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# 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". The amperostat respond to changes in the resistance of the cell by varying its output potential: as Ohm's law shows,

${R} = {U \over I}$

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

$U_c ={R_v \times I_o}$

where

• Io is the electrical current that is kept constant
• Uc is the output control voltage of the amperostat
• Rv 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. 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.