1.There are many types of fixed resistors. The choice of which material and structure should be determined according to the specific requirements of the application circuit. Non wire wound resistors with small distributed inductance and distributed capacitance shall be selected for high-frequency circuits, such as carbon film resistors, metal resistors and metal oxide film resistors, thin film resistors, thick film resistors, alloy resistors, anti-corrosion coating resistors, etc. Low noise resistors, such as metal film resistor, carbon film resistor and wire wound resistor, shall be selected for high gain small signal amplification circuit, instead of synthetic carbon film resistor and organic solid resistor with high noise.
The resistance value of the selected resistor shall be close to a nominal value calculated in the application circuit, and the standard series resistor shall be preferred. The allowable error of resistor used in general circuit is ± 5% ~ ± 10%. Resistors used in precision instruments and special circuits shall be precision resistors. For resistors with a precision of less than 1%, such as 0.01%, 0.1% and 0.5%, jabisin resistors shall be used. The rated power of the selected resistor shall meet the requirements for the power capacity of the resistor in the application circuit. Generally, the power of the resistor shall not be increased or reduced at will.
If the circuit requires a power type resistor, its rated power can be 1 ~ 2 times higher than that required by the actual application circuit. 2. Selection of fuse resistor
Fuse resistor a resistor with a protective function. When selecting, its dual performance shall be considered, and its resistance value, power and other parameters shall be selected according to the specific requirements of the circuit. It should not only ensure that it can fuse quickly in case of overload, but also ensure that it can work stably for a long time under normal conditions. If the resistance value is too large or the power is too large, it can not play a protective role.
Three basic principles for resistor selection:
Select the resistors manufactured by the production line certified by the certification authority to implement high-level standards.
Select resistors produced by manufacturers with functional advantages, quality advantages, efficiency advantages, function price ratio advantages and service advantages.
Select the manufacturer in the model catalogue that can meet the above requirements and order the resistor directly from him.
matters needing attention
The resistance shall be checked before use. To check its performance is to measure whether the actual resistance value is consistent with the nominal value and whether the error is within the allowable range. The method is to measure with the resistance gear of the multimeter. Pay attention to two points during measurement
- The measuring range shall be determined according to the measured resistance value, so that the pointer indication is in the middle of the scale line, which is convenient for observation.
- After determining the range of resistance gear, zero adjustment shall be carried out. The method is that the two probes are short circuited (directly collided), adjust the “zero adjustment” appliance to make the pointer accurately point to “0” of Ω scale line, and then measure the resistance value of resistance. In addition, be careful not to touch both ends of the resistance or the metal part of the probe with your hand. Otherwise, it will cause test error.
The resistance measured with a multimeter is close to the nominal value. It can be considered that the quality is basically good. If there is too much difference or it is impossible at all, it is bad.