Wednesday, January 26, 2011

【 Weak current College 】 capacitor testing method and replace 】

Capacitor common markup is direct marking of the common unit has a pF, μ F, very easy to recognize. But some small-capacity capacitor is digital marking method, generally have three digits, the first and second digits as a valid number, and the third digit for the multiples means that many back to 0. For example: 343 represents 34000pF, in addition, if a third digit is 9, said 10-1, instead of the 9 th of October, for example: 479 4.7pF said.

Replace the main attention should be paid when the capacitance of the capacitor voltage values generally require no less than the original capacitive voltage requirements. In the requirements more stringent circuits, its capacity is less than the original capacity of ± 20%. In less strict circuit, such as a bypass circuit, General requirements not less than the original capacitance of 1/2 and not greater than the capacitance of the 2 x ~ 6 times. 

1 fixed capacitor testing

A detection of small capacitor 10pF following due to the fixed capacitor 10pF following capacity is too small to be measured using a multimeter, only qualitative check whether there is leakage, the phenomenon of internal short-circuit or breakdown. When measuring, you can use multimeter R×10k retaining, using two tables respectively any received two pin capacitance, the resistance should be infinity. If the measured resistance value (a pointer to the right swing) is zero, then the capacitor leakage damage or internal breakdown.

B testing 10PF ~ 0.01 μ F fixed capacitor is charging phenomena, thus it is good or bad. Multimeter R×1k retaining selection. Two technologies ' > transistor of β value of 100 or more, and penetrate current to some optional 3DG6, model composed of composite pipe silicon transistors. Multimeter red and black table respectively and composite pipe of the emitter and collector c e. Due to the magnification composite transistors, the measured capacitance of charging and discharging process be amplified so that the pointer pendulum amplitude increase multimeter to facilitate observation. It should be noted: in test operations, particularly in measuring smaller capacitance, repeatedly swap measured capacitance pin contact A, B, you can clearly see the multimeter pointers.

C for 0.01 μ F above Fixed capacitors, available multimeter R×10k retaining direct testing capacitors have no charging process and there is no internal short-circuit or leakage, and may act according to the pointer to the right margin size estimation of swing out of the capacitor capacity. 

2 Electrolytic Capacitor Technology ' > Electrolytic Capacitor testing

A capacity for electrolytic capacitor is generally fixed capacitor, so the measurement should be for different size selected appropriate quantum. As a rule of thumb, in General, 1 ~ 47 μ F, available between capacitance R×1k retaining measurement, greater than the capacitance of the 47 μ F R× 100 retaining measurement available. 

B the multimeter red table amount received negative electrode, the black table amount received positive, just contact moments, multimeter pointer is to the right tilt larger skewness (for the same power, the greater the capacity, the greater the swing), then gradually turning to the left until it stops at a certain location. This resistance is Electrolytic Capacitor leakage resistance of forward, this value is slightly larger than the reverse leakage resistance. Actual experience that Electrolytic Capacitor leakage resistance should generally be in more than a few hundred k Ω, otherwise it will not work correctly. In tests, if positive, the reverse is not charging, i.e. table PIN is not moving, then disappear or internal circuit breaker capacity; if the measured resistance is too low or zero, the capacitor leakage current large or breakdown damaged, can no longer be used.

C for the positive and negative signs of electrolytic capacitors, can use the measuring leakage resistance of discrimination. Namely any leakage resistance, to have your mind its size, and then exchange table pen and then measured a resistance. Two measurement resistance value of the time it is being received, the black table by pen received is positive, then red table amount is negative.

D use electric barrier, using a multimeter to a Electrolytic Capacitor, reactive charging method, according to the pointer to the right size of oscillations, you can estimate the capacity of the electrolytic capacitors. 

3 variable capacitor testing

A swirled gently by hand, you should feel very shaft is smooth and should not be felt at times when tight even pine scuffing. Will contain the forward, rear axle, top, bottom, left, right, direction drive, the hinge should be loose.

B with one hand in a swirling hinge, another hand touch dynamic piece group of outer edge, you should not feel any loose phenomenon. The hinge and dynamic between bad variable capacitor, is no longer in use.

C place the multimeter R×10k, hand two tables sum respectively variable capacitor of tablets and tablets of terminations, the other will hinge slowly swirling several pointer back and forth, multimeter should position at infinity. In a swirling the hinge of the process, if the pointer is sometimes point to zero, the motion Tablet and fixed between the shorts point; if encountered an angle, multimeter readout is infinity, but appear a certain resistance, description of the dynamic variable capacitor tablets and tablets between leakage phenomenon.

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