JP3048615B2 - Liquid level detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid level detecting device.

[Conventional technology and its problems]

FIGS. 12, 13 and 14 show a liquid level detecting device according to a first conventional example. In FIG. 12, a container (1) contains a liquid (2), 2) Level L
Level gauge (3) in order to confirm is provided corresponding to a predetermined liquid level L ₀ of the side wall of the container (1).
This is displayed, for example, the upper display line and lower display lines of a predetermined level L ₀ as shown in FIG. 14 becomes a glass window transparent as a level indicating the bounds of the predetermined distance (4a) (4b) is .

Such a level gauge (3) is well-known, but is for visually confirming the liquid level L. The position of the liquid level L relative to the display lines (4a) and (4b) through a transparent glass window is determined. Is detected. However, this is a visual check, and it may be difficult to read the level L when the window is dirty or the surroundings are dark.

FIG. 15 shows a second conventional example in which a liquid (6) is stored in a container (5). In order to measure the liquid level L, a float (7) is arranged in a floating state. A rod 1 is mounted on the upper and lower sides, and is configured so that it can be accurately moved in the vertical direction by a change in the liquid level L by guide members (8a) and (8b) (fixed to a stationary portion). ing. An electric switch (9) is connected to the upper end of the rod l. The level of the float (7) changes in response to the change in the liquid level L of the liquid (6).
contacts a) (exactly vertical movement is guided by 8b) when reduced to a predetermined level L ₀ electric switch (9) is adapted to be opened. Thus the liquid in the container (5) (6) is adapted to detect that falls below a predetermined liquid level L _0.

However, in such a device, the guide member (8
a) Although (8b) is not shown, it is fixed to a stationary part or a part of the container. However, if these are deformed or corroded by the liquid (6), the rod 1 will move up and down or fall exactly. It may stop moving. This will not be able to detect the liquid level L ₀ accurately.

FIG. 16 shows a third conventional example in which a container (10) contains a liquid (13), and the container (10) has a lid (1).
1) is hermetically covered, so that this lid (11)
A closed space (12) is formed between the liquid and the liquid level (L) of the liquid (13). It may be vacuum or filled with some gas. An ultrasonic transmitter (14) and an ultrasonic receiver (15) are attached to the outer surface of the bottom wall of the container (10) in close proximity to each other. An electric signal for exciting the ultrasonic transmitter (14) is supplied from the liquid level measurement circuit (16). Thereby, the ultrasonic waves S are emitted toward the inside of the container (10). This is reflected at the liquid level L of the liquid (13) to become a reflected ultrasonic wave S ', which is received by the ultrasonic receiver (15). This received signal is supplied to the liquid level measurement circuit (16). The measurement output from the circuit (16) is supplied to a liquid height comparator (17), where it is compared with a predetermined level. The time required to return to the ultrasonic receiver (15) after being reflected by the surface level L is measured by the liquid level measurement circuit (16).
Although than it supplies the result to the liquid high comparator (17), it is determined that where there is a higher level than the predetermined liquid level L ₀ greater than this is compared with a predetermined level or time, also when shorter than this time so that it is determined to be lower than the predetermined level L _0, derives a low level signal or a high level signal to the detection terminal of the determination output (18).

That is, in this conventional example, the absolute value of the liquid level L is measured. However, ultrasonic waves must penetrate the liquid to the liquid level L. Especially when the distance is long, the liquid deteriorates, for example, changes in viscosity. The time required for the ultrasonic wave S to reach a certain liquid level may change due to changes in the liquid level or physical properties. In this case, the ultrasonic wave S is above a predetermined level even when compared with the value set in the liquid level comparator (17). Cannot be accurately detected. Or, if a liquid (13) contains any foreign matter that reflects ultrasonic waves,
Due to this reflection, accurate measurement of the liquid level cannot be expected.

FIG. 17 shows a liquid level detecting device according to a fourth conventional example. The liquid (20) is stored in a container (19) and is closed by a lid (27) in this conventional example. An ultrasonic transmitter (22) and an ultrasonic receiver (23) are mounted on the lid (27) in close proximity. Liquid level gauge (24)
Supplies an electric signal for exciting the ultrasonic transmitter (22), thereby emitting an ultrasonic wave S from the ultrasonic transmitter (22) toward the liquid level L of the liquid (20). The reflected wave S 'from L is received by the ultrasonic receiver (23). The received signal is supplied to the liquid level gauge (24). In the conventional example, the ultrasonic signal is transmitted from the ultrasonic transmitter (22) to the reception of the ultrasonic wave by the receiver (23). The time is measured by the liquid level gauge (24), and the measured value is compared with a predetermined value in the setting comparison circuit (25). If the measured value is larger than the predetermined value, it is determined that the liquid level L is below the predetermined level, If it is smaller than this, it is determined that it is above a predetermined level, and a determination output is derived from the terminal (26).

That is, in the conventional example shown in FIG. 17, unlike the conventional example shown in FIG. 16, the ultrasonic wave is reflected to the space (21), and the reflected wave from the liquid surface L is propagated in the space (21). It receives, but if space (21) is vacuum, ultrasonic wave S
Cannot be propagated to the liquid surface L, and therefore, in this conventional example, it cannot be applied when the space (21) is a vacuum.

FIG. 18 shows a fifth prior art example, in which a container (30) contains a liquid (31), and the liquid (31) is open above the container (30). sonic transmitter (32) and the receiver (33) is mounted so that a predetermined level L _0. In this conventional example, the ultrasonic transmitter (3
The ultrasound from 2) receiver opposed thereto (it is to fire toward the 33), but transmitter when the liquid level L of the liquid (31) is above a predetermined level L ₀ (32) Is transmitted to the receiver (33) with its attenuation reduced, so that the reception level of the receiver (33) is relatively high. Thus it is determined that is above the predetermined level L _0. The ultrasonic waves from the liquid the liquid level L (31) and falls below a predetermined level L ₀ transmitter (32) is greatly attenuated because through the gas. Therefore, the level of the ultrasonic wave received by the receiver (33) becomes low. Liquid level L of the Thereby the container (30) in the liquid (31) is determined to be in less than the predetermined level L _0. As shown in FIG. 18, the liquid level L is at a predetermined level L _0.
, The reception level is between the relatively high value and the relatively low value.

Such container (30) also in the conventional example liquid (31) in the level of but it is possible to determine the high and low for a given level L ₀ transmitter (32) and the receiver exactly a predetermined (33) Must be mounted in line with L ₀ level. If it can not be determined accurately whether this is above or in the following below a predetermined level L ₀ if incorrect. Even if the container (30) is made of plastic, for example, even if the container (30) is precisely aligned and mounted at a predetermined level, the container (30) is easily deformed by heat and deforms, so that the relative mounting position changes. This can not be the level of liquid (31) in the container (30) to accurately determine the underlying or is above a predetermined level L _0.

[Problems to be solved by the invention]

The present invention has been made in view of the various problems described above, and an object of the present invention is to provide a liquid level detection device that can eliminate the above-described conventional disadvantages.

[Means for solving the problem]

The above object is to provide a container for storing a liquid, wherein at least a side wall portion adjacent to a liquid surface at a predetermined level is formed of an ultrasonically permeable material, and an ultrasonic transmitter is provided on an outer surface of the side wall portion with the predetermined level. Mounted on the same level as the level, on the concentric circle centered on the transmitter near the transmitter, and on the outer surface of the side wall portion at least at the same level as the predetermined level and above and below the predetermined level. This is achieved by a liquid level detecting device, wherein a receiver for receiving the ultrasonic waves emitted from the transmitter is attached, and the liquid level is detected based on a combination of reception levels of these receivers.

[Action]

Since the side wall portion adjacent to the liquid level at a predetermined level is formed of a material that transmits ultrasonic waves, ultrasonic waves from the transmitter attached to the outer surface of the side wall portion pass through the side wall portion and pass through the inner surface of the container. Ultrasound reflected from the interface between the liquid film and the medium it contacts reaches the receiver. Since the reception level greatly differs depending on whether the medium is a liquid, a gas, or a vacuum, the level of the liquid in the container can be detected from this. According to the present invention, an ultrasonic receiver is attached at least at the same level as the ultrasonic transmitter and above and below the ultrasonic transmitter, and the liquid level is detected based on a combination of the reception levels of these receivers. Therefore, it is possible to accurately detect the liquid level.

[Embodiment] Hereinafter, a liquid level detecting device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a container (51) provided with a liquid level detecting device (54) of the first embodiment.
2) is accommodated, and a liquid level L defines a space (53) above. In this embodiment, this space (53) communicates with the atmosphere.

FIG. 2 shows a related structure between the liquid level detecting device (54) and the controller (64). The liquid level detecting device (54) is described in detail in FIGS. 3 and 4. A hole (51a) is formed in one side wall of the cage container (51), and a mounting plate (55) made of an ultrasonic-permeable material is liquid-tightly fixed to the hole (51a). Although this is circular as shown in FIG. 4, an ultrasonic transmitter (56) is attached to the center thereof, and this transmitter (5)
Ultrasonic receivers M, T, and B are mounted on a circle C centering on 6). Mounting level of the transmitter (56) is mounted so as to become the same as the predetermined liquid level L ₀ of a liquid (52) in the container (51) as shown in Figure 3. At the same level, the receiver M is mounted on the mounting plate (55). These receivers M, T and B have the same configuration, but the transmitter (5
M to represent the relative position to 6)
(Center), T (top), and B (bottom).

As shown in FIG. 2, the transmitter (56) is connected to a controller (64) via an electric wire (60), and a transmitter (65) inside the controller (64).
Connected to. The transmitting unit (65) is configured to supply an electric signal of an ultrasonic frequency to the transmitter (56), thereby performing ultrasonic vibration, and emitting an ultrasonic wave from the transmitter (56). . Each of the receivers M, T, and B is connected to a receiving section (66) in the controller (64) via electric lines (61), (62), and (63). That is, the reception outputs of these receivers M, T, and B are supplied to a reception section (66), and processed by a comparator (67) connected to this output terminal into a signal that can be compared with each set value. (67)
Is supplied to the next-stage logic circuit (68). The logic circuit (68) outputs outputs for determining the liquid surface level L of the liquid (52) in the container (51) to the output terminals a, b, c, and c by a combination of logics described later. It emits to any of d, e, f and g.

The liquid level detecting device according to the embodiment of the present invention is configured as described above. Next, this operation will be described.

First, the operation principle of the present invention will be described with reference to FIG. The mounting plate (55) is made of an ultrasonic-permeable material as described above, and the ultrasonic transmitter (56) is mounted on the mounting plate (55). The ultrasonic wave from this transmitter (56) is 3
The reflected waves are transmitted to the receivers M, T and B in the form of reflected waves. That is, the first reflected wave (I) is an ultrasonic wave reflected from the surface of the mounting plate (55). The second reflected wave (II) is a reflected wave from the interface between the liquid film adhering to the inner surface of the mounting plate (55) and the ultrasonic medium (liquid or air) inside the container (51). . This reflected wave is a relatively weak reflected wave if it is a reflected wave from the interface between the liquid film and the liquid, and a strong reflected wave if this interface is an interface between the liquid film and the gas, that is, the atmosphere. is there. Third ultrasonic reflected wave (III)
Is an ultrasonic wave that is propagated into the container and is a reflected wave from some obstacle or an opposing wall surface inside the container. When passing through the gas in the container (51), the component (III) is almost zero because it is almost reflected at the interface on the inner surface of the container (51) as described above, and propagates through the liquid (52). Even in this case, the amount of attenuation is smaller than that of the gas, but it is much lower than the level of the type II reflected wave from the interface between the liquid film and the gas. Therefore, according to the embodiment of the present invention, among the reflected waves I, II and III, the intensity of the type II reflected wave is used as an ultrasonic reflected wave for judging the liquid level.

Figure 6A is higher than the liquid level L ₀ liquid level L of predetermined liquid (52), and in a case where there from above the receiver T above, the inner surface of the mounting plate in this case (55) The intensity of the reflected wave of the ultrasonic wave at the interface between the liquid film and the liquid (52) attached to the receiver is relatively low in any of the receivers T, M, and B (this level is L).

Although higher than the liquid level L is a predetermined level L ₀ of a liquid (52) is above the receiver T and the same level in Figure 6B. In this case, the reflected wave of the ultrasonic wave from the interface on the inner surface of the opposed mounting plate (55) of the receiver T is a half reflected wave of the gas and the liquid, so that the entire interface faces the gas. The output level is an intermediate value between the case where the liquid and the liquid are faced (this level is m). Further, since the interface on the inner surface of the mounting plate (55) where the center receiver M and the lower receiver B face each other is in contact with the liquid (52), its reflection intensity is small. Therefore, their reception levels are relatively low.

FIG. 6C shows that the liquid level L is higher than the predetermined level L ₀ and is halfway between the level of the receiver T and the transmitter (56), ie the center receiver M, but in this case the upper receiver T
The output of (1) has a large reflection intensity because the interface between the inner surface of the mounting plate (55) and the opposing surface is in contact with gas, and therefore the reception level is high (this level is H). However, since the interface between the mounting plates (55) of the other receivers M and B facing each other is a liquid, the reception level is low.

FIG. 6D shows that the liquid level 52 of the liquid (52) is a predetermined level L _0.
, Ie, the same as the level of the transmitter (56). In this case, since the medium in contact with the interface of the inner surface of the mounting plate (55) facing the upper receiver T is a gas, the reflection intensity of the ultrasonic wave is large, and thus the reception output is high. The reception level of the receiver M is the same as that of the receiver T in FIG. 6B.
, Its received output is at an intermediate level. Also, the reception level of the lower receiver B is low because the reflection intensity of the ultrasonic wave at the interface is small.

The 6E figure below is higher than the receiver B of the lower level L is a predetermined level L ₀ of a liquid (52). Therefore, in this case, the output of the receiver T is high and the output of the receiver M is high, but the receiver B
Output is low.

FIG. 6F shows that the liquid level L of the liquid (52) is a predetermined level L _0.
Lower and equal to the level of receiver B,
In this case, the reception level of the receiver T is high and the level of the receiver M is high, but the output of the receiver B is at an intermediate level.

FIG. 6G shows that the level L of the liquid (52) is
All become high level lower than M and B.

The relatively high output of each receiver M, T, and B in each state as described above is indicated by H, the relatively low output is indicated by L, and the output at an intermediate level between them is indicated by m. Table 1 shows the table. As is apparent from the table, the combinations of the output levels of the receivers T, M, and B are all different in each of the states A to G. The output levels at the output terminals a to g from the logic circuit (68) in the controller (64) in the figure are shown in Table 1 in the order of A to G. When expressed as +3, +2, +1, 0, -1, -2 and -3, signals at the levels shown in FIG. 2 are generated from the respective output terminals a to g. Thus, the level of the liquid level L of the liquid (52) in the container (51) can be determined by automatically judging the state from A to G.

FIG. 7 shows a liquid level detecting device (7) according to a second embodiment of the present invention.
The container (70) to which 3) is attached is shown. The container (70) is entirely made of a material that can transmit ultrasonic waves, contains a liquid (71), and has a space (72) that communicates with the atmosphere by the liquid level L. ). FIG. 8 is a liquid level detecting device (73) in FIG.
In this embodiment, the same ultrasonic transmitter S, receiver T, M and B as in the first embodiment are mounted on a circular substrate (74) made of a material which can transmit ultrasonic waves. The substrate (74) is attached to the surface of the container (70) by an adhesive (76) which also guides the ultrasonic waves. Other configurations and operations are the same as those of the first embodiment.
Because such in the case you change the predetermined liquid level L ₀ configuration can immediately cope with this it can be said that in this respect is the advantageous than the first embodiment.

FIG. 9 shows a main part of the liquid level detecting device according to the third embodiment. An ultrasonic transmitter S and a receiver T having the same structure as described above are mounted on an ultrasonically permeable mounting plate (80). Although M and B are mounted, a conical recess (80a) is formed on the inner surface side of the mounting plate (80). Other configurations are the same as those of the first and second embodiments, but according to the present embodiment, the ultrasonic wave W from the ultrasonic transmitter S is applied to the liquid film on the inner surface of the mounting plate (80) and the gas G of the medium or When the reflected wave W 'at the interface with the liquid Q is received, the level of the reflected wave is in the concave portion (80a) and the ultrasonic wave W from the ultrasonic transmitter S is conical on the side of the concave portion (80a) as shown. The reflection at the surface increases the intensity, and therefore, the difference between the case where the interface medium is a liquid and the case where the interface medium is a gas is large. Therefore, the sensitivity is further improved.

Generally, the directivity of an ultrasonic wave increases as its frequency increases, and therefore, the reflection level of the ultrasonic wave reflected in each direction decreases, which is particularly effective in such a case.

FIGS. 10 and 11 show a liquid level detecting device according to a fourth embodiment of the present invention. The liquid level detecting device is shown as (90) as a whole on a mounting plate (91) made of a material having ultrasonic permeability. Adhesive layer (9
A configuration corresponding to the above-described transmitter and receiver via 2) is provided. However, in the present embodiment, these are formed of a film or a thin film made of a piezoelectric material. That is, a thin film (93) (94) made of a piezoelectric material is formed on the adhesive layer (92).
a) (94b), (95) and (96) are formed, and they have a shape as shown in FIG. 10, and electrodes are attached to both sides thereof. As shown in the figure, (101), (102) and (103) are buried in the adhesive layer (92) and the electrodes (97) (98a) (99) (1
00) is a closed-loop-shaped piezoelectric thin film (93)
(94a), (94b), (95), and (96).

In the above configuration, the central piezoelectric thin film (93) corresponds to the transmitter (56) or S described above, and the piezoelectric thin films (94a) and (94b) on both sides correspond to the central receiver M. It is. The piezoelectric thin film (95) corresponds to the receiver T, and the thin film (96) corresponds to the receiver B. Also, the center of the piezoelectric thin film (93) as the center ultrasonic wave transmitter is on the same level as the predetermined liquid level as in the above embodiment.

Note also Although this both sides according to the present embodiment is the provided two as receivers M located above a predetermined liquid level L ₀ indicating the position of the center above embodiment by connecting them in this case in parallel Obviously, the same effect as in the example can be obtained.

As described above, each embodiment of the present invention has been described.
The present invention is not limited thereto, and various modifications are possible based on the technical idea of the present invention.

For example, in the above embodiment, three receivers are arranged on concentric circles. However, the number of these receivers may be further increased. In this case, an output table as shown in Table 1 is created, and thereby the liquid is precisely defined. Obviously, surface levels can be detected.

In the above embodiments, the upper space defined by the liquid level L in each container is all in communication with the atmosphere. However, the upper opening is closed and the vacuum is established. It is clear that the same effects as in the above embodiment can be obtained.

In the above embodiments, the material of the liquid is not particularly specified, but the present invention can be applied without any problem to the oil particularly used for vacuum equipment.

〔The invention's effect〕

As described above, according to the liquid level detection device of the present invention, all the disadvantages of the conventional examples are eliminated, and the upper space defined by the liquid level in the container is vacuum or not. The liquid level can be accurately detected.
Also, since no mechanically operated structure is used in the container, its accuracy can always be guaranteed.

[Brief description of the drawings]

FIG. 1 is a schematic side sectional view of a container provided with a liquid level detecting device according to a first embodiment of the present invention, FIG. 2 is a block diagram showing the relationship between the liquid level detecting device and a control circuit in the same embodiment, 3 is an enlarged sectional view of the liquid level detecting device, FIG. 4 is an enlarged front view of the same, FIG. 5 is an enlarged sectional view of a main part for explaining the operation of the embodiment, and FIGS. 6A to 6G. Is a partially enlarged cross-sectional view for explaining the operation of the embodiment, FIG. 7 is a schematic cross-sectional view of a main part having a liquid level detecting device according to a second embodiment of the present invention, and FIG. FIG. 9 is an enlarged sectional view of the device, and FIG.
FIG. 10 is an enlarged cross-sectional view of the liquid level detecting device of the embodiment, FIG. 10 is a front view of the liquid level detecting device of the fourth embodiment of the present invention, FIG. 11 is a cross-sectional view taken along line XI-XI in FIG. FIG. 12 to FIG.
FIG. 12 is a schematic cross-sectional view of a container provided with a liquid level detecting device of the first conventional example, FIG. 13 is a side view of the same, and FIG. 14 is a level gauge in the same device. FIG. 15 is a schematic sectional view of a container provided with a liquid level detecting device of a second conventional example, and FIG. 16 is a schematic diagram showing an electric circuit of a container provided with a liquid level detecting device of a third conventional example. FIG. 17 is a schematic sectional view showing an electric circuit of a container provided with the liquid level detecting device of the fourth conventional example, and FIG. 18 is a schematic sectional view of a container provided with the liquid level detecting device of the fifth conventional example. FIG. In the figures, (54) (73) (90) ... liquid level detecting device (55) (80) ... mounting plate (56), S ... ultrasonic transmitter M, T, B ... ultrasonic reception (93) (94a) (94b) (95) (96) ... Piezoelectric film

Claims (3)

(57) [Claims] 1. A container for accommodating a liquid, wherein at least a side wall portion adjacent to a liquid surface at a predetermined level is formed of an ultrasonic wave transmitting material, and an ultrasonic transmitter is provided on an outer surface of the side wall portion. Mounted on the same level as the level, on the concentric circle centered on the transmitter near the transmitter, and on the outer surface of the side wall portion at least at the same level as the predetermined level and above and below the predetermined level. A liquid level detecting device, comprising: a receiver for receiving an ultrasonic wave emitted from the transmitter; and detecting a liquid level based on a combination of reception levels of the receivers. 2. The liquid level detecting device according to claim 1, wherein a conical recess having the predetermined level as a center line is formed on an inner surface side of the side wall portion. 3. The liquid level detecting device according to claim 1, wherein at least one of the receiver and the transmitter is formed of a film or a thin film made of a piezoelectric material.