Resistor is an object of an electrical circuit that serves to reduce the current strength in it. Resistors are also used to reduce the voltage in individual sections and divide the current into its components. On electrical circuits, resistors are indicated by small rectangles with a pair of leads (one each on two opposite sides). Abroad, resistors are shown as a broken line.
Resistors have three main parameters:
- Rated resistance (resistor values).
- Tolerance.
- Power dissipation.
Resistor ratings are the value of their nominal resistance, that is, the value specified by the manufacturer. Rated resistance is measured in ohms. Resistors are used in almost all industries containing at least a few electrical devices. This causes a huge range of resistance values. However, there are resistor values that are universal.
It is very difficult to make a resistor with a certain exact value, so a value such as tolerance is used. For example,if the indicated nominal resistance is 10 ohms, then in fact it will be approximately 9.98-10.1 ohms. This possible error is called tolerance and is measured as a percentage.
Power dissipation is another of the most important determinants of a resistor. Let us explain the meaning of this quantity. The resistor through which the electric current passes is constantly heated. Heating depends on the power of the current. Each resistor has a certain temperature limit, after which it overheats and burns out. Dissipated power is the value of electric current power at which the resistor will burn out. Like resistor values, power dissipation is a constant value for each resistor. It is specified by the manufacturer. On electrical circuits, the power dissipation of resistors should also be indicated. For its designation, oblique, horizontal and vertical lines are used. From the lines depicted on the resistor icon, special combinations are created denoting different power values. Standard values in small circuits range between 1/8 watt and five watts. The power dissipation for any resistor can be calculated from Ohm's law for a section of the circuit. To determine it, you need to know the current strength in the circuit and the nominal resistance value of the resistor.
All resistance ratings are standardized. That is, there are some standard resistor values. These values, in theirturn, are also grouped into rows of resistor values. For direct current, there are 6 such rows: E6, E12, E24, E48, E96, E192.
For alternating currents, only rows E6 and occasionally E3 are used. The numbers in the names of the rows indicate the number of possible denominations in this row. For example, a number of E6 ratings assumes only the following possible resistances: 1, 0; fifteen; 2, 2; 3, 3; 4, 7; 6, 8.
