RU2695030C1 - Device for double-probe measurement of phase shifts of distributed rc-structure - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention can be used to estimate electrophysical characteristics of media described by a model of distributed RC-structures. Disclosed is a device for double-probe measurement of phase shifts of a distributed RC structure, into which operational amplifier (5) is inserted, an inverted input of which is connected to one probe (4) and through a first resistor (R1) – with its output and a signal input of phase-sensitive element (6), which output is connected to analogue-to-digital converter (ADC) 7 input. PC output (9) is connected to the control input of generator (1), the output of which is connected to other probe (3) and the reference input of phase-sensitive element (6). Both probes are connected to the distributed RC structure (2) used as the measured device; non-inverting input of operational amplifier (5) through second resistor (R2) is connected to common bus.

EFFECT: high accuracy of measuring electrophysical parameters of a distributed RC structure, simplifying and accelerating the measurement process.

1 cl, 2 dwg

Description

The device of two-probe measurement of phase shifts of a distributed RC-structure refers to the measurement technique and can be used to assess the electrophysical characteristics of the media described by the model of distributed RC-structures.

The known devices for measuring phase shifts of distributed RC structures are based on isolating individual harmonic signals of the same frequency and measuring the time interval between points with the same phase and then dividing by the period of the harmonic signal (For example, article Siblini A., Souquet S., Mesnard G. Automatic VLF sinusoidal signals./ Electronique Techn. And Industry, 1984, No. 11, pp. 62-66; books 1) VP Bukhgolts, E.T. Tisevich Capacitive converters in systems of automatic control and management. - M .: Energy, 1972, 2) Measurements in industry. Reference book. Book 1 / Under. Ed. P.Profosa ”, p. 359; RF patent №2244937 C1 Two-probe method of measuring phase shifts in a balance ring, IPC G01R 25/02, publ. 01/20/2005, bul. No. 1, etc.).

For the measurement of phase shifts, a sinusoidal signal generator is used, controlled in accordance with the program for finding the desired result. The program includes both various connections of the measurement object and the processing of the obtained results. This lengthens the measurement process, is a source of errors, which ultimately increases the cost and reduces the accuracy of measuring phase shifts.

Closest to the proposed device is described in the patent of the Russian Federation No. 2244937, G01R 25/02, adopted for the prototype.

The layout of the prototype device is shown in FIG. 1, where indicated:

1 - generator;

2 - measured device (distributed RC-structure);

3, 4 - probes;

6 - dual probe phase sensitive element;

7, 14 - the first and second analog-to-digital converter (ADC);

8 - interface;

9 - PC;

10 - 3-decibel balanced divider;

11 - phase modulator;

12, 13 - the first and second valves;

15, 16 - the first and second detector sections.

The prototype device contains a series-connected 1, 3-decibel balanced divider 10, phase modulator 11, measured device 2, and a second valve 13, the output of which is connected to the first input of the two-probe phase-sensitive element 6. Another output of the 3-decibel balanced divider 10 through the first valve 12 is connected to the second input of the two-probe phase-sensitive element 6. In this case, the first probe 3 of the two-probe phase-sensitive element 6 is connected in series with the first detector section 15 and the first The CPU 7 is connected to the corresponding input interfaces (matching) 8. The second probe 4 through a serially connected second detecting section 16 and the second ADC 14 is connected to a corresponding input of the coupling device 8, whose output is connected with the PC 9.

The device prototype works as follows.

The continuous microwave signal from the generator 1 is divided into two arms with equal amplitudes in a 3-decibel balanced divider 10. Next, the signal from one of the arms of the 3-decibel balanced divider 10 is fed to the phase modulator 11 and through the measured device 2 and the second valve 13 - to the first input of the two-probe phase-sensitive element 6. The signal from the second arm (reference signal) through the first valve 12 enters the second input of the two-probe phase-sensitive element 6. Next, the signals from the two-probe phase-sensitive element 6 are detected The first 15 and second 16 detector sections, respectively, are digitized in the first 6 and second 14 analog-to-digital converters and received through the interface device 8 in the PC 9.

The measurement cycle consists of two clock cycles differing by the state of the phase modulator 11 (0 or 180 degrees), each of which measures the amplitudes of the signals from two probes 3 and 4 of the two-probe phase-sensitive element 6 following a command from PC 9, followed by calculating the phase shift entered by the measured device 2, according to the proposed for this method, the expression with the registration results in the PC 9.

The disadvantages of the prototype device are its complexity, the long duration of the measurement process, the low accuracy of the measurement result due to the influence of the parasitic parameters of the probes and switching devices.

To solve this problem, the device for measuring the phase shifts of a distributed RC structure, comprising a generator, a measuring device, a phase-sensitive element and two probes, as well as serially connected analog-to-digital converter (ADC), matching device and personal computer (PC), according to the invention, An operational amplifier is introduced, the inverse input of which is connected to one probe and through the first resistor to its output and signal input of the phase-sensitive element, the output of which is connected to the input of the ADC, When the output of the PC connected to the control input of the generator, whose output is connected to the other probe and the reference input of phase change element, wherein both probes are connected to a distributed RC-structure, is used as a measuring device; non-inverted input of the operational amplifier through the second resistor is connected to the common bus.

The scheme of the proposed device is shown in figure 2, where indicated:

1 - generator;

2 - distributed RC-structure (measured device);

3, 4 - the first and second probes;

5 - operational amplifier;

6 - phase sensitive element;

7 - analog-to-digital converter (ADC);

8 - matching device;

9 - personal computer (PC);

R1, R2 - the first and second resistors.

The proposed device contains serially connected operational amplifier 5 and a phase-sensitive element 6, the output of which is connected through serially connected ADC 7 and matching device 8 by bus to PC 9, the output of which is connected to the control input of generator 1, one output of which is connected to common bus. At the same time, another output of the generator 1 is connected to the first probe 3 and the reference input of the phase-sensitive element 6. The output of the operational amplifier 5 through the first resistor R1 is connected to its inverse input and the second probe 4. The non-inverted input of the operational amplifier 5 is connected to the common bus through the second resistor R2. Thus, in the negative feedback of the operational amplifier 5 through two probes 3 and 4 a distributed RC-structure 2 is connected, which is the measured device.

The proposed device works as follows.

Distributed RC-structure 2 is connected through the first 3 and second 4 probes to the negative reverse circuit of the operational amplifier 5, which ensures the appearance of a harmonic signal at its output. The phase-sensitive element 6 converts the change in phase of the signal into a change in amplitude, which is obtained at its output.

The harmonic signal of the 1 U _G generator set using the PC 9 is fed to the first probe 3 connected to the distributed RC structure 2. As a result, the output of the operational amplifier U _U will have a harmonic signal defined by the following formula:

, (1) $$U_{\mathrm{Have}}=U_R\left[\frac{j\omega R{C}_{RC}}{j\omega R_{RC}{C}_{RC}+\mathrm{one}}\right]$$

, (one)

where U _G - the voltage at the output of the generator 1; U _Y - the voltage at the output of the operational amplifier 5; R is the value of the resistor 6 of the operational amplifier 5; j = (- 1) ^½ is the imaginary unit; ω = 2πf is the circular frequency of the harmonic signal; R _RC and C _RC are equivalent resistance and capacitance of a distributed RC structure.

Equivalent capacity of a distributed RC structure can be defined as

, (2) $$C_{RC}=A\cdot {\epsilon }_a$$

, (2)

– конструктивный параметр зонда, м; $${\epsilon }_a={\epsilon }_0\epsilon$$

– абсолютная диэлектрическая проницаемость среды ( $${\epsilon }_0={(36\pi \cdot {10}^9)}^{-1}$$

, Ф/м; $$\epsilon$$

– относительная диэлектрическая проницаемость; $$C_{RC}$$

- ёмкость датчика, Ф.Where $$A$$

- constructive parameter of the probe, m; $${\epsilon }_a={\epsilon }_0\epsilon$$

- absolute dielectric constant of the medium ( $${\epsilon }_0={(36\pi \cdot {\mathrm{ten}}^9)}^{-\mathrm{one}}$$

, F / m; $$\epsilon$$

- relative dielectric constant; $$C_{RC}$$

- sensor capacity, F.

Equivalent resistance is represented as

, (3) $$R_{\mathrm{TO}\mathrm{WITH}}=A^{-\mathrm{one}}{\sigma }^{-\mathrm{one}}$$

, (3)

– тот же конструктивный параметр датчика, м; $$\sigma$$

– удельная электропроводность среды, См/м; $$R_{КС}$$

- активное сопротивление датчика, Ом.Where $$A$$

- the same design parameter of the sensor, m; $$\sigma$$

- specific electrical conductivity of the medium, S / m; $$R_{\mathrm{TO}\mathrm{WITH}}$$

- active resistance of the sensor, Ohm.

Therefore, the product R _RC * C _RC can be represented as

. (4) $$R_{\mathrm{TO}\mathrm{WITH}}{C}_{RC}=A^{-\mathrm{one}}\cdot {\sigma }^{-\mathrm{one}}\cdot A\cdot {\epsilon }_a={\epsilon }_a/\sigma$$

. (four)

Substituting the result (4) into formula (1), one can determine the phase shift of the harmonic signal φ resulting from the output of the operational amplifier 5 relative to the signal at the output of the generator 1

. (5) $$\phi =arcctg\left(\frac{\omega \cdot {\epsilon }_a}{\sigma }\right)$$

. (five)

The reference input of the phase-sensitive element 6 receives a harmonic signal from the generator 1 output, and its signal input receives a harmonic signal from the output of the operational amplifier 5. The output of the phase-sensitive element 6 produces a signal proportional to the phase shift φ according to the formula (5) and is fed to the ADC input 7, from the output of which through the interface device 8, this signal enters the PC 9, where it is memorized and processed. To control the operation of the generator 1, the output of the PC 9 is used, with the help of which the setpoint frequency of the generator 1 is set, on and off.

To ensure a given accuracy of measuring the phase shift φ, the ratings of resistors R1 and R2 should be the same. Formula (5) also indicates the absence of the influence of the design parameters of probes 2 and 4 on the result of measuring the phase shift.

Phase sensitive element can be performed, for example, as described in the book Marché J. Operational amplifiers and their application. Per. from French L. "Energy", 1974, p. 86, fig. 5-57.

Other blocks are well known and their implementation is not difficult.

The proposed device can be used to determine other characteristics of a distributed RC structure: the dielectric loss tangent, the conductivity of the underlying surface, the dielectric constant, etc. in the same way as described in the patent of the Russian Federation 2671299, G01V 3/08 /

Thus, in comparison with the prototype, the claimed device allows improving the accuracy of measuring the electrophysical parameters of a distributed RC structure while simplifying and speeding up the measurement process.

Claims (1)

A device for measuring the phase shifts of a distributed RC structure, comprising a generator, a measured device, a phase-sensitive element and two probes, as well as serially connected analog-to-digital converter (ADC), a matching device and a personal computer (PC), characterized in that an operational amplifier is inserted, the inverse input of which is connected to one probe and through the first resistor to its output and to the signal input of the phase-sensitive element, the output of which is connected to the input of the ADC, while the output of the PC is connected to the control -governing generator input, whose output is connected to the other probe and the reference input of phase change element, wherein both probes are connected to a distributed RC-structure, is used as a measuring device; non-inverted input of the operational amplifier through the second resistor is connected to the common bus.

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