JPH01100414A - Ultrasonic-wave flow velocity measuring apparatus - Google Patents

Abstract

PURPOSE:To measure the flow velocity of fluid stably at high measuring accuracy even if a received waveform level is fluctuated, by reciprocating an ultrasonic wave between two points in the fluid, and outputting a wave received signal when the received signal corresponding to the arrival of said ultrasonic wave exceeds a reference signal. CONSTITUTION:Ultrasonic wave transmitting and receiving devices 5 and 6 are arranged on a flow pipe 4, in which fluid flows in the direction of an arrow V with a distance (l) being separated. Switching is performed with a send/ receive switching circuit 7 so that an ultrasonic wave is transmitted from the transmitting and receiving device 5 to 6 and from 6 to 5. A voltage signal D corresponding to the signal received with the receiver 5 or 6 is multiplied by a constant factor, and a reference voltage E is obtained. The reference voltage E is compared with a voltage signal C2, which is obtained by delaying a voltage signal C1 in a delay circuit 12 in a voltage comparator 13. When the voltage signal C2 is larger than the reference voltage E, a high level '1' is outputted. Then the number of clock pulses CP corresponding to a time when an output signal H of an FF 18 is at a high level '1' is counted in a counter 20. Thus the flow velocity is computed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic flow rate measuring device that measures the flow rate of a fluid using ultrasonic waves.

[Prior art] Ultrasonic flow velocity measurement has conventionally been used to measure the flow velocity of a fluid by transmitting ultrasonic waves into a fluid, receiving the ultrasonic waves propagating through the fluid, and measuring the propagation time of the ultrasonic waves. The device is known. In such an ultrasonic flow rate apl determination device,
Ultrasonic waves propagating in a fluid are received by an ultrasonic receiver and converted into a voltage signal. After amplifying this voltage signal to a predetermined level with an amplifier, a preset reference voltage (hereinafter referred to as a trigger level) is applied. ), the time when the voltage signal corresponding to the ultrasonic wave exceeds the trigger level or the zero cross point (the point where the voltage signal crosses OV) immediately after the voltage signal corresponding to the ultrasonic wave exceeds the trigger level is when the ultrasonic wave is detected. It was the time of arrival.

However, ultrasonic waves propagating in a fluid
The amount of attenuation varies depending on the temperature of the fluid, impurities in the fluid, etc., and reflection, refraction, etc. occur on the propagation path due to temperature distribution and other non-uniformities in the fluid, so it is difficult to receive it with an ultrasonic receiver. The received wave level fluctuates significantly. In particular, when the fluid is gas, it is more affected than when it is liquid.

FIG. 5 is a diagram illustrating a situation in which the received wave level fluctuates. In Fig. 5, A is an ultrasonic signal transmitted from an ultrasonic transmitter (hereinafter referred to as a transmitted wave), B is an ultrasonic signal received by an ultrasonic receiver (hereinafter referred to as a received wave), and C is an ultrasonic signal received by an ultrasonic receiver (hereinafter referred to as a received wave). This is a zero-crossing pulse that is output when the received wave crosses the first zero-crossing point after crossing the trigger level vth. Note that the received wave B is shown with the time axis expanded. Fifth
As shown in the figure, the zero-crossing pulse corresponding to the received wave Bl is C1, but the zero-crossing pulse corresponding to the received wave B2 is C2, and the propagation time is measured as changing from t2 to t3.

[Problems to be solved by the invention] By the way, in order to capture the received wave stably, AGC (automatic gain control) has traditionally been applied to the received wave amplification circuit to keep the received wave level constant and compare it with the trigger level. A method was used to do so.

However, the AGC applied to the amplification circuit of the received wave (or the voltage signal corresponding to the received wave) is determined by the level of the received wave before the AGC is applied. Therefore,
Even if AGC is applied to the received wave amplifier circuit, it does not predict the level of the received wave that will be received in the future, so it is effective when the received wave level fluctuates slowly, but when the received wave level fluctuates rapidly ( If the level of the received wave fluctuates quickly), there is a risk that it will not only have no effect, but may even have the opposite effect. (Since there is at least a time interval between transmitting the transmitted waves, the level of the received waves may fluctuate during this time.) Therefore, if there are temperature irregularities or fluctuations in the ultrasonic propagation fluid, the received waves As the level changes,
This will result in a large error within the measurement value.

The present invention has been made to solve these problems, and an object of the present invention is to provide an ultrasonic flow rate measuring device that can measure the flow rate of a fluid stably and with high measurement accuracy even when the received wave level fluctuates. It is something to do.

[Means for Solving the Problems] As a first invention, the ultrasonic flow velocity measuring device according to the present invention is characterized in that ultrasonic waves are transmitted from a first point in a fluid to a second point and a second point.
The ultrasonic wave is switched to propagate from the point to the first point, and the received signal corresponding to the ultrasonic wave that has reached the first point and the received signal that corresponds to the ultrasonic wave that has reached the second point are sequentially selected and output. a switching means, a reference signal output means for outputting a reference signal proportional to the amplitude of the received signal, and a delay means for outputting a delayed received signal obtained by delaying the received signal by at least the time until the reference signal is output; and comparison means for outputting a received signal when the delayed received signal becomes larger than the reference signal.

Further, as a second invention, an ultrasonic output means for outputting a first ultrasonic wave and a second ultrasonic wave having substantially the same waveform as the first ultrasonic wave into a fluid at short intervals; A second ultrasonic wave is transmitted from the first point to the second point and from the second point to the first point.
and the first received signal corresponding to the first ultrasonic wave and the second ultrasonic wave that reached the first point, and the first received signal that corresponded to the second ultrasonic wave that reached the second point. a switching means for sequentially selectively outputting the ultrasonic wave and a second received signal corresponding to the second ultrasonic wave; a reference signal outputting means for outputting a reference signal proportional to the amplitude of the first received signal;
and comparison means for outputting a received signal when the second received signal becomes larger than the reference signal.

[Operation] In the first invention, the switching means moves from the first point to the second point.
The ultrasound is switched so that it propagates from the point and the second point to the first point, and the received signals corresponding to the ultrasound that have reached the first point and the second point are sequentially selected and output, and the reference signal is The output means outputs a reference signal having a magnitude proportional to the amplitude of the received signal, the delay means outputs a delayed received signal obtained by delaying the received signal, and the comparison means outputs a delayed received signal when the delayed received signal becomes larger than the reference signal. , outputs the received signal.

Further, in the second invention, the ultrasonic output means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals, and the switching means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals, and the switching means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals, and the switching means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals, and the switching means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals, and the switching means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals, and the switching means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals, and the switching means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals, and the switching means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals, and the switching means outputs the first ultrasonic wave and the second ultrasonic wave at short intervals. Switching so that the first ultrasonic wave and the second ultrasonic wave are respectively propagated to the first point, and the first reception corresponding to the first ultrasonic wave and the second ultrasonic wave that have reached the first point. signal and second
The reference signal output means sequentially selects and outputs the second reception signal corresponding to the first ultrasound wave and the second ultrasound wave that have arrived at the point, and the reference signal output means outputs a reference signal whose magnitude is proportional to the amplitude of the first reception signal. The comparing means outputs a received signal when the second received signal becomes larger than the reference signal.

[Embodiment] FIG. 1 is a circuit block diagram of an ultrasonic flow rate measuring device according to an embodiment of the present invention. In FIG. 1, 1 is a clock pulse generation circuit that outputs a clock pulse CP of a predetermined frequency, and 2 is a clock pulse generation circuit that appropriately divides the clock pulse CP of the clock pulse generation circuit 1 to generate a timing pulse T necessary for the operation of this device. 5.6 is a timing pulse generation circuit that outputs a timing pulse; 3 is a transmission circuit that outputs a transmission signal B in response to the transmission command signal A output from the timing pulse generation circuit 2; 4 is a flow tube through which fluid flows in the direction of arrow V; is an ultrasonic transducer placed in the flow tube 4 at a distance g, and 7 is a transmitted signal B.
A transmitting/receiving switching circuit that switches so that the transmitted waves corresponding to , 8 is a receiving circuit that outputs a voltage signal corresponding to the received signal received by the ultrasonic receiver 5 or 6, and 9 is a voltage signal corresponding to the received signal received by the ultrasonic receiver 5 or 6. 10 is a peak hole +++aX circuit that detects and holds the maximum value D of the voltage signal; 11 is a constant detection circuit II that outputs the maximum value D of the voltage signal;
ax Multiplied by the number K, the voltage signal E (E-K・D
), 12 is a delay circuit that outputs voltage signal C2 delayed by AaX predetermined time from voltage signal C1, and 13 is a delay circuit that compares voltage signal C2 with reference voltage E, and voltage signal C2 is smaller than reference voltage E. When it is large, high level "1"
A voltage comparator 14 outputs a comparison signal of the voltage signal C2.
is compared with the reference voltage VR which is normally set to Ov, and when the voltage signal C2 crosses the reference voltage VR, the high level "
A voltage comparator 15 outputs a comparison signal of ``1'', and when a comparison signal of high level ``1'' is output from the voltage comparator 13, outputs a pulse signal F with a width corresponding to approximately one period of the voltage signal R. 16 is a monostable multivibrator that outputs a zero-cross pulse with a predetermined pulse width when a high-level "1" comparison signal is output from the voltage comparator 14; 17 is a monostable multivibrator 15 and Both outputs of 1B are “
An AND gate 18 outputs a zero-cross pulse G when the signal is ``1'', the transmission command signal A is input to the set terminal S, the zero-cross pulse G is input to the reset terminal R, and the output terminal Q outputs a high level ``1'' or a low level rOJ. 19 is a flip-flop IB that outputs a signal H.
2o is a flip-flop which outputs a clock pulse CP only while the output signal H of 8 is at a high level "1". 21 is a signal processing circuit that calculates the flow velocity based on the count value of the counter 2o, and 22 is a display that displays the calculated flow velocity.

The operation of the ultrasonic flow rate measuring device configured as described above is explained in the second section.
This will be explained based on the timing chart shown in the figure. Second
In the figure, waveforms indicated by symbols A to H indicate output waveforms in the essential parts of the circuit shown in FIG.

When the transmission command signal A is output from the timing pulse generation circuit 2 (see FIG. 2(a)), the transmission circuit 3 outputs the transmission signal B (see FIG. 2(b)).
The peak hold circuit IO is reset by the output of . Further, since the flip-flop 18 is set by the output of the transmission command signal A and outputs a signal H of high level "1", the counter 20 is activated by the clock pulse generation circuit 1.
begins counting the number of clock pulses CP output by (see FIG. 2 (1)).

In response to the output of the transmission command signal A, the transmission/reception switching circuit 7 outputs the transmission signal B output from the transmission circuit 3 to the ultrasonic transducer 5 under the control of the timing pulse generation circuit 2. The ultrasonic transducer 5 converts the transmission signal B into an ultrasonic signal and transmits it into the fluid as a transmission wave. The ultrasonic transducer 6 receives the transmission wave transmitted from the ultrasonic transducer 5 and converts it into a voltage signal.

The reception amplification circuits 8 and 9 each amplify the voltage signal output from the ultrasonic transducer 6 via the transmission/reception switching circuit 7,
A voltage signal C1 having a magnitude corresponding to the received signal is outputted to the peak hold circuit 10 and the delay circuit 12, respectively (see FIGS. 2(d) and (e)). The peak hold circuit IO holds the peak value of the voltage signal. Coefficient unit 11
is the voltage signal E (E-K・D) with a magnitude obtained by multiplying the maximum value D of the voltage signal held by the peak hold circuit IO by the number K of -complete image aX
(see Fig. 2(f)). Further, the multilayer ax extension circuit 12 outputs a voltage signal C2 obtained by delaying the voltage signal C by a predetermined delay time t.

The voltage comparator 18 compares the voltage signal C2 with the voltage signal E as a trigger level, and the voltage signal c2 is compared with the voltage signal E.
When it becomes larger, a comparison signal of high level "1" is output. When the voltage comparator 13 outputs a comparison signal of high level "1", the monostable multivibrator 15
A pulse signal F having a width corresponding to approximately one period of the voltage signal C2 is output (see FIG. 2(g)).

By the way, the voltage signal C2 is always the maximum value D of the voltage signal.
The voltage signal aX, which has a magnitude obtained by multiplying by a coefficient K, lags behind E by a delay time td. Further, since the voltage signal C2 and the voltage signal C2 have originally propagated along the same propagation path, the fluctuations caused by temperature irregularities in the fluid and other disturbances are the same except for the time difference.

Therefore, the voltage signal E will vary in accordance with the variation in the voltage signal C2. For example, the maximum value D of the voltage signal
If the coefficient K of the coefficient multiplier 11 is set so that aX becomes 1/2 the magnitude of the voltage signal C2 (voltage signal E-D /2), then the voltage signal C2 becomes TMa
x, the voltage comparator 13 outputs a comparison signal of level "1" when the voltage signal C2 exceeds 1/2 of the maximum value D of the voltage signal. In other words, the voltage comparator 13 detects that the voltage signal C2 gradually increases from 0 and, for example, when it exceeds the voltage signal E at the third peak of the voltage signal C2, as long as the voltage signals C2 and D change in a similar manner. , no matter how the amplitudes of the voltage signals C2 and D change, the third peak of the voltage signal C2 is at a high level.
A comparison signal of "1" is output.

On the other hand, the voltage comparator 14 indicates that a reception signal corresponding to the voltage signal C2 has been received at the time when the voltage signal C2 crosses the reference voltage vR (in this embodiment, the time when the voltage signal crosses from a positive value to a negative value). A comparison signal of high level "1" is output. When the voltage comparator 14 outputs a comparison signal of high level "1", the monostable multi-by-break IB outputs a voltage signal C2.
A zero-cross pulse with a pulse width corresponding to approximately 1/2 period or less is output (see FIG. 2(h)).

The AND gate 17 performs a logical product of the outputs of the monostable multivibrator 15 and IB, and selects a specific peak of the voltage signal C2 (for example, the third peak of the voltage signal C2), regardless of the magnitude of the amplitude of the voltage signal C2. ) outputs a zero-crossing pulse G corresponding to the zero-crossing point immediately after.

The flip-flop 18 set by the output of the transmission command signal A is reset by the zero cross pulse G. Note that the voltage comparator 14 outputs a zero-crossing pulse every time the voltage signal C2 crosses a zero-crossing point, but as long as the voltage signal C2 does not exceed the voltage signal E, the voltage comparator 13 outputs a comparison signal of high level "1". is not output, the flip-flop 18 is not reset. The counter 20 stops counting the number of clock pulses CP by resetting the flip-flop 18 (see FIG. 2 (1)).
.

Therefore, the counter 20 has a time t1 corresponding to the propagation time of the forward ultrasound wave, a delay time t, and a trigger delay time 12.
The number of pulses of the clock pulse CP is counted for the sum of the times. Since the trigger delay time 12 can be kept constant, if the delay time t is known, the propagation time T (-tl (forward direction)) of the ultrasound in the forward direction can be measured based on the count value. . Once the forward propagation time of the ultrasonic waves has been measured in the manner described above, the reverse propagation time is now measured. That is, the transmission/reception switching circuit 7 is switched to propagate the ultrasonic waves from the ultrasonic transducers 6 to 5, and the propagation time T (-tl (reverse direction)) is measured.

The signal processing circuit 21 calculates the flow velocity V of the fluid based on the forward propagation time T1 and the reverse propagation time T2 of the ultrasound measured by the counter 20. In this embodiment, a basic method of calculating the flow velocity V based on the forward and reverse propagation times will be described. That is, if the distance between the ultrasonic transducers 5 and 6 is g1, the angle between the line segment connecting the ultrasonic transducers 5 and 6 and the flow velocity direction of the fluid is θ, and the speed of sound in the fluid is C, then The propagation time T1 in the direction and the propagation time T2 in the opposite direction are T1-1 / (c + vcos θ)T2 = 1
/ (c-vcos θ). Propagation time T and T
2, the frequency f with the relationship f l -172T 1 T2-112T2 and the frequency f of the difference between T2 is f - f
-T2-m(77g) cos θ. Since the distance ρ and the angle θ are known, the flow velocity V can be easily calculated from the frequency f.

The display 22 displays the flow velocity V calculated by the signal processing circuit 21.

FIG. 3 is a circuit block diagram of another embodiment of the ultrasonic flow rate measuring device according to one embodiment of the present invention. In FIG. 3, parts that perform the same functions as those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. Further, in FIG. 3, the OR gate 23 is operated by the transmission command signals A and A2 successively outputted from the timing pulse generation circuit 2.
Predetermined time■ Pulse signal with a predetermined width delayed. and C6 to the receiving circuit 8
This is a reception gate generation circuit that outputs signals to and 9. In addition, the transmission command signal A, the pulse signal DG, and the transmission command signal A
The interval between the pulse signal C6 and the pulse signal C6 is calculated in advance from the diameter of the flow tube 4.

By the way, in the embodiment shown in FIG. 1, the delay circuit 12 delays the voltage signal C1 by a predetermined delay time t.

only delayed. However, in the case of an ultrasonic flow velocity measurement device for gas, the delay time t is several tens to 100 μs, and the delay time ta
A stability of 0.1 μs or more is required. Such a delay element is large and expensive.

Therefore, in this embodiment, the propagation time can be measured without using the delay circuit 12.

Hereinafter, the operation of the ultrasonic flow rate measuring device having the above configuration will be explained based on the timing chart shown in FIG. 4.

When the transmission circuit 3 outputs the transmission command signals A and A2 from the timing pulse generation circuit 2 at very short intervals compared to the interval at which the transmission command signal A is output in the above embodiment (see FIG. 4(a) Reference) ■ Transmission command signal A and transmission signals B and B2 corresponding to A2
(See FIG. 4(b)). Also, transmission command signal A
(and A2), the pin hold circuit 10 is reset. Furthermore, since the flip-flop 18 is set by the output of the transmission command signal A2 and outputs a signal H of high level "1",
The counter 20 starts counting the number of clock pulses CP output by the clock pulse generation circuit 1 (see Fig. 4).
See j).

The transmission/reception switching circuit 7 outputs the transmission signals B 2 and B2 to the ultrasonic transducer 5 in response to the output of the transmission command signals A 1 and A2. The ultrasonic transducer 5 converts the transmission signals B 1 and B 2 into ultrasonic signals and transmits them into the fluid as transmission waves. The ultrasonic transducer 6 receives the transmission wave transmitted from the ultrasonic transducer 5 and converts it into a voltage signal.

The reception gate generation circuit 24 sends a pulse signal to the reception amplifier circuit 8 in synchronization with the timing when the ultrasonic transducer 6 receives the transmission wave. (see FIG. 4(c)), the receiving amplifier circuit 8 amplifies the voltage signal output from the ultrasonic transducer 6 via the transmitting/receiving switching circuit 7, and generates a voltage corresponding to the received signal. The signal is output to the peak hold circuit 10 (see FIG. 4(d)). The peak hold circuit 10 holds the peak value of the voltage signal. Further, the coefficient unit 11 outputs the maximum value D of the voltage signal held by the peak hold circuit 10.
A voltage signal En+ax .multidot. is multiplied by a constant coefficient K (see FIG. 4(c)).

Further, when the reception gate generation circuit 24 outputs a pulse signal C6 to the reception amplifier circuit 9 in synchronization with the timing at which the ultrasonic transducer 6 receives the transmission wave (see FIG. 4(r)), the reception amplifier circuit 9 amplifies the voltage signal output from the ultrasonic transducer 6 and outputs the voltage signal C to the voltage comparators 13 and 14 (see FIG. 4(g)). The voltage comparator 13 compares the voltage signal C with the voltage signal E as a trigger level, and when the voltage signal C becomes larger than the voltage signal E, it outputs a comparison signal of high level "1". In the monostable multi-by-break 15, the voltage comparator 13 is at high level "1"
When the comparison signal is outputted, a pulse signal F having a width corresponding to approximately one period of the voltage signal C is outputted (see Fig. 4 (h)).
.

On the other hand, the voltage comparator 14 outputs a comparison signal of high level "1" indicating that a reception signal corresponding to the voltage signal C has been received at the time when the voltage signal C crosses the reference voltage VR. Monostable multivibrator 16 is connected to voltage comparator 14
When it outputs a comparison signal of high level "1", it outputs a zero-cross pulse with a pulse width corresponding to approximately 1/2 period or less of the voltage signal C (see FIG. 4 (1)).

The AND gate 17 takes the logical product of the outputs of the monostable multivibrators 15 and 16, and outputs a zero-crossing pulse corresponding to the zero-crossing point immediately after a specific peak of the voltage signal C, regardless of the amplitude of the voltage signal C. do.

The flip-flop 18 set by the output of the transmission command signal A2 is reset by the zero-cross pulse G. The counter 20 stops counting the number of clock pulses CP by resetting the flip-flop 18,
The measurement of the propagation time T1 of the ultrasonic wave in the forward direction is completed (see FIG. 4(j)).

Similarly, the propagation time T2 in the opposite direction is measured.

The signal processing circuit 21 calculates the flow velocity V of the fluid based on the forward propagation time T1 and the reverse propagation time T2 of the ultrasound measured by the counter 20. The display 22 displays the flow velocity V calculated by the signal processing circuit 2F.

In this way, since the propagation time is directly measured in this embodiment, no error is introduced into this processing process.

[Effects of the Invention] As explained above, in the first invention, the switching means switches so that the ultrasonic waves propagate from the first point to the second point and from the second point to the first point. At the same time, the received signals corresponding to the ultrasonic waves that have arrived at the first point and the second point are sequentially selected and outputted, and the reference signal output means outputs a reference signal with a magnitude proportional to the amplitude of the received signal, and the delay A delayed received signal is output by delaying the received signal by the time the reference signal is output by the means, and the delayed received signal is outputted by the comparison means while keeping the relative relationship between the received signal and the reference signal, which is the trigger level, constant. Arrival of the received signal is detected by comparing the received signal with a reference signal, and in the second invention, the ultrasonic output means generates the first ultrasonic wave and a waveform substantially the same as the first ultrasonic wave. The switching means outputs the second ultrasonic waves at short intervals, and the switching means propagates the first ultrasonic waves and the second ultrasonic waves from the first point to the second point and from the second point to the first point. At the same time, the first received signal corresponding to the first ultrasonic wave and the second ultrasonic wave that reached the first point, and the first received signal corresponding to the first ultrasonic wave and the second ultrasonic wave that reached the second point The second received signal corresponding to the ultrasonic wave is sequentially selected and outputted, the reference signal output means outputs a reference signal having a magnitude proportional to the amplitude of the first received signal, and the comparison means compares the second received signal with the amplitude of the first received signal. Compare with the reference signal,
Since the arrival of the received signal is detected, it is possible to obtain an ultrasonic flow velocity measurement device that can stably and accurately measure the flow velocity without being affected by fluctuations in the amplitude of the received signal in any case.

[Brief explanation of the drawing]

Fig. 1 is a circuit block diagram of an ultrasonic current velocity measuring device according to an embodiment of the present invention, Fig. 2 is a waveform diagram showing waveforms of each part of the above block diagram, and Fig. 3 is a circuit block diagram of an ultrasonic flow rate measuring device according to an embodiment of the present invention. A circuit block diagram of another embodiment of the ultrasonic flow rate measuring device, FIG. 4 is a waveform diagram showing the waveforms of each part of the above block diagram, and FIG. 5 is an explanation of the situation in which the level of ultrasonic waves propagating in a fluid fluctuates. It is a diagram. DESCRIPTION OF SYMBOLS 1... Clock pulse generation circuit, 2... Timing pulse generation circuit, 3... Transmission circuit, 4... Flow tube, 5
゜6... Ultrasonic transducer, 7... Transmission/reception switching circuit, 8
, 9... receiving circuit, 10... peak hold circuit,
11...Coefficient unit, 12...Delay circuit, 13.14.
... Voltage comparator, 15.18 ... Monostable multivibrator, 17.19 ... AND gate, 18
...Flip-flop, 20...Counter, 21.
... Signal processing circuit, 22 ... Display device, 23 ... OR gate, 24 ... Reception gate generation circuit.

Claims (6)

[Claims] (1) From a first point in a fluid a predetermined distance away to a second point
In an ultrasonic flow rate measuring device that measures the flow velocity of the fluid based on the propagation time of the ultrasonic wave propagating to the point and the propagation time of the ultrasonic wave propagating from the second point to the first point, A received signal corresponding to the ultrasonic wave that has reached the first point, and switching means for sequentially selecting and outputting received signals corresponding to the ultrasound waves that have reached the second point; reference signal outputting means for outputting a reference signal proportional to the amplitude of the received signal; Just the time until
The apparatus is characterized by comprising: a delay means for outputting a delayed received signal obtained by delaying the received signal; and a comparison means for outputting a received signal when the delayed received signal becomes larger than the reference signal. Ultrasonic flow velocity measuring device. (2) The ultrasonic flow rate measuring device according to claim 1, wherein the reference signal has a magnitude obtained by multiplying the maximum value of the received signal by a predetermined coefficient. (3) The comparing means outputs the received signal when the received signal crosses a zero cross point after the received signal becomes larger than the reference signal. The ultrasonic flow velocity measurement device described. (4) From the first point in the fluid a predetermined distance away to the second point
In an ultrasonic flow velocity measuring device that measures the flow velocity of the fluid based on the propagation time of the ultrasonic wave propagating to the point and the propagation time of the ultrasonic wave propagating from the second point to the first point, and a second ultrasonic wave having substantially the same waveform as the first ultrasonic wave into the fluid at short intervals; and the first ultrasonic wave and the second ultrasonic wave are , the first ultrasonic wave is switched to be propagated from the first point to the second point, and from the second point to the first point, and the first ultrasonic wave reaches the first point; A switching means for sequentially selectively outputting a first received signal corresponding to a second ultrasonic wave and a second received signal corresponding to the first ultrasonic wave and the second ultrasonic wave that have reached the second point. and a reference signal output means for outputting a reference signal proportional to the amplitude of the first received signal; and a comparison means for outputting a received signal when the second received signal becomes larger than the reference signal. An ultrasonic flow velocity measuring device comprising: (5) The ultrasonic flow rate measuring device according to claim 4, wherein the reference signal has a magnitude obtained by multiplying the maximum value of the received signal by a predetermined coefficient. (6) Claim 4 or 5, wherein the comparison means outputs the received signal when the received signal crosses a zero cross point after the received signal becomes larger than the reference signal. The ultrasonic flow velocity measurement device described.