JPH05248923A - Level detector - Google Patents

Abstract

PURPOSE:To detect a liquid level in a stable manner by arranging plural electrodes, formed of flexible conductive members, isolated from each other near a level detection position on the outer periphery of a container and providing a sensor which contains the electrodes and conductive liquid to form a capacitor. CONSTITUTION:Various kinds of water solution and water-soluble chemical conductive liquid 5 are filled into a container 4 made of dielectric non-metal material. A sensor 1 in which plural flexible electrodes formed of conductive members such as a conductive plastic, a metal plate and a conductive film are arranged in parallel to a liquid level is stuck near to a level detection position on the outer periphery of the container 4 in which the liquid 5 is filled. In this way, the inside and outside surfaces of the bag container 4 which is made of polyethylene, for example, has contact with the electrodes and the liquid 5 to form a capacitor. The capacitance of the capacitor which is formed by the first electrode 2 and the second electrode 3 of the sensor 1 is connected to a signal conversion circuit 6 via a coaxial cable 12. The capacitance is converted into a signal proportional to the level of the liquid 5 and compared with a set level by a setter 10 by a comparator 11 to perform level detection of the liquid 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level detecting device for detecting the liquid level of an aqueous solution or a water-soluble chemical liquid filled in a container made of a non-metallic material, and more particularly to the detection of the liquid level from the outer peripheral surface of the container. is there.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing an example of a conventional level detecting device, 6 is a signal converting circuit for converting the capacitance of a capacitor into an electric signal, 7 is a charging / discharging circuit, 8 is a shaping circuit, 9
Is an integrating circuit, 10 is a setter, 11 is a comparator, 12 is a coaxial cable, 16 is a container, 18 is an electrode, and 19 is a liquid.

The conventional level detecting device is constructed as described above, and a pair of rod-shaped electrodes 18 are provided at regular intervals in a liquid 19 filled in a cylindrical container 16 made of a non-metallic material, and the liquid 19 is interposed therebetween. Configure a capacitor. At this time, the capacitance C _a between the electrodes 18 is C _a = ε ₁ · s ₁ / d d: distance between the electrodes 18, s ₁ : effective area of the electrodes 18,
ε ₁ : dielectric constant of liquid 19, capacitance C _a is the distance between electrodes 18,
It is governed by the effective area of the electrode 18 as well as the dielectric constant of the liquid 19.

Further, since the effective area S of the electrode 18 is related to the levels of the rod-shaped electrodes 18 facing each other in the container 16 and the liquid 19 interposed therebetween, when the level of the liquid 19 is lowered, the effective area S _{1 of the} electrode 18 is reduced. The capacitance C _a decreases and the capacitance C _a decreases. The level of the liquid 19 in the capacity 16 can be grasped from the capacity C _a . The capacitance C _a is connected to the signal conversion circuit 6 via the coaxial cable 12, and the charge / discharge circuit 7 is connected to the capacitance C a.
charging and discharging at a period that is proportional to _a.

The shaping circuit 8 shapes the pulse generated in each charging / discharging cycle into a pulse waveform having a constant amplitude and duration, and the integrating circuit 9 converts the pulse into an average DC voltage for charging / discharging. Obtain an electrical signal proportional to the period. The electric signal is compared with the set level of the setter 10, and the level of the liquid 19 is detected by the comparator 11.

[0006]

In the conventional level detecting apparatus as described above, a pair of rod-shaped electrodes 18 arranged at regular intervals for detecting the liquid level in the container 16 made of a non-metallic material.
To use. Since the electrode 18 is immersed in the liquid 19 in the container 16, a material that does not adhere to the liquid and is corrosion resistant is used, and the electrode 18 has a waterproof structure, which is expensive. If the adjustment range of the detection level increases according to the size of the container 16, the size of the electrode 18 also increases, and the mounting and replacement of the electrode 18 cannot be performed quickly.

When the size of the container 16 is reduced, the electrode 1
Since the size of 8 is also small, it is difficult to attach it to the container 16 and the level cannot be detected correctly. Volume C _a is liquid 19
The permittivity of is related to ε ₁ , and the permittivity ε ₁ changes depending on the liquid temperature and frequency, so there is a problem that level detection cannot be performed accurately and stably.

The present invention has been made to solve the above problems, and the sensor is further immersed in the liquid 19 without depending on the size of the container 16, the relative arrangement of the electrodes 18 and the dielectric constant ε ₁ of the liquid 19. Simple and quick container 1 without
It is an object of the present invention to provide a level detecting device which can be attached to No. 6 and can stably detect the liquid level.

[0009]

A level detecting device according to the present invention comprises a container made of a non-metallic material filled with a conductive liquid, and a plurality of flexible conductive members near the level detecting position on the outer peripheral surface of the container. A sensor is provided in which electrodes are arranged separately from each other and a capacitor is formed by the electrodes and a conductive liquid.

[0010]

In the present invention, a container made of a non-metal material such as polyethylene or vinyl chloride filled with a conductive liquid such as various aqueous solutions or water-soluble chemicals has a conductive plastic near the liquid level level detection position on the outer peripheral surface thereof. A sensor is provided in which a plurality of electrodes made of a conductive material having flexibility such as a metal plate and a conductive film are arranged separately from each other in a direction parallel to the liquid surface. At this time, a capacitor is composed of the electrode, the dielectric material, and the conductive liquid, and its capacitance changes depending on the liquid level.

The capacitance detected from the two electrodes is converted into an electric signal and compared with a predetermined set level to identify the arrival of the liquid level in the container to the set level. Since the sensor can be freely attached to and detached from the outer peripheral surface of the container, it can quickly respond to changes in the liquid level to be detected and multiple level detection. It can be applied to containers of various sizes and shapes and is not affected by the dielectric constant of liquid. Since the capacitance of the capacitor is not related to the dielectric constant of the liquid, the level detection can be stabilized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the accompanying drawings. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA of FIG.
6 , 7, 8, 9, 10, 11, 12 are the same as those of the conventional device, 1 is a sensor sensitive to the liquid level, and 2 is the first
Electrodes, 3 is the second electrode, 4 is a container made of non-metallic material, 5
Indicates a conductive liquid filled in the container 4.

In the level detecting device constructed as described above, a container 4 made of a dielectric non-metal material such as polyethylene or vinyl chloride is filled with various aqueous solutions or conductive liquids 5 of water-soluble chemicals. A sensor 1 in which a plurality of flexible rectangular electrodes made of a conductive material such as a conductive plastic, a metal plate, and a conductive film are arranged side by side in a direction parallel to the liquid surface is an outer peripheral surface of a container 4 filled with a liquid 5. Attach it near the level detection position.

The first electrode 2 and the second electrode 3 of the sensor 1 in which the inner and outer surfaces of the bag-shaped container 4 made of, for example, a polyethylene material contact the electrodes and the conductive liquid 5 to form a capacitor.
Is connected to the signal conversion circuit 6 via the coaxial cable 12. The capacitance is converted into a DC signal proportional to the level of the liquid 5, and the level of the liquid 5 is detected by comparing the set level of the setter 10 with the comparator 11.

FIG. 3 is an explanatory diagram of the capacitor structure, and FIG. 4 shows an example of an equivalent circuit of the capacitor. In the figure,
Reference numerals 2, 3, 4, and 5 are the same as those in the above-described embodiment, and on one surface of the bag-shaped container 4, for example, a rectangular first electrode 2 and a second electrode 3 made of conductive plastic are parallel to the liquid surface. And are separated from each other in the direction, and the conductive liquid 5 is in contact with the other surface to form electrodes.

The capacitor C ₁ composed of the first electrode 2, the polyethylene and the liquid 5, and the capacitor C ₂ composed of the second electrode 3 and the polyethylene and the liquid 5 are electrically connected to each other through the conductive liquid 5. .. The effective area of the portion where the conductive liquid 5 and the electrode in the container 4 overlap each other is s,
When the thickness of polyethylene in the container 4 is t and the permittivity is ε, the capacitance of the capacitor is C = ε · s / t

When the capacitor C ₁ and the capacitor C ₂ are connected in series by the conductive liquid 5, and the capacitance C between the electrodes is 1 / C = 1 / C ₁ + 1 / C ₂ C ₁ = C ₂ C = C _1/2 , level of liquid 5 is electrode 1
8 the central area of the portion overlapping with each other reaches the position s / 2 next, because capacity becomes half the C = C _1/4.

The above capacity C is not affected even when the level of the liquid 5 is reduced or the shape of the bag of the container 4 is changed. If the level of the liquid 5 further decreases and no electrode is formed on the inner surface of the container 4, the electrodes do not overlap each other and the function as a capacitor is lost. By making the set level of the setter 9 correspond to the capacitance of the capacitor, the liquid level can be detected even in the region where the liquid 5 and the electrode partially overlap.

When the liquid level is lowered and the capacitor cannot be constructed, the fixed capacitance between the electrodes remains, but the value is small, so that the liquid level can be identified accurately and easily. Even if a large number of electrodes are arranged on the outer peripheral surface of the container 4 in a direction parallel to the liquid surface of the liquid 5, the same operation can be performed. The same operation can be performed by disposing electrodes on the outer peripheral surface of the container 4 in a direction perpendicular to the liquid surface of the liquid 5.

As described above, by providing the sensor 1 having the plurality of electrodes 18 on the outer peripheral surface of the container 4 made of a non-metallic material filled with the conductive liquid 5, the level of the liquid 5 is detected by the shape of the container 4. Since it has nothing to do with the size and the dielectric constant of the liquid 5, the reproducibility is high and stable. Further, the sensor 1 in which a plurality of rectangular electrodes made of a conductive material having flexibility such as a conductive plastic, a metal plate and a conductive film is arranged on a substrate having an adhesive force can be freely attached to and detached from the container 4. Therefore, it is possible to quickly respond to changes in the detection level.

When the liquid level falls below the position of the sensor 1, the capacitor loses its function and only the fixed capacitance between the electrodes is left, and this value is small, so that the level detection accuracy can be improved. Since the sensor 1 has a small size and is flexible, it can be applied to the container 4 of various sizes and shapes, particularly for detecting the remaining amount level of the drug solution in the infusion bag filled with the water-soluble drug solution used for drip to a patient in a hospital or the like. ..

[0022] Figure 5 is a fragmentary side view showing another embodiment of the present invention, FIG. 6 is a fragmentary top view of FIG. 5, 1 in FIG, 2,
3, 4 and 5 are the same as those in the above-described embodiment, and for example, in a plant or the like, the level detection of the liquid 5 in the cylindrical container 4 made of a non-metallic material is performed at two positions of the maximum liquid level and the minimum liquid level. In doing so, a small sensor 1 having a conductive member arranged on a flexible and adhesive substrate is used.

Since the sensor 1 can be removably arranged in the vicinity of the detection level position of the container 4, it is possible to detect a plurality of levels and change the levels quickly and easily. The presence or absence of liquid in pipes made of other non-metallic materials can be easily identified.

[0024]

As described above, according to the present invention, the liquid level can be detected by a simple structure in which a plurality of electrodes made of conductive members are arranged on the outer peripheral surface of a container made of a non-metallic material filled with a conductive liquid. It can be applied to containers of various shapes and sizes and is not affected by the dielectric constant of liquid. The sensor can be easily attached to and detached from the outer peripheral surface of the container, and can quickly respond to detection level changes and multiple level detection. Since the capacitance of the capacitor does not depend on the dielectric constant of the liquid, level detection can be performed stably. Since the fixed volume is small when the liquid surface level is lower than that of the sensor, there is an effect that the level detection accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an explanatory diagram of a capacitor configuration.

FIG. 4 shows an example of an equivalent circuit of a capacitor.

FIG. 5 is a side view of an essential part showing another embodiment of the present invention.

FIG. 6 is a top view of a main part of FIG.

FIG. 7 is a block diagram showing an example of a conventional level detection device.

[Explanation of reference numerals] 1 sensor 2 first electrode 3 second electrode 4 container 5 liquid 6 signal conversion circuit 10 setter 11 comparator

Claims (4)

[Claims] 1. A level detection device for detecting a liquid level in a container by comparing a liquid level of a liquid filled in the container with a predetermined set level, wherein the container is made of a non-metallic material filled with a conductive liquid. And a sensor in which a plurality of electrodes made of a flexible conductive member are arranged separately from each other in the vicinity of the level detection position on the outer peripheral surface of the container and a capacitor is formed by the electrodes and the conductive liquid. A level detection device characterized by detecting the liquid level from the liquid level. 2. The level detection device according to claim 1, wherein the non-metallic material of the container is a dielectric material. 3. The level detecting device according to claim 1, wherein the electrodes are arranged separately in a direction parallel to the liquid surface. 4. The level detection device according to claim 1, wherein the electrodes are arranged separately in a direction perpendicular to the liquid surface.