Electronic components refer to the components of electronic components and electrical miniature machines and instruments. They are usually composed of several parts and can be used in similar products. Common electronic components include resistors, capacitors, diodes, audions, inductors and other devices. The following is to introduce the common electronic components of the recognition and role.
Various electronic components in the circuit board
In general circuits, common code identifiers are as follows:
R - resistance
C - capacitor
D - diode
VT- triode, or field effect tube
L - inductance
W - potentiometer
Z - impedance
1. The resistance
Resistors are represented by "R" plus numbers in the circuit, such as "R7" for resistance number 7. The main functions of resistors in the circuit are shunt, current limiting, voltage divider, bias, filter (used in combination with capacitors) and impedance matching. There are two main methods to identify resistance: color code and number code.
The numerical method is mainly used for small circuits such as patches. For example, 103 represents 10000 ω (10 followed by three zeros), which is 10K.
Color code is commonly used for color ring resistors and is expressed as follows:
2. The capacitance
Capacitors in a circuit are usually represented by "C" plus a number. For example, "C160" refers to the capacitor number 160. Capacitance consists of two metal films close together, separated by an insulating material. Capacitors are characterized primarily by direct current isolation.
The identification of capacitance is also two methods, namely color code and number code.
3. The diode
Diode in the circuit is commonly used "D" plus numbers, such as: D9 refers to the number of 9 diode. The main characteristic of diode is unidirectional conductivity, that is, under the action of forward voltage, the conduction resistance is very small; Under the action of reverse voltage, the conduction resistance is extremely large or infinite.
The identification of the diode is relatively easy, you can directly determine the polarity of the diode by the symbol "P", "N"; The positive and negative poles of leds can be identified by the length of the pins, with long pins being positive and short pins being negative.
Triode is commonly used in the circuit "Q" plus a number, such as: Q3 stands for the triode number 3. Triode is a special device with two PN junctions inside and amplification capability.
The arrangement of triode pins has certain rules. When the plane is facing itself, there are three pins E, B and C from left to right, which are easy to identify.
Inductance in the circuit is commonly used "L" plus a number, such as: L10 refers to the inductance number 10, inductance coil is made of insulated wire on the insulating skeleton of a certain number of turns.
Inductance is generally recognized by direct standard method and color standard method, color standard method is similar to resistance. For example, brown, black, gold, and gold represent 1uH (5% error) inductance.
How are electronic components tested
A, AC and DC current measurement
According to the size of the measured current choose proper current measurement range and red pens and insert an "A" current jack, dc measurement, red pens and (insert) of the socket of current contact voltage high end, low black pens and contact voltage, at the end of the forward current from red pens and into the multimeter, flowed from black pens and again, when it comes to measuring the size of the current is not clear, Use the maximum range first, then gradually reduce the range for accurate measurement.
Identification and testing of electronic components
Two, ac and DC voltage measurement
The red pen is inserted into the "V/ ω" jack, and the appropriate voltage measurement range is selected according to the voltage. The black pen contacts the "ground" end of the circuit, and the red pen contacts the measuring point in the circuit. In particular, the frequency of the digital multimeter to measure the AC voltage is very low (45-500Hz), and the voltage amplitude of the medium and high frequency signal should be measured by the AC millivolt meter.
Identification and testing of electronic components
Three, resistance measurement
Resistance measurement is relatively simple red pen into the "V/ ω" jack, black pen into the "COM" jack, according to the size of the resistance to select the appropriate resistance, red and black pen respectively contact both ends of the resistance, observe the reading. In particular, when measuring the circuit resistance (resistance on the circuit board), you should first turn off the power supply of the circuit, so as not to cause jitter in the reading. Do not use resistance to measure current or voltage (especially 220V ac voltage). Otherwise, the multimeter may be damaged. Note that the resistance should not have parallel branches during the circuit detection. The resistance of the relatively large selection (such as measuring the resistance of 10M) should be the first two pen short circuit, the value of the display may be 1M. After each measurement, the measured result should be subtracted from this value, which is the actual resistance value (when the resistance range is high, the error will be relatively large).
Four, short open circuit detection
Turn the function and range switch to buzzer position, test the two pens respectively, if there is short circuit, the buzzer will ring. This method can be used to detect the on-off condition of circuit lines. Note: a buzzer does not necessarily indicate a short circuit between two points. It can also be heard if the resistance between two points is low (20 ω).
Five, digital multimeter capacitance detection method
Capacitance detection has a dedicated capacitance meter to measure capacitance capacity, can also be measured by a multimeter. As shown in the figure below
Some digital multimeters are used to measure capacitance. UT51 has a range of 200μ and 20μ. When measuring, the red pen is received from the current end hole, the black pen is received from the COM end hole, the function tap selects the capacitor tap, and then the red and black pen is connected to the discharge capacitor two pins (pay attention to polarity), select the appropriate range after reading the display data. 200μ range, suitable for measuring capacitance between 20uF and 200μF; 20μ range, suitable for measuring capacitance between 2μF and 20μF.
Six, inductor detection
Put the multimeter in resistance, and connect the red and black markers to either of the leading ends of the color code inductor, at which point the pointer should swing to the right. According to the measured resistance value, can be specifically divided into the following three cases for identification:
1. The resistance value of the measured color code inductor is zero, and there is a short-circuit fault inside.
2. There is a direct relationship between the dc resistance value of the measured color code inductor and the enameled wire diameter and winding number of the inductor coil. As long as the resistance value can be measured, it can be considered that the measured color code inductor is normal.
Seven, diode positive and negative resistance, pressure drop and good or bad judgment
First of all, it should be emphasized that when a digital multimeter is used to measure a diode, it measures the forward voltage of the diode, while a pointer multimeter measures the forward and reverse resistance of the diode. Diodes are germanium and silicon tubes. Germanium tube forward pressure drop is smaller than silicon tube, 0.1-0.3V for germanium diode, 0.5-0.8V for silicon diode.