JPH0334013B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid boundary surface detection device capable of detecting the position of a boundary surface between liquids having different specific gravities in a tank storing a plurality of liquids having different specific gravities. It is something.

[Prior Art] When there are two liquids with different specific gravities (for example, oil and water) in a storage tank, the height (depth) of each liquid must be measured in order to know the amount of each liquid. Therefore, the following method has conventionally been used.

(b) Install two level gauges in the tank, use one level gauge to measure the liquid level at the interface between the gas and the first liquid with low specific gravity, and use a local level gauge to measure the liquid level at the interface between the first liquid and the gas. The liquid boundary surface, which is the boundary surface of the second liquid having a large specific gravity, is measured.

(b) Lower the tank scale (a scaled steel tape with a weight suspended from the tip) under the tank and find out the height from the wetness of the liquid. That is, if a special paste that changes color depending on the second liquid is applied to the tank gauge, the height of the second liquid can be determined by the change in the color of the paste.

(c) Submerge the sampler into the liquid in the same way as when measuring a tank, take a sample of the liquid from a predetermined area, and investigate the state of the boundary between the two liquids.
This is not originally done to find out the height of the liquid, but to investigate the state of the boundary between two liquids (generally, the interface between two liquids is not completely separated). You can find out the approximate height.

[Problem that the invention seeks to solve]

However, these conventional methods have the following problems. First, regarding method (a), conventional liquid level gauges detect the vertical movement of the interface by changes in the buoyant force that the displacer receives from the two liquids, and then make the displacer follow the interface and measure it at that time. The height is determined by the length of the thread (tape or wire), and measurement using this method is unstable because the difference in specific gravity between the two liquids is usually extremely small. Furthermore, sludge (deposits) often accumulates on the displacer, and the balance point may gradually shift, making measurement impossible. Furthermore, the balance point of the displacer changes due to a quantitative change in buoyancy based on a change in the specific gravity of the two liquids, and the detection point is affected by the specific gravity of the liquid.

Next, method (b) requires manpower and is disadvantageous in terms of safety and cost. Method (c) also has the same drawbacks as (b) in that it requires manual labor, and also has the drawback that it is difficult to capture the liquid boundary surface.

Therefore, it is an object of the present invention to provide a boundary surface detection device that does not have the above-mentioned drawbacks and can reliably detect a liquid boundary surface with a single device.

[Means for solving problems]

Conventionally, when measuring the liquid level or the interface between liquids with different specific gravities using a self-balancing liquid level gauge with a servo mechanism, a displacer as a detection end (the mass of which is larger than the mass of the liquid it displaces) is used. The measurement is performed while the liquid (displacer) is in equilibrium and stationary at the liquid surface or liquid interface. FIG. 4 is an explanatory diagram showing the relationship of forces applied to a stationary displacer. In the same figure, W
When is the weight of the displacer, F is the buoyant force, V is the volume of the part of the displacer submerged in the liquid, ρ is the specific gravity of the liquid, and T is the tension of the measuring wire, the following relationship is established.

T=W−F (1) F=ρV (2) In equation (1), since W is known, T changes according to F. Therefore, the displacer is made to follow the liquid level or liquid interface by the servo mechanism so that the change in F is captured and T is always constant.

However, in the present invention, W, T, and F are set in equation (1) so that even if the displacer receives the buoyant force F of the liquid, it can descend to the bottom of the tank without being balanced. FIG. 2 is an explanatory diagram showing the features of this invention. In the figure, 1 is a tank, 2 is a displacer, and 3 is a measuring wire lifting mechanism. In the present invention, the displacer 2 is first rolled up in the gas, and when measurement is started, the displacer 2 passes through the liquids 1, 2..., n and hits the bottom plate of the tank 1, and the tension T of the measuring wire becomes zero.

In this case, since the displacer 2 continues to descend continuously, the mechanical relationship is different from the static case as in equation (1), and the displacer 2 is subject to resistance such as the viscosity of the liquid. This can be expressed as a formula as follows.

T=W-F-R...(3) However, R is the resistance due to viscosity etc. which the displacer receives from the liquid.

The position of the liquid interface can be determined by continuously measuring the wire tension T in equation (3) and processing it as follows.

Figure 3 shows the experimental results of measuring the tension T of a liquid container in which three types of liquids with different specific gravity are separated into three phases and left still, passing through the displacer as described above. be. Same figure A
shows the relationship between the tension value T and the time t, B shows the relationship between the time t and a value obtained by differentiating the tension value T with respect to time, and C shows the depth of each phase.

~ in Figure 3A is ~ in Figure 3B, respectively.
3A correspond to a' to d' in FIGS. 3B and C, respectively. ~ indicates when the lower end of the displacer 2 reaches the surface of liquid 1 to liquid 3 and the bottom of the container, respectively, ~ a',
~ b' and ~ c' represent the process in which the displacer 2 passes through the interface between gas and liquid 1, liquid 1 and liquid 2, and liquid 2 and liquid 3, respectively.
d' shows the process in which the displacer 2 reaches the bottom of the container and the tire tension becomes zero. Here, in the process of moving from b' to d' in Figure 3A, there is a part where the tension value drops and then rises again, but this is due to the resistance R in equation (3).
This occurs from the time the lower end of the displacer 2 reaches the boundary surface until the entire displacer 2 is submerged in the liquid below, and when the entire displacer 2 is completely submerged in the liquid below, the tension becomes constant. Become.

As can be seen from these figures, the wire tension changes rapidly at the liquid interface, and the present invention provides two judgment means based on these changes to reliably detect the interface. The first means of judgment is based on the differential value of the tension that changes when the displacer passes the boundary surface, and a preset reference value (the difference between the tension value when the upper liquid passes and the tension value when the lower liquid passes). (approximately 1/2 value subtracted from the tension value when the upper liquid passes) and the tension value that decreases at the interface, and if it is below the reference value, the output is output from the comparison means. It is to judge. The second determining means determines whether the output from the comparing means matches the differential value delayed by a certain time.

[Effect]

The first determining means functions to determine that the displacer has passed approximately half of the boundary surface. However, if the differential value appears due to noise even though the displacer has not passed through the boundary surface, and the decrease in the tension value at that time exceeds the above-mentioned reference value, the first judgment means makes the mistake of assuming that this is correct and incorporating the liquid level data. The second determining means operates to display the liquid level data only when it is confirmed that the displacer has reliably passed the boundary surface without making such an error.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to illustrated embodiments.

FIG. 1 is a block diagram showing a preferred embodiment of the invention. This device consists of three parts: a tension detection/measurement wire drive section, an automatic measurement section, and a display/transmission section, which are shown surrounded by broken lines in the figure. The configuration of each of these parts is as shown in the figure. For convenience, the structure and operation will be explained at the same time.

Assume that the displacer 2 is now rolled up to near the top of the tank 1. Furthermore, the following values are manually input into the set value circuit 10 as set values. The first value is the tension value T ₀ and the first value when the displacer 2 is in the gas phase.
The difference from the tension value T ₁ in the liquid phase (T ₀ −
T ₁ ), and the second value is the difference between the tension value T ₁ when in the first liquid phase and the tension value T ₂ when in the second liquid phase ₍ Approximately 1/2 of T ₂ )
, and the same applies hereafter up to the n-th liquid phase. These tension values are known because they can be known in advance by lowering the displacer 2.

When the start button of the measurement start circuit 21 is pressed, a winding command is issued and the measurement wire winding/winding control circuit 7 is activated.
operates, drives the motor 9 via the motor drive circuit 8, and the displacer 2 starts to descend. At the same time, the counter 23 and shift data buffers 1, 2, 2 are reset by a reset signal from the measurement start circuit 21.
4 and 25 are cleared, and the first value of the measured value circuit 10 and the tension value at that time (tension detector 4
and is supplied via the tension value circuit 5. )
In the subtraction circuit 11 using (tension setting value)
is calculated, and this is entered into the hold circuit 12 and held as the first reference value.

When the displacer 2 continues to descend and reaches the first liquid phase, the tension value changes. The tension value at this time and the first reference value are determined by the comparison circuit 13.
If the tension value is smaller than the reference value, the comparison circuit 13 produces an output. On the other hand, when the tension value changes, the differentiator circuit 14 produces an output. Both of these outputs simultaneously enter a decision circuit 18 which is an AND gate and produces an output which is sent to a data storage memory 22. The data storage memory 22 receives a signal digitized by the liquid level A-D conversion circuit 17 from the liquid level value sent out by the measuring wire lifting mechanism 3 of the tension detection/measuring wire drive section. The liquid level value at that time is stored only when the output is applied.
This value is also sent to shift data buffer 124. On the other hand, the output from the differentiating circuit 14 is sent to a delay circuit 15 and delayed for a certain period of time. At this time, if the comparison circuit 13 is still producing an output, both outputs are simultaneously input to the judgment circuit 219, which is an AND gate, so that the judgment circuit 219 produces an output. This output increments the counter 23 by one and uses it as a value for interface discrimination (this value is also sent to the shift data buffer 124), and is used as a command for updating the reference value of the hold circuit 12.
Further, the judgment circuit 219 outputs a shift clock and sends the counter value and liquid level value of the shift data buffer 124 to the display meter 27 of the display/transmission unit to distinguish between interfaces and display them as liquid level values, and at the same time outputs the second shift data. Shift to buffer 225. Also,
When it is desired to view the value of the display meter 27 in the control room 29, it is transmitted to the receiver in the control room 29 via the remote transmission circuit 28.

On the other hand, the displacer 2 continues to descend and passes through the interface between the first liquid phase and the second liquid phase, but the interface detection in this case is also the same as described above. However, the shift data buffer 124 contains the newly measured data of the second liquid phase, and the shift data buffer 225 contains the previously measured data of the first liquid phase. When the data of the second liquid phase is displayed on the display meter 27 by the shift clock, the subtracter 26
The difference is that the liquid level value of the shift data buffer 1 is subtracted from the liquid level value of the shift data buffer 2, and this is displayed on the display meter 27 as the liquid phase width.

Here, we will explain how malfunctions do not occur even if the tension is temporarily lowered due to noise being picked up in the above-mentioned measurement process.

For example, suppose that the tension suddenly drops for some reason while the displacer 2 is moving down the first liquid phase. However, if the value does not fall below the reference value of the hold circuit 12, the comparator circuit 13 will not produce an output and even if the differentiator circuit 14 operates, the judgment circuit 18 will not produce an output, so there is no problem. On the other hand, when the tension value falls below the reference value of the hold circuit 12, outputs are simultaneously output from the comparison circuit 13 and the differentiation circuit 14, and the liquid level value at that time is stored in the data storage memory 22 by the output of the judgment circuit 118. Remember.
However, considering the judgment circuit 219, since noise occurs for an extremely short time, the comparison circuit 1
The output from 3 disappears in an even shorter time. Since the output from the differentiating circuit 14 is delayed by the delay circuit 15, the output from the differentiating circuit 14 is delayed by the determining circuit 21.
9, the output from the comparison circuit 13 has disappeared, and the judgment circuit 219 does not produce an output. In this way, even if noise below the reference value enters while the displacer 2 is passing through the first liquid phase, the liquid level value in the data storage memory 22 is simply updated, and the display meter 27
does not appear in

When the displacer 2 passes through the interface between the first liquid phase and the second liquid phase, the tension value falls below the reference value of the hold circuit 12 and remains at this value.
Therefore, the comparator circuit 13 continues to output. At the same time, the differentiating circuit 14 produces an output, so the determination circuit 118 produces an output, and the liquid level value at that time is updated in the data storage memory 22.
On the other hand, in the judgment circuit 219, even if the output of the differentiating circuit 14 is delayed, the output from the comparison circuit 13 continues, so that the two outputs always match, and an output can be obtained from the judgment circuit 219. This output operates the counter 23, outputs the shift clock, and transfers the liquid level value of the shift data buffer 124 connected to the data storage memory 22 to the display meter 27, and the interface between the first liquid phase and the second liquid phase is transferred to the display meter 27. The liquid level value is displayed on the display meter 27. In this way, normal operation is performed without causing any malfunction.

While repeating the same process, the displacer 2 continues to descend and finally reaches the bottom of the tank.
When the displacer 2 reaches the bottom of the tank, the tension becomes zero, and the tension zero value detection circuit 6 operates to issue a winding command, and the measurement wire is passed through the winding up/down control circuit 7 and the motor drive circuit 8 to the motor 9.
is driven to start winding up the displacer 2. The measuring wire lifting mechanism 3 is equipped with an upper limit stopping mechanism, and automatically stops when the displacer 2 comes near the top of the tank. At the same time, the command is sent to the interval timer 2 via the upper limit stop circuit 16.
Sent to 0. After receiving this command, the interval timer 20 sends a measurement start command to the measurement start circuit 21 after a certain period of time (for example, one hour if the measurement cycle is once per hour) has elapsed. Upon receiving this command, the measurement start circuit 21 issues a reset signal to the counter 23, shift data buffer 1,
2, 24, and 25 are cleared, and winding down of the displacer 2 is started. This is the same operation as the first one. Therefore, if the start button is pressed only the first time, the measurement will be automatically repeated at a predetermined period from the next time onwards.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and can be modified and changed in various ways within the scope of the claims. For example, instead of automatically repeating the measurement at regular intervals, it may be performed at arbitrary appropriate intervals.
Further, the determining means does not necessarily have to be an AND gate. Further, if the tension value is converted into digital data by analog-to-digital conversion, the entire automatic measurement section can be replaced with a microprocessor.

〔Effect of the invention〕

(b) In order to establish the interface position of multiple liquids with different specific gravities, it is necessary to install multiple conventional level gauges or use a special level gauge with multiple balancers and indicators. However, according to the present invention, only one device is required, which is advantageous in terms of cost.

(b) In the conventional method, the displacer is constantly submerged in liquid for equilibrium, so foreign matter such as sludge and carbon adheres and accumulates on the surface of the displacer, shifting the equilibrium point and causing errors. However, in the present invention, the displacer is constantly moving during measurement, and is rolled up except when it enters the liquid for measurement, so that foreign matter does not adhere or accumulate and the tension is reduced. drift will not occur.

(c) The present invention is a dynamic measurement method in which the resistance value is added to the detection when the displacer reaches the liquid interface, so even the interface between two liquids with a small difference in specific gravity can be reliably detected. be able to. (Since the boundary surface generally forms a layer in an emulsion state, a special resistance is exerted.) (d) Since the present invention has two determination means, the probability of malfunction occurring is extremely small. Even if a malfunction occurs, it can be canceled out by using a repeat measurement method.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the features of the present invention, Fig. 3 is a characteristic diagram of experimental results showing the principle of the invention, Fig. 4 is a liquid stationary on the liquid level. FIG. 3 is an explanatory diagram showing the force relationship applied to the displacer. 2... Displacer, 3, 7, 8, 9... Measuring wire elevating means, 4, 5... Tension detection means, 13... Comparing means, 14... Differentiating means, 15
. . . delay means, 18 . . . means for determining whether the output of the comparing means and the output of the differentiating means match, 19 . . . means for determining whether the output of the comparing means and the output of the delay means match.

Claims (1)

[Scope of Claims] 1. A displacer with a specific gravity greater than that of the lowest liquid, and a measuring thread lifting means for lowering the displacer so as to pass through an interface between a plurality of liquids with different specific gravity. a means for detecting the tension of the measuring thread; a means for comparing the tension value with a predetermined reference value; a means for differentiating the tension value; and a means for delaying the output of the differentiating means for a certain period of time; a first determining means for determining whether the output of the comparing means and the output of the differentiating means match; and a second determining means for determining whether the output of the comparing means and the output of the delaying means match; When the first and second determining means simultaneously determine that they match, it is determined that the displacer is passing through an interface between liquids having different specific gravities, and the liquid interface is detected. Detection device.