Precision resistors are pivotal in electronic devices, particularly where high accuracy is imperative. Broadly, they are categorized into three types: metal film resistors, wirewound resistors, and block resistors, each with distinct characteristics and applications.
1. Metal Film Resistor
Metal film resistors, the most prevalent type of precision resistors, boast a small temperature coefficient. This means they maintain stable resistance values despite temperature variations, making them ideal for high-accuracy electronic equipment. However, their vulnerability lies in the film component, susceptible to damage during helical cutting and crimping processes.
2. Wirewound Resistor
Wirewound resistors, once the go-to in high-precision devices, are still common in the electronics field. They utilize three main types of resistance wire materials:
- Constantan: Traditional, with commendable heat resistance. Its downside? A less-than-ideal temperature coefficient and higher thermal electromotive force from copper, potentially impacting accuracy.
- Manganese Copper: A popular choice for its smaller temperature coefficient and lower thermal electromotive force than copper, despite its inferior heat resistance compared to constantan.
- Evanohm: Comprising a nickel-chromium-aluminum-copper alloy, it boasts the smallest temperature coefficient. However, its hardness poses challenges in welding.
3. Block Resistance
Block resistors, or metal foil resistors, involve an alloy resistance layer adhered to a ceramic substrate. Brands like Vishay lead this category, employing nickel-chromium resistance alloys and leveraging ceramic substrates for temperature compensation. This achieves exceptionally low temperature coefficients, sometimes under 1ppm/℃. In the domestic sphere, models like RJ711, though not as advanced, still find their niche in the local market.