A galvanostat (also known as amperostat) is a

control Control may refer to: Basic meanings Economics and business * Control (management), an element of management * Control, an element of management accounting * Comptroller (or controller), a senior financial officer in an organization * Controllin ...

and

measuring Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determining how large or small a physical quantity is as compared ...

device capable of keeping the

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

through an

electrolytic cell An electrolytic cell is an electrochemical cell that utilizes an external source of electrical energy to force a chemical reaction that would not otherwise occur. The external energy source is a voltage applied between the cell′s two electrod ...

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 A practical electrical power source which is a linear electric circuit may, according to Thévenin's theorem, be represented as an ideal voltage source in series with an impedance. This impedance is termed the internal resistance of the source. ...

. The designation "''galvanostat''" is mainly used in

electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ...

: this device differs from common constant current sources by its ability to supply ''and

measure Measure may refer to: * Measurement, the assignment of a number to a characteristic of an object or event Law * Ballot measure, proposed legislation in the United States * Church of England Measure, legislation of the Church of England * Mea ...

'' a wide range of

s (from picoamperes to

amperes The ampere (, ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to elect ...

) 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 Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

are

directly proportional In mathematics, two sequences of numbers, often experimental data, are proportional or directly proportional if their corresponding elements have a constant ratio, which is called the coefficient of proportionality or proportionality constan ...

, i.e. :

U_c =

where *''

I_o

'' is the electric current that is kept constant *''

U_c

'' is the output control voltage of the amperostat *''

R_v

'' 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 ''

U

'' with a resistor ''

R_

'' connected in series: in order to force an almost constant current through a load, this resistor shall be much higher than the load resistor

R_

. As a matter of fact, the current ''

I

'' through the load is given by :

I = \frac

and if

R_x

R_

, the current ''

I

'' is approximately determined by ''

R_x

'' as follows :

I \cong \frac

This simple realization requires rather high voltages (~100 V) to keep the load

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 amperes (A); typical construction for use in the lower range of feed currents uses

operational amplifier An operational amplifier (often op amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative to c ...

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

External links

*Pierre R. Roberge (Webmaster) "
Galvanostat
'", corrosion-doctors.or

Electroanalytical chemistry devices

Technical realization

Example of application

See also

External links