Resistors are components, which resist or limit the flow of electric current in a circuit. They are designed to protect a circuit. The unit of measure is the ohm. An additional important characteristic is the wattage rating which indicates the power needed for the resistor to function.
Resistors are rated with a tolerance, which indicates the upper and lower limits of variation from a components nominal value i.e., an allowable deviation. These ratings are usually indicated by a % value. The lower the % ratings are on a part the better the tolerance.
Most film resistors are identified by a system of different color bands indicating the ohms, tolerance and a failure rate when applicable.
The wattage rating is determined by size.
Rating power (W) |
Thickness (mm) |
Length (mm) |
---|---|---|
1/8 | 2 | 3 |
1/4 | 2 | 6 |
1 | 3.5 | 12 |
2 | 5 | 15 |
Resistors are produced in many styles and can be composed of a variety of different materials, each of which provides its unique resistance properties.
Adjustable Wireound | MELF | Thick Film Surface Mount Chip |
Aluminum Wirewound | Metal Film | Thin Film Surface Mount Chip |
Axial Wirewound (Silicon Vitreous Enamel) |
Metal Oxide | Tubular Wirewound |
Carbon Composition | Potentiometers | Variable Cermet and Wirewound |
Carbon Film Ceramic Cased (Sandstone) Wirewound |
Resistor Networks | |
Fixed Cermet | Rheostats |
Allen Bradley | Futaba | Mepco | S.E.I (Stackpole) |
Angstrom | Hardwick | Meritek | Shallcross |
BI Technology (formerly Beckman Industrial) |
Huntington Electric | Milwaukee Resistor | Spectrol |
Bourns | Iskra | Ohmite | Tel-Labs |
Bradford (BEI) | IRC | Pacific | Tocos |
Caddock | Jaro | Philips | Tru-Ohm |
Cal-R | Kelvin | Piher | Vishay |
Clarostat | KOA | RCD | Vitrohm |
Colber | KRL | RCL | Ward Leonard |
Corning (CGW) | Ktronics | R.G.Allen | Yageo |
CTS | Lectrohm | Rohm | |
Dale | Memcor | Sage |