An article allows you to identify common electronic components (illustration)

The resistance is represented by "R" plus numbers in the circuit. For example, R13 represents the resistance numbered 13. The main functions of resistance in the circuit are shunting, current limiting, voltage dividing, bias, filtering (combined with capacitors) and impedance matching.

Symbols of resistors

Parameter identification: the unit of resistance is Ohm (Ω), and the unit of magnification is kiloohm (K Ω), megaohm (m Ω), etc. The conversion method is: 1 megohm =1000 kiloohm =1000000 ohm. There are three Parameter annotation methods, namely, direct scale method, color scale method and number scale method.

1MΩ=1000KΩ=1000000Ω

The number scaling method is mainly used for small volume circuits such as patch. For example, 103 means 10000 Ω (10 followed by 3 zeros), that is, 10K

Patch resistance identification

The color ring marking method is most used, and now examples are as follows:

The resistance and error of carbon resistors and some 1/8 watt carbon film resistors are represented by color rings. There are three or four color rings on the resistance. Close to the resistance end is the first color ring, and the rest are the second, third and fourth color rings in sequence, as shown in Figure 1. The first color ring represents the largest digit of the resistance value, the second color ring represents the second digit, and the third color ring represents that the resistance value should not have several zeros. The fourth color ring represents the error of resistance value. See Table 1 for the numbers or meanings represented by the color ring.For example, there is a carbon resistor, which has four color rings, in the order of red, black, red and gold. The resistance value of this resistance is 2000 Ω, and the error is ± 5%. As shown below.

Red, black, red, gold. Resistance value is 2000 Ω =2k

For example, there is a carbon resistor, which has three color rings of brown, green and black. Its resistance value is 15 Ω, and the error is ± 20%.

Color ring resistance is the most widely used resistance type in various electronic devices. No matter how it is installed, the maintainer can easily read out its resistance value, which is convenient for detection and replacement. However, in practice, it is found that the arrangement order of some color ring resistors is not very clear, and it is often easy to read wrong. When identifying, the following skills can be used to judge:

Skill 1: first find the color ring that marks the error, so as to arrange the order of the color ring. The most commonly used colors to represent the resistance error are: gold, silver, brown, especially the gold ring and silver ring, which are rarely used as the first ring of the resistance color ring, so as long as there are gold ring and silver ring in the resistance, it can be basically recognized as the last ring of the color ring resistance.

Skill 2: whether the brown ring is an error marker. Brown ring is often used as both error ring and significant number ring, and often appears in the first ring and the last ring at the same time, making it difficult to identify who is the first ring. In practice, it can be judged according to the interval between the color rings: for example, for the resistance of a five color ring, the interval between the fifth ring and the fourth ring is wider than that between the first ring and the second ring, so the arrangement order of the color rings can be determined.

Skill 3: when the sequence of color rings cannot be determined only by the distance between color rings, the production sequence value of resistance can also be used to distinguish. For example, the color ring reading sequence of a resistor is: Brown, black, black, yellow, brown, and its value is 100 × 10000=1m Ω, the error is 1%, which belongs to the normal resistance series value. If it is read in reverse order: Brown, yellow, black, black, brown, the value is 140 × 1 Ω =140 Ω, with an error of 1%. Obviously, the resistance value read out according to the latter order is not available in the production series of resistance, so the latter color ring order is wrong.

2、 Capacitance

1. Capacitance is generally represented by "C" plus numbers in the circuit (for example, c223 represents the capacitance numbered 223). Capacitance is an element composed of two metal films close together and separated by insulating materials. The main characteristic of the capacitor is to isolate direct current AC.

Capacitor on circuit board

The size of capacitance is the size of stored electric energy. The blocking effect of capacitance on AC signal is called capacitive reactance, which is related to the frequency and capacitance of AC signal.

Capacitive reactance xc=1/2 π F C (f represents the frequency of AC signal, C represents the capacitance)

The types of capacitors commonly used in telephones include electrolytic capacitors, ceramic chip capacitors, chip capacitors, monolith capacitors, tantalum capacitors and polyester capacitors.

2. Identification method: the identification method of capacitance is basically the same as that of resistance, including direct calibration method, color coding method and number coding method. The basic unit of capacitance is expressed in farad (f), and other units include millifahd (MF), microf (UF), NF (NF), and PF (PF).

Among them: 1 farad =103 millifahrenheit =106 micro Fahrenheit =109 nanofahrenheit =1012 capacitance with large capacity is directly marked on the capacitance, for example, the capacitance value of capacitance with small capacity of 10 uf/16v is represented by letters or numbers on the capacitance.

Letter representation: 1m=1000 UF 1p2=1.2pf 1n=1000pf

Digital representation: generally, three digits are used to represent the capacity, the first two digits are significant digits, and the third digit is magnification.

For example, 102 means 10 × 102pf=1000pf 224 means 22 × 104PF=0.22 uF