To indicate the resistance value, resistors are marked with resistance values on the surface when they leave the factory. The resistance value marked on the resistor is called the nominal resistance value. The actual resistance value of a resistor often has a certain difference from the nominal resistance value, and this difference is called the error. The main methods for marking the nominal resistance value and error of resistors are direct marking and color ring marking.
- Direct Marking Method
The direct marking method refers to the method of directly marking the resistance value and error on the resistor using alphanumeric characters (numbers and letters). The units of resistance value in the direct marking method are ohm (Ω), kilohm (kΩ), and megohm (MΩ).
There are generally two ways to represent the error: one is to use Roman numerals I, II, III to represent errors of ±5%, ±10%, ±20% respectively. If not marked, the error is ±20%; the other is to use letters to represent errors, and the corresponding errors for each letter are shown in the table, such as J and K representing errors of ±5% and ±10% respectively.
Table of Letters and Resistance Value Errors
Common Forms and Examples of Direct Marking Method
2. Color Ring Marking Method
The color ring marking method refers to the method of marking resistance value and error on the resistor using different colored rings.
The two resistors in the figure use the color ring marking method to mark the resistance value and error. Among them, one resistor has four color rings, called a four-ring resistor; the other resistor has five color rings, called a five-ring resistor, and the resistance value accuracy of the five-ring resistor is higher than that of the four-ring resistor.
Color Ring Resistor
(1) Meaning of Color Rings
To correctly identify the resistance value and error of color ring resistors, you need to understand the meanings represented by various color rings.
The meanings represented by each color ring of the color ring resistor are shown in the table.
Table of Meanings and Values Represented by Color Rings of Four-Ring Color Ring Resistors
(2) Reading Four-Ring Resistors
The reading of resistance value and error of four-ring resistors is shown in the figure.
Reading of Resistance Value and Error of Four-Ring Resistors
The specific process of reading four-ring resistors is as follows.
Step 1: Determine the order of the color rings.
The order of the color rings of a four-ring resistor is determined as follows:
① The fourth color ring of a four-ring resistor is the error ring, generally gold or silver. Therefore, if the color of the ring near one pin of the resistor is gold or silver, that ring must be the fourth ring, and the order of the three rings arranged from that ring to the other pin is three, two, one.
② For resistors marked according to the color ring standard, the fourth ring is generally far away from the third ring.
Step 2: Read the color rings.
According to the first and second rings as significant digit rings, the third ring as a multiplier ring, and the fourth ring as an error ring, read the resistance value and error of the color ring resistor based on the values represented by each color ring in the reference table.
(3) Reading Five-Ring Resistors
The method of reading the resistance value and error of five-ring resistors is basically the same as that of four-ring resistors, except that the first, second, and third rings of five-ring resistors are significant digit rings, the fourth ring is a multiplier ring, and the fifth ring is an error ring. In addition, the color of the error ring of a five-ring resistor may be gold, silver, brown, red, green, blue, or purple. The reading of five-ring resistors is shown in the figure.
Reading of Resistance Value and Error of Five-Ring Resistors