The Universal Shunt

A device that enabled galvanometers to measure very large currents The Universal Shunt was used to adjust the sensitivity of a galvanometer. In the test set it also helped to protect the galvanometer from overloading when dealing with currents of an unknown strength.

How it worked A Universal Shunt, shown here connected to the Mirror Galvanometer in the Test Set. With a circuit of unknown strength, testing would begin with the shunt set to its lowest value, which protected the galvanometer from almost all of the current.

In this circuit, the current through the galvanometer depends upon the following relationship: Resistance of the galvanometer plus the resistance of the whole circuit, divided by the resistance of the shunt. Since current is proportional to Rgalvo + Rtotal/Rshunt halving the value of Rshunt doubles the sensitivity of the galvanometer, regardless of the resistance of the other components.