JPH0778445B2 - Ultrasonic interface level meter - Google Patents

Description

Description: [Industrial application] The present invention relates to an ultrasonic interface level meter for detecting the mutual interface level of a gas, a liquid, a granular material, a gel-like substance or the like in a container, and particularly to the outside of the container. Therefore, it is most suitable for detecting the medium in the mounting container without mechanically processing the container.

[Prior Art] Conventionally, as one of the ultrasonic interface level meters of this type, an ultrasonic liquid level meter that detects a liquid level in a container is known. Among the ultrasonic level gauges, those capable of detecting the liquid level of the content liquid, particularly from the outside of the container, without subjecting the container to mechanical processing are disclosed in, for example, JP-A-60-214226. Kai 61-
There are those disclosed in Japanese Patent No. 29722, Japanese Patent Laid-Open No. 60-262019 (hereinafter referred to as the first, second, and third publications in this order).

In the device of the first publication, the wave transmitter and the wave receiver are attached at opposite positions in one horizontal cross section of the container, and the ultrasonic wave input from the wave detector is detected by the wave receiver. Then, the liquid level is measured.

In the second publication, a liquid level gauge integrated with a wave transmission / reception function is attached to the outer wall of the container, and the ultrasonic wave radiated into the liquid through the wall is reflected by the opposite wall to receive the reflected wave and the liquid is received. It is intended to know the presence or absence of.

Further, in the third publication, a liquid level gauge having an integrated wave transmitting / receiving function is attached to the outer wall of the container, and the ultrasonic wave incident on the outer wall hits the inner wall and is reflected.
It is intended to know the presence or absence of the content liquid by utilizing the fact that the duration of the echo varies depending on whether or not the liquid is in contact with the inner wall surface.

[Problems to be Solved by the Invention] However, in the above-mentioned first publication, only a single level of the liquid level in the container can be detected, and it can be used only as an upper limit liquid level gauge or a lower limit liquid level gauge. .

In the second publication, as long as the liquid level gauge is fixedly mounted, it is not possible to detect the continuously changing liquid surface at the level as in the first publication, and the upper limit of the liquid level is set. There is no change in that it is a limit level gauge that detects the lower limit.

Further, it is possible to detect the current liquid level by moving the liquid level gauge up and down along the wall surface, but it is troublesome to move the liquid level gauge one by one, and it is not possible to move the liquid level gauge one by one. Aside from the principle difficulty of always maintaining the transmittance of the ultrasonic waves to the wall surface at the location of, even if the container is large or installed in a place where it is difficult to approach, The movement of the liquid level gauge along the wall surface becomes even more difficult, and in practice, it is unavoidable that the applicable range is limited as a limit level gauge.

Regarding the above-mentioned problems, the same is true of the third publication. In the former two cases, the transmitted sound wave or the reflected sound wave between the inner walls of the container is different from the multiple sound wave inside the container shell wall. The only difference is that it is a reflected wave.

[Object of the Invention] The present invention has been made in view of the above problems in the conventional technique, and is not limited to a single interface level of a medium, and a plurality of containers in a container can be formed without moving the wave receiver. It is an object of the present invention to provide an ultrasonic interface level meter that can detect the interface level of the medium.

[Means for Solving the Problems] The gist of the present invention for achieving the above-mentioned object is as follows: (1) A transmitter of an ultrasonic interface level meter with a measurement area of a medium detection surface in a container being sandwiched therebetween. A wave receiver is provided, and the ultrasonic signal from the wave transmitter is converted into a burst wave having a predetermined period, and the ultrasonic wave is radiated into the medium from the inner wall surface in contact with the medium into the shell wall. It is characterized in that the number of reflections of reflected waves traveling back and forth inside the container through the shell wall and the medium is made to be incident on the receiver as the number of time-delayed signals corresponding to the interface level of the medium. Ultrasonic interface level meter.

(2) A wave transmitter and a wave receiver of an ultrasonic liquid level gauge are arranged across a measurement area of a medium detection surface in a container, and an ultrasonic signal from the wave transmitter is converted into a burst wave having a predetermined cycle. In addition, 2d · cos θ ₁ = mλ ₁ (m = 0,1,2 ...) where the ultrasonic wave leaks into the medium from the inner wall surface in contact with the medium is a maximum value, where d is a shell The plate thickness of the wall, θ ₁ is the inclination angle of the ultrasonic wave incident on the shell wall, λ ₁ is the ultrasonic wave incident on θ ₁ and / or λ ₁ that satisfies the wavelength of the ultrasonic wave inside the shell wall. The number of reflections of the reflected wave traveling back and forth inside the container through the shell wall and the medium is made incident on the receiver as the number of time-delayed signals corresponding to the interface level of the medium. It exists in the ultrasonic interface level meter described in 1.

[Operation] In the medium container, the transmitter and the receiver of the interface level meter are
Install with the expected fluctuation range of the medium sandwiched. At this time, either the wave transmitter or the wave receiver may be on the upper side and any of the wave receiver may be on the lower side.

The ultrasonic wave radiated from the wave transmitter into the vessel shell wall is a continuous wave because not only the transmitted wave that travels the shortest distance from the wave receiver but also the acoustic wave that has reached through the detour path inside the shell wall are superposed. It is difficult to distinguish meaningful sound waves. Therefore, a burst wave having a constant period and width is radiated.

When the inner surface of the shell wall is not in contact with the medium, the ultrasonic signal radiated into the shell wall almost diffuses into the air inside the container due to the isolated difference in the intrinsic acoustic impedance between the solid container and air. Instead, it propagates as multiple reflected waves in the shell wall. Then, when it reaches a place in contact with the medium, the characteristic acoustic impedance of the container and the characteristic acoustic impedance of the medium are close to each other, and the ultrasonic signal is transmitted through the inner wall surface into the medium. The signal ultrasonic wave radiated from the wave transmitter has a conditional expression that the leakage of the ultrasonic wave from the inner wall surface to the medium has a maximum value, 2d · cos θ ₁ = mλ ₁ (m = 0, 1, 2, ...) d is the thickness of the shell wall, θ ₁ is the inclination angle of the ultrasonic wave in the shell wall, and λ ₁ is θ ₁ and / or λ ₁ that satisfies the wavelength of the ultrasonic wave in the shell wall. From the inner wall surface in contact with the medium, ultrasonic waves are efficiently radiated and leaked into the medium.

Then, the ultrasonic signal radiated from the transmitter leaks from the inner wall surface in contact with the medium, the leaked ultrasonic wave enters the shell wall again from the facing inner wall surface, is reflected by the outer wall surface, and is reflected inside the shell wall. It passes through and leaks again to the medium. When such reflection is repeated and reaches the medium, it is subsequently incident on the wave receiver as multiple reflected waves in the shell wall. If the transmitter is above the medium, it enters the receiver first as multiple reflections in the shell wall and below the interface level of the medium as inter-wall reflected waves passing through the medium.

In any case, the reflected wave between the wall surfaces is received by the wave receiver as a time delay signal corresponding to the number of reflections. For example, if the reflection between the wall surfaces is three times, four pulse waveforms including the signal of the transmitted wave in the shell wall are observed.

Since the number of reflections is stepwise proportional to the interface level of the medium, it is possible to know the interface level of the medium in the container by this number of times, that is, the number of time-delayed pulses obtained by the wave receiver.

[Embodiment] Next, an embodiment in which the present invention is applied to an ultrasonic meter will be described with reference to the drawings.

FIG. 1 shows the configuration of the ultrasonic level gauge 10.

An ultrasonic liquid level gauge (hereinafter, simply referred to as a liquid level gauge) 10 includes a wave transmitter 11 attached to a lower portion of a liquid container V and a wave receiver 12 attached to an upper portion with an expected liquid level in between. Has become. (The positions of the wave transmitter 11 and the wave receiver 12 may be reversed.) The wave transmitter 11 and the wave receiver 12 have the same structure, and an external view is shown in FIG. The sectional view is shown in FIG. That is, a piezoelectric element 14 made of zirconate / lead titanate (PZT), which is a transmitting means, is fixedly provided in the casing 13 in water as a transmission medium. A thin film 15 is stretched on the surface in contact with the container V. However, casing 13
Is a solid body, and a medium such as water is not required as long as air is not present on the contact surface with the container V with an adhesive or the like.

The wave transmitter 11 includes a high frequency oscillating means for oscillating the working frequency of the piezoelectric element 14 capable of satisfying the relationship between the incident angle and the frequency depending on the directional characteristic and the frequency characteristic, for example, the voltage controlled oscillator VC
For example, a pulse generator 16 having a pulse generating means for pulse-modulating this high frequency is coupled with O and the like. Then, from the wave transmitter 11, a pulse-modulated wave (burst wave) of a carrier having a used frequency is transmitted as an ultrasonic signal.

One of the wave receivers 12 has an amplifier 17 for amplifying the received signal,
A signal processing / display device including a signal processing circuit including a counter for processing an input signal, a comparator, and the like, and display means for displaying a liquid level obtained as a processing result.
Eighteen are equipped.

Now, as shown in FIGS. 3 (a) and 3 (b), the density (g /
cm ³ ), sound velocity (m / s) and incident angle (rad) as (ρ ₀ , C
₀ , θ), container wall density (g / cm ³ ), sound velocity (m / s) and incident angle (rad) (ρ ₁ , C ₁ , θ ₁ ), density in liquid (g / cm ³ ) , Sound velocity (m / s) and incident angle (rad) (ρ
₂ , C ₂ , θ ₂ ), the thickness of the container wall is d (m), and the wavelength of the incident ultrasonic wave in the container wall is λ ₁ (m). However, θ is an angle at which total reflection does not occur.

If only the longitudinal wave is treated here, this is the same as the case where the ultrasonic wave is obliquely incident into the liquid of three layers, so the transmittance D of the ultrasonic wave from the transmitter to the liquid is calculated by Boyle and Rswlinson as follows. It is known to be expressed as a formula.

Then, the conditional expression in which the transmittance D has a maximum value is Boyle
And Rawlinson, and it is 2dcosθ ₁ = mλ ₁ (m = 0,1,2,3, ...).

In reality, the incident ultrasonic waves are not only longitudinal waves but also the transmittance D due to the characteristics of the transmitter and the receiver and inclusions.
Does not follow the formula. However, since the conditional expression having the maximum value is valid for the longitudinal wave, if only the longitudinal wave is treated, the conditional expression having the maximum value gives the expression when the thickness d of the container wall is given. As you can see, θ ₁ and /
Alternatively, by providing λ ₁ , it is possible to obtain a liquid level meter that reacts sharply to changes in the liquid level.

Therefore, for example, when the liquid level is very low as shown in FIG. 4 (a), the signal ultrasonic waves emitted from the wave transmitter 11 efficiently leak into the liquid, but reach the wall surface of the facing container. Before reaching the liquid surface, there is no leakage into the air due to the difference in the incident angle and the inherent acoustic impedance between the liquid and air, and the light is reflected and reflected intricately inside the container, and the leakage is repeatedly attenuated. Then, only the transmitted wave is received by the wave receiver 12.

The operation will be described below with reference to FIGS. 4 (a) to 5 (d).

As described above, when the liquid level is low, the receiver 12 receives only the transmitted wave signal a ₀ as shown in FIG. It has little attenuation.

When the liquid is a little large as shown in FIG. 4 (b), the signal wave leaking into the liquid is transmitted from the facing wall surface of the container to the inside of the shell wall, is reflected by the outer wall surface, and returns to the liquid again. Although it is reflected on the outer wall surface and leaks again into the liquid, it cannot reach the facing wall surface, and the effective reflected wave is only once.
As shown in FIG. 5, only one reflected wave signal a ₁ is observed as a delayed pulse in addition to the transmitted wave signal a ₀ .

If the liquid surface is higher as shown in FIG.
As shown in FIG. 7C, _two time delay signals a ₁ and a 2 are obtained.

FIG. 4 (d) shows a case where three reflected wave signals a ₁ , a ₂ and a ₃ are obtained at a high liquid level as shown in FIG. 5 (d).

As shown in each of FIG. 5, when the reflected wave increases, the signal received earlier such as the transmitted wave leaks more and the signal level decreases.

In the present embodiment, the wave transmitter 11 is attached to the lower portion and the wave receiver 12 is attached to the upper portion of the container V with the measurement region sandwiched between them. However, the attachment method may be reversed.

In the ultrasonic liquid level meter 10 of the present invention, the wall surface in contact with the liquid is long, and the liquid has a large specific acoustic impedance, so that leakage into the liquid is increased, and the signal level of the direct wave is reduced. Information can be surely obtained.

[Advantages of the Invention] The present invention has a wave transmitter and a wave receiver attached across a measurement area of a detection medium, makes a transmission signal from the wave transmitter a burst wave of a predetermined period, and also has an inner wall surface in contact with the medium. The ultrasonic wave is made incident so that it leaks from the liquid into the liquid, and the number of reflections of the reflected wave traveling back and forth inside the container through the shell wall and the medium is received as the number of delayed signals corresponding to the interface level of the medium. Since it is made incident on the wave device, even in the case where the medium has a large specific acoustic impedance, and the medium interface level is high and the number of leaked waves is large and the transmitted wave signal level becomes minute,
You can certainly get information about the media interface level,
It has become possible to detect multiple media interface levels in a container without moving the transmitter and receiver.

[Brief description of drawings]

1 to 5 (d) show an embodiment of the present invention, FIG. 1 is an overall configuration diagram, and FIG. 2 (a) is an external view of a transmitter and a receiver. 2 (b) is a sectional view of the same, FIG. 3 is an explanatory diagram of the principle of leakage, and FIGS. 4 (a) to 4 (d) are explanatory diagrams of the action showing the relationship between the liquid surface level and the number of reflected waves. Fifth
FIGS. 4 (a) to 5 (d) are shown in FIGS. 4 (a) to 4 respectively.
It is an action explanatory view of a reflected wave signal corresponding to Drawing (d). 10 …… Ultrasonic liquid level gauge 11 …… Transmitter 12 …… Receiver 13 …… Casing 14 …… Piezoelectric element 16 …… Pulse generator 17 …… Amplifier 18 …… Signal processing / display device V …… Liquid Container a ₀ …… Direct wave a ₁ …… One-time reflected wave signal a ₂ …… Two-time reflected wave signal a ₃ …… Three-time reflected wave signal

Claims (2)

[Claims] 1. A wave transmitter and a wave receiver of an ultrasonic interface level meter are arranged across a measurement area of a medium detection surface in a container, and an ultrasonic signal from the wave transmitter is burst in a predetermined cycle. The ultrasonic wave is made to enter the shell wall so that the ultrasonic wave leaks into the medium from the inner wall surface in contact with the medium, and the number of reflections of the reflected wave traveling back and forth inside the container through the shell wall and the medium is reflected. The ultrasonic interface level meter is characterized in that the number of time-delayed signals corresponding to the interface level of the medium is made incident on the wave receiver. 2. A wave transmitter and a wave receiver of an ultrasonic liquid level gauge are arranged across a measurement area of a medium detection surface in a container, and an ultrasonic signal from the wave transmitter is burst in a predetermined cycle. Waveform and the following conditional expression in which the leakage of ultrasonic waves from the inner wall surface in contact with the medium to the medium has a maximum value, 2d · cos θ ₁ = mλ ₁ (m = 0, 1, 2, ...) where d Is the thickness of the shell wall, θ ₁ is the inclination angle of the ultrasonic wave incident into the shell wall, and λ ₁ is the ultrasonic wave with θ ₁ and / or λ ₁ that satisfies the wavelength of the ultrasonic wave in the shell wall. It is characterized in that the number of reflections of reflected waves that are made incident and travel back and forth inside the container through the shell wall and the medium is made incident on the receiver as the number of time-delayed signals corresponding to the interface level of the medium. The ultrasonic interface level meter according to claim 1.