JP2000146649A - Method for measuring propagation delay time of ultrasonic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the point of time of arrival of sound waves not in an initial rise section at which received waves are unstable but at the timing when a received waveform is stabilized after the lapse of a predetermined delay time at the time of measuring the propagation delay time of ultrasonic waves. SOLUTION: By shortening the time to impress a transmitter with a high-frequency voltage, making large an external impedance viewed from the transmitter, and lengthening the reverberation duration of ultrasonic waves, a series of received waveforms which rise, once drop, and suddenly rise as indicated in 1, 2, 3, 4, 5, 6, 7, and 8 in Fig 1 are made to occur in the waveform of a received voltage. Then, the received waves which suddenly rise are triggered, the time between the instant when the ultrasonic waves are projected and the instant when the waves are triggered is measured, and predetermined delay time is subtracted from the measured time to obtain the propagation delay time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

2. Description of the Related Art As shown in FIG. 2, ultrasonic transducers (31) and (32) are arranged opposite to each other in flowing water flowing at a flow rate (V) in a pipe (30) to transmit ultrasonic waves. If the propagation time is measured by transmitting and receiving the flowing water in the forward and reverse directions and measuring the propagation time between transmission and reception, the flow velocity (V) is proportional to the difference between the forward and reverse propagation times. Is measured. The present invention relates to a method for measuring a propagation time, which is the basis of an anemometer.

[0002]

2. Description of the Related Art In a conventional propagation time measuring method, a high-frequency voltage is applied to a transmitter for a long time to transmit a powerful sound wave as shown by a dotted line (41) in FIG. When detecting the arrival time of the sound wave, the second wave of the reception voltage waveform shown by the dotted line (43) in FIG. 5 is triggered by the threshold value (44) (the threshold value is set and compared with the signal voltage). And the point of coincidence is detected), and the point of arrival of the sound wave is determined. In this method, if the amplitude of the received wave fluctuates, the triggered received wave may be the first wave or the third wave, and the measurement may be performed in an incorrect order, which may cause an error. Therefore, the received wave (4
An amplitude stabilizing circuit may be added so that the peak value of the envelope of (3) is always constant, or (for example, Showa 53.8.29)
Ultrasonic technology handbook page 593) A circuit that can always trigger the same number of received waves by a method of tracking the number of the received wave when first measured (for example, recent sensor page 176 issued by the Institute of Electrical Engineers of Japan, 63.6) Has been added.

[0003]

The conventional method of adding an amplitude stabilizing circuit and the conventional tracking method have the disadvantage that the circuit becomes complicated and the apparatus becomes expensive. The present invention proposes a method for simply and reliably triggering a target reception wave without adding a particularly complicated circuit.

[0004]

In FIG. 2, when the four-pole double-throw changeover switch (35) is turned on to the right, the transmitter (21) is turned on.
And the high-frequency transmitter (33) are connected via a pair of reversely connected diodes (36). This increases the external impedance seen from the transmitter to reduce the braking effect,
This is to extend the reverberation time. The receiver (32) is connected to a high sensitivity amplifier (34). When the changeover switch (35) is turned ON to the left, (32) becomes a transmitter,
These transmitters and receivers use piezoelectric ceramic vibrators for both transmission and reception so that (31) is a receiver.

When a short-time high-frequency voltage of less than one cycle as shown by a solid line in FIG.
As shown by the solid line (40) in FIG. 4, the amplitude of the sound wave has a steep rise but is immediately attenuated, and thereafter, has a waveform in which reverberation continues for a while. When this sound wave arrives at the receiver (32), it starts to resonate, and the output voltage of the high-sensitivity amplifier (34) (hereinafter referred to as reception voltage) rises as shown by the solid line (42) in FIG. It descends without growing. Thereafter, the received voltage rises sharply again due to the reverberation of the sound wave. In order to explain this phenomenon in more detail, the sound wave curve (4
0) and the rising portion of the reception voltage curve (42) drawn in FIG. 5 are enlarged and shown in FIG. 1 and the relationship between them is described.

Referring to FIG. 1, the relationship between the intensity of the sound wave and the reception voltage curve will be described graphically. If a sound wave having a constant amplitude (h) is continuously received, the reception voltage curve is the curve (21,22,23,24,25,6,27,2) in FIG.
8). At the time of (6) when the reception voltage curve starts to rise sharply, the curve of the sound wave emitted when applied for a short time (11.12.13.14.15.6.17.)
18), both curves are drawn so as to intersect at the time (6) when the transition from rapid decay to gentle reverberation occurs. In the real case,
The assumed receiving voltage curve is determined by the receiving sensitivity characteristic peculiar to the receiver with respect to the assumed amplitude value of the sound wave. The sound wave curve is determined by the characteristic of the applied voltage versus the transmission sound pressure specific to the transmitter. If the voltage does not change, the application time is adjusted to shift to the time (11) of the start of the attenuation of the sound wave amplitude and reverberation. It is possible to shorten or delay the timing (6).

[0007] The actual reception voltage curve (1, 2, 3, 4, 5, 5)
・ 6 ・ 7 ・ 8) can be obtained diagrammatically as follows.
Peak value _{H 1} is assumed received voltage of the first wave (1) (2
If the magnitude of 1) and _{E 1} and the amplitude of the sound wave (11) and _{S 1}

(Equation 1) Becomes The peak value of _{H 2} amplitude _{S 2} Tosureba second wave of the sound wave to the magnitude of the received voltage (22) and _{E 2} (12) (2) is

(Equation 2) Becomes Hereinafter in the same manner peak value H ₈ eighth wave (8) is the size of the assumed received voltage (28) and E ₈ waves (1
If the amplitude of the 8) and _{S 3}

(Equation 3) Becomes Here, on the left side of the sixth wave, the ratio between the amplitude of the sound wave and h is much larger than _1, and the envelope connecting the peak values H ₁ H ₂ H ₃ H ₄ H ₅ of the actual reception voltage has a mountain shape. . In particular, H ₃ H ₄ H ₅ becomes larger than h and temporarily drops to the received wave (6). In this way, once received wave (6)
Is formed. Next, on the right side of the sixth wave, the ratio between the sound wave and h is close to 1 and the actual reception voltage H
₇ H ₈ is slightly smaller than the reception voltage _E 7 _{E 8} was assumed. Since the right side is a region where the reception voltage rises sharply, a reception wave that rises sharply like the eighth wave appears. Thus, once the received wave starts rising, it falls once,
A series of received waveforms that rapidly rise again (1) (2) (3)
(4) (5) (6) (7) (8) are obtained.

[0008]

FIG. 2 shows a pipe (30) having a diameter of 1.3 cm.
The transmitters / receivers (31) and (32) each using a piezoelectric vibrator in the flowing water are arranged facing each other at a distance of 20 Cm. Resonant frequency of the transducer is 200KH _z, the applied voltage of the high-frequency oscillator (33) was amplitude 20V, application time 1 cycle. The amplification factor of the amplifier (34) was 10000 times or more, and the output was observed with a synchroscope to obtain the waveform of FIG. Period of the resonant frequency from the time when the reception wave of the eighth-wave appears arrives waves (200KH _z) (5μ
S), which is 8 times (40 μS), which is constant. Therefore, the threshold value was set at the position (10), the time from the launch to the detection of the eighth wave was measured, and the propagation time could be obtained by subtracting 40 μS, which is a constant delay time, from this. .

[0009]

The sound wave generated when a short-time voltage is applied to the transmitter The waveform of (40) in FIG. 4 is determined by the characteristic of the transmitter-applied voltage versus the transmission sound pressure. Received Waveform at the Time of Reception FIG. 5 (42) shows that the reception sensitivity characteristic unique to the receiver and the waveform of the sound wave are combined, and (1-2) in FIG.
(3, 4, 5, 6, 7, 8). Therefore, the time when the rapidly rising received wave (8) appears in the received waveform is hardly affected by a change in the amplification factor or a fluctuation in the amplitude of the sound wave. The time from the arrival of a sound wave to the detection of a rapidly rising received wave is determined by the period of the resonance frequency and the order of the detected received wave, and is constant. That is, the propagation time measuring method of the present invention requires a special amplitude stabilizing circuit and a tracking method, and enables stable measurement.

[Brief description of the drawings]

FIG. 1 is a detailed explanatory diagram showing a relationship between a waveform of an ultrasonic wave and a received waveform.

FIG. 2 is a circuit diagram

FIG. 3 is a waveform of a high-frequency voltage

FIG. 4 is a waveform of an ultrasonic wave.

FIG. 5 is a waveform of a reception voltage.

FIG. 6 is an example of a reception voltage waveform.

[Explanation of symbols]

1, 2, 3, 4, 5, 6, 7, 8 Actual received voltage waveforms 11, 12, 13, 14, 15, 16, 17, 18
Waveform of sound wave 21 ・ 22 ・ 23 ・ 24 ・ 25 ・ 26 ・ 27 ・ 28
Assumed reception voltage waveform 30 Pipeline 31 ・ 32 Transmitter / receiver c Sound speed of ultrasonic wave V Flow velocity 33 High frequency transmitter 34 High sensitivity amplifier 35 Quadrupole double throw switch 36 ・ 38 Diode 40 Sound wave at short time application 41 Long time application Sound wave at time 42 Received voltage waveform when applied for a short time 43 Received voltage waveform when applied for a long time 10 Threshold value to be set when implementing the present invention 44 Threshold value to be set by conventional method

Claims (1)

[Claims] An ultrasonic wave transmitter and a transmitter for exciting the transmitter are connected via a pair of reverse-connected diodes, and a short-time voltage is applied from the transmitter. When the sound wave arrives at the receiver, the received wave once rises, but falls following the attenuation of the sound wave, and then the receiver is energized by the continuing reverberation, and the received wave soars again A series of received waveforms is formed, and at this steep rising portion, a received wave exceeding a threshold is detected, and the time from when the sound wave is emitted to when the received wave is detected is measured. A measurement method in which a certain delay time from arrival to detection is subtracted to obtain an ultrasonic propagation time.