Device for measuring concentration in mixture

FIELD: measuring engineering.

SUBSTANCE: device has long line whose end is connected with a sensor which is in a contact with the mixture. The sensor is connected to the circuit of generator which is connected with frequency meter. The sensor is made of a capacitor which is connected to the line through the main inductive coils and to the generator through the two additional coils. The line can be made of coaxial line or shielded two-wire line provided with the capacitive sensor made of cylindrical capacitor or shielded flat capacitor, respectively. The surface of at least one of the wires of the sensor which is in a contact with the mixture can be covered with a dielectric shell.

EFFECT: enhanced accuracy of measuring.

3 cl, 4 dwg

The invention relates to measuring technique and can be used for high-precision determination of the concentration of mixtures of different substances in tanks (process tanks, measuring cells and the like). In particular, it can be applied for measuring the concentration of the water-alcohol solutions, wine and wines in the wine industry.

Known devices for determining the concentration of mixtures based on differences in the electrophysical parameters of the fluids forming the mixture (U.S. Pat. USA N 4751476, NCI: 331/65; U.S. Pat. USA N 4767982, NCI: 324/640; European Pat. N EP 0902276, M CL: G 01 N 22/00; monograph: V.A. Viktorov, Lunkin BV, Sablukov A.S. radio-wave measurement of parameters of technological processes. M.: Nauka. 1989. S-177). These devices include capacitive and high-frequency (HF) radio wave sensing elements (capacitors, segments long lines, resonators and other). The drawback of such measuring devices is their low accuracy, due to the dependence of the measurement results from the dispersion and instability in practice, values of input capacitors communications HF radio wave sensors with electronic modules measuring devices.

It is also known technical solution (monograph: V.A. Viktorov, Lunkin BV, Sablukov A.S. high-Frequency measuring method is not elektricheskij values. M.: Nauka. 1989. P.42-43, 87-88), which contains the device description, the technical essence is the closest to the proposed device and is taken as a prototype. This device is a prototype contains a segment of the long lines that is included as a frequency control element in an oscillator circuit connected to the frequency counter. This device allows you to define various process parameters, including the concentration of the mixture of substances.

A disadvantage of this device prototype is a low accuracy of measurement due to instability used capacitive input connection.

The aim of the invention is to improve the accuracy of measurement.

The goal in the proposed device for measuring the concentration of a mixture of substances, containing a segment of a long line terminator in contact with a controlled mixture of the sensing element included with elements of communication in customizados oscillator circuit connected to the frequency provided by the fact that the sensitive element is made capacitive, and elements of communication - in the form of coils with one main connected to the input of a segment of a long line, and two additional, connected to the oscillator windings. A long line can be made in view of the coaxial line, and the capacitive sensor element in the form of a cylindrical capacitor. A long line can be made in the form of a shielded two-wire line, and a capacitive sensing element in the form of a flat capacitor. The surface conductors of the sensing element in contact with a controlled substance, can be covered with a dielectric shell.

A distinctive signs, according to the authors, is, first, a long line is a coaxial line with a capacitive sensor element in the form of a cylindrical capacitor or in the form of a shielded two-wire line with a capacitive sensor element in the form of shielded planar capacitor. Secondly, the implementation of the elements of communication cut a long line with the oscillator in the form of coils with one main connected to the input of a segment of a long line, and two additional, connected to the oscillator windings. Thirdly, the surface of at least one of the conductors of the sensing element in contact with a controlled substance, covered by a dielectric sheath.

The set of distinctive features of the proposed device makes it new properties provide significant opportunities to reduce the impact of unstable couples the TRS inputs on the informative value of the parameter as well as reducing the dimensions (length long lines).

This property provides a useful effect, formulated in the objectives of the proposals.

Figure 1 and figure 2 schematically depicts variants of the proposed device. Figure 3 shows the equivalent circuit of the sensor of the device. Figure 4 shows the experimentally obtained plot of the change of the operating frequency on the concentration of the water-alcohol mixture. Here we have introduced the notation: 1 - sensitive element, 2 - piece long line, 3 - coil, 4 - oscillator, 5 - meter, 6, 7 and 8, respectively, primary and secondary winding coils, a 9 - dielectric shell, 10, 11, 12 and 13 of the electrodes of the sensing element, 14 - metal cavity 15 is grounded conductor (screen).

In the first variant of realization of the device the sensor element 1 can be made in the form of a capacitor with coaxial spaced plates (figure 1). Its Central electrode 10 is placed in a sealed dielectric shell 9. The outer electrode 11 (the screen) is electrically connected to the outer conductor of the coaxial line 2. In the second variant of realization of the device (figure 2) sensor element 1 may be a plate capacitor consisting of two electrodes 12 and 13, in use the second cavity 14 (screen). This cavity (screen) electrically connected to the grounded conductor 15 - screen two-wire line 2, is made, in particular in the form of a metal pipe. At least one or each (as shown in figure 2) of these electrodes in figure 1 and figure 2 also entered into a pressurized dielectric shell 9.

In the first variant of realization of the device (figure 1) piece long lines are made in the form of a segment of coaxial line with the sensor element 1 at one of its ends to form a cylindrical capacitor; the other end of the segment of this line is connected to the inductor 3. In the second case (figure 2) cut long lines are made in the form of a segment of a shielded two-wire line with shielded planar capacitor on one end; the other end of this line segment as in the first variant of realization of the device connected to the inductor 3.

The inductor 3 contains three windings 6, 7 and 8: one basic 6 and two additional 7 and 8. The primary winding 6 is connected with a segment of a long line (coaxial or two-wire) sensor element 1, and the secondary windings 7 and 8 are used for inductive coupling with the oscillator 4 and are intended, respectively, for excitation of electromagnetic waves in the segment of long lines and removal of informative signal. PR is additional windings 7 and 8 must have a minimum of communication directly between themselves. Therefore, they are located at opposite ends of the primary winding 6.

The device operates as follows. The sensing element 1, the length of the longest line 2 and the coil 3 forms an electromagnetic oscillating system. Resonant frequency of the electromagnetic waves depends on the parameters of all of its elements. The parameters of a segment of a long line 2 and the coil 3 is stable and practically does not depend on the parameters of controlled substances. Therefore, the resonance frequency varies functional only with the capacitance of the sensing element 1, which, in turn, depends on the electrophysical parameters (dielectric constant, tangent of dielectric loss angle) controlled substance, which fills the space between the conductors of the sensing element 1. In particular, such a substance may be water-alcohol mixture or wine, the percentage of alcohol which is to be determined.

Since this oscillatory system is included in customizados the oscillator circuit 4, which in the long line segment 2 with the load sensitive element 1 is excited by electromagnetic oscillations. The frequency of oscillation of the oscillator 4 corresponds to the resonant frequency of this oscillatory systemize frequency generation using a frequency counter 5, connected to the oscillator 4, you can define the electrophysical parameters of controlled substance and functionally associated with them the concentration of the mixture of substances.

Water/alcohol mixture, including water-alcohol solutions, wine, wine, etc. are imperfect dielectrics. Therefore, to increase the quality factor of the considered vibrational system and, accordingly, the possibility of obtaining information by measuring the frequency of oscillation dependent on the resonant frequency of the vibrating system, at least one electrode, in particular the Central electrode of the coaxial sensor element (cylindrical capacitor), and one or both electrodes symmetrical sensing element (flat capacitor), respectively, in the first and second variants of its implementation, is placed in a dielectric sheath 9, preventing the same penetration of a controlled substance in the space between the conductors cut the long line 2 (see figure 1 and figure 2). When this substance with arbitrary electrophysical parameters is here one of the layers of a two-layer dielectric, characterized by an effective dielectric constant.

The operating frequency range of a segment of a long line 2 with the stress sensitive element 1 depends on the length of the OTP the lubricant line. At a length of 1 m operating frequency ~ 75 MHz (for short-circuited at one end of the line segment; the frequency change is determined by the measurement range of the concentration of the mixture).

The considered length of longest line 2 with the target sensor element 1 and the inductor 3 - oscillatory system can in General be represented as the equivalent circuit shown in figure 3. Are denoted as follows: L is the inductance of the actual coil; L_NRthe inductance introduced by the elements of communication; C_NR- capacity introduced by the elements of communication; C_l- capacity of a segment of a long line connecting the inductor and the sensing element 1; C_se- capacity sensor element in the absence of a controlled substance.

Thus, in particular, in an actual device on the basis of a segment of coaxial long line values for these elements are as follows: L=5 mH, C_l=2 pF_se=6,5 pF. The sizes of the segment of coaxial line: length 100 mm, diameter of outer conductor (screen) 10 mm, the diameter of the inner conductor 1 mm Dimensions sensing element: length 50 mm, diameter of the screen 23 mm, the diameter of the inner conductor 12 mm, the thickness of the dielectric coating PTFE 1 mm using these values, the working frequency of the device is ~ 25 MHz in the absence of a controlled substance and ~ 12 MHz when preparing the drop it in the water-alcohol solution. Figure 4 shows experimentally obtained plot of the change of the operating frequency f - f(9,2%), in kilohertz, percentage of alcohol in water in the range of its change of 9.2%to 15.1%. Here ƒ(9,2%) - the value of the operating frequency f C=9.2 percent. When conducting these measurements are applied considering the device on the basis of a segment of coaxial line with the above parameters. This graph shows the health of the device and the possibilities of its practical application for measuring the concentration of substances.

To ensure maximum sensitivity to the monitored parameter (concentration) requires the following inequality: C_se>>_l+C_NR. In practice, do this condition is not always possible; however, when the above-mentioned, in particular, the specific parameter values of the elements of the sensitivity of the device is quite sufficient. In addition, to ensure minimum error is necessary to minimize the value of_NRbecause this value is the most unstable. Its value is determined by the relevant capacity of the communication lines and self-capacitance of the oscillator.

A comparative analysis of two types of communication - capacitive as in the prototype, and inductive considered here, the preference trail is tons to do, since this type of link capacity With_NRminimum.

In addition, to ensure reliable operation of the device with symmetric sensitive element is a flat capacitor must have symmetrical (with two additional windings) excitation, which is best implemented only when inductive coupling is used in the proposed device.

In the proposed device long line 2 may, at the same operating frequency range, as in the prototype, to have a substantially shorter length due to the appropriate selection of the values of the inductances 6, 7 and 8 of the inductor 3. This allows you greatly reduce the size of the device.

Thus, the proposed device provides high-precision determination of the concentration of various wine, wines, water-alcohol solutions and other mixtures of different substances.

1. Device for measuring the concentration of a mixture of substances, containing a segment of a long line terminator in contact with a controlled mixture of the sensing element included with elements of communication in customizados circuit oscillator connected to a frequency, wherein the sensitive element is made capacitive, and elements of communication - in the form of coils on one core, podsoednineny to the input of a segment of a long line, and two additional, connected to the oscillator windings.

2. Device for measuring the concentration of the mixture of substances according to claim 1, characterized in that the long line is made in the form of a coaxial line, and a capacitive sensing element in the form of a cylindrical capacitor.

3. Device for measuring the concentration of the mixture of substances according to claim 1, characterized in that the long line is made in the form of a shielded two-wire line, and a capacitive sensing element in the form of shielded planar capacitor.

4. Device for measuring the concentration of the mixture of substances according to claim 1, characterized in that the surface of at least one of the conductors of the sensing element in contact with a controlled substance, covered by a dielectric sheath.