RU2730403C1 - Imitation method of checking density meters of a float type - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: invention relates to measurement equipment and can be used for verification of float type densimeters. Disclosed is an imitation method of checking density meters of a float type for poisonous, explosive, combustible liquids and liquefied gases, consisting in measurements of density of a comparator (liquid), using a verified float densimeter and a reference densimeter, and determining absolute error of density measurements. At the same time water or other liquid is used as comparator without harmful, explosive and combustible properties with density higher than measurement range of measured densimeter. Prior to density measurement, float of verified densimeter in its lower part is fixed symmetrically at diametrically opposite points with two weights of definite mass, providing shift of scale range of measurements of density of verified densimeter to value of comparator density. Verification is carried out at normal atmospheric pressure, after verification, loads from float density are removed.EFFECT: high accuracy and reliability of obtained data.1 cl

Description

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

1 - with partial immersion of the float for density measurements in the surface layer of a liquid (surface double-float density meters: level and density floats), for example, described in patents RU No. 2138028 G01F 23/68, G01N 9/10 dated 05.08.1998, US 7,278,311 G01F 23/76 dated May 24, 2006, RU No. 2351903 G01F 23/28 dated December 17, 2007, RF RU No. 2710008 G01F 23/68 dated May 17, 2019;

2 - with full immersion of the float for density measurements in any layer of liquid along the height of the tank (submersible single-float chain densitometers), for example, described in patents RU No. 2273838 G01N 9/12, G01F 23/62 dated May 19, 2005, RU No. 2308019 G01N 9/12 dated 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 (actual) value of the measured quantity.

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

When checking density meters, the following basic methods are used:

1 - direct measurement by a verified density meter of the density of a standard sample of liquid with a known density within the density measurement range of the verified density meter;

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

The known methods for checking density meters have significant disadvantages.

First way:

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

- the set of standard samples is limited in terms of density (there are no standard samples with a density less than 650 kg / m ³ for verification of density meters for liquefied gases).

Second way:

- when checking density meters for poisonous, explosive, flammable liquids, it is necessary to comply with the established safety and labor protection requirements, which significantly complicates and increases the cost of checking density meters; after verification, it is necessary to clean the measuring instruments from hazardous liquids and dispose of these liquids;

- to calibrate densitometers for liquefied gases under saturated vapor pressure, it is necessary to create expensive installations, after verification it is necessary to degass the installation.

The closest to the claimed imitation method for verifying float-type densitometers is a method for 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. The specified 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 of 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."

The task for the solution of which the claimed imitation method for verifying float-type densitometers is intended is to create a simulation method for verifying float-type densitometers, including for poisonous, explosive, flammable liquids and liquefied gases, using water or other liquid as a comparator without harmful, explosive and combustible properties and verification of density meters at atmospheric pressure, which will significantly reduce the cost of verification.

The task is achieved by creating a simulation method for verifying float-type density meters for poisonous, explosive, flammable liquids and liquefied gases, 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 the comparator uses water or other liquid without harmful, explosive and flammable properties with a density higher than the measurement range of the density meter being verified, before measuring the density on the float of the density meter under verification, two weights of a certain mass are fixed symmetrically at diametrically opposite points in its lower part, providing a shift in the scale of the density measurement range of the verified density meter to the density 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 proposed simulation method for verifying float density meters for poisonous, explosive, flammable liquids and liquefied gases is as follows. When checking density meters on the density meter float, 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, and the absolute measurement error of the density of the verified density meter is determined using the formula:

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

ρ _fl. - the density value of the comparator, measured with a reference density meter.

The total mass of the weights is chosen such that the scale of the measuring range of the density meter being verified is shifted by the value of ρ _shift. , after which the density meter can measure the density of the comparator (water).

where ρ _pl. the value of the density of the liquid in the measuring range of the density meter. Thus, you can verify density meters in any density measurement range that has a limitation:

where ρ _to - the density of the comparator.

Recommendations for the correct choice of the comparator are given in the book “Artemiev BG, Lukashov Yu.K. Reference manual for specialists of metrological services. - M .: IPK - Publishing house of standards, 2004. - 840 p. ", On page 187" Comparing factors (including ... natural environments) belong to the fourth group. These factors only require stability over time and uniformity in a volume sufficient to accommodate the compared measuring instruments. ... The absolute value of the quantities characterizing these factors is not so important. 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. "

From the above it follows that, for example, water fully complies with the requirements for comparators.

The mathematical calculations used in the implementation of the proposed simulation method for verifying 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 a liquid and single-float (submersible) with full immersion of the density float in a liquid.

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

Equation of equilibrium of the density float in the working range of measurements (without load):

where M _P is the mass of the density float;

V _P is the volume of the immersed part of the density float;

ρ ₁ is the density of the liquid.

Equation of equilibrium of the level float in the working range of measurements:

where M _U is the mass of the level float;

V _У - the volume of the submerged part of the level float into a liquid with a density ρ ₁ .

After adding equations (4) and (5) we get:

from here

The equilibrium equation for the density float during verification using a comparator with a density equal to ρ ₂ (with a load):

where M _G is the mass of the cargo;

V _G - the volume of cargo, which is

where ρ _G is the density of the cargo material.

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

where V _U2 is the volume of the immersed part of the level float at a density equal to ρ ₂ .

After adding equations (8) and (10) we get:

from here

Shift of the scale of the measuring range of the density meter when checking with a load

moreover

After substituting formulas (7) and (12) into formula (13), we obtain

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

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

Equation of equilibrium of the density float in the working range of density measurements (without load):

from here

where ρ ₁ is the density of the liquid;

M _P is the mass of the density float;

М _Ц - the mass of the chain suspension;

V _P is the volume of the density float;

V _C - the volume of the chain suspension,

in its turn

where L _C is the length of the chain suspension;

M _CP - running weight of the chain suspension;

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

The equilibrium equation for the density float during verification using a comparator with a density equal to ρ ₂ (with a load):

from here

where M _G is the mass of the load during verification;

V _G - cargo volume

where ρ _G is the density of the cargo material.

Shift of the scale of the measuring range of the density meter when checking with a load

moreover

After substituting formulas (17) and (21) into formula (23), we obtain

Thus, by changing the weight of the load, it is possible to verify the submersible density meter in the comparator (for example, in water) at any point of the density measurement range of the density meter being verified (determine the error in density measurements by measuring the density of the comparator with a reference density meter), subject to condition (24).

The enterprise carried out tests to determine the density measurement error of density meters for measuring the density of AI-92 gasoline, kerosene, diesel fuel, liquefied petroleum gas (LPG), first on a comparator, which was water, and then directly in the above products. The results of determining the error of density measurements coincided in both cases, taking into account the error of standard measuring instruments.

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

Claims (1)

A simulation method for verifying float-type densitometers for toxic, explosive, flammable liquids and liquefied gases, 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, characterized in that it is used as a comparator water or other liquid without harmful, explosive and flammable properties with a density higher than the measurement range of the density meter being verified, before density measurement, two weights of a certain mass are fixed symmetrically at diametrically opposite points in its lower part to the float of the density meter under verification, providing a shift in the scale of the density measurement range of the density meter under verification up to comparator density values, verification is carried out at normal atmospheric pressure, after verification, the weights are removed from the density float.