RU2390787C1 - Tester of multiple-element passive bipoles - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: measurement of parametres of passive multiple-element bipoles is performed at influence of pulses of voltage varying as per the law of n degree of time on measuring transducer and at balancing of output voltage of measuring transducer and compensating signal synthesised from voltage pulses having the shape of degree functions of time with degree properties of n to 0. After transient process is completed, there set to zero are voltages on outputs of (n-1)-cascade differentiator connected to output of inverting summator, as well as at the output of the latter. As per the obtained amplitudes of the above pulses there calculated are conductivity parametres, and then - parametres of elements of a bipole.

EFFECT: enlarging functional capabilities, simplifying and standardising the measuring algorithm of parametres R-C, R-L and R-L-C of bipoles having various equivalent circuits.

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Description

The invention relates to measuring technique and, in particular, to a technique for measuring the parameters of objects in the form of passive two-terminal devices with lumped parameters having a multi-element equivalent circuit.

A device is known (RF patent No. 2212677) for determining the parameters of multi-element bipolar circuits with a measuring transducer (IP) made on an operational amplifier (OA) with parallel negative feedback, the circuit of which includes an exemplary resistor and a measured two-terminal RC or RL type [1] . A rectangular pulse of the reference voltage is applied to the input of the IP, the free component of the transient process is extracted from the output voltage of the op-amp, and the integration operation is performed, during the integration at the time t _1, the first value of the integral of the specified voltage is measured, then at the time 2t _1, the second value of the integral from the specified voltage, and from the obtained values of the integral calculate the time constant and the amplitude of the transient at the output of the IP, after which the integrated characteristics are free th component computes bipolar circuit parameters.

The disadvantages of this device are:

1) narrow functionality that allows you to measure the parameters of a small number of two-terminal networks with only two or three elements;

2) the need to change the connection points of the measured two-terminal network either in the feedback circuit or in the input circuit of the op-amp, depending on the configuration of the circuit of the measurement object;

3) measurement errors due to the influence of the frequency properties of the op-amp and stray capacitance on the characteristics of the transient process.

There is a method (RF patent No. 2310872) for determining the parameters of multi-element bipolar circuits, which consists in using the influence on the studied bipolar RC or LR circuit with a step-shaped signal and applying the integration operation to determine the parameters of a bipolar [2]. In the process of integrating the free component of the transient process, measure the first value of the integral of the specified voltage in the area [0 ... t ₁ ]. Next, measure the second value of the integral of the specified voltage on the plot [t ₁ ... 2t ₁ ], then calculate the values of the time constant and the amplitude of the transition process at the output. The measured integral characteristics of the transient process determine the values of the parameters of the two-terminal device.

This method has the same disadvantages as the above-mentioned device according to patent No. 2212677.

A known method (RF patent No. 2180966) for measuring the parameters of a four-element bipolar RC type, based on the transient analysis in a measuring transducer based on an operational amplifier, in the negative feedback circuit of which the measured bipolar is connected, and in the inverting input circuit of the op-amp, an exemplary resistor [ 3]. When a DC voltage jump is applied to the input of the IP, a transient process occurs in the measuring circuit, which consists of the sum of the constant, linearly varying, and exponential components. The two-terminal parameters are calculated from four discrete samples of the output voltage of the PI at time t ₁ , 2t ₁ , 3t ₁ and 4t ₁ after the start of the transition process by solving a system of four equations with four unknowns. Based on the measurement results, the microprocessor controller calculates the constant component, the steepness of the linearly changing component, the time constant and the amplitude of the exponential component of the transient, and from these values - the parameters of the studied two-terminal device.

The disadvantages of this method are:

4) narrow functionality that allows you to measure the parameters of a very limited number of options for bipolar;

5) the need to change the connection points of the measured two-terminal network either in the OS circuit or in the op amp input circuit, depending on the configuration of the circuit of the measurement object;

6) measurement errors due to the influence of stray circuits and frequency properties of the op-amp on the characteristics of the transient process. The closest in technical essence to the proposed one is a multi-element passive bipolar parameters meter (RF patent No. 2144195), made in the form of a four-armed electric bridge, in which a voltage pulse shaper of a cubic shape is used for power [4]. The inputs of the differential amplifier are included in the measuring diagonal of the bridge, and three differentiators connected in series to the output of the differential amplifier. The outputs of the differentiators, as well as the output of the differential amplifier are connected to the inputs of the zero indicator. The bridge is balanced after the end of transient processes in its circuits, sequentially leading to a zero voltage value at the outputs of the first third, then second and first differentiators and, finally, a differential amplifier. The disadvantages of this bridge meter are:

1) a complex circuit of a branch with a multi-element bipolar relationship and a multi-element balancing bipolar, which includes adjustable resistors, capacitors and inductors;

2) bulky analytical expressions for calculating the parameters of the elements of the measured bipolar;

3) a limited set of options for multi-element two-terminal devices, for which balancing conditions are provided for a specific configuration of the bridge circuit.

The problem to which the invention is directed is to expand the functionality that allows measuring the parameters of various types of multi-element passive two-terminal devices: R-C, R-L and R-L-C, simplifying and unifying the procedure for calculating the parameters of measurement objects.

The technical result is achieved by the fact that the input of the measuring transducer (IP), made on the basis of an operational amplifier (op amp), in the circuit of the inverting input of which the measured multi-element bipolar is connected, and a model resistor is supplied in the negative feedback circuit, a voltage pulse that changes during its duration according to the law of the nth degree of time, and the output voltage of the PI after the end of the transition process and to the end of the pulse is balanced by a compensating signal consisting of the sum of the pulses zheniya shaped exponential function of time with exponents from n to 0, and the amplitude values of the components of the compensating signal is calculated parameters bipole. The value of the exponent n is determined by the number of elements and the configuration of the equivalent circuit of the measured bipolar.

The invention is illustrated for the case of a four-element bipolar. At the input of the FE serves voltage pulses of a cubic shape, changing according to the law of the third degree of time:

where U ₃ is the amplitude of the pulse of a cubic shape, t _and is its duration.

The operator image of the voltage u ₃ (t) at the input of the IP has the form

and the operator image of the voltage at the output of the IP

where R ₀ is the resistance of the reference resistor; Y (p) is the operator image of the two-terminal conductivity.

For a four-element bipolar with finite (non-zero and not infinite) DC resistance, the conductivity in the operator form in the general case can be represented as a fractional rational function of the second order

where the coefficients of the polynomials of the denominator a ₀ , a ₁ , a ₂ and the numerator b ₀ , b ₁ , b _{2 are} determined by the components of the equivalent circuit of the two-terminal network. Hence the operator image of the voltage at the output of the IP can be represented as the sum of simple fractions:

where Y ₀ , Y ₁ , Y ₂ , Y ₃ are the parameters of the complex conductivity of a two-terminal network. For non-zero values of a ₀ and b ₀ , which takes place for a large group of real two-terminal networks, the values Y ₀ , Y ₁ , Y ₂ , Y _{3 are} determined by the values of the parameters of the elements of the two-terminal network:

For a two-terminal network with conductivity of the form (4), b ₃ = 0 and ₃ = 0. The last term in the brackets of formula (5) determines the free component, and the rest - the forced component of the voltage at the output of the IP, which is installed at the end of the transition process in a two-terminal network.

Values characterizing the transition process:

The steady-state voltage at the output of the IP is the sum of the pulses of cubic, quadratic, linear and rectangular shapes:

Expression (8) can be represented as

Where

U _3.m = -R ₀ Y ₀ U ₃ - the amplitude of the cubic component of the voltage;

- амплитуда квадратичной составляющей;

- the amplitude of the quadratic component;

- амплитуда линейной составляющей;

- the amplitude of the linear component;

- амплитуда постоянного напряжения.

- the amplitude of the constant voltage.

As can be seen from expression (9), the amplitude values of the components of the output voltage of the IP contain information about the parameters of the two-terminal device. By measuring the amplitudes U _3.m , U _2.m , U _1.m , U _0.m , we can determine the conductivity parameters of the two-terminal network Y ₀ , Y ₁ , Y ₂ , Y ₃ , and then calculate the values of the parameters of the two-terminal devices: resistance of resistors, capacitors, inductors of coils. The amplitudes U _3.m , U _2.m , U _1.m , U _0.m are _measured by balancing the output voltage of the transmitter and the compensating signal synthesized from voltage pulses in the form of a power time function with exponents from 3 to 0, and voltage pulses with exponents from 1 to 3 are formed from a rectangular voltage pulse using three series-connected non-inverting integrators. The balancing is carried out by adjusting the amplitudes of the pulses that make up the compensating signal, sequentially leading to a zero value of the signals obtained by triple differentiation of the difference between the output voltage of the PI and the compensating signal after the end of the transition process in the two-terminal network.

The scheme and operation of the device for measuring the parameters of four-element passive two-terminal devices are illustrated in figure 1.

The measuring transducer contains a first operational amplifier 1, in the feedback circuit of which an exemplary resistor 2 is included, and in the input circuit there is a measured two-terminal device, which, as an example, consists of a first resistor 3 and parallel-connected inductor 4, a second resistor 5 and a capacitor 6 The cubic voltage pulse generator consists of a rectangular pulse generator 7, a first non-inverting integrator 8, a second non-inverting integrator 9 and a third non-inverting integrator ora 10. The generator 7 has a synchronizing input. The meter also contains an inverting adder on the second operational amplifier 11, the input of which through a resistor 12 is connected to the output of the first operational amplifier 1, and a resistor 13 is included in the feedback circuit, the resistances of the resistors 12 and 13 are equal to the resistance of the reference resistor 2. Four multipliers are introduced into the meter digital-to-analog converter (DAC) and three analog switches, the analog input of the first DAC 14 is connected to the connection point of the output of the generator 7 and the input of the first integrator 8, the analog input of the second D AP 15 is connected to the connection point of the output of the first integrator 8 and the input of the second integrator 9, the analog input of the third DAC 16 is connected to the connection point of the output of the second integrator 9 and the input of the third integrator 10, the analog input of the fourth DAC 17 is connected to the connection point of the output of the third integrator 10 and the input measuring transducer. The digital inputs of the first DAC 14, the second DAC 15, the third DAC 16 and the fourth DAC 17 are connected to the data buses of the microprocessor controller (MPC) 18, the output of the DAC 14 is connected to the input of the first analog switch 19, the output of the DAC 15 to the input of the second analog switch 20, the output of the DAC 16 with the input of the third analog switch 21. The first output of the first analog switch 19, the first output of the second analog switch 20 and the first output of the third analog switch 21 are combined with the inverting input of the operational amplifier 1, the second output the first analog switch 19, the second output of the second analog switch 20, the second output of the third analog switch 21 and the output of the DAC 17 are combined with the inverting input of the operational amplifier 11. To the output of the operational amplifier 11 is connected a three-stage differentiator on differentiating RC circuits: the first stage contains a capacitor 22 and a resistor 23, the second stage is the capacitor 24 and the resistor 25, the third stage is the capacitor 26 and the resistor 27.

The device operates as follows.

According to the synchronization signals from the IPC 18, the generator 7 generates a sequence of rectangular voltage pulses of duration t _and with an amplitude of U ₀ . In this case, at the output of the first integrator 8, pulses of linearly varying voltage with an amplitude of U _{1 are formed} :

at the output of the second integrator 9 - voltage pulses, changing according to the law of a quadratic parabola with amplitude U ₂ :

at the output of the third integrator 10 - voltage pulses, changing according to the law of a cubic parabola with an amplitude of U ₃ :

The voltage u ₃ (t) is supplied to the input of the measuring transducer, and voltage pulses are formed at the output of the op-amp 1, which contain free and forced components. After the end of the transient process and until the end of the pulse, only the forced component of the voltage u _IP (t) remains, which consists of cubic, quadratic, linear and flat (rectangular) voltages:

The amplitudes of these components are U _3.m = -R ₀ Y ₀ U ₃ ,

зависят от параметров объекта измерения. В частности, операторное изображение проводимости двухполюсника 3, 4, 5, 6 с параметрами R₃, L₄, R₅, С₆ имеет вид

depend on the parameters of the measurement object. In particular, the operator image of the conductivity of a two-terminal 3, 4, 5, 6 with parameters R ₃ , L ₄ , R ₅ , C ₆ has the form

The values of Y ₀ , Y ₁ , Y ₂ , Y ₃ according to formulas (6) are equal

Note that the conductivity parameter Y ₀ always has a positive sign, and the remaining parameters, depending on the two-terminal circuit, can be both positive and negative. Moreover, as can be seen from the example of parameter Y ₃ , the sign of this parameter for the two-terminal system under consideration depends on the relationship between the values of the parameters of the circuit elements. At

знак параметра Y₃ положительный, а при

the sign of the parameter Y _{3 is} positive, and when

- отрицательный. Исходя из упомянутых обстоятельств, необходимо предусмотреть возможность выбора полярности отдельных составляющих компенсирующего сигнала при уравновешивании его с выходным напряжением ИП u_ИП(t).

- negative. Based on the above circumstances, it is necessary to provide for the possibility of choosing the polarity of the individual components of the compensating signal when balancing it with the output voltage of the IP u U _IP (t).

The output voltage of the IP is supplied to the input of the inverting adder, made on the second op-amp 11, the transmission coefficient of which is determined by resistors 12 and 13, which have the same resistance with the model resistor 2, i.e. R ₁₂ = R ₁₃ = R ₀ . Therefore, the voltage at the output of the op-amp 11 will be equal to

To measure the amplitudes U _3.m , U _2.m , U _1.m , U _0.m , a compensating signal is formed from the sum of voltage pulses of the same shape and with the same amplitudes as the components of the output voltage IP u _IP (t) . For this multiplying digital to analog converters are used to form a weighted currents resistive circuits matrix type R-2R, which allow changing the reference voltage U _REF widely including polarity reversal. The output current of the DAC is proportional to the product of the reference voltage by the input digital code D:

which allows you to directly use such DACs to multiply the analog signal to a digital code. The inputs of the reference voltage (U _REF ) of the DAC 14, 15, 16, 17 are supplied with pulses of constant, linear, quadratic and cubic voltage from the outputs of the pulse generator 7 and integrators 8, 9, 10, respectively, and the digital inputs of the DAC from the microprocessor controller 18 are codes transmission coefficients K _0, K _1, K _2, K _3, respectively. DAC output signals are in the form of current pulses:

The current of the fourth DAC 17 is fed into the input circuit of the OS 11 to compensate for the cubic component of the output voltage of the IP, and the currents of the other DACs, depending on the polarity of the amplitudes of the constant, linear, and quadratic components of the voltage of the IP, are switched using analog switches 19, 20, and 21 or to the input the circuit of the first op-amp 1, or to the inverting input of the second op-amp 11. The currents of those pulses that correspond to the positive values of the parameters Y ₁ , Y ₂ , Y ₃ are supplied to the input of the op-amp 11, otherwise the currents are switched to the input circuit of the op-amp 1.

After the end of the transition process in the measuring transducer at the output of the OS 11 a signal is generated corresponding to the difference of the output voltage of the IP

and compensating voltage

By successive approximation, the microprocessor controller sets such values of the coefficients K ₃ , K ₂ , K ₁ and K ₀ , which provide balancing of the voltage u _IP (t) and the compensating voltage u _IP (t) at the output of the op amp 11. The balancing conditions are:

Balancing should be performed in the above sequence, since the value of Y ₀ is included in the expression for Y ₁ , the values of Y ₀ and Y ₁ are included in the formula for Y ₂ , the values of Y ₀ , Y ₁ and Y ₂ are included in the formula for Y ₃ . In order to selectively control the amplitude of the cubic component of the compensating voltage, i.e. coefficient K ₃ , the output voltage of the summing op-amp 11 is supplied to the differentiator, which contains three differentiating RC circuits connected in series: capacitor 22 and resistor 23, capacitor 24 and resistor 25, capacitor 26 and resistor 27. All three RC circuits have the same constant value RC time. The transfer function from the input of the differentiator to the output of the third RC circuit has the form

and at the output of the third RC circuit, a constant voltage is generated and fed to the input of the first measuring channel MPK 18, proportional to the difference in the amplitudes of the cubic components of the voltage of the IP and the compensating signal:

The compensation of the cubic component is carried out by bringing to zero the output voltage of the third RC circuit u _3RC (t) by adjusting the coefficient K ₃ .

Then the IPC analyzes the voltage at the output of the second differentiating RC circuit. The transfer function from the input of the differentiator to the output of the second RC circuit has the form

and at the output of the second RC circuit, a constant voltage is formed and fed to the input of the second measuring channel MPK 18, proportional to the difference in the amplitudes of the quadratic components of the voltage of the IP and the compensating signal:

Compensation of the quadratic component is carried out by bringing to zero the output voltage of the second RC circuit u _2RC (t) by adjusting the coefficient K ₂ . In this case, the IPC determines the polarity of the quadratic component of the compensating voltage and controls the switching of the third analog switch 21.

After that, the IPC analyzes the voltage at the output of the first differentiating RC circuit. The transfer function from the input of the differentiator to the output of the first RC circuit has the form

and at the output of the first RC circuit, a constant voltage is generated and fed to the input of the third measuring channel of the IPC 18, proportional to the difference in the amplitudes of the linear components of the voltage of the IP and the compensating signal:

The compensation of the linear component is carried out by bringing to zero the output voltage of the first RC circuit u _1RC (t) by adjusting the coefficient K ₁ . When this IPC determines the polarity of the linear component of the compensating voltage and controls the switching of the second analog switch 20.

And finally, to compensate for the constant component of the voltage pulse at the output of the measuring transducer, the IPC determines the polarity and leads to zero the output voltage of the OS 11, which is fed to the input of the fourth measuring channel,

adjusting the coefficient K ₀ . When this IPC determines the polarity of the DC component of the compensating voltage and controls the switching of the first analog switch 19.

After four stages of balancing the voltages u _IP (t) and u _to (t) IPC 18 using formulas (19) - (22) determines the conductivity parameters of the two-terminal network Y ₀ , Y ₁ , Y ₂ , Y ₃ , and then, using the obtained values values Y ₀ , Y ₁ , Y ₂ , Y ₃ and expressions (11) - (14), calculates the parameters of the two-terminal devices:

The meter allows you to use the above algorithm to determine the parameters of various options for bipolar circuits. Consider a few more examples of multi-element bipolar circuits, the diagrams of which are depicted in figure 2.

Example 1. A four-element R-C two-terminal device contains a first resistor 28, a capacitor 29 and a second resistor 30 are connected in parallel with it, a capacitor 31 is connected in parallel with the last one. An operator image of the two-terminal conductivity is expressed as

The parameters Y ₀ , Y ₁ , Y ₂ , Y ₃ according to formulas (6) are equal

Using the found values of Y ₀ , Y ₁ , Y ₂ , Y ₃ and expressions (24), the parameters of the elements R ₂₈ , C ₂₉ , R ₃₀ , C ₃₁ are calculated.

Example 2. The R-C type three-element bipolar contains a first capacitor 32, in series with which a resistor 33 and a second capacitor 34 are connected in parallel. This bipolar is obtained from the circuit of the previous example by disconnecting the resistor 29 and has zero direct current conductivity. The operator image of its conductivity has the form

The parameters Y ₀ , Y ₁ , Y ₂ , Y ₃ according to formulas (6) are equal

It is seen that the first stage of balancing can be excluded and set the coefficient K ₃ = 0. Using the found values of Y ₁ , Y ₂ , Y ₃ and expressions (26), the parameters of the elements C ₃₂ , R ₃₃ , C ₃₄ are calculated.

Example 3. The four-element bipolar R-L type contains a series-connected first resistor 35 and a first inductor 36, in parallel with which is connected a series circuit containing a second resistor 37 and a second inductor 38. The operator image of the conductivity of a two-terminal network is expressed as

The parameters Y ₀ , Y ₁ , Y ₂ , Y ₃ according to formulas (6) are equal

Using the found values of Y ₀ , Y ₁ , Y ₂ , Y ₃ and expressions (28), the parameters of the elements R ₃₅ , L ₃₆ , R ₃₇ , L ₃₈ are calculated.

Example 4. The R-L type three-pole bipolar contains a first resistor 39 and an inductance 40 connected in series, in parallel with which a second resistor 41 is connected. This two-terminal is obtained from the circuit of the previous example when the second inductor 38 is disconnected. The operator image of the conductivity of the two-terminal network has the form

To measure the parameters Y ₀ , Y ₁ , Y ₂ in accordance with formulas (6)

three stages of balancing are necessary. Expressions (30) allow you to calculate the parameters of the elements R ₃₉ , L ₄₀ , R ₄₁ .

Example 5. The four-element bipolar R-L type contains a first resistor 42, in parallel with which is connected a series circuit consisting of a capacitor 43, a second resistor 44 and an inductor 45. The operator image of the conductivity of a two-terminal network is expressed as

The values of Y ₀ , Y ₁ , Y ₂ , Y ₃ according to formulas (6) are equal

Example 6. The R-L type three-element bipolar is a series circuit comprising a capacitor 46, a resistor 47, and an inductor 48. This two-terminal is obtained from the circuit of the previous example when the first resistor 42 is disconnected. The two-terminal has zero DC conductivity. The operator image of the conductivity of a two-terminal network is expressed as

The values of Y ₀ , Y ₁ , Y ₂ , Y ₃ according to formulas (6) are equal

Thus, the proposed device significantly increases the number of variants of the measured multi-element passive bipolar. Using the generalized values of Y ₀ , Y ₁ , Y ₂ , Y ₃ allows you to unify and simplify the procedure for calculating the parameters of the elements of two-terminal systems of various configurations of the equivalent circuit.

Information sources

1. RF patent No. 2212677, G01R 27/02. A device for determining the parameters of multi-element bipolar circuits / N.N. Khrisanov, DB Frolagin, publ. 09/20/2003.

2. RF patent No. 2310872, G01R 27/02. The method of determining the parameters of multi-element bipolar circuits / N.N. Khrisanov, publ. 11/20/2007.

3. RF patent No. 2180966, G01R 27/26. The method of determining the parameters of bipolar / M.R.Safarov, L.V. Sarvarov, Yu.D. Kolovertnov, G.Yu. Kolovertnov, publ. 03/27/2002.

4. RF patent No. 2144195, G01R 17/10. Bridge meter of parameters of multi-element passive two-terminal / V.I. Ivanov, G.I. Peredelsky, publ. 2000, Bull. No. 1.

Claims (1)

A multi-element passive two-terminal parameter meter containing a measuring transducer based on the first operational amplifier, the reference resistor is included in the feedback circuit, and the measured two-terminal, a cubic voltage pulse shaper, which consists of a series-connected rectangular pulse generator, the first non-inverting, is included in the input circuit integrator, second non-inverting integrator and third non-inverting integrator, microprocessor controller (IPC ), an inverting adder on the second operational amplifier, in the input and feedback circuits of which are connected resistors that have the same resistance as an exemplary resistor, the input of the inverting adder is connected to the output of the measuring transducer, and three series-connected differentiating RC circuits are connected to the output of the inverting adder, the output of the third differentiating RC circuit is connected to the first measuring input of the IPC, the output of the second differentiating RC circuit is connected to the second measuring input of the IPC, the output is th differentiating RC circuit - with the third measuring input of the IPC, the fourth measuring input of the MPC is connected to the output of the inverting adder, characterized in that the meter additionally has four multiplying digital-to-analog converters (DACs) and three analog switches, the analog input of the first DAC is connected to the connection point the output of the rectangular pulse generator and the input of the first integrator, the output of the first DAC is connected to the input of the first analog switch, the analog input of the second DAC is connected to the connection point the output of the first integrator and the input of the second integrator, the output of the second DAC is connected to the input of the second analog switch, the analog input of the third DAC is connected to the connection point of the output of the second integrator and the input of the third integrator, the output of the third DAC is connected to the input of the third analog switch, the analog input of the fourth DAC is connected to the connection point of the output of the third integrator and the input of the measuring transducer, the digital inputs of the first DAC, the second DAC, the third DAC and the fourth DAC are connected to the data buses IPC, the control inputs of the first, second and third analog switches are connected to the corresponding outputs of the IPC, the first output of the first analog switch, the first output of the second analog switch and the first output of the third analog switch are combined with the inverting input of the first operational amplifier, the second output of the first analog switch, the second output the second analog switch, the second output of the third analog switch and the output of the fourth DAC are combined with the inverting input of the second operation ion amplifier.

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