JPH0778444B2 - Ultrasonic detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an interfacial level of gas, liquid, granular material, gel-like substance, etc. in a container and an ultrasonic interface level for detecting the presence or absence of a detection medium itself. The present invention relates to a detector using ultrasonic waves such as a meter and an ultrasonic medium detector.

[Prior Art] Conventionally, for example, an ultrasonic liquid level gauge that detects a liquid level in a container is known. Among the ultrasonic liquid level meters, those capable of detecting the liquid level of the internal solution from the outside of the container without performing mechanical processing on the container are disclosed, for example, in JP-A-60-214226. There are those disclosed in Japanese Patent Laid-Open No. 61-29722, 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.

Further, in the method of 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. It seeks to know the presence or absence of liquid.

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 from the outer wall hits the inner wall and is reflected.
However, the duration of the echo is different depending on whether or not the liquid is in contact with the inner wall surface, so that the presence or absence of the content liquid is known.

[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.

It should be noted that the above-mentioned first and second publications are difficult to apply to a container whose wall surface is irregular, for example, a container whose radiation direction and reflection direction intersect.

[Object of the Invention] The present invention has been made in view of the above problems in the conventional technique, and not only the detection medium in the container can be detected irrespective of the property of the detection medium, but also the irregularity. It is applicable to shaped containers and containers with a tilted posture, and the regulations on the mounting positions and number of wave transmitters and wave receivers are lenient, and the range of application is wide and easy to use. Is intended to provide.

[Means for Solving the Problem] The gist of the present invention for achieving the above-mentioned object is as follows. (1) An ultrasonic wave transmitter is attached to an ultrasonic wave propagation member in contact with a detection medium, and its attachment position At a position different from that, a wave receiver for receiving a transmitted wave in which a signal from the wave transmitter propagates in the shell wall of the ultrasonic wave propagation member by multiple reflection is attached, A detector using ultrasonic waves for detecting a change in the transmitted wave due to a leak wave of ultrasonic waves from a wall surface into a detection medium.

(2) An ultrasonic wave transmitter is attached to the ultrasonic wave propagating member in contact with the detection medium, and the ultrasonic wave propagating member is provided with a signal from the ultrasonic wave transmitter at a position sandwiching the measurement area of the detection medium from the mounting position. A receiver that receives a transmitted wave propagating through multiple reflections inside the shell wall is attached, and the leakage of ultrasonic waves from the wall surface of the ultrasonic wave propagation member in contact with the detection medium into the detection medium is cos θ ₁ = mλ ₁ (m = 0,1,2, ...) where d is the thickness of the shell wall, θ ₁ is the refraction angle of the ultrasonic wave incident on the shell wall, and λ ₁ is the shell wall The ultrasonic wave is made to enter by θ ₁ and / or λ ₁ that satisfies the wavelength of the ultrasonic wave in the inside, and the change in the transmitted wave in the wave receiver is detected to detect the interface level of the detection medium. A detector using ultrasonic waves according to claim 1.

(3) Regarding the mounting position of the wave transmitter and the wave receiver to the container, there is a height difference that sandwiches the measurement area of the detection medium in the vertical direction, and the height difference occurs at the angular position in the horizontal plane. The detector using ultrasonic waves according to claim 1 or 2, wherein the detector is freely selected and installed in a range in which a transmitted wave that changes depending on a tilt angle of a device and a directional characteristic of a vibrator while being held can be received.

(4) A detector using ultrasonic waves according to any one of claims 1 to 3, wherein a plurality of wave receivers are provided at positions separated from each other with respect to a single wave transmitter.

[Operation] The ultrasonic wave radiated from the wave transmitter into the vessel shell wall is superposed with the transmitted wave that propagates the shortest distance from the wave receiver, and also the transmitted wave that has reached through the detour path in the shell wall. Therefore, it is difficult to distinguish meaningful transmitted waves with continuous waves.

Therefore, a burst wave having a constant period and width is radiated, and the amplitude change of the transmitted wave to the receiver due to the ultrasonic signal is observed.

When the shell wall surface is not in contact with the detection medium, the ultrasonic signal radiated into the shell wall does not pass through the shell wall without being transmitted to the outside due to the difference in the intrinsic acoustic impedance with the shell wall surface as a boundary. Propagate as multiple reflected waves inside.

However, the difference between the specific acoustic impedances is small at the place in contact with the detection medium, and the ultrasonic signal is transmitted from the inner wall surface into the detection medium.

At this time, the ultrasonic signal radiated from the transmitter has a conditional expression in which the leakage of the ultrasonic wave from the inner wall surface into the detection 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 signal in the shell wall, and λ ₁ is θ ₁ and / or θ ₁ that satisfies the wavelength of the ultrasonic wave in the shell wall. If λ ₁ is selected, ultrasonic waves are efficiently leaked into the detection medium from the wall surface in contact with the detection medium.

Then, the amplitude of the ultrasonic signal received by the receiver fluctuates slightly depending on the portion where the inner wall surface contacts the detection medium, that is, depending on the level of the detection medium, from which the state of the detection medium in the container can be known. .

However, the ultrasonic signal transmitted through the detection medium is also transmitted from the other wall surface into the shell wall and reflected on the outer wall surface, and after repeating such transmission and reflection, it is also received by the receiver. It is possible to discriminate sufficiently in time.

Further, in the case where a plurality of wave receivers are attached, the interface level of the detection medium can be detected with higher accuracy, and it is possible to accurately cope with a deformed wall surface having a complicated shape.

Furthermore, when a detector using ultrasonic waves is used as an interface level meter, if the transmitter is installed near the bottom of the container, the receiver will be installed above the container with the measurement area of the detection medium in between. To be The mounting positions of the wave transmitter and the wave receiver may be opposite to the above.

Regarding the vertical relationship between the wave transmitter and the wave receiver, the measurement area of the detection medium is sandwiched between the upper and lower parts of the outer wall surface of the container as described above, but the upper and lower angular positions in the respective horizontal planes. Is only required to be able to receive the transmitted wave, and it is not necessary to arrange them vertically.

[Examples] Next, various examples in which the present invention is applied to an ultrasonic liquid level gauge will be described with reference to the drawings.

FIG. 1 shows the configuration of the ultrasonic level gauge 10 according to the first embodiment.

An ultrasonic liquid level gauge (hereinafter, simply referred to as a liquid level gauge) 10 includes a wave transmitter 11 attached to an upper portion of a liquid container V, and a wave receiver 12 attached with an expected liquid level near the bottom portion. It consists of (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, the casing 13 is provided with a piezoelectric element 14 of zirconate / lead titanate (PZT), which is a transmitting means, fixed in water as a transmission medium. A thin film 15 is stretched on the surface in contact with the container V. However, as long as the casing 13 is a solid body and the contact surface with the container V is made to eliminate the inclusion of air with an adhesive or the like, a medium such as water is not required.

The wave transmitter 11 has a directional characteristic and a frequency characteristic, and can satisfy the relationship between the incident angle and the frequency.
A pulse generator 16 having pulse generation means for pulse-modulating this high frequency is coupled to both C 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 18 having a signal processing circuit for processing an input signal and a display means for displaying the liquid level obtained as a result of the processing is provided.

FIG. 3 shows a principle diagram of an ultrasonic liquid level gauge 10 which should be called a leaky type of the present invention.

When the liquid level is high as indicated by the solid line a as shown in the figure, the leaked liquid (transmitted wave) l ₁ is substantially close to 0, and l ₂ and l ₃ are greatly leaked, and the transmitter 11 The transmitted wave from is weakened due to leakage and is received by the wave receiver 12.

On the other hand, when the liquid level is low as shown by the broken line b, the substantial leaky wave is only l _3, and the signal to the wave receiver 12 is strong.

Now, as shown in Fig. 4 (a), the density (g / cm ³ ) of the transmitter,
The speed of sound (m / s) and the incident angle (rad) are (ρ ₀ , C ₀ ,
θ), the density of the container wall (g / cm ³ ), the speed of sound (m / s) and the incident angle (rad) (ρ ₁ , C ₁ , θ ₁ ), the density in the liquid (g / c)
m ³ ), sound velocity (m / s) and incident angle (rad) are (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 waves are treated here, this is the same as when the ultrasonic waves are obliquely incident on the three layers of liquid, so the transmittance D of the ultrasonic waves from the transmitter to the liquid is calculated by Boyle and Rawlion. It is known that is expressed by

Therefore, the conditional expression in which the transmittance D has a maximum value is Boyle and R
It is derived by calculation by awlinson and becomes 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. To satisfy 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.

As shown in FIG. 4 (b), leaky waves are generated so as to satisfy the above condition even during multiple reflection in the shell wall. At this time,
Consider the hypothetical incident wave assuming that there is a transmitter in the air.

Next, a second embodiment will be described with reference to FIGS. 5 (a) and 5 (b).

In this embodiment, as shown in the figure, the wave transmitter 11 and the wave receiver 12 are provided at an angle α on the cylindrical wall surface of the container V. The distance h separating the upper and lower parts is the same as in the first embodiment shown by the broken line.

In the arrangement as in the present embodiment, the transmission path from the wave transmitter 11 to the wave receiver 12 becomes long as shown by the arrow d in the figure, the specific acoustic impedance is remarkably small, the leakage is small, and the in-wall attenuation is small. Therefore, it is applied to a container containing a liquid such as a liquefied carbon dioxide gas having a poor level detection ability.

At this time, the inclination angles from the vertical direction of the incident direction of the wave transmitter and the wave receiving direction of the wave receiver, and the respective directions of the wave transmitter and the wave receiver, with reference to the case where the wave is installed vertically in the angle α propagation path d It can be freely selected within the range that can be received due to the spread of the transmitted wave due to the characteristics.

Next, FIG. 6 shows the arrangement of the third embodiment.

In the arrangement according to the present embodiment, a plurality of wave receivers 12 are arranged with a free specification within a range in which a transmitted wave can be received with respect to a single wave transmitter 11, as shown by an arrow in the drawing. Then, the difference in the receiving distance to each wave receiver 12 can be obtained, and when the liquid level is between the wave receivers 12, the level can be detected more accurately.

Further, FIG. 7 shows a fourth embodiment in which the liquid level gauge 10 is attached to a container W having a free outer surface other than the cylindrical wall surface.

As shown in the drawing, it has a wall surface inclined with respect to the liquid surface, and it is shown that the liquid surface can be detected which cannot be achieved by the conventional transmission type or reflection type.

Further, FIG. 8 shows the fifth embodiment, and in this way, it is possible to detect the medium B which is a precipitate such as dust and impurities in the medium A.

That is, in the state where the medium A is usually in contact with the wall surface of the bottom of the container,
By detecting the change state of the transmitted wave due to the leakage in the medium A in advance, it is possible to detect the change of the transmitted wave by the change of the acoustic impedance of the precipitate B medium.
The presence or absence of the B medium as a precipitate can be detected.

The amount of B medium deposited can also be detected by catching the change in the transmitted wave that is reflected from the interface with the A medium and propagates again as a transmitted wave, depending on the amount of the B medium that is a precipitate.

[Advantages of the Invention] According to the present invention, a wave transmitter and a wave receiver are attached to an ultrasonic wave propagation member so as to receive a transmitted wave propagating by multiple reflections inside a container shell wall, and in contact with a detection medium. By detecting the change of the input signal of the transmitted wave in the receiver by the leakage of the ultrasonic wave from the wall surface of the ultrasonic wave propagation member into the detection medium, the interface level of the detection medium in the container and the presence or absence thereof can be detected. Not only can it be detected, but it can also be applied to irregularly shaped containers and containers with an inclined posture.Moreover, the regulations regarding the mounting positions and the number of wave transmitters and wave receivers are loose, and the range of application is wide and it can be used. It's easy to do.

Especially, by freely selecting and mounting the transmitter and the receiver in a range in which the transmitted wave can be received while maintaining the height difference, it is possible to lengthen the transmission path and to provide a medium with a small specific acoustic impedance. However, the level can be accurately detected.

Further, in the case where a plurality of wave receivers are provided at positions separated from each other on the outer wall surface with respect to a single wave transmitter, level detection can be performed more accurately.

[Brief description of drawings]

1 to 4 show a first embodiment of the present invention. FIG. 1 is an overall configuration diagram, FIG. 2 (a) is an external view of a wave transmitter and a wave receiver, and FIG. (B) is a sectional view, FIG. 3 is an explanatory view of the principle, FIG. 4 is an explanatory view of ultrasonic wave propagation, and FIGS. 5 (a) and 5 (b) are the second embodiment. FIG. 5 (a) is a front view, FIG. 5 (b) is a plan view, FIG. 6 is an explanatory view showing the arrangement of the third embodiment, and FIG. 7 is an explanatory view showing a configuration example of the fourth embodiment. FIG. 8 is an explanatory view showing the fifth embodiment. 10 …… Ultrasonic level gauge 11 …… Transmitter 12 …… Receiver 13 …… Casing 14 …… Piezoelectric element 16 …… Pulse generator 17 …… Amplifier 18 …… Signal processing / display device V …… Liquid Container W ... Liquid container

Claims (4)

[Claims] 1. An ultrasonic wave transmitter is attached to an ultrasonic wave propagating member in contact with a detection medium, and a signal from the ultrasonic wave transmitter is provided at a position sandwiching a measurement region of the detection medium with respect to the mounting position. While installing a receiver for receiving a transmitted wave propagating by multiple reflection in the shell wall of the propagation member, the leakage of ultrasonic waves from the wall surface of the ultrasonic propagation member in contact with the detection medium into the detection medium is the following conditional expression, 2d · cos θ ₁ = mλ ₁ (m = 0, 1, 2, ...), where d is the thickness of the shell wall, θ ₁ is the refraction angle of the ultrasonic wave incident on the shell wall, and λ ₁ is It is possible to detect the interface level of the detection medium by injecting an ultrasonic wave with θ ₁ and / or λ ₁ that satisfies the wavelength of the ultrasonic wave in the shell wall, and detecting the change of the transmitted wave in the receiver. A detector that uses the characteristic ultrasonic waves. 2. The wave transmitter and the wave receiver, which are attached to a container made of an ultrasonic wave propagating member in contact with the detection medium, have a height difference with respect to their attachment positions in the vertical direction so as to sandwich the measurement region of the detection medium. At the same time, at the angular position in the horizontal plane, the transmitted wave that changes depending on the incident direction of the wave transmitter, the wave receiving direction of the wave receiver, the wave transmitter, and the directional characteristics of the wave receiver while maintaining the height difference. 2. The detector using ultrasonic waves according to claim 1, wherein the detectors are freely selected and attached to respective ranges in which the spread of the waves can be received. 3. A detector using ultrasonic waves according to claim 1, wherein a plurality of said wave receivers are provided at positions separated from each other with respect to a single said wave transmitter. 4. The detector using ultrasonic waves according to claim 1, wherein a liquid member is used as a medium for transmitting ultrasonic signals inside the wave transmitter and inside the wave receiver.