JPH09325059A - Ultrasonic flow speed meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure flow speed of a fluid with precision. SOLUTION: Relating to a propagation time in which an ultrasonic wave outputted from a transmission ultrasonic wave vibrator 4 reaches a reception ultrasonic wave vibrator 6, when the flow speed of a fluid at a measurement path 3 is measured based on a propagation time and a path length of the measurement path 3, based on the lapse time starting from when a control part 8 outputs a transmission start signal to a transmission circuit 5 till when a reception circuit 7 receives/judges and outputs a reception judgement signal, a capacitive element 13 is which an electric charge is accumulated while the output of a voltage conversion circuit 2 supplied to the reception circuit 7 while the voltage of a battery 1 is converted is smoothed and a power source control circuit 12 which controls the action of the voltage conversion circuit 2 are provided, and, the power source control circuit 12, after the transmission start signal is outputted, stops the action of the voltage conversion circuit 2 at least when the reception circuit 7 performs reception judgement, so that, the reception circuit 7 can be driven only with an accumulated electric charge of the capacitive element 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to means for improving the measurement accuracy of an ultrasonic velocity meter that measures the flow velocity of gas or liquid using ultrasonic waves.

[0002]

2. Description of the Related Art A conventional ultrasonic velocity meter will be described below with reference to the drawings. FIG. 10 is a block diagram showing the configuration of a conventional ultrasonic velocity meter. In the figure, 1 is a power supply, 2 is a voltage conversion circuit for stepping up or down the power supply 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 that drives the oscillator 4, a reception ultrasonic oscillator 6 that receives the ultrasonic waves transmitted from the transmission ultrasonic oscillator 4, and a reception ultrasonic oscillator 7 that uses the output of the voltage conversion circuit 2 as a power source. A receiving circuit 6 receives the output of 6 and a control unit 8 receives the output of the receiving circuit 7 by sending a transmission start signal to the transmitting circuit 5.

The operation of the above configuration will be described. The transmission circuit 5 that receives the transmission start signal from the control unit 8 outputs a pulse for a certain period of time to drive the transmission ultrasonic transducer 4.
The ultrasonic wave transmitted from the transmitting ultrasonic transducer 4 propagates through the fluid to be measured, is received by the receiving ultrasonic transducer 6 after t seconds have passed, and is received by the control circuit 8 after the receiving circuit 7 makes the receiving judgment. It is output as a signal. As shown in FIG. 11, the receiving circuit 7 compares the output of the receiving ultrasonic transducer 6 with the amplifier 9 that amplifies the received output and compares the output of the amplifier 9 with the reference voltage 10 to perform reception determination. And a 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 the time when the transmission start signal is output to the time when the reception determination signal of the receiving circuit 7 is input to obtain the propagation time t, and from this propagation time t, the flow velocity v of the fluid to be measured is calculated. It is calculated by the equation (1).

Now, the effective distance in the flow direction between the ultrasonic transducers is L, the sound velocity 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 When it is positive, v = (L / t) −c (1) Further, the ultrasonic transducer 4 for transmission and the ultrasonic transducer 6 for reception are switched to change the fluid to be measured. There is also a method in which the propagation time from upstream to downstream and from downstream to upstream are measured, and the velocity v is calculated by the equation (2).

Now, assuming that the propagation time from upstream to downstream is t1 and the propagation time from downstream to upstream is t2, v = L / 2. (1 / t1-1 / t2) .... (2) According to this method, since the flow velocity can be measured without being affected by the change in the sound velocity c, it is widely used for measuring the flow velocity, the flow rate, the distance and the like.

The power supply 1 supplies to the measurement circuit the voltage of the battery, the voltage obtained by boosting the commercial power supply using a switching element, or the voltage transformed by the voltage conversion circuit 2 that steps down the voltage using a regulator.

[0007]

In such a conventional ultrasonic velocity meter, when performing highly accurate measurement, for example, when measuring several mm / s, the measurement accuracy of t requires several ns. However, it is difficult to obtain the target accuracy due to the fluctuation of the voltage generated by the regulator of the voltage conversion circuit 2, that is, the ripple component or the noise generated by the switching element of the voltage conversion circuit 2.

That is, when the distance between the transmitting ultrasonic transducer 4 and the receiving ultrasonic transducer 6 is about 100 mm and the driving voltage of the transmitting ultrasonic transducer 4 is 5 v, a general transmitting ultrasonic vibration is generated. The sensitivity between the child 4 and the receiving ultrasonic transducer 6 is about -80 to -50 dB. Further, 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 the received output is amplified by the amplifier 9 by several hundred times, if noise enters the input part of the amplifier 9, it is amplified by several hundred times and a large error occurs.

Further, the reception frequency of ultrasonic waves is 200 KH.
When z and the amplitude are 3V (pp), the output signal of the amplifier 9 is V = sin (ωt), and the inclination of the signal is 2 · 10 ⁶ · cos (ωt) [V / s]. Reception judgment is performed by comparing this signal with a reference voltage. In this case, the timing at which the measurement accuracy is highest is where the slope is maximum, and the value is 2.10 ⁶ [V /
s]. However, even if the reception determination is performed at the maximum inclination level, the reference voltage to be compared with the output signal of the amplifier 9 may be, for example, 1 due to noise or ripple component of the power supply.
There was a problem that an error of 5 ns would occur when the fluctuation was 0 mV.

The present invention solves the above problems, and an object of the present invention is to provide an ultrasonic velocity meter capable of measuring the flow velocity with high accuracy while avoiding the influence of the level fluctuation of the power supply and noise.

[0011]

According to a first aspect of the present invention, a capacitive element is connected to the output of a voltage conversion circuit that supplies power to a receiving circuit to smooth the output voltage and accumulate electric charge. This is an ultrasonic velocity meter in which the operation of the voltage conversion circuit is stopped when the reception circuit performs the reception determination process, and the reception circuit is driven by the electric charge accumulated in the capacitive element. As a result, when the reception circuit executes the reception determination process, it is possible to avoid the influence of voltage fluctuation and noise of the voltage conversion circuit, and it is possible to accurately measure the flow velocity.

According to a second aspect of the present invention, 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. It is an ultrasonic velocity meter according to 1. As a result, the voltage conversion circuit is stopped from the time when the ultrasonic wave is transmitted, and when the receiving circuit determines reception, it is not affected by the voltage fluctuation and noise of the voltage conversion circuit when the voltage conversion circuit is in operation, and the flow velocity is highly accurate. Can be measured. Also,
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.

According to a third aspect of the present invention, the voltage conversion circuit is operated and then stopped until a predetermined time elapses before the ultrasonic wave is transmitted to the receiving ultrasonic vibrator. It is an ultrasonic velocity meter according to 1. As a result, the amount of charge accumulated in the capacitive element is increased, and the receiving circuit is driven only by the capacitive element at the time of reception determination, so that the voltage change due to the power consumption of the receiving circuit is reduced and the flow velocity is measured with high accuracy. be able to.

In the present invention according to claim 4, the voltage conversion circuit is operated and then stopped until a time slightly shorter than the propagation time of the ultrasonic wave measured last time after the ultrasonic wave is transmitted. The ultrasonic velocity meter according to claim 1 configured as described above. This allows the charge accumulation in the capacitive element to be continued until just before the reception determination 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 can receive the reception determination. 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.

According to a fifth aspect of the present invention, the ultrasonic wave is detected at a level lower than the reception determination level of the receiving circuit, and the voltage converting circuit is operated and stopped until that time. Sonic velocity meter. As a result, since the charge accumulation in the capacitive element can be continued until just before the reception judgment, the charge accumulation amount of the capacitive element can be maximized, and the reception circuit is driven only by the capacitive element when the reception judgment is made. It is possible to further reduce the voltage change due to the power consumption of the circuit and measure the flow velocity with higher accuracy.

The present invention according to claim 6 is the ultrasonic velocity meter according to claim 1, wherein the capacitive element and the receiving circuit are not branched. This makes it possible to supply all the accumulated charges of the capacitive element to the receiving circuit to reduce voltage fluctuations, prevent noise from detouring from other components, and measure the flow velocity with high accuracy.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention according to claim 1, the voltage conversion circuit means a means for boosting the voltage of a power source such as a battery having less voltage fluctuation and noise and supplying the voltage to a receiving circuit. Although a chopper circuit is used, other means may be used. Also, a capacitive element means an element that accumulates electric charge, connects to the output of the voltage conversion circuit to smooth the output voltage, accumulates electric charge, stops the operation of the voltage conversion circuit, and then receives the accumulated electric charge. It is used as a power supply to drive the circuit. Therefore, the capacitance value of the capacitive element can be appropriately determined to be large enough to drive the receiving circuit. A capacitor is used in the embodiment. In addition, the power supply control circuit controls the operation of the voltage conversion circuit to control the start or stop of the operation.

Further, by setting the transmission start signal to be a rectangular wave which rises at the start of transmission and falls at the timing when the receiving means can sufficiently complete the reception detection processing, the start of transmission can be instructed at the rise and the fall thereof. Can instruct to restart the voltage conversion circuit. 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 ultrasonic transducer for reception, 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. Further, the control unit is realized by program processing by a microcomputer.

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 reception circuit only by discharging from the capacitive element. .

In the present invention according to claim 3, a timer is provided in the power supply control circuit to measure a fixed time after the start of transmission, and the operation of the voltage conversion circuit is stopped when the time is up. This fixed time is set to be shorter than the propagation time assuming the propagation time of the ultrasonic waves to reach the ultrasonic transducer for reception. These processes can be realized by a microcomputer program process.

In the present invention according to claim 4, a memory is provided in the power supply control circuit to store the propagation time measured last time, a clock is provided to measure the elapsed time from the start of transmission, and the elapsed time is calculated by the comparing means. The operation of the voltage conversion circuit is stopped when an elapsed time slightly shorter than the previous propagation time is reached as compared with the previous propagation time. These processes can be realized by a microcomputer program process.

In the present invention according to claim 5, the power supply control circuit is provided with reception detection, 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. .

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.

Examples will be described below.

[0025]

【Example】

(Embodiment 1) Hereinafter, Embodiment 1 of the ultrasonic velocity meter of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of this embodiment. In addition, the same components as those in FIG. In the figure, the transmission ultrasonic transducer 4 is driven by the transmission circuit 5 which receives a transmission start signal from the control unit 8 and outputs ultrasonic waves to the measurement path 3. The receiving ultrasonic transducer 6 converts the received ultrasonic wave into an electric signal and outputs it as a reception output to the receiving circuit 7. Receiver circuit 7
Receives the reception output and outputs a reception determination signal to the control unit 8. Reference numeral 1 is a power supply composed of a battery, 2 is a chopper circuit, and a voltage conversion circuit for boosting the voltage of the power supply 1 and outputting the boosted voltage,
12 is a power supply control circuit for controlling the operation of the voltage conversion circuit 2,
Reference numeral 13 is a capacitive element composed of a capacitor for accumulating charges according to the output voltage of the voltage conversion circuit 2.

FIG. 2 is a block diagram showing the structure of the receiving circuit 7 in this embodiment, which is the same as the structure shown in FIG. As shown in the figure, an amplifier 9 for amplifying the received output
And a comparator 11 that compares the output of the amplifier 9 with the reference voltage 10 to perform reception determination, and outputs a reception determination signal when the output of the ultrasonic transducer for reception reaches the reference voltage value.

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 that receives the transmission start signal from the control unit 8 outputs a pulse for a certain period of time to drive the transmission ultrasonic transducer 4. The ultrasonic wave transmitted from the transmitting ultrasonic transducer 4 propagates in 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 the output of the transmission start signal to the reception of the reception determination signal, obtains the propagation time t, and obtains the flow velocity using the equation (1).

In the above operation, the power supply control circuit 12
The voltage conversion circuit 2 is operated until the transmission start signal is input from the control unit 8, electric power is accumulated in the capacitive element 13, and the operation of the voltage conversion circuit 2 is stopped when the transmission start signal is input from the control unit 8. Next, when the control unit 8 inputs the reception determination signal from the reception circuit 7, the transmission start signal is turned off, and in response to this, the power supply control circuit 12 restarts the operation of the voltage conversion circuit 2 to supply power to the capacitive element 13. Supply and prepare for the next measurement. Even when the voltage conversion circuit 2 is stopped, the capacitive element 1
Since a current flows from 3 to the receiving circuit 7, the output voltage of the capacitive element 13 slightly drops during that time.
By setting the capacitance of 3 to be sufficiently larger than the current consumption of the receiving circuit 7, the drop in voltage hardly affects the measurement accuracy.

As described above, since the voltage conversion circuit 2 is stopped at the time of ultrasonic wave reception, noise or ripple is not generated. Further, when the voltage conversion circuit 2 is stopped, the electric power is discharged from the capacitive element 13 to the receiving circuit 7 only, so that the change in the output voltage of the capacitive element 13 can be reduced and the transmitting circuit 5 or the control unit 8 can be used. Can be prevented from propagating through the power supply line.

(Second Embodiment) A second embodiment of the ultrasonic velocity meter of the present invention will be described below with reference to the drawings.

FIG. 4 shows the power supply control circuit 12 in this embodiment.
FIG. 3 is a block diagram showing the configuration of FIG. The present embodiment is different from the first embodiment in that the power supply control circuit 12 includes a timer 14 and the voltage conversion circuit 2 is stopped after a lapse of a certain time after the transmission start signal is input from the control unit 8. It is in.

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 receives 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 also inputs the transmission start signal from the control unit 8. Then, the power supply control circuit 12 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 to be slightly shorter than the shortest ultrasonic wave 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 reception circuit 7 receives the ultrasonic wave, and the operation stop time of the power supply conversion circuit 2 can be shortened.

As described above, according to this embodiment, the voltage drop of the capacitive element 13 can be reduced by continuing the operation of the voltage conversion circuit 2 until just before the reception circuit 7 receives the ultrasonic wave. Moreover, since the operation of the voltage conversion circuit 2 is stopped at the time when the reception circuit 7 receives the ultrasonic wave, the influence of noise and voltage fluctuation can be prevented, and the measurement can be performed with higher accuracy.

(Embodiment 3) Hereinafter, Embodiment 3 of the ultrasonic velocity meter of the present invention will be described with reference to the drawings.

FIG. 6 shows the power supply control circuit 12 in this embodiment.
FIG. 3 is a block diagram showing the configuration of FIG. In the figure, 15 is a memory for receiving and storing measured data from the control unit 8 after measurement, 16 is a clock for inputting a transmission start signal of the control unit 8 and measuring elapsed time thereafter, 17 is a memory 15 and a clock 1.
6 is a comparator which outputs the result to the voltage conversion circuit 2. The present embodiment is different from the second embodiment in that the time for continuing the operation of the voltage conversion circuit 2 from the measurement start time is determined based on the previous measurement result.

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 receives 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 also inputs the transmission start signal from the control unit 8. The power supply control circuit 12 starts the operation of the clock 16 and continues the operation of the voltage conversion circuit 2. Next, the comparator 17 constantly compares the elapsed time of the clock 16 with the previous measurement result stored in the memory 15, that is, the previously measured ultrasonic wave propagation time, and the time 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 to be short with respect to the rate at which the flow velocity changes, the timing for stopping the voltage conversion circuit 2 changes according to the flow velocity, and the reception circuit 7 receives the voltage before the voltage conversion circuit 2 stops. It receives no output.

As described above, according to this embodiment, since the time for which the operation of the voltage conversion circuit 2 is continued after the start of transmission is set based on the previous measurement data, the continuation time is set according to the change in the flow velocity. It is possible to measure with higher accuracy.

(Embodiment 4) Hereinafter, Embodiment 4 of the ultrasonic velocity meter of the present invention will be described with reference to the drawings.

FIG. 8 shows the power supply control circuit 12 in this embodiment.
FIG. 3 is a block diagram showing the configuration of FIG. In the figure, the power supply control circuit 12 in this embodiment has an amplifier 18 that amplifies a reception output that is input via the reception circuit 7, a second reference voltage 19, and an output voltage of the amplifier 18 that is a second reference voltage 19. And a reception circuit 7 for determining reception by comparing
Is detecting the timing immediately before the reception determination is performed to stop the operation of the voltage conversion circuit 2.

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 operate. 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, the voltage conversion circuit 2 is surely stopped at the initial stage when the reception output is actually input, so that the voltage conversion circuit 2 does not operate when the reception circuit 7 is receiving. For this reason, even if the change in the flow velocity is earlier than the measurement interval, the timing for stopping the voltage conversion circuit 2 can always be changed according to the flow velocity, so that a wide range of flow velocity can be accurately measured with a simple configuration. You can Needless to say, the set value of the second reference voltage 19 is not always set lower than the reference voltage 10 due to the gain of the amplifier 18.

[0042]

As is apparent from the above description, according to the present invention, the operation of the voltage conversion circuit is stopped at least when the power supply control circuit performs the reception determination processing by the reception circuit. Ripple does not occur when determining the reception timing, the measurement error can be reduced, and a highly accurate ultrasonic velocity meter can be realized.

The operation of the voltage conversion circuit is stopped when a certain time has elapsed from the start of transmission, and the shortest ultrasonic wave between the ultrasonic transducer for transmission and the ultrasonic transducer for reception is kept for the certain time. Since it is set slightly shorter than the propagation time,
Since the time from stopping the voltage conversion circuit to receiving ultrasonic waves can be set short and the electric power supplied from the capacitive element to the receiving circuit can be reduced, the voltage supplied to the receiving circuit can be reduced. Can be made smaller, and thus a more accurate ultrasonic velocity meter can be realized. Also, the capacitance value of the capacitive element can be selected small.

Further, the propagation time measured last time is stored, and the voltage conversion circuit is stopped when a time slightly shorter than the propagation time measured last time from the start of transmission, so that the measurement interval is changed. Since it can be set shorter than the time ratio and the timing for stopping the voltage conversion circuit can be changed according to the flow velocity, it is possible to accurately measure a wider range of flow velocity.

Further, the power supply control circuit receives the reception output from the ultrasonic transducer for reception, makes a reception judgment earlier than the reception circuit outputs the reception judgment signal, and stops the voltage conversion circuit at that timing. Since the voltage conversion circuit is surely stopped at the initial stage when the reception output is input, the timing of stopping the voltage conversion circuit can be changed according to the flow speed even if the change of the flow speed is earlier than the measurement interval. Therefore, a wide range of flow velocity can be accurately measured with a simple configuration.

Further, by configuring the connection between the capacitive element and the receiving circuit with a path that does not branch to another, when the voltage conversion circuit is stopped, the capacitive element can be operated without changing the circuit operation that affects the measurement. Since it is possible to suppress the electric power discharge from the capacitor to the minimum, it is possible to reduce the capacitance of the capacitive element. Further, it is possible to remove noise propagating from the transmission circuit or the control unit through the power supply line,
It is possible to realize an ultrasonic velocity meter that is resistant to noise, inexpensive, and highly accurate.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of an ultrasonic velocity meter of the present invention.

FIG. 2 is a block diagram showing a configuration of a receiving circuit according to the first embodiment.

FIG. 3 is a timing chart showing the operation of the first embodiment.

FIG. 4 is a block diagram showing the configuration of a power supply control circuit in Embodiment 2 of the ultrasonic velocity meter of the present invention.

FIG. 5 is a timing chart showing the operation of the second embodiment.

FIG. 6 is a block diagram showing the configuration of a power supply control circuit in Embodiment 3 of the ultrasonic velocity meter of the present invention.

FIG. 7 is a timing chart showing the operation of the third embodiment.

FIG. 8 is a block diagram showing a configuration of a power supply control circuit in Embodiment 4 of the ultrasonic velocity meter of the present invention.

FIG. 9 is a timing chart showing the operation of the fourth embodiment.

FIG. 10 is a block diagram showing a configuration of a conventional ultrasonic velocity meter.

FIG. 11 is a block diagram showing a configuration of a receiving circuit in the same velocity meter.

FIG. 12 is a waveform chart showing the reception output of the ultrasonic transducer for reception.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery (power supply) 2 Voltage conversion circuit 3 Measurement path 4 Transmission ultrasonic transducer 5 Transmission circuit 6 Reception ultrasonic transducer 7 Reception circuit 8 Controller 9 Amplifier 10 Reference voltage 11 Comparator 12 Power control circuit 13 Capacitive Element 14 Timer 15 Memory 16 Clock 17 Comparator 18 Amplifier 19 Second Reference Voltage 20 Comparator

Claims (6)

[Claims] 1. A power supply, a voltage conversion circuit that converts an output voltage of the power supply, a capacitive element that accumulates charges while smoothing an output voltage of the voltage conversion circuit, and a transmission ultrasonic wave that transmits an ultrasonic wave. A transducer, a transmission circuit that drives the transmission ultrasonic transducer, and a reception ultrasonic vibration that receives an ultrasonic wave that has arrived from the transmission ultrasonic transducer via a measurement path and outputs a reception output. And a receiver circuit that uses the output of the voltage conversion circuit as a power source, receives the reception output of the ultrasonic transducer for reception, and outputs a reception determination signal by reception determination processing, and controls the operation of the voltage conversion circuit. The power supply control circuit and the propagation time of the ultrasonic waves output by the ultrasonic transducer for transmission reaching the ultrasonic transducer for reception are the elapsed times from the output time of the transmission start signal to the input time of the reception determination signal. Measured based on time However, the power supply control circuit includes a control unit that controls the overall operation while measuring the flow velocity of the fluid in the measurement path according to the propagation time and the path length of the measurement path, and the power supply control circuit includes the transmission start signal from the control unit. After the input, the operation of the voltage conversion circuit is stopped at least when the reception circuit executes the reception determination process, and the reception circuit is driven by the electric charge accumulated in the capacitive element. 2. The ultrasonic velocity meter according to claim 1, wherein the power supply control circuit controls so as to stop the operation of the voltage conversion circuit at the time point when the transmission start signal is input from the control unit. 3. The ultrasonic velocity meter according to claim 1, wherein the power supply control circuit controls so as to stop the operation of the voltage conversion circuit at a time point when a predetermined time has elapsed since the transmission start signal was input from the control unit. 4. The power supply control circuit stores the propagation time measured last time, and when a time slightly shorter than the stored propagation time elapses after the control unit outputs a transmission start signal, The ultrasonic flowmeter according to claim 1, which is controlled to stop its operation. 5. The power supply control circuit controls so that the reception circuit determines the reception output of the reception ultrasonic transducer at a level lower than the reception determination level, and stops the operation of the voltage conversion circuit at that time. Ultrasonic current meter. 6. The ultrasonic velocity meter according to claim 1, wherein a path between the capacitive element and the receiving circuit does not branch to another.