JPH06337721A - Liquid level measuring instrument - Google Patents

Abstract

PURPOSE:To improve the precision of liquid level measurement by calculating the height to the liquid surface of a solution from the proportional relation among the total pressure of the bottom surface of a tank which is measured by a static pressure sensor, the pressure difference between the upper and lower parts of the tank which is measured by a differential pressure sensor, and a predetermined distance. CONSTITUTION:This measuring instrument is equipped with an arithmetic processing part 5 which calculates the height up to the liquid surface of the solution from the proportional relation among the total pressure obtained by the static pressure sensor 2, the pressure difference measured by the pressure difference sensor 1, and the predetermined distance, the differential pressure sensor 1, and the static pressure sensor 2. Then the pressure of two opening parts 7 and 8 provided at specific positions of different level in a container such as the tank 6 is guided to the differential pressure sensor 1, which measures their pressure difference to obtain a signal indicating the density of the liquid in the container. Further, the pressure of the opening part 7 positioned at a lower position between the opening parts 7 and 8 is guided to the static pressure sensor 2, which obtains a signal corresponding to the liquid level of the container 6; and the liquid level signal is corrected with the density signal of the liquid based upon the differential pressure sensor signal to obtain a liquid level signal from which the influence of the density of the liquid is excluded.

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 measuring the liquid level of a tank or the like.

[0002]

2. Description of the Related Art In the conventional method for measuring the liquid level of an open tank, a pressure gauge is attached to the lower part of the tank, and the distance from the pressure gauge attachment portion to the tank liquid level, that is, the tank liquid level is L.
Then, the pressure P measured by the pressure gauge is as follows.

P = ρ × L × g (1) where ρ represents the density of the liquid in the tank, and g represents the gravitational acceleration having a constant value. When the density ρ of the liquid in the tank is constant and known, K = ρ × g (K is a constant coefficient), and therefore the equation (1) becomes the equation (2).

L = (1 / K) × P (2) From equation (2), the tank liquid level L can be obtained from the pressure P, and an output corresponding to the tank liquid level L can be output from the pressure gauge.

However, when the density of the liquid in the tank is changed to another value, the coefficient (1 / K) of the equation (2) is changed, and the relationship between the pressure P and the tank liquid level L is changed. It is necessary to change the coefficient of the pressure gauge for determining the liquid level to another value. Further, when the density ρ of the liquid changes with time, it is necessary to measure the density ρ with a densitometer and perform a correction calculation with a calculator to obtain the tank liquid level.

[0006]

As described in the above-mentioned prior art, in the tank level measurement when the density of the liquid in the tank changes, the cumbersome operation of changing the coefficient of the pressure gauge each time. Was required, or a density meter was separately provided, a signal from the density meter was obtained, and a correction operation was performed to set the tank liquid level, which required a troublesome and expensive method.

The present invention does not require a troublesome operation such as changing the coefficient of a pressure gauge, and is troublesome such as providing a density meter separately, does not require cost, and is a tank liquid in which the density of the liquid changes. It is an object of the present invention to provide a liquid level measuring device that automatically and inexpensively realizes position measurement.

[0008]

A liquid level measuring device according to the present invention comprises a tank for exchanging and storing solutions having different densities, a tank lower side surface opening formed on a lower side surface of the tank, and the tank. A differential pressure for measuring the pressure difference of the solution expressed between the tank upper side opening and the tank upper side opening opened up by a predetermined distance from the lower side opening. A sensor, a static pressure sensor installed at the same horizontal height as the bottom of the tank to measure the total pressure expressed up to the liquid level of the solution, and a total pressure and differential pressure sensor measured by this static pressure sensor. It is characterized in that it is provided with an arithmetic processing unit for calculating the height of the solution to the liquid surface from the proportional relationship between the pressure difference and a predetermined distance.

[0009]

In the liquid level measuring device of the present invention, the tank lower side surface opening is opened in the lower side surface of the tank of the tank for exchanging and storing the solutions having different densities, and the tank lower side surface opening is set at a predetermined distance from the tank lower side surface opening. Open the tank upper side opening above, measure the pressure difference of the solution expressed between the tank upper side opening and the tank lower side opening, and install the static pressure sensor at the same horizontal height as the bottom of the tank. The total pressure expressed up to the liquid level of the solution is measured, and the proportional relationship between the total pressure measured by the static pressure sensor and the pressure difference measured by the differential pressure sensor and the predetermined distance Calculate the height of.

[0010]

EXAMPLE An example of the present invention will be described below. In FIG. 1, 6 is a tank for exchanging and storing solutions having different densities, 7 is a lower tank side opening opened on the lower side of the tank 6, and 8 is a predetermined distance 9 from the lower tank side opening 7. Of the tank upper side opening, which is opened only upwardly, 1 is a differential pressure sensor for measuring the pressure difference of the solution expressed between the tank upper side opening 8 and the tank lower side opening 7, and 2 is of the tank 6. A static pressure sensor that is installed at the same horizontal height as the bottom surface and measures the total pressure expressed up to the liquid surface of the solution,
5 is the total pressure measured by the static pressure sensor 2 and the pressure difference measured by the differential pressure sensor 1 and a predetermined distance 9
Is a calculation processing unit that calculates the height of the solution to the liquid surface from the proportional relationship between the two, which is equipped with a differential pressure sensor 1 and a pressure sensor, and which is provided at two predetermined positions with different levels of containers such as tanks. The pressure of each of the openings is guided to the differential pressure sensor 1 through the openings, and the difference between the pressures is measured to obtain a signal of the density of the liquid in the container. The pressure at the opening is guided to a pressure sensor, a signal corresponding to the liquid level in the container is obtained, and the liquid level signal is corrected and calculated by the liquid density signal based on the differential pressure sensor signal, and the influence of the liquid density The liquid level measuring device is characterized in that a liquid level signal excluding the above is obtained.

FIG. 1 shows the configuration of an embodiment of the liquid level measuring device for an open tank according to the present invention. Reference numeral 1 is a differential pressure sensor. 2 is a static pressure sensor. Reference numeral 3 is a high pressure side pressure guiding portion.
Reference numeral 4 is a low pressure side pressure guiding portion. Reference numeral 5 is an arithmetic processing unit. 6 is a tank. Reference numeral 7 denotes a tank lower side surface opening located near the bottom of the tank. Reference numeral 8 denotes a tank upper side surface opening located at a predetermined height above the tank lower side surface opening 7. Both the tank lower side surface opening 7 and the tank upper side surface opening 8 are arranged below the liquid level in the tank.

The tank lower side opening 7 and the high pressure side pressure guiding portion 3 of the liquid level measuring device are connected by piping, and the tank upper side opening 8 and the low pressure side pressure guiding portion 4 of the liquid level measuring device are also connected by piping. To be done. The differential pressure sensor 1 has a pressure P _H at the tank lower side surface opening 7 applied via the high pressure side pressure guiding portion 3 and a tank upper side surface opening 8 applied via the low pressure side pressure guiding portion 4.
The static pressure sensor 2, which is a sensor that measures the difference in pressure P _L at the point, is a sensor that measures the pressure P _H at the location at the tank lower side surface opening 7 that is applied via the high-pressure side pressure guiding portion 3.
After the processor 5 that the differential pressure sensor 1 and the static pressure sensor 2 is converted into easily processed electrical signals detected signal, from the differential pressure sensor a signal corresponding to P _H from the pressure sensor (P _H -
The correction calculation is performed using a signal corresponding to P _L ), and is converted into an output signal corresponding to the tank liquid level.

Let L be the distance between the tank lower side opening 7 and the liquid level of the tank, that is, the tank liquid level. Further, the distance between the tank lower side opening 7 and the tank upper side opening 8 is a. Let ρ be the density of the liquid in the tank. When the gravitational acceleration is g, the pressure P _H of 7 locations to be measured by the pressure sensor 2, the difference between the pressure point locations and 8 of 7 as measured by the differential pressure sensor (P _H -P _L) respectively below Is calculated as follows.

[0014] _{P H = ρ × L × g} (3) (P H -P L) = ρ × L × g- (ρ × L-a) × g = ρ × a × g (4) Equation (4) transforming _{ρ = (P H -P L)} / (a × g) (5) equation (5) into equation (3) _{P H = (P H -P L} ) / (a × g) × L × g = (P _H −P _L ) / a × L (6) By modifying the equation (6), L = (P _H × a) / (P _H −P _L ) (7) a is a constant coefficient. Therefore, by performing the arithmetic processing as shown in Expression (7) on the differential pressure sensor signal and the pressure sensor signal in the arithmetic processing unit, the correct tank liquid level L can be obtained without being affected by the density of the liquid. .

[0015]

As described above, since the tank liquid level can be measured without being affected by the density of the liquid, it is not necessary to change the coefficient of the measuring instrument each time the density of the liquid is switched, and the density can be corrected. Therefore, it is not necessary to prepare a separate densitometer, the working efficiency is improved, the accuracy of the liquid level measurement is improved, and these improvements can be realized at low cost.

[Brief description of drawings]

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

[Explanation of symbols]

 1 differential pressure sensor 2 static pressure sensor 5 arithmetic processing unit

Claims (1)

[Claims] 1. A tank for exchanging and storing solutions having different densities, a tank lower side surface opening formed in a lower side surface of the tank, and a tank opened upward a predetermined distance from the tank lower side surface opening. A tank upper side opening, a differential pressure sensor for measuring the pressure difference of the solution expressed between the tank upper side opening and the tank lower side opening, and the same horizontal height as the bottom surface of the tank. And a static pressure sensor for measuring the total pressure expressed up to the liquid level of the solution, the total pressure measured by the static pressure sensor and the pressure difference measured by the differential pressure sensor, and A liquid level measuring device, comprising: an arithmetic processing unit that calculates the height of the solution to the liquid surface from a proportional relationship of a predetermined distance.