A qualified precision resistor must have the characteristics of small aging, small temperature drift and small deviation. At the same time, it is best to have high reliability, large power margin, small temperature rise, low noise, small series inductance distributed capacitance, small voltage coefficient, welding, Vibration and tension are not easy to change, etc.
 

The most important parameter to measure a precise resistance is aging, followed by a temperature coefficient. As to whether the resistance superscript is 1 / 0. 1 or 0. 01, this is a deviation and does not represent "precision" directly. Precision resistor aging refers to its long-term stability, that is, the resistance changes at room temperature and atmospheric pressure on the shelf and over a relatively long period of time (say, one year). Aging is therefore often expressed by how many ppm changes each year. Aging is therefore an irreversible process that, like aging, can no longer return to its original form.

The resistance value of precision resistance will be changed by various factors. If the stability of precision resistance is not good, it is meaningless to have high precision. Provided that the precision of precision resistor is ±0.01%, but after a few months of storage or hundreds of hours of load, the resistance may change more than ±280ppm or more. The TCR of the precision resistance is usually small, so it is usually expressed by how many ppm per degree change, which is called the temperature coefficient. If the temperature coefficient of a resistance is 100ppm/ ℃, the resistance increases by 0.01% for every temperature rise. Similarly, the negative temperature coefficient indicates that the resistance decreases with the increase of temperature. When we say the temperature coefficient, we sometimes omit the latter / ℃. For example, the temperature coefficient of a certain resistance is 8 ppm, which means 8ppm/ ℃.
 

There are a lot of precision resistors in the domestic market, but they are mixed. When using precision resistors, we should consider the stability of precision resistors first, rather than pursuing its high precision unilaterally.