JPS58191924A - Ultrasonic flow meter using positive feedback loop - Google Patents

Abstract

PURPOSE:To enhance a detection speed, by providing a frequency selecting means in a positive feedback loop consisting of a speaker for ultrasonic radiation arranged on one side of a passage pipe, a microphone arranged on the opposite side, and an output amplifying circuit. CONSTITUTION:When the gain of the positive feedback loop constituted with a speaker 2 arranged in a passage pipe 1, a microphone 3, and an amplifying circuit 4 is set to a value very larger than one and a white noise is used as a trigger signal to oscillate a fluid, a frequency where a length L between the speaker 2 and the microphone 3 is N times as high as the wavelength of acoustic waves in the fluid is oscillated. Since an oscillation frequency (f) is changed as a primary function of a fluid speed V, the speed V is obtained on a basis of the frequency (f), and the sectional area of the pipe 1 is multiplied to obtain a flow rate. Meanwhile, since the number of frequencies (f) is infinite, the narrow- band microphone 3, the narrow-band speaker 2, or the like is used as the frequency selecting function means to specify preliminarily one value as N.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flow needle using positive feedback.

BACKGROUND ART A single ultrasonic flow needle has been widely used as a means for measuring the flow rate and flow rate of a fluid such as air passing through a flow pipe. One of the methods is the fil, 7 around method.

/Fugu around method is, as is well known,
Two pairs of electro-acoustic, acoustic-electric transducers are placed opposite to each other, and the flow rate of the fluid is calculated from the time it takes for the ultrasonic waves to propagate through the fluid between them.
However, the conventional single-around P method had the following drawbacks.

(11) Since the measurement is based on the propagation time of the ultrasonic waves between a pair of electroacoustic and acoustoelectric transducers arranged opposite to each other, the detection speed cannot be increased.

(2) Since the width of change in propagation time is generally small, it is difficult to increase measurement sensitivity.

(3) On the receiving side, pulsed ultrasound is detected, so
It is easily affected by noise, etc., and easily causes measurement errors.

An object of the present invention is to improve the above-mentioned drawbacks, and to provide an ultrasonic flow needle that is high speed, highly sensitive, hardly affected by stuttering noise, etc., and has little measurement error. In order to achieve the purpose, in the present invention, a speaker and a microphone are arranged opposite to each other on both sides of a flow pipe,
A positive feedback (oscillation) loop is constructed by supplying the amplified output of the microphone to an 18θ speaker, and a frequency selection system is arranged within the loop.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention. In the figure, 1#'i is a flow path pipe through which fluid such as air passes, 2#: is on one side of the front flow path pipe 1,
A speaker, typically an electroacoustic transducer, arranged to emit ultrasonic waves toward a fluid within it.

3 is emitted from the PiiJ speaker 2 and passes through the fluid,
A microphone (generally an acousto-electrical transducer) 4 receives the ultrasound propagating along the path indicated by the dotted line and outputs a corresponding electrical signal; 4 is supplied with the electrical output of the microphone; This is an amplification circuit that amplifies and applies the signal to the speaker 2.

As is clear, the primary speaker 2, microphone 5, and amplifier circuit 4 in FIG. 1 constitute a positive feedback (4?i) loop f.

= iJ In the configuration described above, when the start switch (not shown) is closed and a signal is input into the first feedback (oscillation) loop for a certain period of time, this signal is transmitted from the microphone → amplifier circuit → speaker → fluid Medium (f wave) → circulates through the closed loop circuit of the microphone.

At this time, the phase difference between the input and output of the amplifier fI & (b) path is zero, and from the increase S degree A of the amplifier circuit, the loop t1M
If the gain G (loop din) of the closed circuit loop, which is obtained by subtracting the attenuation amount B during one cycle of the signal, is 19 or more, the input of the signal is stopped and the bird stutters, and the positive feedback loop continues to oscillate. .

Here, we set the amplification degree M to be much larger than the attenuation amount B, and set the first loop r in to G > 1, and use white noise etc. as the signal. When a signal is triggered, it stops oscillating at various frequencies such that the phase difference between the input and output of the amplifier circuit becomes zero, and the oscillation continues even after the signal stops outputting.

This will be further explained in detail with reference to FIG. 2. FIG. 2 shows the phase of each part in the configuration of FIG. 1, and in the figure, the same reference numerals as in FIG. 1 represent the same parts. Further, the symbols in the figure are defined as follows.

ψm Phase ψ2 of the input voltage of the amplifier circuit 40... Phase ψ6 of the output voltage of the amplifier circuit 4... Phase shift fas that occurs during speaker conversion... ω phase ψ adjustment of the output voltage of the speaker... Manual power of the microphone Phase of sound pressure ψm... Phase shift caused by VC during microphone conversion As is clear from Figure 5J12, each phase and (
Monthly Plan Phase 4 (1)...For VC, the equation (I/2) holds true.

ψa8−ψ2+ψθ ・・・・・・・・・(1) ψ
au>+ψm-ψ1...'...hull 2) However, in order for [, ψ1zψ2 to hold true, equation (3) should hold.

fas −ψam−dem + pm ・・・・・・
(3) Here, assuming that ψ6 and ψm are constant, the phase of the output sound pressure of the speaker! a- and the phase of the human sound pressure of the microphone ψI! If the phase difference with Lm is a certain value, oscillation will continue.

For simplicity, assuming that the configuration is such that ψIO+f days = 0, the following equation (4) can be obtained from equation (3).

ψam −ψ&e (4) That is, in the previous circuit, when the phases of the input sound pressure of the microphone 30 and the output sound pressure of the speaker 4 become equal, oscillation continues. From this, it can be seen that the distance between the speaker 2 and the microphone 5 is N of the wavelength of the f-wave in the fluid.
The closed loop circuit ri oscillates at a frequency that is multiplied by ri (N is a positive integer).

As mentioned above, when the spinning closed loop circuit continues to oscillate at the frequency f, the line connecting the speaker 2 and the microphone 5 - the length of the (ultrasound) propagation path is Ll, and the propagation path is the tube axis. Let the angle between the two be -, and the propagation velocity of the (N) sound wave in the fluid when the flow velocity of the fluid in the flow path pipe 1 is zero is U, then the propagation velocity of the (ultrasound) sound wave in the fluid is: ・υ
+ V coo θ. Therefore, the frequency 'ri of the circuit is given by the following equation (5).

If we measure the oscillation frequency of the 1-Z circuit when the fluid flow velocity ■ is zero, then we get (6
) can be used to obtain N.

As is clear, N is a constant for a certain oscillation frequency. Therefore, equation (5) can be expressed as equation (7).

f=, 10, V... River... (The force, that is, the oscillation frequency f changes as a linear function of the fluid flow velocity V, so if you measure the oscillation frequency if, (7)
The flow velocity V is determined from the formula, and by multiplying this by the cross-sectional area of the flow path pipe 1, the flow rate is determined.

As is clear from the above explanation, the change in the oscillation frequency with respect to the flow rate (flow velocity) is as shown in FIG. 3, with N as a parameter. As we will see, a certain flow rate (fL
There are an infinite number of values for H.

Therefore, when measuring the actual flow rate and flow velocity, H
It is necessary to select and specify one value.

As a means for selecting and specifying one value from a large number of H values, in the present invention, one means for a frequency selection function is provided in one closed Luzo. As the frequency selection steering means, various devices such as narrowband microphones, speakers, passive filters, active filters, and dizotal tweeters can be used. We will explain some of the practical methods for determining the percentage.

1. Insert a bandpass filter at an appropriate location within the A-D. Then, as shown in FIG. 4, the bandwidth of the bandpass filter is set to a frequency width that corresponds to the flow velocity (flow rate) measurement range B&C and does not overlap with N of other cages.

Insert a variable bandpass filter whose center frequency varies by OT into the loop. An example of the circuit configuration in this case is shown in Figure 45.

In FIG. 5, the same reference numerals as in FIG. 1 represent the same parts. In the figure, amplifier circuit #i front stage amplifier 4-
1 and a post-stage amplifier 4-2, and between the two, there is a p1 variable band bandpass filter 6 whose central wave number can be varied.
is inserted. Reference numeral 7 denotes a chest wave number-to-voltage converter for converting the output frequency of the amplifier 4-2 into a voltage and controlling the center frequency of the variable band pan-V pass filter.

-Positive 4j1 (oscillation) f [gives inertia.

In the configuration shown in FIG. 1, even when the period of the signal received by the microphone 5C is disturbed due to a sudden change in the flow velocity, etc., the vortex generated in the flow inside the flow path pipe 1 is is directly amplified by the amplifier circuit 4 to drive the speaker.

For this reason, the stability of the roots collapses, and in that state, it becomes stable again at the closest value of N.

Therefore, it is necessary to have a structure in which the oscillation frequency does not easily fluctuate due to short-term periodic fluctuations in the received waves.

For this purpose, in addition to slowing down the response speed of the roots, it is also necessary to give the VC1 roots themselves inertia like a flywheel. It is sufficient to add an i1 extension circuit to.

However, in such a method, since the manual waveform of the microbo 250 only drives the speaker 2 after a fixed time delay, the change in the oscillation frequency caused by the disturbance of the received wave remains unchanged. In other words, with such a method, it is not possible to suppress the fluctuation of the value of N. The symbols denote the same parts.

8 is a PLi-circuit composed of a phase comparator 81, a low-pass filter 82 and a voltage controlled oscillator 83.

As is clear from the comparison with Fig. 5, Fig. w16 uses a PLL (PhaseLoc
ked LOJI)) This is a book with a circuit inserted.

As is clear, in the configuration shown in the VCl s6 diagram, the following 02 loops are formed (Ll) Microphone 5 → Amplification Wi4-1 → PLL →
Amplifier 4-2"→Speaker 2→Microphone 3 (L2) Phase comparator 81→Low-pass filter 82-Voltage control device 83→Phase comparator 81 The first roots L1 including the microphone and speaker are stabilized. The time it takes for VCJII to stabilize is T, the time it takes for the PL, L circuit, that is, the second loop L2, to stabilize.
, and if there is a relationship T, ) TI between them, the time for the roof 'L1 of sl to stabilize is approximately TI.

Therefore, even if the received wave period fluctuates for a short time due to external noise or vortices generated in the fluid, the oscillation frequency of the second loop L2 made up of the PLL circuit will not change significantly.
Stable oscillation can be obtained as a whole of the system shown in FIG.

In other words, the circuit shown in FIG. 6 has a ! J1 Rou-7' It behaves like L1 with inertia.

FIG. 7 shows an example of the results of actually measuring the air flow rate in the flow pipe according to the present invention. This figure also shows that the oscillation frequency and the flow rate have a nearly linear relationship.

As is clear from the above description, according to the present invention, not only can the flow rate be measured by simply measuring the oscillation frequency of a positive feedback (oscillation) loop including a microphone and a speaker, but also one cycle of the oscillation frequency is , it becomes 1/N of the time it takes for the signal to go around the loop, so it becomes possible to shorten the measurement time to 1/y of that in the sing-around method and increase the accuracy by N times.

Furthermore, there is an advantage that the structure can be simplified compared to the conventional single-around method.

Furthermore, since the loop is kept in a resonant state, the BlN ratio becomes good, and from this point of view as well, the measurement accuracy is improved.

[Brief Description of the Drawings] Figure 1 is a schematic configuration diagram of an embodiment of the present invention, Figure 2 is a block diagram for explaining its operation, and Figure 3 is the oscillation frequency and flow rate (flow velocity) in the present invention. FIG. 4 is a diagram similar to FIG. 6 for explaining the method of specifying and selecting the value of H. FIG. FIG. 6 is a schematic diagram of still another embodiment of the present invention, and FIG. 7 is a diagram showing an actual measurement example of the relationship between the flow rate and the oscillation frequency in the present invention. 1...fiM'l, 2...Speaker, 3...742
mouth, F7.4...Amplification circuit, 4-1.4-2...Amplifier, 6...''Tf band pan r pass filter, 7...
・Frequency-voltage converter, 8...PLL circuit agent Patent attorney Hiraki

Claims (5)

[Claims] (1) A flow pipe through which a fluid such as air passes,
1. A suze force disposed on one side of the flow pipe and radiating ultrasonic waves or sound waves toward the fluid; and a speaker disposed on the opposite side of the flow pipe facing the speaker. a microphone that receives ultrasonic waves or sound waves emitted from the force and propagated in the fluid and converts them into electrical signals; amplifies the electrical signal output from the microphone; and supplies the amplified output signal to the speaker. An ultrasonic wave amplifier using a conformal quantity loop, comprising an amplifier circuit and a frequency selection means provided in a positive feedback loop consisting of the microphone, the amplifier circuit and the speaker. Total (2) Ultrasonic waves using a positive feedback loop according to claim 1, wherein *a is that the frequency selection means is to provide narrowband characteristics to at least one of the speaker and the microphone. flow needle. (3) An ultrasonic flow needle using one of the two positive feedback loops described in Paragraph 1 of the Patent Enclosure, characterized in that the frequency/wave frequency selection means is an amplifier circuit having a panned path characteristic. (4) The center frequency of the bandpass characteristic is controlled so that it almost matches the frequency of the amplifier circuit. 7. An ultrasonic flow needle using the positive feedback loop according to claim 5. (5) A flow path pipe through which a fluid such as air passes, and an ultra-f
gi. Alternatively, a sugi force that emits sound waves is reassembled on the opposite side of the flow pipe, facing the speaker, and emits ultrasonic waves or sound waves that have been emitted from the speaker and propagated in the fluid. a microphone for receiving the signal and converting it into an electrical signal; a PLL circuit to which the output electrical signal of the microphone is supplied; and means for supplying the output electrical signal of the PLL circuit to the speaker; An ultrasonic flowmeter using a positive feedback loop in which the resonance frequency is approximately the same as the oscillation frequency of the feedback loop consisting of the microphone, the PLL circuit, and the speaker.