View source for Galvanostat

A '''galvanostat''', (also known as '''amperostat''') is a [[control system|control]] and [[measuring]] device capable of keeping the [[Electric current|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 [[current source|constant current sources]] by its ability to supply ''and [[measurements|measure]]'' a wide range of  [[Electric current|current]]s (from [[picoampere]]s to [[amperes]]) of [[Electrical polarity|both polarities]].

The galvanostat responds to changes in the [[Electrical resistance|resistance]] of the cell by varying its output potential: as [[Ohm's law]] shows, 
:<math>{R} = {U \over I}</math> 
the variable system resistance and the controlled [[voltage]] are [[Directly proportional#Definition|directly proportional]], i.e.
:<math> U_c ={R_v \times I_o}</math>
where 
*''<math>I_o</math>'' is the electric current that is kept constant
*''<math>U_c</math>'' is the output control voltage of the amperostat
*''<math>R_v</math>'' is the electrical resistance that varies;
thus, an increase of the load resistance implies an increase of the voltage the amperostat applies to the load. 

== Technical realization ==

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

:<math> I = \frac{U}{R_x + R_{load}} </math>

and if <math>R_x</math>>><math>R_{load}</math>, the current ''<math>I</math>'' is approximately determined by ''<math>R_x</math>'' as follows

:<math>I \cong \frac{U}{R_x}</math>

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

== Example of application ==

Galvanostatic deposition techniques can be used for some thin film deposition applications where there is no need to control morphology of the thin film.{{Citation needed|date=January 2016}}

== See also ==
*[[Current source]]
*[[Potentiostat]]

== External links ==

*Pierre R. Roberge (Webmaster) "''[http://www.corrosion-doctors.org/Instrumentation/galvanostat.htm Galvanostat]''", corrosion-doctors.org [http://www.corrosion-doctors.org/Principles/Glossary.htm Electrochemistry Dictionary].

[[Category:Electroanalytical chemistry devices]]