To determine the effects of temperature variation on a copper trace shunt resistor, the traces were placed in a temperature chamber to control the ambient temperature. It should be noted that fewer data points were taken in the chamber due to the added time needed for the board to reach the chamber temperature between trace measurements. Also, only the three inch separation is considered. As in the case of the room temperature measurements, it is possible to plot how resistance changes with current. Similar trends were observed relative to room temperature, and the plots are shown in Figure 2-6. The 100-mil, bottom tap off plots are used to demonstrate the changes across temperature, as every trace width performed similarly.

The plots in Figure 2-6 show that, as ambient temperature increases, the resistance also increases which is consistent both with what is expected and previous results. Figure 2-7 demonstrates how much the resistance changes with temperature by plotting the maximum recorded resistance for each trace with respect to the ambient temperature. The 0 A measured resistance is not included.

The plots in Figure 2-7 indicate that as ambient temperature increases, so does the measured resistance. This is an important factor to keep in mind, as the operating temperature of an application using a copper trace current shunt must be taken into account for proper calibration. As in the case of the room temperature environment, the average percent errors, this time across a range of temperatures, were calculated and are displayed in Table 2-4.

The values in Table 2-4 demonstrate potential design considerations. All traces except the 1750-mil trace experienced a decrease in errors as temperature increased. The 1750-mil trace had its lowest error at 25C. This is because resistance increases with temperature, and since all of the traces with the exception of the 1750-mil trace started at significantly lower resistances than expected due to the PCB manufacturing process, it makes sense that as the temperature and resistance rises they approach the ideal value. For applications that might be significantly warmer than 25°C, a smaller trace might be acceptable depending on the temperature rise.