RU2795557C1 - Simulation method for verification of float-type density meters for liquids with high density - Google Patents

Abstract

FIELD: measuring means.

SUBSTANCE: verification of float-type density meters used in liquid tanks. The simulation method for verification of float-type density meters for liquids with high density, used for harmful, explosive and combustible liquids, consists in measuring the density of the comparator liquid using a verified float density meter and a reference density meter and determining the absolute error of density measurements. As a comparator liquid, a liquid without harmful, explosive and combustible properties with a density below the measurement range of the verified density meter, such as distilled water, is used. Moreover, the mass of the float without load is preliminarily calculated for the density of the comparator liquid used, verification is carried out in the liquid comparator without suspension of the load at normal atmospheric pressure, and after verification, the load is suspended to the float and the scale of the density measurement range of the verified density meter is shifted to the value of the density of the liquid in the tank, the weight of the load is determined by the density of the liquid in the tank.

EFFECT: increase in the accuracy of verification of float-type density meters for liquids with a high density, while at the same time the verification conditions are safe.

2 cl

Description

Currently, there are many devices for measuring the density of liquids in tanks - density meters. Float-type density meters are widely used. The most accurate density meters in this class are magnetostrictive float density meters. There are two main types of such density meters:

1 - with partial immersion of a float for density measurements in the surface layer of a liquid (surface two-float density meters: level and density floats), for example, described in patents RU No. G01F 23/76 of May 24, 2006, RU No. 2351903 G01F 23/28 of December 17, 2007, RF RU No. 2710008 G01F 23/68 of May 17, 2019;

2 - with full immersion of the float for density measurements in any liquid layer along the height of the tank (submersible single-float chain density meters), for example, described in patents RU No. 2273838 G01N 9/12, G01F 23/62 of 05/19/2005, RU No. G01N 9/12 of 20.04.2006

Since the density meter is a measuring instrument, there is a problem of determining the quality of measurements, the main characteristic of which is the measurement error - the deviation of the measurement results from the true (real) value of the measured value.

Determination of measurement error is carried out in the process of verification of measuring instruments after their manufacture or repair - primary verification and during operation - periodic verification.

When calibrating density meters, the following main methods are used:

1 - direct measurement by a verified density meter of the density of a standard sample of a liquid with a known density, which is in the density measurement range of the verified density meter;

2 - comparison of the readings of the verified density meter and the reference density meter, when measuring the density of the liquid - comparator, and the density of the comparator must be in the range of measurements of the density of the verified and reference density meters.

Known methods for calibrating density meters have significant drawbacks.

First way:

- standard samples of comparators have a high cost and a limited service life due to contamination during verification;

- the set of standard samples is limited in terms of density.

Second way:

- when calibrating densitometers for harmful, explosive and combustible liquids, it is necessary to comply with the established safety and labor protection requirements, which significantly complicates and increases the cost of calibrating densitometers; after verification, it is necessary to clean the measuring instruments from hazardous liquids and dispose of these liquids.

The most common method for calibrating float-type density meters is the method of comparing the readings of the density meter being verified with the readings of a reference density meter when measuring the density of a liquid (comparator), the disadvantages of which are described above. This method is set out in the State verification scheme for density measuring instruments, approved by order of the Federal Agency for Technical Regulation and Metrology dated November 1, 2019 No. 2603. According to this method (clause 7.2) “Working standards are used to transfer density to density measuring instruments by comparison using a comparator ... Water, liquids of carbon composition, acid solutions, Thule solutions, liquefied hydrocarbon gases are used as a comparator.”

A simulation method for calibrating float-type density meters for toxic, explosive, flammable liquids and liquefied gases is known, described in RF patent No. liquid) using a verified float density meter and a reference density meter, and determining the absolute error of density measurements, while water or another liquid without harmful, explosive and combustible properties is used as a comparator with a density above the measurement range of the verified density meter, before measuring density on the float of the verified density meter in its lower part, two weights of a certain mass are fixed symmetrically at diametrically opposite points, providing a shift in the scale of the density measurement range of the density meter being verified to the density value of the comparator, verification is carried out at normal atmospheric pressure, after verification, the weights are removed from the density float.

The essence of the well-known simulation method for checking float-type density meters for poisonous, explosive, flammable liquids and liquefied gases is as follows. When checking the density meters on the density float of the density meter, two weights of a certain mass are fixed symmetrically at diametrically opposite points in its lower part to shift the density measurement range, and the density meter is placed in a liquid (comparator), which, for example, is water. In this case, the density of the comparator is higher than the density measurement range of the density meter being verified. The density of the comparator is measured using a reference density meter and a verified density meter, while the absolute measurement error of the density of the verified density meter is determined by the formula:

where ρ _meas. - value of the comparator density measured by the verified density meter, taking into account the shift of the scale of the measurement range;

ρ _fl. is the comparator density value measured with a reference density meter.

The total weight of the loads is chosen so as to provide a shift in the scale of the measurement range of the verified density meter by the value ρ _shift. , after which the density meter can measure the density of the comparator (water) with a load and the density of the liquid in the tank without a load.

where ρ _pl. - the value of the density of the liquid in the measurement range of the density meter.

Thus, it is possible to verify density meters in any range of density measurements, which has a limitation:

where ρ _to - the density of the comparator.

As can be seen from the description, the well-known simulation method for calibrating float-type densitometers makes it possible to calibrate densitometers for liquids whose density is less than or equal to that of water.

However, it often becomes necessary to calibrate density meters operating in liquids with a density greater than that of water.

The task for the solution of which the claimed simulation method for checking float-type density meters for liquids with high density is intended is to create a simulation method for checking float-type density meters used in tanks for liquids with high density, including for harmful, explosive, combustible liquids using as comparator of water or other liquid without harmful, explosive and combustible properties and verification of density meters at atmospheric pressure, which will significantly reduce the cost of verification and create safe verification conditions.

The task is achieved by creating a simulation method for verifying float-type density meters for liquids with a high density used for harmful, explosive and combustible liquids, which consists in measuring the density of a comparator (liquid) using a verified float density meter and a reference density meter and determining the absolute error of density measurements, while as a comparator, water or another liquid without harmful, explosive and combustible properties with a density below the measurement range of the verified density meter is used, on the float of the verified density meter there is a device for securing a load of a certain mass, while the weight of the float without load is calculated for the density of the used comparator, for example, distilled water, verification is carried out in a comparator without suspension of the load at normal atmospheric pressure, after verification, the load is suspended from the float and the scale of the density measurement range of the verified density meter is shifted to the value of the density of the liquid in the tank, the weight of the load is determined by the density of the liquid in the tank.

Recommendations for the correct choice of comparator are given in the book “Artemiev B.G., Lukashov Yu.K. Reference manual for specialists of metrological services. - M.: IPK - Standards Publishing House, 2004. - 840 p., p. 187 “The fourth group includes comparating factors (including ... natural environments). For these factors, only stability in time and homogeneity in a volume sufficient to accommodate the compared measuring instruments are required ... The absolute value of the quantities characterizing these factors is not so significant. It is only necessary that they ensure the functioning of the means being compared in their measurement ranges. It is enough to control their stability.”

It follows from the above that, for example, water fully complies with the requirements for comparators.

Mathematical calculations used in the implementation of the proposed simulation method for verification of float-type density meters are given below for two types of float density meters: two-float (surface) with partial immersion of the density float in the liquid and single-float (submersible) with full immersion of the density float in the liquid.

Surface density meter (two-float) with partial immersion of the density float.

Equilibrium equation of the density float in the operating measurement range (with load):

where ρ ₁ is the density of the liquid;

M _P - mass of the density float;

M _G - mass of cargo;

V _P1 - the volume of the immersed part of the density float in a liquid with a density equal to ρ ₁ ;

V _G - the volume of cargo, which is equal to

where ρ _G is the density of the cargo material.

Equilibrium equation of the level float in the operating measurement range

where M _Y is the mass of the level float;

V _U1 - the volume of the submerged part of the level float at a density equal to ρ ₁ .

After adding equations (4) and (6) we get:

from here

The equilibrium equation of the density float during verification using a comparator with a density equal to ρ ₂ (without load):

where V _P2 is the volume of the immersed part of the density float in a liquid with a density equal to ρ ₂ (comparator).

The equilibrium equation of the level float during verification using a comparator with a density equal to ρ ₂ :

where M _Y is the mass of the level float;

V _U2 - the volume of the immersed part of the level float in the liquid with a density ρ ₂ .

After adding equations (9) and (10) we get:

from here

Shift of the scale of the measurement range of the density meter during verification without load

and

After substituting the values ρ ₁ and ρ ₂ into formula (13) from formulas (8) and (12), we obtain

Thus, by changing the mass of the load, it is possible to calibrate the surface float densitometer in the comparator (for example, in water) at any point in the density measurement range of the verifiable densitometer (determine the density measurement error by measuring the density of the comparator with a reference density meter) provided that condition (14) is met.

Submersible density meter (single-float chain with full immersion of the density float).

Equilibrium equation of the density float in the working range of density measurements (with load):

from here

where ρ ₁ is the density of the liquid;

M _P - mass of the density float;

M _C - mass of the chain suspension;

M _G - mass of cargo during verification;

V _P - the volume of the density float;

V _C - the volume of the chain suspension;

V _G - cargo volume.

where ρ _G is the density of the cargo material.

The equilibrium equation of the density float during verification using a comparator with a density equal to ρ ₂ (without load):

from here

where ρ ₂ is the density of the comparator;

in its turn

where L _C - the length of the chain suspension;

M _CPU - linear mass of the chain suspension;

where ρ _C is the density of the material of the chain suspension.

Shift of the scale of the measurement range of the density meter during verification with a load

and

After substituting formulas (17) and (20) into formula (23), we obtain

Thus, by changing the mass of the load, it is possible to calibrate the submersible density meter in the comparator (for example, in water) at any point in the density measurement range of the verified density meter (determine the density measurement error by measuring the density of the comparator with a reference density meter), provided that condition (24) is met.

At the enterprise, tests were carried out to determine the error in measuring the density of densitometers for measuring the density of antifreeze, first on a comparator, which was used as distilled water, and then directly in antifreeze. The results of determining the density measurement error coincided in both cases, taking into account the error of reference measuring instruments.

The tests were carried out both on surface (two-float) density meters and on submersible (single-float chain) density meters. The results obtained fully confirmed the accuracy of the proposed simulation method for checking float-type density meters for high-density liquids.

Claims (2)

1. Simulation method for verification of float-type density meters for liquids with high density, used for harmful, explosive and combustible liquids, which consists in measuring the density of the comparator liquid using a verified float density meter and a reference density meter and determining the absolute error of density measurements, while as a liquid -comparator, a liquid without harmful, explosive and combustible properties is used with a density below the measurement range of the verified density meter, while the float of the verified density meter has a device for securing a load of a certain mass, characterized in that the weight of the float without load is preliminarily calculated for the density of the comparator liquid used, verification is carried out in a liquid comparator without suspension of a load at normal atmospheric pressure, and after verification, the load is suspended from the float and the scale of the density measurement range of the verified density meter is shifted to the value of the density of the liquid in the tank, the weight of the load is determined by the density of the liquid in the tank. 2. A simulation method for checking float-type density meters for high-density liquids according to claim 1, characterized in that distilled water is used as a comparator liquid.