RU2150709C1 - All-pass multiple-arm alternating current transformer bridge for measuring parameters of three-piece dipoles using serial rlc circuit and method for its balancing - Google Patents

Abstract

FIELD: electric instruments. SUBSTANCE: method involves separate sampling of measured parameters according to switch turn number of grounded windings of voltage transformers with close inductive connection, when constant resistor is used in comparison arm and amplitude zero indicator is used in measuring arm of multiple-arm alternating current transformer bridge. Bridge balancing method involves balancing with respect to two different-type parameters at frequency, which is greater than given sampling frequency of measured parameters, and subsequent balancing operations with respect to sampling parameter of measured capacitance and sampling parameter of measured inductance at frequencies, which are less and greater than given frequency. EFFECT: increased precision and speed of parameters measurement using serial RLC circuit. 2 cl, 1 dwg

Description

 The invention relates to the field of electrical engineering, and in particular to bridge methods for measuring alternating current parameters of three-element bipolar circuits according to a serial RLC-scheme, independent of frequency.

Known closest to the claimed device in the group of inventions for a combination of features of the same purpose and therefore selected as a prototype frequency-independent four-arm AC bridge for measuring the parameters of a series oscillatory circuit (AS 413430 (USSR), MKI ² G 01 R 17 / 10. B.I., 1974, N 4, see also the book of Kneller V.Yu., Borovskikh LP "Determination of the parameters of multi-element two-terminal networks. - Moscow: Energoatomizdat, 1986, p. 104, Fig. 2.54) equipped with an amplitude null indicator. The disadvantage that prevents the achievement of the technical result indicated below, of the prototype of the claimed device in the group of inventions, is the use of two adjustable elements R, C and a series inductance coil L in series with them in the comparison arm, and the ratio of the adjustable element R in one of the arms, as a result a significant measurement error occurs due to the presence of shunt capacitances of the switching elements, with which the parameters of the said adjustable elements are changed, due to and leakage capacitances and due to the residual parameters of the inductor L, which are significant and also frequency-dependent. In addition, the prototype of the claimed device does not have a separate readout of the measured parameters, and the adjustment of two heterogeneous parameters of its three-element comparison arm to achieve frequency-independent phase equilibrium of the bridge are strongly dependent on each other, which leads to an extremely poor convergence of the balancing process in three the parameters of the first prototype, that is, the specified prototype of the claimed device in the group of inventions.

 From the second drawback of the noted first prototype, the method of balancing in three parameters is selected, selected as the prototype of the method in the claimed group of inventions, as N 849100 (USSR), G 01 R 27/02, B.I., 1981, N 27, p. 168 (see also the book by A. A. Tyukavin "Measurement of the parameters of three- and four-element bipolar AC bridges", Sarat. Univ., 1988, pp. 55-58), providing satisfactory convergence in three parameters of the balancing process frequency-independent bridges of alternating current and in the case of measuring the parameters of three-element two-terminal networks according to a serial RCL-scheme. This method consists of N operations of balancing the bridge in two parameters at the first frequency with the given values of the third parameter of the comparison arm in terms of the phase sign of the unbalance signal that appears after the balanced bridge is transferred to the second measurement frequency. The disadvantage of the second prototype, that is, the prototype of the method in the claimed group of inventions, also hindering the achievement of the technical result indicated below, lies in the use of a phase-sensitive null indicator on the second frequency, which is significantly inferior in sensitivity to the amplitude null indicator, as a result of which the highest bridge accuracy is not achieved measuring parameters of sequential RLC two-terminal devices. In addition, the need for N balancing operations in two parameters (N is equal to the number of binary bits of the third parameter of the comparison arm), although with directionally set values of the third parameter of the comparison circuit, it drags out the balancing process in three parameters, which is the second disadvantage of the second prototype.

 The single essence of the claimed group of inventions is to ensure high accuracy and short duration of measurement of the parameters of three-element two-terminal devices according to a sequential RLC-scheme.

 This single technical result in the implementation of the group of inventions is achieved in a frequency-independent multi-arm transformer AC bridge for measuring the parameters of three-element bipolar circuits using a serial RLC circuit consisting of a main voltage transformer connected by a primary winding to a tunable frequency generator, the first of four of which are grounded secondary windings through a constant measure of resistance it is connected to the ungrounded top of the measuring diagonal of the bridge, in which A selective amplitude zero indicator is turned on, as well as consisting of a precision voltage combiner, a differentiator and an integrator, the operational amplifiers of which have grounded power supplies, an auxiliary voltage transformer with grounded two windings, the marked integrator connected to its output winding.

 A feature of the claimed device is that the second secondary winding of the main voltage transformer is connected to the primary winding of the auxiliary voltage transformer, the third secondary winding is connected to the input of the differentiator, and its fourth secondary winding is connected to one of the inputs of the voltage adder, to the other two inputs of which are connected separately with its output clamps the mentioned differentiator and integrator, and between the ungrounded top of the measuring diagonal and the output The measured voltage is switched on by the pressure adder, and the third and fourth secondary windings of the main voltage transformer and the primary winding of the auxiliary voltage transformer are adjustable.

 The specified single technical result in the implementation of the group of inventions according to the object-method is achieved in the method of balancing in three parameters, containing the operation of balancing at the measurement frequencies by adjusting two parameters and by adjusting one parameter.

A feature of the claimed method in this group, according to which, first, at a frequency greater than a given reference frequency of the measured parameters, the bridge is balanced by two parameters at a convergence angle of 90 ^o , and then at frequencies lower and higher than the specified reference frequency , alternately carry out the operations of balancing the bridge, respectively, according to the parameter for reading the measured capacitance and the parameter for reading the measured inductance.

 The claimed group of inventions meets the requirement of unity of invention, since the group of diverse inventions forms a single inventive concept, moreover, one of the claimed objects of the group - the method is designed to implement another object of the group - the device. In this case, both objects of the group of inventions are aimed at solving the same problem with obtaining a single technical result.

 The analysis of the prior art by the applicant, including a search by patent and scientific and technical sources of information containing information about analogues of the claimed group of inventions for both the device object and the method object, allowed to establish that the applicant did not find analogues for both the method and and for the device of the claimed group, characterized by features identical to all the essential features of both the device and the method of the claimed group of inventions. The determination from the list of identified prototype analogues for both the device and the method of the claimed group of inventions, which are the closest in the totality of the characteristics of the analogues, made it possible to identify the set of distinguishing features essential for the applicant's technical result for each of the declared objects of the group set forth in the formula inventions.

 Therefore, each of the objects of the group of inventions meets the condition of "novelty."

To verify the compliance of each object of the claimed group of inventions with the condition "inventive step", the applicant conducted an additional search for known solutions in order to identify features that match the distinctive features of the selected prototypes for each object of the claimed group of inventions. The search results showed that each object of the claimed group of inventions does not follow explicitly from the prior art for the specialist, since the influence of the transformations provided for by the essential features of each of the objects of the claimed group of inventions on the achievement of the technical result is not revealed from the prior art, in particular the following transformations are not provided for in each of the objects of the claimed group of inventions:
the addition of a known means by any known part, attached to it according to known rules, to achieve a technical result, in respect of which the effect of such an addition is established;
the creation of a tool consisting of known parts, the choice of which and the connection between them is based on known rules, recommendations, and the technical result achieved in this case is determined only by the known properties of the parts of this tool and the connections between them.

 The described group of inventions is not based on a change in the quantitative characteristic (s), the presentation of such signs in the relationship or a change in its type, we mean the case when the fact of the influence of each of these signs on the technical result is known, and new values of these signs or their relationship could be obtained based on known dependencies, patterns.

 Therefore, each of the objects of the claimed group of inventions meets the condition of "inventive step".

перестраиваемой частоты; подключенный к вторичной обмотке w₃ основного трансформатора 1 прецизионный дифференциатор 5 на операционном усилителе ОУЗ и образцовых элементах C₃, R₃; 6, 7, 8 - входные зажимы прецизионного сумматора напряжений 9, выполненного на операционном усилителе ОУ1 и четырех образцовых резисторах r; измеряемый двухполюсник 10, подключенный к выходному зажиму 11 сумматора напряжений 9 и к незаземленной вершине 12 измерительной диагонали 12-13 моста, в которую включен избирательный амплитудный нуль-индикатор 14; прецизионный интегратор 15 на операционном усилителе ОУ2 и образцовых элементах R₂, C₂; вспомогательный трансформатор напряжения 16 с тесной индуктивной связью, первичная заземленная обмотка m₁ которого подсоединена накоротко к вторичной обмотке w₂ основного трансформатора 1, а вторичная заземленная обмотка m₂ которого подсоединена к входу интегратора 15; выходной зажим 17 вторичной обмотки w₁ основного трансформатора 1, между которым и вершиной 12 измерительной диагонали находится плечо сравнения с включенной в него постоянной мерой сопротивления R₁; 18 - ключ. Входные зажимы 6, 7, 8 сумматора 9 подсоединены соответственно к выходам интегратора 15, дифференциатора 5, к вторичной обмотке w₄ основного трансформатора 1.The drawing shows a diagram of a device in the claimed group of inventions. The device is a frequency-independent multi-arm transformer bridge of alternating current, comprising: a main voltage transformer 1 with close inductive coupling with four grounded secondary windings w ₁ - w ₄ connected by terminals 2, 3 of its primary winding W ₀ to a sinusoidal voltage generator 4

tunable frequency; connected to the secondary winding w _{3 of the} main transformer 1, a precision differentiator 5 on the operational amplifier OUZ and model elements C ₃ , R ₃ ; 6, 7, 8 - input terminals of a precision voltage adder 9, made on the operational amplifier OU1 and four reference resistors r; a measured two-terminal 10 connected to the output terminal 11 of the voltage adder 9 and to the ungrounded top 12 of the measuring diagonal 12-13 of the bridge, which includes a selective amplitude zero indicator 14; precision integrator 15 on an operational amplifier ОУ2 and reference elements R ₂ , C ₂ ; auxiliary voltage transformer 16 with a close inductive coupling, the primary grounded winding m _{1 of} which is connected shortly to the secondary winding w _{2 of the} main transformer 1, and the secondary grounded winding m _{2 of} which is connected to the input of the integrator 15; the output terminal 17 of the secondary winding w _{1 of the} main transformer 1, between which and the top 12 of the measuring diagonal there is a comparison arm with a constant measure of resistance R ₁ included in it; 18 is the key. The input terminals 6, 7, 8 of the adder 9 are connected respectively to the outputs of the integrator 15, the differentiator 5, to the secondary winding w _{4 of the} main transformer 1.

с обмоток w₁, m₂, w₃, w₄ могут сниматься через точные повторители напряжения с достаточно малым выходным сопротивлением).The windings of voltage transformers 1, 16 have negligible complex resistances due to their scattering inductances and active resistances. (To fulfill this voltage condition

windings w ₁ , m ₂ , w ₃ , w ₄ can be removed through precise voltage followers with a sufficiently small output resistance).

 The sinusoidal voltage generator 4 has a negligible output impedance.

A constant measure of resistance R ₁ in the arm of resistance 12-17 is considered ideal, that is, “pure”, since its residual reactive parameters in a multi-arm transformer bridge are easily compensated.

, проходящим через измеряемый двухполюсник 10, и током

, протекающим по ветви с мерой сопротивления R₁, являющейся плечом сравнения.The input resistance of the amplitude null indicator 14 is large enough, due to which, in the bridge disequilibrium mode, the equality between the current

passing through the measured two-terminal 10, and current

flowing along a branch with a measure of resistance R ₁ , which is the shoulder of comparison.

 Differentiator 5, adder 9, integrator 15 are considered ideal (this is facilitated by the use of selective zero indicator 14), that is, having an ideal transfer function and zero output resistances. Operational amplifiers ОУ1, ОУ2, ОУЗ have grounded power sources.

где

а в свою очередь, напряжение

, снимаемое с обмотки w₁, напряжение

на выходе сумматора 9 (при замкнутом ключе 18) выражаются как:

Подставляя выражения (2) - (5) в равенство (1), имеем следующее уравнение равновесия моста (при замкнутом ключе 18):

Если уравнение равновесия (6) выполняется при любом значении частоты, мост находится в измерительном состоянии и производится отсчет измеряемых параметров по формулам:
R_x=(R₁/w₁)w_4,0, (7)
L_x(R₁C₃R₃/w₁)w_3,0, (8)
C_x=(w₁C₂R₂/m₂w₂R₁)m_1,0, (9)
где w_4,0, w_3,0, m_1,0 - отсчеты чисел витков регулируемых обмоток w₄, w₃, m₁.In the equilibrium state of the bridge, the potentials of the vertices 12, 13 of the measuring diagonal are equal to each other, and therefore strict equality holds:

Where

and in turn voltage

removed from the winding w ₁ voltage

at the output of the adder 9 (with the key 18 closed) are expressed as:

Substituting expressions (2) - (5) into equality (1), we have the following equation of equilibrium of the bridge (with closed key 18):

If the equilibrium equation (6) is performed at any value of the frequency, the bridge is in the measuring state and the measured parameters are counted by the formulas:
R _x = (R ₁ / w ₁ ) w _4.0 , (7)
L _x (R ₁ C ₃ R ₃ / w ₁ ) w _3.0 , (8)
C _x = (w ₁ C ₂ R ₂ / m ₂ w ₂ R ₁ ) m _1,0 , (9)
where w _4.0 , w _3.0 , m _1.0 are the samples of the number of turns of the adjustable windings w ₄ , w ₃ , m ₁ .

As follows from expressions (7) - (9) and the diagram in the drawing, the claimed bridge is characterized by a separate readout of the measured parameters R _x , L _x , C _x according to the number of turns of the regulated grounded windings w ₄ , w ₃ , m ₁ when used in the comparison arm a constant measure of resistance R ₁ , which is “pure”. Therefore, the claimed bridge, unlike the first prototype, is free from the shunting effect of capacitance of switching elements, leakage capacitance, as well as from the influence of spurious parameters of an exemplary measure of resistance in the shoulder of comparison and in it, compared with the first prototype, a significant increase in the accuracy of measurement of the parameters of three-element two-terminal devices using serial RLC diagram.

где
Z_x = R_x+jωL_x+1/jωC_x.
Относительные чувствительности моста по регулируемым параметрам w₃, m₁ на основе (10) выражаются как:

Поэтому их отношение равно:

Согласно соотношению (13) относительная чувствительность моста по параметру w₃ по сравнению с относительной чувствительностью по параметру m₁ растет в функции квадрата частоты при изменении последней.In the nonequilibrium state of the bridge, the unbalance voltage in the idle mode in the measuring diagonal 12-13 is presented in the form (with the key 18 closed):

Where
Z _x = R _x + jωL _x + 1 / jωC _x .
The relative sensitivity of the bridge by adjustable parameters w ₃ , m ₁ based on (10) are expressed as:

Therefore, their ratio is:

According to relation (13), the relative sensitivity of the bridge with respect to the parameter w ₃ in comparison with the relative sensitivity with respect to the parameter m ₁ grows as a function of the square of the frequency when the latter changes.

The claimed method of balancing the bridge is carried out according to the parameters w ₃ , m ₁ for counting the reactive parameters L _x , C _x (see formulas (8), (9)) and consists of the following operations carried out in the frequency band relative to a given frequency ω _{0 of the} measured parameters.

, где k₁ > 1, регулировками двух параметров w₃, w₄. Угол сходимости по ним равен 90^o при прямых линиях уравновешивания, как это следует из выражения (10). Ключ 18 при первой операции разомкнут. По окончании уравновешивания моста уравнение (6) записывается в виде:

В соответствии с (14) в конце первого уравновешивания значения параметров w₃, w₄ получают равными:
w_4,1=(w₁/R₁)R_x, (15)
w_3,1 = L_xα(1-1/βk $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ ), (16)
где
α = w₁/R₁C₃R₃, (17)
β = ω $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ C_xL_x. (18)
Из формул (15), (7) следует, что в конце первого уравновешивания получают равенство:
w_4,1 = w_4,0. (19)
то есть в конце первой операции получают значение параметра w₄, по которому производят отсчет измеряемого активного сопротивления R_x по формуле (7).The first operation of the claimed method, that is, the first balancing of the bridge, is carried out at a frequency

, where k ₁ > 1, by adjusting two parameters w ₃ , w ₄ . The angle of convergence along them is 90 ^o with straight lines of equilibrium, as follows from expression (10). Key 18 during the first operation is open. At the end of the balancing of the bridge, equation (6) is written as:

In accordance with (14) at the end of the first balancing, the values of the parameters w ₃ , w ₄ are equal to:
w _4.1 = (w ₁ / R ₁ ) R _x , (15)
w _3.1 = L _x α (1-1 / βk $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ ), (16)
Where
α = w ₁ / R ₁ C ₃ R ₃ , (17)
β = ω $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ C _x L _x . (18)
From the formulas (15), (7) it follows that at the end of the first balancing get the equality:
w _4.1 = w _4.0 . (19)
that is, at the end of the first operation, the value of the parameter w _{4 is} obtained, according to which the measured active resistance R _{x is} counted according to the formula (7).

При учете (15) - (18) на основе уравнения равновесия (20) значение регулируемого параметра m₁ в конце второй операции получают равным:
m_1,2 = γC_x/(1-k $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ /k $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ ), (21)
где
γ = m₂w₂R₁/w₁R₂C₂. (22)
Третью операцию (то есть третье уравновешивание моста) проводят на частоте ω₃ = k₃ω₀ , где k₃ > 1, регулировкой параметра w₃ при w₄ = w_4,1 и при m₁ = m_1,2, определяемом по (21), (22). По достижении нулевого показания нуль-индикатора 14 в конце третьей операции на основе (6) значение параметра w₃ получают равным:
w_3,3 = αL_x(1-k $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ /βk $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ k $\genfrac{}{}{0ex}{}{\text{2}}{\text{3}}$ ), (23)
Четвертую операцию (то есть четвертое уравновешивание моста) проводят на частоте ω₄ = k₄ω₀, где k₄ < 1, регулировкой параметра m₁ при w₄ = w_4,1 и при w₃ = w_3,3 определяемом по (23), (17). В конце четвертой операции получают значение:
m_1,4 = γC_x/(1-k $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ k $\genfrac{}{}{0ex}{}{\text{2}}{\text{4}}$ /k $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ k $\genfrac{}{}{0ex}{}{\text{2}}{\text{3}}$ ). (24)
Аналогично проводят пятое и следующие уравновешивания моста.The second operation of the claimed method (i.e., the second balancing of the bridge) is carried out at the frequency ω ₂ = k ₂ ω ₀ , where k ₂ <1, by adjusting the parameter m ₁ with the values of the parameter w ₄ = w _4.1 and the parameter w found at the end of the first operation ₃ = w _3,1 (key 18 is closed during the second and next operations). At the end of the second operation, the equilibrium equation (6) is written as:

When taking into account (15) - (18) based on the equilibrium equation (20), the value of the adjustable parameter m ₁ at the end of the second operation is equal to:
m _1,2 = γC _x / (1-k $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ / k $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ ), (21)
Where
γ = m ₂ w ₂ R ₁ / w ₁ R ₂ C ₂ . (22)
The third operation (that is, the third balancing of the bridge) is carried out at the frequency ω ₃ = k ₃ ω ₀ , where k ₃ > 1, by adjusting the parameter w ₃ when w ₄ = w _4,1 and when m ₁ = m _1,2 , determined by (21), (22). Upon reaching the zero reading of the zero indicator 14 at the end of the third operation based on (6), the value of the parameter w ₃ is equal to:
w _3,3 = αL _x (1-k $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ / βk $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ k $\genfrac{}{}{0ex}{}{\text{2}}{\text{3}}$ ), (23)
The fourth operation (i.e., the fourth balancing of the bridge) is carried out at a frequency of ω ₄ = k ₄ ω ₀ , where k ₄ <1, by adjusting the parameter m ₁ with w ₄ = w _4.1 and with w ₃ = w _3.3 determined by ( 23), (17). At the end of the fourth operation get the value:
m _1.4 = γC _x / (1-k $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ k $\genfrac{}{}{0ex}{}{\text{2}}{\text{4}}$ / k $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ k $\genfrac{}{}{0ex}{}{\text{2}}{\text{3}}$ ) (24)
Similarly spend the fifth and next balancing of the bridge.

а при четном l получают значение параметра m₁, равное:

В формулах (25), (26) все k_j < 1 (что соответствует частотам измерения ω_j < ω₀) и все k_i > 1 (что соответствует частотам измерения ω_i > ω₀). Значения k_j и k_i при первых 2 - 4 операциях заявленного способа берут существенно отличающимися от 1, а затем берут в соответствии с границами полосы частот, в которой определяются параметры R_x, L_x, C_x (эта полоса содержит частоту ω₀).By conducting l balancing (l odd) get the value of the parameter w ₃ equal to:

and when even l get the value of the parameter m ₁ equal to:

In formulas (25), (26), all k _j <1 (which corresponds to the measurement frequencies ω _j <ω ₀ ) and all k _i > 1 (which corresponds to the measurement frequencies ω _i > ω ₀ ). The values of k _j and k _i in the first 2 to 4 operations of the claimed method are taken significantly different from 1, and then taken in accordance with the boundaries of the frequency band in which the parameters R _x , L _x , C _x are determined (this band contains the frequency ω ₀ ) .

The expression in square brackets in formulas (25), (26) tends to 1 with increasing l. Therefore, after l balancing the bridge (or method operations), based on formulas (25), (26) and (8), (9) with taking into account expressions (17), (22) we obtain the equalities:
w _{3, l} = w _3.0 (27)
m _{1, l} = m _1,0 , (28)
that is, the measured values of the parameters w ₃ , m ₁ are obtained in the frequency-independent equilibrium state of the bridge.

So, after l balancing according to the claimed method at frequencies ω _j <ω ₀ and ω _i > ω _{0, the} bridge is in a frequency-independent equilibrium state, which is a measuring state, and the measured parameters are counted by formulas (7), (8), ( nine).

где

- допустимая относительная погрешность отсчета параметра w₃, или находится из выражения:

где

- допустимая относительная погрешность отсчета параметра m₁.The required number l of balances according to the claimed method is found from the expression:

Where

- the permissible relative error in the reading of the parameter w ₃ , or is found from the expression:

Where

- permissible relative error of the reading of the parameter m ₁ .

имеем необходимое число операций l=5.If, for example, all k _i = 2, and all k _j = 0.5, then for β = 1 and for an allowable error

we have the required number of operations l = 5.

 As follows from the description of l operations of the claimed method, each of them ends with the installation of the equilibrium of the bridge in amplitude. Due to this, according to the claimed method, it is sufficient to use only the unbalance signal module information in the balancing process in three parameters, that is, it is sufficient to use, in contrast to the second prototype, only a selective amplitude zero indicator to set the bridge-independent equilibrium state of the bridge, which ensures maximum measurement accuracy parameters of serial RLC bipolar using the declared bridge.

From the description of l operations of the claimed method, it follows that only one (first) balancing of the bridge is carried out according to two parameters with respect to w ₃ and w ₄ , and with optimal convergence along them. The remaining (l-1) equilibria of the bridge at the measurement frequencies ω _j , ω _i are carried out according to one parameter (either m ₁ or w ₃ ).

 Since the number l of equilibria of the bridge in accordance with formulas (29), (30) can easily be made smaller than the number N of binary digits of the adjustable parameters necessary to obtain a given accuracy of reading of the measured parameters, and (l-1) equilibrations are performed according to one parameter, then is significantly faster than in two parameters, the claimed balancing method is characterized by using information about the unbalance signal module only, the better convergence of the balancing process in three parameters than the second prototype, according to The third process of balancing in three parameters consists of N operations of balancing the bridge in two parameters.

. Кроме того, за счет использования избирательного амплитудного нуль-индикатора 14 уже в конце первой операции способа значение w_4,1 мало отличается от истинного значения w_4,0 и коррекция при второй операции (и тем более следующих операциях) способа проводится в младших разрядах параметра w₄. Размер коррекции с ростом номера операции l уменьшается. Поэтому указанные коррекции мало влияют на длительность каждой из (l-1) операций предложенного способа, проводимых, как это описывалось, по одному параметру. По мере приближения к частотно-независимому состоянию равновесия моста благодаря применению избирательного амплитудного нуль-индикатора необходимость в коррекции w₄ = var отпадает и операции заявленного способа проводятся по одному параметру (либо m₁, либо w₃), как они выше и описывались. Необходимое число l операций заявленного способа остается таким же и в случае проведения коррекций параметра w₄, то есть определяется по формулам (29), (30).Note that at the end of the first operation of the claimed method, the state of equilibrium of the bridge is far from frequency-independent and even the higher harmonics of the bridge supply voltage, along which the bridge is unbalanced, can have a noticeable effect on the readings of even the selective amplitude zero indicator 14. Therefore, the first operation, carried out according to two parameters (w ₃ and w ₄ ), may not end at the maximum sensitivity of the amplitude zero indicator 14, and the value of the parameter w _4.1 found at the end of the first operation may slightly differ from the true measured value of the parameter w ₄ = w _4.0 . In this case, it becomes necessary to correct the value of w _4.1 . Since the second and subsequent operations end like the first operation by obtaining the bridge equilibrium in amplitude, the claimed method allows the bridge to be balanced by the parameter w ₄ (see equilibrium equation (20) in order to obtain a zero indication of the null indicator 14 at frequencies ω _i and ω _j at its maximum sensitivity, that is, it allows the correction of the value of the parameter w ₄ obtained during the previous operation of the method .. The angle of convergence of the bridge in parameters m ₁ , w ₄ and parameters w ₃ , w ₄ at frequencies respectively ω _j and ω _i when making corrections is equal to 90 ^o with straight lines of balancing, as follows from expression (10) for the unbalance voltage

. In addition, due to the use of selective amplitude zero indicator 14, already at the end of the first operation of the method, the value of w _4.1 differs little from the true value of w _4.0 and the correction during the second operation (and especially the following operations) of the method is carried out in the lower bits of the parameter w ₄ . The size of the correction decreases with increasing operation number l. Therefore, these corrections have little effect on the duration of each of the (l-1) operations of the proposed method, carried out, as described, by one parameter. As we approach the frequency-independent equilibrium state of the bridge due to the use of a selective amplitude null indicator, the need for correction w ₄ = var disappears and the operations of the claimed method are carried out according to one parameter (either m ₁ or w ₃ ), as described above. The required number l of operations of the claimed method remains the same in the case of corrections of the parameter w ₄ , that is, is determined by the formulas (29), (30).

We also note that the first operation of the claimed method can be performed with the key 18 closed and an arbitrary value of the parameter m ₁ (and not infinitely large, as was allowed in the description of the first operation of the method), since the parameter w ₄ defines only the real part of the expressions in curly brackets in equations (6), (10). The number of operations l is also determined by formulas (29), (30).

 Thus, in the claimed bridge and the claimed method, compared with the first and second prototype, significantly higher accuracy and shorter measurement time of the parameters of the three-element bipolar circuits according to the sequential RLC scheme are provided, that is, a single essence of the claimed group of inventions is achieved.

 The implementation of the claimed group of inventions does not cause fundamental difficulties, since the bridge uses high-quality transformer assemblies with close inductive coupling, a precision integrator, a voltage adder, a measure of resistance, a selective amplitude (extreme) zero indicator, which are typical units of known multi-arm transformer extreme AC bridges for measuring parameters using a two-element circuit (for example, digital bridges P5016, P5083). The implementation of a precision differentiator on an operational amplifier also does not cause difficulties due to the use of a selective amplitude zero indicator in the claimed bridge, which is tuned to each measurement frequency.

The implementation of the claimed method of balancing the three parameters of the claimed bridge also does not cause difficulties, since this method contains one easily automated balancing operation on two parameters with a convergence angle of 90 ^o and (l-1) balancing operations on one parameter, moreover the number (l-1) is always small. The indicated correction of the parameter w ₄ during the second and subsequent operations of the claimed method is easily feasible and has little effect on the duration of the measurement.

Claims (2)

 1. Frequency-independent multi-arm transformer bridge of alternating current for measuring the parameters of three-element bipolar circuits according to a serial RLC circuit, consisting of a main voltage transformer connected by a primary winding to a tunable frequency generator, the first of four grounded secondary windings of which is connected to an ungrounded top through a constant measure of resistance measuring diagonal of the bridge, which includes a selective amplitude null indicator, as well as consisting of precision voltage adders, a differentiator and an integrator, the operational amplifiers of which have grounded power sources, an auxiliary voltage transformer with grounded two windings, to the output winding of which an aforementioned integrator is connected with its input, characterized in that the second secondary winding of the main voltage transformer is connected to the primary winding of the auxiliary transformer voltage, the third secondary winding is connected to the input of the differentiator, the fourth is its secondary winding connected to one of the inputs of the voltage adder, to the other two inputs of which the aforementioned differentiator and integrator are connected separately by their output terminals, and between the ungrounded top of the measuring diagonal and the output terminal of the voltage adder, the measured two-terminal device is connected, the third and fourth secondary windings of the main voltage transformer and the primary winding auxiliary voltage transformer made adjustable. 2. A method for balancing a frequency-independent multi-arm transformer bridge, comprising balancing operations at measurement frequencies by adjusting two parameters and by adjusting one parameter, characterized in that at first, at a frequency greater than a given reference frequency of the measured parameters, the bridge is balanced in two parameters at the angle of convergence over them equal to 90 ^o , and then at frequencies less than and greater than the specified reference frequency, alternately carry out the operations of balancing the bridge, respectively by parameter for reading measured capacitance and parameter for reading measured inductance.