SU1137316A1 - Device for measuring liquid level - Google Patents

Abstract

A LEVEL MEASUREMENT DEVICE containing a piezometric tube, a differential pressure sensor connected to a piezometric tube and a closed gas cavity of a container with a controlled fluid. characterized in that, in order to improve measurement accuracy, an absolute pressure sensor connected to a piezometric tube, two scaling links, two adders, a setting device, a reference signal and a dividing unit are inserted into it, and the differential pressure sensor code is connected to the input of the first scaling link, the output of the absolute pressure sensor is connected to the first input of the first adder and to the first input of the dividing unit; the output of the first scaling link is connected to the first input of the second adder; Nala connected to the second input of the first adder, whose output is connected to the input of the second refinement level, the output of the second scaling unit is connected to the second input of the dividing block, g whose output is connected to the second input of the second adder. po DO 9)

Description

one

The invention relates to a measurement technique (specifically, to devices for measuring the level of a liquid) and can be used in various industries and agriculture.

A piezometric level meter is known by the method in which the pressure in a piezometric tube immersed in a liquid is varied within the limits sufficient to bring the level of fluid in it to a reference point deposited on the tube, as well. The measured level is determined by the value of this pressure RP.

However, it is not possible with a known device to ensure continuous measurement of the level of a liquid in pressure vessels, since an adjustable source of compressed gas is necessary.

Closest to the present invention is a piezometric level gauge used in pressure vessels containing two tubes and a differential pressure sensor 2,

However, due to the compression of gas in the piezometric tube, it is filled with liquid, the height of the column which reflects the displacement of the pressure point in the fluid layer, and the unambiguous relationship between the gas pressure in the piezometric tube and the liquid level is lost.

The purpose of the invention is to improve the accuracy of measuring the level of a liquid.

The goal is achieved by the fact that in the device for measuring the level of a liquid containing a piezometric tube, a differential pressure sensor connected to a piezometric tube and a closed gas cavity of a container with controlled liquid, an absolute pressure sensor connected to a piezometric tube is inserted, two scaling links, two adders , the reference signal adjuster and the dividing unit, with the output of the differential pressure sensor connected to the input of the first scaling link, the output of the absolute pressure sensor Connected to the first input of the first adder and to the first input of the division unit, the output of the first scaling link is connected to the first input of the second adder, the reference signal generator is connected to the second input of the first

7316, 2

an adder, the output of which is connected to the input of the second scaling link, the output of the second scaling link is connected to the second input 5 of the division unit, the output of which is connected to the second input of the second adder,,

The drawing shows a block diagram of the device.

10 The device comprises a piezometric tube 1, lowered into the tank and connected to the differential pressure sensor 2 and the absolute pressure sensor 3, pipe 4, scaling

15 link 5, adder 6, reference signal adjuster 7, scaling link 8, division block 9, adder 10.

The device works in the following way.

0 When the tank is filled with liquid, the end of the piezometric tube 1 is immersed in a liquid and then the absolute pressure at its open end P- begins to exceed the absolute

5 gas pressure P which is in the tank until the liquid reaches the end of the tube 1. Under the action of the difference; pressure, s (the seat flows into the tube 1 and compresses the gas in it to the value of the absolute pressure P, which is equal to

(one)

R ,

where p is the specific density of the fluid;

q is the acceleration of free fall;

h - having settled from the viewpoint of a liquid column in tube 1, Nebrega by temperature changes of gas in tube 1 can be recorded

R"(

(2)

,

where V, Vn - the volume of gas in the tube 1

respectively, at pressures P and P,

However d

V,

(3)

four

where d is the diameter of the tube 1,

Solving together equations (1) and (3) and eliminating h, we get

P 2 - V

7d

From equation (2) follows / PZ-PI

P (- 7

"

"T, where t is the length

tube 1, then

(P, - P,) f

pq P However

,,,

where N. is the fluid level in the tank

relative to the end of the tube

one;

PJ, - absolute gas pressure

above the liquid mirror-. Denoting P-. Pq, we get

(P - P,) f Pq

(BUT)

Р-г f

In the proposed device, Pd is measured by differential pressure sensor 2, P is measured by absolute pressure sensor 3, and P is measured and set by means of pressure sensor 3 and reference signal setter 7, and the output signals C of sensors 2 and 3 are related to measured values of the ratio C KrR, where Kr is the coefficient of sensitivity of the sensor ,.

The output signal from the sensor 2 pressure difference is fed to the input mas1373f64

stacking link 5, the magnitude of the gain which is equal to

1 TO

five

- Sensitivity coefficient Kg, for the second differential pressure sensor.

The output signal from the absolute pressure sensor 3 is fed to the input of the adder biv block 9 division. The second term of the adder 6 is the signal from the setpoint 7 of the reference signal, which is fixed and set when the device is tuned before filling the tank with a liquid equal in magnitude and opposite in sign to the signal from the output of sensor 3 so that the output signal of the adder 10 is zero. The output signal of the adder 6 arrives T to the input of the scaling link 8 ,,

t

5. Having a gain factor of Kg

The signal from the output of the scaling link 8 is fed to the input of the NIN block 9, where its value is divided by the output signal; sensor 3. From the output of dividing unit 9, the signal enters the adder 10, where it is summed with the output signal of the scaling link 5, and from the output of which it can flow to the secondary measuring device or to the control system. The functions of blocks 5 ... 10 can be carried out both by means of electroautomatics and pneumoautomatics combined into a computing unit, in addition to standard pressure sensors.

Claims (1)

A LIQUID LEVEL MEASUREMENT DEVICE comprising a piezometric tube, a pressure difference sensor connected to a piezometric tube and a closed gas cavity of a container with a controlled liquid, characterized in that, in order to increase the accuracy of measurement, an absolute pressure sensor connected to the piezometric tube is introduced into it, two scaling links, two adders, a master, a reference signal and a division unit, the output of the differential pressure sensor connected to the input of the first scaling link, the output of the sensor pressure switch is connected to the first input of the first adder and to the first input of the division unit, the output of the first scaling unit is connected to the first input of the second adder, the reference signal generator is connected to the second input of the first adder, the output of which is connected to the input of the second scaling unit, the output of the second scaling unit is connected to the second input of the division unit, the output of which is connected to the second input of the second adder. LUo., 1137316