SU1368812A2 - Electrochemical system impedance meter - Google Patents

Abstract

The invention relates to electrical measuring equipment and serves to increase the accuracy of measuring the minor impedance component, especially with component ratios. significantly different from one. The meter contains a cell 1 with reference electrodes 2, auxiliary 3, worker 4 and polarizing 5, porous diaphragm 6, current transformer 7, potentiostat 9, phase-sensing detector unit 11, electronically controlled attenuator 12, harmonic oscillator 13, amplifier 14, a current to voltage converter 15, a quadrature phase shifter 17, and a block of 20 indicators. To achieve this goal, a voltage follower 8, a switch 16, an electronically controlled attenuator 18, a modular indicator 19 of quasi-equilibrium are introduced, and new functional connections are formed. 1 il. with (L

Description

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The invention relates to electrical measuring equipment, can be used primarily to study the properties of electrochemical systems according to the results of measurements of the impedance of these systems in a wide range of frequencies when they are polarized with a given current or potential, and is an improvement of the known device according to the author. St. 1101756,

The purpose of the invention is to improve the measurement accuracy of the non-primary impedance component, especially when the ratios of the components differ significantly (by an order of magnitude or more) from one.

The drawing shows a functional diagram of an impedance meter of electrochemical systems.

The meter contains a cell 1 with a solution, a reference electrode 2, an auxiliary 3, a worker 4 and a polarizing 5 electrodes, a porous diaphragm 6, a current transformer 7, a voltage follower 8, a potentiostat 9, a connecting cable 10, a unit 11 of phase-sensitive Detectors, the first electronically controlled attenuator 12, 13 harmonic oscillator, amplifier 14, current-to-voltage converter 15, switch 16, quadrature phase shifter 17, second electronically controlled attenuator 18, modular pointer 19 quasi-equilibrium and indicator 20 Hur

Moreover, the reference electrode 2, the auxiliary 3, the worker 4 and the polarizing 5 electrodes are immersed in the solution cell 1. The polarizing electrode 5 is separated from the main cell volume by the porous diaphragm 6, which prevents the reaction products that form on the polarizing electrode from getting into the main cell volume. when a constant component of current flows through it. The working electrode 4 is connected through the primary winding of the current transformer 7 and the output of the voltage follower B to the common wire of the meter. Potentiostat 9 is connected by its potential input and output respectively to the reference electrode 2 and the polarizing electrode 5. A signal is connected between the common wire and the auxiliary electrode 3 via the connecting cable 10.

input of the unit 11. phase-sensitive detectors and the output of the first electron

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15

20

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25

35

40

five

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but a controlled attenuator 12, the signal input of which is connected to the harmonic oscillator 13, and the control input through the detector and error signal amplifier setting the desired value of the variable component of the working electrode 4 and the current measuring converter 15 in voltage is connected to the first secondary output windings. Transformer 7 current. The output of the current-to-voltage measuring converter 15 is connected to the first input of the switch 16, the reference input of the block 11 of phase-sensitive detectors and the input of the quadrature phase shifter 17 connected by its output to the second inputs of the reference block 11 of phase-sensitive detectors and the switch 16, which is combined by its output with the input of the second electronic - a controlled attenuator 18 and the first input of the modular indicator 19, quasi-equilibrium, the second input of which is connected to the input of the voltage follower 8, the first input of the indicator 20 indicator moat and output electronically controlled attenuator 18, a control input connected to the output of the modular indicator quasi-equilibrium, second and third inputs of the display unit connected to outputs of the phase-sensitive detector unit.

Measuring impedance electrochemical systems works as follows.

In the initial state, the switch 16 is set to the position corresponding to the zero potential at its output. In the meter circuit, which includes a serially connected output of an electronically controlled attenuator 12, a connecting cable 10, an electromechanical cell between the auxiliary 3 and the working 4 electrodes with a measured pulse Z |, the primary winding of the current transformer 7 and the output of the voltage follower 8, the setpoint harmonic component ip current mode is organized. For this, the current t is transmitted through the current transformer 7 to the current measuring converter 15 to the voltage forming the voltage

one

15

equal to

i, ipk C-Kij) -iK, k ,,,

31368812

where K and K, y are, respectively, the voltage output of the repeater 8, the voltage required to transmit the current transformer 7 and the current to current measuring converter 15.

The voltage in the detector and amplifier 14 of the error signal is detected, compared in level with the terminal O, i.e. connected to the common data exemplary U, and then to the output, then the voltage U, formed at the output of the first electronically controlled attenuator 12, the divided error signal is amplified here and fed to the control input of the electronically controlled attenuator 12, changing its output voltage and, therefore, the magnitude of the current ip so that the statistical error is neglected, at the input of the detector and amplifier 14 of the error signal is

/ U, 5 / and „. (2) From expression (2), taking into account (1) the name and. The voltage U, enters the block 15 11 phase-sensitive detectors,

where is decomposed into real and imaginary components

20

Reil, K / Zjcosq KR; ImU, K | z / sincpn KX,

on which the required R and X components of the measured impedance b, expression (3) are read directly. If one of the components prevails in the measured impedance, in order to increase the accuracy of measuring the minor component, the switch 16 is set to the position corresponding to the nature of the dominant component. In electrochemical systems, the ratios are traditional.

UT

/ IP / and, // to,. To „/.

If in the working frequency range of the meter Kj K, -, and K, j K, 5, then the value of / ip /, y K const does not depend on the change of the measured impedance 2 „. In the meter under consideration, the direction of the vector U, y is taken as the origin of the phase angles of the other vectors. Therefore, the voltage U as a reference is fed to the inputs of the block 17 of phase-sensitive detectors and the quadrature phase shifter 1 7,

Current 1., flowing through the measured impedance Z, creates a voltage drop across it

and ipZ K / ZH / (COSCP + jsincfj

 KR jKX, (3)

where q) is the phase shift between vectors and and IP;

J 1-1;

R / ZjcosCf;

X sincp - real and imaginary components - impedance vectors IP and u, 5 antiphase.

Since in the initial state, the voltage meter on the primary winding of the current transformer 7 and

zero (the secondary winding of the transformer operates in a mode close to short circuit due to the low input resistance of the current-to-current converter 15), and the switch 16 in the initial state of the meter is set to full and. The voltage U, enters the block 15 11 phase-sensitive detectors,

where is decomposed into real and imaginary components

20

Reil, K / Zjcosq KR; ImU, K | z / sincpn KX,

on which the required R and X components of the measured impedance b, expression (3) are directly counted. If one of the components prevails in the measured impedance, in order to increase the accuracy of measuring the minor component, the switch 16 is set to the position corresponding to the nature of the dominant component. In electrochemical systems, the ratios are traditional.

Consider an example of the operation of the device in the case of measuring impedance

ZM with the predominant component R. At the indicated ratio of the components Z ,. switch 16 is set to

the position R, and the inputs of the electronically controlled attenuator 18 and the modular indicator 19 of quasi-equilibrium supply voltage and, from the output of the current measuring converter 15, to the voltage. Voltage U, 5 is mastabilized in an electronically controlled attenuator 1B and then applied through the voltage repeater 8 between the second end of the primary winding of the current transformer 7

and common drive. In this case, the voltage

and.

, B-18;

where Kg 1;

55 18 the value of the coefficient of transmission of the corresponding nodes, and Ug and U | a are in phase and, therefore, antiphase the direction of the current 1p. The value kaffiii1M ta K, g us5136

is modulated by a modular indicator 19 of quasi-equilibrium so that a quasi-equilibrium takes place in the measuring circuit,

uu ,, / and, - (and ,, - uu, 5) / - / it- (and, 8 +

+ Lee ,,) ,, / and;, / - / and, o, (4)

where K, is the transfer ratio of the indicator 19.

If relation (4) is not satisfied, i.e. or whether ,,: 0, then, at the output of the modular indicator 19 of quasi-equilibrium, a positive voltage is respectively generated and K, g increases or a negative voltage and K, g decreases. The change in K, d occurs until relation (4) is not fulfilled. In this case, the following relations are valid in the measuring circuit:

and „UN- U, g; ReU., UmU, 0;

/ and, g / Ipl, KZ sintf; / U, J ReU, e KZ.costf.

(5) (6)

With the predominant value of the imaginary component (X) of the impedance ZH, the switch 16 is set to X. In this case, the inputs of the electronically controlled attenuator 18 and the modular indicator 19 quasi-equilibrium are connected to the output of the quadrature phase shifter 17, which forms the voltage 47 When the quasi-equilibrium is reached characterized by equality

uu ;, / u.-j (u.8- li, 5) / - / UH- j (U, e + uU, 5) ,, О, (7)

in the measuring circuit

  UH-jU, s; Re {jU, e Imu ,, Oh,

50

| u; j ReUH KZ, cosC; “; (Q) / jU, e | ImU, KZ ,. (9)

As follows from expressions (5), (6) and (8), (9), when the quasi-equilibria (4) or, 55 (7) reach the measuring circuit, the desired values of the components R and X of the impedance Z can be directly measured by the values of the output modules stress U ,, (UJj) and 11, (jU | g)

0

five

50

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electronically controlled attenuators 12 and 18 or by the values of their transfer coefficients K, .j and K, g.

Claims (1)

If the condition of the quasi-balance of the weight is set roughly (for example, if a sufficiently high speed of the modular gauge is needed) quasi-equilibrium the discreteness of setting the transmission coefficient of the electronically controlled attenuator DC, p is chosen large, in particular LC, g 0.01 KISMOKC) G o voltage vector U ( or i) contains information about both the minor component U, and the over or under-compensated value of the dominant component. In this case, the predominant component Z is counted by the sum of the counts of the value of the modulating voltage module U, g and jU, g and the output voltage (including polarity) of the block 11 of phase-sensitive detectors, whose reference signal is collinear to the prevailing component Z, the count the minor component is produced by the value of the output voltage of the phase-sensitive detector, whose reference signal is colliarine with the minor component. Invention Formula Impedance meter of electrochemical systems according to ed. St. No. 1101756, characterized in that, in order to improve the measurement accuracy of the non-fundamental impedance component, a switch, a modular quasi-equilibrium indicator, an electronically controlled attenuator and a voltage follower are included in it, the output of which is connected between the second terminal of the primary current transformer and the common impedance meter, and the input is connected to the first inputs of the modular quasi-equilibrium indicator and the block of reading devices and the output of the second electronically controlled attenuator connected by its own the control input with the output of the quasi-equilibrium modular indicator, and the signal input with the second input of the quasi-equilibrium modular indicator and switch output, the first input of which is connected to the output of the current-to-voltage measuring converter, and the second input is connected to the output of the quadrature phase shifter, and the third one is connected to the common impedance meter