Four-wire sense resistors provide two power connections and two sense wires in order to make a precision measurement. Newer two-wire devices are available in values as low as 250 micro-ohms (µ?), with wide pads to minimize inductance. In the most simplistic case, we could assume that a device such as this can be represented as a single resistor with two connections. But in real applications that assumption could lead to incorrect measurements as demonstrated in this article.
Using a simple, but precise test set up, measurements are taken on a 1-m? 5% metal-foil current-sense resistor mounted to a small PCB. These measurements enable development of a finite element analysis model, which provides insights into the PCB’s influence over the resistor’s actual value in an application and what steps designers can take to obtain the desired or specified value.