The device measures the differential voltage developed across a resistor when current flows through it. This resistor is commonly referred to as a current-sensing resistor or a current-shunt resistor, with each term commonly used interchangeably. The flexible design of the device allows a wide range of input signals to be measured across this current-sensing resistor.

Selecting the value of this current-sensing resistor is based primarily on two factors: the required accuracy of the current measurement and the allowable power dissipation across the resistor. The larger the voltage developed across this resistor the more accurate of a measurement that can be made because of the fixed internal amplifier errors. These fixed internal amplifier errors, which are dominated by the internal offset voltage of the device, result in a larger measurement uncertainty when the input signal gets smaller. When the input signal gets larger, the measurement uncertainty is reduced because the fixed errors become a smaller percentage of the signal being measured.

A system design trade-off for improving the measurement accuracy through the use of the larger input signals is the increase in the power dissipated across the current-sensing resistor. Increasing the value of the current-shunt resistor increases the differential voltage developed across the resistor when current passes through it. However, the power that is then dissipated across this component also increases. Decreasing the value of the current-shunt resistor value reduces the power dissipation requirements of the resistor, but increases the measurement errors resulting from the decreasing input signal. Finding the optimal value for the shunt resistor requires factoring both the accuracy requirement of the application and allowable power dissipation into the selection of the component. An increasing amount of very low ohmic value resistors are becoming available with values reaching down to 200 μΩ with power dissipations of up to 5 W, thus enabling very large currents to be accurately monitored using sensing resistors.

The maximum value for the current-sensing resistor that can be chosen is based on the full-scale current to be measured, the full-scale input range of the circuitry following the device, and the device gain selected. The minimum value for the current-sensing resistor is typically a design-based decision because maximizing the input range of the circuitry following the device is commonly preferred. Full-scale output signals that are significantly less than the full input range of the circuitry following the device output can limit the ability of the system to exercise the full dynamic range of system control based on the current measurement.