Symbols with engineered values are one thing but Physical Resistor creation is another. Technology is where the creation of actual resistors comes into play. The opposition to current flow presented by a material is dependent on its conductivity, cross-sectional area, and applied voltage. Wire made from various metals, carbon composition, carbon film or metal film are all used to control current. Resistors are made with values ranging from milliOhms to MegOhms. The Tolerance ratings range from .1% to 20%. Most Fixed resistors are classified into the following groups:
Wire-wound Resistor – Metallic, ceramic, or porcelain bodies
Carbon Composition Resistor – Made of carbon dust or graphite paste
Film or Cermet Resistor – Made from conductive metal oxide paste
Semiconductor Resistor – surface-mount thin film technology
Wire Wound Resistors (Power Resistors)
Carbon Composition Resistor
Carbon Film Generates less noise than carbon composition, Low tolerance, Low cost, and Wide operating range
Metal Film Resistors operate better at higher frequencies than carbon film. They are usually 1% precision and more temperature stable than carbon film type
The above pictures show through hole Axial resistors. The term axial refers to components that lay flat as opposed to Radial components that stand up as shown below:
The term “Ceramic Resister” can be used for resisters that are only encased in ceramic. The term also applies to resistors that simply contain ceramic composition as a resistive element. Ceramic resistors can be used in high heat applications. But, they are noisy and not recommended for small signal use. Ceramic resistors come as radial and axial mount devices.
Much of through-hole technology has been upgraded to the superior surface mount technology(SMT). Manufacturing efficiency including logistics costs, all became improved with the advent of SMT. Components manufactured for SMT are referred to as surface-mount device (SMD).
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