JPH0921667A - Flow rate measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the lower consumption of an ultrasonic flow meter. SOLUTION: The flow rate measuring apparatus includes a first vibrator 5 and a second vibrator 6 provided on a fluid conduit 4, a flow rate calculating means 12 for calculating a flow rate based on a signal of a measurement circuit for measuring signal transmission time between the vibrators, a measurement completion means 15 for informing of completion of flow rate measurement by the flow rate calculation means 12, a voltage control means 16 for controlling supply voltage to the measurement circuit by the measurement completion means 15 or a measurement start means 14 and a period variable means 13 for changing a period of the measurement start means 14 based on a value of the flow rate calculation means 12. A measurement period can be lengthened while accuracy in the flow rate is maintained, and the supply voltage is reduced during the measurement period to reduce the power consumption, thereby lengthening the service life of a battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring device for measuring the flow rate of gas or the like using ultrasonic waves.

[0002]

2. Description of the Related Art A conventional flow rate measuring device of this type is known, for example, from Japanese Patent Laid-Open No. 4-328424.
As shown in FIG. 1, ultrasonic transducers 2 and 3 are provided in a part of the fluid line 1 so as to face each other in the flow direction, and ultrasonic waves are generated from the transducer 1 in the flow direction. When it is detected by, the ultrasonic wave is again generated from the vibrator 1, the time is measured by repeating this, and conversely, the ultrasonic wave is generated from the vibrator 2 against the flow and the same repetition time is measured. The velocity of the fluid was calculated from the difference.

[0003]

However, in the above-mentioned conventional flow rate measuring device, the measurement start signal is determined to be a certain frequency or a function including a random function, and even when the fluid is not flowing. The measurement was performed at the determined sampling frequency. For this reason, electric power is frequently used, and in the case of battery driving, it is necessary to replace the battery within a short period of time, and reduction of power consumption has been a problem.

The present invention has been made to solve the above problems and has an object to reduce power consumption.

[0005]

In order to achieve the above object, the flow rate measuring device of the present invention has the following configuration.

That is, the first transducer provided in the fluid conduit, the second transducer for receiving the ultrasonic signal transmitted from the first transducer, and the measurement for measuring the signal transmission time between the transducers. Circuit, flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, measurement start means for starting measurement by the vibrator, measurement end means for notifying completion of flow rate measurement by the flow rate calculation means, and measurement end means Alternatively, it comprises voltage control means for controlling the supply voltage of the measuring circuit by the measurement starting means, and cycle changing means for changing the cycle of the measurement starting means based on the value of the flow rate calculating means.

Further, a first oscillator provided in the fluid conduit, a second oscillator for receiving an ultrasonic signal transmitted from the first oscillator, and a measurement for measuring a signal transmission time between the oscillators. Circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by the vibrator, and an average for changing the average value of the cycle of the measurement circuit based on the value of the flow rate calculation means. It is provided with period changing means, irregular value generating means for generating a random value, and period changing means for adding the signal of the irregular value generating means to the signal of the average period changing means.

Further, a first oscillator provided in the fluid conduit, a second oscillator for receiving an ultrasonic signal transmitted from the first oscillator, and a measurement for measuring a signal propagation time between the oscillators. Circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by the vibrator, and a cycle of the measurement start means increased according to the number of times the flow rate calculation means detects a zero value. And a means for changing the period.

Further, a first oscillator provided in the fluid conduit, a second oscillator for receiving an ultrasonic signal transmitted from the first oscillator, and a measurement for measuring a signal transmission time between the oscillators. Circuit, flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, measurement start means for starting measurement by the vibrator, and variable cycle for increasing the cycle of the measurement start means when the zero value of the flow rate calculation means is detected. And means for integrating the flow rate values of the flow rate calculation means, and adding a value obtained by multiplying the flow rate value by the elapsed time from the previous measurement when a flow rate equal to or greater than a predetermined value is detected after the zero value is detected. It is a thing.

Further, a first oscillator provided in the fluid conduit, a second oscillator for receiving an ultrasonic signal transmitted from the first oscillator, and a measurement for measuring a signal propagation time between the oscillators. Circuit, flow rate calculation means for calculating the flow rate based on the signal of the measurement circuit, measurement start means for starting measurement by the oscillator, and increasing the cycle of the measurement start means when the zero value of the flow rate calculation means is detected. The cycle variable means and the integration calculation means for integrating the flow rate values of the flow rate calculation means and not adding the flow rate values when a flow rate of a predetermined value or more is detected after continuous zero value detection.

Further, a first oscillator provided in the fluid conduit, a second oscillator for receiving the ultrasonic signal transmitted from the first oscillator, and a measurement for measuring a signal propagation time between the oscillators. Circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by the vibrator, and a cycle for increasing the cycle of the measurement start means when a zero value of the flow rate calculation means is detected. A variable means and an integrating calculation means for integrating the flow rate values of the flow rate calculation means and for multiplying the flow rate value by a predetermined coefficient and adding it when a flow rate of a predetermined value or more is detected after continuous zero value detection. is there.

Further, the first vibrator provided in the fluid conduit, the second vibrator for receiving the ultrasonic signal transmitted from the first vibrator, and the ultrasonic transmission between the vibrators are repeated a plurality of times. Means, a number setting means for setting the number of times of the repeating means, a measuring circuit for measuring the cumulative time of the signal propagation time, a flow rate calculating means for calculating the flow rate based on the signal of the measuring circuit, and a measurement by the vibrator. Measurement start means for starting, cycle changing means for increasing the cycle of the measurement start means after detection of the zero value of the flow rate calculating means, and search and measurement means for decreasing the value of the number of times setting means during the measurement cycle Is.

Also, a first oscillator provided in the fluid conduit, a second oscillator for receiving the ultrasonic signal transmitted from the first oscillator, and a measurement for measuring the signal transmission time between the oscillators. Circuit, flow rate calculation means for calculating the flow rate based on the signal of the measurement circuit, measurement start means for starting measurement by the vibrator, and cycle changing means for changing the cycle of the measurement start means based on the value of the flow rate calculation means And coefficient setting means for changing the coefficient of the flow rate calculation means according to the value of the cycle changing means.

[0014]

The present invention has the above-mentioned structure and changes the measurement cycle according to the flow rate.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a first oscillator 5 that transmits ultrasonic waves and a second oscillator 6 that receives ultrasonic waves are arranged in the flow direction in the middle of the fluid conduit 4. Reference numeral 7 is a transmission circuit to the first vibrator 5, 8 is an amplifier circuit for a signal received by the second vibrator 6, and the amplified signal is compared with a reference signal by a comparison circuit 9,
The time from the transmission to the reception is obtained by the time measuring means 10 such as a timer counter, and the time from the transmitting circuit 7 to the time measuring means 10 is obtained.
The measuring circuit 11 is formed up to. The flow rate calculation means 12 obtains a flow rate value in consideration of the size of the conduit and the flow state according to the ultrasonic wave propagation time by the time measurement means 10, and the cycle changing means 13 measures the measurement cycle by the value of the flow rate calculation means 12. And the timing of signal transmission to the transmission circuit 7 is adjusted by the measurement starting means 14 according to the value of the cycle varying means 13. Further, the calculation end of the flow rate calculation means 12 is sent to the measurement end means 15, and the voltage control means 16 lowers the voltage of the measurement circuit 11 in synchronization with the measurement end means 15. Further, the voltage of the measurement circuit 14 is restored in synchronization with the start of the measurement by the measurement starting means 14.

Next, the operation will be described. A burst signal is sent from the measuring circuit 14 from the transmitting circuit 7
The ultrasonic signal transmitted by the oscillator 5 propagates in the flow, is received by the second oscillator 6, is processed by the amplification circuit 8 and the comparison circuit 9, and the time from transmission to reception is measured by the time measuring means 10. Measure.

When the sound in the stationary fluid is c and the velocity of the fluid flow is v, the propagation velocity of the ultrasonic wave in the forward direction of the flow is (c +
v). When the distance between the transducers 5 and 6 is L and the angle formed by the ultrasonic wave propagation axis and the central axis of the duct is φ, the time t at which the ultrasonic waves arrive is t = L / (c + vCOSφ) (1 ), And from the equation (1), v = (L / t−c) / COSφ (2), and if L and φ are known, the flow velocity v can be obtained by measuring t. From this flow velocity, the flow rate Q becomes Q = KSv (3), where S is the passing area and K is the correction count.

For example, in the case of accurately obtaining the integrated value as in a gas meter, the measurement needs to be complicated. Especially when the flow rate is large, it is necessary to shorten the measurement sampling time to reduce the error, but when the flow rate is relatively small or zero, there is almost no error even if the measurement sampling time is delayed. Therefore, the measurement interval can be changed according to the flow rate calculation means 12. FIG. 2 shows the state of measurement when the flow rate changes with time. When the value of the flow rate calculation means 12 is small, the period changing means 13 increases the measurement time interval so that the value of the flow rate calculation means 12 becomes smaller. The interval of measurement time is made smaller as it becomes larger. As described above, the measurement cycle is changed depending on the flow rate value, but the voltage of the measurement circuit 11 is reduced between the measurements. That is, when the flow rate calculation means 12 finishes measuring the flow rate, a signal is sent to the measurement termination means 15, and the voltage control means 16 lowers the voltage or makes it zero. Before the measurement is started by the measurement starting means 14, the voltage control means 16 restores the voltage of the measuring circuit 11 to the original.

FIG. 3 shows a second embodiment of the present invention, in which the average value of the measurement cycle is changed by the cycle changing means 17 according to the value of the flow rate calculating means 12, and the signal for generating a random value is an irregular value. It is generated by the generating means 18, and the value of the average period changing means 17 and the added value of the period changing means 13 are added to change the period of signal transmission to the measurement starting means 14. At this time, the measurement cycle changes irregularly within a predetermined range by the signal of the irregular value generating means 18 even if the flow rate value is constant. The value of the irregular value generating means 18 is set to be zero on average.

FIG. 4 shows a third embodiment of the present invention, in which when the value of the flow rate calculating means 12 is zero, the measurement cycle is changed by the zero number detecting means 19 by the cycle changing means 13.
The measurement cycle of the measurement starting means 14 is increased as the number of times of zero flow rate continuously increases. FIG. 5 shows a state in which the measurement time interval is changing with the change in the flow rate with time. At this time, even if zero flow rate continues for a long period of time, a large flow rate may suddenly flow out, so an upper limit is set to avoid making the measurement cycle extremely long.

FIG. 6 shows a fourth embodiment of the present invention, in which the value of the flow rate calculation means 12 is integrated by the integration calculation means 20 to obtain 1
To calculate the integrated value for one day, one month or one year,
It is used for gas meters. FIG. 7 shows a case where a large flow rate suddenly starts to flow after the flow rate has become zero several times and the measurement cycle has increased. In FIG. 7, after the flow rate of zero has continued several times, it is assumed that there are actually flow rates as shown in a to b. The measurement is zero at the time T9, and the flow rate is measured at the next measurement time time T10. b will be measured. At this time, there are three types of methods for integrating in the integration calculating means 20. As a first method, the value of the flow rate b is set to the time T10-T9.
This is a method of adding a value multiplied by a time difference (hereinafter referred to as Δt9), and at this time, the integrated value is always calculated more than the actual value. As a second method, there is a time difference Δ in the value (zero) of the flow rate a.
This is a method of adding a value multiplied by t9, that is, adding 0, and at this time, the integrated value is always smaller than the actual value. As a third method, a value obtained by multiplying a constant value (0.1 to 0.9) of the flow rate b by a time difference Δt9 is added, and when the constant is 0.5, half the flow rate b in FIG. Δt for the value
The value multiplied by 9 is added. That is, the line connecting the flow rate c and the flow rate b is added.

FIG. 8 shows a fifth embodiment of the present invention, in which the ultrasonic wave transmission from the transmitting means 7 to the comparing means 9 is repeated by the number of times set by the number of times setting means 22 by the repeating means 21, and the accumulated time is calculated. It is measured by the timing means 10. When the value of the flow rate calculation means 12 continuously measures a zero value, the value of the measurement cycle is changed by the cycle changing means 13 along with the number of times, and the number of repetitions is reduced, that is, the number of transmissions of the transducer is reduced. Alternatively, the search and measurement unit 23, which has reduced the power consumption by shortening the measurement time, performs the measurement for obtaining the outline of the flow rate value. The interval between the flow rate and the measurement time at this time is shown in FIG. Obtain accurate flow rate T3, T4, T5, T6
During the measurement, the search measurement is performed at times T3 ', T4', T5 ', and T6'. As shown in FIG. 8, if the flow rate above a predetermined value is detected in the search measurement of T6 ′, the next measurement will be T
The measurement is performed with a shorter measurement period such as 7 and T8.

FIG. 10 shows a sixth embodiment of the present invention, in which the cycle changing means 13 changes the measurement cycle according to the value of the flow rate calculating means 12 and the flow rate coefficient of the flow rate calculating means 12 is changed by the coefficient setting means 24. To do. The flow rate coefficient is corrected in consideration of the fact that the operation time of the electronic circuit and the ultrasonic transducer changes due to the change of the measurement cycle, which changes the response and sensitivity.

[0024]

As described above, according to the present invention, the following effects can be obtained.

(1) The first transducer provided in the fluid conduit, the second transducer that receives the ultrasonic signal transmitted from the first transducer, and the signal transmission time between the transducers are measured. A measurement circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by a vibrator, a measurement end means for notifying completion of flow rate measurement by the flow rate calculation means, and a measurement end Means or the measurement starting means for controlling the supply voltage of the measuring circuit, and the cycle changing means for changing the cycle of the measurement starting means based on the value of the flow rate calculating means. Accurate measurement can be performed with a short cycle, power consumption can be reduced by increasing the measurement cycle when the flow rate value is small, and power consumption can be reduced by reducing or zeroing the circuit voltage during intermittent measurement. of It is possible to measure the reduction, it is possible to increase the battery life.

(2) The first transducer provided in the fluid conduit, the second transducer receiving the ultrasonic signal transmitted from the first transducer, and the signal transmission time between the transducers are measured. A measurement circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by a vibrator, and an average value of the cycle of the measurement circuit based on the value of the flow rate calculation means. Since the average period changing means, the irregular value generating means for generating a random value, and the period changing means for adding the signal of the irregular value generating means to the signal of the average period changing means are provided, High accuracy can be maintained even if the measurement cycle is long, even with respect to the temporary fluctuation.

(3) The signal transmission time between the first vibrator provided in the fluid conduit, the second vibrator receiving the ultrasonic signal transmitted from the first vibrator, and the vibrator is measured. A measurement circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by a vibrator, and a cycle of the measurement start means according to the number of times the flow rate calculation means detects a zero value. Since it is equipped with a cycle changing means for enlarging, the measurement cycle can be taken long when the flow rate value is zero, that is, when the fluid is not used. It can be greatly reduced.

(4) The first transducer provided in the fluid conduit, the second transducer that receives the ultrasonic signal transmitted from the first transducer, and the signal transmission time between the transducers are measured. A measurement circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by a vibrator, and a cycle for increasing the cycle of the measurement start means when the zero value of the flow rate calculation means is detected. A variable means and an integration calculation means for integrating the flow rate values of the flow rate calculation means and adding a value obtained by multiplying the flow rate value by the elapsed time from the previous measurement when a flow rate of a predetermined value or more is detected after the zero value is detected. Therefore, the flow rate value that suddenly begins to flow when the measurement cycle becomes long is measured a little more, which acts on the safety side when the integrated value of the dangerous fluid leakage amount is obtained.

(5) The signal transmission time between the first vibrator provided in the fluid conduit, the second vibrator receiving the ultrasonic signal transmitted from the first vibrator, and the vibrator is measured. A measurement circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by the vibrator, and a cycle of the measurement start means when the zero value of the flow rate calculation means is detected is increased. Since the measurement cycle is provided, the flow rate value of the flow rate calculation means is integrated and the integration calculation means that does not add the flow rate value when a flow rate of a predetermined value or more is detected after continuous zero value detection is performed. When it becomes long, the flow rate value that suddenly starts to flow will be measured less,
This works on the safety side when the integrated value of flow rate is always supplied more than necessary amount.

(6) The signal transmission time between the first transducer provided in the fluid conduit, the second transducer receiving the ultrasonic signal transmitted from the first transducer, and the transducer is measured. A measurement circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by a vibrator, and a cycle of the measurement start means when the zero value of the flow rate calculation means is detected. Since the cycle variable means and the integration calculation means for integrating the flow rate values of the flow rate calculation means and for multiplying the flow rate value by a predetermined coefficient and adding it when a flow rate of a predetermined value or more is detected after continuous zero value detection is provided. The flow rate value that suddenly starts to flow when the measurement cycle becomes long can be increased or decreased depending on the situation, and the average value can be used to obtain a nearly accurate integrated value in the long run. .

(7) The first transducer provided in the fluid conduit, the second transducer that receives the ultrasonic signal transmitted from the first transducer, and the ultrasonic transmission between the transducers are performed a plurality of times. Repeating means, number-of-times setting means for setting the number of times of repeating means, measuring circuit for measuring the cumulative time of signal propagation time, flow rate calculating means for calculating the flow rate based on the signal of the measuring circuit, and measurement by the vibrator. The measurement start means for starting the measurement, the cycle changing means for increasing the cycle of the measurement start means after the zero value of the flow rate calculating means is detected, and the search and measurement means for decreasing the value of the number of times setting means during the measurement cycle are provided. Therefore, even if a large flow rate unexpectedly flows when the measurement cycle is long, it is possible to start the flow of the fluid with a small amount of power consumption.

(8) Measure the signal transmission time between the first oscillator provided in the fluid conduit, the second oscillator receiving the ultrasonic signal transmitted from the first oscillator, and the oscillator. A measurement circuit, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, a measurement start means for starting measurement by a vibrator, and a cycle variable for changing the cycle of the measurement start means based on the value of the flow rate calculation means. Since the means and the coefficient setting means for changing the coefficient of the flow rate calculating means according to the value of the cycle changing means are provided, the ultrasonic vibrator and the circuit of the ultrasonic transducer and the circuit are longer than those in the case where the measurement cycle is long and continuous measurement is performed. An error due to a change in state can be corrected by the flow coefficient.

[Brief description of drawings]

FIG. 1 is a control block diagram of a flow rate measuring device according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a change over time in the flow rate of the device.

FIG. 3 is a control block diagram of a flow rate measuring device according to a second embodiment of the present invention.

FIG. 4 is a control block diagram of a flow rate measuring device according to a third embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a change over time in the flow rate of the device.

FIG. 6 is a control block diagram of a flow rate measuring device according to a fourth embodiment of the present invention.

FIG. 7 is a characteristic diagram showing a change over time in the flow rate of the device.

FIG. 8 is a control block diagram of a flow rate measuring device according to a fifth embodiment of the present invention.

FIG. 9 is a characteristic diagram showing a change over time in the flow rate of the device.

FIG. 10 is a control block diagram of a flow rate measuring device according to a sixth embodiment of the present invention.

FIG. 11 is a control block diagram of a conventional flow rate measuring device.

[Explanation of symbols]

 4 Fluid Pipe 5 First Oscillator 6 Second Oscillator 10 Timing Means 11 Measuring Circuit 12 Flow Rate Calculating Means 13 Cycle Changing Means 14 Measurement Starting Means 15 Measurement Ending Means 16 Voltage Control Means 17 Average Cycle Changing Means 18 Random Value Generation Means 19 Zero count detecting means 20 Integration calculating means 21 Repeating means 22 Number setting means 23 Search and measurement means 24 Coefficient setting means

Claims (10)

[Claims] 1. A first vibrator provided in a fluid conduit, a second vibrator for receiving an ultrasonic wave signal transmitted from the first vibrator, and a signal transfer time between the vibrators are measured. Measuring circuit, a flow rate calculating means for calculating a flow rate based on a signal from the measuring circuit, a measurement starting means for starting measurement by the vibrator, and a measurement ending means for notifying completion of flow rate measurement by the flow rate calculating means. And voltage control means for controlling the supply voltage of the measurement circuit by the measurement end means or the measurement start means, and cycle changing means for changing the cycle of the measurement start means based on the value of the flow rate calculation means. Flow measuring device. 2. A first vibrator provided in a fluid conduit, a second vibrator for receiving an ultrasonic wave signal transmitted from the first vibrator, and a signal transfer time between the vibrators are measured. Measuring circuit, a flow rate calculating means for calculating a flow rate based on a signal of the measuring circuit, a measurement starting means for starting measurement by the vibrator, and a cycle of the measuring means based on the value of the flow rate calculating means. A flow rate including an average period changing means for changing the average value, an irregular value generating means for generating a random value, and a period changing means for adding the signal of the irregular value generating means to the signal of the average period changing means. Measuring device. 3. A first vibrator provided in a fluid conduit, a second vibrator for receiving an ultrasonic wave signal transmitted from the first vibrator, and a signal transfer time between the vibrators are measured. Measuring circuit, a flow rate calculating means for calculating a flow rate based on a signal from the measuring circuit, a measurement starting means for starting measurement by the vibrator, and the measurement according to the number of times of zero value detection by the flow rate calculating means. A flow rate measuring device comprising: a cycle varying means for increasing the cycle of the starting means. 4. The flow rate measuring device according to claim 3, wherein an upper limit is set for the cycle of the cycle changing means. 5. A first transducer provided in a fluid conduit, a second transducer that receives an ultrasonic signal transmitted from the first transducer, and a signal transfer time between the transducers are measured. Measuring circuit, a flow rate calculating means for calculating a flow rate based on a signal from the measuring circuit, a measurement starting means for starting measurement by the vibrator, and a measurement starting means for measuring the zero value of the flow rate calculating means. Cycle changing means for increasing the cycle and the flow rate value of the flow rate calculating means are integrated, and when a flow rate of a predetermined value or more is detected after the zero value is detected, a value obtained by multiplying the flow rate value by the elapsed time from the previous measurement is added. A flow rate measuring device comprising: 6. A first transducer provided in a fluid conduit, a second transducer that receives an ultrasonic signal transmitted from the first transducer, and a signal transfer time between the transducers are measured. Measuring circuit, a flow rate calculating means for calculating a flow rate based on a signal from the measuring circuit, an integrating calculating means for integrating the values of the flow rate calculating means, a measurement starting means for starting measurement by the vibrator, and Cycle changing means for increasing the cycle of the measurement starting means when the value of the flow rate calculating means is zero and the flow rate value of the flow rate calculating means are integrated, and a flow rate of a predetermined value or more is detected after the continuous zero detection. A flow rate measuring device provided with an integration calculation means that does not add the flow rate values when the above. 7. A first transducer provided in a fluid conduit, a second transducer that receives an ultrasonic signal transmitted from the first transducer, and a signal transfer time between the transducers are measured. Measuring circuit, a flow rate calculating means for calculating a flow rate based on a signal from the measuring circuit, a measurement starting means for starting measurement by the vibrator, and a measurement start when the value of the flow rate calculating means is zero. A cycle variable means for increasing the cycle of the means and a value of the flow rate calculation means are integrated, and when a flow rate of a predetermined value or more is detected after the continuous zero detection, the flow rate value is multiplied by a predetermined coefficient and added. And a flow rate measuring device having means. 8. A first oscillator provided in a fluid conduit, a second oscillator for receiving an ultrasonic signal transmitted from the first oscillator, and ultrasonic transmission between the oscillators a plurality of times. Repeating means for performing, number-of-times setting means for setting the number of times of the repeating means, a measuring circuit for measuring an accumulated time of signal propagation time, a flow rate calculating means for calculating a flow rate based on a signal of the measuring circuit, A measurement start means for starting measurement by the vibrator, a cycle changing means for increasing the cycle of the measurement start means after detection of the zero value of the flow rate calculation means, and a value for the number of times setting means during the measurement cycle. A flow rate measuring device equipped with a reduced search and measurement means. 9. The flow rate measuring device according to claim 3, wherein the measurement cycle is set to an initial value when the flow rate value by the search measuring means is not zero. 10. A first oscillator provided in the fluid conduit, and a second oscillator for receiving an ultrasonic signal transmitted from the first oscillator.
A vibrator, a measurement circuit for measuring a signal transfer time between the vibrators, a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, and a measurement start means for starting measurement by the vibrator, A flow rate measuring device including cycle changing means for changing the cycle of the measurement starting means based on the value of the flow rate calculating means, and coefficient setting means for changing the coefficient of the flow rate calculating means according to the value of the cycle changing means. .