What are the characteristics of precision resistors?

Precision resistors are frequently used in circuits. A precision resistor is a resistor whose resistance value error, thermal stability (temperature coefficient), and distributed parameters (distributed capacitance and distributed inductance) all meet certain standards.

Precision resistors can be classified into several types based on their materials, including metal film precision resistors, wire-wound precision resistors, and metal foil precision resistors.

Metal film precision resistors have high accuracy, but their temperature coefficient of resistance and distributed parameters are slightly lower.

Wire-wound precision resistors have high resistance accuracy and temperature coefficient, but low distributed parameter performance.

Metal foil precision resistors have high precision, resistance temperature coefficient, and distributed parameters: precision can reach 10-6, temperature coefficient can reach ±0.3×10-6/℃, distributed capacitance can be less than 0.5pF, and distributed inductance can be less than 0.1μH.

Since the price of the three types of precision resistors mentioned above increases with performance, they should be selected appropriately based on the actual application. For example, in DC or very low-frequency AC circuits, wire-wound precision resistors or metal film precision resistors are generally sufficient; there is no need to choose expensive metal foil precision resistors. Metal film precision resistors are typically cylindrical; wire-wound precision resistors come in cylindrical, flat cylindrical, and rectangular frame shapes; metal foil precision resistors are often block-shaped or sheet-shaped. When wire-wound precision resistors have a large number of turns, a non-inductive winding method is often used, with the number of turns wound in the forward and reverse directions being the same to minimize distributed inductance. Rectangular frame wire-wound precision resistors are usually custom-made by equipment manufacturers according to their needs and are commonly used in instruments and meters.