Resistance of two

Components are the foundation of all electronic equipment, security system maintenance, cannot do without security equipment, although we are not focused on maintenance equipment, but as a system maintenance technician, understand some components of the basic knowledge, in the process of maintenance often get twice the result with half the effort.

If the equipment is the basis of the security system, the cable is the central nerve of the whole system, connecting these devices. Understanding the characteristics of various cables helps us maintain the entire system.

1. Main parameters of resistance

The main parameters of resistance are nominal resistance, rated power and allowable error.

(1) The basic unit of resistance value is ohm, represented by "ω", and commonly used units are kilohm (㏀) and megohm (㏁). It represents the resistance ability of the conductor to the current, and the resistance value marked on the resistance is the nominal resistance value of the resistance.

(2) There will be a deviation between the nominal resistance value of the resistance and its actual resistance value. This deviation is the allowable error within the allowable range.

(3) the rated power of the resistance is in the specified operating temperature range, the resistance can work reliably for a long time can withstand the maximum power, commonly used are 1/16W, 1/8W, 1/6W, 1/4W, 1/2W, 1W, 2W, 3W and so on.

2. Marking method of plug-in resistance

The marking methods of resistors include direct marking method, text symbol method, number marking method and color ring method. There are also special notes for very small patch resistors.

Direct marking method: mark the resistance value on the surface of the resistor with numbers and unit symbols. The allowable error is directly expressed as a percentage. If no deviation is marked on the resistor, it is ±20%. For example, 2.7㏀±5%.

Literal notation: a regular combination of Arabic numerals and literal notation is used to indicate the nominal resistance value, the allowable deviation of which is also indicated by literal notation. The number before the symbol indicates the integer resistance, followed by the first and second decimal resistance. The allowable errors are: ±0.5%, ±1%, ±2%, ±5%, ±10%, ±20% respectively.

Numerical notation: Marking resistors with three digit numbers. From left to right, the first and second values are valid, and the third digit is multiplied by 10 to the power of something, that is, the number of zeros, in euros. Deviations are usually indicated by literal symbols. For example, 102K (1㏀±10%, J represents error ±5%, K represents error ±10%, M represents error ±20%).

Color ring method: mark the nominal resistance and allowable deviation on the surface of the resistor with strips or dots of different colors. The basic unit of color ring method is "ohm", most foreign resistors use color code method.

When the resistance is four rings, the last ring must be gold or silver, the first two digits are significant, the third digit is multiplied by something to the power of 10, and the fourth digit is allowed deviation.

When the resistance is five rings, the distance between the last ring and the front four rings is larger. The first three digits are significant, the fourth digit is multiplied by 10 to the power of something, and the fifth digit is the allowable deviation.

Five color rings are commonly used to represent the color ring mark of precision resistance. The first to third color rings indicate the effective number of resistance, the fourth color ring indicates the power of 10, and the fifth color ring indicates the allowable deviation.

3. Marking method of patch resistance

The common labeling methods for patch resistors are: conventional 3-digit labeling method, conventional 4-digit labeling method, and 2 digits followed by 1 digit letter notation. The labeling method with letters is not as intuitive and convenient as that with numbers.

Three-digit notation: The first two digits represent the significant number of the resistance value, and the third digit represents the power multiplied by 10, in ohms. When the resistance is less than 10 ω, R is used to indicate the decimal point of the resistance value in the 3-digit notation.

Four-digit notation: The first three digits represent the significant number of the resistance value, and the fourth digit represents the power multiplied by 10, in ohms. The reading method is similar to the 3-digit notation method.

Two-digit plus one-digit letter notation: This method uses the first two digits as a numeric code, rather than a significant number representing the resistance value, and the following letters to indicate the power of 10 to which the significant number should be multiplied, in ohms. For the valid digit corresponding to the specific digit code, you can query the digit code table of precision chip resistance.