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Galvanostat

A galvanostat is a control and measuring device capable to keep constant the current flowing through an electrolytic cell in coulometric titrations, disregarding changes in the load itself. Synonym is "amperostat".

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Its main feature is its nearly "infinite" (i.e. extremely high respect to common loads) internal resistance.

The designation "galvanostat" is mainly used in electrochemistry: this device differs from common constant current sources by its ability to supply and measure a wide range of currents (from picoamperes to amperes) of both polarities.

Technical Realization

The simpler galvanostat consists of a high-voltage source producing a constant voltage $U$ with a resistor $R x$ connected in series: in order to force the flow of an almost constant current through a load, this resistor shall be much higher than the load resistor $R l o a d$ . As a matter of fact, the current $I$ flowingh through the load is given by

$I = \frac{U}{R_x + R_{load}}$

and if $R x$ >> $R l o a d$ , the current $I$ is approximately determined by $R x$ as follows

$I \cong \frac{U}{R_x}$

This simple realization requires rather high voltages (~100 V) to keep the load current constant with sufficient approximation for all practical purposes. Therefore, more complex versions of galvanostats, using electronic amplifiers with feedback and lower voltages, have been developed and produced. This instruments are capable to feed constant currents in the ranges from few picoamperes (pA) to several amperes (A): typical construction for use in the lower range of feed currents uses operational amplifiers.