SU1476317A1 - Method of measuring level of liquid metal - Google Patents

Abstract

The invention can be applied in metallurgy for contactless measurement of the level of a liquid metal in ladles, molds, molds, etc. The goal is to expand the functional area by making it possible to measure the level of a liquid metal in containers of various sizes and purposes. The method consists in forming an open microwave resonator, one of the mirrors of which is the surface 1 of the liquid metal in the tank, and the other is the metal mirror 2 located above this surface. The level of the liquid metal is determined by the number of longitudinal oscillations excited in the open resonator during deviation frequencies of electromagnetic waves exciting these oscillations in a fixed frequency range. 3 il.

Description

1

The invention relates to metallurgy and measurement technology and can be used to measure the level of an electrically conductive substance in various process vessels of metallurgical production, for example, in crystallizers of continuous casting plants for ferrous and non-ferrous metals, in molds, ladles, etc.

The purpose of the invention is to expand the field of application by making it possible to measure the level of a liquid metal in open containers.

FIG. 1 shows an open microwave resonator; in fig. 2 is a graph of the number of excited longitudinal modes of vibration versus level for various wavelength ranges; in fig. 3 is a functional diagram of the device implementing the method.

To measure the level of the proposed method, an open microwave resonator containing two reflective metal mirrors is arranged (Fig. 1). As one of the mirrors, the surface 1 of the liquid metal in the tank is used, the distance to which must be determined, and the other is a special reflector - a concave mirror 2 (Fig. 1) or flat with a diameter of 20-30 cm. In such an open resonator high-Q oscillations exist, and electromagnetic energy is concentrated in the form of a narrow beam in the region shown in FIG. 1 dotted line (this area is shaded).

The resonant vibration frequencies of a resonator with flat mirrors are expressed by the formula.

Ј P 1 2-3 (1)

where / is the distance between the mirrors;

q - number of longitudinal type of oscillations

(harmonics); C is the speed of light; e, c is the dielectric and magnetic permeability of the substance in the space between the mirrors.

The wavelengths corresponding to these frequencies are determined by the formula

(2,3 ...)

(2) 45

In the case of a resonator consisting of a flat (liquid metal surface in the method under consideration) and a concave mirror, the wavelengths of the oscillations excited in the resonator are expressed as:

2F

. . / r (, 2, 3 ...), (3)

9+ -arcsmy //./

where R is the radius of curvature of the concave mirror.

When the term l / narcsiny d- in the denominator of the right side of the formula (3) can be neglected, that is, the formula (3) coincides with

formula (2), corresponding to the resonator with flat mirrors. The condition is easily implemented in practice, as is usual. At the same time, the presence of a concave mirror in the resonator is preferable to a flat one, since such a resonator is less sensitive in practice to the distortions of the mirrors and requires less accurate alignment.

It can be seen from formulas (1) and (3) that the oscillation spectrum of the resonator on longitudinal types TEM sod is equidistant. In this case, the distance between adjacent resonant pulses along the frequency axis can serve as a single measure of the determined distance.

As an informative parameter with a significant range of variation of the distance (greater than half the wavelength) to the surface of the liquid metal, the number N of natural oscillations of the resonator can be used, excited in the frequency range Af / 2- / i, where f and / 2 are the lower and upper values variable oscillator frequency of the exciting oscillations in the resonator, which is determined by the dependence

(four)

NsJ ± vVL

Formula (4) follows directly from formula (1) for resonant (natural) frequencies of resonator oscillations and can be written as

one

- jr) l, L2

(five)

where K and A, 2 are the boundary values of the wavelength corresponding to the frequencies i and / 2.

Let us estimate the value of N depending on the change in the measured distance / to the surface of the controlled medium. This value depends on the oscillator frequency deviation in the working frequency range f, / 2, i.e., A.2, K wavelengths. The graph of N (/) as / varies within 0 + 1000 mm for different ranges A, C, H is shown in FIG. 2

The error in measuring the distance (level) A / is related to the error in determining N by

0

five

2 (i / A., - iA2y (6)

When the value A / corresponds to the error (step) of a discrete reading of the value of the measured level A / I.

With A, mm, mm, we have a discrete reference step of A / i level of 4 mm, which corresponds to a relative error of 8 0.4% for the measured range of + 1000 mm. With mm, A. mm, we find mm,, with MM, KI 4 mm, we will have mm,, 2%,

and at mm, A, mm we get L / 1 1 mm,, 1%, etc.

These data show that the choice of the deviation of the working length (frequency) of the generator can significantly affect the accuracy of the discrete level measurement and obtain a larger value from a practical point of view.

FIG. 3 shows a functional diagram of a device implementing the proposed method, where 1 is the surface of a liquid metal, 2 is a metal mirror, 3 is a generator of frequency-modulated oscillations, 4 is a valve, 5, 6, 7 are waveguides, 8 is a detector, 9 is an amplifier, 10 - counter resonant pulses.

The method is carried out as follows.

Electromagnetic oscillations of the microwave generator of frequency-modulated oscillations 3 are transmitted through waveguide 5 through valve 4 (an unwinding device preventing the propagation of waves in the opposite direction — from the load (resonator) to the generator) to the open resonator formed by a concave metal mirror 2 and the surface of the liquid metal 1. The oscillations in the resonator are excited by the open end of the waveguide 6 through a small hole in the center of the mirror; Oscillations are also collected, which are transmitted to the detector 8 and then to the amplifier 9 and the counter 10 of the number of detected resonant pulses through the waveguide 7. If the alternating frequency of the generator coincides with the clock

five

0

five

0

Tota of any type of longitudinal oscillations in the resonator, oscillations of this type are excited; the detector 8 extracts the corresponding resonant pulse, which, after amplification, enters the counter 10 as the counting unit.

Depending on the measurement conditions (measurement range, permissible error), the working wavelengths may be in the centimeter or millimeter wavelength range.

Note that the metal mirror 2 of the resonator can be made of brass, aluminum, steel, etc., followed by polishing. To facilitate construction, instead of a solid metal mirror, a metal grill or perforated mirror (holes) along its surface can be applied; This does not impair the functional properties of an open resonator.

Claims (1)

Invention Formula A method of measuring the level of a liquid metal, which involves exciting microwave oscillations in a fixed frequency range above the metal surface and counting the number of types of excited oscillations, characterized in that, in order to expand the scope of application by using measurements in open containers, the oscillations excite above the surface of the liquid metal normal to it, and as the counting use longitudinal types of excited oscillations. 200 400 600 800 1000 Ј, mm FIG. 2 , 2 lMMtbt-lMM tf-L, H mm, 2 2f1M D 6-A, 8mm, 2 Chmm nd Chmm g - / 60mm, L2 3QMM 0mm C5 XX X //// / ///////// х FIG. five