Galvanostat
5298902
199833293
2008-03-21T14:37:25Z
Mild Bill Hiccup
5202324
"current flow" --> "current"
A '''galvanostat''' is a [[control]] and [[measuring]] device capable to keep constant the [[Electric current|current]] through an [[electrolytic cell]] in [[coulometric]] [[titrations]], disregarding changes in the load itself. A synonym is "''[[amperostat]]''".
Its main feature is its ''nearly'' "''infinite''" (i.e. extremely high respect to common loads) internal [[electrical resistance|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 [[Polarity (physics)|both polarities]].
== 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.
== See also ==
*[[Amperostat]]
*[[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:Electrochemistry]]