There are several ways to make resistors for electrical or electronic circuits. Carbon resistors are made by attaching leads to a bar or rod of carbon material. The material is usually made by suspending carbon particles in a plastic material. The material “mix determines resistance.”

Carbon resistors have some serious limitations. They cannot dissipate much power, and are difficult to make with small resistance tolerances. However, automated manufacturing makes them in large quantities, so their cost is low.

Some resistors are made with metal films or oxides. These resistors are small and can be manufactured with good tolerances. But, they cannot handle higher power levels. Another type of film resistor is made with conductive inks. They are inexpensive, but are unstable and have limited power dissipation and poor resistance tolerances.

Wirewound resistors are made by winding a length of wire on an insulating core. They can dissipate large power levels compared to other types, and can be made with extremely tight resistance tolerances and controlled temperature characteristics.

Its length, cross-section area, and material determine the resistance of a wire. Copper is a good conductor, but has some resistance (to current flow.) A small diameter copper wire, 100 feet long, may have a resistance of a few ohms. However, a small diameter nickel alloy wire only one foot long may have a resistance of several thousand ohms.

Riedon makes wire wound resistors using wire of several metal alloys and sizes. The selection of wire depends on several factors. For example, a high resistance design would require a long copper wire and the resistor would be large. The same resistor could be made with a short length of nickel alloy wire, resulting in a much smaller device. However, when a high precision resistor is required, it is easier to trim resistance by removing a few inches of a low resistance wire, than by trimming millimeters of high resistance wire.