JPH05649B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses a coaxial cylindrical liquid level to measure the liquid level height, remaining amount, etc. (hereinafter referred to as "liquid level") in a liquid storage tank. This invention relates to a capacitive liquid level measuring device using a sensor.

[Conventional technology]

Generally, in underground tanks of gasoline filling stations, liquid level measuring devices are used to constantly monitor the remaining amount of oil.

Conventionally, this type of liquid level measuring device has a coaxial cylindrical liquid level sensor formed by coaxially cylindrical outer and inner cylinders each made of a single metal cylinder. is inserted into the liquid storage tank, and the liquid level height is measured based on the interelectrode capacitance formed between the outer cylinder and the inner cylinder of the liquid level sensor according to the liquid level height. It's summery.

That is, if the axial length of the outer cylinder and inner cylinder is l, the liquid level height is △l, the inner diameter of the outer cylinder is d ₁ , the outer diameter of the inner cylinder is d ₂ , and the dielectric constant of the liquid to be tested is ε. , the interelectrode capacitance C formed between the inner and outer cylinders is: C=0.2416/log ₁₀ (d ₁ /d ₂ )×{l+Δl(ε-1)
} =K×{l+Δl(ε−1)} (1) However, it is known that K=0.2416/log ₁₀ (d ₁ /d ₂ ). As a result, by performing frequency conversion, voltage conversion, etc. on the detected capacitance C, the liquid level height Δl can be measured, or the liquid level in the liquid storage tank corresponding to the liquid level height Δl can be measured. can be measured.

[Problem to be solved by the invention]

Here, as is clear from equation (1), the interelectrode capacitance C of the liquid level sensor is a function of the dielectric constant ε of the liquid to be tested, and therefore the measured liquid level height is also a function of the dielectric constant ε. be.

However, in liquid level measuring devices according to the prior art, the dielectric constant ε of the liquid to be tested, such as gasoline or diesel oil, is determined in advance by assigning a nominal value as a constant, which is approximately constant depending on the type of liquid, and then calculating the electrostatic constant. It is common to detect the capacitance C and calculate the liquid level height.

However, in reality, the true dielectric constant ε (effective dielectric constant) of the test liquid varies depending on the region of crude oil production and each refinery, and is different from the nominal value. There is a problem in that even if liquid level is detected based on the above, accurate measurement cannot be made. On the other hand, when setting and inputting the dielectric constant ε as a constant into the calculation device, there is a problem that if a different constant is set due to an error in the input procedure, an incorrect calculation result will always be output.

The present invention was developed in view of the problems of the prior art, and it is possible to measure the effective dielectric constant of a liquid to be tested stored in a liquid storage tank by using an inner cylinder that constitutes a liquid level sensor and by simply switching a switch. It is an object of the present invention to provide a capacitance type liquid level measuring device that can perform manual or automatic measurement using the method of the present invention and provide the measurement results as accurate constants to an arithmetic device.

[Means to solve the problem]

In order to achieve the above object, a capacitive liquid level measuring device according to the present invention has a coaxial cylindrical liquid level sensor consisting of an outer cylinder and an inner cylinder inserted into a liquid storage tank. The liquid level height is measured based on the interelectrode capacitance formed between the outer cylinder and the inner cylinder of the liquid level sensor according to the surface height.

The feature of the present invention is that the liquid level sensor is
It is formed by an outer cylinder of a book and two inner cylinders consisting of an upper inner cylinder and a lower inner cylinder, and an insulating member is inserted between the upper inner cylinder and the lower inner cylinder of the inner cylinder, and the outer cylinder is The tube and the calculation device are connected via a first signal line, the upper inner tube and the calculation device are connected by a second signal line and a common signal line, and the lower inner tube and the calculation device are connected via a second signal line and a common signal line. It is connected to the device by a third signal line and a common signal line, and in order to make the lower inner cylinder also serve as a sensor for measuring the dielectric constant of the liquid to be tested, the second and third signal lines are connected to the common signal line. A changeover switch is provided for connection to each computing device via the line.

The arithmetic device detects an interelectrode capacitance formed between the upper inner cylinder and the outer cylinder when the changeover switch is in an operating state in which only the upper inner cylinder is connected to the arithmetic device. , determine whether or not the detected capacitance is larger than a predetermined interelectrode capacitance when no test liquid is present between the upper inner cylinder and the outer cylinder, and under the condition that this judgment result is large. When the selector switch is operated to connect only the lower inner cylinder to the arithmetic unit, it is assumed that the liquid to be tested is present between the lower inner cylinder and the outer cylinder, and the connection between the lower inner cylinder and the outer cylinder is determined. When the dielectric constant of the test liquid is calculated and set from the inter-electrode capacitance formed between the electrodes, and the changeover switch is set to an operating state in which both the upper inner cylinder and the lower inner cylinder are connected to the calculation device, The liquid level height of the test liquid in the liquid storage tank is measured based on the interelectrode capacitance formed between the upper and lower inner cylinders and the outer cylinder and the dielectric constant set above. It is structured as follows.

[Effect]

With this configuration, for example, each time the liquid storage tank is filled, the changeover switch is operated to connect only the upper inner cylinder to the computing device, and the computing device is connected between the upper inner barrel and the outer barrel. detecting the inter-electrode capacitance formed in the upper inner cylinder and the outer cylinder, and determining whether the detected capacitance is larger than a predetermined inter-electrode capacitance when no test liquid is present between the upper inner cylinder and the outer cylinder. Determine whether
Make sure that the liquid to be tested is present between the upper inner cylinder and the outer cylinder.

Next, when it is determined through the above operation that the liquid to be tested is present between the upper inner cylinder and the outer cylinder, operate the changeover switch to connect only the lower inner cylinder to the calculation device, and The calculation device calculates the dielectric constant of the test liquid from the interelectrode capacitance formed between the lower inner cylinder and the outer cylinder, assuming that the test liquid is present between the lower inner cylinder and the outer cylinder. , is set as the dielectric constant of the newly filled test liquid.

Furthermore, when measuring the liquid level height, operate the changeover switch to connect both the upper inner cylinder and the lower inner cylinder to a calculation device, and the calculation device is formed between the upper and lower inner cylinders and the outer cylinder. Based on the inter-electrode capacitance and the dielectric constant set as described above, the upper inner cylinder and the lower inner cylinder are regarded as one inner cylinder, so that the upper inner cylinder and the lower inner cylinder are regarded as one inner cylinder. Normal liquid level measurement is possible from the capacitance.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the drawings, 1 is a liquid storage tank, 2 is a liquid stored in the liquid storage tank 1, 3 is the liquid level, and 4 is a coaxial cylindrical liquid level sensor inserted into the liquid storage tank 1. The liquid level sensor 4 has an outer cylinder 5 made of one cylinder, and an inner cylinder 6 coaxially inserted into the outer cylinder 5, and the inner cylinder 6 has an upper inner cylinder 6A.
The lower inner cylinder 6A is composed of two cylinders, and the lower end of the upper inner cylinder 6A and the upper end of the lower inner cylinder 6B are connected via an insulating member 7. In addition, 8 is an insulating member provided at the lower ends of the outer cylinder 5 and the lower inner cylinder 6B, and the insulating member 8 is seated on the bottom surface of the liquid storage tank 1. On the other hand, 9 is the outer cylinder 5 and the upper inner cylinder. Another insulating member provided at the upper end of 6A, this insulating member 9, slightly protrudes from the upper surface of the liquid storage tank 1.

Reference numeral 10 denotes a calculation device, and the calculation device 10 includes a calculation circuit 11 that calculates the liquid level height and dielectric constant ε based on the detected capacitance as described later, and a switch 12A that can be opened and closed. ,12B
It is composed of a changeover switch 12 having a. The input side of the arithmetic device 10 is a first
It is connected to the outer cylinder 5 via a signal line 13, and is also connected to the second and third signals and a common signal line 1 to be described later.
8 to the upper inner cylinder 6A and lower inner cylinder 6B, respectively, and the output side is connected to the liquid level gauge 16.

Here, the switch 12 of the changeover switch 12
A is provided in the middle of the second signal line 14, switch 12B is provided in the middle of the third signal line 15,
These signal lines 14 and 15 are connected at a connection point 17 to form one common signal line 18, which is then connected to the arithmetic circuit 11. In this way, the second and third signal lines 14 and 15 connect to the connection point 17.
Thereafter, as a result of being connected by the common signal line 18, the capacitance formed by the outer cylinder 5 and the upper inner cylinder 6A is C _a , and the capacitance formed by the outer cylinder 5 and the lower inner cylinder 6B is C a . When the capacitance is C _b , switch 1
When 2A and 12B are closed, these capacitances are
C _a and C _b will be electrically connected in parallel.

The present embodiment is configured as described above, and its operation will be described next.

Now, as shown in the drawing, liquid 2 is stored in the liquid storage tank 1 in a nearly full state, and the liquid level 3
is located at an axially intermediate position of the upper inner cylinder 6A.

Then, the length of the upper inner cylinder 6A is l _a , and the length of the lower inner cylinder 6 is
The length of B is l _b , the constant K determined by the inner diameter d ₁ of the outer cylinder 5 and the outer diameter d ₂ of the inner cylinder 6 is K=0.2416/log ₁₀ (d ₁ /d ₂ ), (1) The capacitances C _a and C _b are measured in the same manner as in the prior art described in the formula.

First, in order to measure the capacitance C _a formed between the outer cylinder 5 and the upper inner cylinder 6A, selector switch 1 is
The second switch 12A is closed and the second switch 12B is opened. As a result, if the length of the upper inner cylinder 6A immersed in the liquid 2 _{is Δla} , the dielectric constant of air is ε ₀ , and the dielectric constant of the liquid 2 is ε, then the capacitance _Ca is calculated as follows: Ca=K{ Δla×ε+(la−Δla)×ε ₀ }…(2) Since the dielectric constant ε ₀ of air is ε ₀ ≒1,
Equation (2) becomes equation (3) below.

Ca=K{la+Δla(ε-1)}...(3) Next, in order to measure the capacitance C _b formed between the outer cylinder 5 and the lower inner cylinder 6B, switch 1
The second switch 12A is opened and the second switch 12B is closed. At this time, since the lower inner cylinder 6B is immersed in the liquid 2 over its entire length l _b , the capacitance is
C _b is expressed by the following formula (4).

Cb=K×lb×ε...(4) Furthermore, in order to measure the total capacitance _Cs formed by the outer cylinder 5 and the inner cylinder 6, both switches 12A and 12B of the changeover switch 12 are closed. do. As a result, the total capacitance _Cs is calculated from equations (3) and (4) as follows: Cs=Ca+Cb=K×{la+lb+(lb+Δla)×(ε-1)}
…(5) It can be detected as. Here, (lb +
Δla) is the length of the upper inner cylinder 6A and lower inner cylinder 6B immersed in the liquid 2, and since it is a constant except for the dielectric constant (ε-1), (ε-1) can be detected accurately. If the total capacitance Cs is determined, the liquid level height (lb+la) can be measured.

On the other hand, in the above explanation, the liquid level 3 in the liquid storage tank 1 is in the state shown in the drawing, but when the liquid level 3 drops halfway down the lower inner cylinder 6B, the upper inner cylinder 6B
Since A is not immersed in the liquid surface, its capacitance Ca′ is Ca′=K×la …(6), and the capacitance Cb′ of the lower inner cylinder 6B is Cb′ as in equation (3). It is obtained as =K×{l _b +Δl _b (ε−1)} (7). Therefore, the total capacitance _Cs when both switches 12A and 12B of the changeover switch 12 are closed is calculated from equations (6) and (7) as follows: Cs=Ca′+Cb′=K×{la+lb+Δlb(ε -1)} ...(8), which is obtained by setting (l _b + Δl _a ) in equation (5) to Δl _b .

Thus, the general formula over the range of the total liquid level height in the liquid storage tank 1 is: Cs=K×{(la+lb)+(Δla+Δlb)×(ε−1)
}
...(9), and by considering the upper inner cylinder 6A and the lower inner cylinder 6B as one inner cylinder 6, and considering l≒la+lb Δl≒Δla+Δlb...(10), the conventional technology shown in equation (1) can be solved. The liquid level can be detected in the same way as the previous one.

Therefore, when the upper inner cylinder 6A is not immersed in the liquid 2, that is, when Δla=0, the capacitance C _a ′ is (6)
As is clear from the equation, the dielectric constant ε is not included, and all are known values determined by constants. On the other hand, the capacitance Ca when the upper inner cylinder 6A is immersed in the liquid 2 is
This is equation (3). Therefore, by closing the switch 12A of the changeover switch 12 and opening the switch 12B, when the arithmetic circuit 11 side determines that Ca>Ca' (11), the liquid level 3 is equal to the upper inner cylinder 6A. It is higher than the lower surface position, indicating that the lower inner cylinder 6B is completely immersed in the liquid 2.

Therefore, when the liquid level satisfies equation (11), for example when the liquid storage tank 1 is full, switch 12A of the changeover switch 12 is opened and switch 12B is closed. By measuring the capacitance C _b according to equation (4), the dielectric constant ε can be determined as ε=K′×Cb/lb (12) where K′=1/K.

By the way, the liquid stored in the liquid storage tank 1 is
Generally, the effective dielectric constant differs each time the tank is consumed and refilled, and it is customary for the tank to be almost full when refilled.

Therefore, each time the liquid 2 is replenished into the liquid storage tank 1, after confirming the conditions of equation (11) by operating the changeover switch 12, calculate the capacitance C _b using equation (4), and then calculate the capacitance C b using equation (4).
If the dielectric constant ε is determined from the formula and the dielectric constant is updated and set in the arithmetic circuit 11, the determined dielectric constant will be used until the liquid 2 in the liquid storage tank 1 is consumed and the next time it is replenished. Equation (9) can be used to calculate the liquid level height, allowing highly accurate liquid level detection.

Moreover, the lower inner cylinder 6B can be made as long as about 80% of the height of the liquid storage tank 1, and the longer length of the lower inner cylinder 6B means that l _b in equation (12) , C _b are large, the value of the dielectric constant ε can also be determined with high accuracy.

Note that the changeover switch 12 is an automatic changeover switch, and the arithmetic circuit 11 is constituted by a microcomputer, and the above-mentioned series of operations can be performed, for example, in a second
By incorporating the program shown in FIGS. 3 and 3, an automatic liquid level measuring device can be constructed.

In addition, in the embodiment, a sensor dedicated to the liquid level is used as the liquid level sensor 4, but as shown in Japanese Patent Publication No. 60-35614, a liquid level sensor that can also measure the height of the water level accumulated at the inner bottom of the liquid storage tank 1 may be used. can also be applied.

On the other hand, since the upper inner cylinder 6A and the lower inner cylinder 6B are connected via the insulating member 7, when the liquid level becomes higher than the position of the insulating member 7, the capacitance and the liquid level height theoretically increase. Although there is a difference in level between the two, the value can be practically ignored.

Furthermore, it goes without saying that the liquid level measuring device of the present invention is defined as a concept that also includes a tank remaining amount measuring device.

〔Effect of the invention〕

The capacitance type liquid level measuring device according to the present invention is as described in detail above, and has a split inner cylinder consisting of an upper inner cylinder and a lower inner cylinder. A changeover switch is provided to selectively connect the signal line that connects the cylinder to the calculation device, and by switching the changeover switch, it can also be used as a dielectric constant measurement sensor, so that the upper inner cylinder can be connected to the calculation device. After confirming that the liquid has been refilled in the liquid storage tank, measure and set the effective dielectric constant of the liquid stored in the liquid storage tank with the lower inner cylinder connected to the calculation device. With the upper and lower inner cylinders connected in series and connected to the arithmetic unit via each signal line and the common signal line using a changeover switch, the capacitance between the electrodes formed between the inner and outer cylinders is measured as described above. It is possible to measure the liquid level height based on the new dielectric constant set in There is no need to provide any equipment, and it is highly effective in terms of cost and installation work.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing a capacitive liquid level measuring device according to an embodiment, FIG. 2 is a flowchart showing a liquid level measurement process, and FIG. 3 is a flowchart showing a dielectric constant measurement process. 1...Liquid storage tank, 2...Liquid, 3...Liquid level, 4...Liquid level sensor, 5...Outer cylinder, 6...Inner cylinder, 6A...Upper inner cylinder, 6B...Lower inner cylinder, 7, 8, 9...Insulation Part, 1
0... Arithmetic device, 11... Arithmetic circuit, 12... Changeover switch, 12A, 12B... Switch, 13... First signal line, 14... Second signal line, 15... Third signal line, 17... Connection point, 18...Common signal line.

Claims (1)

[Claims] 1 It has a coaxial cylindrical liquid level sensor consisting of an outer cylinder and an inner cylinder that are inserted into a liquid storage tank, and a cylinder is formed between the outer cylinder and the inner cylinder of the liquid level sensor according to the liquid level height. In a capacitive liquid level measuring device that measures the liquid level based on the interelectrode capacitance,
The liquid level sensor is formed by one outer cylinder and two inner cylinders consisting of an upper inner cylinder and a lower inner cylinder, and an insulating member is provided between the upper inner cylinder and the lower inner cylinder of the inner cylinders. is inserted, the outer cylinder and the arithmetic device are connected via a first signal line, and the upper inner cylinder and the arithmetic device are connected by a second signal line and a common signal line,
The lower inner cylinder and the arithmetic unit are connected by a third signal line and a common signal line, and the lower inner cylinder also serves as a sensor for measuring the dielectric constant of the liquid to be tested.
A changeover switch is provided for respectively connecting the second and third signal lines to the arithmetic device via a common signal line, and the arithmetic device is in an operating state in which only the upper inner cylinder is connected to the arithmetic device. In this case, the inter-electrode capacitance formed between the upper inner cylinder and the outer cylinder is detected, and the detected capacitance indicates that the liquid to be detected is present between the upper inner cylinder and the outer cylinder. It is determined whether the capacitance between the electrodes is larger than a predetermined capacitance in the case where the capacitance between the electrodes is not set, and when the changeover switch is set to an operation state in which only the lower inner cylinder is connected to the arithmetic device under the condition that the result of this judgment is large, the capacitance between the electrodes is Assuming that the test liquid is present between the lower inner cylinder and the outer cylinder, the dielectric constant of the test liquid is calculated and set from the interelectrode capacitance formed between the lower inner cylinder and the outer cylinder. Further, when the changeover switch is operated to connect both the upper inner cylinder and the lower inner cylinder to the computing device, the interelectrode capacitance formed between the upper and lower inner cylinders and the outer cylinder and the 1. A capacitance type liquid level measuring device, characterized in that the liquid level measuring device is configured to measure the liquid level height of the test liquid in the liquid storage tank based on the dielectric constant set by the above-mentioned dielectric constant.