SU873152A1 - Passive non-resonance two-terminal network parameter converter - Google Patents

Description

(54) CONVERTER PARAMETERS OF PASSIVE NONRESONANT TWO-POLES

one

The invention relates to electrical measuring equipment and can be used to measure the components of the complex values of alternating current when converting parameters of contactless capacitive sensors, the replacement circuit of which consists of a known insulator capacitance and complex conductivity, the components of which carry information about the object being studied.

A device for converting the parameters of a passive two-terminal device is known, which contains a sinusoidal voltage generator, a two-terminal test, operational amplifiers, a phase-sensitive inductor, a controlled voltage divider, voltage ratio meters, voltage transformers and current tl)

The disadvantage of this device is in-. Low accuracy is associated with the complexity of the transformation structure.

Also known is a transducer of vapor-meters of passive non-resonant two-terminal networks, which contains a generator of sinusoidal voltage, a two-terminal explored, the input of which is connected to the input of the first operational amplifier with a capacitor in

the negative feedback circuit, the second operational amplifier with the reference element in the negative feedback circuit, the input of which is connected by a capacitor to the output of the first operational amplifier and the resistor of the voltage divider output, a phase-sensitive indicator, the measurement input of which is connected to

10 by the output of the second operational amplifier, transformer, voltage ratio meters. In this converter, signals are formed that coincide in magnitude and phase with the current,

5 flowing through the bipolar circuit under study, and the voltage drop across the measured parallel connection of the active and capacitive conductivities, the voltage signal using 20 s for decomposing the current signal using the compensation method 2.

However, the presence of two signals (current and voltage), which vary depending on the magnitude of the measured

25 of the conductivity, as well as the frequency of the operating voltages, complicates the transformation structure, necessitating the use of two voltage ratio meters, which adversely affects the accuracy

converter The capacitance included in the bipolar circuit under study and connected in series with the measured conductivity represents a great resistance for low frequency currents. Therefore, in a known transducer, with a sufficiently small value of the indicated capacitance, the pickup signal at the output of the first operational amplifier may exceed the useful signal.

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

The goal is achieved by including a sinusoidal voltage generator, a first operational amplifier with a capacitor in the feedback circuit, a coupling capacitor, a second operational amplifier with a reference element in the feedback circuit, a voltage divider, in the converter of parameters of passive nonresonant two-terminal networks. the first communication resistor, an inverter, and a phase-sensitive indicator; one of the converter inputs is connected to the series-connected first operational amplifier, a capacitor with In other words, by the second operational amplifier and phase-sensitive indicator, the output of the sinusoidal voltage generator is through an inverter, the voltage divider and the first communication resistor are connected to the input of the second operational amplifier and a third operational amplifier is inserted in the feedback circuit, and the amplifier input is connected through the resistor with the output of the alternating voltage generator and through the feedback circuit with the output of the first operational amplifier, and the output of the third operational amplifier is connected to another input of the converter ovatel.

As a result of the introduction of the third operational amplifier in the converter, the signal at the output of the second operational amplifier is determined only by the parameters of the measured part of the two-pole, while the voltage on it is constant and does not depend on the value of the known capacitance replacement, which simplifies the transformation structure, and therefore improves the accuracy of the converter, allows further processing of the signal from the output of the second operational amplifier by the known methods used in reobrazovanii parameters simpler two-terminal-element.

The drawing shows the .control circuit converter.

The converter circuit contains a sinusoidal voltage generator l, a third operational amplifier 2, resistors 3–6, two-pole device 7 under study, capacitors 8 and 9, resistor 10, capacitors 11–13, first and second operational amplifiers 14 and 15, filters 16 and 17, phase-sensitive indicators 18 and 19, phase shifter 20, inverter 21, dividers 22 and 23, model element 24. 5 The converter operates as follows.

The input of the studied two-terminal 7 from the output of the operational amplifier 2 receives the voltage U, determined by the formula:

R-fo

E)

shse

c. J f 4 j

.)

iio

 lVC-,

where and is the voltage at the output of the summing amplifier;

E is the voltage of generator 1; W - the angular part of the measuring voltage.

In this case, the voltage drop on the measured conductivity, formed by

parallel connection of elements 9 and 10, is equal to

MO

U --- E

R ,, +.

q, 0

If KlSd% S. (3), which is easy to perform at any frequencies, for example, by selecting the value of R, then the voltage across the measured conductivity

and - E - and does not depend on chastok

You are generator 1, not the value of the measured conductivity. The output voltage of the amplifier 14

, .nil

W

- R,

the higher, the lower the capacitance Cd and the frequencies W. Therefore, low-frequency current pickups (for example, the industrial part), which can be low in the object from 1, significantly ruin the work of the amplifier 14, reducing the measurement accuracy. Filter 16, creating deep negative feedback, and filter 17, breaking

positive feedback, suppressing the pickup signal, increasing the noise immunity of the converter, as well as helping to stabilize its DC operating mode.

an inverter 21, adjustable voltage dividers 22 and 23, a resistor 6 and a capacitor 13 allow you to set the necessary compensating current at the input of the amplifier 15. In this case, if a resistor is used as

model element 24, the voltage at the output of the amplifier 15 is equal to: eip9 4R4C, J) (where K is the transfer ratio of the inverter 21.; the division factors of the voltage dividers 22 and 23; .bM is the nominal active H on, the conductivity, the value of which is set by the voltage divider 22; - the nominal capacitance of which is set by the voltage divider 23. The phase-sensitive indicators 18/19 fix, respectively, the magnitude of the deviations of the capacitive and active conductivities from their nominal values. Due to the fact that the voltage on the measured conductivity does not depend on its parameters and the frequency of the working voltages due to the introduction of a third operational amplifier, the transformation structure is simplified, the number of tunable elements is minimized, which improves the accuracy of the converter. are

Claims (2)

low-frequency nzvodki, increasing its noise immunity. Claims of the Inverter of parameters of passive nonresonant two-terminal network, comprising a sinusoidal voltage generator, a first operational amplifier with a capacitor in a feedback circuit, a coupling capacitor, a second operational amplifier with a reference element in the feedback circuit, a voltage divider, a first resistor, an inverter and a phase-sensitive indicator, one of the inputs of the converter being connected to the series-connected first operational amplifier, coupling capacitor, and second operative The indicator and onnym.usilitelem faeochuvstvitelnym torus sinusoidal voltage generator output voltage through the inverter, a voltage divider and a first resistor connected to the communication input of the second operational amplifier, characterized in that, in order to increase accuracy, it is entered in the third one-. a feedback amplifier with a resistor in the feedback circuit, wherein the amplifier input is connected via a resistor to the output of an alternating voltage generator and through a positive feedback circuit to the output of the first operational amplifier, and the output of the third operational amplifier is connected to another converter input. Sources of information taken into consideration during the examination 1. USSR author's certificate No. 507830, cl. G 01 R 27/00, 1973. 2. Authors certificate of the USSR 495617, cl. G 01 R 27/00, 1974 (prototype).