Potentiostats and galvanostats are electrochemical instruments used in electrochemistry, battery and fuel cell testing, corrosion control, voltammetry, biomedical research, surface imaging, and related applications. Potentiostats are used to keep the potential (voltage) between a working electrode and a reference electrode at a constant value. Galvanostats are used to maintain a constant flow of current through an electrolytic cell. With potentiostats, the signal from the reference electrode is fed through an impedance transformer which amplifies the input current, but leaves the voltage unchanged. An input resistor protects the buffer from static loads, and a capacitor reduces the intrinsic noise. Like potentiostats, galvanostats function as electronic amplifiers with low feedback. A simple galvanostat produces a constant voltage with a resistor connected in series. To force the flow of a near-constant current through a load, this resistor needs to function at considerably higher levels than the load resistor. A more complex galvanostat can feed a constant current ranging from a few picoamperes (pA) to several amperes (A).