Using a clipped length of copper wire will demonstrate this point. In a motor drive, the torque will fall off as the motor operates due to the increasing resistance of the copper sense resistor, as it heats. Wire made of alloys with low TCs are available for use instead. But sometimes a copper sense resistor, whether as a discrete wire resistor or a circuit-board trace, can be used to advantage. Actual Sense Resistors One simple approach to sense resistors is to make your own out of a low TC conductive material.
Smaller diameters are available and the wire can be bought by the roll.
Cut the wire to length for the desired resistance, tin the ends, and solder into the board. By keeping the half-loop area small, inductance is minimized. The one shown has a resistance of 25 m . Several companies, such as Caddock Electronics, now supply these accurate, low TC, power resistors at an attractive price for power-circuit design. Manganin, however, is superior to nichrome in TC and long-term stability of resistance value.