Liquid level detection device

Abstract

To solve a problem in which a value of a liquid level detected by an electrode varies depending on a surrounding environment such as temperature and humidity, and a full level cannot be detected correctly, with the result that a liquid in a vessel overflows.SOLUTION: A sensor 3 forming electrostatic capacity with a liquid has a first electrode 4 and a second electrode 5. The first electrode 4 has a shaft portion 4a provided in a vertical direction as a direction in which a liquid level changes; and a plurality of arm portions 4b electrically connected to the shaft portion 4a and provided in a horizontal direction. In the arm portions 4b, the lengths of the plurality of arm portions 4b other than an arm portion at a lower end are equal to one another, and the arm portion 4b at the lower end is longer than the other arm portions 4b. The second electrode 5 is formed in rotational symmetry with the first electrode 4, and the first electrode 4 and the second electrode 5 are not electrically connected. The plurality of arm portions 4b of the first electrode 4, other than the arm portion at the lower end, and a plurality of arm portions 5b of the second electrode 5, other than an arm portion at an upper end, are all arranged so as to face each other. Therefore, because a liquid level can be accurately estimated, there is no possibility that a full level cannot be detected correctly, resulting in overflow of a liquid in a vessel.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to a liquid level detection device for detecting the liquid level of a liquid in a container.

Background Art

[0002] Patent Document 1 discloses a liquid level detection device for detecting a liquid level, which includes a substrate and a plurality of electrode pairs including a plurality of electrodes, and the plurality of electrodes use electrodes whose capacitance changes with respect to the change amount of the liquid level.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In liquid level detection using a capacitance-type liquid level detection device, variations occur due to the surrounding environment such as temperature and humidity, and full water cannot be correctly detected, which may lead to the risk of water leakage. In addition, there is a problem that the number of components increases when another sensor for detecting full water is provided.

Means for Solving the Problems

[0005] In order to solve the above problems, in claim 1 of the present invention, in a liquid level detection device provided with two conductive detection members that form a capacitance with a liquid that increases and decreases in a liquid storage body, and capacitance detection means that outputs a detection value in response to a change in capacitance, one of the conductive detection members has a shaft portion provided in the vertical direction as the direction in which the liquid level changes, and a plurality of arm portions provided in the horizontal direction and electrically connected to the shaft portion. The lengths of the plurality of arm portions other than the lower end are equal, the arm portion at the lower end is longer than the other arm portions, and the other conductive detection member is formed rotationally symmetric with the one conductive detection member. The one conductive detection member and the other conductive detection member are not electrically connected, and the plurality of arm portions other than the lower end of the one conductive detection member and the plurality of arm portions other than the upper end of the other conductive detection member are arranged so as to all face each other.

[0006] Further, in claim 2 of the present invention, a pair of conductive detection members formed by the one conductive detection member and the other conductive detection member are provided with upper ends of the pair of conductive detection members at a height corresponding to the upper limit liquid level, and lower ends of the pair of conductive detection members are provided at a height corresponding to the lower limit liquid level.

[0007] Further, in claim 3 of the present invention, the capacitance detection means estimates the upper limit liquid level, the lower limit liquid level, and a variable liquid level between the upper limit liquid level and the lower limit liquid level according to the capacitance detected by the one conductive detection member, the capacitance detected by the other conductive detection member, and the difference between the capacitance detected by the one conductive detection member and the capacitance detected by the other conductive detection member.

[0008] Further, in claim 4 of the present invention, the capacitance detection means compares the capacitance detected by the one conductive detection member, the capacitance detected by the other conductive detection member, and a predetermined capacitance corresponding to a plurality of liquid levels corresponding to the plurality of arm portions provided in advance, so that the liquid level between the upper limit liquid level and the lower limit liquid level can be detected step by step.

Effects of the Invention

[0009] According to the present invention, the liquid level can be accurately detected using one electrode and the other electrode.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0011] The liquid level detection device 1 is used to detect the liquid level of, for example, water as a liquid that increases and decreases in a liquid storage body (not shown). As shown in FIG. 1, the liquid level detection device 1 includes a control unit 2 as capacitance detection means and a sensor 3 as a conductive detection member.

[0012] In the liquid level detection device 1, the capacitance detected by the sensor 3 is input to the control unit 2, and the liquid level is estimated based on the input capacitance.

[0013] As shown in FIG. 1, the sensor 3 includes a first electrode 4 as one conductive detection member and a second electrode 5 as the other conductive detection member as a pair of conductive detection members.

[0014] The first electrode 4 has a shaft portion 4a provided in the vertical direction as the direction in which the liquid level changes, and a plurality of arm portions 4b provided in the horizontal direction and electrically connected to the shaft portion 4a. The length of the shaft portion 4a in the height direction has a length corresponding to the height of the lowermost part of the arm portion 4b and the uppermost part of the arm portion 5b (to be described later). The length of the shaft portion 4a in the horizontal direction has a length such that there is no hindrance to the detection of capacitance. The lengths of the plurality of arm portions 4b other than the lower end are equal, and the arm portion 4b at the lower end is formed longer than the other arm portions 4b. Also, the plurality of arm portions 4b are formed such that the intervals between the arm portions 4b are equal. The length of the arm portion 4b in the height direction and the length in the horizontal direction have lengths such that there is no hindrance to the detection of capacitance after satisfying the relationship between the lower end of the arm portion 4b and the lengths of the arm portions 4b other than the lower end described above.

[0015] The second electrode 5 is formed rotationally symmetric with respect to the first electrode 4. The second electrode 5 has a shaft portion 5a provided in the vertical direction as the direction in which the liquid level changes, and a plurality of arm portions 5b provided in the horizontal direction and electrically connected to the shaft portion 5a. The length of the shaft portion 5a in the height direction has a length corresponding to the height of the lowermost part of the arm portion 4b and the uppermost part of the arm portion 5b. The length of the shaft portion 5a in the horizontal direction has a length such that there is no hindrance to the detection of capacitance. The lengths of the plurality of arm portions 5b other than the upper end are equal, and the arm portion 5b at the upper end is formed longer than the other arm portions 5b. Also, the plurality of arm portions 5b are formed such that the intervals between the arm portions 5b are equal. The length of the arm portion 5b in the height direction and the length in the horizontal direction have lengths such that there is no hindrance to the detection of capacitance after satisfying the relationship between the upper end of the arm portion 5b and the lengths of the arm portions 5b other than the upper end described above.

[0016] Also, between the first electrode 4 and the second electrode 5, at least a non-electrically connected interval is provided, and a plurality of arm portions 4b other than the lower end of the first electrode 4 and a plurality of arm portions 5b other than the upper end of the second electrode 5 are formed so as to all face each other.

[0017] The arm portion 4b at the lower end is arranged at a height corresponding to, for example, an empty liquid level as the desired liquid level, and the arm portion 5b at the upper end is arranged at a height corresponding to, for example, a full water level as the desired liquid level.

[0018] Next, the change in the detected capacitance according to the change in the liquid level using the liquid level detection device 1 will be described with reference to FIG. 2. FIG. 2 shows a variable capacitance according to the change in the liquid level detected using the first electrode 4 and the second electrode 5. When the liquid level rises, the area of the first electrode 4 in proximity to the liquid increases, and accordingly, the capacitance detected by the first electrode 4 also increases. When the liquid level rises, the area of the second electrode 5 in proximity to the liquid increases, and accordingly, the capacitance detected by the second electrode 5 also increases. By comparing the capacitance values detected by the first electrode 4 and the second electrode 5 with the capacitance corresponding to a preset liquid level, it is possible to estimate the liquid level.

[0019] Next, a method for stepwise estimating a variable liquid level between the empty liquid level and the full water liquid level using the liquid level detection device 1 will be described with reference to FIG. 2. FIG. 2 shows a variable capacitance according to the change in the liquid level detected using the first electrode 4 and the second electrode 5. When the liquid level rises, the area of the first electrode 4 in proximity to the liquid increases, and accordingly, the capacitance detected by the first electrode 4 also increases. When the liquid level rises, the area of the second electrode 5 in proximity to the liquid increases, and accordingly, the capacitance detected by the second electrode 5 also increases. The control unit 2 can estimate the liquid level by comparing the capacitance values detected by the first electrode 4 and the second electrode 5 with the capacitance corresponding to a preset liquid level.

[0020] At this time, at the liquid levels corresponding to the plurality of arm portions 4b and 5b, the area of the first electrode 4, the second electrode 5, and the liquid in proximity is the total area of the shaft portions 4a, 5a, arm portions 4b, and 5b, and the capacitance detected by the first electrode 4 and the second electrode 5 with respect to the change in the liquid level changes significantly. Also, at liquid levels not corresponding to the plurality of arm portions 4b and 5b, the area of the first electrode 4, the second electrode 5, and the liquid in proximity is the total area of the shaft portions 4a and 5a. As a result, the capacitance detected by the first electrode 4 and the second electrode 5 with respect to the change in the liquid level changes less compared to the case of the liquid level corresponding to the arm portions 4b and 5b.

[0021] The liquid level detection device 1 estimates whether it is the liquid level corresponding to the plurality of arm portions 4b and 5b by comparing the capacitance detected between the first electrode 4 and the second electrode 5 with the capacitance corresponding to the liquid level corresponding to the plurality of provided arm portions 4b and 5b. When the estimated liquid level is the liquid level corresponding to the plurality of arm portions 4b and 5b, the liquid level detection device 1 determines that it is a liquid level detectable liquid level where the capacitance detected between the first electrode 4 and the second electrode 5 changes greatly with the change in the liquid level. On the other hand, when the estimated liquid level is not the liquid level corresponding to the plurality of arm portions 4b and 5b, the liquid level detection device 1 determines that it is a liquid level undetectable liquid level where the capacitance detected between the first electrode 4 and the second electrode 5 changes little with the change in the liquid level. The liquid level detection device 1 performs liquid level detection only for this liquid level detectable liquid level, and compares the capacitance detected between the first electrode 4 and the second electrode 5 with the capacitance corresponding to the liquid level corresponding to the plurality of provided arm portions 4b and 5b. Thus, the liquid level detection device 1 gradually estimates from the capacitance detected between the first electrode 4 and the second electrode 5 which stage of the plurality of arm portions 4b and 5b the corresponding liquid level is. When the liquid level detection device 1 determines that it is a liquid level undetectable liquid level, it does not perform liquid level detection and holds the stepped liquid level estimated as the liquid level detectable liquid level. At this time, when there is no stepped liquid level to be held estimated as the liquid level detectable liquid level, the previously provided initial value is used. Alternatively, even if the liquid level detection device 1 is exceptionally a liquid level undetectable liquid level, it may estimate a nearby stepped liquid level from the capacitance detected between the first electrode 4 and the second electrode 5, and estimate the stepped liquid level within a range that does not interfere with control.

[0022] Next, a method for estimating the empty liquid level and the full water level using the liquid level detection device 1 will be described with reference to FIG. 3. FIG. 3 shows the difference in capacitance detected using the first electrode 4 and the second electrode 5, which changes according to the variable liquid level calculated by the control unit 2. At the empty liquid level, since all surfaces of the first electrode 4 and the second electrode 5 are not close to the liquid, the areas of the surfaces of the first electrode 4, the second electrode 5, and the liquid that are close to each other are equal, and no difference in capacitance occurs.

[0023] When the liquid level rises from the empty liquid level and reaches the liquid level corresponding to the lower end of the arm portion 4b, the area where the lower end of the first electrode 4 is close to the liquid becomes the total area of the lower end of the arm portion 4b and the lower end of the shaft portion 4a, and the area where the lower end of the second electrode 5 is close to the liquid becomes only the area of the lower end of the shaft portion 5a. As a result, a difference occurs in the area where the first electrode 4 and the second electrode 5 are close to the liquid. At this time, since the area where the second electrode 5 is close to the liquid rises less than that of the first electrode 4, a difference also occurs in the capacitance detected by the first electrode 4 and the second electrode 5, and the difference becomes larger.

[0024] A plurality of arm portions 4b other than the upper end of the first electrode 4 and a plurality of arm portions 5b other than the lower end of the second electrode 5 are formed so as to all face each other. As a result, from the liquid level corresponding to the lower end of the arm portion 4b until the liquid level reaches the liquid level corresponding to the upper end of the arm portion 5b, the areas where the first electrode 4 and the second electrode 5 are close to the liquid change equally. Therefore, the difference in capacitance detected by the first electrode 4 and the second electrode 5 does not change and becomes a constant value.

[0025] When the liquid level further rises and reaches the liquid level corresponding to the upper end of the arm portion 5b, the area where the upper end of the first electrode 4 is close to the liquid becomes only the area of the upper end of the shaft portion 4a, and the area where the upper end of the second electrode 5 is close to the liquid becomes the total area of the upper end of the shaft portion 5a and the upper end of the arm portion 5b. As a result, a difference occurs in the area where the first electrode 4 and the second electrode 5 are close to the liquid. At this time, since the area where the second electrode 5 is close to the liquid rises more than that of the first electrode 4, a difference also occurs in the capacitance detected by the first electrode 4 and the second electrode 5, and the difference becomes smaller.

[0026] When the liquid level reaches a level higher than the liquid level corresponding to the upper end of the arm portion 5b, since all surfaces of the first electrode 4 and the second electrode 5 are close to the liquid, the areas where the first electrode 4, the second electrode 5, and the liquid are close to each other become equal, and no difference in capacitance occurs.

[0027] The liquid level detection device 1 estimates an empty liquid level when the absolute value of the capacitance detected by the first electrode 4 and the second electrode 5 is less than a predetermined value and there is no difference in the capacitance detected by the first electrode 4 and the second electrode 5.

[0028] The liquid level detection device 1 estimates a full liquid level when the absolute value of the capacitance detected by the first electrode 4 and the second electrode 5 is greater than a predetermined value and there is no difference in the capacitance detected by the first electrode 4 and the second electrode 5.

[0029] According to the present embodiment, the liquid level detection device 1 estimates an empty liquid level and a full liquid level from the absolute value of the capacitance detected by the first electrode 4 and the second electrode 5 and the difference in the capacitance detected by the first electrode 4 and the second electrode 5. With this, the liquid level detection device 1 can estimate an empty liquid level and a full liquid level without false detection without using a dedicated sensor.

[0030] Further, according to the present embodiment, the liquid level detection device 1 performs liquid level detection only for liquid levels where liquid level detection is possible, does not perform liquid level detection when it is determined that the liquid level is not detectable, and estimates the liquid level step by step. Therefore, it is possible to perform step-by-step estimation of the liquid level with high sensitivity and without error.

[0031] In the present embodiment, the first electrode 4 and the second electrode 5 used in the liquid level detection device 1 have been described by giving an example in which the arm portions 4b and 5b are arranged inside the shaft portions 4a and 5a as shown in FIG. 1. However, although not shown, the arm portions 4b and 5b may be arranged on both sides of the shaft portions 4a and 5a, or the arm portions 4b and 5b may be arranged outside the shaft portions 4a and 5a.

Explanation of Reference Numerals

[0032] 2: Control unit 3: Sensor 4: First electrode 4a: Shaft portion 4b: Arm portion 5: Second electrode 5a: Shaft portion 5b: Arm portion

Claims

1. Two conductive detection members that form a capacitance with a liquid that increases and decreases in the liquid storage body, Capacitance detection means for outputting a detection value in response to a change in capacitance, In a liquid level detection device provided with, One of the conductive detection members has a shaft portion provided in the vertical direction as the direction in which the liquid level changes, and a plurality of arm portions provided in the horizontal direction and electrically connected to the shaft portion. The lengths of the plurality of arm portions other than the lower end are equal, the arm portion at the lower end is longer than the other arm portions, and the other conductive detection member is formed rotationally symmetrically with the one conductive detection member. The one conductive detection member and the other conductive detection member are not electrically connected, and a plurality of the arm portions other than the lower end of the one conductive detection member and a plurality of the arm portions other than the upper end of the other conductive detection member are all arranged so as to face each other. A liquid level detection device characterized by this.

2. The pair of conductive detection members formed by the one conductive detection member and the other conductive detection member are provided with upper ends of the pair of conductive detection members at a height corresponding to the upper limit liquid level, and lower ends of the pair of conductive detection members at a height corresponding to the lower limit liquid level. The liquid level detection device according to claim 1, characterized by this.

3. The capacitance detection means estimates the upper limit liquid level, the lower limit liquid level, and a variable liquid level between the upper limit liquid level and the lower limit liquid level according to the capacitance detected by the one conductive detection member, the capacitance detected by the other conductive detection member, and the difference between the capacitance detected by the one conductive detection member and the capacitance detected by the other conductive detection member. The liquid level detection device according to claim 2, characterized by this.

4. The capacitance detection means compares the capacitance detected by the one conductive detection member, the capacitance detected by the other conductive detection member, and a predetermined capacitance corresponding to a plurality of liquid levels corresponding to the plurality of arm portions provided in advance, so that the liquid level between the upper limit liquid level and the lower limit liquid level can be detected step by step. The liquid level detection device according to claim 3, characterized by this.

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