Film Resistors: Coated Core and a Cut Helix

Most axial-leaded resistors are film resistors. A thin resistive film is put on an insulating core, and a helix is cut through it, turning the film into a long, narrow path; the length of that path sets the resistance. Carbon film resistors use a film of carbon and cover about 1 ohm to 10 megohms at 0.125–5 W. Metal film resistors are usually coated with nickel chromium, applied for example by sputtering in a vacuum; cut the same way, they reach tolerances of 0.5–2 % and temperature coefficients of about 50–100 ppm/K. The value is marked on the body with coloured bands, the electronic colour code.