Amperostat

A galvanostat, (also known as amperostat) is a control and measuring device capable of keeping the current through an electrolytic cell in coulometric titrations constant, disregarding changes in the load itself.

Its main feature is its nearly "infinite" (i.e. extremely high in 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.

The galvanostat responds to changes in the resistance of the cell by varying its output potential: as Ohm's law shows,

the variable system resistance and the controlled voltage are directly proportional, i.e.

where

thus, an increase of the load resistance implies an increase of the voltage the amperostat applies to the load.

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

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