JPS5981514A - Flow meter - Google Patents

Abstract

PURPOSE:To measure a flow rate accurately and stably without any error by detecting the maximum crest value of the receive wave of each acoustic oscillator, detecting the timing of the zero-level crossing of each receive wave after the detection, and detecting the time difference in timing between both as the propagation time difference of an acoustic wave between a couple of acoustic oscillators. CONSTITUTION:A transmitting circuit 13 is driven to send acoustic waves out of the acoustic oscillators 12a and 12b. Maximum crest waves of receive waves detected by the acoustic oscillators 12a and 12b are detected and the timing at which the next wave with the maximum crest value is detected. A time difference detecting circuit 19 calculates the time difference in detection timing between zero-cross detecting circuits 18a and 18b and measures the difference between the propagation time of an acoustic wave from 12a to 12b and that from 12b to 12a. This propagation time difference is multiplied by a coefficient to find the velocity of fluid in piping 11 and this velocity is multiplied by the sectional area of the piping 11 to find the flow rate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a flowmeter that measures a flow rate by transmitting and receiving sound waves using a pair of acoustic vibrators.

[Technical background of the invention and its problems]

As shown in FIG. 1, this type of flowmeter includes a pair of acoustic vibrators 2a in a pipe 1 through which fluid flows.

2b diagonally facing each other, each acoustic vibrator 2
The sound waves simultaneously transmitted from the acoustic transducers a and 2b are received by the acoustic transducers 2b and 2a on opposite sides, and the flow rate in the pipe 1 is measured from the difference in propagation time.

FIG. 2 is an example of the waveform of a sound wave received by an acoustic vibrator. Conventionally, the piping 1 A propagation time difference proportional to the velocity of the flow inside was obtained. The flow velocity can be determined by multiplying this propagation time difference by a coefficient, and by further multiplying the flow velocity by the cross-sectional area of the pipe 1, the flow rate can be calculated.

However, with this method, the flow rate is fast and fluctuates, and the pipe 1
When the composition of the fluid flowing inside the pipe changes and the sound waves are attenuated while propagating inside the pipe, and the amplitude of the received wave becomes smaller, the received wave that was previously captured as shown in Figure 2 (a) 1st
When the peak value of the wave 4 becomes smaller than the threshold value 3 as shown in FIG. 4(b), the first wave 4 cannot be detected and the next second wave 5 is not detected. At this time, if the amplitude of the received wave from the other acoustic transducer is sufficiently large and the first wave 4 exceeds the threshold 3 as shown in FIG. 2(a), and the first wave 4 is normally captured, then both When measuring the time difference between the timings at which the received waves exceed the threshold value 3, an error corresponding to one wavelength of the sound wave occurs than the true propagation time difference, resulting in a large error in flow rate measurement.

[Purpose of the invention]

An object of the present invention is to provide a flow meter that can eliminate the above-mentioned measurement errors caused by attenuation of sound waves propagating in piping and can accurately and stably measure a flow rate.

[Summary of the invention]

The present invention detects the maximum wave height value of the received wave of each acoustic transducer, detects the timing at which each received wave crosses the zero level after that detection, and calculates the time difference between the two timings between the pair of acoustic transducers. The flow rate is measured by detecting the difference in propagation time of sound waves between the two.

That is, instead of detecting the timing at which the received wave first crosses a certain threshold as in the conventional method, the timing at which the received wave crosses the zero level immediately after the maximum peak value is detected, and the time difference between these timings is taken as the propagation time difference.

〔Effect of the invention〕

According to the present invention, even if the sound wave is attenuated while propagating inside the pipe due to a change in the flow velocity or a change in the composition of the fluid flowing inside the pipe, the position of the maximum peak value of the received wave will remain unchanged. Since it is constant, the maximum peak value can be detected reliably and easily, and the timing of the zero cross point immediately after this maximum peak value can also be detected reliably. Therefore, in the measurement of the propagation time difference, a large error of one or more wavelengths of sound waves does not occur as in the conventional method, and it becomes possible to stably and accurately measure the flow rate.

[Embodiment 0 of the Invention] Figure 3 is a block diagram of a flowmeter according to one embodiment of the present invention. In the figure, reference numeral 11 denotes a pipe through which fluid flows, and a pair of acoustic vibrators 12a and 12b are attached to this pipe 11 so as to face each other diagonally with respect to the length direction of the pipe 1. These acoustic imagers 12a and 12b are simultaneously driven by the output of the transmitting circuit 13 and generate sound waves (for example, ultrasonic waves).
is transmitted into the pipe 11. The transmitted sound waves are received by the acoustic camera on the opposite side and converted into electrical signals via receiving circuits 14h and 14b.

The outputs of the receiving circuits 14a and 14b are input to peak value detection circuits 151L and 15b that detect the peak value of the received wave, and the outputs of the peak value detection circuits 15a and 16b hold and output the peak value of the received wave one wavelength before. The signal is input to peak value storage circuits 16a, 16b and comparison circuits 17a, 17b. Comparison circuit 17 a.

17b is the peak value detection circuit 15th, the output of 15b, and 1
The outputs of the wave height storage circuits 16a and 16b, which are the wave height values before the wavelength, are compared, and only when the output of the wave height 9 straight storage circuits 16a and 16b is larger, the next stage zero cross detection circuits 18a and 18b are activated. Activate. Zero cross detection circuit 18th.

Reference numeral 18b detects the timing at which the received waves, that is, the outputs of the receiving circuits 14a and 14b cross the zero level (zero crossing point). The time difference between these timings is detected by the time difference detection circuit 19.

Next, the operation of this embodiment will be explained.

The transmitting circuit 13 simultaneously drives the acoustic vibrators 12a and 12b, thereby causing the acoustic vibrator 12a.

The sound waves transmitted from 12b propagate within the pipe 11 and reach the acoustic transducers 12b on opposite sides.

12a is reached. Regarding the acoustic vibrator 12a side, the receiving circuit 14a detects a received wave as shown in FIG. 4, and supplies it to the next-stage peak value detection circuit 15a. The peak value detection circuit 151L first detects the peak value of the first wave 4 of the received wave.

The peak value storage circuit 16a stores the peak value of the first wave. Next, the peak value detection circuit 15a detects the peak value of the second wave 5 of the received wave. Here, the comparison circuit 17a is the peak value detection circuit 15.
The peak value of the second wave of the received wave detected in step a is compared with the peak value of the first wave of the received wave stored in the wave height storage circuit 16IL. Since the second peak value is larger, comparison circuit 1
7a does not detect this, and the peak value storage circuit 16a newly stores the peak value of the second wave.

In this way, the detection of the wave height value and the comparison with the wave height value of the previous wave are performed one after another, and the maximum wave height value 21 of the received wave is stored in the wave height storage circuit 16a. Next, the wave height detection circuit 15a detects the wave height 22 of the next wave after the maximum wave height 21 of the received wave.
Detect. Since the peak value stored in the peak value storage circuit 16a, that is, the maximum peak value of the received wave, is larger, the comparison circuit 17a keeps the next stage zero-cross detection circuit 18a in an operating state. Zero cross detection circuit 1
When 8m enters the operating state, it detects timing 23 when the received wave crosses the zero level.

The maximum wave height value of the received wave detected by the other acoustic vibrator 12b is similarly detected, and the timing at which the next wave after the maximum wave height crosses the zero level is detected. The time difference detection circuit 19 detects the time difference between the detection timings of the zero cross detection circuits 18g and 18b, that is, the timing when the next wave after the maximum wave height value of the received wave of the acoustic vibrator 12a crosses the zero level, and the maximum wave height of the received wave of the acoustic vibrator 12b. The time difference between the timing at which the next wave of the wave height crosses the zero level is taken, and the difference between the propagation time from 12a to 12b and the propagation time from 12b to 12h of the sound wave between the acoustic transducers 12th and 12b is measured. By multiplying this propagation time difference by a coefficient, the velocity of the fluid flowing inside the pipe 11 can be determined, and by multiplying this flow velocity by the cross-sectional area of the pipe 11, the flow rate can be determined.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view to explain the basic principle of a flowmeter related to the present invention, and Fig. 2(b) is a cross-sectional view of a received wave to explain the method of measuring the propagation time difference in a conventional flowmeter. The i-shaped diagram and FIG. 3 are block diagrams showing the configuration of a flowmeter according to an embodiment of the present invention, and FIG. 4 is a waveform diagram of a received wave to explain a method of measuring a propagation time difference in the same embodiment. . 11... Piping, 12a, 12b... Acoustic vibrator, 1
3...Transmission circuit, 14a, 1'4b...Reception circuit, 1
5'a, 15b... Peak value detection circuit, 16
a. 16b... Peak value storage circuit, 17a, 17b... Comparison circuit, 18h, 18b... Zero cross detection circuit, 1
9... Time difference detection circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 W! :l2b (a) (b)

Claims (1)

[Claims] A pair of acoustic transducers are installed facing each other in a pipe through which fluid flows, and the propagation time difference required for the sound waves simultaneously transmitted from each acoustic transducer into the pipe to reach the acoustic transducer on the opposite side is determined by In a flow meter that measures the flow rate in a pipe, means for detecting the maximum wave height value of the received waves of each acoustic vibrator, and detecting the maximum wave height value of each acoustic vibrator after the maximum wave height value is detected by the means. 1. A flowmeter comprising means for detecting the timings of crossing the υ level, and means for detecting a time difference between the timings detected by the means as the propagation time difference.