DD148387B1 - CIRCUIT ARRANGEMENT FOR CHRONOPOTENTIOMETRIC MEASUREMENTS - Google Patents

Description

Circuit arrangement for chronopotentiometric measurements

Field of application of the invention

The invention is applicable to electronic analyzers which allow the performance of chronopotentiometric measurements.

Characteristic of the known technical solutions

The chronopotenticmetry is a measurement method that allows to obtain knowledge about the kinetics of slektronenprozessen · Иіг fast-running reactions it is necessary to make the switch from potentiostatic to the Gaivanostatischen state in the shortest possible time ·

There is a circuit arrangement known / 1 /, which realizes the galvanostatic operation in that the potentiostatic input variables are compensated by means of an additional operational amplifier. The complete compensation of the potentiostatic input variables makes high demands on the quality of the additional amplifier and on the accuracy of the resistors used for its wiring. There must be six resistances in their vows very exactly match, otherwise errors in the galvanc- static regulation occur. The switching speed of the potentiostatic in the galvanostatic state is in this arrangement by the

/ 1 /: J.SlectrocIiem.Soc. 117 (1970) 3, IGAC-IC44

Time constants of the additional amplifier reduced.

Furthermore, a circuit arrangement has been proposed / 2 /, in which for the potentiostatic and for galvanostatic operation depending on a separate controller, which can be optionally switched to a power amplifier, «

In order to enable the fastest possible switching between the operating modes, it is necessary to track the respective non-engaged controller by means of additional switches.

Object of the invention

The aim of the invention is to facilitate the switching from potentiostatic to galvanostatic control required in chroncpotentiometric measurements in a simpler, more accurate and faster manner.

Explanation of the essence of the invention

The invention has for its object to reduce the burden of controllers and amplifiers.

According to the invention, this is arranged in an arrangement with a potentiostatic control loop in which an electrochemical casting cell with measuring, reference and counter electrode and a control amplifier, wherein the control amplifier is assigned a voltage source for generating the desired voltage for the potentiostatic operation whose input at the Reference electrode is located and whose output is connected to the counter electrode, thereby achieved that inserted in the potentiostatic control circuit between the output of the control amplifier and the counter electrode of the measuring cell, a switch

/ 2 / B -7? 159 275

is and that with the connection point of the counter electrode and switch, a terminal of an electronically controlled power source for galvanostatic operation via a Gleichstromleiteinrichtung is firmly connected.

As a switch z. 3. a field-effect transistor can be used. · In the closed state of the switch, the potentiostatic rule is present. As a result of the permanently connected current source, a current is simultaneously fed into the potentiostatic control circuit in this state. This current is expediently chosen to be equal to the value required for the galvanostatic control. The injected current is a disturbance for the potentiostatic control circuit. However, Sr is compensated in its effect on the potentiostatically controlled process in the electrochemical cell.

The potentiostatic control loop is interrupted by opening the switch. · Only the current of the current source flows through the measuring cell. Since the S + rom was chosen to be the same as that required for galvanostatic control, the galvanostatic control is realized by opening the switch.

By eliminating time-constant auxiliary control amplifiers, such as those used in the arrangements of the prior art, a substantial increase in the switching speed is achieved. Errors in the control accuracy due to the non-ideal behavior of the auxiliary or reserve controllers are avoided.

embodiment

The invention will be explained in an embodiment with reference to a drawing.

In the drawing, an electrochemical measuring cell Z is shown, which has a Ließelektrode Ы, a reference electrode R and a counter electrode G. The measuring cell Z is located in a potentiostatic control loop, which in particular has a variable gain amplifier У. Associated with this is a voltage source U, which supplies the setpoint voltage for potentiostatic operation. The control amplifier V is followed by a switch S in the form of an eldeffekttransistor3, by means of which the potentiostatic control loop is opened.

To the potentiostatic control circuit, an electronically controlled current source Q is coupled so that it also lies on the counter electrode G of the measuring cell Z. The current supplied by the power source is expediently chosen to be equal to the '.7erѢ required for the galvanostatic control.

In potentiostatic operation, the switch 3 is initially closed, d. H. that the output of the control amplifier V is located at the counter electrode. At the same time, a current enters the control circuit from the current source Q. This current is a disturbance to the control loop. However, the effect of this current on the potentiostatically controlled process in the reject cell is compensated by the control loop.

By opening the potentiostatic control circuit by means of the switch 3, the galvanostatic control case is realized by the currently acting as a disturbance current L-, the current source Q now flows through the Ließzelle Z.

Claims (2)

invention claim 1. Circuit arrangement for chronopotentiometric measurements with a potentiostatic control loop, in which an electrochemical Iießungszelle with I £ eß-, reference and counter electrode and a control amplifier are arranged, wherein the control amplifier is assigned a voltage source for generating the set voltage for potentiostatic operation, the input is located at the reference electrode and whose output is connected to the counter electrode, characterized in that in the potentiostatic control loop between the output of the control amplifier O ") and the counter electrode (G) of the measuring cell, a switch (S) is inserted and that with the connection point of counter electrode (G) and switch (S) a terminal of an electronically controlled current source (Q) for galvanostatic operation via a DC Leiteinrichtung is firmly connected. 2. Arrangement according to item 1, characterized in that a Peldeffekttransistor is arranged as a switch (3) . For this 1 sheet drawing