JPH0933308A - Ultrasonic flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the measuring accuracy of an ultrasonic flow meter using a sing-around method. SOLUTION: A time chart obtained when ultrasonic waves are emitted in the flow forward direction and the propagation delay time t1 is measured is shown in the figure. A transmitter is driven by a drive pulse P1 at the time of a start. The transmitter is vibrated to emit ultrasonic waves toward a receiver, and an electric signal S11 is generated. A third wave of S11 is detected by a detecting circuit to obtain a signal P11. A drive pulse P2 is applied to the transmitter by a signal P21 obtained when the third wave of an electric signal S21 of the receiver is detected. These actions are repeated, and the propagation time t1 is obtained from the time T1 to the Nth signal P2N and the average of the delay time τ. The propagation time in the reverse direction is likewise obtained, and the flow rate is calculated from them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of an ultrasonic flowmeter using a sing-around method.

[0002]

2. Description of the Related Art An ultrasonic flowmeter using a time shearing method in which only one sing-around system is switched over time is known.

The principle of the sing-around method using the time shearing method will be described with reference to FIG. In FIG. 3, 1 is a flow tube, and 2 and 3 are a set of transducers provided at an upstream portion and a downstream portion of the flow tube 1 at a distance L. V indicates the flow velocity of the fluid flow.

First, the ultrasonic wave pulse is emitted from the wave transmitter 2 in the forward direction, and the ultrasonic wave pulse is received by the wave receiver 3. When a drive pulse is applied to the wave transmitter 2 based on this received signal, the wave transmitter 2 again emits an ultrasonic pulse, and thereafter this repetition is repeated. The cycle of this repetition, that is, the forward sing-around cycle t ₁ is t ₁ = L / (C + V) where C is the speed of sound in the stationary fluid and V is the speed of the fluid flow.

The forward sing-around frequency f
₁ is the inverse of the period t _1, the _{f 1 = 1 / t 1 =} (C + V) / L.

Next, the direction of the ultrasonic waves is switched to the opposite direction to the flow, the ultrasonic wave pulse is emitted from the wave transmitter 3 in the opposite direction, and the ultrasonic wave is received by the wave receiver 2. Transmitter 3 based on this received signal
When a driving pulse is applied to the ultrasonic wave, the ultrasonic wave pulse is again emitted from the wave transmitter 2, and this repetition is repeated thereafter. This repeating cycle, that is, the backward sing-around cycle t
₂ becomes _{t 2 = L / (C-} V).

In addition, the reverse sing-around frequency f
₂ is the reciprocal of the period t ₁ and is f ₂ = 1 / t ₂ = (CV) / L.

The difference Δf between f ₁ and f ₂ is Δf = f ₁ −f ₂ = (1 / t ₁ ) − (1 / t ₂ ) = 2V
/ L 2, and from this, the velocity V of the fluid flow can be determined as V = LΔf / 2 regardless of the speed of sound.

By the way, one of the transmitters / receivers 2, 3 2
In the forward direction in which the wave transmitter is used as the wave transmitter and the other wave is used as the wave receiver, when the wave transmitter 2 is excited by the short drive pulse P ₁ , an ultrasonic pulse is emitted from the wave transmitter 2 and this is received. The wave is received by the wave filter 3 and the received wave shown in FIG. 4 is generated as an electric signal.

The received wave is a small signal at the beginning indicated by symbol a, and its peak value gradually increases with the first wave, the second wave, the third wave, the fourth wave, and the fifth wave, and thereafter the signal gradually decreases. Become.

The forward propagation time of the ultrasonic wave from the wave transmitter 2 to the wave receiver 3 is originally the time t ₁ in FIG. 4, but it is also the S / N relationship to detect the leading point a. However, since it is inaccurate, the zero cross point of the third wave or the fifth wave is actually detected. In FIG. 4, this detection is performed at the zero-cross point at the end of the third wave, and the detection point is indicated by the symbol b.

Therefore, the ultrasonic wave is detected after the actual propagation time t ₁ of the ultrasonic wave by a time τ between the signs a and b, and this τ is one of the causes of the measurement error of the flowmeter. τ
Is about [3 / (2
f)] + α, where α is a value due to the delay of the amplifier circuit and the comparison circuit for detecting the zero cross point “b”.

Although FIG. 4 illustrates the forward propagation time t ₁ , the same applies to the reverse propagation time t _{2 in} which the wave transmitter / receiver 3 is used as the wave transmitter and the wave transmitter / receiver 2 is used as the wave receiver. You can say something like that.

The propagation times t ₁ and t ₂ require nsec (nanosecond) order measurement accuracy because of the accuracy required of the flowmeter, but it is difficult to generate a clock with a cycle of nsec order. , Nt ₁ and Nt ₂ are measured by repeating a plurality of times (N times) in the forward direction and the reverse direction as described above, and these measured values are 1 / N.
By doing so, t ₁ and t ₂ that are as accurate as possible are calculated.

FIG. 5 shows this time chart when the forward repeating operation is performed. P1, P2, P3, P
4 ... PN is a drive pulse for exciting the wave transmitter 2. When the wave transmitter 2 is excited by the drive pulse P1 and emits an ultrasonic wave, the ultrasonic wave reaches the wave receiver 3 after a lapse of the propagation time t ₁ , and a received wave is generated as shown in FIG. This received wave is input to a third wave detection circuit (not shown), and the zero cross point at the end of the third wave of the received wave is detected.

At the same time when this zero-cross point is detected, the transmitter 2 is excited by the drive pulse P2, and the transmitter 2 emits ultrasonic waves again. This ultrasonic wave arrives at the wave receiver 3 with a delay of propagation time t ₁ , the zero cross point of the third wave of the received wave is detected, and at the same time, the wave transmitter 2 is excited by the next drive pulse P3. This is repeated N times, and the zero-cross point of the third wave of the ultrasonic wave received from the wave transmitter 2 excited by the drive pulse PN is detected to end the forward repeating operation.

During this period, the time T ₁ from the drive pulse P1 to the zero cross point of the third wave of the last received wave is measured, and the forward propagation time T ₁ is t ₁ = (T ₁ −Nτ) / N calculate.

The delay time τ is approximately equal to the above value [3 /
(2f)] + α, but the value measured under actual conditions is stored and used. Further, generally, when the zero cross point of the mth wave of the received wave is detected, the delay time τ is approximately [m / (2f)] + α.

[0019]

SUMMARY OF THE INVENTION In the above conventional technique,
If N is set to a large value, for example, 1000, there is an advantage that the measurement accuracy does not deteriorate even if the clock for measuring the time T is on the order of nsec to μsec, but the delay time τ is uncertain and the flow rate measurement It was a factor of error.

The delay time τ is approximately [m / (2
f)] + α, and f at the rising edge of the received wave is uncertain,
In addition, α depends on the difference in the elements of the electronic circuit such as the amplification circuit and the comparison circuit that configure the m-th wave detection circuit and the difference in the temperature, and is not theoretically calculated and varies.

There is a problem that this variation cannot be ignored as a factor of flow rate measurement error. Further, in a flowmeter having a small diameter and a small distance L, the propagation time t ₁ or t
The value of the delay time τ with respect to ₂ also causes a large error that cannot be ignored, and there was also a problem that it impedes the practical application of a small flow meter.

Furthermore, in order to reduce the delay α due to the electronic circuit, a high-performance and high-speed electronic element must be adopted, which is expensive and consumes a large amount of current. Therefore, in the present invention, the period of the clock for measuring time is set to n.
An object of the present invention is to provide an ultrasonic flowmeter capable of solving these problems while maintaining the goodness of the sing-around method using the repetition of N cycles, which does not require the practically difficult value of sec order. And

[0023]

In order to achieve the above object, the invention of claim 1 has a pair of transducers (2) and (3), and one of the transducers (2) is transmitted. The ultrasonic wave is emitted as a wave forwarder in the forward direction of the flow, and the ultrasonic wave is received by the other wave transmitter / receiver (3) a plurality of times (N), and then the other wave transmitter / receiver. The ultrasonic wave is emitted in the reverse direction of the flow using (3) as a wave transmitter, and this ultrasonic wave is received a plurality of times (N) by receiving the other wave transmitter / receiver (2) as a wave receiver. When using it as a transmitter in an ultrasonic flowmeter that transmits and receives ultrasonic waves in the fluid in parallel or oblique directions using the singaround method, which measures the flow velocity of the fluid from the forward and reverse propagation times of Emits ultrasonic waves into the fluid due to the vibration and responds to the vibration. Transducer for outputting an electrical signal (2)
(3) and the only m-th wave detection circuit (5) that receives the electric signals of the transducers (2) and (3), detects the m-th wave thereof, and outputs a detection signal, and the m-th wave. Of the plurality (N) of detection signals output from the detection circuit (5), from the m-th wave detection signal (P11) of the first electric signal from the wave transmitter to the Nth electric wave from the wave receiver. M-th wave detection signal (P2
N) the first timer (6) for measuring the time (T ₁ or T ₂ ) and the m-th wave detection signal (P2) of the electric signal of the receiver.
1, P22, ..., P2 (N−1)), the m-th wave detection signal (P12, P13,
..., P1N) The second timer (7) for measuring the average value of the delay time (τ) and the Nth mth wave detection signal (P2N) of the receiver are detected and the Nth reception is performed. The counter (8) that outputs an end signal and the wave transmitter of the wave transmitters / receivers (2) and (3) are driven by the start signal, and thereafter, the wave received from the m-th wave detection circuit (5) is received. Drive signal (10) for driving the wave transmitter for each m-th wave detection signal (P21, P22, ..., P2 (N-1)) of the wave transmitter, and a start signal for the wave transmitter drive circuit (10) And receiving the N-th reception end signal from the counter (8),
An arithmetic control circuit (9) for calculating a flow rate from the measured value (T ₁ ) (T ₂ ) of the timer (6) and the average value of the delay time (τ) which is the measured value of the second timer (7) An ultrasonic flowmeter characterized by comprising:

According to a second aspect of the present invention, in the ultrasonic flowmeter according to the first aspect, at the time of start, the electric signal from the wave transmitter is transmitted in m-th order.
Input to the wave detection circuit, the receiver is switched and connected to the m-th wave detection circuit (5) by the time the ultrasonic wave from the transmitter at the start reaches the receiver, and the m-th wave detection circuit (5 ) Receives the m-th wave of the electric signal from the wave receiver, the wave transmitter is switched and connected to the m-th wave detection circuit (5), and thereafter the ultrasonic wave from the wave transmitter reaches the wave receiver. The electric signal from the wave receiver is again m-th
It is characterized by comprising a signal switching device (4) which repeats switching connection so as to be inputted to the wave detection circuit (5).

The invention of claim 3 is the ultrasonic flowmeter according to claim 1 or 2, characterized in that m is 3 or 5 in the m-th wave detection circuit (5). The invention of claim 4 is the ultrasonic flowmeter according to claim 1, 2 or 3, characterized in that the m-th wave detection circuit (5) detects a zero-cross point at the end of the m-th electric vibration. It is what

[0026]

When the ultrasonic wave is emitted in the forward direction of the fluid flow, the upstream side transducer (2) of the pair of the transducers (2) and (3) is used as a transmitter. The side wave transmitter / receiver (3) is used as a wave receiver.

First, upon receiving a start signal from the arithmetic control circuit (9), the wave transmitter drive circuit (10) causes the wave transmitter (2) to operate.
Drive to vibrate. The wave transmitter (2) emits ultrasonic waves toward the wave receiver (3) by this vibration, and at the same time generates an electric signal according to the vibration. By configuring the wave transmitters / receivers (2) and (3) with ultrasonic vibrators such as piezoelectric vibrators, it is possible to generate an electric signal according to the vibration of the vibrator (wave transmitter) in this way. , This electric signal is transmitted to the transmitter drive circuit (1
Even after the short drive pulse from 0) disappears, it occurs only for some time while the transmitter is oscillating.

The m-th wave detection circuit (5) receives the electric signal from the wave transmitter (2) at this time, detects the m-th wave, and outputs a detection signal. Upon receiving the m-th wave detection signal, the first timer (6) starts time counting.

The ultrasonic waves emitted from the wave transmitter (2) reach the wave receiver (3) after a lapse of forward propagation time,
The wave receiver (3) receives this ultrasonic wave and generates an electric signal as a received wave.

The m-th wave detection circuit (5) receiving the electric signal detects the m-th wave of the received electric signal and detects the detection signal by the first and second timers (6) and (7) and the counter (8). ).

Upon receiving the m-th wave detection signal, the wave transmitter drive circuit (10) drives the wave transmitter (2) to emit the second ultrasonic wave in the forward direction. At the same time, the wave transmitter (2) generates an electric signal corresponding to the vibration.

This second electric signal from the wave transmitter (2) is input to the m-th wave detection circuit, the m-th wave is detected, and the detection signals are detected by the first and second timers (6) ( Enter in 7). The m-th wave detection signal is input to the second timer (7), and a delay described later together with the m-th wave detection signal of the received electric signal from the wave receiver (3) immediately before the m-th wave detection signal. It is used to calculate the average value of time (τ). The average value is calculated from the delay time (τ) of an arbitrary number of times, regardless of the count value of the counter (8).

The delay time (τ) is almost constant, and the largest cause of the change is the temperature. Therefore, it is possible to measure and update the average value of the delay time (τ) over a period in which the temperature can be regarded as constant, for example, about one hour.

The ultrasonic wave is repeatedly emitted by driving the wave transmitter (2) for each m-th wave detection signal of the electric signal received by the wave receiver (3), and the ultrasonic wave is repeated a predetermined number of times (N). Fired,
At the time when the m-th wave detection signal of the N-th received electric signal is output, the first timer (6) detects the N-th wave from the m-th wave detection signal of the first electric signal from the transmitter (2). The measurement of the time (T ₁ ) until the m-th wave detection signal (P2N) of the received electric signal is finished and input to the arithmetic control circuit (9).

Further, the counter (8) is the N of the wave receiver (3).
The mth wave detection signal (P2N) is detected and the Nth reception end signal is input to the arithmetic control circuit (9). The arithmetic and control circuit (9) recognizes that the measurement in the forward direction has been completed up to a predetermined number (N) of times, and the measurement control circuit (9) of the pair of the transducers (2) and (3) performs the measurement in the reverse direction. Among these, (3) is switched to use as a wave transmitter and (2) is used as a wave receiver, and the system is controlled so that measurement in the reverse direction is performed a predetermined number (N) of times.

Since the measurement in the reverse direction is repeated in the same manner as in the case of the measurement in the forward direction, detailed description will be omitted.
Even in the measurement in the reverse direction, the m-th wave of the electric signal received by the predetermined plural (N) -th receiver (2) from the m-th wave detection signal of the electric signal of the handset (3) at the start (first) The time (T ₂ ) to the detection signal is measured by the first timer (6).

The arithmetic control circuit (9) calculates the forward propagation time (t ₁ ) of the ultrasonic wave from the average value of the time (T ₁ ) and the delay time (τ) and the number of repetitions (N), for example, It is calculated as t ₁ = [T ₁ − (N−1) · (average value of N)] / N, or t ₁ = (T ₁ / N) − (average value of τ).

Further, calculating backward propagation time (t ₂₎ the time (T ₂₎ and the delay time and the average value of (tau), since the repetition count (N), forward propagation time (t ₁₎ In the same manner as the above, for example, t ₂ = [T ₂ − (N−1) · (average value of τ)] / N, or t ₂ = (T ₁ / N) − (average value of τ ).

According to the second aspect of the invention, the electrical signal of the wave transmitter is input to the m-th wave detection circuit (5) for at least the period required to detect the m-th wave of the electrical signal of the wave transmitter, and at least The signal switch (4) is switched and connected so as to input the received electric signal of the wave receiver to the m-th wave detection circuit (5) for a period required to detect the m-th wave of the electric signal of the wave receiver. Since the m-th wave of the electric signal of the transmitter and the m-th wave of the received electric signal of the receiver are accurately repeated without interfering with each other using the unique m-th wave detection circuit (5). To detect.

In the invention of claim 3, the third wave or the fifth wave is
Since it detects, it avoids the beginning of the waveform that is easily affected by noise.
The time based on the signal detected in the part with a large S / N.
(T ₁) (T_Two) And delay time (τ) can be measured.
Wear.

According to the fourth aspect of the present invention, since the zero cross point is detected, the adverse effect of the change in the amplification degree of the m-th wave detection circuit (5) is not exerted.

[0042]

1 is an embodiment of an ultrasonic flowmeter of the present invention, and FIG. 2 is a time chart when ultrasonic waves are emitted in the forward direction of the flow in the embodiment of FIG.

In these figures, 2 is a wave transmitter / receiver provided upstream of a channel (not shown) (for example, channel 1 in FIG. 3), and 3 is a wave transmitter / receiver provided downstream of the same channel. , Are arranged facing each other in a known manner.

The set of transmitters / receivers 2 and 3 is installed so that ultrasonic waves are transmitted / received in a direction parallel or oblique to the flow. In addition, these wave transmitters / receivers 2 and 3 are composed of ultrasonic vibrators such as piezoelectric vibrators. Therefore,
When these wave transmitters / receivers 2 and 3 are used as wave transmitters, a short drive pulse is applied, and after this drive pulse disappears, it vibrates at its natural frequency for a while and emits ultrasonic waves. , An electric signal according to the vibration is generated by the piezoelectric effect.

The waveform of this electric signal is shown in FIG. In addition, A, B, C and D in FIG.
The voltage waveforms of the parts marked B, C and D are shown. Reference numeral 4 is a signal switch, which selectively switches electrical signals of the one wave transmitter / receiver 2 and the other wave transmitter / receiver 3 to connect / input to the m-th wave detection circuit 5.

In the embodiment, the m-th wave detecting circuit 5 detects the zero cross point at the end of the third wave of the electric signal of the transmitter / receiver 2 or 3, and outputs the detection signal to the first timer 6 and the first timer 6. 2, the timer 7, the counter 8, the signal switch 4, and the wave transmitter drive circuit 10 described later.

Further, the m-th wave detection circuit 5 includes a signal switch 4
Amplifier circuit 5a for amplifying the electric signal of the transmitter / receiver 2 or 3 inputted via the comparator circuit, and a comparator circuit for detecting the zero cross point at the end of the third wave of the output signal of the amplifier circuit 5a and outputting the detection signal. 5b and.

An arithmetic control circuit 9 controls the system and calculates the flow rate based on signals from the first timer 6, the second timer 7 and the counter 8. Reference numeral 10 denotes a wave transmitter drive circuit, which periodically vibrates by applying short drive pulses to the wave transmitter / receiver 2 during forward measurement and to the wave transmitter / receiver 3 during backward measurement to cause the fluid 14 to emit ultrasonic waves. .

Reference numeral 11 denotes a transmission / reception changeover switch, and the changeover switch is located at the position shown in the figure at the time of forward measurement in which one of the wave transmission / reception units 2 is used as a wave transmission unit, and the other transmission / reception unit 3 is used as a wave transmission unit. At the time of utilizing the reverse direction measurement, the position is switched to the opposite position as shown.

At the time of forward measurement in FIG. 1, the wave transmitter drive circuit receives the start signal from the arithmetic control circuit 9 and applies the first drive pulse P1 shown in FIG. 2 to the wave transmitter 2. Next, FIG.
The operation during forward measurement in the embodiment of FIG. 1 will be described with reference to the time chart of FIG.

At the start, the wave transmitter drive circuit 10 applies a short drive pulse P1 to the wave transmitter 2 in response to a start signal from the arithmetic control circuit 9, and the piezoelectric vibrator (ultrasonic vibration) of the wave transmitter 2 is applied. Child) to drive.

The wave transmitter 2 emits ultrasonic waves toward the wave receiver 3 into the fluid by this vibration, and at the same time, generates an electric signal S11 according to the vibration. This electric signal is input to the m-th wave detection circuit 5 via the signal switch 4, and the zero cross point at the end of the third wave is detected. P11 of FIG. 2 is the third wave detection signal at this time, and the first timer 6 starts measuring the time T ₁ from the time of this third wave detection signal P11.

The signal switch 4 is switched from the illustrated state until the ultrasonic wave from the wave transmitter 2 due to the drive pulse P1 reaches the wave receiver 3, and the electric signal S21 received by the wave receiver 3 is switched. Is input to the m-th wave detection circuit 5 via the signal switch 4, and the third wave is detected at the zero cross point at the end of the third wave.
The wave detection signal P21 is output.

The wave transmitter drive circuit 10 receives the third wave detection signal P21, applies the drive pulse P2 to the wave transmitter 2, and emits the second ultrasonic wave. Further, since the signal switch 4 is switched to the illustrated state in response to the third wave detection signal P21, it is caused by the vibration of the wave transmitter 2 when the wave transmitter 2 emits the second ultrasonic wave. The electric signal S12 is input to the m-th wave detection circuit 5 via the signal switch 4, and the third signal
The third wave detection signal P12 at the zero cross point at the end of the wave
Is output.

The interval between the third wave detection signals P21 and P12, that is, the delay time τ is counted by the second timer 7 and used for measuring the average value of the delay time τ. In this manner, thereafter, the drive pulses P3, P4, ..., PN are periodically applied to the wave transmitter 2 to complete the forward measurement N times, for example, 1000 times.

When the third wave detection signal P2N of the Nth received electric signal from the wave receiver 3 is input to the counter 8, the counter 8 counts up and it is calculated that the forward measurement is completed N times. Notify the control circuit 9.

Therefore, the arithmetic control circuit 9 switches the transmission / reception changeover switch 11 from the state shown in FIG. 1, and uses the wave transmitter / receiver 3 as a wave transmitter and the wave transmitter / receiver 2 as a wave receiver to perform measurement in the opposite direction. To do.

Since the measurement in the reverse direction is similar to the measurement in the forward direction, its description will be omitted. Propagation times t ₁ and t ₂ in the forward direction and the backward direction are obtained from the average values of the times T ₁ , T ₂ and the delay time τ thus measured, as described in the above description of the operation, and based on these numerical values, As in the prior art, the speed and flow rate of the fluid are determined.

[0059]

Since the ultrasonic flowmeter of the present invention is configured as described above, the fluctuations in the delay time (τ) due to the temperature difference are canceled out, so that the propagation time (t ₁ ) (t ₂ ) is reduced. Since the measurement can be performed with high accuracy, the accuracy of the flow meter can be improved.

Further, since the adverse effect of the delay time (τ) is reduced, a small flow meter having a short propagation time (t ₁ ) (t ₂ ) can be put to practical use with good accuracy. Furthermore, since the electronic circuit element used for the m-th wave detection circuit that affects the delay time (τ) does not need high performance and high speed, it is useful for power saving and cost reduction.

Further, in the invention of claim 2, the only m-th wave detection circuit (5) is the m-th wave of each electric signal of the transmitter and the receiver.
The waves can be accurately detected without interference, and the system can operate stably.

Further, according to the invention of claim 3, it is possible to realize the flow rate measurement with higher accuracy by reducing the influence of noise. Further, in the invention of claim 4, it is less susceptible to fluctuations in the electrical amplification degree of the m-th wave detection circuit, and this aspect also contributes to improvement in the accuracy of the flowmeter.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a time chart of the embodiment of FIG.

FIG. 3 is a schematic diagram illustrating the principle of an ultrasonic flowmeter using the sing-around method.

FIG. 4 is a diagram showing an electric signal waveform for explaining the operation of the m-th wave detection circuit of the related art.

FIG. 5 is a time chart of a conventional technique.

[Explanation of symbols]

2, 3 Transducer (ultrasonic transducer) 4 Signal switcher 5th m-wave detection circuit 6 First timer 7 Second timer 8 Counter 9 Operation control circuit 10 Transmitter drive circuit 11 Transmitter / receiver switch P ₁ , P ₂ , ..., PN drive pulse S11, S12, ..., S1N electrical signal from the transmitter S21, S22, ..., S2N electrical signal from the receiver P11, P12, ..., P1N electrical from the transmitter Third wave detection signal of signal P21, P22, ..., P2N Third wave detection signal of electric signal from receiver T ₁ , T ₂ time t ₁ , t ₂ propagation time τ delay time

Claims (4)

[Claims] 1. A set of transducers (2) and (3) is provided, and one of the transducers (2) is used as a transmitter to emit ultrasonic waves in the forward direction of the flow and the other ultrasonic waves. The receiving and receiving of the wave transmitter / receiver (3) as the wave receiver is repeated a plurality of times (N), and then the other wave transmitter / receiver (3) is used as the wave transmitter to emit ultrasonic waves in the opposite direction of the flow. The sing-around method in which the reception of this ultrasonic wave by the other transducer (2) is repeated a plurality of times (N) to measure the flow velocity of the fluid from the propagation time of the ultrasonic wave in the forward and reverse directions. In an ultrasonic flowmeter that transmits and receives ultrasonic waves in a fluid in a direction parallel or oblique to the flow, when used as a transmitter, the vibrations emit ultrasonic waves into the fluid and respond to the vibration. Transducers (2) and (3) that output electric signals, and transducers (2) Enter the electric signal 3), the first m
A m-th wave detection circuit (5) that detects a wave and outputs a detection signal, and a wave transmitter from the plurality (N) of detection signals output from the m-th wave detection circuit (5) M of the first electrical signal of
A first timer (6) for measuring the time (T ₁ or T ₂ ) from the wave detection signal (P11) to the mth wave detection signal (P2N) of the Nth electrical signal from the receiver, and M-th wave detection signal (P21, P22,
, P2 (N-1)) to the m-th wave detection signal (P12, P13, ..., P1N) of the electrical signal of the subsequent wave transmitter, the second value for measuring the average value of the delay time (τ) A timer (7) and a counter (8) that detects the Nth mth wave detection signal (P2N) of the receiver and outputs the Nth reception end signal.
And driving the wave transmitter of the wave receivers (2) and (3) with the start signal, and thereafter, the m-th wave detection signal (P21) of the wave receiver output from the m-th wave detection circuit (5). , P22,
, P2 (N-1)), a wave transmitter drive circuit (10) for driving the wave transmitter, and a start signal to the wave transmitter drive circuit (10), and the N from the counter (8). In response to the th reception end signal, the measured value (T ₁ ) (T ₂ ) of the first timer (6)
And an arithmetic control circuit (9) for calculating a flow rate from an average value of delay time (τ) which is a measured value of the second timer (7). 2. The electric signal from the wave transmitter is input to the m-th wave detection circuit at the time of start, and the ultrasonic wave from the wave transmitter at the time of start reaches the m-th wave receiver. When the m-th wave detection circuit (5) receives the m-th wave of the electric signal from the receiver, the transmitter is switched and connected to the m-th wave detection circuit (5). , And then the ultrasonic wave from the transmitter reaches the m-th signal again until the ultrasonic wave reaches the receiver.
The ultrasonic flowmeter according to claim 1, further comprising a signal switch (4) that repeats switching connection so as to be input to the wave detection circuit (5). 3. The ultrasonic flowmeter according to claim 1, wherein m is 3 or 5 in the m-th wave detection circuit (5). 4. The ultrasonic flowmeter according to claim 1, 2 or 3, wherein the m-th wave detection circuit (5) detects a zero cross point at the end of the m-th electric vibration.