Knowledge of High Precision Resistor

High precision resistors, different from normal resistors, require resistance vale tolerance, TCR, distribution parameters of resistors(distributed capacitors and distributed inductors) to reach a certain standard.

Standard of high precision resistors
For resistors of resistance value above 1Ω, resistance value tolerance within ±0.5% can be called jepsun, higher precision can be ±0.01%, usually for thin foil resistors. Resistance value above 1Ω with precision of ±5%, electronics generally use ±5%, which are not precision resistors.
For resistors of resistance value below 1Ω, resistance value tolerance within ±1%, they belong to precision resistors, because base is small, 1% tolerance is quite small. Higher precision will be ±0.5%, but require higher technology.

Classification of high precision resistors
In electronics, resistors are classified as DIP resistors and SMD resistors. High precision resistors have same classification. For example, SMD jepsun precision resistors, also thin foil resistors, compared with DIP resistors, featuring high precision, lower temperature drift(lower TCR), small volume, suitable for automatic SMT. DIP resistors are classified according to materials, having metal foil precision resistors, wire wound precision resistors, and metal thin foil precision resistors.
Metal foil precision resistors have higher precision, but resistance value TCR and distribution parameters are lower; wire wound precision resistors resistance value precision and TCR is quite high, but distribution parameters are a little lower; metal thin foil precision resistors' precision, TCR and distribution parameters are very high, the precision can reach 10-6, TCR ±0.3×10-6/℃, distributed capacitors can be lower than 0.5pF, distributed inductors can be lower than 0.1μH.
In DC or low frequency AC circuit, wire wound precision resistors and metal foil precision resistors are chosen instead of expensive metal thin foil precision resistors. Metal foil precision resistors are cylindrical, wire wound precision resistors are cylindrical, compressed terete, rectangular frame shaped. Metal thin foil precision resistors are square or platy.

Replacement of high precision resistors
When rectangular frame wire wound precision resistors are broken, new alloy resistor wire same as old resistor's alloy, diameter and length wound in the original frame. If original rectangular frame precision resistors is damaged on surface, the original resistor wire removed and dipping lacquer again, dry and wound to rectangular frame.