In the world of electronic components, precision resistors occupy a niche, and their accuracy and stability are critical to the design of high-performance electronic devices. The definition of precision resistors involves several key elements, including temperature coefficient, aging rate and initial adjustment error. These factors jointly determine the performance and applicable scenarios of the resistor.
Effect of temperature coefficient
The temperature coefficient, usually expressed in ppm/℃, reflects the effect of temperature changes on the resistance value. Ideally, the resistance value should be stable, but in reality, small changes in temperature can cause the resistance value to fluctuate. For example, a resistor with a temperature coefficient of 100ppm/°C means that the resistance value will change by 0.01% for every 1°C change in temperature. In precision electronic measurement and control systems, this variation can result in significant performance differences.
Aging rate considerations
The aging rate of a resistor refers to the long-term stability, which indicates the tendency of the resistance to change over time. Even a resistor that is extremely accurate when shipped from the factory will degrade in accuracy over time if it has a high aging rate, affecting the performance of the entire electronic system. Aging rate is usually measured in ppm/year or %/year, and this indicator is critical to ensuring long-term reliable operation of electronic equipment.
initial adjustment error
Although initial adjustment error is not considered a major concern in some cases because it can be corrected through calibration as long as it remains stable, it is still an important measure of a resistor's accuracy when first used.
Classification and application of precision resistors
There are various types of precision resistors, including metal film resistors, wirewound resistors, and block resistors, each type being suitable for different applications due to its unique properties.
Metal film resistors: are widely used because of their low temperature coefficient and relatively stable resistance. However, its thin-film structure makes it relatively fragile and needs to be designed with this in mind.
Wirewound resistors: This type of resistor once became the first choice for high-precision equipment due to its excellent accuracy and stability. They use different resistance wire materials, including constantan, manganese copper, and Evanohm, each with different characteristics, such as temperature coefficient and heat resistance.
Block resistor (metal foil resistor): Represented by foreign manufacturers such as Vishay, this type of resistor uses nickel-chromium resistance alloy and ceramic substrate to further reduce the temperature coefficient and achieve extremely high accuracy.