SU1226159A1 - Differential vibrational densimeter - Google Patents

Abstract

The differential vibration densitometer is designed to measure the density of a fluid in a stream with variable speed and pressure in the petrochemical, chemical, and other industries. The invention makes it possible to increase the measurement accuracy by compensating for the error of pressure change and the flow rate of the medium in the resolvers. Differential vibration densitometer contains two tubular resonators with a controlled medium supply device into both resonators, resonator excitation systems and a frequency meter, the resonators having the same length and area of flow channels, as well as different wall thicknesses and static inertia moments of cross sections, which can be determined from Ii. .Г .. А - / i where I ;, Ijj are the static moments of inertia of the resonator sections; A, B - constant resonators equal to the ratio of their linear masses to the area of their flow channels; f is the value of the controlled density at which full compensation of the error due to changes in the velocity and pressure of the medium is achieved. 2 Il.

Description

The invention relates to analytical instrumentation and can be used to measure the density of a liquid in a stream with variable speed and pressure in the petrochemical, chemical and other industries.

The purpose of the invention is to improve the measurement accuracy by compensating for the error of pressure change and the flow rate of the medium in the resonators.

Figure 1 shows the device, a general view; figure 2 - section aa in figure 1.

The device contains two resonators 1 and 2, made at the same time in the form of two twin tuning forks installed on common grounds and having branches arranged in mutually perpendicular planes. The common bases of the tuning forks are mounted on membrane boxes 3, through which they communicate with the process pipe 4. The static moment of inertia of 1 section of the branches of the first tuning fork relative to the axis) Y is larger than the static moment of inertia Ij of the second tuning fork on the axis XX, and the wall thickness f of the first tuning fork less than wall thickness & second tuning fork, i.e. . To excite the oscillations of the second tuning fork, the exciter 5, amplifier 6, receiver 7 are used, and the exciter 8, amplifier 9 and receiver 10 are used to excite oscillations of the branches of the first tuning fork. The excitation systems are connected to a frequency mixer 11, which is connected to a measuring device through a low-frequency filter 12 13.

The controlled medium is supplied through pipeline 4, passes through the branches of tuning forks 1 and 2, and discharge through the pipeline 4. Pressure P, and consequently, the flow velocity V of the medium through the branches of the tuning fork changes. This leads to a change in the proper frequencies, fjp of oscillations of tuning forks. which are excited (8, 9, 10 and 5, 6, 7, respectively), the frequency difference is allocated in the mixer 11 and the low-pass filter 12, does not depend on the change in pressure P and the speed and flow of the medium. Difference Frequency f depends only on the cont.

59 1 the roll density p and is recorded by the device 13.

The main resonant frequency of the bend oscillations of the tubular resonator through which the controlled medium flows is determined by the expression

f., - f, E-t-YauU ",

de a - constant, depending on the type of attachment of the ends; F - area of the flow channel

vibrator; P, V - pressure and flow rate

controlled environment; 1 - the length of the vibrator; P - controlled density; EI - bending vibrator stiffness. Considering that

aFl

2

EI

 0.5

relation (1) can be simplified by decomposition in the power series and limited to two terms in the series:

1 P -f P V f ,, fp (l-aFl) (2)

For vibrators of the considered sensor, the natural frequencies, provided that, are from the ratios

/.JTZ:

 2 TG i; t + ha

(3)

,, А / Е1 ,,,

2f 2 l V m

2 uT LS O

where D is constant; l ,, the length of the vibrators; m is the mass of a unit of wall length

vibrators; t, is the mass of liquid; t is the distributed mass of cargo. The output frequency of the differential sensor when, is equal to

f - f .f / .EI -3 ip × 21GR V ra,. + ni

EI

- 2

(five)

When P and V, the output frequency is f- p

 P + P V

, p (l-aFl -2- | g- ..O-aFljSfJLv;

P

(6)

The error of the sensor due to the influence of pressure and flow rate of the medium is found from the ratio

cf- .v

Vp f

a.

.P-: -Mr- -irHii VP

- f

gr (7)

, The condition applies

1 -iLf .P i: Substituting 33 equality

Sheni (3)

g

(7

In ZERO at (8) (8), relations (4) are obtained

1 +

t,

(9)

one

- -th

It is obvious that equality (9) cannot be fulfilled, since equation-f 0 is obtained, I do not have ™ which reduces the physical meaning.

The pressure compensation conditions and the flow rates of the medium are

-I 1g

get B + P

A +

(ten)

(eleven)

Relation (11) is constructively implemented in the proposed differential sensor, which makes it possible to increase the measurement accuracy at the expense of the complex.

Pensation of pressure or flow rate of the controlled medium.

Claims (1)

1..I. A, B static moments of inertia of resonator sections; constant resonators, equal to the ratio of their linear masses to the area of the flow channels; p is the value of the controlled density at which full compensation of the error due to changes in the velocity and pressure of the medium is achieved. f