JP3689977B2 - Ultrasonic current meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a means for improving the measurement accuracy of an ultrasonic flowmeter that measures the flow velocity of a gas or liquid using ultrasonic waves.
[0002]
[Prior art]
Hereinafter, a conventional ultrasonic velocity meter will be described with reference to the drawings. FIG. 10 is a block diagram showing the configuration of a conventional ultrasonic velocimeter. In the figure, 1 is a power source, 2 is a voltage conversion circuit for stepping up or down the power source 1, 3 is a measurement path through which a fluid flows, 4 is an ultrasonic transducer for transmission installed in the measurement path 3, and 5 is an ultrasonic wave for transmission. A transmission circuit for driving the transducer 4, a reception ultrasonic transducer 6 for receiving ultrasonic waves transmitted from the transmission ultrasonic transducer 4, and a reception ultrasonic transducer 7 using the output of the voltage conversion circuit 2 as a power source 6 is a receiving circuit that receives the output of 6 and 8 is a control unit that sends a transmission start signal to the transmitting circuit 5 and receives the output of the receiving circuit 7.
[0003]
The operation of the above configuration will be described. The transmission circuit 5 to which the transmission start signal is input from the control unit 8 outputs a pulse for a fixed time, and drives the transmission ultrasonic transducer 4. The ultrasonic wave transmitted from the ultrasonic transducer for transmission 4 propagates in the fluid to be measured, is received by the ultrasonic transducer for reception 6 after elapse of t seconds, and is received by the control unit 8 after reception determination by the reception circuit 7. Output as a signal. As shown in FIG. 11, the reception circuit 7 receives the amplifier 9 for receiving and amplifying the reception output of the ultrasonic transducer 6 for reception, and compares the output of the amplifier 9 with the reference voltage 10 to perform reception determination. The reception determination signal is output when the reception output of the reception ultrasonic transducer 6 reaches the reference voltage 10. The control unit 8 measures the time from when the transmission start signal is output to when the reception determination signal is input to the receiving circuit 7 to obtain the propagation time t. From this propagation time t, the flow velocity v of the fluid to be measured is obtained. Obtained by equation (1).
[0004]
Now, the effective distance in the flow direction between the ultrasonic transducers is L, the speed of sound is c, the flow velocity of the fluid to be measured is v, and the direction from the transmitting ultrasonic transducer 4 to the receiving ultrasonic transducer 6 is positive. When
v = (L / t) -c (1)
Further, the transmission ultrasonic transducer 4 and the reception ultrasonic transducer 6 are switched to measure the propagation time from the upstream to the downstream of the fluid to be measured, and from the downstream to the upstream, and the velocity v is expressed by the equation (2). There is also a way to ask for.
[0005]
Now, when the propagation time t1 from the upstream to the downstream, and the propagation time t2 from the downstream to the upstream,
v = L / 2 (1/1 / 1-1 / t2) (2)
According to this method, the flow velocity can be measured without being affected by the change in the sound velocity c, and thus it is widely used for measuring the flow velocity, the flow rate, the distance, and the like.
[0006]
The power supply 1 supplies the measurement circuit with a battery voltage, a voltage obtained by boosting a commercial power supply using a switching element, or a voltage transformed by a voltage conversion circuit 2 that steps down using a regulator.
[0007]
[Problems to be solved by the invention]
In such a conventional ultrasonic current meter, when measuring with high accuracy, for example, when measuring several mm / s, the measurement accuracy of t is required to be several ns, but the regulator of the voltage conversion circuit 2 It is difficult to obtain the target accuracy due to fluctuations in the voltage generated by the voltage, that is, ripple components or noise generated by the switching elements of the voltage conversion circuit 2.
[0008]
That is, when the distance between the transmission ultrasonic transducer 4 and the reception ultrasonic transducer 6 is about 100 mm and the drive voltage of the transmission ultrasonic transducer 4 is 5 v, The sensitivity to the receiving ultrasonic transducer 6 is about −80 to −50 dB. The reception output output from the reception ultrasonic transducer 6 has a waveform as shown in FIG. 12, and its level is about several mV. Since this received output is amplified several hundred times by the amplifier 9, if noise enters the input section of the amplifier 9, it is amplified several hundred times and a large error is generated.
[0009]
Further, when the ultrasonic reception frequency is 200 KHz and the amplitude is 3 V (pp), the output signal of the amplifier 9 is V = sin (ωt)
And the slope of the signal is
2 · 10 ⁶ · cos (ωt) [V / s]
It becomes. This signal and the reference voltage are compared to determine reception. In this case, the timing with the highest measurement accuracy is where the slope is maximum, and its value is 2 · 10 6 [V / s]. However, even if reception determination is performed at a level with the maximum inclination, an error of 5 ns will occur if the reference voltage compared with the output signal of the amplifier 9 fluctuates, for example, by 10 mV due to noise or a ripple component of the power supply. There was a problem.
[0010]
The present invention solves the above-described problems, and an object of the present invention is to provide an ultrasonic anemometer capable of measuring the flow velocity with high accuracy while avoiding the influence of power level fluctuation and noise.
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, when a capacitive element is connected to the output of the voltage conversion circuit that supplies power to the receiving circuit to smooth the output voltage and charge is accumulated, at least when the receiving circuit performs reception determination processing. This is an ultrasonic velocimeter in which the operation of the voltage conversion circuit is stopped and the receiving circuit is driven by the accumulated charge of the capacitive element. Thereby, when the reception circuit executes the reception determination process, the influence of voltage fluctuation and noise of the voltage conversion circuit can be avoided, and the flow velocity can be accurately measured.
[0012]
The present invention according to claim 2 relates to claim 1, wherein the operation of the voltage conversion circuit is stopped when the transmission start signal is output, and the receiving circuit is driven by the electric charge accumulated in the capacitive element. Ultrasonic anemometer. As a result, the voltage conversion circuit is stopped from the time when the ultrasonic wave is transmitted, and when the reception circuit determines reception, the voltage conversion circuit is not affected by voltage fluctuation and noise of the voltage conversion circuit, and the flow rate is highly accurate. Can be measured. In addition, since the amount of electricity consumed by the receiving circuit from the capacitive element can be reduced, the capacitance value of the capacitive element can be selected to be a small value.
[0013]
The present invention according to claim 3 relates to claim 1, wherein the voltage conversion circuit is operated and then stopped until a predetermined time elapses after the ultrasonic wave is transmitted and before reaching the receiving ultrasonic transducer. Ultrasonic anemometer. As a result, the amount of charge accumulated in the capacitive element is increased, and the reception circuit is driven only by the capacitive element at the time of reception determination, so the voltage change due to power consumption of the reception circuit is reduced and the flow rate is measured with high accuracy. be able to.
[0014]
According to the fourth aspect of the present invention, the voltage conversion circuit is operated and then stopped until a time slightly shorter than the ultrasonic propagation time measured last time after the ultrasonic wave is transmitted. An ultrasonic velocimeter according to claim 1. As a result, the charge accumulation in the capacitive element can be continued until just before the reception judgment in response to the change in the flow velocity, so that the charge accumulation amount of the capacitive element can be further increased, and only the capacitive element is received at the time of the reception judgment. Since the circuit is driven, the voltage change due to the power consumption of the receiving circuit can be further reduced and the flow velocity can be measured with higher accuracy.
[0015]
The present invention according to claim 5 detects ultrasonic waves at a level lower than the reception judgment level of the receiving circuit, and operates and stops the voltage conversion circuit up to that point, and then stops the ultrasonic current meter according to claim 1. It is. As a result, the charge accumulation in the capacitive element can be continued until immediately before the reception determination, so that the charge accumulation amount of the capacitive element can be increased to the limit, and the reception circuit is driven only by the capacitive element at the time of reception determination. The change in voltage due to the power consumption of the circuit can be further reduced, and the flow velocity can be measured with higher accuracy.
[0016]
The present invention according to claim 6 is the ultrasonic anemometer according to claim 1 in which the capacitive element and the receiving circuit are not branched to any other place. As a result, all charges accumulated in the capacitive element are supplied to the receiving circuit to reduce voltage fluctuations, and noise can be prevented from detouring from other components, and the flow velocity can be measured with high accuracy.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention according to claim 1, the voltage conversion circuit means means for boosting the voltage of a power source such as a battery with little voltage fluctuation and noise and supplying the voltage to the receiving circuit. In the embodiment, a chopper circuit is used. It may be a means. Capacitive element means an element that accumulates charge. It is connected to the output of the voltage conversion circuit to smooth the output voltage, accumulate the charge, and receive the accumulated charge after stopping the operation of the voltage conversion circuit. A power source for driving the circuit is used. Therefore, the capacitance value of the capacitive element can be determined in accordance with the actual condition so as to be large enough to drive the receiving circuit. In the embodiment, a capacitor is used. The power supply control circuit controls the operation of the voltage conversion circuit to control operation start or operation stop.
[0018]
In addition, by making the transmission start signal a rectangular wave that rises at the start of transmission and falls at a timing at which the receiving means can sufficiently complete the reception detection process, it is possible to instruct the start of transmission at the rise and voltage conversion at the fall The circuit can be instructed to restart. The transmission circuit drives the ultrasonic transducer for transmission for a predetermined time from the time when the transmission start signal is input, and transmits the ultrasonic wave having the predetermined time width. The reception circuit inputs the reception output of the reception ultrasonic transducer, amplifies it by an amplifier, compares it with a reference voltage value by a comparator, and outputs a reception detection signal when the reference value is reached. The control unit is realized by program processing by a microcomputer.
[0019]
In the present invention according to claim 2, the power supply control circuit stops the operation of the voltage conversion circuit when the transmission start signal is input from the control unit, and drives the receiving circuit only by the discharge from the capacitive element.
[0020]
In the present invention according to claim 3, a timer is provided in the power supply control circuit to measure a certain time after the start of transmission, and the operation of the voltage conversion circuit is stopped at the time up. This fixed time is set to be shorter than the propagation time assuming the propagation time for the ultrasonic wave to reach the receiving ultrasonic transducer. These processes can be realized by microcomputer program processing.
[0021]
In the present invention according to claim 4, a memory is provided in the power supply control circuit to store the previously measured propagation time, and a clock is provided to measure the elapsed time from the start of transmission. The operation of the voltage conversion circuit is stopped when an elapsed time that is slightly shorter than the previous propagation time is reached. These processes can be realized by microcomputer program processing.
[0022]
In the present invention according to claim 5, reception detection is provided in the power supply control circuit, the arrival of ultrasonic waves is detected at a level lower than the reception detection level of the reception circuit, and the operation of the voltage conversion circuit is stopped at that timing.
[0023]
In the present invention according to claim 6, the power supply line from the capacitive element to the receiving circuit is not branched to another circuit.
[0024]
Examples will be described below.
[0025]
【Example】
(Example 1)
Hereinafter, an ultrasonic current meter according to a first embodiment of the present invention will be described with reference to the drawings.
[0026]
FIG. 1 is a block diagram showing the configuration of this embodiment. In addition, the same number is attached | subjected to the same component as FIG. 10, and description is abbreviate | omitted. In the figure, the ultrasonic transducer for transmission 4 is driven by a transmission circuit 5 that receives a transmission start signal from the control unit 8, and outputs ultrasonic waves to the measurement path 3. The reception ultrasonic transducer 6 converts the received ultrasonic wave into an electric signal and outputs it as a reception output to the reception circuit 7. The reception circuit 7 receives the reception output and outputs a reception determination signal to the control unit 8. Reference numeral 1 denotes a battery-made power supply, 2 a chopper circuit, a voltage conversion circuit that boosts and outputs the voltage of the power supply 1, 12 a power supply control circuit that controls the operation of the voltage conversion circuit 2, and 13 a voltage conversion circuit 2 is a capacitive element composed of a capacitor that accumulates electric charges with an output voltage of 2.
[0027]
FIG. 2 is a block diagram showing the configuration of the receiving circuit 7 in this embodiment, which is the same as the configuration shown in FIG. As shown in the figure, an amplifier 9 that amplifies the reception output, a comparator 11 that compares the output of the amplifier 9 with the reference voltage 10 and performs reception determination, and the output of the ultrasonic transducer for reception is the reference voltage. When the value is reached, a reception determination signal is output.
[0028]
The operation of the above configuration will be described. FIG. 3 is a timing chart showing the operation of this embodiment. The transmission circuit 5 to which the transmission start signal is input from the control unit 8 outputs a pulse for a predetermined time, and drives the transmission ultrasonic transducer 4. The ultrasonic wave transmitted from the transmitting ultrasonic transducer 4 propagates through the fluid to be measured and is received by the receiving ultrasonic transducer 6 after t seconds. The reception circuit 7 amplifies the reception output of the reception ultrasonic transducer 6 by the amplifier 9, compares it with the reference voltage value 10 by the comparator 11, and outputs a reception determination signal to the control unit 8 and the power supply control circuit 12. The control unit 8 measures the time from when the transmission start signal is output until the reception determination signal is received to obtain the propagation time t, and obtains the flow velocity using the equation (1).
[0029]
In the above operation, the power supply control circuit 12 operates the voltage conversion circuit 2 until the transmission start signal is input from the control unit 8, accumulates electric power in the capacitive element 13, and inputs the transmission start signal from the control unit 8. The operation of the voltage conversion circuit 2 is stopped. Next, the control unit 8 of the transmission start signal and inputs the reception determination signal from the receiving circuit 7 is turned off, the power supply control circuit 12 in response to it restarts the operation of the voltage converter circuit 2, the power to the capacitive element 13 To prepare for the next measurement. Since the current flows from the capacitive element 13 to the receiving circuit 7 during the stop period of the voltage conversion circuit 2, the output voltage of the capacitive element 13 slightly decreases during this period, but the capacity of the capacitive element 13 is reduced to the receiving circuit 7. By setting it sufficiently large compared to the current consumption, the voltage drop hardly affects the measurement accuracy.
[0030]
As described above, since the voltage conversion circuit 2 is stopped at the time of ultrasonic reception, no noise or ripple is generated. Further, when the voltage conversion circuit 2 is stopped, the power discharge destination from the capacitive element 13 is only the reception circuit 7, so that the change in the output voltage of the capacitive element 13 can be reduced and the transmission circuit 5 or the control unit 8. Can be prevented from propagating through the power line.
[0031]
(Example 2)
Hereinafter, Example 2 of the ultrasonic velocity meter of the present invention will be described with reference to the drawings.
[0032]
FIG. 4 is a block diagram showing the configuration of the power supply control circuit 12 in this embodiment.
[0033]
The difference between the present embodiment and the first embodiment is that the power supply control circuit 12 includes a timer 14 and the voltage conversion circuit 2 is stopped after a predetermined time has elapsed after the transmission start signal is input from the control unit 8. It is in.
[0034]
The operation of the above configuration will be described. FIG. 5 is a timing chart showing the operation of this embodiment. As shown in the figure, the transmission circuit 5 that has received the transmission start signal from the control unit 8 outputs a pulse for a certain period of time to drive the ultrasonic transducer 4 for transmission, and receives the transmission start signal from the control unit 8. The power supply control circuit 12 thus started starts the operation of the timer 14 and continues the operation of the voltage conversion circuit 2. Next, when the timer 14 counts a certain time, the operation of the voltage conversion circuit 2 is stopped at that time. The set time of the timer 14 is set slightly shorter than the shortest ultrasonic propagation time between the transmitting ultrasonic transducer 4 and the receiving ultrasonic transducer 6. Therefore, the voltage conversion circuit 2 can be reliably stopped before the receiving circuit 7 receives the ultrasonic wave, and the operation stop time of the power supply conversion circuit 2 can be shortened.
[0035]
As described above, according to the present embodiment, the operation of the voltage conversion circuit 2 is continued until a time just before the reception circuit 7 receives the ultrasonic wave, whereby the voltage drop of the capacitive element 13 can be reduced and the reception can be performed. Since the operation of the voltage conversion circuit 2 is stopped at the time when the circuit 7 receives the ultrasonic wave, it is possible to prevent the influence of noise and voltage fluctuation, and to measure with higher accuracy.
[0036]
(Example 3)
Hereinafter, Example 3 of the ultrasonic velocity meter of the present invention will be described with reference to the drawings.
[0037]
FIG. 6 is a block diagram showing the configuration of the power supply control circuit 12 in this embodiment.
[0038]
In the figure, reference numeral 15 denotes a memory that receives and stores measurement data from the control unit 8 after measurement, 16 denotes a clock that receives a transmission start signal from the control unit 8 and measures the elapsed time thereafter, and 17 denotes a memory 15 and a clock 16. Is a comparator that outputs the result to the voltage conversion circuit 2. This embodiment is different from the second embodiment in that the time for which the operation of the voltage conversion circuit 2 is continued from the measurement start time is determined based on the previous measurement result.
[0039]
The operation of the above configuration will be described. FIG. 7 is a timing chart showing the operation of this embodiment. The memory 15 stores the previous measurement data. As shown in the figure, the transmission circuit 5 that has received the transmission start signal from the control unit 8 outputs a pulse for a certain period of time to drive the ultrasonic transducer 4 for transmission, and receives the transmission start signal from the control unit 8. The power supply control circuit 12 starts the operation of the timepiece 16 and continues the operation of the voltage conversion circuit 2. Next, the comparator 17 always compares the elapsed time of the clock 16 with the previous measurement result stored in the memory 15, that is, the ultrasonic propagation time measured last time, and is slightly shorter than the previous measurement result. For example, an output for stopping the voltage conversion circuit 2 is generated 100 μs faster. In this case, by setting the measurement interval short with respect to the rate at which the flow rate changes, the timing for stopping the voltage conversion circuit 2 changes according to the flow rate, and the reception circuit 7 receives the signal before the voltage conversion circuit 2 stops. No output is received.
[0040]
As described above, according to the present embodiment, since the time for continuing the operation of the voltage conversion circuit 2 after the start of transmission is set based on the previous measurement data, the duration can be set in accordance with the change in the flow velocity. It can be measured with high accuracy.
[0041]
(Example 4)
Hereinafter, Example 4 of the ultrasonic velocity meter of the present invention will be described with reference to the drawings.
[0042]
FIG. 8 is a block diagram showing the configuration of the power supply control circuit 12 in this embodiment. In the figure, the power supply control circuit 12 in this embodiment includes an amplifier 18 that amplifies a reception output input via the reception circuit 7, a second reference voltage 19, and an output voltage of the amplifier 18 as a second reference voltage 19. And a comparator 20 that makes a reception determination in comparison with the above, and detects the timing immediately before the reception circuit 7 makes a reception determination to stop the operation of the voltage conversion circuit 2.
[0043]
The operation of the above configuration will be described. FIG. 9 is a timing chart showing the operation of this embodiment. As shown in the figure, the reception output has a waveform in which the amplitude gradually increases. By setting the second reference voltage lower than the reference voltage 10 in the reception circuit 7, the power supply control circuit 12 causes the reception circuit 7 to The reception determination is performed slightly faster than the reception determination signal is output, and the operation of the voltage conversion circuit 2 is stopped at that timing. In this operation, since the voltage conversion circuit 2 is surely stopped at the initial stage when the reception output is actually input, the voltage conversion circuit 2 does not operate when the reception circuit 7 determines reception. For this reason, even when the change in the flow rate is earlier than the measurement interval, the timing for stopping the voltage conversion circuit 2 can always be changed according to the flow rate, so that a wide range of flow rates can be accurately measured with a simple configuration. Can do. Needless to say, the set value of the second reference voltage 19 is not necessarily set lower than the reference voltage 10 due to the gain of the amplifier 18.
[0044]
As is apparent from the description of the following, according to the embodiments of the present invention, the following effects can be obtained.
[0045]
Since at least the reception circuit performs reception determination processing by the power supply control circuit, the operation of the voltage conversion circuit is stopped. Therefore, noise and ripple generated by the voltage conversion circuit do not occur when determining the reception timing, and the measurement error is reduced. And an ultrasonic anemometer with high accuracy can be realized.
[0046]
Further, the operation of the voltage conversion circuit is stopped when a certain time has elapsed from the start of transmission, and the certain time is shorter than the shortest ultrasonic propagation time between the transmitting ultrasonic transducer and the receiving ultrasonic transducer. Since it is set slightly shorter, the time from when the voltage conversion circuit is stopped to when the ultrasonic wave is received can be set shorter, and the power supplied from the capacitive element to the receiving circuit can be reduced. The drop in the voltage supplied to the circuit can be reduced, and therefore a more accurate ultrasonic current meter can be realized. In addition, the capacitance value of the capacitive element can be selected to be small.
[0047]
Also, memorize the propagation time measured last time, and stop the voltage conversion circuit when the time slightly shorter than the propagation time of the previous measurement has elapsed from the start of transmission, so that the measurement interval changes the flow rate. Since the timing for stopping the voltage conversion circuit can be changed according to the flow velocity, a wider range of flow velocity can be measured with high accuracy.
[0048]
In addition, the power supply control circuit receives the reception output from the reception ultrasonic transducer, performs reception determination earlier than the reception circuit outputs the reception determination signal, stops the voltage conversion circuit at that timing, and receives the signal. Since the voltage conversion circuit is surely stopped at the initial stage when the output is input, even when the change in the flow rate is earlier than the measurement interval, the timing for stopping the voltage conversion circuit can be changed according to the flow rate, A wide range of flow velocities can be accurately measured with a simple configuration.
[0049]
In addition, since the connection between the capacitive element and the receiving circuit is configured by a path that does not branch to the other, the power from the capacitive element can be changed without changing the circuit operation that affects the measurement when the voltage conversion circuit is stopped. Since emission can be minimized, the capacitance of the capacitive element can be reduced. In addition, it is possible to realize a high-accuracy ultrasonic current meter that is resistant to noise and can be removed from noise transmitted from the transmission circuit or the control unit through the power supply line.
[0050]
【The invention's effect】
As is apparent from the above description, the present invention stops the operation of the voltage conversion circuit when at least the reception circuit performs reception determination processing by the power supply control circuit. It does not occur at the time of determination, the measurement error can be reduced, and an ultrasonic velocimeter with high accuracy can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a first embodiment of an ultrasonic current meter according to the present invention. FIG. 2 is a block diagram showing a configuration of a receiving circuit in the first embodiment. FIG. 3 shows an operation of the first embodiment. FIG. 4 is a block diagram showing the configuration of a power supply control circuit in the second embodiment of the ultrasonic current meter of the present invention. FIG. 5 is a timing chart showing the operation of the second embodiment. FIG. 7 is a timing chart showing the operation of the third embodiment of the current meter. FIG. 8 is a timing chart showing the operation of the third embodiment. FIG. FIG. 9 is a timing chart showing the operation of the fourth embodiment. FIG. 10 is a block diagram showing the structure of a conventional ultrasonic velocimeter. FIG. 11 is a block diagram showing the structure of a receiving circuit in the velocimeter. Figure 【Figure Waveform diagram showing a reception output of the 2] for receiving ultrasonic transducers [Description of symbols]
1 Battery (Power)
DESCRIPTION OF SYMBOLS 2 Voltage conversion circuit 3 Measurement path | route 4 Transmission ultrasonic transducer | transmission 5 Transmission circuit 6 Reception ultrasonic transducer | vibrator 7 Reception circuit 8 Control part 9 Amplifier 10 Reference voltage 11 Comparator 12 Power supply control circuit 13 Capacitive element 14 Timer 15 Memory 16 Clock 17 Comparator 18 Amplifier 19 Second Reference Voltage 20 Comparator

Claims (6)

  A power supply, a voltage conversion circuit that converts the output voltage of the power supply, a capacitive element that accumulates charges while smoothing the output voltage of the voltage conversion circuit, an ultrasonic transducer for transmission that transmits ultrasonic waves, A transmission circuit that drives the ultrasonic transducer for transmission; an ultrasonic transducer for reception that receives ultrasonic waves from the ultrasonic transducer for transmission via a measurement path and outputs a reception output; and the voltage An output of the conversion circuit as a power supply, a reception circuit that inputs a reception output of the ultrasonic transducer for reception and outputs a reception determination signal by a reception determination process; a power supply control circuit that controls the operation of the voltage conversion circuit; The propagation time for the ultrasonic wave output from the transmitting ultrasonic transducer to reach the receiving ultrasonic transducer is measured based on the elapsed time from the output time of the transmission start signal to the input time of the reception determination signal. And its propagation And a control unit that controls the overall operation of the flow rate of the fluid in the measurement path according to the interval and the path length of the measurement path, and the power supply control circuit inputs the transmission start signal from the control unit. An ultrasonic velocimeter in which the operation of the voltage conversion circuit is stopped and the receiving circuit is driven by the accumulated charge of the capacitive element at least when the receiving circuit executes reception determination processing.   The ultrasonic current meter according to claim 1, wherein the power supply control circuit controls the operation of the voltage conversion circuit to stop when a transmission start signal is input from the control unit.   The ultrasonic current meter according to claim 1, wherein the power supply control circuit controls the operation of the voltage conversion circuit to stop when a predetermined time has elapsed since the transmission start signal was input from the control unit.   The power supply control circuit stores the previously measured propagation time, and stops the operation of the voltage conversion circuit when a time slightly shorter than the stored propagation time has elapsed after the control unit outputs the transmission start signal. The ultrasonic velocimeter of Claim 1 controlled to. Power supply control circuit, receiving determined by a lower level than the receiving circuit receiving level for determining received power of the receiving ultrasonic transducer, according to claim 1, wherein the control to stop the operation of the voltage conversion circuit at the time acoustic Doppler Current Profiler of.   The ultrasonic anemometer according to any one of claims 1 to 5, wherein the ultrasonic current meter is configured by a path that does not branch between the capacitive element and the receiving circuit.

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