Galvanostat
Encyclopedia
A galvanostat 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. A synonym is "amperostat
".
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 current
s (from picoamperes to amperes) of both polarities.
with a resistor 
connected in series: in order to force an almost constant current through a load, this resistor shall be much higher than the load resistor 
. As a matter of fact, the current 
through the load is given by
and if
>>
, the current 
is approximately determined by 
as follows
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. These instruments are capable to feed constant currents in the ranges from few picoamperes (pA) to several ampere
s (A); typical construction for use in the lower range of feed currents uses operational amplifier
s.
Control system
A control system is a device, or set of devices to manage, command, direct or regulate the behavior of other devices or system.There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls...
and measuring device capable of keeping the current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
through an electrolytic cell
Electrolytic cell
An electrolytic cell decomposes chemical compounds by means of electrical energy, in a process called electrolysis; the Greek word lysis means to break up. The result is that the chemical energy is increased...
in coulometric titrations constant, disregarding changes in the load itself. A synonym is "amperostat
Amperostat
An amperostat is a control and measuring device used to keep constant the current flowing though electrolytic cells in coulometric titrations, disregarding changes in the load itself. Synonym is "galvanostat"...
".
Its main feature is its nearly "infinite" (i.e. extremely high respect to common loads) internal resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
.
The designation "galvanostat" is mainly used in electrochemistry
Electrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
: this device differs from common constant current sources
Current source
A current source is an electrical or electronic device that delivers or absorbs electric current. A current source is the dual of a voltage source. The term constant-current sink is sometimes used for sources fed from a negative voltage supply...
by its ability to supply and measure a wide range of current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
s (from picoamperes to amperes) of both polarities.
Technical realization
The simpler galvanostat consists of a high-voltage source producing a constant voltage with a resistor connected in series: in order to force an almost constant current through a load, this resistor shall be much higher than the load resistor . As a matter of fact, the current through the load is given byand if
>>, the current is approximately determined by as followsThis simple realization requires rather high voltages (~100 V) to keep the load current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
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. These instruments are capable to feed constant currents in the ranges from few picoamperes (pA) to several ampere
Ampere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
s (A); typical construction for use in the lower range of feed currents uses operational amplifier
Operational amplifier
An operational amplifier is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output...
s.
External links
- Pierre R. Roberge (Webmaster) "Galvanostat", corrosion-doctors.org Electrochemistry Dictionary.