A DC shunt resistor is a small-value, precision resistor that is placed in series with a load so the current through that load can be determined. The voltage across the DC shunt is measured and Ohm’s law lets us find the corresponding current. The environment, physical orientation, electrical connection, and the current through the DC shunt all have a bearing on the accuracy and the longevity of a DC shunt.
It sounds simple, but I’ve seen plenty of engineers puzzled by the details. I saw it in students during my time as a professor of electrical engineering and electronics engineering technology, and I saw it in my colleagues at Sundstrand Corporation, an aerospace company, where I split my time working as an engineer. My split personality earned me the moniker “Professor” at Sundstrand.
Joe, a former cubemate, was one such puzzled engineer. He was working on a DC converter project in which the load current was to be monitored using a 50-ampere, 50mV DC shunt. He wanted the calibration laboratory to verify the resistance of the shunt and learn the calibration cycle. He informed the calibration laboratory technician the shunt would be exposed to a maximum current of 40 amperes, which is 20 percent below the shunt’s full-scale current.
The calibration technician informed Joe that DC shunts are not calibrated and therefore do not have a calibration cycle. Further, he told Joe that a current of 40 amperes is too large for a 50-ampere DC shunt. Seeing Joe’s look of confusion, he suggested that Joe “ask the professor.”