Ammetre

[technoguy]

To measure larger currents, a resistor called a shunt is placed in parallel with the meter. Most of the current flows through the shunt, and only a small fraction flows through the meter. With this solution, arbitrarily large currents can be measured with a single meter. Traditionally, the meter used with a shunt reaches full-scale deflection when a voltage of 50mV is placed across its coil, so shunts are typically designed to produce a voltage drop of 50mV when carrying their full rated current.

[vipl]

A voltmeter is a device used to measure the voltage potential between two points in an electrical circuit. Technically, all voltmeters are ammeters, as they measure current rather than voltage. Although current is measured in amps, Ohm's Law, which establishes the relationship between voltage, current and resistance, can be used to scale the amps to volts.