JP2006308439A - Flow measuring device of fluid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flow measuring device which improves measurement accuracy by ensuring the detection location of a reception point when a reception waveform amplitude varies. <P>SOLUTION: The device includes a pair of ultrasonic sensors 72 and 73 arranged in the flow path 71 of the fluid, a transmission means 74 for driving the ultrasonic sensors 72 and 73, a comparing means 87 for receiving the signals from the ultrasonic sensors 72 and 73 and detecting the reception by comparing the reception signal with a threshold value, a reception means 75 having a determining means 86 for determining right or wrong of the comparison results of the comparison means 87 and a time counting means 76 for counting the propagation time of ultrasonic wave. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fluid flow measuring apparatus that measures flow velocity and / or flow rate by ultrasonic waves in particular.

  FIG. 15 shows an ultrasonic flow meter as an example of a conventional fluid flow measuring device. In FIG. 15, the first vibrator 2 that transmits ultrasonic waves and the second vibrator 3 that receives ultrasonic waves are arranged in the middle of the fluid conduit 1 so as to cross the flow direction obliquely.

  4 is a transmission circuit to the first vibrator 2, and 5 is an amplification circuit for a signal received by the second vibrator 3. This amplified signal is compared with a reference signal by the comparison circuit 6, and the time from transmission to reception is shown. Is calculated by the time counting means 7 such as a timer counter, and the flow rate value of the fluid is calculated according to the ultrasonic propagation time, and the corresponding flow rate value is calculated by the calculation means 8 in consideration of the size of the pipe line and the flow state. The timing of signal transmission to the transmission circuit 4 trigger means 10 is adjusted via the measurement interval changing means 9 according to the value of the calculation means 8.

  Next, the operation will be described. A burst signal is transmitted from the transmission circuit 4 from the trigger means 10. The ultrasonic signal transmitted from the first vibrator 2 is transmitted through the flow and received by the second vibrator 3. The signal processing is performed by the amplifier circuit 5 and the comparison circuit 6, and the time from transmission to reception is measured by the time measuring means 7 (see, for example, Patent Document 1).

If the sound in the static fluid is c and the flow speed of the fluid is v, the propagation speed of the ultrasonic wave in the flow direction is (c + v). When the distance between the transducers 5 and 6 is L, and the angle formed by the ultrasonic transmission axis and the central axis of the pipe is φ, the time T that the ultrasonic wave reaches is:
T = L / (c + v × cos φ) (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. From this flow velocity, if the flow rate Q is S and the correction count is K,
Q = K × S × v (3)
It becomes.

  FIG. 16 shows another conventional example, in which transmission to reception are repeated by the repeater 11 and repeated for the number of times set by the setting unit 12. Further, after switching between oscillation and reception by the switching means 13, the same is repeated.

  That is, an ultrasonic wave is transmitted from the first vibrator 2 by the oscillation circuit 4, and this ultrasonic wave is received by the second vibrator 3 and reaches the comparison circuit 6 via the amplifier circuit 5. To trigger the transmission circuit 4.

  This repetition is performed the number of times set by the repetition setting means 12, and when the set number of times is reached, the time required for the repetition is measured by the time measuring means 7. After that, the transmission and reception of the first vibrator 2 and the second vibrator 3 are reversely connected by the switching means 13, and this time the ultrasonic wave is sent from the second vibrator 3 to the first vibrator 2. Similarly, the arrival time is obtained, and the flow rate and / or flow rate value is calculated by the calculation means 8 using this difference.

If the sound in the static fluid is c and the fluid flow speed is v, the propagation speed of the ultrasonic wave in the forward direction is (c + v) and the propagation speed in the reverse direction is (cv). Become. When the distance between the transducers 2 and 3 is L, the angle formed by 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, respectively. Is
T1 = n × L / (c + v × cos φ) (4)
T2 = n × L / (c−v × cos φ) (5)
From the 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 extremely small when the flow rate is small and the number of repetitions is small, and it is difficult to measure accurately. Therefore, when the number of measurements is set to a large value and the error is relatively small, and the flow rate increases, T1-T2 Since the difference becomes large, the measurement becomes easy. In this case, the number of repeated settings is reduced, the sampling interval is increased, and the error is reduced. That is, the number of repetition setting means 11 is changed by the calculation means 8.

  In addition, a measurement method that uses ultrasonic waves to measure ultrasonic propagation time with high accuracy in a short time and with low power consumption has been proposed (see, for example, Patent Document 2).

  As shown in FIG. 17, the vibrator 2 transmits and receives an ultrasonic signal to and from the inner surface of the fluid conduit 1, and the comparison means 6 compares the AC received signal of the vibrator 2 with a threshold over a plurality of periods. And a time measuring means 7 for measuring a plurality of propagation times for each detection by the comparison means 6 from transmission of the vibrator 2, and a time calculating means 14 for calculating the propagation time from the average value of the time measured values of the time measuring means 7. It is.

  As a result, a measurement value obtained by comparing with the comparison means many times by one ultrasonic transmission / reception can be obtained. Therefore, by obtaining the average value, a highly accurate propagation time measurement value can be obtained in a short time, and the consumption is low. It is described so that measurement can be performed with electric power.

  The method shown in FIG. 16 is a method of calculating the flow rate by using two transducers to switch between transmission and reception, obtaining the flow velocity from the ultrasonic wave propagation time obtained from each received waveform. Since the reception waveform of the vibrator has several waves, it is necessary to obtain the propagation time using a predetermined wave.

  For example, since the received waveform is as shown in FIG. 18, the time from the transmission is measured by the clock at the point P1 where the third wave exceeding the threshold intersects the reference value. Since the actual arrival point of the received wave is PT, the time from PT to P1 is treated as a fixed value and corrected at the time of calculation.

Because of this method, there is a problem that if the propagation time is detected by a wave other than the third wave determined due to a change in the received waveform due to the flow of gas, the temperature characteristics of the ultrasonic sensor, or noise, a large measurement error occurs. There is.
JP-A-8-122117 (FIGS. 1 and 7) Japanese Patent Laid-Open No. 10-30947 (FIG. 1)

  However, the two ultrasonic sensors are alternately switched to transmission and reception, the time for propagation of each ultrasonic wave is obtained, the flow velocity is calculated from the difference between the reciprocal numbers thereof, and the pipe line (both the flow path is also connected). In the conventional measuring device that obtains the flow rate in consideration of the cross-sectional area of (say), the received waveform greatly affects the measurement accuracy. This point will be described in detail with reference to the drawings.

  Now, in the measurement system, ultrasonic sensors 51 and 52 are arranged in a flow path 50 as shown in FIG. 19, and a transmission circuit 54 is connected to the ultrasonic sensor 51 and a receiving circuit 55 is connected to the ultrasonic sensor 52 by a switching circuit 53. Then, the propagation time T1 of the ultrasonic wave in the gas is measured, and then the transmission circuit 54 is connected to the ultrasonic sensor 52 and the reception circuit 55 is connected to the ultrasonic sensor 51 by the switching circuit 53, and the propagation time of the ultrasonic wave in the gas T2 is measured, and the flow rate is obtained from the time difference between the two.

  FIG. 20 is a timing chart showing a transmission signal to the ultrasonic sensor, a received signal and a clock operation for measuring the time.

  (A-1), (a-2), and (a-3) are the cases where the ultrasonic sensor 51 is on the transmitting side and the ultrasonic sensor 52 is on the receiving side, and (b-1) and (b-) in FIG. 2) and (b-3) are cases where the ultrasonic sensor 51 is on the receiving side and the ultrasonic sensor 52 is on the transmitting side.

  Since the gas has a flow in the direction shown in FIG. 19, 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.

  When a waveform exceeding the threshold value comes, it is determined as a received waveform, and a point P1 where the received waveform intersects with a reference value is set as a detection point. The propagation time of the ultrasonic wave 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.

  The ultrasonic wave radiated from the ultrasonic sensor has some spread, and when the ultrasonic wave propagates, it hits the wall surface that constitutes the flow path, the received waveform is a synthesis of ultrasonic waves that enter through various paths Since it becomes a wave, the state of the synthesized wave may change depending on the flow velocity of the gas.

  When such a waveform change occurs, the second wave and the third wave cannot be distinguished from each other with the set fixed threshold value, and there is a problem that a large measurement error occurs when the propagation time is detected with a wave that is not the third wave.

  In addition, as described above, there is a problem that a large measurement error occurs even when the propagation time is detected by a wave other than the third wave determined due to the temperature characteristics of the ultrasonic sensor or noise.

  The present invention solves such a conventional problem, and an object of the present invention is to provide a fluid flow measuring device capable of highly accurate measurement.

  In order to solve the conventional problem, an ultrasonic flowmeter of the present invention includes an ultrasonic sensor disposed in a flow path through which fluid flows, a transmission unit that drives the ultrasonic sensor, and an ultrasonic sensor from the ultrasonic sensor. The receiving means comprises a receiving means for receiving a signal and a time measuring means for measuring the propagation time of the ultrasonic wave. The receiving means compares the threshold value with the received signal to detect reception, and the validity of the comparison result of the comparing means. The generation of a large measurement error can be eliminated by providing the determination means for determining.

  The ultrasonic flowmeter of the present invention improves the accuracy of measurement by accurately detecting the received wave even if the received waveform of the ultrasonic wave changes due to the influence of flow velocity and temperature, and judging whether the wave is correct. There is an effect that can be.

  According to a first aspect of the present invention, there is provided an ultrasonic sensor disposed in a flow path through which a fluid passes, a transmission unit that drives the ultrasonic sensor, a reception unit that receives a signal from the ultrasonic sensor, and an ultrasonic propagation time. The receiving means includes a comparing means for detecting reception by comparing a threshold value with a received signal, and a judging means for judging whether the comparison result of the comparing means is correct.

  Since the reception waveform of the ultrasonic sensor has continuity in vibrator vibration, even if only one transmission signal is given, it becomes a waveform of a plurality of cycles. The received waveform has an envelope in which the waveform peak value gradually increases and then decreases. For this reason, when the reception waveform is detected by the comparison means, what level of reception wave is detected depends on what level the threshold value of the comparison means is set. However, since the envelope of the received waveform varies with temperature and flow velocity, it is difficult to limit the number of waves detected with the set threshold.

  Therefore, for example, when there is no flow rate, even if a threshold value is set so that detection is performed at the third wave, if the flow rate is large, detection at the fourth wave may occur at this threshold value. When one wave is shifted, the propagation time measurement is increased or decreased by a time corresponding to one period, resulting in a large measurement error.

  Therefore, the threshold value is set to a value very close to the reference value of the received signal. Here, the reference value is the case where the received signal is either positive or negative by superimposing the DC component so that the circuit can process the received signal of the ultrasonic sensor, which is an AC signal. The direct current component is shown.

  In this way, by setting the threshold value to a value very close to the reference value, it becomes possible to immediately detect a waveform change when received, and it becomes easier to detect the first wave of reception. The peak value of the first received wave also changes depending on the temperature and flow velocity, but the threshold value is set to a value lower than the minimum value of the change range of the peak value, so that the first wave can be reliably captured.

  However, since the threshold is set to a value close to the reference value, it is easy for the comparator to operate and output an erroneous signal at the reference value on which noise is superimposed.

  Therefore, by providing a determination unit that determines whether the output signal from the comparison unit is correct or incorrect, it is possible to prevent measurement using an incorrect signal.

  In the second invention, in particular, the comparison means of the first invention compares the received waveform with the two threshold values with respect to the reference value, and the judgment means determines whether the result of the comparison means is from which of the two threshold values. Judge whether it was detected first.

  For example, if two threshold values, positive and negative, are provided with respect to the reference value, a threshold value to be compared first and a threshold value to be detected later are always determined when a correct signal is detected. It can be determined that the detected signal is incorrect.

  In particular, in the third invention, in the second invention, the time from the comparison at one of the two thresholds to the comparison at the other threshold is counted, thereby correcting the correctness of the signal of the comparison means. Judgment is made by the judging means. For example, in two threshold values provided positive and negative with respect to the reference value, when a correct signal is detected, the time interval between the threshold value to be compared first and the threshold value to be detected later is determined within a certain range. Therefore, by measuring this time interval, it is possible to determine whether the output signal of the comparison means is correct or incorrect.

  In particular, the fourth invention can save the number of circuit elements by providing a comparison means in which the threshold value can be switched and compared by a plurality of threshold values in the second invention.

  In particular, the fifth invention includes a plurality of ultrasonic sensors arranged in the flow path through which the fluid passes in the first invention, and the ultrasonic wave when transmitted from one ultrasonic sensor to the other ultrasonic sensor is provided. In obtaining the flow velocity and / or flow rate from the propagation time T1 and the propagation time T2 of the ultrasonic wave when transmitted in the opposite direction, the wave number of the received wave is counted and the correctness of the received wave is judged by comparing the wave number. Judgment means is provided.

  Thus, if the wave number when transmitted from one ultrasonic sensor to the other ultrasonic sensor is different from the wave number when transmitted in the opposite direction, it can be determined that the comparison result of the comparison means is incorrect.

  The sixth aspect of the invention is particularly the determination means using the peak hold circuit in the fifth aspect of the invention. As a result, the wave number can be obtained from the number of updates of the peak value.

  In particular, the seventh invention is a judging means having a peak hold circuit and a comparing means in the sixth invention. By comparing the peak hold circuit output and the received wave, a pulse signal for obtaining the wave number can be formed.

  In an eighth aspect of the invention, in particular, in the seventh aspect of the invention, the time measuring means is provided, and the time of the pulse interval formed for obtaining the wave number is timed, so that the correctness of the formed pulse signal is determined by the determining means. become able to.

(Embodiment 1)
Embodiment 1 of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to this embodiment.

  In FIG. 1, ultrasonic sensors 72 and 73 are disposed in a flow path 71 through which gas flows. A transmission signal is sent from the transmission means 74 to the ultrasonic sensors 72 and 73. Further, the reception signal of the ultrasonic sensor is transmitted to the receiving means 75.

  Transmission and reception are selected by the switching means 77. When one ultrasonic sensor 72 is selected to connect to the transmission means 74, the other ultrasonic sensor 73 is selected to connect to the reception means 75.

  If the gas flow is from left to right as shown in the figure, the ultrasonic wave transmitted by the ultrasonic sensor 72 reaches the ultrasonic sensor 73 after the propagation time T1. On the contrary, the ultrasonic wave transmitted by the ultrasonic sensor 73 reaches the ultrasonic sensor 72 after the propagation time T2, but T1 <T2 from the gas flow direction. These propagation times T1 and T2 are timed by the time measuring means 76.

  The calculating means 79 obtains the flow rate based on the data from the time measuring means 76.

  The above is the main part of the ultrasonic measuring device 78.

  FIG. 2 shows a transmission (transmission means) waveform, a reception (reception means) waveform, and a clock (time measurement means) waveform of the ultrasonic sensor, and (a-1), (a-2), and (a-3) in FIG. ) Is a case where each is transmitted from the ultrasonic sensor 72 and received by the ultrasonic sensor 73.

  According to (a-1) in the figure, the transmission signal has three waves, and the reception waveform is as shown in (a-2) in the figure. The ultrasonic wave propagation time T1 is corrected by counting the time from TA1 to TA7, which is the point where the received waveform intersects the reference value, with the clock in FIG. Is required. (B-1), (b-2), and (b-3) in the figure are cases where the ultrasonic wave is transmitted from the ultrasonic sensor 73 and received by the ultrasonic sensor 72, and the ultrasonic propagation time T2 is similarly determined. Desired.

  The threshold shown in the figure is provided to detect a received wave and serves as an input signal to the comparing means of the receiving means. When reception is detected using the comparison means, further comparison means are used to detect points intersecting the reference values, TA1 to TA7 and TB1 to TB7.

  Next, the receiving means will be described with reference to FIG. The reception signals of the ultrasonic sensors 72 and 73 are input to the amplification means 80 of the reception means 75 via the switching means 77. The amplified signal is further amplified by the amplification means 81 and input to the comparison means 83 and 84.

  The reference value setting unit 85 gives a reference value. This is superimposed on the AC reception signal and also input to the comparison means 87. The signals from the comparison means 83 and 84 are input to the determination means 86. The comparison means 83 and 84 detect the reception, and the determination means 86 determines whether the reception is correct or incorrect.

  If the determination is positive, the comparison means 87 to which the reference value is given compares the received wave with the reference value, and detects intersecting points (TA1 to TA7 and TB1 to TB7 in FIG. 2). The signal of the comparison means 87 is transmitted to the time measuring means 76, and the propagation time is calculated.

  FIG. 4 shows the waveforms of the input signal and output signal of the comparison means when transmitted from the ultrasonic sensor 72 and received by the ultrasonic sensor 73. FIG. 4A shows the input signal and the threshold value of the comparison means 83. A and the threshold value B of the comparison means 84 are described together. FIG. 4B shows the output signal of the comparison means 83, and FIG.

  In normal operation, the output signal of the comparison means 83 first becomes HI, and the output signal of the comparison means 84 becomes HI later. Further, the output signal of the comparison unit 83 and the output signal of the comparison unit 84 do not become HI at the same time. Such a determination is made by the determination means to determine whether the reception is correct. If it is determined that the reception is correct, the comparison unit 87 detects the intersections TA1 to TA7 with the reference value, and obtains the propagation time from the transmission.

  FIG. 5 shows the waveforms of the input signal and output signal of the comparison means when similarly transmitted from the ultrasonic sensor 72 and received by the ultrasonic sensor 73. FIG. 5 (a) shows the input signal which is the received signal. From the state in which noise or the like is superimposed on the first wave and the output of the comparison means 83 in FIG. 7B does not become HI without exceeding the threshold A, the output of the comparison means 84 in FIG. It shows the state that became. In this case, the determination means determines that the received signal is incorrect, and performs measurement again without calculating the propagation time.

  FIG. 6 shows the waveforms of the input signal and the output signal of the comparison means when similarly transmitted from the ultrasonic sensor 72 and received by the ultrasonic sensor 73. FIG. 6A shows the input signal as the received signal. (B) shows the output of the comparison means 83, (c) shows the output of the comparison means 84, and (d) shows the output of the comparison means 87.

  When reception is normally detected, the comparison means 87 always rises to HI when the outputs of the comparison means 83 and 84 are LOW, and similarly falls to LOW when the outputs of the comparison means A 83 and 84 are LOW. The determination means can determine whether the received signal is correct or not by determining whether such logic is established.

  FIG. 7A shows the waveforms of the input signal and output signal of the comparison means when similarly transmitted from the ultrasonic sensor 72 and received by the ultrasonic sensor 73, and FIG. 7A shows the input signal which is the received signal. 4B shows the output of the comparison means 83, FIG. 4C shows the output of the comparison means 84, and FIG. 4D shows the clock.

  The clock operates from the rise of the output of the comparison unit 83 to the rise of the output of the comparison unit 84. The judging means counts the number of clocks and obtains the operating time thereof, thereby judging whether the output signals of the comparing means 83 and 84 are correct.

  FIG. 8 shows the waveforms of the input signal and output signal of the comparison means, and the amplitude of the received waveform (input signal) in FIG. 8 (a) is smaller than that in FIG. 7 (a). 8B shows the output of the comparison means 83, FIG. 8C shows the output of the comparison means B, and FIG. 8D shows the clock. The clock operates from the rise of the output of the comparison means 83 to the rise of the output of the comparison means 84, but the number of clocks is smaller than in the case of FIG.

  As described above, the number of clocks (operation time) varies depending on the reception waveform, but in normal cases, the operation time falls within the period from ¼ period to ½ period of the reception wave. It is determined that the received waveform is incorrect.

  FIG. 9 shows another configuration for judging whether the received waveform is correct or not. The parts common to the circuit block diagram shown in FIG. 3 are denoted by the same reference numerals, and the detailed description of FIG. The amplified received signal from the amplifying means 81 is received by the peak hold circuit 88, and the judging means 86 counts the number of times the peak value is updated.

  The amplified received signal from the amplifying unit 81 is also input to the comparing unit 87. The comparison means 87 outputs a comparison result between the received wave and the reference value.

  FIG. 10 shows waveforms of respective parts of the circuit block diagram shown in FIG. FIG. 5A shows an amplified received signal from the amplifying unit 81 and a signal that becomes an input signal of the peak hold circuit 88. This reception signal is a waveform when transmitted from the ultrasonic sensor 72 and received by the ultrasonic sensor 73.

  FIG. 5B shows an output signal of the peak hold circuit 88, and shows how the peak value is updated for each peak of the received waveform that is the input signal. FIG. 6C shows an internal signal of the determination means 86, which is a signal waveform of a circuit unit that receives a signal of the peak hold circuit 88 and generates a pulse every time the peak value is updated.

  The judging means 86 stores the number of updates of the peak value by this pulse. In this case, the number of updates is four. The amplified received signal from the amplifying means 81 shown in FIG. The comparison unit 87 compares the reference value with the received signal, and the output is input to the time measuring unit 76.

  However, the operation of the comparison means 87 is performed after the first pulse of the determination means internal signal A in FIG. The time measuring means 76 obtains the time from points TA1 to TA7 at which the reference value shown in FIG. The obtained times TA1 to TA7 are temporarily stored.

  Next, the operation is transmitted from the ultrasonic sensor 73 and received by the ultrasonic sensor 72. Since the figure is equivalent to that in FIG. 10, the figure is omitted, but similarly, the time at the point where the reference value obtained by the time measuring means 76 intersects the received signal is defined as TB1 to TB7. When the propagation time is obtained from the reciprocal difference of time as shown in Expression (6), for example, the propagation time is obtained from a pair of data of TA1 and TB1, and similarly, a pair such as TA2 and TB2, TA3 and TB3, respectively. Obtain from the data.

  However, since TA2 and TB2 are propagation times of the second wave, this is taken into consideration when calculating. Similarly, consider that TA3 and TB3 are the third wave. If the propagation time is obtained in this way, seven data are obtained. If these seven data are averaged, the ultrasonic sensor 72 and the ultrasonic sensor 73 each transmit and receive one time as in the conventional example. Compared with the case where the flow velocity is obtained from a pair of propagation time data, measurement data with less variation can be obtained.

  FIG. 11 shows the waveform of each part similar to FIG. 10, but the received signal in FIG. 11A is a waveform when transmitted from the ultrasonic sensor 73 and received by the ultrasonic sensor 72. The peak value of the received waveform is lower than that in FIG. 10 because of the flow velocity, but the wave number until the peak is reached does not change (the wave number changes when there is a change in the characteristics of the ultrasonic sensor due to temperature change). However, also in this case, the wave number until the received waveform reaches the peak is the same in the case where it is transmitted from the ultrasonic sensor 72 and received by the ultrasonic sensor 73 and the opposite case).

  For this reason, the peak hold circuit cannot capture the first wave of the received waveform as shown in FIG. Accordingly, since the internal signal of the judging means is also output from the second wave of the received wave, the comparing means 87 obtains the time from TB2 to TB7 where the reference value and the received signal intersect.

  In this case, the number of updates of the peak value is 3, and the number of updates is one less than in FIG. 10C. Therefore, the determination unit 86 determines that TB1 could not be detected, and these data are not applied. The measurement is started again from the beginning, or the following is applied from a pair of data of TA2 and TB2.

  Similarly, FIG. 12 shows waveforms of respective parts of the circuit block diagram shown in FIG. (A) is a transmission signal of the ultrasonic sensor 72, (b) is a reception signal of the ultrasonic sensor 73, (c) is a peak hold circuit output signal, (d) is a cutting means internal signal A, (e ) Represents a clock.

  FIG. 2B shows a state in which noise is superimposed particularly between transmission and reception. The peak hold circuit output in FIG. 6 (c) represents a state where noise is detected. FIG. 6D shows a pulse output at a timing when there is a voltage change according to the peak hold circuit output. Since noise is detected, the pulse interval shown in FIG. 4E measured by the clock shown in FIG. 3E has no fixed period.

  If a period close to the transmission signal is not found in this pulse, the peak hold circuit output is reset. Further, the pulse interval has a certain period in the portion where the correct received signal is detected.

  Thus, by measuring the pulse period using the clock, it is possible to distinguish the correct signal from the received signal from noise. It is possible to know the wave number until the received signal reaches the peak by the number of pulses having a certain period.

(Embodiment 2)
In FIG. 13, a peak hold circuit 88 and comparison means 89 are provided. The comparing unit 89 compares the output of the peak hold circuit 88 with the received wave signal that is a signal from the amplifying unit 81, and outputs a pulse signal for counting the wave number of the received wave.

  FIG. 14 is a waveform diagram showing a partial waveform of the circuit block diagram shown in FIG. The signal obtained by comparing (a) the received wave signal (comparison means D input signal) and (b) the peak hold circuit output signal (comparison means D input signal) by the comparison means D determines the wave number of (c). Pulse signal {comparison means D output signal (determination means internal signal)}.

  In the figure, the signal levels of (a) and (b) are adjusted so as to detect from the peak of the received wave to the next one wave.

  Since the rising interval of the pulse signal for obtaining the wave number of (c) is a value that is substantially close to the period of the received wave, this is confirmed using the clock of (d) and the correctness of the received wave is judged. The wave number of the received wave can be obtained by counting (b) pulse signals.

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

The block diagram which shows the structure of the ultrasonic flow measuring apparatus of Embodiment 1 of this invention. Waveform diagram of the same ultrasonic flow measuring device Circuit block diagram of receiving means in the ultrasonic flow measuring device Waveform diagram of the ultrasonic flow measurement device Waveform diagram of the ultrasonic flow measurement device Waveform diagram of the same ultrasonic flow measuring device Waveform diagram of the same ultrasonic flow measuring device Waveform diagram of the same ultrasonic flow measuring device Circuit block diagram of receiving means in the ultrasonic flow measuring apparatus according to Embodiment 2 of the present invention Waveform diagram of receiving means of the same ultrasonic flow measuring device Waveform diagram of receiving means of the same ultrasonic flow measuring device Waveform diagram of receiving means of the same ultrasonic flow measuring device Circuit block diagram of receiving means of the same ultrasonic flow measuring device Waveform diagram of receiving means of the same ultrasonic flow measuring device Control block diagram showing the configuration of the conventional ultrasonic flow measuring device Control block diagram showing the configuration of another conventional ultrasonic flow measuring device Control block diagram showing the configuration of another conventional ultrasonic flow measuring device Received signal waveform diagram of ultrasonic sensor of conventional ultrasonic flow measuring device Block diagram showing the configuration of the conventional ultrasonic flow measuring device Waveform diagram of the conventional ultrasonic flow measurement device

Explanation of symbols

71 Flow path 72, 73 Ultrasonic sensor 74 Transmission means 75 Reception means 76 Timekeeping means 86 Judgment means 87 Comparison means 88 Peak hold circuit 89 Comparison means

Claims (8)

A pair of ultrasonic sensors arranged in the flow path through which the fluid passes, transmission means for driving the ultrasonic sensors, and signals from the ultrasonic sensors are received, and reception is detected by comparing the threshold and the received signal. And a receiving means having a judging means for judging whether the comparison result of the comparing means is correct and a time measuring means for measuring the propagation time of the ultrasonic wave. 2. The comparison unit according to claim 1, wherein the comparison unit compares the received waveform with two threshold values with respect to a reference value, and the determination unit determines which of the two threshold values is detected first. Fluid flow measuring device. It has time measuring means, and the time from comparison between one of the two thresholds to comparison with the other threshold is counted, so that the correctness of the signal of the comparison means is judged by the judging means. The fluid flow measuring device according to claim 2. The fluid flow measuring device according to claim 2, further comprising a comparison unit configured to switch the threshold values and to compare with a plurality of threshold values. The flow velocity and / or flow rate is determined based on the propagation time difference between the ultrasonic propagation time T1 when transmitted from one ultrasonic sensor to the other ultrasonic sensor and the ultrasonic propagation time T2 when transmitted in the opposite direction. The fluid flow measuring device according to claim 1, further comprising: a determination unit configured to determine the wave number of the received wave, and to determine whether the received wave is correct by comparing the wave numbers. 6. The fluid flow measuring device according to claim 5, wherein the judging means includes a peak hold circuit, and the wave number comparison is performed based on the number of times the peak value of the peak hold circuit is updated. The judging means has a peak hold circuit for detecting the peak of the received wave and a comparing means, and the comparing means compares the peak hold circuit output with the received wave to form a pulse signal for obtaining the wave number; The fluid flow measuring device according to claim 6. 8. The fluid flow measuring device according to claim 7, further comprising a time measuring unit, wherein the determination unit determines whether the formed pulse signal is correct by measuring the time of the pulse interval formed to determine the wave number. .

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