JP2007322194A - Fluid flow measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce errors contained in measured propagation time or arrival time of ultrasonic waves to attain precise flow measurement. <P>SOLUTION: A pair of ultrasonic transducers 23 and 24 are disposed opposed each other on the upstream and the downstreams of a flow passage 22 with a fluid flowing therethrough; the one side ultrasonic transducer is driven to transmit the ultrasonic waves toward the other ultrasonic transducer, a large number of zero-cross memories is operated sequentially, while zero-cross memory values are determined; the effectiveness of the zero-cross memory values is determined after a prescribed time; and the propagation time of the ultrasonic wave is computed, based on the effective zero-cross memory value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flow measurement device for a fluid such as a gas or water that measures the flow velocity and / or flow rate of a fluid using ultrasonic waves.

  A conventional fluid flow measuring device will be described with reference to FIG. 8. A pair of ultrasonic transducers 102 and 103 are arranged on the upstream side and the downstream side of a flow path 101 through which a fluid flows, and the ultrasonic waves are fluidized. Is crossed diagonally.

  Then, the flow velocity of the fluid is measured from the propagation time of the ultrasonic wave propagating between the pair of ultrasonic transducers 102 and 103, and the flow rate is calculated based on this.

In addition, the solid line arrow 104 in a figure shows the direction through which a fluid flows, and the broken line arrow 105 has shown the direction through which an ultrasonic wave propagates. The direction in which the fluid flows and the direction in which the ultrasonic waves propagate intersect at an angle θ (for example, see Patent Document 1).
JP 2002-13958 A

  However, in the conventional measuring apparatus, an ultrasonic wave is propagated from the upstream ultrasonic transducer 102 to the downstream ultrasonic transducer 103, and the ultrasonic propagation time Tud is determined, and the downstream ultrasonic transducer 103 is also transmitted. The ultrasonic wave is propagated from the ultrasonic wave to the ultrasonic transducer 102 on the upstream side, the ultrasonic wave propagation time Tdu is measured alternately, the time difference is calculated using the measured ultrasonic wave propagation times Tud and Tdu, and the flow rate is calculated. It was.

  At this time, a reference level is set to a received waveform portion where a predetermined amplitude can be obtained as a trigger level, and a propagation time is measured. Therefore, the propagation time of the ultrasonic wave cannot be measured using the zero cross point before the trigger level.

  For this reason, an uncertain time is included in the arrival time of the ultrasonic wave, which may cause an error, and there is a problem that high-precision flow measurement cannot be realized.

  That is, the ultrasonic reception waveform generally rises at a frequency driven by a drive circuit, and sequentially changes to a vibration frequency unique to the ultrasonic transducer.

  Alternatively, since the reception waveform of the ultrasonic wave is affected by the reflected wave from the side wall of the flow path or the like, the frequency at the rising portion near the reception point is stable, but the trigger level is relatively high. In the portion where the reception amplitude is large, a difference occurs in the waveform received between the upstream side and the downstream side, which is detected as an error in propagation time.

  In addition, since the ultrasonic wave reflected by the side wall of the channel 101 arrives at the received wave with a slight delay and is received as the received wave, the zero cross point may be uncertain.

  The present invention solves the above-described conventional problems, and measures the arrival time of the received ultrasonic cross point and sequentially determines the effectiveness of the zero cross point, so that the zero before the trigger level is determined. An object of the present invention is to realize a highly accurate measurement by reducing the error included in the propagation time of the ultrasonic wave so that the arrival time of the ultrasonic wave can be measured using the cross point.

  In order to solve the above-described conventional problems, a fluid flow measurement device according to the present invention has a pair of ultrasonic transducers arranged opposite to an upstream side and a downstream side of a flow path through which a fluid flows, The transducer is driven to transmit ultrasonic waves to the other ultrasonic transducer, and a number of zero cross memories are operated while sequentially determining the zero cross memory values. The validity of the value is determined, and the ultrasonic propagation time is calculated from the effective zero cross memory value.

  With this configuration, it is possible to measure the propagation time of the ultrasonic wave propagating between the upstream ultrasonic transducer and the downstream ultrasonic transducer, that is, the arrival time of the ultrasonic wave before the trigger level. For this reason, the error included in the propagation time or arrival time of the measured ultrasonic wave can be reduced, and highly accurate flow measurement can be realized.

  Since the ultrasonic flowmeter of the present invention can measure the ultrasonic propagation time or the ultrasonic arrival time using the zero cross point before the trigger level, the ultrasonic propagation time or the ultrasonic arrival time can be measured. The included error can be reduced.

  In the first invention, a pair of ultrasonic transducers are arranged facing the upstream side and the downstream side of the flow path through which the fluid flows, and one ultrasonic transducer is driven to the other ultrasonic transducer. The ultrasonic wave is transmitted toward the multiple zero cross memories and the zero cross memory values are sequentially operated while determining the zero cross memory values, and the validity of the zero cross memory values is determined after a predetermined time, and the effective zero cross memory values are determined. The ultrasonic propagation time was calculated from

  With this configuration, a trigger point is set in a portion having a relatively large amplitude of the received waveform, the trigger is stably operated, and a zero cross point near the reception point having a relatively small reception amplitude is used for propagation time measurement. Therefore, it is possible to measure the propagation time with little error.

  In the second invention, in particular, in the first invention, the sequentially obtained zero cross memory values are separated by a predetermined interval determined by the frequency for driving the ultrasonic transducer and within two times the predetermined interval. Only in this case, the zero cross memory is determined to be valid and operated.

  With this configuration, the obtained zero cross point can be determined easily and in a short time. Therefore, the zero cross determination can be made a power saving configuration.

  In particular, the third invention is configured such that the predetermined time for determining the validity of the zero-cross memory value of the first invention is a predetermined gate time. That is, the optimum gate time is set from the temperature of the fluid and the propagation time of the ultrasonic wave, and the effectiveness of zero crossing is determined after the gate time has elapsed. Therefore, useless time for determining the effectiveness of zero crossing can be deleted, and a power saving configuration can be obtained.

  In particular, the fourth invention is configured such that the predetermined time for determining the validity of the zero cross memory value of the first invention is the time of the peak value of the received ultrasonic waveform. With this configuration, a stable predetermined time is obtained, and the measurement of the propagation time is stabilized.

In particular, the fifth invention is characterized in that the predetermined time for determining the validity of the zero cross memory value of the first invention is the time of the zero cross when the received ultrasonic waveform is differentiated after being shaped into a packet. It was set as the structure to do. With this configuration, the predetermined time for determining the effectiveness is stabilized, and the measurement of the propagation time is stabilized.

  In the sixth invention, in particular, the predetermined time for determining the validity of the zero-cross memory value of the first invention is a zero-cross time exceeding a predetermined reference level of the received ultrasonic waveform; did. With this configuration, it is possible to set a reference level where the reception waveform has a relatively large reception amplitude, to realize stable zero cross determination, and to stabilize the measurement of propagation time.

  In particular, the seventh invention is configured to have a plurality of zero cross memories of the first invention. Since the propagation time can be measured from a plurality of zero crosses, the measured value is stabilized.

  In the eighth aspect of the invention, in particular, the ultrasonic wave propagation time is measured from the plurality of zero crosses of the seventh aspect of the invention, so that highly accurate ultrasonic measurement can be realized. In addition, when the propagation time is measured from an even number of zero crosses, it is possible to perform measurement that is resistant to noise and has a large S / N, and a more accurate measurement side is possible.

  In particular, the ninth invention is a fluid supply management system in which a measurement result obtained by any one of the first to eighth measuring devices is input to a host computer on the fluid supply side.

  Therefore, for example, when the target fluid is gas, the integrated value for a predetermined period of the measuring device installed in each home is imported into the host computer using the network, or the integrated period for the predetermined period acquired individually by the meter reader. By inputting the value into the host computer, the billing work can be processed in a lump, and the gas leak in each household can be monitored according to what is connected with the network. This is made possible by high-precision measurement.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments. Moreover, what attached | subjected the same number in the figure has shown the same structure, and used the first thing for the concrete description.

(Embodiment 1)
FIG. 1 shows a fluid flow measurement device 21 according to Embodiment 1 of the present invention, in which a pair of ultrasonic transducers 23 and 24 are diagonally opposed to an upstream side and a downstream side of a fluid flow path 22. It is set so that the ultrasonic wave crosses diagonally the fluid flowing through the flow path 22.

The distance Ld between the ultrasonic transducers 23 and 24 was about 100 mm, and the cross-sectional area Sr of the flow path 22 was about 30 mm ² .

  In the figure, a solid line arrow 25 indicates the direction in which the fluid flows, and a broken line arrow 26 indicates the direction in which the ultrasonic wave propagates. The direction in which the fluid flows is an angle θ (45 degrees) from the direction in which the ultrasonic wave propagates. ).

  FIG. 2 shows a block diagram of the fluid flow measuring device 21 in which the trigger circuit 30 outputs a start command to the drive circuit 31 and the time circuit 32 at predetermined intervals. Upon receiving the start command, the drive circuit 31 outputs a drive signal to the transmission-side ultrasonic transducer (for example, the upstream ultrasonic transducer 23) selected by the transmission-side switching SW33.

  The ultrasonic wave transmitted by the transmission side ultrasonic transducer into the fluid in the flow path is received by the ultrasonic transducer selected by the reception side switching SW 34 (for example, the ultrasonic transducer 24 on the downstream side) and the signal is received. Is amplified by an amplifier 35. On the other hand, the time circuit 32 that has received the start command generates time pulses at regular intervals.

  In addition, a gate open signal is sent to the detection circuit 37 after a predetermined elapsed time. Upon receiving the gate opening signal, the detection circuit 37 detects a zero-cross point from the ultrasonic reception wave, and outputs the ultrasonic reception time to the control / arithmetic circuit 36.

  The control / arithmetic circuit 36 receives the zero-crossing time when the ultrasonic wave propagation is detected from the detection circuit 37 and one time pulse from the time circuit 32 to recognize the passage of time, and determines the ultrasonic wave propagation time.

  This ultrasonic transmission / detection is repeated while sequentially updating the gate time. When the gate opening signal output to the detection circuit 37 exceeds the ultrasonic wave propagation time, a periodic detection time is obtained, and it can be detected that the ultrasonic wave has arrived.

  The above will be described with reference to FIG. FIG. 3A shows a drive signal 38 composed of a rectangular burst signal of 500 [kHz]. The ultrasonic reception signal 39 indicates a signal received by the ultrasonic transducer on the reception side. FIG. 3B shows an enlarged view of the portion 40 surrounded by a circle in FIG. Reference numeral 41 denotes a ground (zero) level of the signal.

  Since the received signal 39 is a received waveform having a period of 500 [kHz], it is a periodic signal having a wavelength of about 2 [μsec], and the zero cross points are spaced at an interval of about 1 [μsec]. Note that the true propagation time of the ultrasonic wave is indicated by Ts, and the gate opening time is indicated by Tg.

  When the gate opening time Tg is smaller than the ultrasonic propagation time Ts (Tg <Ts), the detection circuit 37 receives the gate opening time and at the same time detects a zero black point with a signal at a noise level (see FIG. 3b). A time as large as the gate opening time is output as the detection time Tk as the ultrasonic propagation time.

  On the other hand, when the gate opening time is sequentially updated and becomes longer than the ultrasonic propagation time Ts (Tg> Ts), the detection time Tk as a zero cross point detected by the detection circuit 37 from FIG. It becomes.

  As described above, the time Tc1 of the first zero cross point and the second zero cross point Tc2 are compared, and if there is a time difference of, for example, a predetermined interval determined by the frequency of the drive waveform 38, the first zero cross point It is determined that the cross point and the second zero cross point are correct zero cross points of the received waveform.

  As described above, a plurality of zero cross points are required for the determination of the zero cross point, but the first zero cross point is set as the propagation time of the ultrasonic wave, and the zero cross point immediately after the rising of the received waveform is propagated as the ultrasonic wave. By setting the time, the propagation time of the ultrasonic wave can be accurately detected without being influenced by the reflected wave in the flow path.

  Therefore, highly accurate ultrasonic measurement can be realized. In addition, since it is possible to stop the zero-crossing operation after determining that the zero-crossing point is valid, a power saving configuration can be achieved.

  Using the ultrasonic propagation time Ts thus obtained, the control / calculation circuit 36 calculates the fluid flow velocity, flow rate, and the like.

Specifically, the arrival time of ultrasonic waves from the upstream ultrasonic transducer 23 to the downstream ultrasonic transducer 24 is Tud, and from the downstream ultrasonic transducer 24 to the upstream ultrasonic transducer 23. When the arrival time of the ultrasonic wave is Tdu, the propagation velocity of the ultrasonic wave propagating through the fluid is Vs, and the flow velocity of the fluid is Vf,
Tud = Ld / [Vs + Vf · cos θ] and Tdu = Ld / [Vs−Vf · cos θ]. From these,
Vs + Vf · cos θ = Ld / Tud, Vs−Vf · cos θ = Ld / Tdu, and by subtracting both sides,
2 * Vf · cos θ = (Ld / Tud) − (Ld / Tdu) = Ld * [(1 / Tud) − (1 / Tdu)]
It becomes. Therefore,
Vf = {Ld / [2 · cos θ]} * [(1 / Tud) − (1 / Tdu)]
Thus, the fluid flow velocity Vf is obtained.
Furthermore, the flow rate Qm is obtained by multiplying the cross-sectional area Sr of the flow path 22. That is, Qm = Sr * Vf is the measured flow rate value.

  Thus, the arrival time Tud from the upstream ultrasonic transducer 23 to the downstream ultrasonic transducer 24 and the arrival time Tdu from the downstream ultrasonic transducer 24 to the upstream ultrasonic transducer 23 are as follows. Thus, the flow rate Qm of the fluid flowing through the flow path is obtained. In this way, a highly accurate ultrasonic flow velocity / flow meter is realized.

  In the above embodiment, the crossing angle between the direction in which the fluid flows and the direction in which the ultrasonic wave propagates is set to 45 degrees. However, any angle that affects the propagation time of the ultrasonic wave may be used. It may be other than the vertical direction and may be parallel.

  Further, although the propagation time determination method has been described as single-shot measurement, it can be sufficiently applied to a sing-around method or the like.

(Embodiment 2)
In the first embodiment, the time difference for determining the effectiveness of the zero cross point is set to a predetermined time interval determined by the frequency of the drive waveform 38, but more effective is 0 of the predetermined time interval determined by the frequency of the drive waveform 38. Suppose that the distance is 4 times to 1.6 times.

  By doing so, malfunctions were significantly reduced. Since the determination of the zero cross has been made wider, it is possible to determine the zero cross point even if the received waveform is slightly deformed. Since the ultrasonic reception time can be determined from the first and second zero cross points, the operation of the time circuit 32 can be stopped after this time, so the ultrasonic flow velocity / flow meter is omitted. It can be a power configuration.

(Embodiment 3)
The time for determining the effectiveness of the zero crossing point was set as a predetermined gate time. The gate time was determined as follows.

  As described above, the ultrasonic wave propagation speed Vs was obtained using the ultrasonic wave arrival time, Tud and Tdu, and the gate time Tg was set.

Tud = Ld / (Vs + Vf · cos θ), Tdu = Ld / (Vs−Vf · cos θ)
It becomes. From these,
Vs + Vf · cos θ = Ld / Tud, Vs−Vf · cos θ = Ld / Tdu, and when these two sides are added,
2 * Vs = (Ld / Tud) + (Ld / Tdu) = Ld * [(1 / Tud) + (1 / Tdu)]
It becomes. Therefore,
Vs = (Ld / 2) * [(1 / Tud) + (1 / Tdu)]
Thus, the propagation velocity Vs of the ultrasonic wave propagating in the fluid is obtained. Since the distance L between the upstream and downstream ultrasonic transducers is known in advance, the gate time is
Tg = (L / Vs) −α.

  Α was appropriately set in consideration of the fact that the ultrasonic wave arrives faster at the maximum flow rate. Usually, it is about several to several tens of microseconds. Since the zero cross point is thus operated after the gate time Tg, it can be operated efficiently and a power saving configuration can be achieved.

(Embodiment 4)
The time for determining the effectiveness of the zero cross point is the time for the peak value of the received waveform to arrive. By doing so, since the amplitude of the received waveform is large, it is possible to operate stably.

  In the case of the received waveform shown in FIG. 3, since there are about six peak waves before the peak value of the received waveform, there are about 10 to 11 zero cross points. Since there are many zero cross points in this way, it is possible to determine the effectiveness of the zero cross point detected most quickly from these many zero cross points, so the ultrasonic arrival time can be accurately determined. Therefore, it is possible to realize an ultrasonic flow velocity / flow meter that operates stably.

(Embodiment 5)
The time for determining the effectiveness of the zero cross point was defined as the zero cross point when the received waveform was shaped into a packet and differentiated. Specifically, as shown in FIG.

  That is, in FIG. 4, a thin solid line 42 indicates an ultrasonic reception waveform, and a thin dotted line 43 indicates a waveform obtained by vertically inverting the reception waveform 42. A thick solid line 44 indicates an envelope between the reception waveform 42 and the inverted reception waveform 43.

  Next, as shown in FIG. 5, the envelope curve 44 was differentiated to obtain a broken line 45, and a zero cross point 46 was obtained. The zero-cross point 46 substantially coincides with the peak value time of the received waveform shown in the fourth embodiment. That is, the peak value time can be uniquely determined, and the time is stable and fixed. Therefore, an ultrasonic flow velocity / flow meter that operates stably can be realized.

(Embodiment 6)
The time for determining the effectiveness of the zero cross point was set to the zero cross point immediately after exceeding the predetermined reference level of the ultrasonic reception waveform. Specifically, as shown in FIG.

  47 indicates a received waveform of the ultrasonic wave, and a broken line 48 indicates a predetermined reference level (Vref). In the figure, the reference level 48 is set between the peaks V3 and V4 of the received waveform 47 of the ultrasonic wave. The next zero cross point 49 exceeding the set reference level 48 is set as a time for determining the effectiveness of the zero cross point.

  By selecting the peaks V3 and V4 having a relatively large amplitude and the first half of the received waveform in this way, the received waveform can be stabilized even if it is deformed due to the influence of fluid temperature or reflection. The time for determining the zero cross point can be obtained.

  In this case, there are 5 to 6 zero cross points before the zero cross point determination time. Since the propagation time of ultrasonic waves can be determined from these 5 to 6 zero cross points, an ultrasonic flow velocity / flow meter that operates stably can be realized.

(Embodiment 7)
In the above embodiment, the earliest detected zero cross point is determined as the ultrasonic propagation time. However, an average value from many zero cross points can be used as the ultrasonic propagation time. For example, when obtaining the propagation time of ultrasonic waves from a plurality of zero cross points, it is possible to realize ultrasonic flow velocity / flow rate measurement that is stable against noise.

  For example, it is stable even when the zero potential of the received waveform changes due to electromagnetic noise or the like. FIG. 7 shows the relationship between the received waveform of ultrasonic waves and the zero potential.

  In FIG. 7, 50 indicates a received waveform, a thick solid line 51 indicates a true zero potential, and a broken line 52 indicates a zero potential that fluctuates in the positive (+) direction due to some electromagnetic noise. In this case, the zero cross point 53 at the rising edge of the received waveform is slower than the true zero cross point.

  Also, the zero cross point 54 at the fall of the received waveform is earlier than the true zero cross point. For this reason, although the ultrasonic flow velocity / flow meter includes an error, by determining the average value as the propagation time of the ultrasonic wave, the accuracy is improved by offsetting fast and slow. Thus, by obtaining the propagation time of ultrasonic waves from a plurality of zero cross points, an ultrasonic flow velocity / flow meter resistant to electromagnetic noise can be realized.

  And the measurement result obtained with the measuring device of each said embodiment can be inputted into the host computer by the side of a fluid supply, and can be used as a fluid supply management system.

  For example, when the target fluid is gas, the integrated value for a predetermined period of a measuring device installed in each home is imported into a host computer using a network, or the integrated value for a predetermined period acquired individually by a meter reader is used. By inputting to the host computer, billing work can be processed in a batch, and gas leaks in each household can be monitored according to what is connected via the network.

  As described above, the ultrasonic flow velocity / flow meter according to the present invention determines the zero cross point immediately after ultrasonic propagation as the ultrasonic propagation time, so that a highly accurate ultrasonic flow velocity / flow meter can be realized. In addition, since the operation of the zero cross point can be limited to the minimum necessary time, a power saving configuration can be achieved. In addition, since the ultrasonic propagation time can be determined using a plurality of zero cross points, an ultrasonic flow velocity / flow meter resistant to electromagnetic noise can be realized. In addition, it can be applied to various measuring instruments for measuring the propagation time of ultrasonic waves.

Sectional drawing of the flow measurement apparatus in embodiment of this invention Block diagram (A) The figure which showed the drive waveform and received waveform of the measuring device, (b) The enlarged view of a received waveform The figure explaining the synthesis | combination of the ultrasonic reception waveform in other embodiment of this invention The figure explaining the synthesis | combination of the ultrasonic wave reception waveform in other embodiment of this invention. Ultrasonic wave reception waveform diagram according to still another embodiment of the present invention Ultrasonic wave reception waveform diagram according to still another embodiment of the present invention Cross section of a conventional measuring device

Explanation of symbols

21 Ultrasonic flow meter 22 Flow path 23 Upstream ultrasonic transducer 24 Downstream ultrasonic transducer 31 Drive circuit 33 Transmission switch SW
34 Receiving side switch SW
37 Detection circuit 38 Drive waveform 39 Received waveform

Claims (9)

A pair of ultrasonic transducers are arranged facing the upstream and downstream sides of the flow path through which the fluid flows, and one ultrasonic transducer is driven to transmit ultrasonic waves to the other ultrasonic transducer. In addition, a number of zero-cross memories are operated while sequentially determining the zero-cross memory values, and the validity of the zero-cross memory values is determined after a predetermined time, and the ultrasonic propagation time is determined from the effective zero-cross memory values. Fluid flow measurement device designed to perform calculations. The zero-cross memory is determined to be valid and operated only when the sequentially obtained zero-cross memory values are separated by a predetermined interval determined by the frequency at which the ultrasonic transducer is driven and within twice the predetermined interval. Item 2. The fluid flow measuring device according to Item 1. 2. The fluid flow measuring device according to claim 1, wherein the predetermined time for determining the validity of the zero-cross memory value is a predetermined gate time. 2. The fluid flow measuring device according to claim 1, wherein the predetermined time for determining the validity of the zero cross memory value is the time of the peak value of the received ultrasonic waveform. 2. The fluid flow measuring device according to claim 1, wherein the predetermined time for determining the validity of the zero cross memory value is a zero cross time when the received ultrasonic waveform is differentiated after being shaped into a packet. The fluid flow measuring device according to claim 1, wherein the predetermined time for determining the validity of the zero cross memory value is a zero cross time exceeding a predetermined reference level of the received ultrasonic waveform. 2. The fluid flow measuring device according to claim 1, comprising a plurality of zero cross memories. 8. The fluid flow measuring device according to claim 7, wherein an average propagation time during which the ultrasonic wave propagates is obtained from a plurality of zero cross memories. A fluid supply management system configured to input a measurement result obtained by the fluid flow measurement device according to claim 1 to a host computer on a fluid supply side.

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