SU442380A1 - Capacitive Level Sensor - Google Patents

Description

one

The invention relates to the field of automation of liquid processes, in particular, can be applied in cryogenic technology in systems of automatic filling and maintaining the level of cryogenic liquid in various capacities.

Known capacitive level sensors, containing an electric capacitor with an external in the inner plates in the form of coaxial located cylinders and bends from them.

However, the known sensor, when operating on a cryogenic liquid, has several disadvantages:

a) cryogenic liquids have very low dielectric constant values and therefore the sensitivity of the sensor is small.

b) when working on supercooled liquids, there are large errors due to the strong dependence of the dielectric constant of the cryogenic liquid on

its temperature, which does not allow to clearly fix the maximum value of the level. I

c) it is difficult to use in systems of automatic pouring and maintaining level I

a cryogenic fluid, since in the process of filling a vessel, the interface of the phases f oscillates and the nature of the change in the capacitance of the sensor is oscillatory.

The invention eliminates these drawbacks by virtue of the fact that all the electrical and external genera of the outer lining (for example, of a cylindrical shape) / hermetically are interconnected by a conductive ring-shaped bottom and have a glass construction with a through inner bore. The inner (inner) plate of the capacitor is placed inside the outer plate so that the upper edges of the electrodes of the inner plate are located below the upper edges of the inner electrode (cylinder) and the height of the latter is made lower than the height of the outer electrode of the outer plate of the capacitor.

FIG. Figure 1 shows the design of the proposed capacitive sensor, and in Figure 1-1a the moment when the sensor detects the limiting value of the level is shown; 16 previous moment.

I Capacitance limit value /

The level of a cryogenic liquid is an electric condenser, such as a coaxial structure, and consists of an outer lining 1 and an inner lining 2. The outer lining 1 has two cylindrical electrodes of different heights and diameters, which are connected by a conductive ring bottom and form a kind of glass with a through inner hole formed by the inner surface of the inner cylindrical electrode.

The outer lining 1 is attached to the wall of the vessel 3 by means of a rigid cylinder 4. The inner lining 2 is placed inside the lining 1 between its cylindrical electrodes and attached with conductor 5 and an insulator (for example, ceramic) 6 embedded in the wall of the vessel 3. Petal 7 serves to solder the screen of the coaxial cable (or common bus generator).

The method of mounting the capacitive sensor to the vessel wall may be different.

Triangles are marked on the drawing the boundary between the liquid and vapor phase.

Capacitive sensor works as follows.

When a vessel is filled with a cryogenic liquid (from the dielectric constant |,) its level / 1 rises (see Fig. 1b).

The capacitive sensor is immersed in a liquid, while the liquid passes into the inner hole inside, the heated electrode VI washes the outer surface of the outer electrode of the outer plate 1 of the capacitor, and the working space between the outer 1 and inner 2 plates of the capacitor does not fill, and therefore the electrical capacitance C capacitive sensor does not change, even if the limit value of the level h, which

pr} units

need to be fixed, the value will remain very small. do

With a further increase in the level of tl

it reaches the limit value i

before

corresponding to the upper edge of the inner electrode of the outer facing 1. The curved / fire liquid begins to overflow and quickly fills a small volume of the working space of the capacitive sensor (see Fig. 1a); the electrical capacitance of the latter is then increased by

the value of D, B & n p vapor permeability. A change in the temperature of a cryogenic liquid does not affect the moment of its capacity change by an amount. This moment in time coincides only with the moment of reaching the level

liquid h limit value h

before

If the rising level of cryogenVO & h liquid is not calm, i.e. the interface is oscillating, then in this case the sensor works well, so. as the filling of the working space of a condenser with liquid occurs from the inner passage of the inner cylinder of the outer lining. The diameter of the inner cylinder is chosen so that the interface of the phase in it rises with muffled vibrations and the inner cylinder plays the role of an Ugandy.

External waves of the fluid can not overwhelm the sensor before filling its working space.

from the inner passage, since the cylinders of the outer lining of the capacitor have a distinct height, and the outer one is higher than the inner one.

When draining the liquid from the vessel sensor

it ceases to be washed by the cryogenic liquid, and its small volume, located in the working space of the sensor, quickly evaporates due to the influx of heat from the vessel wall, fasteners. After that, the sensor is again ready for operation.

Subject invention

A capacitive level sensor, containing an electric condenser with external and internal lining in the form of coaxial cylinders and cylinders from them, characterized in that

increasing the steepness of its characteristics and increasing the reliability of functioning, the outer capacitor plate is made of at least two cylindrical rings which are interconnected with each other,

the first of which is located outside the inner lining cylinder and the second inside, with the upper edge of the second located below the upper edge of the first and above the upper edge of the cylinder of the inner lining