Identification and detection methods of common electronic components

Electronic components are the basis of electronic products. Understanding the types, structures, and performance of commonly used electronic components and being able to choose them correctly is the basis for learning and mastering electronic technology. Commonly used electronic components include: resistors, capacitors, inductors, potentiometers, transformers, etc. In terms of installation methods, they can currently be divided into two categories: traditional installation (also known as through-hole installation, namely DIP) and surface installation (also known as SMT or SMD). Transistors and diodes are called electronic devices.


Methods for identifying electronic components 1. Identification of resistors Electronic components Resistors are represented by "R" plus numbers in circuits, such as: R1 represents a resistor numbered 1. The main functions of resistors in circuits are current shunting, current limiting, voltage division, biasing, etc. 1. Parameter identification: The unit of resistance is ohm (Ω), and the multiplier units are: kilo-ohm (KΩ), mega-ohm (MΩ), etc. The conversion method is: 1 megohm = 1000 kilo-ohm = 1000000 ohms. There are three methods for marking resistor parameters, namely direct marking method, color marking method and digital marking method. a. The digital marking method is mainly used for small-volume circuits such as SMDs, such as: 472 represents 47×100Ω (ie 4.7K); 104 represents 100K b. The color ring marking method is the most used. Examples are as follows: four-color ring resistors and five-color ring resistors (precision resistors). The relationship between the color code position and the magnification of the resistor is shown in the following table: Color Effective Numbers Multiplication Permitted Deviation (%) Silver / x0.01 ±10 Gold / x0.1 ±5 Black 0 +0 / Brown 1 x10 ±1 Red 2 x100 ±2 Orange 3 x1000 / Yellow 4 x10000 / Green 5 x100000 ±0.5 Blue 6 x1000000 ±0.2 Purple 7 x10000000 ±0.1 Gray 8 x100000000 / White 9 x1000000000. 2: The capacitor identification method for electronic components is basically the same as the resistor identification method, which is divided into three types: direct marking method, color marking method and digital marking method. The basic unit of capacitance is expressed in farad (F), and other units include: millifarad (mF), microfarad (uF), nanofarad (nF), and picofarad (pF). Among them: 1 farad = 103 millifarad = 106 microfarad = 109 nanofarad = 1012 picofarad The capacitance value of a large capacitor is directly marked on the capacitor, such as 10 uF/16V. The capacitance value of a small capacitor is represented by letters or numbers on the capacitor. 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 represent the significant digits, and the third digit is the multiple. For example: 102 represents 10×102PF=1000PF 224 represents 22×104PF=0.22 uF3. Capacitor capacity error table symbol FGJKLM allowable error ±1% ±2% ±5% ±10% ±15% ±20% For example: a ceramic capacitor is 104J, which means the capacity is 0. 1 uF, the error is ±5%. Three: Crystal diodes. The diode identification of electronic components is very simple. The N pole (negative pole) of a low-power diode is mostly marked with a color circle on the surface of the diode. Some diodes also use special diode symbols to indicate the P pole (positive pole) or the N pole (negative pole). There are also symbols marked as "P" and "N" to determine the polarity of the diode. The positive and negative poles of the light-emitting diode can be identified by the length of the pins. The long pin is positive and the short pin is negative. 3. Test precautions: When using a digital multimeter to measure the diode, the red test pen is connected to the positive pole of the diode and the black test pen is connected to the negative pole of the diode. The resistance value measured at this time is the forward conduction resistance value of the diode, which is exactly the opposite of the connection method of the pointer multimeter. 4. The commonly used 1N4000 series diode withstand voltage comparison is as follows: Model 1N4001 1N4002 1N4003 1N4004 1N4005 1N4006 1N4007 Withstand voltage (V) 50 100 200 400 600 800 1000 current (A) are all 1.
How to detect electronic components 1. Measurement of AC and DC current According to the size of the measured current, select the appropriate current measurement range and insert the red test lead into the "A" current jack. When measuring DC, the red test lead (inserted into the current jack) touches the high voltage end, and the black test lead touches the low voltage end. The forward current flows from the red test lead into the multimeter and then flows out from the black test lead. When the current size to be measured is unclear, first use the largest range to measure, and then gradually reduce the range to measure accurately.

2. Measurement of AC and DC voltage Insert the red test lead into the "V/Ω" jack, select the appropriate voltage measurement range according to the voltage, touch the "ground" end of the circuit with the black test lead, and touch the point to be measured in the circuit with the red test lead. It should be noted that the frequency of the AC voltage measured by the digital multimeter is very low (45-500Hz), and the voltage amplitude of the medium and high frequency signal should be measured with an AC millivoltmeter.

3. Resistance measurement The measurement of resistance is relatively simple. Insert the red test lead into the "V/Ω" jack, and the black test lead into the "com" jack. Select the appropriate resistance range according to the size of the resistance. The red and black test leads touch the two ends of the resistance respectively, and observe the reading. In particular, when measuring the in-circuit resistance (the resistance on the circuit board), the power supply of the circuit should be turned off first to avoid jitter in the reading. It is forbidden to use the resistance range to measure current or voltage (especially AC 220V voltage), otherwise it is easy to damage the multimeter. When testing in-circuit, pay attention to the resistance that there should be no parallel branches. When the resistance range is relatively large (for example, measuring a 10M resistor), the two test leads should be short-circuited first, and the displayed value may be 1M. After each measurement, this value should be subtracted from the measurement result to obtain the actual resistance value (when the resistance range is high, the error will be relatively large).

4. Short and open circuit detection Turn the function and range switches to the buzzer position, and test the points with two test leads. If there is a short circuit, the buzzer will sound. This method can be used to detect the on-off status of the circuit. Note: The buzzer does not necessarily mean that the circuit between the two points is short-circuited. It will also sound if the resistance between the two points is relatively small (20Ω).

5. Digital multimeter capacitance detection method There are special capacitance meters to measure capacitance, and it can also be measured with a multimeter. As shown in the figure below

Some digital multimeters have the function of measuring capacitance. The range of UT51 is divided into two levels: 200μ and 20μ. When measuring, first connect the red test lead to the current terminal hole, the black test lead to the COM terminal hole, select the capacitance level in the function range, and then connect the red and black test leads to the two pins of the discharged capacitor (pay attention to the polarity). After selecting the appropriate range, you can read the displayed data. The 200μ range is suitable for measuring capacitance between 20uF and 200μF; the 20μ range is suitable for measuring capacitance between 2μF and 20μF.

6. Inductor detection Set the multimeter to the resistance range, and connect the red and black test leads to any lead-out terminal of the color-coded inductor. At this time, the pointer should swing to the right. According to the measured resistance value, it can be identified in the following three situations: 1. The resistance value of the color-coded inductor under test is zero, and there is a short-circuit fault inside it. 2. The DC resistance value of the color-coded inductor under test is directly related to the diameter of the enameled wire used to wind the inductor coil and the number of windings. As long as the resistance value can be measured, it can be considered that the color-coded inductor under test is normal.

7. The forward and reverse resistance, voltage drop and judgment of the quality of the diode. The first thing to emphasize is that when a digital multimeter is used to measure a diode, the actual measurement is the forward voltage value of the diode, while the pointer multimeter measures the forward and reverse resistance value of the diode. Diodes are divided into germanium tubes and silicon tubes. The forward voltage drop of a germanium tube is smaller than that of a silicon tube. 0.1-0.3V is a germanium diode, and 0.5-0.8V is a silicon diode.