JPH07198449A - Liquid level measuring instrument - Google Patents

Abstract

PURPOSE:To provide an electrode rod type level measuring instrument with a high resolution for a variety of liquids. CONSTITUTION:When the level of a liquid is raised or lowered and it is detected that the liquid surface level reaches a reference level by a reference level detection means, the potential difference between electrodes at that time is obtained. Then, based on the potential difference and liquid surface, an electrical conduction coefficient is calculated where there is no error between the actually measured value of the liquid surface level by an electrical conduction coefficient calculation part 20 and a theoretical value calculated by a liquid surface level calculation means. Then, the internal resistance of a measuring circuit is modified according to a target liquid quality by an internal resistance adjustment part based on the electrical conduction coefficient and the liquid surface level is calculated based on the internal resistance which is modified by the internal resistance adjustment part, thus accurately measuring the liquid surface level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level measuring device for inserting a plurality of electrodes into a liquid, applying a voltage between the electrodes, and calculating the liquid level from the potential difference between the electrodes at that time. It is about.

[0002]

2. Description of the Related Art As a conventional liquid level detecting device, there is one shown in FIG. 14, for example. That is, three first to third electrode rods 2a, 2 having different lengths are provided in the tank 1.
Place b and 2c. Then, a sin type AC voltage is applied between the longest first electrode rod (which becomes a reference potential) 2a and the second electrode rod 2b and between the first electrode rod 2a and the third electrode rod 2c. Is being applied. Then, in this state, the liquid 3 is flown into the tank 1, and the liquid surface 3a of the liquid 3 as illustrated is between the tip of the second electrode rod 2b and the third electrode rod 2c (levels LL to LU). ), The first electrode rod 2a and the second electrode rod 2b are in a conductive state via the liquid 3, but the first electrode rod 2a and the third electrode rod 2c are connected to each other. It remains non-conducting.

Further, when the liquid 3 further flows into the tank 1 from the state shown in the figure and the liquid level 3a thereof becomes equal to or higher than the level LU, the second electrode rod 2b and the third electrode rod 2c also become conductive. On the other hand, when the liquid 3 flows out of the tank 1 and the liquid level 3a becomes lower than the level LL from the state shown in the figure, the first and second electrode rods 2a and 2b are also non-conductive.

Since the voltage value between the electrode rods greatly changes in accordance with the change in the conducting / non-conducting state, such a change is detected by the detecting device (comparator or the like) 4 to turn on / off the liquid. Position information (lower than LL, LL and L
During U, three types (higher than LU) are output.

[0005]

However, the above-mentioned conventional apparatus has the following various problems. That is, in the configuration described above, since a rapid change in the voltage value between the electrode rods is detected by the comparator, it is possible to measure whether or not the liquid level (liquid level) of the liquid is at a predetermined position (lower end position of the electrode rod). It is possible, but continuous liquid level measurement is not possible.

By the way, when a plurality of electrode rods are both submerged in the liquid 3, the plurality of electrode rods become conductive through the liquid 3 as described above, but the electrode rods become longer as the submersion distance becomes longer. The potential difference between them is reduced. That is, since there is a predetermined correlation between the water immersion distance (liquid level) and the potential difference, the change in the potential difference due to the change in the liquid level is investigated in advance, and the correlation is expressed in a logical formula to determine the actual liquid level At the time of measurement, the liquid level can be calculated by detecting the potential difference between the electrodes, substituting it into the above logical expression, and performing a predetermined calculation process.

However, since the state of such a change in the potential difference changes depending on the electric conductivity of the liquid, it can be applied only to the liquid having the same electric conductivity as the liquid used when the logical expression was obtained. Moreover, since the fluctuation amount of the potential difference varies depending on the temperature, the error of the measuring instrument, the influence of the installation environment, etc., the logical value and the actually measured value often do not match.

Even if the logical value and the actually measured value are substantially the same, the variation in the potential difference due to the variation in the liquid level (distance of the electrode rod) is not constant, and the liquid level is As it increases, the rate of change in the potential difference decreases, and accurate liquid level calculation cannot be performed, resulting in poor accuracy. That is, it becomes difficult to measure at a place where the liquid level is high.

The present invention has been made in view of the above background, and an object of the present invention is to accurately measure the liquid level without being affected by the electrical conductivity of the liquid or the installation environment. In addition, it is possible to provide a liquid level measuring device that can perform measurement with the highest possible accuracy (high resolution) within the measurement range, and that can accurately measure even at a high liquid level.

[0010]

In order to achieve the above-mentioned object, in a liquid level measuring apparatus according to the present invention, a predetermined voltage is applied between a plurality of electrodes that can be inserted into a liquid and the electrodes. Based on a liquid level measuring device including a voltage applying unit and a liquid level calculating unit that calculates a liquid level of the liquid based on a potential difference between the electrodes, the liquid level of the liquid is preset. And a reference level detection means for detecting that the reference level has been reached, and a potential difference between the electrodes when the current liquid level is the reference level, and the potential difference and the measured value of the liquid level from the reference level. Based on an electric conductivity coefficient calculating means for calculating an electric conductivity coefficient for eliminating an error from a logical value calculated by the liquid surface level calculating means, and an electric conductivity coefficient obtained by the electric conductivity coefficient calculating means. An internal resistance changing means for changing the internal resistance of the measuring circuit according to the target liquid quality, and the liquid level calculating means calculates the liquid level based on the internal resistance changed by the internal resistance changing means. I did it.

Further, the internal resistance changing means divides the measuring range of the internal resistance of the measuring circuit into several sections based on the electric conductivity coefficient obtained by the electric conductivity coefficient calculating means, and optimizes each section. The internal resistance may be obtained.

[0012]

With this configuration, when the liquid level of the liquid is raised and lowered and the reference level detecting means detects that the liquid level has reached the reference level, the potential difference between the electrodes at that time is obtained. Since the potential difference is known to be when the liquid level reaches the reference level, the measured value of the liquid level and the theoretical value calculated by the liquid level calculation means are based on both of them. Calculate the electrical conductivity coefficient so that there is no error with. In other words, the potential difference is input to the liquid surface level calculation means, and the coefficient that the liquid surface level obtained by performing the arithmetic processing using the electric conductivity coefficient becomes the reference level is obtained. Then, based on the electric conductivity coefficient thus obtained, the internal resistance changing means changes the internal resistance of the measuring circuit according to the target liquid quality, and the liquid level calculating means changes the internal resistance changing means. By calculating the liquid level based on the obtained internal resistance, there is no difference between the logical value (calculation result obtained by the liquid level calculating means) and the actually measured value, and accurate liquid level measurement is performed.

Further, the rate of change of the potential difference with respect to the change of the liquid level is extremely large at a place where the liquid level is low if the internal resistance (the resistance in the measuring circuit other than the resistance of the liquid located between the electrode rods) is too large. Large and highly accurate measurement is possible, but the amount of change immediately decreases and measurement is impossible (large error).
Becomes On the other hand, if the resistance value is too small, the amount of change in the potential difference is small as a whole and highly accurate liquid level measurement cannot be performed. Therefore, the resistance value determining means obtains a predetermined internal resistance value that is high in the entire rate of change of the potential difference between the electrodes within the measurement range of the liquid level in accordance with the quality of the liquid to be measured. . Then, the relationship between the potential difference between the electrodes and the liquid level at the determined internal resistance value is obtained, the measurement range of this liquid level is divided into several sections, and the maximum resolution for each section is realized. By obtaining the possible internal resistance and calculating the liquid level based on this internal resistance, it is possible to perform highly accurate measurement as a whole.

[0014]

Embodiments of the liquid level measuring apparatus according to the present invention will be described in detail below with reference to the accompanying drawings. First, the principle of liquid level measurement according to the present invention will be described. Now, as shown in FIG. 1, two relatively long first and second electrode rods 10 and 11 having the same shape are provided in a tank 12. It is arranged to be immersed in the stored liquid 13. The electrode rods 10 and 11 are connected to a power source 15 so that a constant voltage VO is applied.

A measuring unit 16 for measuring the potential difference V between the first and second electrode rods 10 and 11 is connected, and the output of the measuring unit 16 is the liquid level calculation unit 1.
Connected to 7. The liquid level calculation unit 17 calculates the level (liquid level) of the liquid surface 13a of the liquid 13 based on the applied potential difference V and displays the level on the display unit 18. Specifically, the calculation shown below is performed. It is supposed to process.

That is, the first and second electrode rods 10, 11
Is a, the distance between the first and second electrode rods 10 and 11 is d, the electrical conductivity of the liquid is σ, the internal resistance r of the measuring device, and the lower ends of the first and second electrode rods 10 and 11. Assuming that the distance from the liquid surface to the liquid surface is L, the resistance value R (L) created between the first and second electrode rods 10 and 11 is given by the following equation.

[0017]

[Equation 1] Therefore, the potential difference V between the electrode rods to be measured is given by the following formula.

[0018]

[Equation 2] Therefore, since d, a, σ, and VO are constants, by substituting the potential difference V measured by the measuring unit 16 into the above equation and solving for L, the liquid 13 of the first and second electrode rods 10 and 11 can be obtained. The water immersion distance L is known, and the tank 12
Since the distance from the bottom surface to the lower ends of the first and second electrode rods 10 and 11 is known, the liquid level can be calculated by adding the water immersion distance L to this distance. And
The liquid level calculator 17 performs the various calculations.

From the above equation, the relationship between the liquid level L and the potential difference V is hyperbolic as shown by the broken line in FIG. 2, and the voltage value V decreases as the liquid level L increases. There is. On the other hand, while actually changing the liquid level L (the value of the liquid level is measured by another means), the potential difference V between the first and second electrode rods 10 and 11 at that time is measured, and the relationship is graphed. Is represented by the two-dot chain line in the figure,
It can be seen that there is a difference between the theoretical value and the actually measured value, as in the conventional problems described above. Here, looking at the two characteristics, it can be seen that the shapes of the curves are close to each other, although there are certain differences.
Therefore, it is considered that there is an error in the value of the coefficient in the calculation formula (theoretical formula) that causes the difference between the two curves. Therefore, it is necessary to make a predetermined correction.

Looking at each coefficient, a, d and π are known. On the other hand, the electric conductivity σ easily changes depending on the temperature and the surrounding environment, and it is difficult to measure the electric conductivity σ of the liquid 13 every time the level is measured. Further, the internal resistance r also changes depending on how the voltage V between the electrode rods changes.

Therefore, in the present invention, the concept of electric conductivity σ ′ including the above-mentioned difference (error) caused by the condition of the ambient environment, the error in the circuit, etc. is introduced to the electric conductivity σ, and the theoretical formula Such an electric conductivity coefficient σ ′ is used instead of the electric conductivity σ in the inside, and the internal resistance r is changed depending on the liquid quality, focusing on the fact that the change state of the voltage V between the electrode rods changes depending on the internal resistance r, Furthermore, we decided to obtain a learning value close to the actual measurement value by dividing the measurement range into several sections and calculating the liquid level by changing the internal resistance for each section.

Therefore, in the embodiment of the present invention, as shown in FIG. 1, the output of the measuring section 16 is connected to the electric conduction coefficient calculating section 20 for calculating the coefficient σ '. Further, a third electrode rod 21, which is shorter than the first and second electrode rods 10 and 11, is formed so as to hang parallel to the both electrode rods 10 and 11. And
The distance from the lower end of the first electrode rod 10 to the lower end of the third electrode rod 21 is adjusted to be L1. A power supply 22 is connected between the first electrode rod 10 and the third electrode rod 21 to apply a voltage VO, and the first and third electrode rods 10 and 21 are connected to each other. Is connected to the measuring unit 23, and the potential difference Vt between the electrode rods 10 and 21 is Vt.
Is measured and the measurement result is sent to the comparator 24. The output of the comparator 24 (trigger signal)
Is connected to the electric conductivity coefficient calculation unit 20 described above, and gives a processing start signal.

That is, the voltage V measured by the measuring unit 23
t is the first and third electrode rods 1 when the liquid level is lower than L1.
Since 0 and 21 are open, Vt = VO. When the liquid level rises to L1, both electrode rods 1
Since 0 and 21 are conducted to form a current circuit, Vt between both electrode rods 10 and 21 is rapidly reduced (see FIG. 3).

When the potential difference at the time of L1 is Vs, by setting the input voltage to the other input terminal of the comparator 24 to Vs, the output of the comparator 24 has a liquid level of L1. And the trigger signal changes.

Therefore, it is known that the liquid level when the trigger signal changes is L1, and at the same time,
The potential difference V1 between the second electrode rods 10 and 11 is measured by the measuring unit 16
Can be detected through. Therefore, by substituting the liquid level L1 and the potential difference V1 into L and V of the voltage theoretical formula described above and solving for σ, the solution at that time is the electrical conductivity coefficient σ ′. That is, in this example, the first electrode rod 10, the third electrode rod 21, the power supply 22, the measuring unit 23, and the comparator 24 constitute the reference level detecting means.

Therefore, in the electric conductivity coefficient calculating section 20, if the output of the comparator 24 changes, the predetermined arithmetic processing is performed based on the potential difference V given from the measuring section 16. The electric conductivity coefficient σ ′ thus obtained is calculated by using the actually measured potential difference V1 and the liquid level L1 performed for the current state of the liquid 13 for which the liquid level is to be measured. It becomes a coefficient that reflects the above. The function of the electric conductivity coefficient calculating unit 20 is as shown in the flowchart of FIG.
The relationship between the liquid level L and the potential difference V obtained by the liquid level calculation unit 17 based on the set electric conductivity coefficient σ ′ is shown in FIG.
As indicated by the solid line, it is close to the measured value.

Further, in the embodiment of the present invention, the output of the electric conductivity coefficient calculating section 20 is also sent to the resistance value determining section 25 of the next stage. That is, as shown in FIG. 5, when the internal resistance r is changed, the liquid level L and the first and second electrode rods 1
The correlation of the potential V (L) between 0 and 11 also changes. This is also clear from the above voltage theoretical formula, and r is 0
When set to, the graph approaches a horizontal straight line, while when r is increased, the graph shows that when the liquid level is slightly higher than 0, the voltage sharply decreases to 0, and thereafter does not change so much.

That is, if r is made too small, the amount of change in voltage with respect to the amount of displacement of the liquid level is small overall (resolution).
The detection accuracy is low overall. On the other hand, if r is set too high, the resolution will be extremely high in the range where the liquid level is relatively small, but it will decrease immediately thereafter and accurate liquid level measurement will not be possible.
That is, if the internal resistance is too large or, conversely, too small, the range (measurable range) where the predetermined resolution can be obtained becomes short.

Therefore, the internal resistance r capable of realizing the maximum resolution is obtained by the resistance value determining unit 25, and the relationship between the electrode rod voltage V (L) and the liquid level L at this internal resistance r is obtained. It was decided to divide the measurement range for the position L into several sections and calculate the liquid level by changing the internal resistance for each section to obtain a learning value close to the actual measurement value. The specific processing (principle) is as follows.

First, the curve having the maximum resolution referred to in the embodiment of the present invention means that the minimum value of the rate of change of the curve (the amount of change in the voltage with respect to the change in the liquid level) in the group of curves shown in FIG. It is the maximum curve in the measurement range.

Then, as described above, the potential difference V with respect to the liquid level L is expressed by the following equation, and the internal resistance r and the displacement L
Can be expressed as a function with a variable.

[0032]

[Equation 3] Therefore, the amount of change in voltage with respect to the change in displacement is obtained by partially differentiating the above expression with respect to L, and is represented by the following expression.

[0033]

[Equation 4] As is clear from the above equation, the maximum liquid level in the measurement range is LM
Then, the displacement amount becomes minimum when L = LM, and the resolution h (r) at that time is expressed by the following equation.

[0034]

[Equation 5] The resolution h specified by the above equation is a function of the variable r, and when this equation is partially differentiated by r,

[0035]

[Equation 6] Becomes Therefore, when r1 = α / (β · LM), h (r
1) = V0 / (4 · LM), which is the maximum value. Therefore, the optimum internal resistance r1 for obtaining the maximum resolution h is as follows.

[0036]

[Equation 7] Next, the voltage V (L) between the electrode rods when the internal resistance is r1.
And the liquid level L are obtained, and the liquid level L is equally divided as shown in FIG. Here, sections LM (0) to LM (1)
Resistance rk (1) that can realize the maximum resolution for
Is

[0037]

[Equation 8] Becomes Hereinafter, similarly, the resistances for rk (2) to rk (n) are obtained. Next, the internal resistance r1 causes the voltage V
(L) is measured, and which section is LM (0) to LM
It is determined whether or not it is in (1). If the section i (i = 1 to n) in which the voltage V (L) is included is determined, the resistance is changed to rk.
Set to (i). The internal resistance rk (i) causes the voltage V
(L) is measured and the liquid level L is calculated.

As described above, the sections LM (0) to L
Since the measurement is performed using the optimum resistance value for each M (1), the measurement accuracy can be improved and the calculated liquid level L
Since the parameters σ ′ and rk (n) have already been obtained and corrected, the liquid level L is calculated based on the corrected parameters. Therefore, the liquid level displayed on the display unit 18 is actually measured. It will represent the value exactly.

Here, an algorithm for measuring the liquid level using the liquid level measuring apparatus of the present invention will be described. First, the theoretical formulas are summarized as follows.

[0040]

[Equation 9] [Calculation of electrical conductivity coefficient σ '] Electrode rod 1 at liquid level L1
Since the voltage between 0 and 11 is V1, substituting into the theoretical formula,

[0041]

[Equation 10] Here, since only σ is the unknown,
Σ can be calculated from the formula of [Equation 9]. Let this value be σ ′. σ'is not the electrical conductivity of the liquid. Measured voltage V1
Since it is obtained by using the liquid level LI and LI, σ'is a coefficient that reflects the state of the surrounding environment, the error on the circuit, and the like. This is called the electric conductivity coefficient.

[Calculation of Internal Resistance] After obtaining the electric conductivity coefficient σ ′,

[0043]

[Equation 11] Is calculated and the internal resistance value is adjusted with an electronic volume or the like to be r1. Think the same way

[0044]

[Equation 12] To calculate.

[Calculation of Liquid Level] The liquid level L when the voltage between the electrode rods 10 and 11 is V is as follows. The value of i is determined depending on which section the voltage V is in.

[0046]

[Equation 13] Since the unknown number is only the liquid level L, the liquid level L can be calculated from the formula of [Equation 13]. By adjusting the internal resistance, the characteristics of the actually measured value and the learned value shown in FIG. 2 fluctuate as much as a curve for obtaining an optimum high resolution, but both characteristics fluctuate in the same manner. The result of liquid level calculation based on the learned value and the measured value remain substantially in agreement.

Next, the operation of the above-described embodiment will be described with reference to FIG.
This will be described with reference to the flowchart shown in. That is, first, when the apparatus is turned on to measure the liquid level, various parameters are set (step S10).
1, 102). The liquid level of the liquid 13 at that time is the third
Is higher than the lower end position L1 of the electrode rod 21 (the third electrode rod 21 is submerged in the liquid), the liquid 13 is discharged to lower the liquid level, and conversely the liquid level of the liquid 13 is decreased. When it is lower than L1, the liquid 13 is caused to flow in to raise the liquid level.

Next, the level of the trigger signal is fetched (step S103). And the trigger signal changes,
That is, it is determined whether or not the liquid level becomes L1 (step S104), and if the trigger signal changes in state (L = L1), the internal resistance is set to an arbitrary value r (step S10).
5).

Next, the electric potential difference V (L) between the first and second electrode rods 10 and 11 is taken in (step S106), and the electrical conductivity of the liquid 13 to be measured is measured using the electrical conductivity coefficient calculating section 20. Degree and surrounding environment and measuring device (circuit)
The electric conductivity coefficient σ ′ determined based on the error of (1) is calculated (step S107).

Next, the internal resistance r1 of the entire measurement range is determined based on the obtained electric conductivity coefficient σ '(step S
108). Then, the relationship between the electrode rod voltage V (L) and the liquid level L at this internal resistance r1 is obtained, and this liquid level L is equally divided as shown in FIG. Here, the section LM (0)
˜LM (1) is calculated according to the flowchart shown in FIG. 9 for the internal resistances rk (1) to rk (n) that can realize the maximum resolution (step S).
109).

Next, the voltage V (L) between the first and second electrode rods 10 and 11 is fetched (step S110), and the voltage V
The range p in which (L) exists is obtained according to the flowchart shown in FIG. 10 (step S111), and the internal resistance is set to r.
It is set to k (p) (step S112).

Next, the voltage V (L) between the first and second electrode rods 10 and 11 is taken in (step S113), the theoretical formula is calculated by the liquid level calculation unit 17, and the flow chart shown in FIG. 11 is obtained. Therefore, the liquid level L is calculated (step S11
4) and outputs it to the display unit 18 (step S11).
5) and returns to step S102. At this time, since the calculated liquid level L has been corrected by already obtaining the respective parameters σ ′ and rk (n), the liquid level is calculated based on the corrected parameters, and therefore the display unit 18 displays the liquid level. The displayed liquid level will accurately represent the measured value.

In step S104, it is determined whether or not the liquid level becomes L1, and if the state of the trigger signal does not change,
Step S110, Step S111, Step S11
2, step S113, step S114, step S
After 115, the process returns to step 102.

In this example, each time the liquid level fluctuates and passes through L1, the electrical conductivity coefficient σ'and the internal resistance rk (n) are calculated.
Since the calculation (correction) is performed, the calculation formula for obtaining the liquid level L is always the optimum numerical value according to various conditions at that time (learning / correction is continuously performed), and the measured value is not displaced accurately. In addition, it is possible to measure the liquid level over a wide range while maintaining high resolution.

FIG. 12 shows a specific circuit formation for implementing the level measuring apparatus described above. As shown in the figure, an internal resistance adjusting unit 30 is arranged between the power supply 15 and the second electrode rod 11. The internal resistance adjusting unit 30 corresponds to the variable resistance r shown in FIG. Also, the first
The potential difference V between the second electrode rods 10 and 11 as well as the first and third
The potential difference Vt between the electrode rods 10 and 21 is measured by a measuring unit (not shown), is sent to the A / D conversion unit 31, is converted into a digital signal there, and is then sent to the microcomputer 32. This microcomputer 32 is equivalent to the liquid level calculation unit 1 described above.
7, an electric conduction coefficient calculation unit 20, a comparator 24, a resistance value determination unit 25, etc. are configured, and a predetermined control signal is supplied to the internal resistance adjustment unit 30 so as to obtain a resistance value for obtaining the determined high resolution. Is sent.

Further, as shown in FIG. 13, the internal resistance adjusting section 30 is used for the known reference resistance r0 used for calculating the electric conductivity coefficient σ'and for the actual level measurement. The variable resistor r1 or rk (i) is connected in parallel between both terminals 1 and 2, and the switch is switched by a control signal from the microcomputer 32 so that either one of the resistors is connected to the circuit. The variable resistor r1 is, for example, an electronic volume.

Further, the reference resistance r0 is the internal resistance adjusting section 3
When connected to both terminals of 0, the variable resistor r1 constitutes a closed circuit in which a resistor r2 and a reference power source 35 (voltage Vs) are connected in series, and a voltage drop occurs between the terminals of the resistors r1 and r2. The voltage Vr is sent to the microcomputer 32 via the A / D converter 31.

To explain the operation of this embodiment, first, the reference resistance r0 is connected to the terminals 1 and 2 of the internal resistance adjusting section 30 to change the liquid level L. And the potential difference Vt
When a trigger is applied across a certain threshold value, the potential difference Vm at that time is taken in and the electric conduction coefficient σ ′ is calculated.

When a trigger is applied, a resistance value r1 suitable for the calculated electric conductivity coefficient σ'is calculated. Then, the measurement range is divided into sections, VL (i) and rk (i), respectively.
To calculate. To adjust the resistance value r1, the reference power source 35
(Voltage Vs), resistor r2, variable resistor r1 form a closed circuit, and while checking the value of the voltage Vr between terminals, the variable resistor r1 is adjusted to the optimum value.

When the adjustment of the variable resistance r1 is completed, the resistance r1 is connected to the terminals 1 and 2, and in this state, the potential difference Vm.
To measure. Then, the section in which the potential difference Vm falls is calculated, and the resistance value is adjusted by the same method as the resistance r1 so that the optimum internal resistance rk (i) in the section is obtained. When the adjustment of the internal resistance rk (i) is completed, the terminals 1 and 2 are connected to the resistance rk (i), and the potential difference Vm is measured in this state to calculate the liquid level information L.

In each of the above examples, a DC voltage was used as the power source, but it is needless to say that an AC power source may be used. After doing various processing (level measurement,
Correction processing, etc.).

Furthermore, in the above-described embodiment, the first electrode rod 10 for actually measuring the liquid level is used (also used) as a part of the reference level detecting means, but it is formed independently. Of course, you can do that.

[0063]

As described above, in the liquid level measuring apparatus according to the present invention, when the liquid level of the liquid is raised and lowered and the reference level detecting means detects that the liquid level becomes the reference level, Determine the potential difference between the electrodes. Since the potential difference is known to be when the liquid level reaches the reference level, the measured value of the liquid level and the theoretical value calculated by the liquid level calculation means are based on both of them. Calculate the electrical conductivity coefficient so that there is no error with.
In other words, the potential difference is input to the liquid surface level calculation means, and the coefficient that the liquid surface level obtained by performing the arithmetic processing using the electric conductivity coefficient becomes the reference level is obtained. Then, based on the electric conductivity coefficient thus obtained, the internal resistance changing means changes the internal resistance of the measuring circuit according to the target liquid quality, and the liquid level calculating means changes the internal resistance changing means. By calculating the liquid level based on the internal resistance
Logical value (calculation result obtained by liquid level calculation means)
There is no difference between the measured value and the measured value, and accurate liquid level measurement is performed.

Therefore, an electrode rod type level measuring instrument can be realized for various liquids, and even if the liquid quality changes, learning corresponding to it can be obtained. It is possible to realize the above level measuring device, and further, it is possible to obtain the effect that an electrode rod type level measuring device having a high resolution for various liquids can be realized.

Further, the rate of change of the potential difference with respect to the change of the liquid surface level is extremely large at a place where the liquid surface level is low if the internal resistance (the resistance component in the measuring circuit other than the resistance of the liquid located between the electrode rods) is too large. Large and highly accurate measurement is possible, but the amount of change immediately decreases and measurement is impossible (large error).
Becomes On the other hand, if the resistance value is too small, the amount of change in the potential difference is small as a whole and highly accurate liquid level measurement cannot be performed. Therefore, the resistance value determining means obtains a predetermined internal resistance value that is high in the entire rate of change of the potential difference between the electrodes within the measurement range of the liquid level in accordance with the quality of the liquid to be measured. . Then, the relationship between the potential difference between the electrodes and the liquid level at the determined internal resistance value is obtained, the measurement range of this liquid level is divided into several sections, and the maximum resolution for each section is realized. By obtaining the possible internal resistance and calculating the liquid level based on this internal resistance, it is possible to perform highly accurate measurement as a whole.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a liquid level measuring device according to the present invention.

FIG. 2 is a graph showing the relationship between the liquid level (liquid level) and the potential difference between the first and second electrode rods.

FIG. 3 is a graph showing the relationship between the liquid level (liquid level) and the potential difference between the first and third electrode rods.

FIG. 4 is a flowchart showing a part of the function of the electric conductivity coefficient calculation unit.

FIG. 5 is a graph showing the relationship between the liquid level (liquid level) and the potential difference between the first and second electrode rods when the internal resistance is changed.

FIG. 6 is a graph showing a relationship between the liquid level L when the internal resistance is r1 and the potential difference between the first and second electrode rods with respect to the liquid level L.

FIG. 7 is a flowchart showing a part of the function of an internal resistance determination unit.

FIG. 8 is a flowchart illustrating the operation of this embodiment.

FIG. 9 is a calculation flowchart of LM (i), VL (i), and rk (i).

FIG. 10 is a flowchart for obtaining the existence range of the voltage V (L).

FIG. 11 is a liquid level calculation flowchart.

FIG. 12 is a diagram showing an example of a specific circuit configuration of the liquid level measuring device according to the present invention.

FIG. 13 is a diagram showing an internal configuration of an internal resistance adjusting unit.

FIG. 14 is a schematic configuration diagram showing a conventional liquid level measuring device.

[Explanation of symbols]

 10 First Electrode Rod 11 Second Electrode Rod 13 Liquid 15 Power Supply 16 Measuring Unit 17 Liquid Level Calculating Unit 20 Electric Conduction Coefficient Calculating Unit (Electric Conduction Coefficient Calculating Means) 21 Third Electrode Rod (Reference Level Detecting Means) 22 Power supply (reference level detection means) 23 Measuring section (reference level detection means) 24 Comparator (reference level detection means) 25 Resistance value determination section (resistance value determination means) 31 Internal resistance adjustment section r, r1 Variable resistance

Claims (2)

[Claims] 1. A plurality of electrodes that can be inserted into a liquid, a voltage applying unit that applies a predetermined voltage between the electrodes, and a liquid surface that calculates a liquid surface level of the liquid based on a potential difference between the electrodes. A liquid level measuring device comprising level calculation means, wherein a reference level detection means for detecting that the liquid level of the liquid has reached a preset reference level, and a current liquid level is the reference level The electric conduction for receiving an electric potential difference between the electrodes and calculating an electric conduction coefficient for eliminating an error between the measured value of the liquid level and the theoretical value calculated by the liquid level calculating means from the potential difference and the reference level. And a coefficient calculating unit, and an internal resistance changing unit that changes the internal resistance of the measuring circuit according to the target liquid quality based on the electric conductivity obtained by the electric conductivity calculating unit. The liquid level measuring device is characterized in that the output means calculates the liquid level based on the internal resistance changed by the internal resistance changing means. 2. The internal resistance changing means divides the measuring range of the internal resistance of the measuring circuit into several sections on the basis of the electric conductivity coefficient obtained by the electric conductivity coefficient calculating means, and makes an optimum value for each section. The liquid level measuring device according to claim 1, wherein the internal resistance is obtained.