Resistors are passive electronic components with high usage in electronic devices .
Principal characteristic of the resistors is resistance (opposition to current flow ) .Are many types of resistors : for hard currents , for light currents , fixed value resistors , variable resistors and other types .This types of resistors presented can be classify by other parameters and manufactured process in many categories .
Main parameters of resistor are :
-tolerance t is noted in percents and represents the maximum accepted deviation of real resistance over the nominal value Rn .
- dispersion power and nominal voltage Un represents the maximum electrical power supported by the resistor .
Nominal standard power rating in watts for resistor are : .05, 0.1, 0.125, 0.25, 0.5., 1, 2, 4, 6, 12, 16, 25, 40, 50, 100W .
Usual the for a long life of the resistor the dispersed power from the circuit must be a ½ than nominal power .
Are many types of resistors and each type can be marked with a special standard symbol .The main symbols of resistors can be viewed in the table bellow .
a: resistor , general symbol
b: resistor , tolerated symbol
c: resistor , un-standard symbol
d: resistor with variable resistance
e: resistor with mobile contact
f: resistor with mobile contact and stop position
g: potentiometer with mobile contact
h: potentiometer with mobile contact, general symbol
i: potentiometer with preset adjustment
j: two plugs resistor
k: shunt resistor
l: thermal resistor
m: thermistor general symbol
n: thermistor tolerated symbol
o: varistor general symbol
p: varistor tolerated symbol
The main parameters of the resistors can be marked using many methods like :
-color code marked on the body of the resistors with colored bands
- with letters
- with alphanumeric codes