RU2260809C2 - Method for determination of two-terminal network parameters - Google Patents

Abstract

FIELD: measuring the parameters of produced electric and radio articles (resistors, capacitors, inductances), and also the parameters of the transducers of physical processes (temperature, pressure and level of liquid and granular media) at industrial installations and transport vehicles.

SUBSTANCE: proposed method consists in shaping the sinusoidal voltage in a measurable two-terminal network at n frequencies, where n is the number of elements of the two-terminal network in its equivalent circuit. The values of complex currents through the two-terminal network and standard are measured at each of n frequencies. The two-terminal network parameters are determined by its equivalent circuit and by fixed results of measuring the complex currents through the two-terminal network and standard at each of n frequencies.

EFFECT: possibility of measuring the parameters of a two-terminal network, remote from measurement means; simplification of the design of measurement means when conserving their high metrological qualities owing to simplification of action sequence.

1 cl, 5 dwg

Description

The invention relates to electrical engineering, and in particular to the measurement of electrical parameters of two-terminal devices, which is of significant practical interest for monitoring a wide range of manufactured radio products (resistors, capacitors, inductors), as well as two-terminal devices used as sensors of physical processes (temperature, pressure, liquid level and bulk media, etc.) at industrial facilities and vehicles.

A known method for determining the parameters of a two-terminal device described in patent No. 2144196, class. G 01 R 17/10, 27/02, which consists in balancing the bridge at the first frequency using the sign of the information projection of the unbalance signal at the second frequency, specifying the size of the controlled effects by changing one of the three adjustable parameters of the comparison arm in the definition of the unbalance signal modulus to the second frequency, and their direction is selected by the sign of the increment of this module during the test measurement of the third parameter of the comparison arm relative to its established value.

The disadvantages of the analogue include the low accuracy of determining the parameters of a two-terminal terminal remote for some distance (for example, a capacitive level sensor), low speed in some cases of its use, for example, in signaling devices when a level of a non-conductive liquid passes a given tank height.

The specifics of the operation of rocket and space technology products for measuring the parameters of bipolar sets its own requirements, contributing to the search for new technical solutions in the field of measurements. Denote the most characteristic of them:

- remoteness up to 500 meters of the measuring object from the measuring instrument. An example of this is the process of determining the parameters of the complex resistance of a capacitive refueling level sensor mounted in a rocket tank, which is located in the test building or on the launch complex during refueling with fuel components;

- high accuracy in measuring the parameters of a remote two-terminal device, which is a capacitive level sensor. Obviously, the accuracy of the measurement is directly related to the volume of guaranteed fuel reserves on board the rocket. The higher the accuracy, the lower the guaranteed fuel reserves, the higher the efficiency of the rocket, allowing to bring a large payload;

- the requirement of high technology rocket preparation, excluding the procedure for pre-setting the measurement equipment by a human operator;

- high speed of determining the parameters of the two-terminal network, which allows to expand the functionality of the measurement method and use it in a similar way in the level gauge of the on-board terminal automatic control system, which is the rocket fuel consumption control system.

The above requirements are prerequisites for finding more effective ways to determine the parameters of two-terminal devices.

The closest in technical essence and the achieved positive effect to the claimed method is the method described in the article by Yu.R. Agamalov, D.A. Bobylev, V.Yu. Kneller \ Measuring instrument-analyzer of complex resistance parameters based on personal computer \ in the journal \ Measuring technique \, 1996, No. 6, selected as a prototype or in the literature [1].

A method for determining the parameters of a two-terminal device, which consists in generating a sinusoidal voltage on a two-terminal device, measuring the complex current through a standard, and then determining the parameters of the two-terminal device, taking into account its equivalent circuit.

, где n - целое число. В результате каждого измерительного цикла получается напряжение, которое соответствует проекции вектора измеряемого напряжения на вектор фазосдвигающего опорного напряжения (симметричный прямоугольный меандр). Коды, несущие информацию о проекциях вектора измеряемого напряжения на вектор опорного напряжения, поступают в персональную электронную вычислительную машину (ПЭВМ) для вычисления действительной и мнимой составляющих напряжений на объекте измерения и резистивной мере. Из описания видно, что способ измерения, использованный в прототипе, требует фазовых измерений и четырехпроводной схемы подключения измеряемого двухполюсника.The method is based on one of the methods of indirectly measuring the parameters of the immitance during the formation of the voltage of a sinusoidal effect on the measurement object, which has found application due to the invariance with respect to the nature of the measurement object and its equivalent circuit. According to this method, two complex currents are measured, which are converted into proportional voltages, the voltage at the measurement object and at the resistive measure. In order to obtain the measurement information necessary for calculating the complex resistance or conductivity, the measurement circuit is connected cyclically from PC signals to the measurement object first and then to the resistive measure with the corresponding phase switching of the reference voltage with discreteness

where n is an integer. As a result of each measurement cycle, a voltage is obtained that corresponds to the projection of the measured voltage vector onto the phase-shifting reference voltage vector (symmetrical rectangular meander). Codes that carry information about the projections of the measured voltage vector onto the reference voltage vector are sent to a personal electronic computer (PC) for calculating the real and imaginary voltage components at the measurement object and resistive measure. It can be seen from the description that the measurement method used in the prototype requires phase measurements and a four-wire connection circuit for the measured two-terminal network.

When using the prototype for measuring the parameters of a remote measurement object, a result is obtained with a large measurement error. This is because the sinusoidal effect on the remote measurement object will receive an ambiguous phase shift due to the influence of a long line, and therefore, with respect to the cyclically phase-shifting reference meander, the sinusoidal effect will have an indefinite phase shift, which will lead to a significant measurement error.

Thus, the disadvantage of the prototype is the low accuracy of the measurement at a sufficiently remote from the measuring circuit measurement object.

In connection with the foregoing, the objective of the proposed method for determining the parameters of a two-terminal network is to expand the functionality, which consists in the possibility of determining the parameters of a two-terminal network, removed using a long line from the measuring instrument. Moreover, the measuring instruments created on its basis while maintaining high metrological qualities while simplifying the sequence of actions associated with the determination of parameters are quite simple.

The solution of this problem is achieved by the fact that in the method for determining the parameters of a two-terminal network, which consists in generating a sinusoidal voltage on a two-terminal network, measuring the complex current through a standard, followed by determining the parameters of a two-terminal network, taking into account its equivalent circuit, in contrast to the prototype, sinusoidal voltages are generated at n-given frequencies, where n is the number of elements of a two-terminal network, sequentially measure the values of complex currents through a two-terminal network and a reference at each n-h Moreover, after each measurement, their results are recorded, the parameters of the two-terminal are determined by the equivalent circuit and by the fixed measurement results at each of the given frequencies of the complex currents through the two-terminal and the standard.

The set of features that allows the claimed method to use amplitude measurements at n - frequencies, in contrast to the prototype, where phase measurements are used, makes it possible to expand the functionality of the method and to create significant technical advantages when creating real measuring instruments, namely:

- through a long line to determine the parameters of the two-terminal without a noticeable decrease in metrological characteristics (in some practical cases, the length of the connecting line can reach 100-500 meters);

- significantly simplify the structural diagram of the measuring instrument and, accordingly, its circuitry and cost.

For the practical implementation of the claimed method, the authors used the technology of computer-aided design of electronic circuits, built on the use of programmable logic integrated circuits (FPGAs) developed by Xilinx. It uses Foundation Series software. This design package includes a set of tools that allow the development of Xilinx FPGAs, from describing the internal contents of the device to loading the FPGA configuration and debugging directly on the circuit board. Foundation Series software allows you to implement all the necessary functions, including the implementation of numerical methods for calculating values.

Figure 1 presents the equivalent circuit of a two-element bipolar, the elements of which - inductance and resistor - are connected in series.

Figure 2 presents the equivalent circuit of a two-element bipolar, the elements of which, being the capacitance and inductance, are connected in parallel.

Figure 3 presents the equivalent circuit of the four-element bipolar.

Figure 4 presents a vector diagram of the equivalent circuit of the two-terminal network according to figure 3.

Figure 5 presents the equivalent circuit of a capacitive refueling level sensor.

The implementation of the method will consider the following examples. Figure 1 presents the equivalent circuit of a two-element bipolar, the elements of which are a resistor and inductance connected in series. The presented bipolar, the parameters of which must be determined, can be connected to the measuring instrument through a long line.

As a result of the formation of a sinusoidal voltage on the bipolar, a current flows through it, the value of which is determined by the measuring means. Since the two-terminal network is two-link, in accordance with the feature of the claims, it is necessary to measure the complex current I _P at two frequencies ω ₁ and ω ₂ . In this case, the following relations are true:

To determine the voltage values V _ω1 , V _ω2 at the two-terminal network, according to the invention, the complex currents are measured through a standard, for example, a resistor with resistance R _ET . The measurement results are recorded, that is, recorded in the memory of the computing device.

The values of the currents through the standard correspond to the expressions:

,

измерены и зафиксированы. В конечном счете, получаем два уравнения (1), (2) и два неизвестных параметра R, C.So, in accordance with the above features of the claims, the quantities I _ω1 , I _ω2 ,

,

measured and recorded. Ultimately, we obtain two equations (1), (2) and two unknown parameters R, C.

Solving these equations according to the equivalent circuit of the two-terminal network shown in figure 1, we have the following expressions for determining its parameters:

As a means of measurement, as an option, a device may be used, including a frequency-controlled sinusoidal voltage generator, energizing the measured circuit, as well as a current-voltage converter connected in series with an analog-to-digital converter. The latter is connected to a computing device that records the results of measurements of currents through a two-terminal device and a standard and, in accordance with expressions (5) and (6), determines the parameters of the two-terminal device.

,

измерены и зафиксированы, R_ЭТ, ω₁, ω₂ заданы. Поэтому значения параметров R, L определяются зависимостями (5) и (6) при использовании фиксированных и заданных параметров. При необходимости могут быть определены тангенс угла сдвига между током и напряжением, то есть могут быть определены все параметры двухполюсника.In expressions (5) and (6), the quantities I _ω1 , I _ω2 ,

,

measured and recorded, R _ET , ω ₁ , ω _{2 are} set. Therefore, the values of the parameters R, L are determined by dependencies (5) and (6) when using fixed and specified parameters. If necessary, the tangent of the shear angle between the current and voltage can be determined, that is, all parameters of the two-terminal can be determined.

Consider another example of the implementation of the method. Figure 2 presents the equivalent circuit of a two-element bipolar, the elements of which are inductance and electric capacitance and which are connected in parallel.

As a result of the formation of a sinusoidal voltage at the two-terminal network, a complex current flows through it, which is the sum of two currents, having the following form:

Since the two-terminal network is two-link, in accordance with the feature of the claims, measurement of the complex current must be carried out at two frequencies ω ₁ and ω ₂ . In this case, the following expressions are valid for the sum of currents:

Further, according to the feature of the claims, the complex currents are measured sequentially through a two-terminal network and a standard. The values of the currents through the standard correspond to expressions (3) and (4).

According to the given equivalent circuit of the two-terminal network shown in figure 2, we have the following expressions for determining its parameters:

,

измерены и зафиксированы, R_ЭТ, ω₁, ω₂ заданы. Поэтому параметры С и L определяются по зависимостям однозначно.In expressions (11) and (12), the quantities I _ω1 , I _ω2 ,

,

measured and recorded, R _ET , ω ₁ , ω _{2 are} set. Therefore, the parameters C and L are determined by the dependencies uniquely.

Consider a more general case of using the method.

Figure 3 presents the equivalent circuit of the four-link bipolar, and figure 4 is its vector diagram.

As a result of the formation of a sinusoidal voltage on the bipolar, a complex current flows through it.

The active components of the currents along the circuits of the two-terminal network correspond to the expressions:

The active component of the current in the total current circuit can be written as follows

The reactive components of the currents along the circuits of a two-terminal circuit are described by the expressions:

Then the reactive component of the complex current in the two-terminal circuit is written as

From the expressions (13) - (18) it follows that the complex current through the two-terminal network depends on the parameters of the elements (R ₁ , R ₂ , C, L) and the parameters of its supply (V, ω).

According to a feature of the claims, successive measurements of complex currents through a two-terminal device and a reference at each of the four specified frequencies are performed. The measurement results are recorded. Then, according to a given equivalent circuit, four parameters of a two-terminal device are calculated according to four dependencies, using fixed and given values.

As an applied example of the method, we consider the measurement of the parameters of a capacitive level sensor of a tank filling filled with a dielectric fluid (for example, kerosene).

A capacitive level sensor corresponds to the equivalent circuit shown in Fig. 5, where: С _Р is the working electric capacity of the sensor, which carries useful information about the level of the tank refueling. With _P when refueling the tank is a variable, since a change in the value of the electric capacitance makes the dielectric constant of the non-conductive fluid filling the sensor in the tank; R is the leakage current resistance through the dielectric, which depends on the grade of kerosene and the resistance state of the cable network. Due to the specifics of the operation of rocket and space technology products, the capacitive level sensor can be removed up to 500 meters from the measuring instrument. As shown above, the prototype in the presence of a line length will determine the parameters of the capacitive sensor very roughly. Therefore, in order to determine the parameters of the remote fuel level sensor, the claimed method is applied.

As a result of the formation of a sinusoidal voltage at the two-terminal network, the equivalent circuit of which is shown in Fig. 5, the following expressions are valid for the circuit currents:

I _C = V · ω · C;

According to the invention, the values of the complex currents are sequentially measured through a two-terminal network and a standard at two frequencies. The modules of the measured full currents through a two-terminal can be written as follows:

The values of the currents through the standard correspond to expressions (3) and (4).

According to the given equivalent circuit of the two-terminal network, we have the following expressions for determining its parameters:

Obviously, the method for determining the parameters of a two-terminal device with respect to the prototype allows to expand its functionality. The expansion of functionality consists in determining the parameters of a remote two-terminal device. In an example of a specific implementation of the method, the following are determined with high accuracy: the capacitive component of the impedance of the capacitive sensor, depending on the degree of filling with liquid; active component, which is characterized by the grade of kerosene and the state of insulation resistance of the cable network. Taking into account the active component of the dielectric fluid filling the sensor, when determining the level, the accuracy of measuring the level of the charge increases significantly, and accordingly the efficiency of the rocket increases due to a decrease in guaranteed fuel reserves.

Used Books

1. Agamalov Yu.R., Bobylev D.A., Kneller V.Yu. Measuring instrument-analyzer of complex resistance parameters based on a personal computer. Measuring technique. 1996, No. 6, p. 56-60.

2. K. B. Karandeyev, F. B. Grinevich, A. I. Novik. Capacitive self-compensated level gauges. M., \ Energy \, 1966, p. 135.

3. A.I. Novik. \ Systems of automatic balancing of digital extreme bridges of alternating current \, Kiev: Naukova Dumka, 1983, pp. 9-10.

4. RF patent No. 2025666, cl. G 01 F 23/26, \ Multipoint level switch (its variants) \.

5. Patent No. 2144196, cl. G 01 R 17/10, 27/02, \ Method for measuring the parameters of three-element two-terminal networks with frequency-independent AC bridges \.

Claims (1)

A method for determining the parameters of a two-terminal device, which consists in generating a sinusoidal voltage on a two-terminal device, measuring the complex current through a standard, followed by determining the parameters of the two-terminal device, taking into account its equivalent circuit, characterized in that sinusoidal voltages are generated at n given frequencies, where n is the number of elements of the two-terminal device, sequentially measuring the values of complex currents through a two-terminal network and a standard at each of n frequencies, and after each measurement Estimation of their results, determination of the parameters of a two-terminal device is carried out according to the scheme of its substitution and by the fixed measurement results at each of the given frequencies of complex currents through a two-terminal device and a standard.

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