RU2346259C2 - Vibration probe for determination of density of fluid mediums - Google Patents

Abstract

FIELD: physics, measurement.

SUBSTANCE: invention may be used for determination of fluid medium density in different reservoirs, also in pressurised devices. Substance of invention consists in the fact that vibration probe comprising fork equipped with piezoelectric crystal fixed on bent section of fork, and magnetostrictive drive, additionally contains pipe and damping device. Damping device comprises bellows, sleeve and spring. Bellows is installed inside sleeve and tightly cut into vibration probe pipe, and spring is rigidly fixed to sleeve end and fork body.

EFFECT: higher accuracy of measurements.

1 dwg

Description

The invention relates to measuring technique and can be used to determine the density of liquid media in various tanks, including pressure devices.

The prototype of the claimed device is a vibrating device for measuring temperature or other physical properties of liquid media containing a plug equipped with a piezoelectric crystal mounted on a bent portion of the plug and a magnetostrictive drive (application No. 2079940 G01N 9/34, UK).

These devices, as a rule, are installed directly on the lids or side walls of the tanks. In many cases, such constructive solutions are impossible for practical use, especially in enterprises of the nuclear and chemical industries, where under specific conditions there is no access to devices for their maintenance and repair.

Therefore, a vibrating device (probe) must be inserted into the tank using a sealed extension pipe in which the cables (wires) of the electrical circuit are placed.

A common disadvantage of these vibration devices is that when a sealed extension pipe is connected to them, the resonance frequency of the device changes, which leads to a decrease in the accuracy of measuring the density of liquid media.

The oscillation frequency of the vibrating device is determined by the equation

where K is the rigidity of the fork;

M ₀ - the mass of the vibrating device and parts rigidly connected with it, kg;

ΔM is the mass of liquid oscillating with the fork of the vibrating device, kg

The mass of the vibrating device and parts rigidly connected with it depends on the density of the controlled fluid and the volume of the controlled fluid surrounding it and is determined by the expression

where d is the density of the controlled fluid, kg / m ³ ;

S ₁ - the area of the apparatus with a controlled liquid, m ² ,

h ₁ - the height of the liquid column above the plug, m

The mass of fluid oscillating with the plug of the vibrating device is determined by the expression

where S ₂ - the area occupied by the fluid between the plug, m ² ,

h ₂ - the height of the vibrating device, m

Substituting expressions (2) and (3) into expression (1), we have:

From the expression (4) it is seen that the frequency of oscillation of the plug depends not only on the density (d) of the controlled fluid, but also on the height of the fluid column (h ₁ ) located above the plug. The values of S ₁ , S ₂ and h _{2 are} constant and do not change during the measurement.

The technical problem to be solved by the claimed invention is directed is to increase the accuracy of determining the density of liquid media when the level of the controlled liquid changes.

The problem is solved using the claimed device. In the vibration probe (see drawing) containing the plug 1, equipped with a piezoelectric crystal and magnetostrictive drive 6, mounted on the bent portion of the plug 1, and the pipe 2, a damping device is inserted located between them and representing a bellows 3, a cup 4 and a spring 5, moreover, the bellows is located inside the glass and hermetically cut into the pipe 2, which protects the electrical conductors passing inside the bellows from piezoelectric crystals and magnetostrictive drive 6 from the influence of an aggressive medium. The spring, rigidly connected to the end of the glass and the housing 7 of the plug 1, is designed to reduce the mechanical stresses on the bellows and, therefore, to increase the reliability of the device.

The operation of the vibration probe with a damping device is as follows. When voltage is applied to the drive, the plug begins to vibrate with a resonant frequency, which depends on the physical properties of the fluid being controlled. Oscillations of the plug 1 lead to compression-extension of the bellows 3 and the spring 5 with the oscillation frequency of the rods. Due to the compression-tension of the bellows 3 and the spring 5, the vibrations of the plug 1 are not transmitted to the pipe 2. Thus, the pipe 2 is not involved in the creation of a resonant frequency and expression (4) in this case has the form

From the expression (5) it can be seen that the frequency of oscillation of the plug depends only on the parameters of the plug K, S ₂ and h ₂ , which are determined by the geometric dimensions of the plug and do not change during the measurement, and on the density of the controlled fluid and does not depend on the level of the controlled fluid h ₁ , which increases the accuracy of measurement and expands the scope of the device at the enterprises of nuclear, chemical and other industries when inside a hardware installation through the use of an extension pipe.

Claims (1)

Vibration probe for determining the density of liquid media, comprising a plug equipped with a piezoelectric crystal fixed on a bent portion of the plug and a magnetostrictive drive, characterized in that a pipe and a damping device consisting of a bellows, a cup and a spring are additionally inserted into it, the bellows being located inside the cup and hermetically embedded in the tube of the vibration probe, and the spring is rigidly connected to the end of the glass and the body of the fork.