A new trimming approach for shunt resistors used in metering applications

A growing number of smart energy meters and electric charging stations have sparked a demand for a high precision, low value shunt resistors to measure the flow of electrical current. This paper investigates the possibility of trimming 100 micro ohms Manganin shunt resistors with tolerance of 5 percent to improve their accuracy and performance for use in smart energy meters. In theory, reducing the standard 5 percent tolerance of the shunt resistors can be achieved by removing controlled amounts of the resistive material. In this experiment, theoretical analysis is carried out to determine the maximum amount of resistive material that can be removed from Manganin shunt resistor to reduce its standard tolerance of 5 percent. Two alternative designs are then used to trim the material from the Manganin strip using machining techniques. Implications of the experimental results to the flow of electrical current and temperature rise in the shunt resistors are discussed. Results from the initial trimming trials show that the standard tolerance of 5 percent can be reduced to less than 1 percent.