Precision resistors are often used in high-precision electronic circuits. In fact, the precision resistors refers to the resistance error, the thermal stability (temperature coefficient) of the resistance, the distributed capacitance and the distributed inductance in the distribution parameters of the resistor, and so on. Precision resistors are indispensable in many high-end electronic devices without which they cannot perform properly. For instance, most of the military grade resistors use precision resistor products. Precision resistors are generally classified as below.
 

Precision resistor is divided into metal film precision resistor, wire winding precision resistor and metal foil precision resistor. The precision of metal film precision resistor is higher, but the resistance temperature coefficient and distribution parameter index are lower, the resistance value precision and temperature coefficient index of wire-wound precision resistors are very high, but the distribution parameter index is lower. The precision, temperature coefficient and distribution parameters of the metal foil precision resistor are very high. The temperature coefficient is ±0.3×10^-6/℃, the distribution capacitance is less than 0.5 PF, and the distribution inductance is less than 0.1 μ H.
 

 

The price of the above three kinds of precision resistors increases with the performance, so the application should be reasonable according to the actual situation. For example, in DC or low frequency AC circuits, only wire-wound precision resistor or metal film precision resistor is generally required, and there is no need to choose expensive metal foil precision resistance.
 
The main body of the precision resistance of the metal film is generally cylindrical. The main body of precision resistor include cylindrical, flat column and the long square frame, while the main body for precision resistor is usually in the form of a square or a sheet shape. In order to reduce the distribution inductance. If the number of turns around the precision resistor is much higher, the number of turns of the positive winding and the reverse winding should be the same , so as to reduce the distributed inductance as much as possible.
 

Rectangular frame-shaped wire-wound precision resistors are usually custom-made by equipment manufacturers and are often used in instrumentation. Once the rectangular frame wire in the instrument is damaged, the new alloy wire with the same material, diameter and length as the original alloy wire can be used to replace. If it is only broken in the surface insulation layer, it is only necessary to remove the original resistance wire from the frame, redip the paint, and then rewind it to the original rectangular frame after air-drying treatment.
 
The main difference between the metal film resistor and the precision wire winding resistor is in the performance of the products. Although both are precision resistors, there are still great differences in application due to the difference of temperature coefficient.