Multimeter to measure the quality of chip capacitors
1. Also adjust the multimeter to the appropriate ohm gear. The principle of gear selection is: 1μF capacitors use 20K gears, 1-100μF capacitors use 2K gears, greater than 100, μF use 200 gears.
2. To judge the polarity, first set the multimeter to 100 or 1K ohms. Assuming that one pole is positive, connect the black lead to it, the red lead to the other pole, record the resistance value, and then discharge the capacitor. That is, let the two poles contact, and then change the test lead to measure the resistance. The black test lead with a large resistance is connected to the positive pole of the capacitor.
3. Then connect the red pen of the multimeter to the positive pole of the capacitor, and the black pen to the negative pole of the capacitor. If the display slowly increases from 0, and finally the overflow symbol 1 is displayed, the capacitor is normal. If it is always displayed as 0, the capacitor is internally short-circuited. If 1 is displayed, the capacitor is internally disconnected.
How to judge the quality of chip capacitors with a digital multimeter?
Detection of Fixed Capacitors
1. Detect small capacitors below 10pF
Because the capacity of the fixed capacitor below 10pF is too small, measuring with a multimeter can only qualitatively check whether there is leakage, internal short circuit or breakdown. When measuring, you can use the multimeter R×10k block, and use two test pens to connect the two pins of the capacitor at will, and the resistance value should be infinite. If the measured resistance (the pointer swings to the right) is zero, it means that the capacitor is damaged by leakage or internal breakdown.
2. Detect whether the 10PF~0.01μF fixed capacitor is charged, and then judge whether it is good or bad. The multimeter selects R×1k block. The β value of the two triodes is above 100, and the penetration current should be small. 3DG6 and other silicon triodes can be selected to form a composite tube. The red and black test leads of the multimeter are respectively connected to the emitter e and collector c of the composite tube. Due to the amplifying effect of the composite triode, the charging and discharging process of the capacitor under test is amplified, so that the pendulum of the multimeter pointer is increased, which is convenient for observation. It should be noted that during the test operation, especially when measuring small-capacity capacitors, it is necessary to repeatedly exchange the pins of the capacitor under test to contact points A and B, in order to clearly see the swing of the multimeter pointer.
3. For fixed capacitors above 0.01μF, the R×10k block of the multimeter can be used to directly test whether the capacitor has a charging process and whether there is an internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.
Detection of electrolytic capacitors
1. Because the capacity of electrolytic capacitors is much larger than that of general fixed capacitors, when measuring, appropriate ranges should be selected for different capacities. According to experience, in general, the capacitance between 1 and 47μF can be measured in R×1k block, and the capacitance larger than 47μF can be measured in R×100 block.
2. Connect the red test lead of the multimeter to the negative electrode and the black test lead to the positive electrode. At the moment of first contact, the multimeter pointer will deflect to the right by a large degree (for the same electrical block, the larger the capacity, the larger the swing), and then gradually to the left Rotate until it stops at a certain position. The resistance value at this time is the forward leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance. The actual use experience shows that the leakage resistance of electrolytic capacitors should generally be above several hundred kΩ, otherwise, it will not work properly. In the test, if there is no charging phenomenon in the forward and reverse directions, that is, the needle does not move, it means that the capacity has disappeared or the internal circuit is broken; Can no longer be used.
3. For electrolytic capacitors whose positive and negative signs are unknown, the above method of measuring leakage resistance can be used to determine them. That is, first measure the leakage resistance arbitrarily, remember its size, and then exchange the test leads to measure a resistance value. The one with the larger resistance value in the two measurements is the forward connection method, that is, the black test lead is connected to the positive electrode, and the red test lead is connected to the negative electrode. D? Use a multimeter to block the electricity, and use the method of forward and reverse charging to the electrolytic capacitor. According to the magnitude of the pointer swinging to the right, the capacity of the electrolytic capacitor can be estimated.
Detection of Variable Capacitors
1. Gently rotate the shaft by hand, it should feel very smooth, and it should not feel loose and tight or even stuck. When the carrier shaft is pushed forward, backward, up, down, left, right, etc., the rotating shaft should not be loose.
2. Rotate the shaft with one hand, and touch the outer edge of the moving film group with the other hand. You should not feel any looseness. A variable capacitor with poor contact between the rotating shaft and the moving plate cannot be used any longer.
3. Put the multimeter in the R×10k block, connect the two test pens to the moving piece of the variable capacitor and the terminal of the fixed piece with one hand, and slowly rotate the shaft with the other hand. Should be stationary at infinity. In the process of rotating the rotating shaft, if the pointer sometimes points to zero, it means that there is a short-circuit point between the moving piece and the fixed piece; if a certain angle is encountered, the multimeter reading is not infinite but a certain resistance value, indicating that the variable capacitor is moving. There is a leakage phenomenon between the plate and the stator.
How to measure the quality of chip capacitors?
How to measure the quality of chip capacitors? SMD capacitors are used in major electronics industries. Because of their small size and appearance, do not confuse them when measuring a large number of SMD capacitors, so as to avoid secondary maintenance. The good and bad methods of measuring chip capacitors are as follows:
1: Capacitor function and representation method.
The capacitor has two metal poles with an insulating medium in between. The characteristics of capacitors are mainly to block DC and AC, so they are mostly used for inter-stage coupling, filtering, decoupling, bypassing and signal tuning. Capacitors are represented by "C" plus a number in the circuit, such as C8, which represents the capacitor numbered 8 in the circuit.
2: Classification of capacitors.
Capacitors are divided into: gas dielectric capacitors, liquid dielectric capacitors, inorganic solid dielectric capacitors, organic solid dielectric capacitors and electrolytic capacitors according to different media. According to the polarity, it is divided into polar capacitors and non-polar capacitors. According to the structure, it can be divided into: fixed capacitor, variable capacitor, fine-tuning capacitor.
3: Capacitor capacity unit and withstand voltage.
The basic unit of capacitance is F (law), and other units are: millifarad (mF), microfarad (uF), nanofarad (nF), and picofarad (pF). Since the capacity of the unit F is too large, we generally see the units of μF, nF, and pF. Conversion relationship: 1F=1000000μF, 1μF=1000nF=1000000pF.
Each capacitor has its withstand voltage value, expressed in V. Generally, the nominal withstand voltage value of electrodeless capacitors is relatively high: 63V, 100V, 160V, 250V, 400V, 600V, 1000V, etc. The withstand voltage of polar capacitors is relatively low. Generally, the nominal withstand voltage values are: 4V, 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 220V, 400V, etc.
4: The capacity of the capacitor.
Capacitor capacity indicates the amount of electrical energy that can be stored. The blocking effect of the capacitor on the AC signal is called capacitive reactance, which is related to the frequency and capacitance of the AC signal. The capacitive reactance XC=1/2πfc (f represents the frequency of the AC signal, and C represents the capacitance).
5: Distinguish and measure the positive and negative electrodes of the capacitor.
The black block with the mark on the capacitor is the negative electrode. There are two semicircles on the capacitor position on the PCB, and the pin corresponding to the colored semicircle is the negative pole. It is also useful to use the length of the pins to distinguish the positive and negative long legs as positive and the short legs as negative.
When we do not know the positive and negative poles of the capacitor, we can measure it with a multimeter. The medium between the two poles of the capacitor is not an absolute insulator, and its resistance is not infinite, but a finite value, generally above 1000 megohms. The resistance between the two poles of a capacitor is called insulation resistance or leakage resistance. The leakage current of the electrolytic capacitor is small (large leakage resistance) only when the positive terminal of the electrolytic capacitor is connected to the positive power supply (black test pen when the electric block is used), and the negative terminal is connected to the negative terminal of the power supply (the red test pen when the power is blocked). On the contrary, the leakage current of the electrolytic capacitor increases (the leakage resistance decreases).
If you don't know it, you can first assume that a certain pole is "+" pole, the multimeter selects R*100 or R*1K block, and then connect the assumed "+" pole to the black test lead of the multimeter, and the other electrode is connected to the red test lead of the multimeter. The test leads are connected, and the scale at which the needle stops (the resistance value of the needle on the left is large) can be directly read out for a digital multimeter. Then discharge the capacitor (the two leads touch each other), and then switch the two test leads to measure again. In the two measurements, when the last position of the watch needle is to the left (or the resistance value is large), the black watch lead is connected to the positive electrode of the electrolytic capacitor.
6: Capacitor labeling method and capacity error.
The labeling methods of capacitors are divided into: direct labeling method, color labeling method and number labeling method. For relatively large capacitors, the direct standard method is often used. If it is 0.005, it means 0.005uF=5nF. If it is 5n, it means 5nF.
Number standard method: Generally, three digits are used to represent the capacity, the first two digits represent significant digits, and the third digit is the power of 10. For example: 102 means 10x10x10PF=1000PF, 203 means 20x10x10x10PF.
The color-coding method, along the direction of the capacitor leads, use different colors to represent different numbers, the first and second rings represent the capacitance, and the third color represents the number of zeros after the significant digits (unit: pF). The values represented by the colors are: black=0, brown=1, red=2, orange=3, yellow=4, green=5, blue=6, purple=7, grey=8, and white=9.
The capacitance error is represented by the symbols F, G, J, K, L, and M, and the allowable errors are respectively ±1%, ±2%, ±5%, ±10%, ±15%, and ±20%.
