JPH0915011A - Ultrasonic wave transmitter and receiver device - Google Patents

Abstract

PURPOSE: To accurately measure flow rate of a gas of which flow rate changes fast by using an ultrasonic wave flowmeter by weakening receiving output of reflection wave of an ultrasonic wave and enhancing accuracy of the measurement of the flow rate. CONSTITUTION: A vibrator 2 provided on the upstream side in a flow tube 1 and a vibrator 3 provided in on the downstream side therein are disposed to be inclined at angle α to each other. The receiving level of a reflection wave which is incident on the vibrator 3 by being reflected by the vibrator 2 after reflected by the vibrator 3 is relatively weaker than the receiving level of a signal wave which is outputted from the vibrator 2 to be directly received by the vibrator 3, so that the measurement accuracy is not adversely affected thereby.

Description

Detailed Description of the Invention

[0001]

2. Description of the Related Art Utilizing the fact that vector addition is established between the velocity of an ultrasonic wave and the velocity of a fluid transmitting it, an ultrasonic wave is emitted in the forward direction and the reverse direction with respect to the flowing direction of the fluid,
A flow rate measurement method using a propagation velocity difference method for measuring the velocity (flow rate) of a fluid by measuring the difference in the propagation time (arrival time) is known (for example, published by Nikkan Kogyo Shimbun in 1979, flow rate). Measurement Handbook, P246-260
reference).

In this flow rate measuring method, as shown in FIG. 3, the order in which the ultrasonic transducers 2 and 3 arranged facing each other at an upstream side and a downstream side of the flow tube 1 are used as a wave transmitter or a wave receiver, respectively. From the propagation times td and tu in the opposite direction, the velocity V of the fluid
There is a time difference method for obtaining V = (tu-td) · C ² / 2Lcosθ, and a time reciprocal difference method for obtaining V = [(1 / td) − (1 / tu)] · L / 2cosθ.

C is the speed of sound, L is the vibrator 2 and the vibrator 3.
, Θ is the center 2a of the vibrator 2 and the center 3a of the vibrator 3
The straight line connecting the lines is the angle formed by the velocity vector V of the fluid (that is, the axis of the tube 1).

[0004]

In the above prior art,
Since the oscillators 2 and 3 are arranged so as to face each other and face each other, when one of the oscillators 2 is pulse-driven as a wave transmitter, a signal wave having a waveform as indicated by reference numeral a in FIG. (Receiver) 3 receives. This signal wave is the oscillator 3
Is reflected by the surface of the oscillator 2, returns to the surface of the oscillator 2, is reflected by the surface of the oscillator 2, and is received by the oscillator 3 as a reflected wave having a waveform indicated by reference numeral B in FIG.

The distance L between the vibrators 2 and 3 is 100 to 20.
At 0 mm, the fluid to be measured is a gas, and the frequency of ultrasonic waves, that is, the driving frequency is 100 kHz to 300.
The received output of the reflected wave when the two oscillators 2 and 3 are arranged opposite to each other under the condition of kHz as shown in FIG. 3 is a signal due to the loss due to the reflection on the oscillator surface and the loss during the medium (gas) propagation. It is about 1/10 of the received output of the wave.

However, in general, the arrival (propagation) time td or tu of the ultrasonic wave is detected by the third wave or the fifth wave of the signal wave A shown in FIG. 4, so that the output of the received signal is small. Therefore, if both transducers face each other, when the temperature and flow velocity of the medium change and the reflected wave overlaps with the signal wave, the reflected wave becomes noise and the arrival time of the ultrasonic wave cannot be detected accurately, and the flow rate measurement However, there was a problem that an error that cannot be ignored was generated, and a flow with a rapid flow rate change could not be accurately measured.

Therefore, it is an object of the present invention to provide an ultrasonic wave transmitting / receiving device for an ultrasonic flowmeter which can solve the above problems.

[0008]

In order to achieve the above-mentioned object, the ultrasonic transmitting / receiving apparatus of the present invention comprises a pair of transducers (2) (3) arranged to face each other upstream and downstream of the flow tube (1). ) Is 100 to 200 mm, the propagation medium is gas, the driving frequency is 100 to 300 kHz, and the propagation time is measured by detecting the third wave or the fifth wave of the signal wave. In an ultrasonic flow meter for measuring a flow rate, the transmitter / receiver surfaces of the vibrators (2) and (3) forming the set of vibrators are arranged at an angle of 4 to 8 ° from the opposite positions. It is what

[0009]

Since the incident angle at which the reflected wave enters the receiver becomes large, the received output of the reflected wave becomes a small ratio to the received output of the signal wave, and so-called S / N is improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment in which 1 is a flow tube and 2 and 3 are flow tubes 1.
Of ultrasonic transducers 2a and 3a, which are arranged at intervals of 100 to 200 mm upstream and downstream of the transducer, are the centers of the vibrating surfaces of the transducers 2 and 3, and θ is a straight line connecting the centers 2a and 3a and the medium The angle at which the (gas) velocity vector V intersects, α is the angle at which the vibrators 2 and 3 are tilted, and is set to 4 to 8 °. The driving frequency of ultrasonic waves is 100 to 300 kHz.

Propagation time (arrival time) td when one oscillator is pulse-driven by an ultrasonic wave of 100 to 300 kHz
And tu detect and measure the third wave or the fifth wave of the signal wave. Then, the flow velocity V is calculated from this propagation time, and finally the flow rate is calculated.

Incidentally, Table 1 shows the maximum amplitudes A and B of the received output of the signal wave and the received output of the reflected wave when the inclination angle α is changed in the range of 0 ° to 10 °. To A and B
The ratio B / A of is also shown. This B / A corresponds to S / N, so to speak.

[0013]

[Table 1]

Therefore, when the inclination α is set to 4 to 8 °, the signal wave reception output A becomes smaller than that when α is 0 °, but is a value that is sufficiently practical. Further, when α is set to 4 to 8 °, the reception output B of the reflected wave becomes small and B / A corresponding to so-called S / N becomes small, so that there is no problem even if the reflected wave overlaps the signal wave. Therefore, the pulse drive interval can be shortened and the measurement interval can be shortened.

As a result, the flow rate of gas whose flow rate changes rapidly can be measured accurately. In addition, since the measurement can be continuously repeated, the accuracy of the flow rate measurement can be improved in that respect as well. 2 is a schematic diagram showing the reflection of ultrasonic signals when the wave transmitter 2 and the wave receiver 3 are arranged so as to be displaced from the positions facing each other. _Although received at an incident angle of ₁ , the reflected wave enters the receiver 3 at a large incident angle α ₂
Received at. Therefore, α ₂ > α ₁ , and the reflected wave is weakened to the extent that there is no problem in measurement. Then, the signal wave slightly shifts from the center 3a of the receiver 3 and the incident angle thereof also deviates from 0 ° by only α _1, so that the magnitude of the signal is somewhat reduced, but it does not hinder the measurement. In FIG. 2, 4
Indicates a signal wave, and 5 indicates a reflected wave.

[0016]

Since the ultrasonic transmitter / receiver of the present invention is configured as described above, the wave transmitter (vibrator) can be driven at a short interval and the flow rate measurement interval can be shortened. The flow rate can be measured accurately.

Further, since the measurement can be continuously performed by effectively utilizing the repetition of the measurement, the resolution of the flow rate measurement can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining an incident angle of a signal wave and a reflected wave on a wave receiver (vibrator) in the embodiment of FIG.

FIG. 3 is a vertical sectional view of a conventional technique.

FIG. 4 is a diagram showing output waveforms of a signal wave and a reflected wave received by a wave receiver (vibrator).

[Explanation of symbols]

1 Flow tube 2, 3 Oscillator 2a, 3a Center of oscillator θ Angle α formed by a straight line connecting the centers 2a, 3a of both oscillators 2, 3 and the flow velocity vector V

Claims (1)

[Claims] 1. A distance between a pair of vibrators (2) and (3) arranged facing each other upstream and downstream of the flow tube (1) is 100 to 200 mm.
The propagation medium is gas and the driving frequency is 100 to 300k.
In the ultrasonic flow meter, which measures the propagation time by detecting the third wave or the fifth wave of the signal wave at Hz, and measuring the flow rate of the fluid from this propagation time, a vibration forming the set of vibrators. Sending children (2) (3)
An ultrasonic transmitting / receiving device, wherein the receiving surfaces are arranged at an angle of 4 to 8 ° from the opposite positions.