Ammeter working principle.

A digital ammeter is an instrument that measures the flow of an electrical current in a circuit. The measurements are given in amperes, the unit for measuring electrical current. Power Distribution Units (PDUs) distribute power to multiple devices through a single electrical source.
ammeter, instrument for measuring either direct (DC) or alternating (AC) electric current, in amperes. An ammeter can measure a wide range of current values because at high values only a small portion of the current is directed through the meter mechanism; a shunt in parallel with the meter carries the major portion.