12, TB13. It becomes. Of these detection points, if only the detection points that intersect the reference value at the fall of the received waveform are selected, TA5, TA7, TA9, TA11, and TB7, TB9, TB11, TB13 are obtained.

  FIG. 5 is a table showing the obtained times for these detection points. The time measuring means 6 needs to obtain these times, and the computing means 7 needs to obtain the flow velocity from these times by the equation (6). In order to determine which detection point time should be substituted for T1 and T2 in the same equation, the difference in time between each of TA5, TA7, TA9, and TA11 and each of TB7, TB9, TB11, and TB13 is obtained. FIG. 6 shows these time differences. Since the figure is obtained by subtracting TBs 7, 9, 11, and 13 from TAs 5, 7, 9, and 11, data having a positive value is meaningless data.

Further, (both transmitted and received signals) period TS signals since Elect 2 × ^{10 -6} seconds, -2 × less than ^{10 -6} seconds value of the drawing (for example, -2.11E −6 = −2.11 × 10 ⁻⁶ ) is meaningless data.

  The remaining data is underlined in the figure, and these combinations are TA7 and TB7, TA9 and TB9, TA11 and TB11. Since these data are combinations of the seventh wave, the ninth wave, and the eleventh wave, they are appropriate data. These values in the figure are all 1.09E-7, but in actual measurement, the values vary slightly due to the influence of the waveform and the influence of noise.

  By substituting TA7 for T1 in equation (6) and substituting TB7 for T2, one sound velocity data can be obtained. Similarly, the second data is obtained by substituting TA9 for T1 and TB9 for T2, and the third data is obtained by substituting TA11 for T1 and TB11 for T2. .

  In this way, three flow rate data can be obtained by performing transmission and reception once in each of the ultrasonic sensors 2 and 3. By taking the average value of these three data, the flow rate measurement is averaged and the variation in data can be reduced.

  In these detection points, only detection points that intersect with the reference value at the falling edge of the received waveform are selected, but detection points that intersect with the reference value at the falling edge of the received waveform can also be added. In this case, a value larger than twice the time difference ΔT (ΔT = T1-T2) at the maximum flow rate is selected as the period TS.

  According to the present embodiment, as shown in FIG. 4, when the nth wave for detecting reception is received by the second ultrasonic sensor 3 and when it is received by the first ultrasonic sensor 2. Even if n is different, accurate measurement is possible.

  As a result, as shown in FIG. 13 (2), an ultrasonic sensor having only one main resonance frequency has a reception waveform that rises slowly as shown in FIG. Even if the wave number tends to be ambiguous, accurate measurement can be performed, so the design freedom of the ultrasonic sensor is expanded, and the acoustic matching layer does not need to be a composite structure, and the structure can be simplified. .

  Further, since the correct measurement can be performed even if the reception waveforms of the first ultrasonic sensor 2 and the second ultrasonic sensor 3 are different, the flow path 1 having a lot of reflection of ultrasonic waves as shown in FIG. But it can also be used. The cross section of the flow path 1 is divided by three thin plates 9.

  The interval between the thin plates 9 is about 2 millimeters, and the fluid passes through four layers of space. A flat type with a narrow space between the fluid passages in this way can easily make the fluid velocity distribution in that space uniform in a wide flow rate region, thus realizing a flow meter with little error over a wide flow rate region. can do. First and second ultrasonic sensors 2 and 3 are arranged at both ends. Since the ultrasonic wave radiated from the ultrasonic sensor has a certain extent, the ultrasonic wave hits the thin plate 9 constituting the upper and lower sides in a narrow space, and propagates while changing its trajectory. When there is a fluid flow, the trajectory changes due to the influence.

  Ultrasound radiated from one ultrasonic sensor spreads, some is reflected by a thin plate, advances while changing its trajectory, and ultrasonic waves that pass through various trajectories when reaching the other ultrasonic sensor This is a composite wave. For this reason, when the received waveforms of the first and second ultrasonic sensors 2 and 3 are compared, the peak value of each wave may be different. However, if the measurement method of this embodiment is used, accurate measurement is possible. It can be performed.

  As described above, the ultrasonic flowmeter according to the present invention can accurately measure the propagation time of ultrasonic waves regardless of the shape of the received waveform of the ultrasonic sensor, and can perform a plurality of propagation times from a single received waveform. Since data can be acquired and averaged, measurement accuracy can be improved, and it is possible to use a flat flow path that easily changes the received waveform of ultrasonic waves. It can be used for commercial and household ultrasonic gas flow measuring devices (gas meters) that measure the flow rate of natural gas and liquefied petroleum gas.

Schematic which shows the structure of the ultrasonic flowmeter in embodiment of this invention Waveform diagram of the ultrasonic flowmeter Characteristic diagram showing the relationship between the maximum flow rate of the ultrasonic flowmeter and the propagation time difference ΔT of ultrasonic waves Waveform diagram of the ultrasonic flowmeter Diagram showing the detection points of the ultrasonic flowmeter and their times The figure which shows the detection point of the same ultrasonic flow meter and those time differences (A) is an external appearance perspective view which shows other embodiment of an ultrasonic flowmeter, (b) is sectional drawing. Control block diagram showing an example of a conventional ultrasonic flowmeter Control block diagram showing another example of conventional ultrasonic flowmeter Control block diagram showing still another example of conventional ultrasonic flowmeter Cross section of ultrasonic sensor The figure which shows the reception output characteristic of the ultrasonic transducer Diagram showing vibration displacement frequency characteristics of ultrasonic transducer Schematic showing the structure of a conventional ultrasonic flowmeter Waveform diagram of conventional ultrasonic flowmeter Received waveform diagram and clock waveform diagram of conventional ultrasonic flowmeter

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flow path 2 1st ultrasonic sensor 3 2nd ultrasonic sensor 4 Transmission means 5 Reception means 6 Timekeeping means 8 Calculation means

Claims (5)

Comprising at least a pair of ultrasonic sensors arranged in a flow path through which fluid flows, a transmission means for supplying a drive signal to the ultrasonic sensor, a reception means for receiving a signal from the ultrasonic sensor, and a time measuring means, The propagation time T1 required until the ultrasonic wave transmitted from the one ultrasonic sensor is received by the other ultrasonic sensor, and conversely, the ultrasonic wave transmitted from the other ultrasonic sensor is received by the one ultrasonic sensor. The transmission time T2 required until the time is measured by the time measuring means, and the transmission means sends a signal having a period TS larger than the time difference ΔT (ΔT = T1-T2) at the maximum flow to the ultrasonic sensor. An ultrasonic flow measurement device that transmits. An operation for detecting the intersection by comparing the AC reception signal waveform of the ultrasonic sensor with a reference value over a plurality of cycles, measuring the propagation time of the plurality of detection points with the time measuring means, and calculating the data of the time measuring means The ultrasonic flow measuring device according to claim 1, further comprising means. Based on the time data of the detection points obtained by comparing the AC reception signals of at least a pair of ultrasonic sensors alternately transmitting and receiving with a reference value over a plurality of cycles, the calculation means calculates the flow velocity and the frequency from each cycle. The ultrasonic flow measuring device according to claim 2, wherein the flow rate is obtained. 4. The ultrasonic sensor according to claim 1, wherein the ultrasonic sensor has a plurality of main resonance frequencies, but the difference between the resonance frequencies is less than 120 kilohertz or only one main resonance frequency. Ultrasonic flow measuring device. The ultrasonic flow measuring device according to any one of claims 1 to 4, wherein the ultrasonic wave propagating in the flow path is set so as to be a complex synthetic wave when hitting a wall surface constituting the flow path.

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