How to test the quality of capacitors?
In the absence of special instrumentation, the quality and quality of capacitors can be measured by multimeter resistance files and judged. Fixed capacitors with large capacitance (more than 1 mu F) can be used to measure the capacitor's two electrodes with a multimeter resistance file (R Then try again by switching the test rod. The larger the swing, the greater the capacitance of the capacitor. If the test rod has been touching the capacitor lead, the meter needle should be near It shows that the leakage current of the capacitor is large, and the quality of the capacitor is poor.
Pressure gauges for small capacitors, with a multimeter to measure the needle often can not see the swing, at this time, you can use an external DC voltage and multimeter DC voltage range for measurement, as shown in Figure 1, that is, the multimeter to the corresponding DC voltage range, negative (black) test rod connected to the negative DC power supply. The positive (red) test rod is connected to one end of the capacitor to be measured, and the other end is connected to the positive pole of the power supply.
When a capacitor with good performance is switched on, the needle of the multimeter should swing greatly; the larger the capacity of the capacitor, the greater the swing of the needle of the multimeter. After swinging, the needle can gradually return to zero. If the needle of the multimeter does not swing when the power supply is switched on, the capacitor fails or the circuit is broken; if the needle keeps indicating the power supply voltage without swinging, it indicates that the capacitor has been broken short circuit; if the needle swings normally, but does not return to zero, it indicates that the capacitor has leakage phenomenon, and the higher the value of the indicated voltage is. It shows that the larger the leakage current is. It should be pointed out that the auxiliary DC voltage of the capacitor with small measuring capacity can not exceed the withstanding voltage of the capacitor under test, so as to avoid the breakdown of the capacitor caused by the measurement. To accurately measure the capacitance of a capacitor, a capacitance bridge or Q meter is required. The above simple detection method can only roughly judge the quality of the pressure gauge capacitor.
Method 1: pointer multimeter measurement.
1, check the electrolytic capacitor with the resistance meter of multimeter.
The two lead wires of the electrolytic capacitor can be divided into positive and negative. When checking its quality, the resistance of the electrolytic capacitor (6V or l0V) with lower voltage withstand should be placed in R 100 or R 6550 Such electrolytic capacitors are good. The larger the capacity of the electrolytic capacitor, the longer the charging time, the slower the pointer oscillating.
2. Judge the positive and negative lead of electrolytic capacitor with multimeter.
Some electrolytic capacitors with low voltage withstand can be judged according to the characteristics of small leakage current (large resistance value) in positive connection and large leakage current in reverse connection if the sign of positive and negative leads is unclear. The specific method is: contact the two leads of the capacitor with the red and black meter pen, remember the size of the leakage current (resistance value) when the pointer swings back and stops, and then connect the positive and negative lead of the capacitor short, and then test the leakage current after adjusting the red and black meter pen. Judging by the small leakage current indication value, the lead that contacts the black pen is the front end of the electrolytic capacitor. This method is difficult to distinguish the polarity of the electrolytic capacitor with its own small leakage current.
3. Check the variable capacitor with multimeter.
The variable capacitor has a set of stator plates and a set of moving plates. The multimeter resistor can check if there is any contact between the moving and fixing pieces, and connect the moving and fixing pieces respectively with the red and black pen, and rotate the shaft handle and the pointer of the ammeter, indicating that there is no short circuit between the moving and fixing pieces.
4. Use the multimeter resistance file to roughly identify the capacitance capacity of 5000PF or more.
The resistance file of multimeter can roughly distinguish the quality of capacitors above 5000PF (those below 5000PF can only judge whether the capacitor is broken down or not). When checking, put the resistance range on the high-grade value of the measurement range, and contact the two pens with the capacitor, then the pointer swing quickly and then restore, reverse connection, swing amplitude than the first greater, and then restore. Such capacitors are good. The larger the capacitor capacity, the greater the oscillation of the meter pointer, and the longer the recovery time of the pointer. We can compare the capacitance of the two capacitors according to the oscillation of the meter pointer.
Two. Testing methods and experience of capacitors
1 detection of fixed capacitors
A detects small capacitance below 10pF.
Because the capacitance of the fixed capacitor below 10pF is too small, it can only be qualitatively checked if it has leakage, internal short circuit or breakdown phenomenon by multimeter. When measuring, the multimeter R *10k block can be selected, and the two pins of the capacitor can be connected with two meter pens arbitrarily. The resistance value should be infinite. If the resistance (pointer to the right) is zero, it indicates that the capacitor is damaged by electric leakage or internal breakdown.
B detects the charging phenomenon of 10PF to 001 F fixed capacitors, and then determines whether they are good or bad. The multimeter selects R * 1K gear. The beta values of the two transistors are all above 100, and the penetration current is small. 3DG6 and other types of silicon triode can be used to form composite pipes. The multimeter's red and black pens respectively.