WRN-420 WRN-421 WRN-422 WRN-423 WRN-343 K type thermocouples
WRN-420 WRN-421 WRN-422 WRN-423 WRN-343 K type thermocouples, electronic circuits often use precision resistors, referred to as precision resistors. The so-called precision resistors refer to resistors whose resistance value error, resistance's thermal stability (temperature coefficient), and resistor's distributed parameters (distributed capacitance and distributed inductance) have reached certain standards.
Precision resistors are divided into materials, including metal film precision resistors, wire wound precision resistors and metal foil precision resistors.
The precision of the metal film precision resistor is higher, but the temperature coefficient of resistance value and the distribution parameter index are slightly lower;
Wire-wound precision resistors have high resistance accuracy and temperature coefficient indicators, but low distribution parameter indicators;
The precision, resistance temperature coefficient and distribution parameters of metal foil precision resistors are very high: the accuracy can reach 10-6, the temperature coefficient can reach ± 0.3 × 10-6 / ℃, and the distributed capacitance can be lower than 0.5pF. The inductance can be lower than 0.1μH.
As the price of the above three types of precision resistors increases with performance, they should be reasonably selected in applications based on actual conditions. For example, in DC or AC circuits with very low frequency, generally only wire-wound precision resistors or metal film precision resistors need to be selected. There is no need to choose expensive metal foil precision resistors.
The main body of metal film precision resistor is usually cylindrical; wire-wound precision resistors are of cylindrical, flat cylindrical and rectangular frame shapes; metal foil precision resistors are often square or sheet-shaped. When there are many turns of wire-wound precision resistors, non-inductive winding is often used. The number of turns in the forward direction and the number of turns in the reverse direction are the same to minimize the distributed inductance. Rectangular frame-shaped wire-wound precision resistors are usually customized by equipment manufacturers according to their needs and are often used in instruments.
Once the rectangular frame-shaped wire wound precision resistance in the instrument is damaged, a new alloy resistance wire with the same material, diameter and length as the original resistance alloy wire can be evenly wound on the original frame instead. If the original rectangular frame-shaped wire-wound precision resistor is only damaged on the surface insulation layer, simply remove the original resistance wire from the frame, re-dip paint (preferably use 1260 insulation varnish with good performance and low price), and then dry it. Then rewind to the original rectangular frame.