Capacitance common way is directly labeled markers, the common unit has pF, μF are two, it is easy to recognize. But some small-capacity capacitor is used numerals law, generally have three-digit, first and second digit as a valid number, the third digit is a multiple, it means that the back to keep the number 0. For example: 343 indicates 34000pF, Further, if the third digit is 9, showing 10-1, rather than 10 9 th, for example: 479 indicates 4.7pF.
When replacing the capacitance main capacitor voltage should be noted that generally require no less than the original value of the capacitor voltage requirements. In the more stringent requirements of the circuit, its capacity is generally not more than ± 20% of the original capacity can be. In the less stringent requirements of the circuit, such as a bypass circuit, generally require no less than 1/2 of the original capacitor capacitance of not more than 2 times the original 1-6 times can be.
A fixed capacitor testing?
A little less than 10pF capacitance detection ?? below 10pF fixed capacitors because capacity is too small, measured with a multimeter, only qualitative check whether there is leakage, an internal short circuit or breakdown. When measured, the choice of a multimeter R × 10k block, any capacitors on the two pins were used two pen, the resistance should be infinite. If the measured resistance value (pointer swing to the right) is zero, then the capacitor leakage damage or internal breakdown.
B 10PF ~ 1000μF detect whether there is a fixed capacitor charging phenomenon, then judge its quality. Multimeter R × 1k block selection. Β value of the two transistors are more than 100, and through the current to have some? 3DG6 other models can be used silicon transistor composed of composite pipe. Multimeter's red and black pen, respectively, composite pipe and collector emitter e c phase. Because the composite triode amplification, the measured capacitance charging and discharging process to be enlarged, so that the multimeter pointer swing rate increase, making it easy to observe. It should be noted that: in the test operation, especially in the smaller capacity when measured capacitance measured capacitance pin to repeatedly swap contacts A, B two points, can clearly see the multimeter pointer swing.
C for more than a fixed capacitance 1000μF available multimeter R × 10k block capacitor directly test whether the charging process and the availability of an internal short circuit or leakage, and to estimate the capacity of the capacitor according to the pointer to the right magnitude of the swing.
Detection 2 electrolytic capacitors
A Because the capacity of the electrolytic capacitor is much greater than the average fixed capacitance, so when the measure should be used in the appropriate range for the different capacity. According to experience, in general, 1 ~ 47μF capacitance between the available R × 1k block measurement, greater than 47μF capacitance measurement available R × 100 block.
B multimeter red pen then negative, then positive black pen, at the moment the fourth year, the meter pointer deflection to the right that is larger skewness (for the same electrical barrier, the greater the capacity, the greater the swing), followed by the gradual swing to the left until it stops at a certain position. In this case the resistance is positive leakage resistance electrolytic capacitors, this value is slightly larger than the reverse leakage resistance. Practical experience shows that the electrolytic capacitor leakage resistance should generally be in the hundreds of kΩ or more, otherwise, it will not work properly. In the test, if positive, no charge reverse phenomenon, namely the hands do not move, then the capacity of the disappearance or internal circuit; if the measured resistance is small or zero, indicating a large capacitor leakage or breakdown damage, It can no longer be used.
C for the positive and negative signs of unknown electrolytic capacitor, can be determine using the above method for measuring the leakage resistance. That is, first measured about any leakage resistance, remember its size, and then swap out a pen and then measured the resistance. Two major resistance measurements of that time would be a positive connection, namely the black pen then the positive electrode, the red pen then is negative.
D using a multimeter power block, using to the electrolytic capacitor, the reverse charge method, based on the size of the magnitude of the pointer swings to the right, you can estimate the capacity electrolytic capacitor.
Detecting a third variable capacitor
A, gently rotating shaft, you should feel very smooth, not feeling tight and sometimes even catching phenomenon loose. The axial load before and after, the time in each direction, the left, right, etc., driven by the shaft of the phenomenon should not be loose.
B, rotating shaft with one hand, the other hand light touch the outer edge of the movable piece group should not feel any loosening. Poor contact between the shaft and the movable piece of the variable capacitor, is no longer continue to use.
C, the multimeter R × 10k block, a hand two tables pen are the variable capacitor terminals movable piece and set pieces, and the other hand to slowly rotating shaft a few back and forth, multimeter pointer should not move at infinity position. In the rotating shaft of the process, if the pointer points to zero at times, indicating the presence of the short circuit between the movable plate and the fixed plate; If you hit a certain point of view, the multimeter reading is not infinite but a certain resistance, indicating that the variable capacitor move leakage phenomenon exists between the sheet and the stator.