How does a Shunt Resistor Work?

A shunt resistor works by measuring either direct or alternating current that flows in an electrical circuit through the voltage drop that is generated across the resistance. Also known as a current shunt, this precision device uses the principle of Ohm's Law, which is mathematically represented by the equation V = I×R, where "V" indicates voltage, "I" denotes current and "R" is resistance.

The functionality of shunt resistors is generally indicated in terms of their current rating, output voltage, resistance drift, resistance accuracy and power rating. Modern ammeters are typically designed with a shunt resistor. This arrangement allows full current load to flow through the ammeter shunt.

Traditional ammeters, meanwhile, require an external shunt resistor. This set-up involves a parallel connection of the shunt resistor. This is common in motor vehicles. The concept behind the application is that only a small portion of the measured current flows through the galvanometer while the rest passes through the shunt resistor. The low-resistance property of shunt resistors enables large currents to be measured without damaging the galvanometer.