JPH03233395A - Sound wavepropagation time measuring method - Google Patents

Abstract

PURPOSE:To accurately measure sound wave propagation time by using two or more sound waves with the same amplitude and different frequencies, and setting a specific point where the zero-cross of the sound wave with the highest frequency occurs as the time of start and completion of the sound wave propagation time. CONSTITUTION:First and second transmission wave outgoing circuits 1, 2 transmit ultrasonic signals W1, W2 with different frequencies, respectively. Electroacoustic converters 4, 5 perform the mutual exchange of an electrical signal and an acoustic signal. An outgoing reference detection circuit 3 detects the point nearest to a zero- cross point from a positive direction to a negative direction of the signal W2 out of the zero-cross points in the positive and negative directions of the signals W1, W2. Also, the circuit 3 outputs a pulse of positive potential to a propagation time measuring circuit 14 when the potential of the signals W1, W2 go less than the ground potential. A reception circuit 12 for outgoing reference detection is comprised similarly, however, it detects the signal delaying by the propagation time between the converters 4, 5 behind the circuit 3. When the pulse from the circuit 3 is outputted, the circuit 14 starts the measurement of the propagation time, and counts the time until no pulse is outputted from the circuit 12.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention utilizes the propagation time of sound waves to calculate distance, fluid flow velocity,
This invention relates to a method for measuring sound wave time in a device for determining thickness, speed of sound, temperature, etc. [Prior art] Fig. 6 is a schematic configuration diagram of an ultrasonic flowmeter that calculates flow rate using the propagation time of sound waves, Fig. 7 is a timing diagram of ultrasonic transmission and reception, and Figs. 8 and 9 are reception diagrams. FIG. The ultrasonic flowmeter shown in FIG. 6 has an electric/acoustic transducer 32 installed on the wall of a tube 31 through which a fluid to be measured flows.
and 33, transmitting and receiving ultrasonic waves between the ultrasonic flowmeter converter 3
4, the propagation time of the sound wave is measured and the linear average flow velocity V of the fluid is determined. In this ultrasonic flowmeter, when an ultrasonic wave is emitted from the electric-acoustic transducer 32 to the electric-acoustic transducer 33, the propagation time is 11, and the propagation time is 11 when the ultrasonic wave is emitted from the electric-acoustic transducer 33 to the electric-acoustic transducer 32. The propagation time when emitting ultrasonic waves is t2
Then, the linear average flow velocity V of the fluid flowing inside the pipe is approximately expressed by the following equation (1). However, D: Inner diameter of the pipe 31 θ: Ultrasonic incident angle from the pipe 31 to the fluid to be measured C: Sound velocity in the fluid to be measured τ: Propagation time required in the measurement circuit other than the propagation time of the sound wave in the fluid to be measured The transmitted waveform shown in Figure 7 (1) is called a damp wave, and after the required number of waves of ultrasonic waves necessary for time measurement are transmitted, unnecessary transmitted waveforms are acoustically damped as soon as possible. There is. Therefore, the electrical-acoustic transducer 3
3, a received waveform as shown in FIG. 7(2) is obtained. [Problems to be Solved by the Invention] By the way, in FIG. 7, there is a method such as Japanese Patent Publication No. 44-31284 to obtain the timing of receiving sound waves. However, the received waveforms are not always at the same level or in the same shape, and for this reason various ideas have been made using AGC and APC. For example, Japanese Patent Application Laid-Open No. 61-59275. However, the transmission and reception using the normal one-frequency pulse method using a dumb wave as shown in Figure 7 has the following common drawbacks, resulting in measurement errors.In equation (1), is the electrical circuit delay l,
The propagation time of the sound wave transmission member other than the fluid to be measured is 2. After the trigger wave is recognized from the time when the signal sound wave first arrives,
The time it takes to cross Ov for the first time is 3 magnitude (the definition of the trigger wave is the same as in JP-A-61-59275). For 3, use the zero cross method of Japanese Patent Publication No. 44-31284 to calculate S in Figure 8 as the trigger wave. However, f is the frequency of the sound wave to be used as a signal, and 3 can be determined in advance in this way. In addition, since , l and 2 can be determined using various measuring instruments, (in equation 11) can be entered into the calculation formula as a constant in advance. However, as shown above, 3 can be obtained. This is when the SL used as the trigger wave is definitely SL.In other words, if the SL used as the trigger wave is actually S2,
3 is, an error occurs immediately after the settings are made, and this results in an error in the reading of the measuring device. However, in either case, there is a possibility of an error in judgment. In the case of an ultrasonic flowmeter, the received waveform as shown in FIG. 8 may become as shown in FIG. 9 depending on the piping to be measured, the fluid to be measured, the sound wave transmission medium such as a coupling agent, and the propagation path. At this time, if the equipment or the oscilloscope observer cannot find So or Sl buried in the noise, they will mistakenly judge S2 to be St, resulting in the above-mentioned error. So and S buried in noise
Even if l can be discovered, there are further problems as follows. Changes in the received waveform due to the above sound wave transmission medium and propagation path are as follows:
It also affects the shape of the received waveform. S defined in FIG. , Stb St, S, . . . The reception level ratio So: St: St: Ss: . . . changes, for example, in FIG. 7, So: S, = 1: 10.
In Figure 8, So: SI= 1: 1
It has become. This occurs due to changes in the waveform synthesis state of various phases, etc., but in such cases, APC't'')
Even if AGc is used, S cannot be used as a trigger wave. In other words, since So:S = 1:1, even if the S+ level is amplified, 30 levels will be amplified at the same time, so St
The waveform of S is not triggered. This is because it will be triggered. An object of the present invention is to provide a sound wave propagation time that can accurately measure the propagation time without making a mistake in the timing of the propagation time measurement even if noise is mixed into the received wave or the shape (level) of the received waveform changes. The objective is to provide a measurement method. [Means for Solving the Problems] The sound wave propagation time measurement method of the present invention simultaneously emits two or more sound waves, each having a substantially constant amplitude for a certain period of time and different frequencies, so that the sound waves with the highest frequency range from positive to negative. , or zero-crossing in a predetermined direction from negative to positive, which is closest to the time when a sound wave of another frequency zero-crosses in a predetermined direction from positive to negative or from negative to positive, and the time The time point at which the sound wave first appears is detected on the transmitting side and the receiving side, and the propagation time of the sound wave is measured using these times as reference times for starting and ending the propagation time measurement, respectively. [Operation] Two or more sound waves each having a substantially constant amplitude for a certain period of time and different frequencies are used, and when the sound wave with the highest frequency crosses zero in a predetermined direction, the sound waves with other frequencies are positive. Since the reference time for the start and end of propagation time measurement is the closest and first point in time to the zero-crossing point in a predetermined direction from negative to negative or from negative to positive, the received wave contains noise. Even if the received wave level changes, there is no risk of misperceiving the timing of the propagation time. [Example] Next, an example of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram of an embodiment of an ultrasonic flowmeter to which the sound wave propagation time measurement method of the present invention is applied, Fig. 2 is a circuit diagram of the transmission reference value detection circuit 3 in Fig. 1, and Fig. 3 4 is an ultrasonic transmission/reception waveform diagram, FIG. 4 is a waveform diagram showing transmitted waves Wl and W2 superimposed, and FIG. 5 is an enlarged view of the vicinity of point A in FIG. 4. The ultrasonic flowmeter of this embodiment includes a first transmission wave transmitting circuit,
Second transmission wave transmission circuit 2, transmission reference value detection circuit 3, electric/acoustic converter 4.5, selector switch 6.7, bandpass filter 8.9, signal amplifier In, 11, and transmission standard. A wave detection receiving circuit 12, a noise gate circuit 13,
It consists of a propagation time measuring circuit 14 and a circuit (not shown) for determining the linear average flow velocity. First transmission wave transmitting circuit 1. The second transmission wave transmitting circuit 2 transmits ultrasonic signals Wl and W2 (FIG. 4) having frequencies f+ and fa (<f,), respectively. Here, Wl is a signal wave for propagation time measurement, and W2 is a signal wave for propagation time measurement W.
This is a signal wave for identifying a reference point for measuring the propagation time of l. The electric/acoustic converter 4.5 mutually converts electric signals and acoustic signals.The changeover switch 6 has a common terminal connected to the first transmission wave transmission circuit 1 and the second transmission wave transmission circuit 2, and a switching terminal connected to the electric signal and the second transmission wave transmission circuit 2. - Connected to acoustic transducer 4.5, signals Wl and w2
is input to the electric/acoustic transducer 4 or 5. The changeover switch 7 has a common terminal connected to the bandpass filters 8 and 9, a switching terminal connected to the electric/acoustic converter 4.5, and a signal wave Wl converted into an electric signal by the electric/acoustic converter 4 or 5.
The signals containing W2 are each output to bandpass filters 8.9. Bandpass filters 8 and 9 each receive a signal wave Wl. W2 is taken out and output to signal amplifiers 10 and 11, respectively. Signal amplifier 10. II are the signal waves Wl and
The 0 oscillation reference detection circuit 3 that amplifies the signal wave w1
Points A and B when zero crosses from positive to negative. C, D, . . ., the circuit detects the point A (Fig. 4) closest to the point in time when the signal wave W2 zero-crosses from positive to negative direction, and as shown in Fig. 5, the signal wave Ill ,
Comparators 21 and 22 that output a positive potential pulse when the potential of W2 falls below the ground potential, a monostable multivibrator 23 that outputs a pulse with a pulse width PWI based on the output pulse of the comparator 22, and the output pulse of the comparator 21. and an AND gate 24 which takes the AND of the output pulses of the monostable multi-bi break 23,
The output pulse of the AND gate 24 is the propagation time measurement circuit 14.
is output to. In this manner, by providing the monostable multivibrator 23, a pulse is output from the transmission reference value detection circuit 3 only at time A, and time A is identified. The transmission reference wave detection receiving circuit 12 has a similar configuration, and includes a signal amplifier 10. Detect time A from the output of II. Naturally, this time point is greater than the time point A detected by the transmission reference value detection circuit 3.
delayed by the propagation time between Propagation time measurement circuit 14
When a pulse is output from the transmission reference value detection circuit 3, it starts measuring the propagation time, and the reception circuit 12 for detecting the transmission reference wave starts measuring the propagation time.
Count the time from when the pulse is output. Note that the propagation time measurement circuit 14 is in the same state as time A at time I.
(FIG. 4) is detected by the transmission reference value detection circuit 3, and outputs a control signal to suppress the output of the pulse, and also controls the changeover switch 6.7. The noise gate circuit 13
Ultrasonic wave Wl transmitted from one side of the acoustic transducer 4.5,
W2 is received by the other electric/acoustic transducer, and by the time point A is detected, noise exceeding the threshold level has entered, and the receiving circuit 12 for detecting the outgoing reference wave has mistakenly recognized this noise as a signal wave. In order to prevent the output of pulses, the operation of the receiving circuit 12 for detecting the transmitted reference wave is stopped until the approximate arrival time of the signal sound wave, which is predicted in advance from the distance between the electric/acoustic transducers 4 and 5. Pulses are not sent to the propagation time measurement circuit 14. Such a noise gate circuit 13 is used in an ultrasonic flowmeter, etc.
This is a type of signal processing technique that is very commonly used, but if noise at a level that exceeds the threshold level comes in between the time the noise gate is released and the time the received wave comes in, the received wave is There remains a risk of misunderstanding. According to the present invention, it is possible to prevent erroneous recognition of such noise. moreover,
In the unlikely event that there are two frequency components such as noise Wl and W2 as described above, the third. 4th. If an identification signal wave of ... is emitted, misrecognition can be more reliably prevented. In this example, a configuration example is shown in which two frequency transmission waves are applied to piezoelectric elements (electrical/acoustic transducers) each having a different resonant frequency, and the reception side is similarly received by a piezoelectric element having a different resonant frequency. , it is also possible to construct the system by modulating the signal wave using amplitude modulation, frequency modulation, etc. using one type of broadband electrical/acoustic exchanger. This embodiment also uses a dumb wave, but differs from the conventional pulse method using a dumb wave in that the rising portion of the pulse is not used. The present invention is not only effective for the above-mentioned ultrasonic flowmeter, but also for all devices that utilize sound wave propagation time measurement (for example, ultrasonic distance meters, ultrasonic thickness meters, sound speed meters, sound probes, fish finders). , CT scan, etc.). [Effects of the Invention] As explained above, the present invention uses two or more sound waves with the same amplitude and different frequencies, and sets a specific time point among the zero-crossing points of the sound wave with the highest frequency as the sound wave propagation time. By using the reference time for the start and end of the measurement, there is no possibility of misperceiving the timing of the propagation time measurement even if the received wave contains noise or the waveform (level) of the received wave changes.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of an ultrasonic flowmeter to which the sound wave propagation time measurement method of the present invention is applied, Fig. 2 is a circuit diagram of the transmission reference value detection circuit 3 in Fig. 1, and Fig. 3 is an ultrasonic transmission/reception waveform diagram, Fig. 4 is a waveform diagram showing transmitted waves Wl and W2 superimposed, Fig. 5 is an enlarged view of the vicinity of point A in Fig. 4, and Fig. 6 is an ultrasonic waveform diagram using the propagation time of the sound wave. A schematic configuration diagram of an ultrasonic flow meter that calculates the flow rate using
9 are received waveform diagrams. DESCRIPTION OF SYMBOLS 1... First transmission wave transmission circuit, 2... Second transmission wave transmission circuit, 3... Transmission reference value detection circuit, 4.5... Electrical/acoustic transducer, 6.7... Changeover switch, 8.9... Bandwidth filter, In, 11... Signal amplifier, 12... Receiving circuit for detecting outgoing reference wave, 13... Noise gate circuit, 14... Propagation time measurement circuit, 21, 22... Comparator, 23... Monostable multivibrator, 24... AND gate.

Claims (1)

[Claims] 1. A device that performs targeted measurement using the propagation time of sound waves, which simultaneously emits two or more sound waves, each with substantially constant amplitude for a certain period of time and different frequencies; At the point in time when the largest sound wave crosses zero in a predetermined direction from positive to negative or negative to positive, the sound waves of other frequencies zero cross in a predetermined direction from positive to negative or from negative to positive. A sound wave propagation time measurement method in which the time point that is closest to the time point and appears first in time is detected on the transmitting side and the receiving side, and the propagation time of the sound wave is measured using these time points as reference times for starting and ending the propagation time measurement, respectively. .