The designations of the resistor ratings on the diagrams and on the components themselves are carried out according to various standards. In addition, some resistors use color rings instead of numbers to encode numbers.
Instructions
Step 1
In the electrical diagram, the resistance of the resistor, given without indicating the units of measurement at all, is expressed in ohms. For example, 200 means 200 ohms. If after the numbers there is a lowercase letter k, we are talking about kilo-ohms: 250 k means 250 kOhm. If on old schemes there is no unit of measurement in the designation, and the number has a fractional part in addition to the integer part, the denomination is expressed in megaohms: 10, 0 stands for 10 MOhm. Newer circuits use a capital M for this: 5 M means 5 MΩ. The capital letter G replaces the unit of measurement Gohm (gigaohm). Such resistors are rare, mainly in ionization chamber based dosimetry equipment.
Step 2
On the resistors themselves, instead of designating the name of the unit Ohm, either the capital Latin letter R or the capital Greek letter Ω (omega) is used. Kilo-ohms are denoted by a capital letter K, mega-ohms - by a capital letter M, gigaomas - by a capital Russian letter G or Latin G. The numbers located not before, but after the letter, are equivalent to the numbers after the decimal point. For example, 2R5 - 2.5 Ohm, 120K - 120 kΩ, 4M7 - 4.7 MΩ. Less commonly, the resistance value is indicated using generally accepted unit designations, for example, 10 kΩ.
Step 3
The color rings on the resistors are used to code different numbers. The colors used are as follows: black - 0, brown - 1, red - 2, orange - 3, yellow - 4, green - 5, blue - 6, purple - 7, gray - 8, white - 9. There can be three or four. All of them, except for the last one, symbolize numbers, and the last one - the number of zeros after these numbers. The resulting number expresses resistance in ohms, which can be converted to more convenient units.
Step 4
If there is a golden stripe after them through a small gap, the resistor has a tolerance of 5%. The silver bar indicates a tolerance of 10%, and if there is none at all, the tolerance for resistance is 20%. Count the stripes from the side opposite to the stripe symbolizing the tolerance.
Step 5
For a resistor that does not have a designation, the resistance can be measured. To do this, de-energize the circuit, discharge the capacitors, make sure with a voltmeter that they are really discharged, and then unsolder one terminal of the resistor and connect an ohmmeter to it. Select the limit at which resistance is displayed most accurately. After reading the reading, disconnect the ohmmeter and solder the disconnected lead back.
