RU2532424C1 - Viscose fibre humidity measuring method - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention relates to measurement equipment, and namely to humidity measurement of fibrous materials, and can be used in textile and cotton industry. The proposed method involves arrangement between two electrodes of a fibre sample, application to them of alternating voltage and monitoring of current flowing through the material. Fibre sample pressing is performed till its volumetric density of material, which exceeds 400 kg/m³; alternating voltage with frequency of ≤50 Hz and 20-100 kHz is subsequently applied to the electrodes; corresponding currents (I₁ and I₂) flowing between the electrodes are monitored, and a value of offset current flowing through the sample is determined by the following formula: $${{\displaystyle I}}_{off}=\sqrt{{{\displaystyle I}}_2^2-{{\displaystyle I}}_1^2}-{{\displaystyle I}}_0,$$

where I₀ - a background value of current, which is controlled between the electrodes on frequency of 20-100 kHz at absence of a fibre between the electrodes; then, the value of water mass of the tested fibre sample is determined based on pre-defined dependence of offset current on mass of water in the fibre.

EFFECT: improvement of sensitivity and measurement accuracy of humidity of a fibre.

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Description

The invention relates to measuring equipment, in particular to measuring the moisture content of fibrous materials, and can be used in the textile and cotton industries.

The residual moisture content of viscose fiber determines its quality and is subject to mandatory control in industrial production. Improving the objectivity of this control allows you to improve the technical and commercial indicators of the fiber.

Known thermogravimetric method for controlling the water content in the fiber, based on the registration of changes in its mass during heating in the drying chamber (Analytical control of the production of artificial fibers. A reference book edited by A.K. Dibrov and BC Matveev. - M.: Chemistry. - 1986.- 334 p.).

The reasons that impede the achievement of the required technical result when using the known method include a high duration (4-5 hours) of measurements and their low objectivity (portions of fiber weighing hundreds of grams are used).

There is a method of determining the moisture content of a substance, based on the multiple passage of electromagnetic microwave signals through its sample and the subsequent determination of the average value of the measured value (RI Saytov, RG Abdeev, N.A. Serafimov and others. - Patent of the Russian Federation No. 2380689 Method of measuring the humidity of materials. Publ. 01/27/2010).

The reasons that impede the achievement of the required technical result when using the known method include the fact that it uses sophisticated experimental equipment and analyzes samples of material weighing tens of grams. As a result, the required objectivity of humidity control of industrial batches of products is also not achieved.

The closest method of the same purpose to the claimed object according to the totality of features is a method for measuring the moisture content of viscose fiber, which consists in applying an alternating voltage to two electrodes between which a sample of the pressed test material is located and measuring its electrical conductivity (I. Foreit. Capacitive sensors of non-electric quantities. - M.-L.: Energy. - 1966. - P.15, 99 - prototype).

For reasons that impede the achievement of the required technical result when using the known method adopted as a prototype, the known method employs a single-frequency mode (from the range of 0.2-5.0 MHz) for measuring the electrical conductivity of samples of the material under study. As a result, the controlled value of the current passing through the fiber, in addition to the bias current (informative parameter), also includes the conduction current. These currents are phase shifted relative to each other by an angle of (90-δ) degrees (δ is the angle characterizing the dielectric loss in the fiber). The values of the components of the controlled current and δ in various ways depend on the frequency of the voltage applied to the sample of the studied fiber, its moisture content and the degree of pressing. Ignoring these factors, as is done in the prototype, leads to significant uncontrolled errors.

The objective of the invention is to increase the sensitivity and accuracy of the dielcometric method for measuring fiber moisture.

This technical result is achieved during the implementation of the invention by the fact that in the known method, comprising applying an alternating voltage to two electrodes, between which a sample of pressed viscose fiber is placed, and measuring its electrical conductivity, the fiber sample is pressed to a bulk material density of more than 400 kg / m ³ . Then alternating voltage with an amplitude of 20-30 V with a frequency of ≤50 Hz and a frequency of (20-100) · 10 ³ Hz is sequentially applied to the electrodes, the corresponding currents (I ₁ and I ₂ ) flowing between the electrodes are controlled, and the bias current value is determined passing through the sample according to the formula:

in which I ₀ is the background current value, controlled between the electrodes at a frequency of (20-100) · 10 ³ Hz in the absence of fiber. After that, the amount of water mass in the fiber sample under study is found based on a previously established dependence of the bias current on the mass of water in the fiber.

The above technical result is achieved by choosing the optimal density of the investigated fiber and using the control of the current passing through it at two different frequencies.

When the fiber density is less than 400 kg / m ³ , the values of the monitored currents I ₁ and I _{2 are} affected by transition capacities at the fiber-measuring electrodes interface, which depend on the mass of the fiber sample and its location relative to the electrodes. At a fiber density greater than 400 kg / m ³ , the indicated interface is enriched with excess water and the transition capacities disappear, which ensures the stability of the recorded signals and minimization of measurement errors.

The current through the fiber, controlled at a frequency less than 50 Hz, is equal to the conduction current (I ₁ ), and at a frequency of 20-100 kHz - the vector sum of the conduction currents and bias current. Moreover, δ with fiber moisture in the practically important range of 4-12% is close to zero. As a result, it is possible to easily determine the true bias current passing through the fiber and uniquely associated with the mass of water in it.

Using the amplitude of an alternating voltage of 20-30 V provides a relative error in measuring currents at a level of 1-2%.

In the process of analyzing the prior art, no technical solutions are identified that are characterized by the features of the claimed invention. A comparison of the proposed solution with the analogue closest in the totality of features made it possible to identify the totality of significant distinguishing features to achieve a technical result. The analysis also showed that the claimed invention does not follow for experts explicitly from the prior art, since no technical solutions have been found in which the water content in viscose fiber is controlled at a certain density based on registration of currents passing through the fiber sample at two different frequencies .

Thus, a comparative analysis of the proposed technical solution and the prior art allowed us to establish that the claimed invention meets the requirement of "novelty" and "inventive step" under the current law.

Drawings illustrating features of the implementation of the proposed method are presented in figures 1-5. Here, Figs. 1-2 show frequency dependences of the real and imaginary parts of the dielectric constant of the fiber, controlled at different moisture levels (ρ _H20 , kg / m ³ : 1-0; 2-40; 3-50; 4-64); figure 3 - frequency dependence of the angle of dielectric loss of the fiber (ρ _H20 , kg / m ³ : 1-0, 2-52, 3-64, 4-76, 5-104); figure 4 - dependence of the bias current passing through the fiber, on the mass of water in it; and figure 5 is a dependence on the degree of compaction of the fiber of the normalized value of the controlled current (fiber moisture 10%, the frequency of the probing voltage is 20 kHz, the amplitude is 20 V).

Information confirming the possibility of implementing the proposed invention to obtain the above technical result are as follows. A sample of viscose fiber is placed in a measuring chamber (a shape close to cubic) and pressed to obtain a fiber density of at least 400 kg / m ³ . Then, a sinusoidal voltage is applied to two measuring electrodes located on the inner surface of the opposite sides of the chamber and the current passing through the fiber is monitored. The magnitude of this current is uniquely related to the amount of water in the fiber sample.

When implementing known methods for controlling fiber moisture (for example, a prototype), current measurements are carried out at a single frequency in the range from 0.2 to 5.0 MHz. At the same time, in the recorded useful signal (I _meas ), in addition to bias currents (I _cm is an informative parameter that is uniquely associated with the water content in the fiber), there is a conduction current (I _pr ) and a stray current passing through the chamber in the absence of fiber (I ₀ ) The amplitude value of the conduction current in an uncontrolled manner depends on the density of the fiber, its chemical composition and humidity. In addition, I _pr shifted relative to I _cm at an angle (90-δ). The dielectric loss angle also depends on the electrophysical properties of the fiber and the frequency of the probe signal. The sought current in this case is determined by the ratio:

From the resulting expression it follows that the determination of the amount of water in the fiber by I _{cm is} carried out with a variable error (I _CR and δ are variable values), which is not possible to take into account.

The indicated uncertainty can be eliminated by an individual determination of the conduction current and the choice of the probe voltage frequency at which the dielectric losses in the fiber are negligible (δ is close to zero).

Conductivity current can be determined using alternating voltage with a frequency not exceeding 50 Hz. At a constant current, these measurements are hindered by the processes of ion-migration polarization of the fiber (current transfer in the volume of electrolytic cells formed in places of local water accumulation in the fiber). At a frequency greater than 50 Hz, a bias current begins to be superimposed on the controlled value and the measurement error I _pr is 3-7%.

The selection of the high-frequency voltage range was carried out on the basis of a study of the electrophysical properties of the fiber — the frequency dependences of the real (ε ′) and imaginary (ε ″) parts of the dielectric constant of the fiber at different water contents were controlled. The obtained dependences are presented in FIG. 1-2, respectively.

The ε ″ dependence has a maximum of about 10 ⁶ Hz, which corresponds to the process of orientation of water molecules (dipoles) adsorbed on the fiber surface in the direction of the applied field. At a fiber moisture content exceeding 12%, ε ″ increases, which indicates the appearance of another polarization mechanism with a long characteristic time — macropolarization of the electrolyte filling individual pores of the fiber.

The real part of the dielectric constant of the fiber at low frequencies (up to 10 ⁵ Hz) varies slightly (figure 2), significantly increasing at a humidity exceeding 11%.

The dielectric loss angle when the fiber moisture is less than 12% and the frequency of the voltage used does not exceed 100 kHz is close to zero (Fig. 3).

When choosing the optimal frequency range of the probing high-frequency voltage, the following circumstances were taken into account. At a frequency less than 20 kHz, the controlled current begins to decrease markedly - the capacitance of the fiber increases. At a frequency greater than 100 kHz, a decrease in ε ′ and an increase in the dielectric loss angle become significant. In the frequency range 20-100 kHz, the desired value of the bias current passing through the fiber can be determined by a simplified formula:

where I ₂ = I _ISM and I ₁ = I _CR - currents through the fiber, controlled at a frequency of 20-100 kHz and 1-50 Hz, respectively.

The desired value of the mass of water in the fiber under study is found according to a pre-established relationship between the bias current passing through the fiber and the water content in it - Fig. 4.

The magnitude of the current passing through the fiber is critical to the degree of compression — FIG. 5. This fact is due to the existence of a transition capacitance at the fiber-electrode surface interface. With a fiber density greater than 400 kg / m ³ , the influence of this factor becomes insignificant.

Implementation of the proposed method was carried out under conditions of production on bales of fiber located in the final pressing chamber (chamber dimensions - 940 × 570 × 500 mm). The amplitude of the voltages applied to the measuring electrodes was 20 V, the frequencies were 20 Hz and 20 kHz, respectively. Assessment of the integral water content in bales of viscose fiber was carried out on the basis of a calibration curve pre-installed on a reduced layout of the compression chamber shown in FIG. 4. After weighing the bale, the moisture content of the fiber (V _ex ) in it was determined, which was then compared with the results of fiber moisture assessment performed 5-6 times by the standard method (B ₀ - thermogravimetric method). The obtained measurement results are presented in the table.

In _ex 8.6-8.8 7.8-8.1 8.4-8.5 12.0-12.4 At ₀ 7.8-13.0 7.2-10.3 8.1-9.4 9.3-13.3

From the analysis of the results it follows that there is a qualitative coincidence of In _ex and In ₀ . Moreover, the developed method is characterized by significantly greater objectivity and repeatability of the results. This circumstance is a consequence of a small sample of fiber portions when using the standard method for assessing its moisture content.

Using the proposed method allows to increase the objectivity of measuring the water content in viscose fiber, which improves its quality and commercial indicators.

Claims (1)

A method for measuring the water content in viscose fiber, which consists in applying an alternating voltage to two electrodes between which a sample of the pressed test material is placed, and measuring its electrical conductivity, characterized in that the fiber sample is pressed to a bulk density of the material exceeding 400 kg / m ³ , then alternating voltage with a frequency of ≤50 Hz and a frequency of 20-100 kHz is sequentially applied to the electrodes, the corresponding currents (I ₁ and I ₂ ) flowing between the electrodes are controlled, and determined the bias current passing through the sample, according to the formula:
$${{\displaystyle I}}_{\mathrm{from}m}=\sqrt{{{\displaystyle I}}_2^2-{{\displaystyle I}}_{\mathrm{one}}^2}-{{\displaystyle I}}_0$$

,
in which I ₀ is the background current value, controlled between the electrodes at a frequency of 20-100 kHz in the absence of fiber, and then find the amount of water mass in the fiber sample under study based on a pre-determined dependence of the bias current on the mass of water in the fiber.

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