JPH07198450A - Liquid level measuring instrument - Google Patents

Abstract

PURPOSE:To measure liquid level without effects of the electrical conductivity of liquid, installation environment, etc., by dipping an electrode in a liquid to be measured, obtaining an electrical conductivity coefficient based on a voltage measured by an electrode for measuring conductivity, and then calculating liquid level based on the voltage measured by the electrode for measuring level and electrical conduction coefficient. CONSTITUTION:Electrode parts A for measuring level consisting of electrodes 10 and 11 with the same diameter and in the same shape are retained in parallel by a retention part 14 and electrode parts B for measuring conductivity consisting of electrodes 16 and 17 with the same diameter and in the same shape are retained in parallel and are dipped into a liquid 13. A power supply 20 is turned on, a voltage is applied to the electrodes 16 and 17, and an electrical conduction coefficient sigma determined by the electrical conductivity of the liquid 13, surrounding environment, circuit error, etc., is calculated 22. Then, a voltage is applied to the electrodes 10 and 11 and a liquid level L is calculated 21 and output 23 according to a measured potential V (L) between electrodes and an obtained electrical conduction coefficient sigma'. Since the coefficient sigma' is corrected every time, the liquid level L accurately displays an actually measured value.

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, for example, one shown in FIG. That is, tank 1
First to third electrode rods 2a, 2 having different lengths
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 object, a liquid level measuring device according to the present invention includes a level measuring electrode unit for measuring a voltage for obtaining a liquid level of a liquid, and a measuring object. Separate the electrical conductivity measurement electrode part for measuring the voltage for obtaining the electrical conductivity coefficient σ'determined based on the electrical conductivity and surrounding environment of the liquid and the error of the measuring device (circuit), A conductivity calculation unit that obtains an electric conductivity coefficient σ ′ based on the voltage measured by the conductivity measurement electrode unit, a voltage measured by the level measurement electrode unit, and an electric conductivity coefficient obtained by the conductivity calculation unit. and a level calculation unit for obtaining the liquid level based on σ ′.

In order to achieve the above-mentioned object, the liquid level measuring device according to the present invention is the liquid level measuring device according to claim 1, wherein the level measuring electrode parts are of the same shape. It is characterized in that it is composed of two long first and second electrode rods, and that the conductivity measuring electrode portion is constituted by fixing the third and fourth electrode rods to a holding member.

[0012]

With this structure, when an electric signal is externally applied to the electrode, the electric conductivity coefficient σ'and the liquid level can be obtained from different electrodes from the electric signal appearing at the electrode due to the characteristics of the liquid.

For this reason, the calculation of the electric conductivity coefficient σ ′ necessary for the calculation and calculation of the liquid level can be always executed, and therefore the liquid level can also be constantly measured. Further, it becomes possible to omit the setting items necessary for liquid level calculation. Further, the liquid level calculation is not affected by the sudden change in the measured electric conductivity coefficient σ ′ of the liquid.

Therefore, the liquid level can be measured accurately without being affected by the electric conductivity of the liquid or the installation environment, and further, the measurement can be performed with the highest accuracy (high resolution) within the measurement range. , It is possible to measure accurately even in a place where the liquid level is high.

[0015]

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 the liquid level measurement according to the present invention will be described. Now, as shown in FIG. 2, two relatively long first and second electrode rods 10 and 11 having the same shape are provided in the 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 (not shown) so that a constant voltage VO is applied.

A level calculator (not shown) for measuring the potential difference V between the first and second electrode rods 10, 11 is connected to the first and second electrode rods 10, 11. This level calculation unit calculates the level (liquid level) of the liquid surface 13a of the liquid 13 based on the given potential difference V and displays it on the output. Specifically, the level calculation unit performs the following calculation processing. It has become.

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 13 is σ, the internal resistance of the measuring device is r, and the first and second electrode rods 10 and 11 are From the bottom of the liquid surface 13
If the distance to a is L, the first and second electrode rods 10,
The resistance value R (L) created between 11 is given by the following equation.

[0018]

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

[0019]

[Equation 2] Further, the expression of [Formula 2] for the liquid level L is the following expression.

[0020]

[Equation 3] Therefore, since d, a, σ, and VO are constants, the first and second electrode rods 10 and 11 can be obtained by substituting the potential difference V measured by the level calculator in the above equation and solving for L.
The water immersion distance L to the liquid 13 of the
Since the distance from the bottom surface of 2 to the lower ends of the first and second electrode rods 10 and 11 is known, the water immersion distance L
Is added to calculate the liquid level. Then, the various types of calculations are performed by the level calculator.

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. 3, 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, π, r
Is 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.

Therefore, in the present invention, the concept of the electrical conductivity coefficient σ'including the above-mentioned difference (error) caused by the condition of the surrounding environment, the error in the circuit, etc. is introduced into the electrical conductivity σ, and the theoretical formula Instead of the electric conductivity σ, the electric conductivity coefficient σ ′ was used to obtain a learning value close to the actual measurement value.

The equation for obtaining the electric conductivity coefficient σ'is
It becomes like the following formula.

[0025]

[Equation 4] In this case, d is the interelectrode distance, a is the electrode radius, r is the circuit resistance, l is the liquid level, V0 is the applied potential, and V1 is the interelectrode potential at the liquid level 1.

In the equation shown in [Equation 4], the interelectrode distance d, the electrode radius a, the circuit resistance r, and the input potential V0 are known, and the liquid level 1 and the interelectrode potential V1 at this liquid level 1 are known. As the means, the above-mentioned conductivity measuring electrode section B was adopted. The third and fourth electrode rods 16 and 17 of the conductivity measuring electrode unit B have a radius a and a length dimension l,
The distance between the electrode rods is d, and the third and fourth electrode rods 16, 1
The length dimension 1 of 7 is equal to the liquid level 1. The inter-electrode potential V1 at the liquid level 1 is derived by understanding the liquid level 1.

Therefore, the electric conductivity coefficient σ'can be obtained by the equation shown in [Equation 4], and the liquid level L can be obtained by the equation shown in [Equation 3].

Therefore, in the embodiment of the present invention, the liquid level measuring device includes a level measuring electrode portion A as shown in FIG.
It is composed of a conductivity measuring electrode section B and a level meter body C.

The level measuring electrode section A is provided in a liquid 13 stored in a tank 12 in which two relatively long first and second electrode rods 10 and 11 having the same shape are held by a holder 14. It is arranged to be immersed. The first and second electrode rods 10 and 11 are metal rods having the same radius a and the same length dimension, and are held by the retainer 14 in parallel with each other, and the distance between the electrode rods is d. Is.

Further, the conductivity measuring electrode portion B has a holding member 15
The third and fourth electrode rods 16 and 17 held by the third and fourth electrode rods 16 and 17 are metal rods having the same radius a and the same length l as the holding member. It is held so as to be parallel to 15, and the distance between the electrode rods is d.
Is. That is, the radius a of each of the third and fourth electrode rods 16 and 17 and the distance d between the electrode rods are equal to the radius a of each of the first and second electrode rods 10 and 11 and the distance d between the electrode rods. It is made equal. The electric wires 18 and 19 connected to the third and fourth electrode rods 16 and 17 are held by the holder 14 at the intermediate portion thereof, and the conductivity measuring electrode portion B is the liquid 13 stored in the tank 12. It is dipped in.

Further, the level meter main body C comprises a power source section 20, a level calculation section 21, a conductivity calculation section 22 and an output section 23. Then, the first and second of the level measuring electrode portion A
The electrode rods 10 and 11 are connected to the input side of the level calculation unit 21, and the electric wires 18 and 19 connected to the third and fourth electrode rods 16 and 17 of the conductivity measuring electrode unit B are It is connected to the input side of the conductivity calculation unit 22. The power supply unit 20 supplies power to the first to fourth electrode rods 10, 11, 16, and 17, and is connected to the power supply input side of each of the level calculation unit 21 and the conductivity calculation unit 22. Further, the output side of the conductivity calculation section 22 is connected to the input side of the level calculation section 21, and the output side of the level calculation section 21 is connected to the input side of the output section 23.

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, the power of the apparatus is turned on to measure the liquid level (step S100). Next, a voltage is applied to the third and fourth electrode rods 16 and 17 via the conductivity measuring electrode portion B (step S101).

Next, the inter-electrode potentials of the third and fourth electrode rods 16 and 17 are measured (step S102), and based on the measured values, the conductivity calculator 22 executes the equation [Equation 4]. Then, the electrical conductivity coefficient σ ′ determined based on the electrical conductivity of the liquid 13 to be measured, the surrounding environment, the error of the measuring device (circuit), etc. is calculated (step S103).

Next, the first and second level measuring electrode portions A are
A voltage is applied to the electrode rods 10 and 11 of the
4) Next, in the level calculator 21, the first and second electrode rods 1
The first and second electrode rods 1 by measuring the inter-electrode potential of 0 and 11
The voltage V (L) between 0 and 11 is fetched (step S10
5), in the level calculator 21, the conductivity calculator 2
Based on the electric conductivity coefficient σ'obtained in step 2, the equation [Equation 3] is executed to calculate the liquid level L (step S106), which is output to the output unit 23 (step S107), and the process returns to step S101. . At this time, since the calculated liquid level L has already been obtained and corrected by the parameter σ ′, the liquid level L is calculated based on the corrected parameter σ ′, and is output to the output unit 23. The liquid level L accurately represents the actual measurement value.

Therefore, even if the liquid level L changes, the electric conductivity coefficient σ ′ is calculated (corrected), and therefore the liquid level L
The calculation formula for obtaining is always the optimum value according to the various conditions at that time (learning and correction are continuously performed), and the measured value does not deviate accurately and a wide range of liquid level can be measured while maintaining high resolution. It can be carried out.

In each of the above embodiments, a DC voltage is used as the power source, but it is needless to say that an AC power source may be used. In such a case, a rectifier circuit or the like is provided to convert to DC. After that, various processes (level measurement, correction process, etc.) are performed.

Further, in the above-mentioned embodiment, as shown in the flow chart of FIG. 4, the level signal is output from step S101 by applying the voltage to the conductivity measuring electrodes (the third and fourth electrode rods 16 and 17). Although the sequence from step S107 is performed, the operation from step S101 to step S103 and the operation from step S105 to step S107 may be simultaneously executed.

[0038]

As described above, the liquid level measuring device according to the present invention has a level measuring electrode section for measuring a voltage for obtaining the liquid level of a liquid, an electric conductivity of a liquid to be measured, and Separated from the conductivity measuring electrode part for measuring the voltage for obtaining the electric conductivity coefficient σ ′ determined based on the ambient environment and the error of the measuring device (circuit), etc., this conductivity measuring electrode part is used. A conductivity calculating unit for obtaining an electric conductivity coefficient σ ′ based on the measured voltage, a liquid based on the voltage measured by the level measuring electrode unit and the electric conductivity coefficient σ ′ obtained by the conductivity calculating unit. Since a level calculator for determining the level is provided, when an electric signal is externally applied to the electrode, the electrical conductivity coefficient σ ′ and the liquid level can be obtained from different electrodes from the electric signal that appears at the electrode due to the characteristics of the liquid. You can ask.

For this reason, the calculation of the electric conductivity coefficient σ'necessary for the measurement calculation of the liquid level can be executed at all times, and therefore the measurement of the liquid level can also be executed at all times. Further, it becomes possible to omit the setting items necessary for liquid level calculation. Further, the liquid level calculation is not affected by the sudden change in the measured electric conductivity coefficient σ ′ of the liquid.

Therefore, the liquid level can be accurately measured without being affected by the electric conductivity of the liquid or the installation environment, and further, the measurement can be performed with the highest accuracy (high resolution) within the measurement range. , It is possible to measure accurately even in a place where the liquid level is high.

Further, the liquid level measuring device according to the present invention is the liquid level measuring device according to claim 1, wherein the level measuring electrode portions are two relatively long first and second electrodes having the same shape. Since the electrode portion for conductivity measurement is configured by fixing the third and fourth electrode rods to the holding member, the electrode portion for conductivity measurement is installed at the installation position of the electrode portion for level measurement. It can be installed without any restrictions.

[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 structural explanatory view of the principle of liquid level measurement according to the present invention.

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

FIG. 4 is a flowchart illustrating the operation of this embodiment.

FIG. 5 is a schematic configuration diagram showing a conventional liquid level measuring device.

[Explanation of symbols]

 10 1st electrode rod 11 2nd electrode rod 12 Tank 13 Liquid 16 3rd electrode rod 17 4th electrode rod 20 Power supply part 21 Level calculation part 22 Conductivity calculation part 23 Output part A Level measurement electrode part B Conductivity measurement electrode section C level meter body

Claims (2)

[Claims] 1. A level measuring electrode section for measuring a voltage for obtaining the liquid level of a liquid, and the electric conductivity of the liquid to be measured, the ambient environment, and an error of a measuring device (circuit). The conductivity measuring electrode for measuring the voltage for obtaining the electric conductivity coefficient σ ′ is separated from each other, and the conductivity for obtaining the electric conductivity coefficient σ ′ is obtained based on the voltage measured by the conductivity measuring electrode section. A liquid comprising: a calculation unit; and a level calculation unit that obtains a liquid level based on the voltage measured by the level measurement electrode unit and the electric conductivity coefficient σ ′ obtained by the conductivity calculation unit. Surface level measuring device. 2. The level measuring electrode portion is composed of two relatively long first and second electrode rods having the same shape, and the conductivity measuring electrode portion is constituted by the third and fourth electrode rods. The liquid level measuring device according to claim 1, wherein the liquid level measuring device is configured by being fixed to a holding member.